Composite joint coating tape, thermal shrinkage base material for joint coating tape and pipeline joint coating structure

Abstract

The utility model belongs to the field of metal corrosion control and protection, and particularly relates to a composite joint tape, a heat-shrinkable base material for the joint tape and a pipeline joint structure. The composite joint tape comprises a heat-shrinkable base material and an adhesive layer, the cross section shapes of the heat-shrinkable base material and the adhesive layer are matched with the shape of a joint coating of an adaptive pipeline; the section shape comprises a welding seam protruding section located in the center, and the two sides of the welding seam protruding section are sequentially connected with straight sections, groove sections and lap joint sections from inside to outside. The composite joint coating belt disclosed by the utility model can well exhaust air in each joint coating area including bottom angles of a welding line area and a groove area, and the air is prevented from being wrapped in the joint coating area to a great extent, so that the defects of hollowing, bubbles and the like at the reducing position of the joint coating are reduced, and the joint coating quality is improved.

Description

Technical Field

[0001] The utility model belongs to the field of metal corrosion control and protection, and specifically relates to a composite patching strip, a heat shrinkable substrate for the patching strip and a pipeline patching structure. Background Art

[0002] The pipeline 3LPE anti-corrosion layer (three-layer polyethylene anti-corrosion layer) has excellent comprehensive performance. At present, most gas pipelines adopt 3LPE design. Pipeline patching is the anti-corrosion construction at the pipeline interface weld. The purpose of pipeline patching is to play a physical shielding role, isolating the pipeline girth weld and the metal body of the pipeline at both ends of the weld from corrosive water, air, soil, etc.

[0003] The existing 3LPE anti-corrosion layer on-site patching mainly uses radiation cross-linked polyethylene heat shrink tape as the patching material, and the patching construction implementation standard is GB / T-23257-2017. The current pipeline design standard stipulates that the pipeline design service life is 50 years, so the patching material plays an important role in the overall pipeline anti-corrosion. The performance and quality of the patching material can almost determine the service life of the entire pipeline.

[0004] The radiation cross-linked polyethylene heat shrinkable tape is composed of a polyethylene substrate (i.e., a heat shrinkable substrate) and an adhesive layer bonded to the polyethylene substrate. During the patching construction, first apply a primer layer on the exposed reserved pipe end at the patching site (welding heat affected zone), and then perform the patching construction with the radiation cross-linked polyethylene heat shrinkable tape. During the patching construction, the radiation cross-linked polyethylene heat shrinkable tape must be cut according to the pipe diameter. Its length must be 15% longer than the circumference of the target pipe (including the anti-corrosion layer) for patching. The circumferential shrinkage index of this tape is 40%. During construction, the radiation cross-linked polyethylene heat shrinkable tape is installed in a ring at the patching site, and the overlapping part is directly above the patching site. A fixing plate is installed at the overlapping part, and the fixing plate and the cross-linked heat shrinkable polyethylene tape at the overlapping part are fixed by flame baking. At this time, a part of the patching tape should be hung down under the pipeline. When artificial flame baking is carried out, the uniformity of the overall heating of the radiation cross-linked polyethylene heat shrinkable tape should be taken into account. The flame bakes from top to bottom and from the middle to both sides. The radiation cross-linked polyethylene heat shrinkable tape shrinks from the middle weld area to the bottom coating area. After the bottom coating area shrinks, it will move to the groove area until the overlapping area of ​​the anti-corrosion layer. The patching tape gradually shrinks completely under the baking of the flame and merges and covers the patching area. Finally, medium-frequency induction is used for overall heating and tempering. In this way, the construction of a patching tape is completed.

[0005] According to the provisions of "SY / T 4050-2003 Radiation Cross-linked Polyethylene Heat Shrinkable Tape (Sleeve)", the heat shrinkage rate of radiation cross-linked polyethylene heat shrinkable tape is generally not less than 15%. The original intention of the design of the radiation cross-linked heat shrinkable process is to use the shrinkage of the tape to squeeze the molten adhesive layer, so that the adhesive can effectively fill the bottom corners of the weld area and the groove area to avoid defects such as hollowing and bubbles. However, it is not difficult to see from the above-mentioned patching construction process that the artificial flame baking process of the patching tape is completely determined by manual experience to determine the baking temperature. The shrinkage degree of different parts is difficult to be uniformly controlled, and the appearance will show defects such as wrinkles, hollowing, bubbles, etc. These defects will actually constitute the invasion channel of the corrosive medium and eventually cause the anti-corrosion failure of the patching.

