Weld defect repairing method for high-pressure and low-pressure ammonia water coexisting pipeline system

Abstract

The invention relates to a method for repairing weld defects of a high-low pressure ammonia water coexistence pipeline system. The method comprises the following steps: polishing a welded junction of a three-way pipeline connection part of the pipeline system; the repair box assembly is arranged at the welded junction in a sleeving mode, a low-pressure side flow guide cavity of the repair box assembly communicates with the low-pressure pipeline, and a high-pressure side flow guide cavity communicates with the high-pressure pipeline; opening a flow guide hole valve of a low-pressure side flow guide cavity to enable ammonia water to flow out, and then opening a flow guide hole valve of a high-pressure side flow guide cavity; the low-pressure pipeline is preheated to the target temperature, and first set energy multi-layer welding is conducted on a low-pressure side welded junction; the high-pressure pipeline is preheated to the target temperature, and second set energy single-layer welding is conducted on the high-pressure side welded junction; post-heat treatment is conducted on the high-pressure side welded junction, and the high-pressure side welded junction is cooled to the environment temperature after being heated to the set temperature; closing the diversion hole valve and opening the high-pressure pipeline valve. The high-pressure side residual ammonia water is prevented from being heated and decomposed to generate gas in a welding high-temperature environment, so that formation of air holes and cracks in a welding seam is prevented.

Description

Technical Field

[0001] This application relates to the field of pipeline construction technology, and in particular to a method for repairing weld defects in a high- and low-pressure ammonia water pipeline system. Background Technology

[0002] In the original construction and repair method for high and low pressure ammonia water pipelines, the low-pressure ammonia water pipeline needs to be continuously operated (to cool raw coal gas, and the supply cannot be stopped), while the high-pressure ammonia water pipeline is only opened intermittently during coke oven coal charging (smokeless coal charging + cleaning of the gas collection pipe). The two are connected by a three-way valve to jointly transport corrosive ammonia water medium. During construction, cracks are controlled by using alkaline welding rods, preheating before welding (temperature meets the requirements of carbon steel pipelines), and hydrogen removal treatment after welding. When repairing defects, a circular arc plate diversion or combined box diversion scheme is adopted, which has the advantages of "no need to shut down the low-pressure medium and high repair efficiency" and solves the corrosion and leakage problem of a single pipeline.

[0003] However, this construction method presents unique technical challenges in ammonia water pipeline systems with both high and low pressure (especially at the T-junction valve connection points): at the T-junction connection, the low-pressure pipeline continuously bears a stable working pressure (to ensure cooling of raw coal gas), while the high-pressure pipeline intermittently bears pulse pressure (instantaneous opening during coal loading), resulting in the T-junction weld being under alternating pressure conditions of "stable low pressure + intermittent high pressure" for a long time; simultaneously, the CN in the ammonia water medium... - The continuous dissolution of the FeS protective film on the weld surface, under alternating pressure, easily leads to "corrosion-stress coupled cracks" at the weld joint. These cracks differ from pure corrosion cracks or pure stress cracks in single-pressure pipelines; their propagation rate is 1.5-2 times that of a single operating condition. Furthermore, due to the lack of targeted stress balancing on the high and low pressure sides after repair, secondary cracking is likely to occur in the short term. In addition, during the repair of this area, the low-pressure pipeline needs to be continuously running (with ammonia flow), and although the high-pressure pipeline can be temporarily shut down, residual ammonia inside the pipe will still evaporate. This results in a dual interference of "medium flow vibration + ammonia mist obstruction" in the tee area: flow vibration makes it difficult to accurately position the repair device, and mist obstruction makes it impossible to control the fusion depth of the high and low pressure weld joints during welding, easily leading to quality problems such as "incomplete penetration of the low-pressure side weld joint and slag inclusion in the high-pressure side weld joint." Summary of the Invention

[0004] This application provides a method for repairing weld defects in a high- and low-pressure ammonia water pipeline system, which can solve the problems in related technologies such as "corrosion-stress coupling cracks are easy to generate, and double interference during repair leads to difficulty in positioning and poor weld quality" at the tee connection of high- and low-pressure ammonia water pipelines.

[0005] This application provides a method for repairing weld defects in a high- and low-pressure ammonia water pipeline system, comprising: Grind the weld joints at the tee connections of the piping system. The repair box assembly is fitted onto the weld joint, so that the low-pressure side guide cavity of the repair box assembly is connected to the low-pressure pipeline and the high-pressure side guide cavity is connected to the high-pressure pipeline. After opening the guide valve of the low-pressure side guide chamber to allow ammonia water to flow out, open the guide valve of the high-pressure side guide chamber. Preheat the low-pressure pipeline to the target temperature, and perform multi-layer welding with the first set energy on the low-pressure side weld joint; Preheat the high-pressure pipeline to the target temperature, and perform single-layer welding with the second set energy on the high-pressure side weld joint; The high-pressure side weld joint is subjected to post-heat treatment, heated to a set temperature and then cooled to ambient temperature. Close the flow guide valve and open the high-pressure pipeline valve.

[0006] In conjunction with the first aspect, in one embodiment, grinding is performed on the weld joint of the tee pipe connection in the piping system, specifically including: Close the high-pressure pipeline valves in the pipeline system and drain the ammonia water from the high-pressure pipeline. Grind the cracks in the weld joint of the tee connection.

[0007] In conjunction with the first aspect, in one embodiment, the repair box assembly has a low-pressure side cavity and a low-pressure side guide cavity communicating with the low-pressure side cavity on one side, and a high-pressure side cavity and a high-pressure side guide cavity communicating with the high-pressure side cavity on the other side. The repair box assembly is fitted onto the weld joint, connecting the low-pressure side guide cavity of the repair box assembly to the low-pressure pipeline and the high-pressure side guide cavity to the high-pressure pipeline, specifically including: Drill positioning holes at the T-junction pipe connection and on the expected adjacent fixed bracket; The repair box assembly is fitted onto the weld joint so that the inner wall of the low-pressure side cavity of the repair box assembly fits against the outer wall of the low-pressure pipe, the inner wall of the high-pressure side cavity fits against the outer wall of the high-pressure pipe, and the low-pressure side guide cavity of the repair box assembly is connected to the low-pressure pipe and the high-pressure side guide cavity is connected to the high-pressure pipe. Insert the positioning pin of the repair box assembly into the positioning hole to fix the repair box assembly.

[0008] In conjunction with the first aspect, in one embodiment, the repair box assembly is fitted onto the weld joint, specifically including: The low-pressure side arc plate is spliced ​​at the low-pressure side of the tee pipe connection to form a low-pressure side shell structure, and a low-pressure side cavity and a low-pressure side guide cavity are formed inside the low-pressure side shell structure. The high-pressure side arc plate is spliced ​​at the high-pressure side of the tee pipe connection to form a high-pressure side shell structure, and a high-pressure side cavity and a high-pressure side flow guide cavity are formed inside the high-pressure side shell structure. The elastic buffer layer is installed at the joint between the low-pressure side shell structure and the high-pressure side shell structure. Install sealing rings at the flow guide holes at both ends of the low-pressure side cavity, and install filter screens at the flow guide holes at both ends of the high-pressure side cavity to complete the fitting of the repair box assembly at the weld joint.

[0009] In conjunction with the first aspect, in one embodiment, a support ear plate is provided on the outer side of the repair box assembly, and an auxiliary device is provided on the repair box assembly, the auxiliary device including a vibration stabilizing clamp and an anti-fog cover; After completing the fitting of the repair box assembly at the weld joint, the method further includes: Fix the vibration stabilizing clip to the bracket ear plate on the outside of the repair box assembly, and connect the vibration stabilizing clip to the fixed bracket; Attach the anti-fog cover to the repair box assembly and seal the contact area between the anti-fog cover and the repair box assembly; Connect the exhaust port of the anti-fog cover to the guide hole on the low-pressure side of the repair box via a hose.

