Method for evaluating misalignment and excess height safety of a hydrogen pipeline girth weld joint
Patent Information
- Application Number
- CN202611508063.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-28
- Publication Date
- 2026-11-03
AI Technical Summary
[0007]本发明针对现有实验室内采用标准小试样无法评估输氢管道环焊接头错边和余高安全性的技术难题，提供了一种低成本的实验研究方法，本发明所采用的技术方案如下：
本发明将输氢管道的壁厚设为拉伸试验试样宽度，从而可以完整保留环焊接头的错边、余高等原始形貌；对环向厚度进行双侧减薄以降低拉伸载荷，规避了夹持端失效问题，可适配配有高压釜的小吨位拉伸试验机；可以基于模拟输氢管道服役环境的高压氢环境进行慢应变速率拉伸试验，以断裂位置是否为管道母材作为判定环焊接头错边、余高应力集中安全性的依据。本发明提供了一种低成本、可工程化应用的实验研究方法，解决了难以用实际环焊接头试样评估错边以及余高安全性的技术难题，为输氢管道安全建设奠定了关键技术基础。
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Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of defect tolerance research on ring welded joints, and discloses an evaluation method for the safety of misalignment and excess height of ring welded joints in hydrogen transportation pipelines. Background Technology
[0002] In pipeline construction, circumferential welds inevitably suffer from defects such as misalignment (where the edges of two workpieces that should be aligned deviate parallel along the thickness direction), excess weld height (the portion of the weld surface that protrudes above the base metal surfaces on both sides), undercut, and incomplete penetration. While there are standards for the quality acceptance of welds in natural gas pipelines, there is no evidence to support whether these standards are applicable to hydrogen pipelines. It is generally believed that weld defect control for hydrogen pipelines should be more stringent, but blindly imposing higher requirements would significantly reduce on-site construction efficiency and increase construction costs.
[0003] Currently, defect tolerance assessments often employ standard small specimens for tensile (smooth round bar) and fracture toughness (single-sided notched three-point bending / CT) tests. However, standard specimens require a smooth and flat test area, which cannot reflect the effects of misalignment and excess height in actual welded joints.
[0004] To study the impact of misalignment and excess height on the performance of pipe joints, plate-shaped tensile specimens with rectangular / arc cross-sections can be used. Engineers designing hydrogen pipelines are most concerned with the impact of defects in the inner wall of the pipeline, which are in direct contact with hydrogen, on safety. However, if samples are taken along the pipe wall thickness direction near the inner wall, the base material thickness on both sides of the misaligned joint will be unequal (see...). Figure 1 During tensile testing, fracture inevitably occurs on the thinner side, which contradicts the actual situation where both sides of the joint are of equal thickness. Although full-wall-thickness specimens can retain misalignment and excess height, to avoid interference from factors such as excess height at the clamping end, the standard rectangular specimen length is approximately 230 mm (see...). Figure 2 (Unit: mm, GB / T 31032 "Welding and Acceptance of Steel Pipelines"), which raises two issues: first, a large-tonnage testing machine is required; second, it is difficult to place it in a high-pressure reactor simulating the service environment of hydrogen pipelines. If electrochemical hydrogen charging is used instead, the environment differs significantly from actual operating conditions, limiting the engineering guidance significance of the test results. If a large-capacity high-pressure reactor is configured on a large-tonnage testing machine, the equipment investment and testing costs will increase significantly, and the larger the volume, the lower the achievable pressure limit. If non-standard full-wall-thickness small specimens are used (reducing the length to below 110 mm), although they can be adapted to conventional hydrogen environment tensile testing machines, plastic deformation during tensile testing preferentially concentrates at the clamping end, easily leading to specimen pull-out (see...). Figure 3 This means that the specimen cannot be fully stretched.
[0005] Furthermore, even if tensile tests under high-pressure hydrogen conditions are successfully conducted, there is currently a lack of clear indicators for evaluating the safety of joints with misalignment and excess height under simulated operating conditions. Current material compatibility testing with hydrogen environments typically uses the hydrogen embrittlement index (i.e., the performance loss rate of the hydrogen environment relative to a reference environment) to evaluate hydrogen embrittlement sensitivity. However, the geometry of misalignment and excess height varies at different locations in the circumferential weld joint, making it difficult to obtain uniform comparative results. Moreover, there is currently no standard for the safety threshold value of the hydrogen embrittlement index.