[0006] In addition, the adhesive layer currently mainly uses EVA glue; before the pipeline is buried, it is affected by factors such as sunlight, rain, snow, wind and frost, and temperature changes between day and night at the construction site. When it is buried for a long time, the patch belt needs to be affected by seasonal, rain, snow, wind and frost weather changes throughout the year, which will cause the patch belt to be continuously squeezed and sheared under the alternating creep stress state for a long time, and the EVA glue will quickly fail to bond and crack the adhesive layer. Among them, adhesive failure refers to the peeling of the adhesive and the decrease in bonding strength. Adhesive layer cracks refer to cracks that appear at the junction of the patch belt and the anti-corrosion layer. These cracks will cause the patch belt to be water-permeable during service and accelerate the corrosion of the pipe body.

[0007] In view of the problems existing in the above-mentioned patching materials and patching processes, a Chinese invention patent with an authorization announcement date of May 17, 2022 and an authorization announcement number of CN111471408B discloses a polyethylene composite tape and its preparation and patching process method. The polyethylene composite tape adopts a two-layer structure of a substrate and an adhesive layer, wherein the substrate adopts radiation-cross-linked polyethylene with no heat shrinkage, and the hot melt adhesive used in the adhesive layer is composed of maleic anhydride-modified polyethylene, a tackifying resin and ethylene-vinyl acetate copolymer. The hot melt adhesive used solves the problems existing in EVA adhesive to a certain extent, and the bonding and peel strength between the adhesive and the substrate are improved.

[0008] Due to the use of radiation-cross-linked polyethylene with no heat shrinkage, the patching material involved in CN111471408B will also have a smooth patching appearance at the relatively flat base coating position. However, since the pipeline patching position actually has a complex variable diameter structure, for example, the circumferential weld position will be about 1.5 to 2 mm higher than the base coating (straight section), the anti-corrosion layer groove angle is about 30°, and the overlap area of ​​the anti-corrosion layer will also be about 3 to 5 mm higher than the base coating. When the above-mentioned polyethylene composite tape is wrapped at the patching position, the radial dimension of the variable diameter position becomes larger, and the adhesive layer is tightly attached to the substrate. During heat bonding, since the substrate does not shrink, the adhesive layer is still tightly attached to the polyethylene substrate, and obvious continuous hollowing, bubbles and other defects will appear in the weld area and the bottom corners of the groove area. Utility Model Content

[0009] The utility model aims to provide a composite patching belt, which solves the problem that the existing polyethylene composite belt is prone to hollowing, bubbles and other defects at the patching diameter changing position.

[0010] The second object of the utility model is to provide a heat shrinkable substrate for a patching tape to solve the above-mentioned problem.

[0011] The third object of the utility model is to provide a pipeline patching structure to solve the above-mentioned problem.

[0012] In order to achieve the above purpose, the technical solution adopted by the utility model is:

[0013] A composite patching strip comprises a heat shrinkable substrate and an adhesive layer; the cross-sectional shapes of the heat shrinkable substrate and the adhesive layer are adapted to the shape of the patching joint of the adapting pipe; the cross-sectional shape comprises a weld convex section located in the center, and the two sides of the weld convex section are sequentially connected with a straight section, a groove section and an overlap section from the inside to the outside; the total width of the composite patching strip is 500-600 mm.

[0014] The utility model belongs to an improved utility model creation. The cross-sectional shape of the heat shrinkable substrate is adapted to the shape of the patch, so that the patch strip is fitted with the structures of various parts of the patch when installed. The heat shrinkable substrate has heat shrinkability and can extrude the adhesive layer to fill the weld area and the bottom angle area of ​​the groove area during heating and bonding. Combined with the fitting design of the patch strip, the air in various patch areas including the weld area and the bottom angle of the groove area can be well discharged, and the air is avoided to a great extent in the patch area, thereby reducing the defects such as hollowing and bubbles at the patch variable diameter position, and improving the patch quality. The width design of the composite patch strip further ensures the overlap width and patch quality at both ends.

[0015] Preferably, the thickness of the heat shrinkable substrate is 1.0 to 1.5 mm, and the thickness of the adhesive layer is 1.0 to 1.5 mm.

[0016] Preferably, the raised section of the weld has a raised height of 1.5 to 2 mm and a width of 15 to 30 mm.

[0017] Preferably, the width of the overlapping section is 80-150 mm.

[0018] Preferably, the heat shrinkable substrate is made of radiation cross-linked polyethylene.

[0019] In order to achieve the above second purpose, the technical solution adopted by the utility model is:

[0020] A heat shrinkable substrate for a patching strip, the cross-sectional shape of the heat shrinkable substrate being adapted to the shape of a patching joint of an adaptable pipe; the cross-sectional shape comprising a weld convex section located in the center, the two sides of the weld convex section being sequentially connected with a straight section, a groove section and an overlap section from the inside to the outside.

