Reasons why welding cannot be performed after corrosion of 304 stainless steel welds and countermeasures
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In the electrolytic manganese industry, fan ducts are made of 304 stainless steel, with A102 welds used for joining these ducts. Since the air circulating within the ducts is primarily carbon dioxide, along with some acidic gases (very dilute sulfuric acid vapor), there is also a small amount of dilute sulfuric acid foam. The temperature of the gas inside the ducts is around 70 degrees, so the ducts feel slightly warm to the touch. Main problem: Three months after the use of the fresh air ducts, the welds began to show signs of corrosion. Small pinholes appeared, and the maintenance staff tried to repair them using A102 welding rods in an attempt to fill those gaps. However, it was found that whenever welding was carried out, the base material would crack, and the cracks grew worse with each welding attempt; there was no solution to this issue. First, I used Kaft metal glue to seal the pinholes, and the result was fairly good; however, it didn’t last long. As a result, I had to carry out a major repair in which the entire pipeline was treated with fiberglass-reinforced plastic for corrosion protection, and now everything is fine. The reason why it cannot be welded has not been identified yet; I would appreciate everyone’s advice.
I guess the weld rod chosen was too thick; try using one with a diameter of 5 mm or less. For 304L stainless steel, cold welding is required, and the weld pool should be shallow.
The presence of sulfuric acid indicates that ferrous sulfate has been formed; this substance is present inside the cracks, and welding causes cracks to appear, so it’s necessary to find a way to remove it completely.
I have encountered similar situations where cracks appeared in the base material surrounding the weld, and these cracks were not repaired. It’s probably intergranular corrosion.
It’s likely that the material of the base metal surrounding the weld has changed.
Carbon ions in carbon dioxide gas cause changes in the material.
304 stainless steel corrodes under acidic conditions at 70°; it is likely that the properties of the wood have changed. It is recommended to use 316L acid-resistant stainless steel, which should yield better results
It’s probably a problem with the base material; take a spectrum analysis first and then select the appropriate welding material.
After using it for three months, corrosion occurred, which indicates that the material chosen was not appropriate; perhaps the sulfuric acid was impure. 316L or 304 should be used. Even if it is repaired, it will still leak after three months of use
In that case, instead of using A102 for your welding rod, use A022
The welding rod was chosen incorrectly; it’s impossible to repair the weld under pressure. I encounter this situation often – during welding, the temperature inside the pipe rises, which causes an increase in pressure. A pressure difference is created between the inside and outside of the pipe, and this leads to more cracks in the weld when welding starts. It’s recommended to stop the process, replace the contents inside the pipe, open the nearby drain valves, and then try welding again; that might work