Causes and solutions for cracking of spiral welded steel pipe welds
Spiral welded steel pipes are widely used in oil and gas transportation, water conservancy projects, bridge construction and other fields due to their high strength, flexible process and high production efficiency. However, during production and use, the problem of weld cracking may have a serious impact on the performance and service life of the steel pipe. This article will start with the main causes of weld cracking, analyze its causes in detail, and propose solutions to help companies effectively avoid this problem during production and use.
1. The main causes of cracking of spiral welded steel pipe welds
The cracking of spiral welded steel pipe welds can be divided into cracking caused by welding and cracking during use. The specific reasons are as follows:
1. Quality problems of welding materials
The chemical composition of welding materials (such as welding wire and flux) directly affects the mechanical properties of the weld. If the welding material contains impurities or the alloy composition is uneven, the ductility and strength of the weld may be insufficient, which may easily lead to cracks.
2. Steel plate material problem
If the steel plate material is uneven or contains internal defects (such as inclusions, pores, etc.), it will cause stress concentration during welding heating, thereby increasing the risk of weld cracking. In addition, if the impurities such as sulfur and phosphorus in the steel are too high, it will also weaken the toughness of the weld.
3. Unreasonable welding process parameters
Parameters such as welding current, voltage, and welding speed are crucial to welding quality. If the parameters are not set properly, it may cause excessive internal stress in the weld or unstable metallographic structure in the heat-affected zone. For example:
Welding speed that is too fast will cause insufficient weld penetration.
Welding current that is too low will cause insufficient weld bonding.
4. Improper heat treatment during welding
During welding, excessive heat input or too fast cooling speed will cause large residual stress in the weld and heat-affected zone, thereby increasing the possibility of cracks. This problem is particularly prominent in the welding of thick-walled pipes.
5. Environmental impact
Environmental factors such as excessive humidity, low temperature, and excessive wind speed may lead to the formation of defects such as pores and cracks during welding. For example, when welding in a low temperature environment, if preheating measures are not taken, the weld of the steel pipe is prone to low-temperature cold cracking.
6. Stress corrosion
During the use of spiral welded steel pipes, they may be affected by corrosive substances in the medium. When corrosion and stress in the weld work together, stress corrosion cracking is likely to occur, especially when transporting corrosive media such as hydrogen sulfide.
2. Classification of weld cracking
Weld cracking can be divided into the following categories according to the formation time, location and cause:
Cold cracking
Mainly occurs after welding cools down, due to the combined action of residual stress and metal embrittlement.
Common in low temperature environment welding and high carbon steel materials.
Hot cracking
Occurs during the cooling and solidification of the welding pool, usually caused by insufficient fluidity of the liquid metal or segregation of alloy elements in the weld.
Delayed cracking
Cracks appear hours or even days after welding is completed, mainly because the hydrogen content in the weld is too high or the stress is not completely released.
Corrosion cracking
After long-term use, it is formed by the combined action of medium corrosion and stress.
3. Solutions to weld cracking
For the above problems, the following measures can be taken to effectively prevent weld cracking:
1. Improve material quality
Select high-quality steel plates and welding materials, and strictly control the chemical composition and metallurgical quality of steel.
Optimize steel production process to reduce impurities and internal defects.
2. Optimize welding process
Select appropriate welding current, voltage and welding speed according to the material and thickness of the steel pipe.
Control welding heat input to avoid overheating or overcooling.
3. Preheating and post-heat treatment
For welding in low temperature environment or thick-walled pipes, preheat the welding area in advance to reduce cooling rate and residual stress.
After welding, post-heat treatment (such as annealing, stress relief treatment) is used to improve weld structure and reduce internal stress.
4. Hydrogen content control
Use low-hydrogen welding materials to reduce the source of hydrogen in the weld.
Perform timely hydrogen diffusion treatment (such as heating and insulation) after welding.
5. Optimize production environment
Improve welding environment conditions and avoid working in high humidity or low temperature environment.
Provide a windproof and moisture-proof welding operation space.
6. Surface protection and anti-corrosion treatment
For steel pipes that transport corrosive media, surface anti-corrosion treatment is performed, such as coating an anti-corrosion layer or using lining materials.
Strengthen the composition control of the medium to avoid excessive sulfide or chloride content.
IV. The key to weld quality control
In addition to taking the above measures, the quality inspection and control of the weld should also be strengthened. Commonly used weld inspection methods include:
Ultrasonic testing (UT)
Used to detect defects such as pores and cracks inside the weld.
Radiographic testing (RT)
Detect the internal quality of the weld through X-rays or gamma rays.
Magnetic particle testing (MT) and penetration testing (PT)
Used to detect surface and near-surface defects of the weld.
Mechanical property testing
Evaluate the comprehensive performance of the weld through tensile, impact and hardness tests.
V. Summary
Spiral welded steel pipe weld cracking is a complex problem caused by the combined action of multiple factors. Solving this problem requires starting from material selection, welding process, environmental control, post-processing and quality inspection. Through scientific management and strict production control, not only can the quality of welds be improved, but also the service life of steel pipes can be effectively extended, providing more reliable guarantees for engineering construction.
Through the above methods, enterprises can establish a better brand image in the fierce market competition, while reducing production and use costs and improving economic benefits.
The above is the content of spiral steel pipe cracking compiled by the editor. If you are interested in steel pipes, you can learn more about them on our website, such as seamless steel pipes, drill pipes, drill collars, screens, and pipe fittings.