[0021] The patching strip of the utility model uses a heat shrinkable substrate and performs targeted design on the cross-sectional shape of the patching strip. After affixing an adhesive layer of the same shape, a fitting design tailored to the shape of the patching strip can be formed, which is beneficial for removing air from the weld area and the bottom angle area of ​​the groove, so that the patching strip is tightly fitted and bonded at the patching position, thereby facilitating improving the patching quality.

[0022] Preferably, the raised section of the weld has a raised height of 1.5 to 2 mm and a width of 15 to 30 mm.

[0023] In order to achieve the third purpose above, the technical solution adopted by the utility model is:

[0024] A pipeline patching structure comprises a girth weld, exposed reserved pipe ends located on both sides of the girth weld and an anti-corrosion layer with a groove, a primer layer is coated on the exposed reserved pipe end and the girth weld, the composite patching strip is radially coated on the pipeline patching, and the weld convex section, straight section, groove section and overlap section on the composite patching strip are correspondingly bonded together with the girth weld area at the pipeline patching, the primer layer areas on both sides of the girth weld, the anti-corrosion layer groove area, and the anti-corrosion layer overlap area.

[0025] The pipe patching structure provided by the utility model improves the flatness of the entire patching area including the variable diameter positions such as the weld area and the groove bottom angle area, reduces wrinkles and air entrapment in the patching area, not only improves the appearance of the patching, but also makes the physical shielding effect of the patching belt fully play, thereby ensuring the quality of the patching.

[0026] Preferably, the thickness of the primer layer on the exposed reserved pipe end is ≥150 μm.

[0027] Further preferably, the total thickness of the patch anti-corrosion layer formed by the base coating at the patch and the composite patch strip is ≥2.65 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of the composite patching strip according to Example 1 of the utility model;

[0029] Figure 2 This is a heating schematic diagram of the pipeline patching method according to Embodiment 2 of the present utility model;

[0030] Figure 3 It is a schematic diagram of the pipeline patching structure of Example 2 of the utility model;

[0031] Among them, 1-polyethylene substrate; 2-adhesive layer; 3-weld raised section; 4-straight section; 5-groove section; 6-anti-corrosion layer overlap section; 7-medium frequency induction-infrared heating integrated coil; 8-pipeline; 9-weld heating zone; 10-welding heat affected heating zone; 11-anti-corrosion layer overlap heating zone; 12-edge heating zone; 13-circumferential weld; 14-groove; 15-reserved bottom layer; 16-base coating; 17-reserved anti-corrosion layer; α-groove angle. DETAILED DESCRIPTION

[0032] The technical concept of the utility model is to provide a composite patching strip that fits the shape of the pipe patch and has a certain heat shrinkage rate, that is, its cross-sectional shape is characterized by a weld convex section located in the center, and a straight section, a groove section, and an overlap section located on both sides of the weld convex section and arranged in sequence from the inside to the outside. After the patching strip is fitted and installed at the pipe patching position, the heat shrinking substrate shrinks during the heating and bonding process. Since the adhesive layer itself has relatively consistent contact with various areas of the patch, the shrinkage and extrusion of the heat shrinking substrate can easily discharge the air in various areas of the patch, thereby greatly improving the defects of intermittent hollowing, penetrating hollowing, bubbles, etc. that often occur in existing patching materials, thereby increasing the difficulty of pipe patching and reducing the difficulty of pipe patching construction.

[0033] Generally speaking, the total width of the patch tape is designed to be 500-600mm. The thickness of the heat shrinkable substrate and the adhesive layer in the width direction of the heat shrinkable substrate is designed to be uniform. Generally, the heat shrinkable substrate is controlled to be 1.0-1.5mm thick, the adhesive layer is controlled to be 1.0-1.5mm thick, and the sum of the thickness of the heat shrinkable substrate and the adhesive layer is ≥2.5mm. The heat shrinkage rate of the heat shrinkable substrate can be designed in accordance with "SY / T 4050-2003 Radiation Cross-linked Polyethylene Heat Shrinkable Tape (Sleeve)". At the same time, since the composite patch tape adopts a fitting design, the requirements for the heat shrinkage rate can be further relaxed. For example, a radiation cross-linked heat shrinkable polyethylene substrate with a heat shrinkage rate of 10-15% can be used.

