Problems that occur when welding thin-walled stainless steel pipes

1. Construction level issues:
Welding is a very professional technique. Many experts, including on-site construction workers, believe that after welding, it cannot be disassembled. In many actual construction sites, it is very inconvenient to make changes, so many construction workers are unwilling to use it. Since argon arc welding requires special equipment, and the thickness of thin-walled stainless steel pipes is very thin, it can only be completed by specialized and certified welders with a certain level. The level of the operator is very high, and in the actual construction site Personnel, mobility is high. If welding is performed by personnel without a welding operation license, current, argon gas, etc. cannot be adjusted reasonably, and due to the influence of construction site space and human factors, false welding, missing welding, or even welding through pipes will often occur. , Although there will be no water leakage during the pressure test, there will be great construction hazards. After a certain period of use, due to thermal expansion and contraction and other factors, it will cause future water leakage.

2. Heat treatment issues:
As thin-walled stainless steel pipes and socket-type pipe fittings, solid solution treatment can be carried out on the welding place when processing in the factory. However, due to the limitation of the construction site when welding pipes and fittings, it is impossible to carry out solid solution treatment because of Austenite When the bulk stainless steel slowly passes through 450 to 800 degrees, carbon is precipitated, and the formed chromium carbide precipitates at the boundary of the crystal material, and the chromium content near it is reduced, forming a chromium-deficient zone, which greatly reduces the corrosion resistance. After long-term use in the future, the most feared intergranular corrosion of stainless steel materials will occur at the weld. If the carbon content of the stainless steel is too high, the pipe will fail in advance at the weld, and this defect must occur in It will only appear after a certain period of use, and it is impossible to try it at the time.

3. The problem of thermal expansion and contraction:
The destructive power of metal materials with temperature changes is very large, so thermal expansion and contraction are very important factors for stainless steel materials. The thermal expansion cannot be simply determined by the value of the pulling force when the product is produced. For example, the threaded connection that was used much in the past is very susceptible to thermal expansion and contraction, because the pipes and fittings cannot be extended or shortened. Fatigue bursts often occur. The greater the temperature difference, the greater the destructive power. Therefore, if the connection of thin-walled stainless steel pipes and pipe fittings is buried and installed, the thermal expansion and contraction properties of the material must be fully considered. However, it is difficult for the socket pipe fittings welded by argon arc welding to achieve the consistency of the parent pipe and the pipe fittings with the weld. , The stress cannot be eliminated, especially in the northern pipelines buried mostly in the summer and autumn, resulting in the maximum negative temperature difference between the water pipe and the buried time of about 35 degrees, especially when the temperature drops rapidly, without the installation of pipeline expansion joints, the pipeline axis Tension will cause the welding of pipes and fittings to crack. If the treatment is not good, the existing pores, virtual welding, etc. will be the defects of damage during thermal expansion and contraction, which will be exposed over time, so buried in the dark Under the circumstances