[0010] In conjunction with the first aspect, in one embodiment, after closing the flow guide valve and before opening the high-pressure pipeline valve, the method further includes: Seal the drainage holes of the repair box assembly; Remove the vibration stabilizing clamp and the anti-fog cover.

[0011] In conjunction with the first aspect, in one embodiment, when splicing the low-pressure side arc plate at the low-pressure side of the tee pipe connection and splicing the high-pressure side arc plate at the high-pressure side of the tee pipe connection, the deviation of the low-pressure side cavity axis, the high-pressure side cavity axis and the tee pipe axis are detected. If the deviation exceeds the preset range, the low-pressure side shell structure and the high-pressure side shell structure are adjusted until the deviation of the low-pressure side cavity axis, the high-pressure side cavity axis and the tee pipe axis is within the preset range.

[0012] In conjunction with the first aspect, in one embodiment, before preheating the low-pressure pipeline to a target temperature and performing multi-layer welding with a first set energy on the low-pressure side weld joint, the method further includes: Dry the welding rods; After drying, the welding rods are stored in an insulated container.

[0013] In conjunction with the first aspect, in one embodiment, the low-pressure pipeline is preheated to a target temperature, and multi-layer welding with a first set energy is performed on the low-pressure side weld joint, specifically including: The repair area of ​​the low-pressure pipeline is heated, and the temperature of the repair area is kept at the target temperature for a set time after the temperature rises. Using the first set energy, multiple symmetrical positions are selected at the low-pressure side weld joint for spot welding positioning, welding slag is cleaned and weld quality is checked; The weld circumference is divided into multiple segments, and segmented symmetrical welding is carried out using alternating welding directions. Each segment is welded using a multi-layer, multi-pass welding process.

[0014] In conjunction with the first aspect, in one embodiment, the high-pressure pipeline is preheated to a target temperature, and a second set energy single-layer welding is performed on the high-pressure side weld joint, specifically including: The repair area of ​​the high-pressure pipeline is heated, and the temperature of the repair area is kept at the target temperature for a set time after the temperature rises. Using the second set energy, multiple symmetrical positions are selected at the high-pressure side weld joint for spot welding positioning, welding slag is cleaned and weld quality is checked; The weld circumference is divided into multiple segments, and symmetrical segmented welding is performed using a unidirectional continuous welding direction, with each segment employing a single-layer welding process.

[0015] The beneficial effects of the technical solutions provided in this application include: This application provides a method for repairing weld defects in a high- and low-pressure ammonia pipeline system. By fitting a repair box assembly onto the weld joint and ensuring communication between the low-pressure side guide chamber and the low-pressure pipeline, and between the high-pressure side guide chamber and the high-pressure pipeline, the method involves opening the low-pressure side guide valve before welding to allow ammonia to flow out, followed by opening the high-pressure side guide valve. This effectively prevents residual ammonia on the high-pressure side from decomposing and generating gas under the high-temperature welding environment, thus preventing the formation of porosity and cracks in the weld. After preheating the low-pressure pipeline to the target temperature, multi-layer welding with a first set energy is performed. By controlling the heat input through layered welding, the thermal stress gradient in the welding area is reduced, lowering the risk of weld deformation and cracking. Simultaneously, single-layer welding with a second set energy is performed on the high-pressure side, followed by subsequent heat treatment. Through precise temperature control and heat treatment processes, residual stress in the weld is eliminated, the uniformity of the weld microstructure is improved, and the toughness and fatigue resistance of the weld are enhanced. Finally, the guide valve is closed and the high-pressure pipeline valve is opened, ensuring the safe and stable operation of the system after repair. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A flowchart illustrating a method for repairing weld defects in a high- and low-pressure ammonia pipeline system provided in this application embodiment. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] This application provides a method for repairing weld defects in a high- and low-pressure ammonia water pipeline system, which can solve the problems in related technologies such as "corrosion-stress coupling cracks are easy to generate, and double interference during repair leads to difficulty in positioning and poor weld quality" at the tee connection of high- and low-pressure ammonia water pipelines.

[0020] This application provides a method for repairing weld defects in a high- and low-pressure ammonia water pipeline system, which includes: 101: Grind the weld joints at the tee connections in the piping system; 102: Place the repair box assembly on the weld joint so that the low-pressure side guide cavity of the repair box assembly is connected to the low-pressure pipeline and the high-pressure side guide cavity is connected to the high-pressure pipeline; 103: After opening the guide valve of the low-pressure side guide chamber to allow ammonia water to flow out, open the guide valve of the high-pressure side guide chamber. 104: Preheat the low-pressure pipeline to the target temperature, and perform multi-layer welding with the first set energy on the low-pressure side weld joint; 105: Preheat the high-pressure pipeline to the target temperature, and perform single-layer welding with the second set energy on the high-pressure side weld joint; 106: Perform post-heat treatment on the high-pressure side weld joint, heating to the set temperature and then cooling to ambient temperature; 107: Close the flow guide valve and open the high-pressure pipeline valve.

[0021] This application addresses the issue of residual ammonia on the high-pressure side decomposing into gas at the weld joint, ensuring connectivity between the low-pressure side guide chamber and the low-pressure pipeline, and between the high-pressure side guide chamber and the high-pressure pipeline. Before welding, the low-pressure side guide valve is opened to allow ammonia to flow out, followed by the high-pressure side guide valve. This effectively prevents the formation of gas by the decomposition of residual ammonia on the high-pressure side under the high-temperature welding environment, thus preventing porosity and cracks in the weld. After preheating the low-pressure pipeline to the target temperature, multi-layer welding with a first set energy is employed. By controlling the heat input through layered welding, the thermal stress gradient in the welding area is reduced, lowering the risk of weld deformation and cracking. Simultaneously, single-layer welding with a second set energy is used on the high-pressure side, followed by post-heat treatment. Through precise temperature control and heat treatment processes, residual stress in the weld is eliminated, the uniformity of the weld microstructure is improved, and the toughness and fatigue resistance of the weld are enhanced. Finally, the guide valve is closed and the high-pressure pipeline valve is opened, ensuring the safe and stable operation of the system after repair.

[0022] The repair box assembly has a low-pressure side cavity and a low-pressure side guide cavity connected to it on one side, and a high-pressure side cavity and a high-pressure side guide cavity connected to it on the other side. The repair box assembly is installed at the weld defect at the tee connection between the high- and low-pressure ammonia water pipelines, covering areas of cracks, corrosion, and other defects and extending outwards by at least 30mm, ensuring complete communication between the low-pressure side guide cavity and the low-pressure ammonia water pipeline, and between the high-pressure side guide cavity and the high-pressure ammonia water pipeline.

[0023] Specifically, the repair box assembly adopts an integrated design of "zonal flow guidance + stress buffering." One side features a low-pressure side cavity and a connected low-pressure side flow guide cavity, while the other side features a high-pressure side cavity and a connected high-pressure side flow guide cavity, forming a completely isolated dual-cavity structure. The main body of the repair box is customized according to the actual pipeline system specifications, made of carbon steel of the same material as the pipeline, and is composed of two arc plates spliced ​​together. The low-pressure side is fitted with a large-sized arc plate (curvature radius matching the pipeline's outer diameter) for DN600 pipelines, while the high-pressure side is fitted with a smaller-sized arc plate of the corresponding specification. The two arc plates are precision-machined to ensure a flatness error of less than 0.2mm at the splicing surface. The inner wall is pre-machined with a 10mm wide and 5mm deep flow guide groove. This size design is based on the flow characteristics of ammonia at room temperature, ensuring sufficient flow guidance capacity while avoiding weakening the shell strength due to excessive groove depth. The surface of the flow guide groove is polished to reduce flow resistance. The inner wall is sandblasted and coated with a 0.1mm thick polytetrafluoroethylene coating to enhance ammonia corrosion resistance. Main body shell, The internal structure is strictly divided into two independent flow chambers based on high and low pressure sides: a low-pressure side flow chamber and a high-pressure side flow chamber. The low-pressure side flow orifice is designed to be 1.2 times the medium flow rate under normal pipeline operation, ensuring that the continuously flowing ammonia water can be fully discharged during welding without generating back pressure. The orifice has a 15° bevel for easy connection with the flow guide pipe and to reduce flow resistance. The high-pressure side flow orifice is designed to be 0.8 times the residual discharge flow rate. This ratio takes into account the actual amount of residual ammonia water after intermittent operation of the high-pressure pipeline, avoiding a sudden pressure drop on the high-pressure side due to an excessively large orifice diameter, which would affect system stability. The opening diameter of the low-pressure side flow chamber is 2mm larger than that of the high-pressure side. This dimensional difference is designed based on the flow characteristics of the continuously flowing ammonia water on the low-pressure side, ensuring that the ammonia water can pass smoothly without generating eddies. At the same time, the smaller orifice diameter on the high-pressure side can effectively control the discharge rate of residual ammonia water during intermittent operation, avoiding sudden pressure changes.