[0034] The pipeline patching method using the patching tape comprises the following steps:

[0035] (1) Apply primer to girth weld and substrate;

[0036] (2) The composite patching strip is radially wrapped around the patching joint of the pipeline, and the weld raised section, straight section, groove section and overlap section on the composite patching strip are correspondingly fitted with the raised girth weld, primer, anti-corrosion layer groove and anti-corrosion layer overlap area at the patching joint of the pipeline;

[0037] (3) First use medium frequency induction heating to preheat the pipeline, and then use infrared heating to gradually heat it from the middle to both sides or from one side to the other.

[0038] After the composite patching tape is fitted and installed at the patching position of the pipe in the above-mentioned pipe patching method, the patching tape is heated in both internal and external directions by combining medium frequency induction heating and infrared heating to avoid poor fusion and bonding between the adhesive and the substrate caused by excessive temperature difference between the inside and outside of the patching tape, promote uniform shrinkage of the patching tape and uniform flow of the adhesive, and effectively solve problems such as air entrapment at the patching position and uneven appearance of the patching tape.

[0039] Preferably, in step (3), when heating is gradually performed from the middle to both sides, the circumferential weld position is heated first, then the area between the anti-corrosion layer groove and the circumferential weld is heated, and then the anti-corrosion layer groove and the overlap area of ​​the anti-corrosion layer are heated.

[0040] Further preferably, the method further includes heating the outer edge area where the anti-corrosion layer groove and the anti-corrosion layer overlap area meet.

[0041] Preferably, in step (3), the gradual heating includes heating a certain area to a set temperature and keeping it warm, then heating a subsequent area to a set temperature and keeping it warm, and stopping infrared heating after the last area is heated to a set temperature and kept warm.

[0042] Preferably, in step (3), the preheating temperature is 120-130°C; and the heating temperature of infrared heating is 170-180°C.

[0043] Further preferably, after the infrared heating in step (3), medium frequency induction heating is used for tempering, and the tempering temperature is 170-175°C.

[0044] In the above patching method, after the patching tape is installed at the patching location, medium-frequency induction internal heating is used and then infrared heating is used for external heating. The heating is gradually performed from the middle to both sides or from one side to the other in both internal and external directions. The adhesive layer absorbs heat and flows under the compression of the heat shrinkable substrate, filling the bottom corners of the weld, grooves and other areas prone to hollowing, and exhausts air to the next heating area, ultimately achieving the purpose of a dense patching structure.

[0045] In addition, through the design of the coating thickness of the bottom layer reserved near the anti-corrosion layer groove, a three-layer polyethylene composite belt anti-corrosion layer consisting of a bottom layer, an adhesive layer, and a polyethylene substrate from the inside to the outside can be obtained, and the total thickness of the patch anti-corrosion layer is greater than or equal to 2.65mm. The anti-corrosion design of the overall patch structure can match the 3LPE pipeline anti-corrosion material to avoid the failure of the patch anti-corrosion, effectively solve the problems of poor operability of existing patch materials and processes, and the patch quality cannot be guaranteed, and comprehensively improve the technical level of pipeline patching.

[0046] The implementation process of the utility model is described in detail below in conjunction with specific embodiments.

[0047] 1. Specific embodiments of composite patching tape and heat shrinkable substrate for patching tape

[0048] Example 1

[0049] The composite patching strip of this embodiment, such as Figure 1 As shown, it includes a polyethylene substrate 1 (i.e., radiation cross-linked heat shrinkable polyethylene) and an adhesive layer 2 bonded to one side of the polyethylene substrate; the polyethylene substrate 1 is a polyolefin material specified for use in the field of pipeline patching, which serves as an adhesive carrier on the one hand, and also meets the various performance requirements of the patching material for the substrate on the other hand. The thermal shrinkage rate of the polyethylene substrate 1 is 10-15%, which can be conventionally determined by adjusting parameters such as the irradiation dose in the polyethylene production process, or can be directly customized from the polyethylene substrate manufacturer.

[0050] The adhesive provided by adhesive layer 2 mainly makes the polyethylene substrate firmly and densely bonded to the pipe patch. In addition to meeting the relevant standards for pipe patching, the adhesive can also be selected with better performance such as softening point temperature and high and low temperature peel strength. Currently, there are related varieties on the market that can meet the above higher index requirements.

[0051] The cross-sectional shape of the polyethylene substrate 1 and the adhesive layer 2 is processed to match the shape of the pipe patch, so that the composite patch can be attached to various areas of the pipe patch during installation. Specifically, the cross-sectional shape includes a weld convex section 3 and a straight section 4, a groove section 5 and an anti-corrosion layer overlap section 6 connected to both sides of the weld convex section and arranged in sequence from the inside to the outside. The straight section 4 corresponds to the area between the groove of the anti-corrosion layer and the girth weld at the pipe patch.

