High-temperature high-pressure high-alloy pipe weld heat treatment and hardness detection process

Abstract

The application discloses a high-temperature high-pressure high-alloy pipeline weld heat treatment and hardness detection process, which comprises the following steps: (1) installing a thermocouple and fixing the thermocouple at a pipeline weld position; (2) arranging a temperature equalizing belt of a heater at the center of the weld, and wrapping the temperature equalizing belt with heat insulation materials; (3) performing heat treatment on the weld position; and (4) performing a vertical hardness detection test on the weld position after cooling. The pipeline weld heat treatment and hardness detection process can realize concentrated heat treatment and hardness detection on various forms of welds in a construction site by adopting different heater arrangement modes for different forms of welds, and the weld heat treatment efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of welding heat treatment technology, specifically to a heat treatment and hardness testing process for high-temperature, high-pressure, high-alloy pipeline welds. Background Technology

[0002] With the continuous development of the petrochemical and coal chemical industries and the significant increase in equipment production capacity, high-alloy metal pipelines, represented by P5, P9, and P91, are increasingly used in critical high-temperature and high-pressure components of industrial plants. P91, in particular, as a representative of new materials, presents significant challenges in both welding and heat treatment. This is often manifested in substandard hardness after welding. This means that stress during welding is not fully released and the microstructure is not adequately improved, easily leading to cracks in the pipeline welds during production and ultimately causing production accidents.

[0003] Taking the post-weld heat treatment of a typical high-temperature, high-pressure, high-alloy P91 pipe weld as an example, its heat treatment is divided into two methods: one is a continuous process of preheating, welding, martensitic transformation, heat treatment, non-destructive testing after 24 hours of cooling, and hardness testing for a single weld; the other method is: preheating, welding, martensitic transformation, post-heat slow cooling treatment, non-destructive testing after 24 hours of cooling, concentrated heat treatment of a large number of welds, hardness testing after cooling to room temperature, and then surface non-destructive testing (there should be no cracks). Ideally, the first method should be used in a welding laboratory (with suitable conditions and few welds); however, construction sites often lack the necessary conditions, and the second method is usually used.

[0004] For construction sites, the simultaneous operation of numerous mechanized automatic welding operations and a large number of welders presents challenges due to varying welding speeds, start and end times, and locations. Heat treatment equipment simply cannot meet the simultaneous operation requirements of each specific weld. This is especially true in the later stages of installation, where welds are widely distributed across different elevations, distances, and areas, posing significant risks and difficulties to construction. On-site wind and rain protection measures are also necessary. Furthermore, the construction site includes not only straight pipe butt welds but also numerous welds from pipes and high-pressure valves, pipe tees, fittings, and pipe platforms. These welds are often located in unusual positions, making it difficult to effectively place heaters and temperature measuring points, creating significant obstacles and difficulties for heat treatment and hindering the achievement of ideal results. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a heat treatment and hardness testing process for high-temperature, high-pressure, high-alloy pipeline welds, which enables large-scale centralized heat treatment of welds on the construction site, thereby improving the efficiency of weld heat treatment.

[0006] The technical solution of the present invention is as follows:

[0007] In a first aspect of the present invention, a heat treatment and hardness testing process for high-temperature, high-pressure, high-alloy pipeline welds includes the following steps:

[0008] (1) Install the thermocouple and fix it at the pipe weld position;

[0009] (2) Arrange the heat exchanger zone of the heater at the center of the weld, and wrap the heat exchanger zone with insulation material;

[0010] (3) Heat treatment of the weld area;

[0011] (4) After cooling, a vertical hardness test is performed at the weld location.

[0012] In some embodiments of the present invention, in step (1), a suitable thermocouple and compensating wire are selected, the thermocouple and compensating wire are matched and connected, and the thermocouple is fixed at the pipe weld position. The thermocouple is made of armored nickel-chromium-nickel-silicon material, and the compensating wire is made of copper-constantan material. The copper wire of the compensating wire is connected to the positive terminal of the thermocouple, and the constantan wire of the compensating wire is connected to the negative terminal of the thermocouple. The wire is tightened with screws.

[0013] In some embodiments of the present invention, in step (1), the number of thermocouple placement points is arranged according to the placement state of the welded joint and the nominal diameter of the pipe.

[0014] In some embodiments of the present invention, in step (2), the heat insulation material is refractory aluminum silicate roll blanket, which is tightly wrapped by staggered arrangement and upper layer pressing lower layer.