[0024] A 1mm thick stainless steel elastic buffer layer is installed between the two cavities. This elastic buffer layer is made of 1mm thick L-shaped 304 stainless steel sheet. The L-shaped design allows it to fit tightly against the joint of the two guide cavities. The edges have a 3mm wide flange, which is welded to the inner wall of the shell to form a stable support structure. The surface is uniformly coated with a 0.1mm thick polytetrafluoroethylene (PTFE) coating. This coating not only provides excellent resistance to ammonia corrosion but also reduces the coefficient of friction between the buffer layer and the ammonia water contact surface. This facilitates the micro-deformation under alternating pressure, effectively absorbing the alternating stress under the "stable low pressure + intermittent high pressure" conditions of high and low pressure pipelines, and alleviating the stress superposition problem of "corrosion-stress coupling crack corrosion". This elastic buffer layer is not a rigid connection but forms a flexible contact with the two cavities through a special process, enabling it to produce micro-deformation of 0.2-0.5mm under alternating high and low pressure, thereby absorbing some of the alternating stress. Three sets of adjustable positioning pins are evenly arranged along the circumference on the outer side of the repair box assembly. Each set of positioning pins consists of a guide rod and a locking nut, which can be finely adjusted according to the actual connection angle of the tee pipe (usually 90° or 45°) to ensure that the repair box assembly fits tightly against the outer wall of the pipe and eliminate poor sealing caused by angular deviation. Each cavity at the bottom is independently equipped with a guide hole with a valve. The valve is a stainless steel ball valve that is resistant to ammonia corrosion. The valve stem extends to the outside of the repair box assembly for easy operation. By opening the high and low pressure side guide holes in stages, the flowing ammonia water on the low pressure side can be discharged first and then the residual medium on the high pressure side can be treated to avoid pressure interference.

[0025] Three sets of bracket ear plates are pre-installed on the outside of the repair box assembly, evenly distributed around the circumference of the repair box assembly. Each set of ear plates is provided with M16 bolt holes for installing vibration stabilizing clamps. A dynamic stabilizing clamp is added to the outside of the repair box assembly. The dynamic stabilizing clamp consists of an arc-shaped clamp body and high-strength bolts. The bolts rigidly connect the repair box assembly to the original fixed support of the pipeline system. The stability of the support is used to counteract the vibration caused by the low-pressure pipeline flow, and the vibration amplitude of the repair area is controlled within a safe range.

[0026] It is also equipped with a "local anti-fog hood," made of transparent polycarbonate material, which has excellent ammonia resistance and mechanical strength. A negative pressure drainage system is formed by connecting the hood to the drainage holes of the repair box assembly via a flexible hose, promptly expelling ammonia mist generated in the welding area and maintaining clear visibility inside the hood. An adjustable sealing strip is provided at the contact point between the anti-fog hood and the repair box assembly to ensure a tight seal and facilitate installation and disassembly. Two independent drainage holes with valves are located at the bottom of the anti-fog hood, connecting to the high and low pressure drainage chambers respectively. The valves are corrosion-resistant stainless steel ball valves for easy operation. Special bolts and clamps are also provided for the secure connection between the repair box assembly and the pipeline.

[0027] The entire repair box assembly resolves media flow interference through zoned flow diversion, alleviates alternating stress through an elastic buffer layer, and, in conjunction with anti-interference auxiliary devices, provides a reliable weld defect repair solution for the tee connection of ammonia water pipelines with both high and low pressure.

[0028] Based on the above embodiments, in this embodiment, the weld joint of the tee pipe connection is ground, specifically including: closing the high-pressure pipe valve of the pipeline system and draining the ammonia water in the high-pressure pipe; and grinding the cracks in the weld joint of the tee connection.

[0029] Specifically, when grinding the weld joint of the tee connection in the piping system, the high-pressure ammonia pipeline system must first be temporarily shut down, while the low-pressure pipeline continues to operate. After closing the high-pressure pipeline valve, the residual ammonia in the pipeline is discharged. During the discharge process, the pressure gauge reading must be monitored to ensure that the discharge pressure of the residual ammonia in the high-pressure pipeline drops to the safe threshold of ≤0.1MPa before proceeding with subsequent operations. This is to avoid the safety hazard caused by sudden splashing of ammonia due to excessive residual pressure. After discharge, an industrial endoscope is used to conduct a comprehensive inspection of the tee weld joint. The specific location, direction, and depth distribution of corrosion-stress coupling cracks are observed in detail using a high-resolution camera and built-in lighting system. The endoscopic inspection should be performed from multiple angles to ensure accurate identification of the crack initiation point and propagation path. Precise guidance is provided for subsequent grinding. Based on the endoscopic inspection results, an angle grinder with a special grinding head is used to treat the cracked area. The grinding range is strictly controlled within 50mm on both sides of the crack. The grinding depth must cover the visible crack and extend to the defect-free metal substrate. It is necessary to ensure complete removal of oxide scale, corrosion products and microcracks, but not to over-grind and weaken the pipe wall thickness. During the grinding process, water cooling or intermittent grinding methods should be used to control the temperature to prevent local overheating from affecting the metal structure. After grinding, the weld surface must achieve a uniform metallic luster, and the surface roughness must be strictly controlled within the range of ≤Ra6.3μm. Excessive roughness will affect the sealing effect of the subsequent repair box, while excessively low roughness will increase the grinding workload and have limited improvement on the welding quality.

[0030] After grinding, acetone or a special cleaning agent must be used to thoroughly remove surface oil and metal shavings. Then, magnetic particle testing is used to confirm that the cracks have been completely removed and there are no new defects. Finally, rust prevention treatment is applied to the ground area to create favorable conditions for subsequent repair box installation and welding operations. The entire grinding process must be carried out in a well-ventilated environment, and an ammonia detector is used to monitor the ammonia concentration in the work area in real time to ensure that it meets the safety operation standards.

[0031] Based on the above embodiments, in this embodiment, the repair box assembly is fitted onto the weld joint, so that the low-pressure side guide cavity of the repair box assembly is connected to the low-pressure pipeline and the high-pressure side guide cavity is connected to the high-pressure pipeline, specifically including: First, drill positioning holes at the T-junction pipe connection and the expected adjacent fixed bracket; then, fit the repair box assembly onto the weld joint so that the inner wall of the low-pressure side cavity of the repair box assembly fits against the outer wall of the low-pressure pipe, the inner wall of the high-pressure side cavity fits against the outer wall of the high-pressure pipe, the low-pressure side guide cavity of the repair box assembly is connected to the low-pressure pipe, and the high-pressure side guide cavity is connected to the high-pressure pipe; finally, insert the positioning pin of the repair box assembly into the positioning hole to fix the repair box assembly.

[0032] Specifically, in the operation of fitting the repair box assembly onto the weld joint, positioning holes are first drilled at the T-junction pipe connection and adjacent fixed supports. Among them, 3-4 positioning holes are drilled on the outer wall of the T-junction pipe corresponding to the positioning pin of the repair box (usually evenly distributed along the circumference). The hole diameter is determined according to the diameter of the positioning pin to ensure that the positioning pin can be stably accommodated without penetrating the pipe wall thickness. At the same time, 3 sets of positioning holes are drilled on the adjacent fixed supports of the T-junction pipe. The hole diameter is strictly matched with the specifications of the vibration stabilizing clamp bolts. The drilling position must avoid the support weld, reinforcing ribs and other key stress parts by at least 50mm to ensure that it will not affect the structural strength of the support. During the drilling process, a carbide drill bit is used in conjunction with a guide sleeve. The length of the guide sleeve is not less than twice the hole diameter to ensure the accuracy and perpendicularity of the hole position. After drilling, metal debris must be removed and deburred.