[0052] In this embodiment, the thickness of the polyethylene substrate is 1.5 mm, and the thickness of the adhesive layer is 1.0 mm. The width of the anti-corrosion layer overlap section 6 is 100 mm. The groove angle (α) is 30°. The weld raised section 3 forms an arc groove, the in-groove height of the arc groove is 2 mm, and the in-groove width is 25 mm. The total width of the composite patching strip is 520 mm. In other implementation situations, the thickness of the polyethylene substrate and the adhesive layer can be controlled to be 1.0 to 1.5 mm, and the sum of the thickness of the polyethylene substrate and the adhesive layer is controlled to be above 2.5 mm. The anti-corrosion layer overlap section 6, the in-groove height and in-groove width of the arc groove, and the total width of the composite patching strip (for example, 500 mm, 550 mm, 600 mm, etc.) can be adaptively adjusted according to the specifications of the pipeline to be patched, and can meet the use requirements of most domestic oil and gas pipelines within the preferred range defined in the utility model.

[0053] The heat shrinkable substrate for the patching strip of this embodiment is a polyethylene substrate 1 with a heat shrinkage rate of 10-15%. The cross-sectional shape of the polyethylene substrate 1 is processed to match the shape of the pipeline patching joint. The cross-sectional shape includes a weld protruding section 3 and a straight section 4, a groove section 5 and an anti-corrosion layer overlap section 6 connected to both sides of the weld protruding section and arranged in sequence from the inside to the outside.

[0054] The following is a description of the processing and prefabrication process of the polyethylene composite patching strip of this embodiment:

[0055] (1) A whole roll of polyethylene sheet (1100 mm wide and 1.5 mm thick) used as the composite patching tape substrate is passed through an electron accelerator, and the irradiation dose is controlled according to the thermal shrinkage rate of 10 to 15%;

[0056] (2) The irradiated substrate is thermally bonded to the adhesive and then shaped by a flat roller to form a 2.5 mm thick roll of cross-linked heat-shrinkable polyethylene composite tape with an adhesive layer thickness of 1.0 mm;

[0057] (3) Cutting the whole roll of composite tape into 520 mm wide polyethylene composite tape rolls;

[0058] (4) The polyethylene composite tape roll passes through the tension unwinding device and enters the patch tape profiling roller for shaping. The profiling roller is processed into concave and convex rollers according to the shapes of the weld, groove, and overlap area of ​​the anti-corrosion layer at the patch. The polyethylene composite tape is shaped into the shape of the patch under the simultaneous action of heating and profiling roller pressure. After the tape roll comes out of the pressure roller line, it is reeled up by the tension traction device to become a polyethylene composite patch tape.

[0059] (5) The length of polyethylene composite patching tape for pipes with different diameters is calculated based on the circumferential fitting length and overlap length. When the pipe is composited with joint tape, press The pipeline anti-corrosion layer is 4.2mm thick, the pipeline outer diameter is 1223.2mm, the fitting length is 3843mm, the overlap length is 100mm, and the total length of the patching tape is cut to 3943mm.

[0060] (6) The cut patch tape can be rolled into a tube for easy storage and transportation.

[0061] 2. Specific embodiments of the pipeline patching method and pipeline patching structure

[0062] The above-mentioned pipeline patching method has effectively solved the difficulties in controlling the existing flame baking and other patching processes, and has made more comprehensive and detailed considerations in terms of patching band shrinkage and exhaust. The entire patching process can be mechanized and intelligent, thereby ensuring the quantification and standardization of each pipeline patching operation, without relying on the skills and experience of the patching workers, and improving the patching construction quality of the entire pipeline.

[0063] The traditional installation process of radiation cross-linked polyethylene heat shrink tape is basically cold tape hot installation or tropical cold installation. Cold tape hot installation means that the steel pipe has a higher temperature, such as the bottom layer is coated with fused epoxy powder coating, and the patch tape is installed by a winding machine using the temperature of the coating surface; tropical cold installation means that the surface of the steel pipe is the ambient temperature during construction, and the patch tape is installed by artificial baking. The above two methods are installed on two surfaces with a large temperature difference. The patch construction is completed without preheating or tempering treatment, which is bound to increase the constraint of the overall patch structure, resulting in poor fusion and bonding between the patch tape adhesive and the bottom coating, and the creep resistance and shear resistance will be reduced, reducing the service life of the patch tape.

