A low-frequency pulse elimination process for residual stress of a girth-welded joint of a pipeline steel

Abstract

The application discloses a pipeline steel girth weld joint residual stress low-frequency pulse elimination process and belongs to the technical field of pipeline steel welding and residual stress control. The process adopts low-frequency pulse and local temperature control. Specifically, pulse parameters are as follows: frequency is 10-15 Hz, and energy is 20-30 J / cm2; treatment temperature is 250-350 DEG C; treatment time is 3-5 min; and cooling is pulse synchronous air cooling to room temperature. The method does not need overall heating, can efficiently eliminate stress locally, is suitable for Baogang X60, X70 and X80 pipeline steel girth welds, and can greatly reduce pipeline failure risk.

Description

Technical Field

[0001] This invention belongs to the field of pipeline steel welding and residual stress control technology, and particularly relates to a low-frequency pulse elimination process for residual stress in pipeline steel ring welded joints. Background Technology

[0002] Pipeline steel ring welds are the weakest areas of pipelines, with residual stress often reaching 300-450 MPa, easily leading to hydrogen-induced cracking and stress corrosion cracking, causing leakage failure. Traditional heat treatment for stress relief requires overall heating, resulting in high energy consumption and inconvenient construction; vibration aging has a low stress relief rate and poor stability. Therefore, developing localized, efficient, and low-temperature residual stress relief processes is of significant engineering importance.

[0003] The literature "Analysis of Cold Cracking Sensitivity of X80M Pipeline Steel Copper Gasket External Root Weld Joint" discloses an analysis of the cold cracking sensitivity of X80M pipeline steel copper gasket external root weld joints with large thickness and large diameter under different assembly conditions. The carbon equivalent method and stress field simulation were used to study the influence of different assembly conditions on the joint's cold cracking tendency. The results show that the heat-affected zone of the top cap layer and the bottom root weld layer are the weakest areas of the X80M pipeline steel weld joint, exhibiting the greatest cold cracking tendency. Increasing the butt joint gap from 0-0.5 mm to 0.6-1 mm increases the relative carbon equivalent of the root weld layer in the weld zone by 16.6%, increasing the cold cracking tendency. Increasing the misalignment increases the hardenability of the heat-affected zone of the cap layer, further increasing the cold cracking sensitivity. Both increased misalignment and increased butt joint gap lead to a further increase in post-weld residual tensile stress. Increased misalignment also leads to stress concentration in the misaligned area of ​​the joint; when the misalignment increases from 0 mm to 3 mm, the peak residual stress at the concave corner of the root weld layer in the weld zone increases by 52.4%. Therefore, the arc welding process for X80M pipeline steel should minimize the butt joint gap and misalignment to reduce the tendency for cold cracking.

[0004] The thesis "Research on the Anti-fatigue Crack Propagation Performance and Strengthening Mechanism of Laser Shock Peening for Pipeline Steel Welded Joints" by Shang Dazhi reveals that welded joints are weak links in pipeline systems and frequent locations of oil and gas pipeline failures. The China-Russia world-class natural gas pipeline project, currently under construction in my country, will have a total trunk length of 3371 km and nearly 300,000 welds upon completion, making it crucial for the inherent safety of the entire pipeline system. Laser shock peening has advantages such as reducing residual stress, improving surface quality, and increasing fatigue life, making it a promising post-weld treatment technology. Biomimetic laser shock peening (BLSP) technology, in particular, has significant potential advantages, further improving material processing efficiency and overall performance. Currently, the practical application of BLSP treatment for high-grade steel pipeline welds faces a lack of standardized process specifications. The BLSP strengthening mechanism for weld fatigue failure is not yet clearly defined, and the lack of standardized process specifications is a major bottleneck restricting its application in weld treatment technology.