[0006] In summary, it is necessary to develop a method for conducting slow strain rate tensile tests on small specimens with full wall thickness on a small-tonnage mechanical property testing machine equipped with a high-pressure environmental chamber, and to use this method to evaluate the safety of misalignment and excess height of welded joints in hydrogen pipeline rings. Summary of the Invention
[0007] This invention addresses the technical challenge of assessing the safety of misalignment and residual height in welded joints of hydrogen transport pipelines using standard small-sample tests in existing laboratories. It provides a low-cost experimental research method, the technical solution of which is as follows: A method for evaluating the safety of misalignment and excess height in ring welded joints of hydrogen transportation pipelines includes the following steps: S1. Prepare a plate-shaped tensile test specimen with a rectangular or arc-shaped cross-section. The tensile test specimen is cut perpendicular to the circumferential weld joint along the longitudinal direction of the hydrogen pipeline. The length direction of the tensile test specimen is the longitudinal direction of the hydrogen pipeline, the width direction of the tensile test specimen is the wall thickness direction of the hydrogen pipeline, and the thickness direction of the tensile test specimen is the circumferential direction of the hydrogen pipeline. The weld is located in the central area along the length direction of the tensile test specimen. The tensile test specimen has misaligned edges and / or excess height. S2. Thinning is performed on both sides of the middle section of the tensile test specimen in the thickness direction to form a parallel length section of the tensile test specimen. S3. The tensile test specimen is clamped on a tensile testing machine equipped with an autoclave, so that the tensile test specimen is placed inside the autoclave. After the autoclave is closed, the service environment of the hydrogen pipeline is simulated inside the autoclave. S4. Start the tensile testing machine to perform a slow strain rate tensile test on the tensile test specimen, with a strain rate ≤ 2 × 10⁻⁶. -5 If the tensile test specimen breaks in the pipe base material area during the tensile process, it indicates that the local stress concentration caused by misalignment and / or excess height is insufficient to make the circumferential weld joint a high-risk area.
[0008] Preferably, the width of the tensile test specimen is equal to the full wall thickness of the hydrogen pipeline, and the middle section of the tensile test specimen is thinned on both sides in the thickness direction.
[0009] Preferably, slow strain rate tensile tests are conducted under simulated hydrogen transportation service conditions, and the safety of misalignment and / or excess height is assessed based on the fracture location of the tensile test specimen: if the fracture occurs in the base material, the misalignment and / or excess height is acceptable; if the fracture occurs in the joint area and the crack initiation originates from a sudden change in the shape of the misalignment and / or excess height, the allowable value of misalignment and / or excess height is reduced; if the tensile test in the hydrogen environment still results in fracture in the base material under the maximum allowable amount of misalignment and / or excess height in the natural gas pipeline standard, the maximum allowable value in the natural gas pipeline standard is directly adopted.
[0010] The beneficial effects of this invention are: This invention sets the wall thickness of the hydrogen pipeline as the width of the tensile test specimen, thus preserving the original morphology of the circumferential weld joint, including misalignment and excess height. Bilateral thinning of the circumferential thickness reduces tensile load, avoiding clamping end failure issues, and is compatible with small-tonnage tensile testing machines equipped with autoclaves. Slow strain rate tensile tests can be conducted in a high-pressure hydrogen environment simulating the service environment of the hydrogen pipeline, using whether the fracture location is in the pipeline base material as the basis for determining the safety of stress concentration in the circumferential weld joint's misalignment and excess height. This invention provides a low-cost, engineering-applicable experimental research method, solving the technical challenge of evaluating the safety of misalignment and excess height using actual circumferential weld joint specimens, and laying a key technological foundation for the safe construction of hydrogen pipelines. Attached Figure Description
[0011] Figure 1 This is a schematic diagram of the cross-section of a non-full wall thickness specimen with a misaligned joint in the prior art; Figure 2 This is a schematic diagram of the standard specimen dimensions for full wall thickness in the prior art; Figure 3 This is a schematic diagram of the pull-out morphology of small-sized full-wall-thickness specimens in the prior art; Figure 4 This is a flowchart of the evaluation method according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the tensile test specimen according to an embodiment of the present invention; Figure 6 This is a tensile stress-strain curve diagram of an embodiment of the present invention; Figure 7 This is a schematic diagram illustrating the use of a tensile testing machine to conduct slow strain rate tensile tests on tensile test specimens. Detailed Implementation
[0012] To better understand the present invention, the following description, in conjunction with the accompanying drawings and embodiments, further clarifies the scope of the invention; however, the scope of the invention is not limited to the embodiments described below. Unless otherwise defined, all technical and scientific terms used in the following embodiments have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in the specification of this invention in the following embodiments is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used in the following embodiments includes any and all combinations of one or more of the associated listed items.
