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Duplex Stainless Steel Pipe safety restrictions and requirements

Nov. 20, 2019

Duplex stainless steel pipe safety restrictions and requirements:

1. It is necessary to control the comparative example. The most suitable ratio is that the ferrite phase and the austenite phase are each half, and the number of one phase cannot exceed 65% at most, so as to ensure the best comprehensive performance. If the two ratios are out of tune, such as too many ferrite phases, it is easy to form a single-phase ferrite in the welded HAZ, which is sensitive to stress corrosion cracking in some media.

Duplex Stainless Steel Pipe

Duplex Stainless Steel Pipe

2. It is necessary to master the organization transformation law of Duplex Stainless Steel Pipe and familiarize with the TTT and CCT transition curves of each steel grade. This is the key to correctly guide the process of heat treatment and thermoforming of duplex stainless steel. The precipitation of the brittle phase of duplex stainless steel should be More sensitive than austenitic stainless steel.

3. The continuous use temperature of the duplex stainless steel tube ranges from -50 to 250 ° C. The lower limit depends on the brittle transition temperature of the steel. The upper limit is limited by the brittleness at 475 ° C. The upper limit temperature cannot exceed 300 ° C.

4. Duplex stainless steel pipe requires rapid cooling after solution treatment, and slow cooling causes precipitation of the brittle phase, which leads to the toughness of steel, especially the resistance to local corrosion.

5. The lower limit temperature of hot working and thermoforming of high chromium molybdenum duplex stainless steel pipe can not be lower than 950 °C, super duplex stainless steel can not be lower than 980 °C, low chromium and molybdenum duplex stainless steel can not be lower than 900 °C, avoiding brittle phase Precipitation causes surface cracks during processing

6. Cannot use the stress relief treatment of 650-800 °C commonly used in Austenitic Stainless Steel Pipe, generally using solution annealing treatment. For the double-phase stainless steel after surfacing the surface of low-alloy steel, it is necessary to carry out the overall treatment at 600-650 °C and must consider the toughness and corrosion resistance due to the precipitation of the brittle phase, especially the local corrosion resistance. The problem of falling is to shorten the healing time in this temperature range as much as possible. The heat treatment of low alloy steel and duplex stainless steel clad plates is also considered.

7. It is necessary to be familiar with the welding rules of duplex stainless steel pipes. It is not possible to apply all kinds of austenitic stainless steel welding. The safe use of duplex stainless steel equipment has a great relationship with the correct welding process of steel. Some equipment failures often Related to welding. The key is the control of line energy and interlayer temperature. It is also important to choose the right solder material. The two comparative examples of welded joints (weld metal and welded HAZ), in particular, the welding of HAZ, maintain the necessary austenite quantity, which is important to ensure that the welded joint has the same performance as the parent metal.

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