Duplex stainless steel pipe safety use restrictions and requirements

• 2018-11-15 10:59:00　Hits: 1571

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.

2. It is necessary to master the law of tissue transformation of duplex stainless steel tubes, and be familiar 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, and the upper limit temperature cannot exceed 300 °C.

4. The duplex stainless steel tube needs to be cooled quickly after solution treatment, and the slow cooling will cause the precipitation of the brittle phase, which leads to the toughness of the steel, especially the local corrosion resistance.

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

6. It is not possible to use the 650-800 ° C stress relief treatment commonly used in austenitic stainless steel, generally using solution annealing treatment. For the double-phase stainless steel surfacing after 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 heating 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. 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.

8. When using duplex stainless steel in different corrosive environments, it should be noted that the corrosion resistance of steel is always relative, although duplex stainless steel has better resistance to local corrosion. For a duplex stainless steel, he is also There is a range of applicable media conditions, including temperature, pressure, media concentration, pH, etc., which need to be carefully selected. Many of the data obtained from the literature and manuals are the results of laboratory corrosion tests, which often differ from the actual conditions of the project. Therefore, it is necessary to pay attention to the selection of materials, if necessary, in the actual medium corrosion test or under field conditions. Hanging test, even simulation of the device.