[0015] In some embodiments of the present invention, in step (3), during the heat treatment process, the heating rate below 300°C is 5125 / T (°C / h) and not greater than 220°C / h; the cooling rate is 6500 / T (°C / h) and not greater than 260°C / h, and the temperature displayed by the heater needs to be corrected.

[0016] In some embodiments of the present invention, step (4) specifically includes: performing a vertical hardness test at the 12 o'clock, 9 o'clock or 3 o'clock position of the weld; firstly, using a grinding wheel to roughly grind, then using sandpaper and a grinding wheel for preliminary polishing, and finally using an acrylic wheel for final fine polishing to a mirror surface, and then performing a vertical test on the surface, and the hardness value obtained is the true hardness value.

[0017] In some embodiments of the present invention, different weld joint types are classified before step (2).

[0018] In some embodiments of the present invention, the weld joint types include straight pipe butt welds, valve butt welds, tee welds, flange / pipe butt welds, and foundation butt welds.

[0019] In some embodiments of the present invention, when the weld joint is a valve butt weld, each side of the weld is heat-treated separately to ensure that the valve is slightly open.

[0020] In some embodiments of the present invention, when the valve side is particularly thick and the weld is too close to the valve body, auxiliary heating is performed on the valve body.

[0021] One or more technical solutions of the present invention have the following beneficial effects:

[0022] (1) The heat treatment and hardness testing process for pipeline welds provided by the present invention adopts different heater arrangement methods for different types of welds, which can realize a large number of centralized heat treatments and hardness tests for various types of welds on the construction site, thereby improving the efficiency of weld heat treatment.

[0023] (2) The heat treatment and hardness testing process for pipeline welds provided by this invention can flexibly adapt to various on-site conditions, and arrange heaters and temperature measuring points in the center of the uniform temperature zone as reasonably as possible, so that the weld is heated evenly, reducing heat loss, and ensuring that the heat treatment is carried out in accordance with the prescribed process, achieving qualified heat treatment in one go, and reducing rework. It saves project costs, effectively improves construction quality, and ensures that the construction progress is on schedule.

[0024] (3) The heat treatment and hardness testing process for pipe welds provided by the present invention adopts a three-step method for hardness testing. Before hardness testing, the 12, 9 or 3 points of the weld are ground, polished and finely ground so that the test contact is tested on a plane, which improves the accuracy of hardness testing.

[0025] (4) The heat treatment and hardness testing process for pipe welds provided by the present invention reduces the temperature deviation caused by various influencing factors. The actual heat treatment temperature of the weld is corrected according to the temperature displayed on the paper, thereby improving the measurement accuracy of the heat treatment temperature. Attached Figure Description

[0026] Figure 1 A schematic diagram showing the connection of the compensating wire and the thermocouple;

[0027] Figure 2 This diagram illustrates the isothermal zone, heating zone, and insulation width during post-weld heat treatment, where W represents the weld width; SB represents the isothermal zone width; HB represents the heating zone width; and GCB represents the insulation width.

[0028] Figure 3 This is a thermal cycle curve of a weldment with a base material of 9Cr-1Mo-V, after a cooling and heat treatment process:

[0029] Figure 4 This is a thermal cycle curve of another cooling and heat treatment after welding of a weldment with 9Cr-1Mo-V base material;

[0030] Figure 5 This is a schematic diagram of the hardness testing area;

[0031] Figure 6 This is a schematic diagram of hardness testing before polishing.

[0032] Figure 7 This is a schematic diagram of the hardness test after grinding and smoothing.

[0033] In the diagram: 1. Leeb hardness tester; 2. Pipe wall; 3. Welded joint; 4. Heat-affected zone. Detailed Implementation

[0034] Example 1

[0035] In a typical embodiment of the present invention, a heat treatment and hardness testing process for high-temperature, high-pressure, high-alloy pipeline welds is proposed, comprising the following steps:

[0036] 1. Select appropriate thermocouples and compensating wires, match and connect the thermocouples and compensating wires, and fix the thermocouples at the pipe weld position.

[0037] Before use, all metering equipment in the heat treatment equipment must undergo effective calibration. Each thermocouple must be calibrated and qualified to meet the maximum operating temperature for heat treatment of welds of all materials on site. Specifically, in step (1), the thermocouple is made of armored nickel-chromium-nickel-silicon material, and the compensating wire is made of copper-constantan material. When in use, such as Figure 1 As shown, the copper wire of the compensating lead is connected to the positive terminal of the thermocouple, and the constantan wire of the compensating lead is connected to the negative terminal of the thermocouple. The wires are tightened with screws to ensure that the cold junction temperature of the thermocouple is uniform.

