When welding stainless steel pipes, the requirements for the welding process are very high, because when welding them, many problems need to be solved, such as heat treatment, cold shrinkage and thermal expansion, and also attention should be paid to on-site construction. Let’s talk about their solutions in detail.
The first is the construction capability. Welding is a kind of professional work. It can’t be disassembled after welding. It is very inconvenient because it needs to be changed in the actual construction site. Because argon arc welding requires special equipment, and the thickness of stainless steel pipe is very thin, there must be a certain level of welders to operate, but the actual site construction site personnel mobility is large, if the welding personnel do not have welding operation certificate, it will not Will reasonably adjust the current, argon, etc., and affected by the construction site space and human factors, often will lead to the phenomenon of virtual welding, leakage welding or even welding through the pipe, although there will be no leakage problems during the pressure test, but will There are a lot of construction hazards. After using for a certain period of time, due to factors such as thermal expansion and contraction, it will lead to water leakage in the future.
The second is the heat treatment problem. As a stainless steel pipe and socket pipe fittings, it can be solution treated at the factory. However, at the construction site, the pipes and fittings are limited by the construction site and are unlikely to be solidified. In the solution treatment, since the austenitic stainless steel slowly passes through 450 to 800 degrees, carbon is precipitated, and the formed chromium carbide precipitates at the boundary of the crystal, and the chromium content in the vicinity thereof is reduced, resulting in a chromium-deficient region, resulting in a great drop in corrosion resistance. . Usually long-term use in the later stage will produce the most worrying intergranular corrosion of stainless steel in the weld. If the carbon content of the stainless steel is too high, the stainless steel pipe will be inadvertently caused at the weld, and the defect will definitely be It will appear after a certain period of use, and it cannot be tested on the spot.
The third point is the problem of thermal expansion and contraction. The destructive force of stainless steel plate material with temperature changes is very strong, so thermal expansion and contraction is very important for stainless steel materials. The effect of 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 originally used is very susceptible to thermal expansion and contraction, because stainless steel pipes and fittings are not extended or shortened. Frequent fatigue bursts often occur, and the greater the temperature difference, the greater the destructive power.
Therefore, if the connection between the stainless steel pipe and the pipe fitting is buried, the thermal expansion and contraction performance of the material must be fully considered. However, it is difficult to achieve the consistency of the parent pipe and the pipe fitting and the weld by the argon arc welding. The stress is relieved, especially in the northern pipelines, mostly in the summer and autumn, which leads to the maximum negative temperature difference of about 35 degrees when the water pipe is generated and buried. Especially when the temperature drops rapidly, the pipe is axially affected without the installation of the pipe expansion joint. Pulling will cause the cracking of the pipe and the pipe fitting. Once the treatment is not good, the existing pores, the virtual welding, etc. are defects that are destroyed during the thermal expansion and contraction, and will be exposed over time, so in the case of burying It is important to pay attention to the use of a reasonable installation process.
Source: China Stainless Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)