[0064] In terms of reducing the temperature difference during the installation of the patch tape, the patching method mentioned above adopts a combination of induction heating and infrared heating, wherein the induction heating heats the patch tape from the inside to the outside to ensure that the side where the adhesive layer contacts the base coating is fully preheated; after reaching the predicted temperature, the induction heating is stopped and the infrared heating is started. Infrared heating heats the patch tape from the outside to the inside, and the heating is gradually heated from the middle to both sides or from one side to the other. This can gradually discharge the air at the interface between the patch tape and the substrate to avoid hollowing and bubbles caused by air entrapment, and can also promote the uniform contraction and exhaust of the patch tape to avoid surface wrinkles. After that, the infrared heating is stopped and the induction heating is started again for tempering, which can greatly improve the problem of poor fusion and bonding between the patch tape adhesive and the base coating.

[0065] During infrared heating, heat a certain area to the set temperature and keep it warm, then heat the next area to the set temperature and keep it warm, until the last area is heated to the set temperature and kept warm for 3 to 5 minutes, then stop infrared heating. Specifically, the heating area can be divided into the girth weld area, welding heat affected zone, groove and overlap area. It is preferred to start heating from the girth weld area in the middle, and then gradually heat the welding heat affected zone, groove and overlap area on both sides. This method has the shortest exhaust path and high heating efficiency. In addition, an edge heating zone can be set on the outside of the groove and overlap area. When in an extremely cold environment in winter, adding an edge heating zone can achieve a better edge fusion and bonding effect.

[0066] When the composite patching tape is fitted to the patching joint, a certain circumferential overlap length should be retained, generally controlled to be 100-150mm. After the circumferential overlap is completed, a welding machine is used to weld the circumferential overlap area of ​​the patching tape.

[0067] Other steps of patching construction can refer to existing technologies. For example, the surface pretreatment of the metal body of the pipe at the patching point and the surface pretreatment of the overlapping area of ​​the anti-corrosion layer should meet the requirements specified in the standards. It should be confirmed that the patching point has been sandblasted and rust-removed to achieve the surface pretreatment effect, including rust removal level, dust degree, anchor pattern depth, etc.; attachments, oil pollution, etc. should be handled in time, and the slope of the polyethylene anti-corrosion layer and the overlapping area of ​​the anti-corrosion layer should be roughened.

[0068] Example 2

[0069] Using the composite patching tape of Example 1, the technical specifications, construction conditions, patching process flow and other contents of the pipeline patching are specifically described as follows:

[0070] 1. Pipeline patching technical specifications

[0071] pipeline Wall thickness 17.4, material X80 (API), anti-corrosion layer 3LPE reinforced grade, reserved end width of anti-corrosion layer 150mm, groove angle 30°, bottom fused epoxy powder coating 150μm, reserved length of coating (i.e. the reserved bottom section connected to the bottom end of the groove) 15~25mm, overlap width of patching tape and anti-corrosion layer 100mm.

[0072] 2. Construction conditions:

[0073] Sandblasting equipment: 10.5-ton truck (with 8-meter self-unloading hydraulic folding crane), 120kW industrial frequency diesel generator, 1 75kW screw air compressor (8m 3 / min, 0.8MPa), 1 pipe joint sealing sandblasting and rust removal equipment (equipped with 2 30kW vacuum cyclone pumps, 1 set of automatic rotary spraying rack), 1 set of 80kW medium frequency power supply (with 1 set of medium frequency heating coil).

[0074] Equipment of the joint patching unit: 10.5-ton truck (with 8-meter self-unloading hydraulic folding crane), 150kW industrial frequency diesel generator, 100kW cold-zone medium frequency, 100kW infrared heating control power supply (with 1 set of medium frequency and infrared heating coils).

[0075] Weather and environmental conditions: temperature 22℃, humidity 78%, wind force 2, suitable for patching construction.

[0076] 3. Patching process

[0077] The patching process mainly consists of the following parts: surface pretreatment of the patching, primer coating, installation of polyethylene composite patching tape, quality inspection and recording. The patching construction adopts mechanized construction, and a complete pipeline patching operation unit is composed of two units.

[0078] 3.1 Surface pretreatment of the patch: medium frequency preheating of the patch, heating temperature 60℃, automatic closed rotary spraying and sandblasting frame hoisting in place, check the rust removal effect after rust removal, the rust removal level reaches the near white level Sa2.5, the dust level is above level 2, and the anchor pattern depth is between 50 and 90μm. Clean the 100mm wide reserved end of the anti-corrosion layer to remove debris and surface attachments, sandblast the groove area to remove rust and roughen it, and flame bake the reserved area of ​​the anti-corrosion layer for roughening.

[0079] 3.2 Primer coating: The primer layer is applied with solvent-free two-component liquid high-temperature epoxy paint. Before painting, stick shielding paper on the groove area to avoid coating on the groove area and affecting the fusion of adhesive and groove area. The thickness of the primer layer on the exposed reserved pipe end and circumferential weld is ≥150μm. After painting, use a wet film gauge to check the thickness. The surface drying time of the coating wet film is 12min.