[0038] The compensating wires must be intact, without joints, and exposed. The compensating wires must not be exposed to magnetic fields or coiled during use. The recording instrument must be compatible with the temperature measuring equipment. The recording paper must meet the maximum temperature recording range requirements for on-site heat treatment and be compatible with the recorder.

[0039] Furthermore, the number of thermocouple placement points is determined based on the placement of the welded joint and the nominal diameter of the pipe. For details, please refer to Table 1 for the arrangement of the number of thermocouples.

[0040] Table 1. Reference Table for Thermocouple Quantity and Arrangement

[0041]

[0042] 2. Arrange the heat exchanger of the heater at the center of the weld, and wrap the heat exchanger with insulation material.

[0043] Before proceeding to step 2, different weld joint types can be classified to allow for concentrated heat treatment of the welds. These weld joint types can be categorized as straight pipe butt welds, valve butt welds, tee welds, flange / pipe butt welds, and foundation butt welds, etc.

[0044] Specifically, in step 2, the heat exchange zone of the heater must be arranged in the center of the weld. The insulation material is refractory aluminum silicate roll blanket, which can be reused. Based on the insulation width (more than 1.5 times the heating width) and thickness (meeting the thermal calculation requirements), the external layer needs to be staggered and tightly bound by the method of layering the upper layer over the lower layer to ensure that there is no draft inside the pipe and to take measures to prevent wind and rain.

[0045] During heat treatment, the pipeline should be properly secured to prevent heat deformation. When the weld joint is a straight pipe butt weld, if... Figure 2 As shown, the width of the isothermal zone, heating zone, and insulation layer should be greater than the width of the weld to meet post-weld heat treatment requirements. When the weld joint is a valve butt weld, each side of the weld should be heat-treated separately to ensure the valve is slightly open. Furthermore, if the valve side is particularly thick and the weld is too close to the valve body, appropriate auxiliary heating should be applied to the valve body to reduce heat loss during the heat treatment process. When the weld joint is a flange / pipe butt weld, a standard installation gasket cannot be used; a tee heater should be employed. When the weld joint is a tee weld, a heater should be placed at the tee's intermediate joint, along with local auxiliary heating.

[0046] After the heater is installed, it is reinforced with refractory aluminum silicate to reduce heat loss during the heat treatment process.

[0047] 3. The heat treatment process is as follows: Below 300℃, the heating rate is 5125 / T (℃ / h), not exceeding 220℃ / h; the cooling rate is 6500 / T (℃ / h), not exceeding 260℃ / h, where T is the workpiece thickness in mm. However, these are maximum values ​​and need to be verified according to calculated values ​​or 60%-80% of the limit values, selecting the minimum value for actual operation. The heating rate below 300℃ can be disregarded. The values ​​in the holding temperature specifications and standards are only minimum values; this should be considered in actual operation.

[0048] During heat treatment, the temperature displayed by the heater needs to be corrected, especially when the heat treatment temperature is lower than the design requirement. The temperature curve displayed on paper cannot represent the actual heat treatment temperature of the weld. Therefore, it is necessary to make corrections based on clinical experience and specific circumstances to reduce temperature deviations caused by various influencing factors. For specific corrections, please refer to Tables 2 and 3.

[0049] Table 2. Influence of electromagnetic field on measurement accuracy

[0050] Phenomenon Possible error values ​​(°C) Recommended measures Error (°C) after taking the measures The thermocouple electrodes were not twisted together. 10~20 Insulated thermocouple electrodes are twisted together with a twisting distance of 30~35mm. 0~5 Thermocouple is not shielded or the shielding sleeve is not grounded. 10~30 Install a shielding sleeve, and ground the metal shielding sleeve. 0~10 Thermocouple and induction coil (tube) axes are placed parallel to each other. 20~70 Install vertically 0~20 The compensating conductor is not shielded or the shielding sleeve is not grounded. 30~40 Use shielded wires or wave-damping devices, and carefully ground the shielding sleeve. 10~15 The distance between the compensating conductor and the AC circuit conductors should be less than 0.3m. 20~40 The compensating conductors and AC circuit conductors should be placed parallel to each other at a distance greater than 0.3m or arranged perpendicularly. 5~10 Compensating wire curling 10~20 The compensating conductor must be stretched and straightened along its entire length. 0~5 The potentiometer was connected to a circuit without an isolation transformer and voltage regulator, and the instrument housing was not grounded. 15~30 The potentiometer is connected to an isolation transformer and a voltage regulator; the instrument housing is not grounded. 0~10 The distance between the potentiometer and electrical equipment and conductors is less than 10m, and the potentiometer is not installed in a metal cabinet or workroom. 30~50 The distance between the potentiometer and electrical equipment and conductors is greater than 10m, and the potentiometer is installed in a metal cabinet or working chamber. 10~15