[0033] Before drilling the positioning hole on the outer wall of the tee, a special positioning template must be used to determine the accurate position. This template is prefabricated according to the specifications of the tee pipe and the dimensions of the repair box assembly. The template has through holes corresponding to the positioning pins of the repair box assembly. The template is fixed to the tee pipe with clamps to ensure that the template fits tightly against the outer wall of the pipe without gaps. Then, the drill bit is guided through the through holes of the template to drill the hole, ensuring that the deviation between the axis of the positioning hole and the axis of the positioning pin of the repair box is ≤1mm. If the deviation exceeds this, the repair box will be installed tilted, affecting the fit with the outer wall of the pipe and the subsequent sealing effect. The repair box assembly is then fitted onto the weld joint. First, apply a thin layer of ammonia-resistant sealant to the outer wall of the pipe and the inner wall of the repair box. Then, slowly rotate and push the repair box assembly to ensure that the inner wall of the low-pressure side cavity is completely in contact with the outer wall of the low-pressure pipe and the inner wall of the high-pressure side cavity is completely in contact with the outer wall of the high-pressure pipe. The gap between the two sides should be controlled within 0.5mm, which can be verified by feeling gauge. At the same time, ensure that the low-pressure side guide cavity of the repair box is completely connected to the low-pressure pipe and the high-pressure side guide cavity is completely connected to the high-pressure pipe. The edge of the guide cavity opening should maintain a safe distance of 5-10mm from the pipe weld to avoid the guide cavity obstructing the weld and affecting the welding quality.

[0034] Finally, insert the positioning pin of the repair box assembly into the drilled positioning hole. The positioning pin adopts a stepped structure design, with a tapered guide section at the front end for easy insertion, a cylindrical working section in the middle to ensure positioning accuracy, and a threaded tail for locking. After insertion, it is fixed by locking the nut to ensure that the repair box assembly will not shift due to vibration or pressure fluctuations during the welding process.

[0035] Furthermore, the repair box assembly is fitted onto the weld joint, specifically including: First, the low-pressure side arc plate is spliced ​​at the low-pressure side of the tee pipe connection to form a low-pressure side shell structure, within which a low-pressure side cavity and a low-pressure side flow guide cavity are formed; then, the high-pressure side arc plate is spliced ​​at the high-pressure side of the tee pipe connection to form a high-pressure side shell structure, within which a high-pressure side cavity and a high-pressure side flow guide cavity are formed. Then, the elastic buffer layer is installed at the joint between the low-pressure side shell structure and the high-pressure side shell structure; finally, sealing rings are installed at the guide holes at both ends of the low-pressure side cavity, and filter screens are installed at the guide holes at both ends of the high-pressure side cavity, thus completing the fitting of the repair box assembly at the weld joint.

[0036] Specifically, in the operation of fitting the repair box assembly onto the weld joint, the parts of the repair box assembly are first processed according to the actual geometric shape and size parameters of the tee pipe and matching requirements: the low-pressure side guide cavity is made of Q235B carbon steel of the same material as the pipe, and the diameter of the guide hole is strictly designed and calculated according to 1.2 times the medium flow rate under normal working conditions of the low-pressure pipe to ensure that the continuously flowing ammonia water can be fully discharged during the welding process without generating back pressure. The roughness of the hole wall is controlled at ≤Ra3.2μm to reduce flow resistance. The orifice is machined with a 3×45° bevel to facilitate connection with the guide pipe and reduce turbulence during medium flow. The high-pressure side guide cavity is also made of Q235B carbon steel. The diameter of the guide hole is determined to be 0.8 times the discharge flow rate of residual ammonia water after intermittent operation of the high-pressure pipe. This ratio takes into account the actual amount of residual medium after the high-pressure pipeline operation is completed, and avoids the pressure drop caused by the excessively large hole diameter, which would affect the stability of the system. The machining accuracy of the hole wall is consistent with that of the low-pressure side guide cavity. The orifice is equipped with a filter screen groove with a depth of 1.5mm and a 100-mesh stainless steel filter screen is pre-installed to prevent impurities in the pipeline from clogging the guide channel.

[0037] The elastic buffer layer is made of 1mm thick 304 stainless steel sheet, precisely machined into an L-shaped structure according to the actual included angle of the three-way two-cavity joint (usually 90° or 45°). The edges of the buffer layer are machined with 0.5mm thick flanges to enhance edge strength, and the surface is uniformly sprayed with a 0.1mm thick polytetrafluoroethylene coating to provide ammonia corrosion resistance.

[0038] The shell of the repair box assembly is made of an arc plate corresponding to the pipe specifications. The inner wall is pre-machined with a 10mm wide and 5mm deep guide groove. This size design is based on the flow characteristics of ammonia at room temperature. The surface of the guide groove is polished to reduce flow resistance, and the guide groove and the guide hole are kept in continuous communication to ensure smooth discharge of the medium.

[0039] After processing, all parts undergo rigorous inspection. An inside micrometer is used to check the diameter deviation of the guide hole, which is controlled within ±0.2mm. A flat plate and feeler gauge are used to check the flatness error of the elastic buffer layer, which does not exceed 0.1mm. At the same time, a special leak test fixture is used to conduct a 0.2MPa pressure leak test on the guide cavity. If there is no leakage after holding the pressure for 10 minutes, it is considered qualified, ensuring that all parts meet the requirements for subsequent assembly.

[0040] The low-pressure side arc plate is initially positioned and spliced ​​at the low-pressure side of the tee pipe connection to form a low-pressure side shell structure, which contains a low-pressure side cavity and a low-pressure side flow guide cavity. Similarly, the high-pressure side arc plate is spliced ​​at the high-pressure side of the tee pipe connection to form a high-pressure side shell structure, which contains a high-pressure side cavity and a high-pressure side flow guide cavity. During the splicing process, four spot welds are used at the splicing point of the two cavities for temporary fixation.

[0041] When splicing the low-pressure side arc plate at the low-pressure side of the tee pipe connection and splicing the high-pressure side arc plate at the high-pressure side of the tee pipe connection, the deviations of the low-pressure side cavity axis, the high-pressure side cavity axis, and the tee pipe axis are detected. If the deviations exceed the preset range, the low-pressure side shell structure and the high-pressure side shell structure are adjusted until the deviations of the low-pressure side cavity axis, the high-pressure side cavity axis, and the tee pipe axis are within the preset range.

[0042] In this embodiment, a laser collimator is used to detect the deviation between the axis of the two cavities and the axis of the three-way pipe. If the deviation exceeds the allowable range, it is finely adjusted by a special tapping tool until the guide cavity is connected to the corresponding pipe, ensuring that the low-pressure side guide cavity is fully connected to the low-pressure pipe and the high-pressure side guide cavity is fully connected to the high-pressure pipe.

[0043] Apply a thin layer of ammonia-resistant sealant evenly to the inside of the joint between the two cavities. Precisely attach the L-shaped elastic buffer layer to the joint, with the edge of the buffer layer facing the inside of the cavity to form an effective seal. Use φ3mm stainless steel rivets to rivet and fix the buffer layer at 50mm intervals. At the same time, use a special pressure clamp to apply a pressure of 0.1MPa and hold the pressure for 5 minutes to ensure that the buffer layer is tightly attached to the shell. At the same time, reserve the amount of compression to meet the micro-deformation requirements of subsequent alternating pressure, so that the elastic buffer layer can generate micro-deformation under high and low pressure alternating pressure to absorb part of the alternating stress.