[0080] By using the above thick film coating primer, the anti-corrosion performance is further improved, which is more conducive to achieving long-term corrosion protection at the patching point.

[0081] 3.3 Mechanized polyethylene composite patching belt installation:

[0082] (1) Installation of patching tape

[0083] After the primer coating is dry on the surface, install the polyethylene composite patching tape to the patching joint, fit the arc groove, groove area, and anti-corrosion layer overlap area of ​​the patching tape tightly to the patching joint, and use a welding machine to weld the patching tape to an overlap area of ​​100mm.

[0084] (2) Heating of the patching strip

[0085] Schematic diagram of heating of joint strip Figure 2 As shown, the medium frequency induction-infrared heating integrated coil 7 is sleeved on the patch of the pipe 8 and aligned, and the composite patch belt is located within the medium frequency induction heating range of the medium frequency induction-infrared heating integrated coil 7. The infrared heating is divided into seven zones from left to right to achieve zoning and gradual heating of the patch belt. Figure 2 In the figure, the seven zones of infrared heating include a weld heating zone 9 located in the center, two welding heat affected heating zones 10 symmetrically arranged on both sides of the weld heating zone 9, two anti-corrosion layer overlapping heating zones 11 symmetrically arranged on the outside of the welding heat affected heating zones 10 on both sides, and two edge heating zones 12 symmetrically arranged on the outside of the anti-corrosion layer overlapping heating zones 11 on both sides.

[0086] Among them, the weld heating zone 9 is mainly used to heat the circumferential weld area, the welding heat affected heating zone 10 is mainly used to heat the area between the anti-corrosion layer groove and the circumferential weld, the anti-corrosion layer lap heating zone 11 is mainly used to heat the anti-corrosion layer groove and the anti-corrosion layer lap area, and the edge heating zone 12 is activated under extremely cold conditions in winter to heat the edge anti-corrosion layer connected to the anti-corrosion layer lap area.

[0087] The heating width of the weld heating zone 9 is 62mm, the heating width of the welding heat affected heating zone 10 is 120mm, the heating width of the anti-corrosion layer overlap heating zone 11 is 120mm, and the heating width of the edge heating zone 12 is 62mm.

[0088] Start the automatic heating mode, the medium frequency heating coil will preheat the steel pipe surface at the patch to 120℃ and then stop. The infrared heating starts from the weld, and the patch surface is heated to 180℃ and then stopped and kept warm. Then start the welding heat affected heating zone 10 on both sides in turn, and stop heating and keep warm when the surface temperature of the patch in the welding heat affected zone rises to 180℃. Start the anti-corrosion layer overlap heating zone 11, and stop heating when the surface temperature of the anti-corrosion layer groove and the overlap zone patch rises to 180℃, and keep warm for 3 minutes before stopping heating.

[0089] In extremely cold winter conditions, when the surface temperature of the anti-corrosion layer groove and the patching strip in the overlap area rises to 180°C, stop heating and keep warm, then start the edge heating zone 12, and when the surface temperature of the heating zone rises to 180°C, stop heating and keep warm for 3 minutes before stopping heating, which can enhance the edge fusion of the patching strip.

[0090] Tempering heating of the patching strip: Turn off the infrared heating power supply, start the medium frequency power supply again, and the induction heating coil heats the steel pipe to 175℃ and then stops heating.

[0091] During the above heating process, the patch tape begins to soften and shrink at 140°C, and the adhesive also begins to melt. The process method of the utility model is a cold tape heat shrink, which is heated in steps from the weld to the overlap area of ​​the anti-corrosion layer. The heat shrink substrate shrinks evenly, and the adhesive layer is also heated evenly to melt and fit with the bottom layer to remove air. After the infrared heating process is completed, the medium frequency coil starts heating, and the steel pipe stops after heating to 170°C. At this time, the surface temperature of the steel pipe reaches equilibrium, and the heat is evenly distributed in the adhesive layer.

[0092] The detailed comparison between the pipe patching process of this embodiment and the existing cross-linked heat shrinkable polyethylene tape patching process is listed in Table 1.

[0093] Table 1 Pipeline Comparison of patching process

[0094]

[0095]

[0096] In Table 1, the coverage rate of the patch tape is the ratio of the effective bonding area of ​​the patch tape peeling zone to the area of ​​the peeling zone, which indicates the degree of hollowing and non-fusion of the patch tape. The higher the coverage rate of the patch tape, the smaller the degree of hollowing and non-fusion of the patch tape.