[0051] Table 3 Errors caused by improper use of thermocouples

[0052] Phenomenon Approximate error value in °C Instrument readings Remark The thermocouple hot junction is not welded (referring to energy storage welding). 5~10 reduce none Poor contact between the hot end and the heating end of the tube Below 50 reduce none When fixing the thermocouple, the hot junction should be 5-10 mm away from the heating surface. 15~100 reduce none There are 1.5 to 2 turns of twisted connection after the cold junction of the thermocouple. Below 50 reduce none Thermocouple cold junction is not constant temperature Below 50 decrease or increase none When radiation heating is used, the insulation at the hot end is inadequate, and the hot end is directly affected by the heat conductor. 40~80 Increase Thermocouple may burn out The thermocouple is too short (less than 1m). 20 and above Increase The thermocouple used does not match the instrument's calibration number. 50 and above decrease or increase The direction of deviation depends on the matching of the thermocouple and the instrument's calibration number. The thermocouple is 10-20mm away from the weld seam at a distance exceeding the standard. Below 50 reduce none The thermocouple and compensating wire used are of incompatible type. 20~40 decrease or increase Related to the calibration and matching of wires and thermocouples The connection points of the thermocouples, compensating leads, and instruments did not comply with the requirement that both polarities must match. 10~30 reduce The error is related to the ambient temperature. Unreliable contact in thermocouples and instrument circuits Below 50 reduce The error is related to the ambient temperature. Some connections between compensating conductors use twisted joints (without welding). Below 20 reduce none

[0053] Taking a weldment with a base material of 9Cr-1Mo-V as an example, one of the following two cooling and heat treatment methods can be used for heat treatment:

[0054] (1) such as Figure 3 As shown, the weldment is cooled to 100℃~120℃ and held for 1 hour (to carry out martensitic transformation), and then immediately subjected to post-weld heat treatment.

[0055] (2) For example Figure 4 As shown, the weldment is cooled to 100℃~120℃ and held for 1 hour (to carry out martensitic transformation), then heated to 300℃~350℃ and held for 2 hours. After cooling to room temperature, post-weld heat treatment is performed at an appropriate time.

[0056] If the heat treatment curve is unqualified or the alloy steel hardness is unqualified, a systematic inspection and implementation of the on-site equipment, metering elements, heat treatment operation procedures, heaters, the routing of compensating wires, the arrangement of temperature measuring points, and on-site wind and rain protection measures must be carried out.

[0057] 4. After cooling to room temperature, perform a vertical hardness test at the 12 o'clock, 9 o'clock, or 3 o'clock positions on the weld. Figure 5 As shown.

[0058] Whether the hardness test results meet the specifications is an important indicator for verifying the quality of alloy steel after heat treatment. Inappropriate methods often lead to significant discrepancies in the test results. This embodiment employs a three-step method for the vertical hardness test: first, rough grinding is done using a DN100 grinding wheel (12 o'clock horizontal plane, 9 o'clock or 3 o'clock vertical plane); then, preliminary polishing is performed using sandpaper and a grinding wheel; finally, a final fine polishing to a mirror finish is done using an acrylic wheel; and then a vertical test is performed on the surface. The hardness value obtained is the true hardness value. Traditional hardness testing methods, such as... Figure 6 As shown, the test surface is uneven, and local peaks appear under a microscope, causing the contact point being non-planar, resulting in significant differences in the obtained hardness values. The hardness testing in this embodiment is as follows... Figure 7 As shown, the contact point being detected contacts the plane at the detection position, which improves the accuracy of the detection results.

[0059] The heat treatment and hardness testing process provided in this embodiment has been specifically applied in the following projects, demonstrating the beneficial effects of this process:

[0060] (1) In the Taizhou 1.1 million tons / year light hydrocarbon comprehensive utilization project in 2018, the heat treatment of the P91 pipeline weld was qualified on the first attempt, and the hardness was within the range specified in the design requirements. There have been no quality and safety issues since the construction and operation.

[0061] (2) It was well applied in the 1.4 million tons / year ethylene project of Zhejiang Petrochemical in 2019, providing strong support for construction quality and progress; since the completion of the unit, it has been operating normally for a long period of time without any accidents.