[0044] Pre-install an ammonia-resistant rubber sealing ring in the low-pressure side guide hole. The diameter of the sealing ring section is determined according to the size of the guide hole, usually Φ8-Φ10mm. During installation, ensure that the sealing ring is not twisted or offset. Install a 100-mesh stainless steel filter screen in the high-pressure side guide hole. Fix the edge of the filter screen by spot welding. Control the welding points to 4-6 points and distribute them evenly to ensure that the filter screen is not loose or deformed, so as to ensure the normal flow guidance function of the guide hole and prevent impurities from entering.

[0045] In addition, since the repair box assembly is provided with a support ear plate on the outside, the repair box assembly is provided with auxiliary devices, including a vibration stabilizing clamp and an anti-fog cover. Therefore, after completing the installation of the repair box assembly at the weld joint, the method further includes: fixing the vibration stabilizing clamp to the bracket ear plate on the outside of the repair box assembly and connecting the vibration stabilizing clamp to the fixed bracket; fastening the anti-fog cover to the repair box assembly and sealing the contact point between the anti-fog cover and the repair box assembly; and connecting the exhaust port of the anti-fog cover to the guide hole on the low-pressure side of the repair box through a hose.

[0046] Specifically, the repair box assembly has bracket ears on its outer side for installing auxiliary devices such as vibration stabilizing clamps and anti-fog covers. After the repair box assembly is fitted onto the weld joint, the vibration stabilizing clamp is fixed to the pre-set bracket ears on the outside of the repair box using M16 stainless steel bolts. First, install the bolts diagonally symmetrically, then install the remaining bolts in a clockwise sequence, ensuring the bolt tightening torque is controlled within the range of 80-100 N·m. After installation, use a dial indicator to check the vibration displacement of the repair box assembly to ensure that the vibration stabilizing clamp can effectively and rigidly connect the repair box to the original fixed support of the pipeline system, reducing vibration interference caused by low-pressure pipeline flow. A transparent PTFE anti-fog cover is then fastened to the top of the repair box assembly. An ammonia-resistant sponge sealing strip is pasted at the contact point between the cover edge and the box body. The sealing strip has a D-shaped cross-section, ensuring a good seal without excessive compression causing rebound failure. The cover is fixed with φ8mm stainless steel bolts at 80mm intervals. After tightening the bolts, the sealing gap is checked with soapy water; no bubbles indicate a good seal.

[0047] Connect the exhaust port of the anti-fog hood to the low-pressure side guide hole of the repair box through an ammonia-resistant hose, and tighten both ends of the hose with clamps to form a negative pressure drainage channel to promptly discharge the ammonia mist generated in the welding area and maintain a clear view inside the hood.

[0048] After assembly, a final quality inspection is conducted. An industrial endoscope is used to inspect the inside of the flow guide cavity to confirm that the flow guide groove and flow guide hole are connected without blockage and that the elastic buffer layer is free from wrinkles and deformation. Compressed air at 0.1 MPa is slowly introduced through the low-pressure side flow guide hole, and the sealing between the two cavities is tested with soapy water to ensure that no air bubbles are generated, indicating a good seal. The installation status of the vibration stabilizing clamp and anti-fog cover is checked to confirm that both are firmly installed without any signs of loosening and that the bolts are tightened in place.

[0049] In addition, after the repair box assembly is installed, use a dial indicator to check the vibration amplitude of the repair box to ensure that it is controlled within the safe range of ≤0.5mm. When opening the valve of the low-pressure side guide hole at the bottom of the repair box assembly, the valve stem should be rotated slowly, and the initial opening angle should be controlled at 15°-20°. After observing that ammonia water begins to flow out on the low-pressure side, gradually increase the opening angle until the flow rate is stable at ≥5L / min. This flow rate setting is determined based on the actual ammonia water flow rate under normal working conditions of the low-pressure pipeline, which can ensure smooth discharge of the medium without causing a sudden drop in pressure due to excessive flow.

[0050] After the ammonia flow rate on the low-pressure side stabilizes, slowly open the high-pressure side guide valve, initially controlling the opening angle to within 10°. Control the flow rate increase by adjusting the valve stem rotation speed to ensure that the high-pressure side ammonia discharge flow rate is ≤3L / min. This flow limit is set to account for the actual amount of residual ammonia after intermittent operation of the high-pressure pipeline, avoiding pressure fluctuations caused by excessive discharge that could affect system stability. During the two-chamber flow diversion process, the pressure change inside the repair box must be closely monitored using a precision pressure gauge in real time to ensure that the pressure inside the repair box is ≤0.05MPa after the guide valve is opened. Excessive pressure will cause the seal between the repair box and the pipeline to fail, resulting in ammonia leakage. At the same time, observe the medium flow in the two chambers through an endoscope to confirm the zonal flow diversion effect of the large-diameter guide chamber on the low-pressure side and the small-diameter guide chamber on the high-pressure side, ensuring that there is no medium stagnation. Stagnant ammonia will rapidly vaporize at the welding high temperature, generating steam pressure and affecting the welding quality.

[0051] Then, use a laser rangefinder again to check the alignment deviation with the weld defect, ensuring it is ≤2mm. Excessive deviation will prevent the repair box assembly from completely covering the defect area or affect the connection between the guide cavity and the pipeline. During the guide process, it is also necessary to observe whether the pre-processed guide groove on the inner wall of the low-pressure side guide cavity effectively guides the medium to the guide hole, and whether the 100-mesh stainless steel filter screen pre-installed in the high-pressure side guide hole remains unobstructed. The temperature and pH value of the ammonia water must be continuously monitored throughout the guide process to ensure they are within a safe range. At the same time, an ammonia gas detector should be used to monitor the ammonia concentration in the work area in real time. When the concentration exceeds 25ppm, the operation should be stopped and ventilation should be strengthened. After the guide system has been running stably for 10 minutes, confirm that there are no bubbles accumulating in the two cavities, no medium stagnation, and no abnormal vibration of the repair box assembly as a whole, before proceeding with the subsequent welding preparation work. This will create a safe and stable working environment for the repair of weld defects at the tee connection of the high and low pressure ammonia water pipeline.

[0052] Based on the above embodiments, in this embodiment, before preheating the low-pressure pipeline to the target temperature and performing multi-layer welding with the first set energy on the low-pressure side weld joint, the method further includes: drying the welding rod; and storing the dried welding rod in an insulation cylinder.

[0053] Specifically, before preheating the low-pressure pipeline to the target temperature and performing multi-layer welding with the first set energy on the low-pressure side weld joint, the welding materials must be strictly treated. Alkaline low-hydrogen welding electrodes should be selected. These electrodes contain calcium carbonate, fluorite, and other components in their coating, which have good crack resistance but are also very easy to absorb moisture from the air. When the electrodes are damp, the moisture in the coating will decompose and produce hydrogen gas under the high temperature of the arc, resulting in excessive diffusible hydrogen content in the weld metal. This makes it very easy for cold cracks to occur during the cooling process of the weld joint, especially in ammonia pipelines where residual stress exists, where the risk is even higher.

[0054] The drying of welding electrodes must be carried out strictly in accordance with the technical parameters provided by the electrode manufacturer. During the drying process, the electrodes should be evenly laid on the drying rack to ensure uniform heat transfer and avoid local overheating that could cause the coating to crack or deteriorate. After drying, the electrodes should be immediately transferred to a preheated, insulated container for storage to effectively prevent them from absorbing moisture again.

[0055] After each use of welding rods, the cylinder cap should be closed immediately to reduce the entry of humid air and strictly control the exposure time of the welding rods to air. Welding rods should be taken out as needed during use to avoid prolonged exposure of large quantities of welding rods to air. Dry welding rod pliers should be used to handle the welding rods, and direct contact with the coating of the welding rods with your hands is prohibited.

[0056] During the equipment debugging process before welding, a DC arc welding machine is selected and set to DC reverse polarity mode (welding electrode connected to the positive terminal and workpiece connected to the negative terminal). This connection method can provide a more stable arc, less spatter and deeper penetration, and is especially suitable for the use of basic low-hydrogen welding electrodes. The output current range of the welding machine needs to be determined according to the diameter of the welding electrode and the wall thickness of the pipe.