[0013] like Figure 4 As shown, this embodiment of the invention provides a method for evaluating the safety of misalignment and excess height in the ring weld joint of a hydrogen transportation pipeline, including the following steps: S1. Prepare a tensile test specimen for conducting slow strain rate tensile tests under high pressure hydrogen environment. The tensile test specimen is cut perpendicular to the circumferential weld joint along the longitudinal direction of the hydrogen pipeline. The length direction of the tensile test specimen is the longitudinal direction of the hydrogen pipeline, the width direction of the tensile test specimen is the wall thickness direction of the hydrogen pipeline, and the thickness direction of the tensile test specimen is the circumferential direction of the hydrogen pipeline. The weld is located in the central area along the length direction of the tensile test specimen. The tensile test specimen has misalignment and / or excess height.
[0014] like Figure 5 As shown, taking the circumferential weld joint of an X60 hydrogen pipeline with a diameter of 610 mm and a base material wall thickness of 14.3 mm as an example, a tensile test specimen of a flat plate structure is cut along the longitudinal direction of the hydrogen pipeline perpendicular to the weld joint. The length of the tensile test specimen is 80 mm, the weld joint is located in the central area of the specimen's length, and the width of the specimen is the full wall thickness of the pipeline, 14.3 mm. The thickness of the specimen is determined based on the parameters of the tensile testing machine, the material strength, and the pipe wall thickness. For example, when using a 50 kgf (49 kN) tensile testing machine, corresponding to an X60 pipe base material with a wall thickness of 14.3 mm (the measured maximum tensile strength is approximately 530 MPa), the calculation basis for the tensile test specimen thickness is as follows: Maximum test force ( F max ) ≥ material tensile strength ( R m ) × Original cross-sectional area ( S 0); Therefore, the maximum cross-sectional area of the specimen S 0= F max / R m = 49 kN / 530 MPa = 92 mm 2 Since the minimum dimension in the width direction of the sample is the original pipe material wall thickness (14.3 mm), the range of sample thickness is: Sample thickness (T) ≤ 92 mm 2 / 14.3mm=6.43mm; Rounded to 6mm.
[0015] Figure 5 The tensile test specimens prepared in this manner have excess height on both sides of their width, with excess heights of 1.77 mm and 2.81 mm on the sides, respectively.
[0016] S2. Thinning is performed on both sides of the middle section of the tensile test specimen along its length (instead of the width direction as is common in the prior art) to form a parallel length segment of the tensile test specimen. This step involves symmetrical thinning on both sides using machining methods such as wire cutting or milling. This not only avoids the problem of clamping end failure that may occur during the test, but also preserves the misalignment or excess height at the ring weld joint, maintaining the original shape of the ring weld joint.
[0017] In this embodiment, after symmetrical thinning on both sides, the thickness of the parallel length section of the X60 steel tensile specimen should be controlled within the range of 1 to 6 mm. If the thickness is less than 1 mm, the specimen stiffness is too low, and bending deformation is likely to occur during processing; if the thickness is greater than 6 mm, the required tensile load exceeds the rated capacity of the tensile testing machine, and the specimen cannot be broken. Figure 5 The thickness of the parallel section of the sample after thinning is 2 mm.
[0018] S3. The tensile test specimen is clamped on a tensile testing machine equipped with a high-pressure vessel, so that the tensile test specimen is placed inside the high-pressure vessel. After the high-pressure vessel is closed, the service environment of the hydrogen transportation pipeline is simulated inside the high-pressure vessel.
[0019] In this embodiment, a 50 kN tensile testing machine equipped with a 3L autoclave (an existing product, such as the CORTEST environmental slow strain rate tensile testing machine from the United States) is used. The tensile test specimen and fixture are placed inside the autoclave. After the autoclave is closed, it is first evacuated to 200 Pa using a vacuum pump. Then, 1.0 MPa high-purity nitrogen and high-purity hydrogen are injected into the autoclave three times each to replace and remove residual oxygen, moisture, etc. Finally, 6.3 MPa high-purity hydrogen is introduced into the autoclave (simulating the service environment of a hydrogen pipeline).
[0020] S4. Start the tensile testing machine to perform a slow strain rate tensile test on the tensile test specimen. If the tensile test specimen breaks in the pipe base material area during the tensile process, it indicates that the local stress concentration caused by misalignment or excess height is insufficient to make the circumferential weld joint a high-risk area.
