Treatment method of 304 stainless steel pipe after welding

304 stainless steel welded steel pipe has relatively good corrosion resistance, heat transfer efficiency, and high-pressure resistance. After the welds of 304 stainless steel welded steel pipes are welded, they must be pickled and passivated. The pickling and passivation of the welds are carried out at the same time as the pickling and passivation of the entire product. However, during the welding process, problems of one kind or another often occur, and local corrosion may occur, and even rust may occur under relatively weak corrosion conditions. Let’s take a look at how to handle 304 stainless steel pipes after welding.

Stainless steel welded steel pipes cause accelerated oxidation on both the inside and outside of the weld and near the weld. Because the discolored areas of oxidation can again be seen, the color is related to the thickness of the oxide layer. Compared with the oxide layer on the stainless steel before welding, the oxide layer in the discolored area is relatively thick, and the composition is changed (chromium is reduced), which reduces the local corrosion resistance. For the inside of pipes, oxidation, and discoloration can be kept to a minimum by using appropriate backflush methods.

After welding stainless steel welded steel pipes, post-weld treatments such as pickling and grinding are often necessary to remove the oxide layer (colored) and restore corrosion resistance. It can often be used as a color diagram to determine whether we need pickling of the welds according to different color levels. However, this decision is subjective and in principle, each color indicates the presence of oxidation and an affected oxide layer and therefore reduced corrosion resistance of stainless steel welded steel pipes.

Contaminated surfaces are usually cleaned using mechanical or chemical methods. Organic chemical contaminants may be caused by lubricants, while inorganic contaminants such as the passage of foreign iron particles may be caused by contact with tools. Usually, all kinds of surface contamination can cause plaque. In addition, foreign iron particles may also cause galvanic corrosion. Plaque and galvanic corrosion problems are both forms of localized corrosion, and we need to treat them with water initially. Surface contamination therefore usually reduces the corrosion resistance of stainless steel.

There are now many post-treatments and methods available to prepare surfaces, remove discoloration, and restore corrosion resistance. Here we should distinguish between chemical and mechanical methods. Chemical methods are pickling (by immersion, with pickling paste or spray), assisted passivation (after pickling), and electrolytic polishing. Mechanical methods include: sandblasting, shot blasting with glass or ceramic particles, obliteration, brushing, and polishing.

No subsequent treatment, either by mechanical or chemical methods, provides corrosion properties suitable for demanding applications. If chemical methods such as pickling, passivation, etc. are used, surface oxides and other pollutants can be removed, but it does not meet the appearance requirements, and it is easy to volatilize chemical substances and cause contamination to the clean room. Therefore, the outer surface needs to be treated mechanically. At the same time, it is possible to use mechanical methods to wipe away previously removed materials, polishing materials, or annihilation materials, causing contamination.

The above is the main content of how to treat 304 stainless steel pipes after welding. Chemical methods such as pickling and electrolytic polishing are the only post-processing methods that can restore the corrosion resistance of stainless steel at welds and other surface damage. These methods are more effective. good.