[0057] The tracked electric heater is selected. The heater should be closely attached to the outer wall of the low-pressure side pipe, and the coverage area should extend 100mm beyond both sides of the weld joint. A layer of high-temperature resistant mica paper should be placed between the heater belt and the pipe to prevent direct contact and local overheating. At the same time, the heater should be avoided from overlapping to prevent uneven temperature. Ceramic electric heating elements are selected. They are mainly used for preheating and post-heat treatment of high-pressure side weld joints. L-shaped or arc-shaped specifications are customized according to the shape of the tee pipe. A thin layer of thermally conductive silicone grease is applied between the heating element and the outer wall of the pipe to improve heat conduction efficiency. The temperature recorder should be a model with 4-8 channel data acquisition function. During debugging, zero point calibration and range calibration are required to ensure that the measurement error is within the allowable range. At the same time, check whether the data storage function and real-time display function are normal.

[0058] K-type thermocouples should be placed as temperature monitoring points at the center of the low-pressure side weld, the center of the high-pressure side weld, and the area between the two welds. The thermocouple measuring ends should be tightly attached to the outer wall of the pipe and fixed with high-temperature resistant ceramic fiber tape. When fixing, it is necessary to ensure good contact between the thermocouple and the pipe surface without gaps. The thermocouple leads should be kept away from the welding area and heat insulation protection measures should be taken to avoid arc interference that could cause temperature reading distortion. For complex parts such as tee pipes, an additional monitoring point should be added at the junction of the low-pressure side weld and the high-pressure side weld to monitor temperature gradient changes. The thermocouples at all temperature monitoring points should be connected to the temperature recorder through compensating wires. The wire length should be appropriate and tangling should be avoided. The connection points should be properly insulated.

[0059] Based on the above embodiments, in this embodiment, the low-pressure pipeline is preheated to the target temperature, and multi-layer welding with a first set energy is performed on the low-pressure side weld joint. Specifically, this includes: firstly, heating the repair area of ​​the low-pressure pipeline, and then holding the repair area at the target temperature for a set time; then using the first set energy to select multiple symmetrical positions on the low-pressure side weld joint for spot welding positioning, cleaning the welding slag and checking the weld quality; finally, dividing the circumference of the weld joint into multiple segments, and performing segmented symmetrical welding using alternating welding directions, wherein each segment adopts a multi-layer, multi-pass welding process, and is welded in multiple layers.

[0060] Preheat the high-pressure pipeline to the target temperature, and perform single-layer welding on the high-pressure side weld joint with the second set energy. Specifically, this includes: first, heating the repair area of ​​the high-pressure pipeline, and then holding the repair area at the target temperature for a set time; then, using the second set energy, spot welding is performed at multiple symmetrical positions on the high-pressure side weld joint, the weld slag is cleaned, and the weld quality is checked; finally, the circumference of the weld joint is divided into multiple segments, and symmetrical segmented welding is performed using a unidirectional continuous welding direction, with each segment using a single-layer welding process.

[0061] Specifically, the preheating area on the low-pressure side extends 100mm from the weld joint to both sides of the pipeline for preheating. This extension distance is determined based on the actual width of the heat-affected zone of the low-pressure pipeline under continuous ammonia flow conditions. It can completely cover the weld and heat-affected zone, while avoiding unnecessary energy consumption due to an excessively large preheating range. The preheating area on the high-pressure side extends 150mm from the weld joint to both sides of the pipeline. This 50mm extension compared to the low-pressure side is to account for the fact that the heat-affected zone of the high-pressure pipeline will be wider under the action of intermittent pulse pressure, and the high-pressure side weld requires a higher preheating temperature and a larger heat conduction range. Therefore, a wider preheating area is needed to reduce the temperature gradient and prevent new thermal stress from being generated due to uneven temperature.

[0062] During the preheating process, the tracked electric heater on the low-pressure side is started at the preheating temperature according to the original construction method. The heating rate is controlled within 50℃ / h to avoid excessively rapid temperature rise and local stress concentration in the pipeline. After the temperature reaches the target value, it is kept at the temperature for 20 minutes to ensure uniform temperature across the pipeline cross section. K-type thermocouples are evenly distributed in the preheating area at 5-7 monitoring points (including the weld center, the boundary of the heat-affected zone, and the transition area). Temperature fluctuations are monitored in real time using a temperature recorder. The temperature difference between adjacent monitoring points is required to be no more than 25℃. If a local temperature is found to be too low, the heater power distribution is adjusted.

[0063] The preheating temperature on the high-pressure side is increased by 50°C according to the original method, and the temperature is also increased at a rate of 50°C / h. After holding at the temperature for 20 minutes, the temperature uniformity is checked. The monitoring point layout is the same as that on the low-pressure side, but monitoring points are added at the weld junction to ensure that the preheating temperature meets the standard and is evenly distributed in the area. In particular, temperature gradient control is more critical in areas with complex tee structures.

[0064] During spot welding, the low-pressure side weld joint is evenly divided into three symmetrical positions with 120° intervals along the circumference for spot welding. The welding current is reduced by 15-20% compared to the formal welding, and the voltage is adjusted accordingly to maintain a stable arc. The welding speed is slightly faster than the formal welding. After spot welding, the welding slag is cleaned immediately. A magnifying glass is used to check whether there are defects such as microcracks and pores in the weld. Unqualified spot welds need to be ground and cleaned before re-welding.

[0065] For the high-pressure side weld joint, three symmetrical positions are selected and staggered by 60° from the low-pressure side weld position for spot welding. The spot welding parameters are basically the same as those for the low-pressure side, but the current is slightly higher by 5-10% to adapt to the higher preheating temperature. After cleaning the welding slag, a quality inspection is carried out.

[0066] After spot welding is completed, a laser collimator is used to check the concentricity of the T-joint and the repair box assembly. The measurement points are evenly distributed along the circumference, with no less than 8 points. If the concentricity deviation is found to exceed 1.5mm, a special copper hammer is used to gently tap the spot weld to adjust it. The force of each tap must be controlled to avoid stress concentration caused by strong correction. After adjustment, the measurement is repeated until the concentricity deviation is controlled within 1mm.

[0067] When performing segmented symmetrical welding, the low-pressure side weld joint is divided into 4 segments with 90° intervals. The welding direction is alternating between clockwise and counterclockwise. The segmented welding starts from the top position. After each segment is welded, the interlayer weld slag is thoroughly cleaned. A wire brush and compressed air are used to ensure that there is no slag inclusion residue before proceeding to the next segment. This alternating welding method can effectively balance the residual welding stress.

[0068] The high-pressure side weld joint is divided into three segments with 120° intervals. A unidirectional continuous welding direction is adopted, and segmented welding is started from the bottom position. After each segment is welded, the weld slag is also cleaned to ensure that there are no impurities between layers.

[0069] In terms of differentiated control of welding parameters, the low-pressure side adopts a low-energy multi-layer multi-pass welding process, with the energy line reduced by about 10% compared to the conventional method. Welding is carried out in 3 layers, and the thickness of each layer and the temperature between layers are controlled. The high-pressure side adopts conventional energy single-layer welding, and the temperature of the heat-affected zone is monitored in real time to prevent excessive temperature from causing grain coarsening and affecting the toughness of the weld.

[0070] In the post-heating and slow cooling stage, within 10 minutes after the high-pressure side weld is completed, a customized L-shaped ceramic electric heating element is covered on the weld and heat-affected zone. The heating element is wrapped with 50mm thick high-temperature resistant ceramic fiber insulation cotton. The heating equipment is started to raise the temperature to the set value and maintain the temperature for 30 minutes. The temperature is recorded every 5 minutes during the heat maintenance period to ensure temperature stability.

[0071] After the insulation is completed, turn off the heating equipment and keep the insulation cotton wrapped to allow the weld to cool naturally. Control the cooling rate and remove the insulation cotton and heating pads only after the weld temperature drops to close to the ambient temperature to avoid excessive cooling and internal stress.