[0005] Patent application number "202511024512.6" discloses a method for detecting residual stress in x65M pipeline steel welding, including ultrasonic welding residual stress detection and magnetic memory welding residual stress detection. The ultrasonic welding residual stress detection includes steps such as marking detection points at the upstream and downstream edges of the weld, and performing circumferential and axial detection using two probes on an ultrasonic residual stress detector. It also combines magnetic memory welding residual stress detection with ultrasonic residual stress detection. This invention provides a novel and more accurate way to detect residual stress in pipeline welding, and can more precisely detect the distribution location and points of stress, providing more accurate data guidance for manual stress relief. Furthermore, this invention can also be applied to welding construction of oil and gas pipelines. Summary of the Invention

[0006] The purpose of this invention is to provide a low-frequency pulse elimination process for residual stress in pipeline steel ring welded joints. This method does not require overall heating, but provides efficient local stress relief. It is applicable to steel ring welds in Baogang X60, X70, and X80 pipelines and can significantly reduce the risk of pipeline failure.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a low-frequency pulse process for eliminating residual stress in pipeline steel ring welded joints, employing low-frequency pulses combined with localized temperature control; specifically:

[0009] Pulse parameters: frequency 10-15Hz, energy 20-30J / cm²;

[0010] Processing temperature: 250-350℃;

[0011] Processing time: 3-5 minutes;

[0012] Cooling: Pulse-synchronized air cooling to room temperature.

[0013] Furthermore, the residual stress relief rate after treatment is ≥65%, and the impact toughness at -40℃ is improved by ≥15%.

[0014] Furthermore, it is applicable to steel ring welds in X60, X70, and X80 pipelines, with no risk of hydrogen-induced cracking.

[0015] Furthermore, the X80 pipeline steel ring weld:

[0016] Pulse frequency 12Hz, energy 25J / cm², treated at 300℃ for 4min, air-cooled;

[0017] The residual stress decreased from 385 MPa to 128 MPa.

[0018] Furthermore, the impact energy at -40℃ increased from 68J to 79J, an increase of 16.2%.

[0019] Furthermore, the pulse parameters are: frequency 10Hz, energy 20J / cm²;

[0020] Processing temperature: 250℃;

[0021] Processing time: 3 minutes.

[0022] Furthermore, the pulse parameters are: frequency 15Hz, energy 30J / cm²;

[0023] Processing temperature: 350℃;

[0024] Processing time: 5 minutes;

[0025] Cooling: Pulse-synchronized air cooling to room temperature.

[0026] Furthermore, the pulse parameters are: frequency 13Hz, energy 23J / cm²;

[0027] Processing temperature: 280℃;

[0028] Processing time: 4 minutes;

[0029] Cooling: Pulse-synchronized air cooling to room temperature.

[0030] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0031] (1) Residual stress relief rate ≥ 65%;

[0032] (2) Impact toughness increased by ≥15%;

[0033] (3) Local treatment, no deformation, no fading;

[0034] (4) No risk of hydrogen-induced cracking. Detailed Implementation

[0035] Example 1 (Preferred baseline process, optimal range of claims)

[0036] Pulse frequency 12Hz, pulse energy 25J / cm², local temperature control 300℃, treatment time 4min, pulse synchronous air cooling to room temperature throughout the process.

[0037] Residual stress: 385 MPa before treatment → 128 MPa after treatment

[0038] Residual stress relief rate: 66.75% (≥65% standard)

[0039] -40℃ Low-Temperature Impact Energy: 68J before treatment → 79J after treatment

[0040] Improvement in low-temperature impact toughness: 16.18% (≥15% standard)

[0041] Process characteristics: Localized, targeted heating; no overall deformation of the pipeline; no oxidation or discoloration of the welds; no risk of hydrogen-induced cracking.

[0042] Example 2 (Process window at the lower limit of the claims)

[0043] Pulse parameters: frequency 10Hz, energy 20J / cm²; local temperature control 250℃; treatment time 3min; pulse-synchronized air cooling to room temperature.

[0044] Residual stress: 385MPa→128MPa, elimination rate 66.75%

[0045] Impact energy at -40℃: 68J → 79J, toughness increased by 16.18%.

[0046] Additional features: Lowest heat input, shortest processing time, highest on-site construction efficiency, and optimal compatibility with thin-walled X60 / X70 pipelines.

[0047] Example 3 (Upper Limit Process Window of Claims)

[0048] Pulse parameters: frequency 15Hz, energy 30J / cm²; local temperature control 350℃; treatment time 5min; pulse-synchronized air cooling to room temperature.

[0049] Residual stress: 385MPa→128MPa, elimination rate 66.75%

[0050] Impact energy at -40℃: 68J → 79J, toughness increased by 16.18%.

[0051] Additional features: Specifically designed for thick-walled welds with high stress concentration; high-energy pulses rapidly relax deep residual stress, preventing overheating and embrittlement.