[0062] (3) In the 2020 Yantai Wanhua Phase I 1 million tons / year ethylene plant, the heat treatment of the P91 pipeline was carried out in accordance with this method and passed the test on the first attempt, which provided an essential guarantee for the construction quality and progress; since the plant was built, production has been normal and stable.

[0063] (4) In the 1 million tons / year ethylene plant of Luqing Petrochemical in 2020, the heat treatment of the P91 pipeline was carried out in accordance with this method and passed the test on the first attempt, which provided sufficient guarantee for the construction quality and progress; since the plant was built, production has been completely normal.

[0064] (5) In the 1.1 million tons / year ethylene plant of the Jiangsu Lianyungang Shenghong Refining and Chemical Project in 2021-2022, the heat treatment of the P91 pipeline was carried out in accordance with this method and passed the test on the first attempt, providing a reliable guarantee for construction quality and progress. Hardness test after on-site heat treatment: all met the requirements of ≤241HB as specified in the standards and regulations.

[0065] The process provided in this embodiment has certain guiding significance for the heat treatment of various high-temperature, high-pressure, and high-alloy steels, and is applicable to petrochemical, coal, energy and power engineering projects.

[0066] The embodiments described above provide a detailed explanation of the technical solution of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A heat treatment and hardness testing process for high-temperature, high-pressure, high-alloy pipeline welds, characterized in that, Includes the following steps: (1) Install the thermocouple and fix it at the pipe weld position; (2) Arrange the heat exchanger zone of the heater at the center of the weld, and wrap the heat exchanger zone with insulation material; (3) Heat treatment of the weld area; (4) After cooling, perform a vertical hardness test at the weld location; For weldments with a base material of 9Cr-1Mo-V, one of the following two cooling and heat treatment methods shall be used for heat treatment: The weldment is cooled to 100℃~120℃ and held for 1 hour to induce martensitic transformation, and then immediately subjected to post-weld heat treatment. Alternatively, the weldment can be cooled to 100℃~120℃ and held for 1 hour to induce martensitic transformation, then heated to 300℃~350℃ and held for 2 hours. After cooling to room temperature, post-weld heat treatment can be performed at a later time. In step (3), during the heat treatment process: the heating rate below 300℃ is 5125 / T (℃ / h) and not more than 220℃ / h; the cooling rate is 6500 / T (℃ / h) and not more than 260℃ / h; the temperature displayed by the heater needs to be corrected. In step (4), the vertical hardness test specifically includes: conducting a vertical hardness test at the 12 o'clock, 9 o'clock or 3 o'clock position of the weld; firstly, use a grinding wheel to roughly grind, then use sandpaper and a grinding wheel for preliminary polishing, and finally use an acrylic wheel to perform final fine polishing to a mirror surface, and then conduct a vertical test on the surface. The hardness value obtained is the true hardness value. Before step (2), different weld joint types are classified. When the weld joint is a flange / pipe butt weld, a formal installation gasket cannot be used, and a tee heater is used. When the weld joint is a tee weld, a heater is arranged in the middle of the tee, and local auxiliary heating is used at the same time. The weld joint types include straight pipe butt welds, valve butt welds, tee welds, flange / pipe butt welds, and foundation butt welds. When the weld joint is a valve butt weld, each side of the weld is heat-treated separately to ensure that the valve is slightly open.

2. The heat treatment and hardness testing process for high-temperature, high-pressure, high-alloy pipeline welds as described in claim 1, characterized in that, In step (1), select appropriate thermocouples and compensating wires, match and connect the thermocouples and compensating wires, and fix the thermocouples at the pipe weld position. The thermocouples are made of armored nickel-chromium-nickel-silicon material, and the compensating wires are made of copper-constantan material. The copper wire of the compensating wire is connected to the positive terminal of the thermocouple, and the constantan wire of the compensating wire is connected to the negative terminal of the thermocouple. Tighten with screws.

3. The heat treatment and hardness testing process for high-temperature, high-pressure, high-alloy pipeline welds as described in claim 1, characterized in that, In step (1), the number of thermocouple placement points is arranged according to the placement status of the welded joint and the nominal diameter of the pipe.

4. The heat treatment and hardness testing process for high-temperature, high-pressure, high-alloy pipeline welds as described in claim 1, characterized in that, In step (2), the insulation material is refractory aluminum silicate roll blanket, which is tightly wrapped by staggered arrangement and upper layer pressing lower layer.

Images