[0072] Finally, a preliminary welding quality inspection is conducted, including three stages: visual inspection, dimensional inspection, and stress release inspection. Visual inspection uses a 5-10x magnifying glass to carefully observe the weld surface, ensuring there are no defects such as cracks, porosity, slag inclusions, or incomplete penetration, paying particular attention to the transition area between the repair box and the pipe connection. Dimensional inspection uses a standard weld gauge to check the weld width and reinforcement height, requiring the reinforcement height to be controlled within the set range, the width to transition evenly, and no undercut. Stress release inspection uses a portable stress meter to measure residual stress values ​​at 8-12 points around the weld, focusing on the connection between the repair box and the pipe, and complex areas such as the tee structure, ensuring that the maximum residual stress does not exceed the set range of the material's yield strength to avoid stress accumulation leading to cracks. Only after all inspection items meet the requirements can subsequent procedures be carried out, providing reliable repair guarantees for weld defects at the tee connection points of high and low pressure ammonia water pipelines.

[0073] Based on the above embodiments, in this embodiment, after closing the flow guide valve and before opening the high-pressure pipeline valve, the method further includes: Seal the flow guide hole of the repair box assembly; remove the vibration stabilizing clamp and anti-fog cover.

[0074] Specifically, after welding is completed, the high and low pressure side guide valves at the bottom of the repair box assembly should be closed in sequence, with the high pressure side closed first and the low pressure side closed later, to avoid backflow of the medium due to pressure imbalance.

[0075] After closing the flow guide valve, wait for the weld to cool naturally to ambient temperature. The specific time depends on the ambient temperature and pipe wall thickness. During the cooling process, maintain insulation around the repair box to avoid additional welding residual stress caused by excessive cooling. At the same time, use an infrared thermometer to monitor the weld temperature regularly and ensure that the temperature drops to close to the ambient temperature before proceeding with subsequent operations. Premature sealing may cause thermal stress to affect the sealing effect.

[0076] After the weld has completely cooled, a triple sealing measure of bolts, ammonia-resistant gaskets, and full welding is implemented on the drainage hole of the repair box body. First, M12 stainless steel bolts (matching the drainage hole) are selected, and the bolt length is determined according to the thickness of the drainage hole to ensure that the bolt can completely pass through the drainage hole and leave sufficient tightening allowance. The ammonia-resistant gasket is made of nitrile rubber, with an inner diameter consistent with the diameter of the drainage hole and an outer diameter larger than the drainage hole to ensure that it can completely cover the edge of the drainage hole after installation. When installing the gasket, it is necessary to ensure that its surface is clean and free of impurities. Place the gasket on the drainage hole and then screw in the stainless steel bolt. By controlling the bolt tightening torque, the gasket compression reaches 20%-30%. This compression range can ensure sufficient sealing pressure without causing permanent deformation and failure of the gasket due to excessive compression. The compression can be indirectly controlled by measuring the change in distance between the bolt head and the surface of the repair box.

[0077] After tightening the bolts, immediately perform full welding to seal the contact area between the bolts and the repair box, ensuring that the weld completely covers the root of the bolt and forms a continuous and dense fusion with the body of the repair box. After welding, the slag must be cleaned and a visual inspection must be performed to ensure that there are no defects such as pores or cracks.

[0078] After the triple sealing is completed, remove the vibration stabilizing clamp and the anti-fog cover in sequence. When removing the vibration stabilizing clamp, first loosen the connecting bolts, taking care to avoid impacting the repair box. Before removing the anti-fog cover, disconnect the hose connection to the guide hole and carefully remove the cover to avoid scratching the surface of the repair box. Then, gradually open the high-pressure ammonia water pipeline valve according to the coke oven charging process requirements to make the system pressure rise steadily, and finally adjust it to the working pressure required by the process. During the opening process, the pressure gauge reading needs to be closely monitored to ensure that the pressure fluctuation after the high-pressure pipeline is opened is controlled within ≤±5%. This fluctuation range meets the pressure stability requirements of the smokeless coal charging process. Excessive pressure fluctuation will affect the coke oven charging effect and the quality of ammonia water injection.

[0079] After the system pressure stabilizes, the tightness of the welded joints is detected by soap water. The soap water is evenly applied to all welds, the sealing parts of the diversion holes, and the connections between the repair box and the pipeline. Focus on inspecting the welded joints of the three-way pipe, the splicing seams of the repair box, and the sealing parts of the diversion holes. Observe for no less than 20 minutes. If no bubbles are generated, it is considered that the seal is qualified. During the detection process, observations need to be made at different angles and lighting conditions to avoid missing small leakage points. If leakage is found, corresponding remedial measures need to be taken according to the leakage location and degree. Small leakage can be solved by re-tightening the bolts or local repair welding, while larger leakage requires re-sealing. The entire seal detection process needs to be carried out in a well-ventilated environment, and an ammonia detector is equipped to monitor the ammonia concentration in the operation area in real time to ensure compliance with safety operation standards. Only when all inspection items meet the requirements can it be confirmed that the repair operation is completed and the system resumes normal operation, providing long-term and reliable protection for the welded joint defects at the three-way connection of the high-low pressure coexisting ammonia pipelines.

[0080] The welded joint between the repair box assembly and the pipeline forms an integrated fixed seal structure through the welding process. This structure is not only the operation carrier for realizing partitioned diversion, precise positioning, and anti-interference functions during the welding process, but also a permanent protective component that adheres to the three-way pipe part of the pipeline after repair.

[0081] After repair, the overall structure formed by the welded joint between the repair box assembly and the pipeline becomes a permanent part of the three-way pipe part. Under the high-low pressure alternating pressure condition, it can produce micro-deformation, continuously absorb part of the alternating stress, and effectively relieve the stress superposition problem of corrosion-stress coupling cracks.

[0082] In this application, the provided repair box adapts to the continuous medium flow through the large-diameter diversion cavity on the low-pressure side and the residual discharge through the small-diameter on the high-pressure side, avoiding the medium retention caused by single-cavity diversion. The elastic buffer layer can produce micro-deformation with the high-low pressure alternating pressure and absorb part of the alternating stress, solving the stress superposition problem of "corrosion-stress coupling cracks".

[0083] The vibration stabilizing clamp transmits vibration through the fixed support (converting the pipeline vibration into the rigid support of the support), reducing the vibration amplitude of the repair box to ≤0.5mm, solving the positioning problem caused by the flow vibration of the low-pressure pipeline. The anti-fog cover introduces the ammonia mist into the diversion hole and discharges it through "cover body enclosure + diversion and exhaust", solving the problem of the mist blocking the vision.

[0084] Reduce the heat input by low heat input welding on the low-pressure side, reducing the residual stress of the welded joint under continuous pressure. Increase the preheating temperature and post-weld heat preservation and slow cooling on the high-pressure side, improving the low-temperature toughness and anti-fatigue ability of the welded joint, and specifically solving the quality problems of "lack of penetration and slag inclusion" of the welded joints on the high-low pressure sides, adapting to their different pressure conditions.

[0085] Taking the repair of the tee connection between the high and low pressure ammonia water pipelines in a coke oven (DN600 low-pressure pipe + DN200 high-pressure pipe) as an example, this construction method was applied: Four months after the site was put into operation, a "corrosion-stress coupling crack" (80mm in length, 3mm in depth) appeared. The original repair method resulted in a recurrence of the crack after one month. When using this method, positioning holes were first drilled and a special repair box was assembled (φ15mm guide hole on the low-pressure side, φ13mm on the high-pressure side, 1mm thick 304 stainless steel elastic buffer layer). The box was then fixed with a vibration stabilizing clamp (vibration amplitude reduced to 0.3mm). After clearing the fog with an anti-fog cover, welding was performed: the preheating temperature on the low-pressure side followed the original method, with a linear energy of 14kJ / cm², and multi-layer, multi-pass welding (3 layers, each 3.5mm thick); the preheating temperature on the high-pressure side was increased by 50℃, followed by a post-heating at 250℃ for 30 minutes. After the repair, a soapy water test showed no leaks, the pressure fluctuation after the high-pressure pipeline was opened was ≤±3%, and the low-pressure pipeline operated continuously without abnormalities. After a 6-month follow-up observation, no signs of corrosion expansion or cracking were observed at the tee weld joint. The secondary cracking cycle was extended by 5 times compared to the original method. The repair process took only 4 hours (the original method required 6 hours) and did not affect the cooling of raw coke oven gas (low-pressure continuous liquid supply) or coal charging operations (high-pressure temporary shutdown followed by rapid recovery). The repair of a single site saved approximately 30,000 yuan in labor and downtime losses.

