Case analysis of welding problems of stainless steel and carbon steel
A customer purchased a batch of stainless steel pipes, made of 309, to transport strong corrosive solutions, but unexpectedly, corrosion leakage occurred after a short period of time. The customer, therefore, raised a quality objection.
Case Analysis:
After receiving the complaint, the supplier immediately organized an on-site inspection and found that the customer added a carbon steel jacket sleeve to the stainless steel tube and welded it together with a 309 welding rod. This processing caused strong corrosion of the 309 stainless steel that should have been corrosion-resistant.
Because when stainless steel and carbon steel are fused, the content of chromium and nickel in stainless steel is reduced, which is not enough to maintain the corrosion resistance in a strong corrosive environment, which leads to a great increase in corrosion rate and ultimately leads to perforation leakage.
Generally speaking, even if the welding is between the same kind of stainless steel, the corrosion resistance of the weld may be lower than that of the base material, and the weld will be selectively corroded in the use environment.
This is because the weld metal is a cast structure with defects such as coarsening of crystal grains, changes in composition, and uneven structure.
To solve these problems, when selecting the electrode, attention should be paid to the alloy element content of the electrode higher than the base metal, and the impurity content should be lower than the base metal.
Case Handling:
The quality objection this time was caused by the welding of stainless steel and carbon steel during customer use.
Therefore, if there is a need for stainless steel and carbon steel welding, a stainless steel backing plate can be lined between the stainless steel tube and the carbon steel fixture as a transition to avoid the stainless steel tube being affected by the carbon steel.