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Safety use restrictions and requirements for duplex stainless steel tubes

Release Date:2016-11-04

Safety use restrictions and requirements for duplex stainless steel tubes

1 need to control the phase ratio, the most suitable proportion is ferrite and austenitic meet each half, and the number of a certain phase up to 65%, so as to ensure the best comprehensive performance. If the two phases are out of balance, such as the ferrite phase is too much, it is easy to form a single phase ferrite in the weld HAZ, which is sensitive to stress corrosion cracking in some media.

2 need to master the changes of microstructure in duplex stainless steel tube, familiar with TTT and CCT transition curve of each steel, this is the right to guide the development of dual phase stainless steel heat treatment, heat molding, key technology, dual phase stainless steel intermetallic phase are more sensitive than austenitic stainless steel.

3 duplex stainless steel tube continuous use temperature range of -50 ~ 250 degrees Celsius, the lower limit depends on the brittleness of the steel temperature, the upper limit of 475 degrees Celsius brittleness limit, the upper limit temperature can not exceed 300.

4 dual phase stainless steel tube solid solution treatment need fast cooling, slow cooling can cause the precipitation of brittle phase, which leads to the toughness of steel, especially the decrease of local corrosion resistance.

The minimum temperature of not 5 high chromium molybdenum dual phase stainless steel tube heat processing and forming of less than 950 DEG C, superduplex stainless steel can not lower than 980 DEG C low Cr Mo dual phase stainless steel can not lower than 900 DEG C, to avoid the precipitation of brittle phases in the process of causing surface crack

6 can not use the austenitic stainless steel commonly used 650-800 to eliminate stress treatment, generally using solid solution annealing treatment. For surfacing in low-alloy steel duplex stainless steel, the need for 600-650 C overall elimination disposal, must be taken into account by the precipitation of brittle phases caused toughness and corrosion resistance, especially the decline of localized corrosion, as far as possible to shorten the heating time in this temperature range. Heat treatment of low alloy steel and duplex stainless steel composite plate should also consider this. [1]

7 familiar with pipe welding of duplex stainless steel, can not apply to all welding of austenitic stainless steel, duplex stainless steel equipment can use a great relationship with the correct welding process of steel, the failure of some equipment is often associated with welding. The key lies in the control of line energy and layer temperature, the correct choice of welding materials is also very important. The proportion of the two phases of the welded joint (weld metal and HAZ), in particular, the amount of austenite necessary to maintain the HAZ, which is important to ensure that the weld joint has the same properties as the base material.

8 in different corrosion environments in the selection of duplex stainless steel, should pay attention to the corrosion resistance of steel is always relative, although duplex stainless steel has good resistance to local corrosion, it is a double phase stainless steel, he is also a suitable medium range of conditions, including temperature, pressure, concentration, medium pH, need to carefully choose. Obtained from the literature and manual data in many laboratory corrosion test results, the actual conditions and engineering often has a gap, so the material in the need to pay attention to, when necessary for corrosion test in the actual medium or coupon tests under field conditions, and simulation test device.