Common Quality Problems Of Stainless Steel Pipes

Common quality problems of stainless steel pipes

Stainless steel pipe, as a fluid pipe with the advantages of corrosion resistance and high pressure resistance, is widely used in many fields such as petroleum, chemical industry, papermaking, shipbuilding, and electric power. However, in actual application, some quality problems inevitably occur. This article aims to analyze these common quality problems and provide a reference for users when selecting and using stainless steel pipes. Usage environment and fluid type First of all, stainless steel is not completely stainless. The so-called rust-free only means that it is stainless at room temperature and normal conditions. However, in special environments or when special fluids are flowing, it must be targeted. Only by using stainless steel of different materials can the corrosion resistance and service life of stainless steel be ensured.

Generally used for the transmission of neutral fluids or ordinary non-corrosive liquids, 304 stainless steel is sufficient, but for the transmission of weak acids, it is best to use 304L or better materials. If the salt content is relatively heavy, such as seawater transmission, 316L material needs to be used. For strong acid transmission, super duplex stainless steel is required. Heat treatment (solid solution) Material selection is only the first step. In addition to ensuring the material (mainly nickel content and chromium content), the corrosion resistance of stainless steel is also more important than heat treatment. Solid solution (heat treatment) - After stainless steel butt welded pipe fittings are cold-pressed into pipe fittings, the product will undergo plastic deformation, the balance between molecules is destroyed, and a large internal stress accumulates, which must be eliminated through solid solution. Solid solution is a special process that rearranges the austenite molecular structure. Process parameters, temperature and time must be strictly controlled. Specialty stainless steels, such as 316Ti, also require stabilization to work best.

The influence of welding Another special link of stainless steel pipe fittings is welding. Large-sized butt-welded pipe fittings are pressed and formed from steel plates, and then welded to form elbows, tees, large and small ends, etc. Welding current is a key parameter, and worker skills are also crucial. RT testing is usually required to verify the welding effect. After welding, the treatment of the weld is also very important. In addition to solid solution, it also needs passivation to prevent intergranular corrosion. The corrosion of stainless steel usually includes the following types: intergranular corrosion, chloride corrosion, stress corrosion, electric corrosion, etc. (the main corrosion form of stainless steel elbows). The causes of each corrosion are different. In material selection, Special attention must be paid during production, installation and use. Only by operating in full compliance with standards can stainless steel exert its true effect. Otherwise, the rust of stainless steel will be worse than that of galvanized steel pipes.

Selection of materials In addition, the selection of old pipes is also one of the main reasons for problems with pipe fittings. Some unscrupulous manufacturers use old pipes to produce pipe fittings in order to save costs. The molecular structure of the old pipes has become fatigued. It may barely last a few years when used in ordinary water supply projects. However, once used in special environments such as high pressure and highly corrosive media, it will be very difficult to use. Leakage is prone to occur, causing irreparable losses to users. Even in many small workshops, the thickness, height, material, surface and process of the stainless steel pipes produced are significantly lower than the standard parameters. Of course, the price must be extremely low. Such products are called market goods.