[0021] After the pressure inside the autoclave stabilizes at 6.3 MPa, start the tensile testing machine at 10... -5The tensile test specimen was stretched at a strain rate of / s. The stress-strain curve during the tensile process was normal (e.g., ...). Figure 6 As shown in the figure, no clamping end was pulled out.
[0022] If the tensile test specimen breaks in the pipe base material area, it means that the local stress concentration caused by misalignment or excess height is insufficient to make the circumferential weld joint a high-risk area, and the misalignment and excess height of the weld are acceptable. If the tensile test specimen breaks at the weld, it indicates that the local stress concentration caused by the welding defect is too high, the risk of weld fracture is high, and the amount of misalignment and excess height needs to be reduced to reduce local stress concentration.
[0023] like Figure 7 As shown, the tensile test specimen eventually fractured in the pipeline base material area, which indicates that the local stress concentration caused by the excess height is insufficient to make the ring weld joint area a high-risk area. This shows that under the service environment of hydrogen pipelines, the excess height of the ring weld joint of 1.77 mm and 2.81 mm are acceptable.
[0024] If, after testing using the above methods, the tensile test specimens all fracture within the pipe base material area after being within the maximum allowable misalignment and / or excess height range of the welding quality acceptance standard for natural gas pipelines, then the misalignment and excess height control of the ring weld joint of the hydrogen pipeline can be directly applied to the welding quality acceptance standard for natural gas pipelines. Otherwise, it is necessary to reduce the amount of misalignment or excess height of the ring weld joint of the hydrogen pipeline until the tensile test specimens fracture within the pipe base material area, or further conduct crack initiation resistance tests on defective parts under hydrogen service environment.
[0025] The above embodiments are one specific implementation method selected by the present invention. Ordinary changes and substitutions made by those skilled in the art within the scope of this technical solution should be included within the protection scope of the present invention.
Claims
1. A method for evaluating the safety of misalignment and excess height in ring welded joints of hydrogen transportation pipelines, characterized in that, Includes the following steps: S1. Prepare a plate-shaped tensile test specimen with a rectangular or arc-shaped cross-section. The tensile test specimen is cut perpendicular to the circumferential weld joint along the longitudinal direction of the hydrogen pipeline. The length direction of the tensile test specimen is the longitudinal direction of the hydrogen pipeline, the width direction of the tensile test specimen is the wall thickness direction of the hydrogen pipeline, and the thickness direction of the tensile test specimen is the circumferential direction of the hydrogen pipeline. The weld is located in the central area along the length direction of the tensile test specimen. The tensile test specimen has misaligned edges and / or excess height. S2. Thinning is performed on both sides of the middle section of the tensile test specimen in the thickness direction to form a parallel length section of the tensile test specimen. S3. The tensile test specimen is clamped on a tensile testing machine equipped with an autoclave, so that the tensile test specimen is placed inside the autoclave. After the autoclave is closed, the service environment of the hydrogen pipeline is simulated inside the autoclave. S4. Start the tensile testing machine to perform a slow strain rate tensile test on the tensile test specimen, with a strain rate ≤ 2 × 10⁻⁶. -5 If the tensile test specimen breaks in the pipe base material area during the tensile process, it indicates that the local stress concentration caused by misalignment and / or excess height is insufficient to make the circumferential weld joint a high-risk area.
2. The method for evaluating the safety of misalignment and excess height of a ring weld joint in a hydrogen transport pipeline according to claim 1, characterized in that, The width of the tensile test specimen is equal to the full wall thickness of the hydrogen pipeline, and the middle section of the tensile test specimen is thinned on both sides in the thickness direction.
3. The method for evaluating the safety of misalignment and excess height of a hydrogen pipeline ring weld joint according to claim 2, characterized in that, Slow strain rate tensile tests were conducted under simulated hydrogen transport service conditions. The safety of misalignment and / or excess height was assessed based on the fracture location of the tensile test specimen: if fracture occurred in the base material, misalignment and / or excess height were acceptable; if fracture occurred in the joint area and the crack initiation originated from a sudden change in the shape of the misalignment and / or excess height, the allowable value of misalignment and / or excess height was reduced; if the specimen still fractured in the base material under tensile testing in a hydrogen environment at the maximum allowable amount of misalignment and / or excess height in the natural gas pipeline standard, the maximum allowable value in the natural gas pipeline standard was directly adopted.