[0086] In summary, the design of the repair box assembly is customized to address the differences in flow rate and stress characteristics between high and low pressure ammonia water pipelines, representing a scenario-based innovation not addressed by existing general-purpose tee repair tools. A differentiated welding process adapted to high and low pressure conditions has been developed. On the low-pressure side, low-energy multi-layer, multi-pass welding is employed to reduce stress concentration under continuous pressure. On the high-pressure side, the preheating temperature is increased, and post-heating slow cooling is added to enhance fatigue resistance. This process design, based on the differences in pressure loads and corrosion risks on the high and low pressure sides, breaks through the limitations of existing technologies that rely on "uniform welding parameters," achieving a synergistic improvement in the corrosion resistance and fatigue resistance of the weld joint.

[0087] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0088] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0089] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for repairing weld defects in a high- and low-pressure ammonia water pipeline system, characterized in that, It includes: Grind the weld joints at the tee connections of the piping system. The repair box assembly is fitted onto the weld joint, so that the low-pressure side guide cavity of the repair box assembly is connected to the low-pressure pipeline and the high-pressure side guide cavity is connected to the high-pressure pipeline. After opening the guide valve of the low-pressure side guide chamber to allow ammonia water to flow out, open the guide valve of the high-pressure side guide chamber. Preheat the low-pressure pipeline to the target temperature, and perform multi-layer welding with the first set energy on the low-pressure side weld joint; Preheat the high-pressure pipeline to the target temperature, and perform single-layer welding with the second set energy on the high-pressure side weld joint; The high-pressure side weld joint is subjected to post-heat treatment, heated to a set temperature and then cooled to ambient temperature. Close the flow guide valve and open the high-pressure pipeline valve.

2. The method for repairing weld defects in a high- and low-pressure ammonia water pipeline system as described in claim 1, characterized in that, Grinding is performed on the weld joints of the tee connections in the piping system, specifically including: Close the high-pressure pipeline valves in the pipeline system and drain the ammonia water from the high-pressure pipeline. Grind the cracks in the weld joint of the tee connection.

3. The method for repairing weld defects in a high- and low-pressure ammonia water pipeline system as described in claim 1, characterized in that: The repair box assembly has a low-pressure side cavity and a low-pressure side guide cavity communicating with the low-pressure side cavity on one side, and a high-pressure side cavity and a high-pressure side guide cavity communicating with the high-pressure side cavity on the other side. The repair box assembly is fitted onto the weld joint, connecting the low-pressure side guide cavity of the repair box assembly to the low-pressure pipeline and the high-pressure side guide cavity to the high-pressure pipeline, specifically including: Drill positioning holes at the T-junction pipe connection and on the expected adjacent fixed bracket; The repair box assembly is fitted onto the weld joint so that the inner wall of the low-pressure side cavity of the repair box assembly fits against the outer wall of the low-pressure pipe, the inner wall of the high-pressure side cavity fits against the outer wall of the high-pressure pipe, and the low-pressure side guide cavity of the repair box assembly is connected to the low-pressure pipe and the high-pressure side guide cavity is connected to the high-pressure pipe. Insert the positioning pin of the repair box assembly into the positioning hole to fix the repair box assembly.

4. The method for repairing weld defects in a high- and low-pressure ammonia water pipeline system as described in claim 3, characterized in that, The repair box assembly is fitted onto the weld joint, specifically including: The low-pressure side arc plate is spliced ​​at the low-pressure side of the tee pipe connection to form a low-pressure side shell structure, and a low-pressure side cavity and a low-pressure side guide cavity are formed inside the low-pressure side shell structure. The high-pressure side arc plate is spliced ​​at the high-pressure side of the tee pipe connection to form a high-pressure side shell structure, and a high-pressure side cavity and a high-pressure side flow guide cavity are formed inside the high-pressure side shell structure. The elastic buffer layer is installed at the joint between the low-pressure side shell structure and the high-pressure side shell structure. Install sealing rings at the flow guide holes at both ends of the low-pressure side cavity, and install filter screens at the flow guide holes at both ends of the high-pressure side cavity to complete the fitting of the repair box assembly at the weld joint.

5. The method for repairing weld defects in a high- and low-pressure ammonia water pipeline system as described in claim 4, characterized in that: The repair box assembly is provided with a support ear plate on the outside, and an auxiliary device is provided on the repair box assembly, the auxiliary device including a vibration stabilizing clamp and an anti-fog cover; After completing the fitting of the repair box assembly at the weld joint, the method further includes: Fix the vibration stabilizing clip to the bracket ear plate on the outside of the repair box assembly, and connect the vibration stabilizing clip to the fixed bracket; Attach the anti-fog cover to the repair box assembly and seal the contact area between the anti-fog cover and the repair box assembly; Connect the exhaust port of the anti-fog cover to the guide hole on the low-pressure side of the repair box via a hose.

6. The method for repairing weld defects in a high- and low-pressure ammonia water pipeline system as described in claim 5, characterized in that, After closing the flow guide valve and before opening the high-pressure pipeline valve, the method further includes: Seal the drainage holes of the repair box assembly; Remove the vibration stabilizing clamp and the anti-fog cover.

7. The method for repairing weld defects in a high- and low-pressure ammonia water pipeline system as described in claim 4, characterized in that: When splicing the low-pressure side arc plate at the low-pressure side of the tee pipe connection and splicing the high-pressure side arc plate at the high-pressure side of the tee pipe connection, the deviations of the low-pressure side cavity axis, the high-pressure side cavity axis, and the tee pipe axis are detected. If the deviations exceed the preset range, the low-pressure side shell structure and the high-pressure side shell structure are adjusted until the deviations of the low-pressure side cavity axis, the high-pressure side cavity axis, and the tee pipe axis are within the preset range.

8. The method for repairing weld defects in a high- and low-pressure ammonia water pipeline system as described in claim 1, characterized in that: Before preheating the low-pressure pipeline to the target temperature and performing multi-layer welding with a first set energy on the low-pressure side weld joint, the method further includes: Dry the welding rods; After drying, the welding rods are stored in an insulated container.

9. The method for repairing weld defects in a high- and low-pressure ammonia water pipeline system as described in claim 1, characterized in that, Preheat the low-pressure pipeline to the target temperature, and perform multi-layer welding with the first set energy on the low-pressure side weld joint, specifically including: The repair area of ​​the low-pressure pipeline is heated, and the temperature of the repair area is kept at the target temperature for a set time after the temperature rises. Using the first set energy, multiple symmetrical positions are selected at the low-pressure side weld joint for spot welding positioning, welding slag is cleaned and weld quality is checked; The weld circumference is divided into multiple segments, and segmented symmetrical welding is carried out using alternating welding directions. Each segment is welded using a multi-layer, multi-pass welding process.

10. The method for repairing weld defects in a high- and low-pressure ammonia water pipeline system as described in claim 1, characterized in that, Preheat the high-pressure pipeline to the target temperature, and perform single-layer welding with a second set energy on the high-pressure side weld joint, specifically including: The repair area of ​​the high-pressure pipeline is heated, and the temperature of the repair area is kept at the target temperature for a set time after the temperature rises. Using the second set energy, multiple symmetrical positions are selected at the high-pressure side weld joint for spot welding positioning, welding slag is cleaned and weld quality is checked; The weld circumference is divided into multiple segments, and symmetrical segmented welding is performed using a unidirectional continuous welding direction, with each segment employing a single-layer welding process.

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