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Processing technology of duplex stainless steel pipe

Jan 19,2022

The riser of offshore oil platform is washed by waves for a long time, so it must have high strength and excellent resistance to pitting corrosion. Among them, dual-phase steel stainless steel pipe has both austenite and ferrite structure, has the advantages of high pitting corrosion resistance coefficient, good mechanical properties and chloride ion corrosion resistance, and is an ideal material for offshore oil platform risers. Then, let's learn about the processing technology of dual-phase steel stainless steel pipe together!

However, the dual-phase stainless steel pipe is very sensitive to the precipitation of the third phase such as intermetallic compounds, and how to control the production process in the process of welding and heat treatment has become a difficulty.

Description of the perfect dual phase stainless steel pipe production process. The priority order specifically includes ultrasonic flaw detection, planing, forming, pre-welding, round, cutting, welding, sizing and heat treatment, welding line inspection, pipe end penetration inspection, hydraulic test, pickling passivation and finished product inspection.

The second is forming. In the production of straight seam welded pipe, the production difficulty is to effectively guarantee the bending moment of the stainless steel edge. The traditional forming technology is difficult to solve, but the yield strength of duplex stainless steel is about twice that of ordinary austenitic stainless steel, and the forming difficulty is also increased.

Flexible forming technology uses the tension effect during winding and bending to apply bending moment to the edge of the stainless steel strip to the maximum extent; in addition, the use of the favorable conditions of the roller without poles can freely adjust the bending edge according to the strength and thickness of the stainless steel strip The forming degree at the time to achieve the best welding conditions.

Welding, a hybrid welding technique using plasma arc welding and tungsten arc welding. First, plasma arc welding is used as through welding, showing the effect of single-sided welding and double-sided forming. Then, tungsten arc welding is carried out on the filling and cover surfaces, and the welding is protected by pure argon. In order to reduce the tendency of harmful phase precipitation, it is preferable to use as low a line energy as possible in the welding process, and the line energy is preferably less than 16kJ/cm. The temperature between the outer layers is extremely important for the welding of duplex stainless steel and must be controlled below 100. Excessive temperature between the layers will increase the tendency of harmful phase precipitation and ultimately affect the performance of the product.

Heat treatment. In the heat treatment after welding, the entire welded pipe is subjected to a solution treatment using an induction furnace. The heat treatment temperature reaches 1050-1120, and the water shower is cooled to below 40.

The presence of austenite in the dual phase structure will reduce the brittleness and grain growth tendency of high chromium ferrite, and improve the weldability and toughness. Chromium-rich ferrite will improve the yield strength, grain boundary corrosion resistance and stress corrosion resistance of austenite in stainless steel, that is, the dual phase structure of ferrite has high strength and high toughness.

The above introduction is the processing technology of duplex steel stainless steel pipe. If you need to know more about stainless steel rectangular pipe, stainless steel sanitary pipe and stainless steel seamless pipe, please feel free to contact us!