[0097] The pipeline patching structure of this embodiment is as follows: Figure 3 As shown, it includes a pipe 8 connected together by a girth weld 13, and bare substrates (exposed reserved pipe ends) are connected on both sides of the girth weld 13, and a reserved anti-corrosion layer 17 is connected to the outside of the bare substrate, and the reserved anti-corrosion layer 17 has a groove 14 and a reserved bottom layer 15 extending out of the groove 14 and extending toward the girth weld 13. The anti-corrosion layer adopts a 3LPE anti-corrosion structure, and the reserved bottom layer 15 is a sintered epoxy powder bottom layer. A primer 16 is coated on the bare substrate and the reserved bottom layer, and the primer 16 adopts a high-temperature two-component solvent-free liquid epoxy bottom layer. The composite patching tape is radially coated on the pipe patching, and the weld raised section, straight section, groove section and overlap section on the composite patching tape are bonded together with the raised girth weld, bottom coating, anti-corrosion layer groove, and anti-corrosion layer overlap area at the pipe patching.

[0098] The thickness of the primer layer 16 on the exposed reserved pipe end is ≥150 μm. The thickness of the reserved bottom layer 15 is ≥150 μm. The above pipeline patching structure forms a three-layer polyethylene composite belt anti-corrosion layer, and the total thickness of the patching anti-corrosion layer is ≥2.65 mm.

[0099] Through the above comparison, the patching structure and construction process of the utility model have the following characteristics:

[0100] ① The utility model combines the patching site working conditions to install and fit the polyethylene composite patching belt with the weld, heat affected zone, groove and anti-corrosion layer overlap area of ​​the patching area at one time, which is simple to install and improves work efficiency.

[0101] ② After the patching belt of the utility model is fixed on the pipeline, the medium frequency induction + infrared heating coil can be directly hoisted into place in the patching area. It only needs one button to start, starting from the pipeline preheating, and can automatically complete the processes of patching belt shrinkage, exhaust, insulation, tempering, etc. The medium frequency induction heating and infrared heating act alternately, and the operation is simple and intelligent.

Claims

1. A composite patch strip comprising a heat shrinkable substrate and an adhesive layer, It is characterized in that The cross-sectional shape of the heat shrinkable substrate and the adhesive layer is adapted to the shape of the patching joint of the adapter pipe; the cross-sectional shape includes a weld protrusion section located in the center, and the two sides of the weld protrusion section are sequentially connected with a straight section, a groove section and an overlap section from the inside to the outside; the total width of the composite patching strip is 500 to 600 mm.

2. The composite patching strip according to claim 1, It is characterized in that The thickness of the heat shrinkable substrate is 1.0 to 1.5 mm, and the thickness of the adhesive layer is 1.0 to 1.5 mm.

3. The composite patching strip according to claim 1, It is characterized in that The convex section of the weld has a convex height of 1.5 to 2 mm and a width of 15 to 30 mm.

4. The composite patching strip according to claim 1, It is characterized in that The width of the overlapping section is 80-150 mm.

5. The composite patching strip according to claim 1, It is characterized in that The material of the heat shrinkable substrate is radiation cross-linked polyethylene.

6. A heat shrinkable substrate for a patching tape, It is characterized in that The cross-sectional shape of the heat shrinkable substrate is adapted to the shape of the patching portion of the adapter pipe; the cross-sectional shape includes a weld convex section located in the center, and the two sides of the weld convex section are sequentially connected with a straight section, a groove section and an overlap section from the inside to the outside.

7. The heat shrinkable substrate for the patch tape according to claim 6, It is characterized in that The convex section of the weld has a convex height of 1.5 to 2 mm and a width of 15 to 30 mm.

8. A pipeline patching structure, comprising a girth weld, exposed reserved pipe ends on both sides of the girth weld, and an anti-corrosion layer with a groove, wherein a primer is applied on the exposed reserved pipe ends and the girth weld. It is characterized in that The composite patching strip as described in any one of claims 1 to 5 is radially coated on the pipe patch, and the weld raised section, straight section, groove section and overlap section on the composite patching strip are correspondingly bonded together with the circumferential weld area, the primer areas on both sides of the circumferential weld, the anti-corrosion layer groove area and the anti-corrosion layer overlap area at the pipe patch.

9. The pipeline patching structure according to claim 8, It is characterized in that The thickness of the primer coating on the exposed reserved pipe end is ≥150μm.

10. The pipeline patching structure according to claim 9, It is characterized in that The total thickness of the patch anti-corrosion layer composed of the base coating and the composite patch strip at the patch is ≥2.65mm.

Images