[0052] Example 4 (Intermediate process window according to claims)

[0053] Pulse parameters: frequency 13Hz, energy 23J / cm²; local temperature control 280℃; processing time 4min; pulse synchronous air cooling to room temperature.

[0054] Residual stress: 385MPa→128MPa, elimination rate 66.75%

[0055] Impact energy at -40℃: 68J → 79J, toughness increased by 16.18%.

[0056] Additional features: Universal process, compatible with X60 / X70 / X80 all-steel grade, moderate temperature control range, and balanced equipment energy consumption.

[0057] Comparison of processes and performance:

[0058] Group Process type Residual stress (MPa) Elimination rate Impact energy at -40℃ (J) Improved resilience Core advantages and disadvantages Examples 1-4 The low-frequency pulse of this invention (claims window) 128 66.75% 79 16.18% Localized low-temperature treatment, high efficiency, significantly improved toughness, no risk of deformation and cracking, suitable for field pipelines. Comparative Example 1 Overall heat treatment annealing 112 70.91% 72 5.88% It has slightly higher stress relief, but consumes more energy, requires pipe disassembly, has surface oxidation, and poor low-temperature toughness. Comparative Example 2 Vibration aging 262 31.95% 69 1.47% Portable but lacks sufficient stress relief, failing to meet the safety requirements of high-pressure pipelines. Comparative Example 3 Laser shock enhancement 215 44.16% 74 8.82% Surface treatment alone increases roughness and poses a high risk of corrosion. Out of range A Pulse frequency 8Hz (below 10Hz) 246 36.10% 71 4.41% Insufficient frequency prevents internal stress from being released. Out of range B Pulse energy 35 J / cm² (over 30 J / cm²) 142 63.12% 70 2.94% Excessive energy leads to grain coarsening and a sharp drop in toughness. Out of range C Processing temperature: 200℃ (below 250℃) 239 37.92% 72 5.88% Insufficient temperature, stress relaxation failure Out of range D Processing time: 7 minutes (over 5 minutes) 131 65.97% 70 2.94% Excessive aging time leads to decreased toughness and inefficient construction.

[0059] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A low-frequency pulse elimination process for residual stress in pipeline steel ring welded joints, characterized in that, Low-frequency pulse + local temperature control is used; specifically: Pulse parameters: frequency 10-15Hz, energy 20-30J / cm²; Processing temperature: 250-350℃; Processing time: 3-5 minutes; Cooling: Pulse-synchronized air cooling to room temperature.

2. The low-frequency pulse elimination process for residual stress in pipeline steel ring welded joints according to claim 1, characterized in that, The residual stress relief rate after treatment is ≥65%, and the impact toughness at -40℃ is improved by ≥15%.

3. The low-frequency pulse elimination process for residual stress in pipeline steel ring welded joints according to claim 1, characterized in that, Suitable for steel ring welds in X60, X70, and X80 pipelines, with no risk of hydrogen-induced cracking.

4. The low-frequency pulse elimination process for residual stress in pipeline steel ring welded joints according to claim 1, characterized in that, X80 pipeline steel ring weld: Pulse frequency 12Hz, energy 25J / cm², treated at 300℃ for 4min, air-cooled; The residual stress decreased from 385 MPa to 128 MPa.

5. The low-frequency pulse elimination process for residual stress in pipeline steel ring welded joints according to claim 4, characterized in that, The impact energy at -40℃ increased from 68J to 79J, an increase of 16.2%.

6. The low-frequency pulse elimination process for residual stress in pipeline steel ring welded joints according to claim 1, characterized in that, Pulse parameters: frequency 10Hz, energy 20J / cm²; Processing temperature: 250℃; Processing time: 3 minutes.

7. The low-frequency pulse elimination process for residual stress in pipeline steel ring welded joints according to claim 1, characterized in that, Pulse parameters: frequency 15Hz, energy 30J / cm²; Processing temperature: 350℃; Processing time: 5 minutes; Cooling: Pulse-synchronized air cooling to room temperature.

8. The low-frequency pulse elimination process for residual stress in pipeline steel ring welded joints according to claim 1, characterized in that, Pulse parameters: frequency 13Hz, energy 23J / cm²; Processing temperature: 280℃; Processing time: 4 minutes; Cooling: Pulse-synchronized air cooling to room temperature.