Stainless steel pipes, as fluid pipes with advantages such as corrosion resistance and high-pressure resistance, are widely used in many fields such as petroleum, chemical industry, papermaking, shipbuilding, and electricity. However, in the actual application process, some quality problems are inevitable. This article aims to analyze these common quality problems and provide a reference for users when selecting and using stainless steel pipes.
Use environment and fluid type First of all, stainless steel is not completely stainless. The so-called rust-free is only stainless at room temperature and in normal conditions. In special environments or when circulating special fluids, stainless steel of different materials must be used in a targeted manner to ensure the corrosion resistance and service life of stainless steel.
Generally, for the transmission of neutral fluids or ordinary non-corrosive liquids, 304 stainless steel is sufficient, but for weak acid transmission, it is best to use 304L or better materials. If the salt content is heavy, such as the transmission of seawater, 316L material is required. For strong acid transmission, super duplex stainless steel material is required.
Heat treatment (solid solution) Material selection is only the first step. The corrosion resistance of stainless steel requires not only material quality (mainly nickel and chromium content) but also heat treatment. Solution treatment (heat treatment) – After the stainless steel butt-welded pipe fittings are cold-pressed into pipe fittings, the product will produce plastic deformation, the balance between molecules will be destroyed, and a large amount of internal stress will be accumulated, which must be eliminated by solution treatment. Solution treatment is a special process that rearranges the austenite molecular structure. The process parameters, temperature, and time must be strictly controlled. Special stainless steels, such as 316Ti, also require stabilization treatment to achieve the best effect.
Impact of Stainless Steel Pipe Welding
Another special link of stainless steel pipe fittings is welding. Large-sized butt-welded pipe fittings are pressed and formed by steel plates and then welded to form elbows, tees, reducers, etc. The welding current is a key parameter, and the worker’s 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 solution treatment, passivation is also required to prevent intergranular corrosion.
Stainless steel corrosion usually includes the following types: intergranular corrosion, chloride ion corrosion, stress corrosion, electrical corrosion, etc. (the main corrosion forms of stainless steel elbows). The causes of each type of corrosion are different. Special attention should be paid to the selection, production, installation, and use of materials. Only by fully following the standard operation can stainless steel play its true effect. Otherwise, stainless steel will rust more than galvanized steel pipes.
Material selection In addition, the use 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 is fatigued. They may barely be used for a few years in ordinary water supply projects, but once they are used in special environments such as high-pressure and highly corrosive media, they are prone to leakage, causing irreparable losses to users. Even many small workshops make stainless steel pipes with thickness, height, material, surface, and process that are much lower than the standard parameters. Of course, the price is definitely extremely low. Such products are called market goods.
Post time: May-07-2025