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Stainless steel is mainly used as cooling tube of carbonization tower in soda ash.

Stainless steel is mainly used as cooling tube of carbonization tower in soda ash.

2019-08-12 15:09

Can stainless steel sheets be blistered with alkali? 00Mo5 stainless steel in soda is mainly used as the cooling tube of carbonization tower. It has excellent resistance to pitting and crevice corrosion, and can even be used for cooling tubes in contact with seawater medium. However, this material is not a standard stainless steel series product, and it is difficult to purchase in the market. Its use is limited to a certain extent, and it has not been widely used. 904L has not only high content of chromium and nickel, but also high content of Mo. It has better corrosion resistance than 00Mo5 stainless steel. In soda production, 904L shows better overall corrosion resistance and pitting resistance. In addition, 904L has good cold and hot workability. In Europe 904L is considered to have excellent corrosion resistance comparable to titanium in soda equipment. In some titanium-poor countries, it has been widely used to replace titanium in soda industry. It can be used not only as the shell material of pressure vessel, but also as forgings and castings on the tube sheet and pump of heat exchanger. In addition, 316L, 304 stainless steel is also widely used in soda equipment, pipes, instruments and valves. In the production of multi-effect evaporation of caustic soda, which is closely related to soda production, pumps and valves made of 0Cr18Ni9Ti stainless steel at high concentration of NaOH 45%, NaCl 20% and boiling temperature 150 C are less than one month, while pipes made of 1Cr18Ni9Ti have a service life of only 11 months. Ultra-pure ferritic stainless steel (000Cr26Mo1) was used in evaporator of concentrated alkali (42% - 46%) production line. The corrosion rate of pipe wall was only 0.018mm/a, and its service life was more than 10 years. 4.2 Bidirectional stainless steel 3RE60 (00Cr18Ni8Mo3Si2) is Austenite-ferrite duplex stainless steel. Some foreign factories use this stainless steel for inner parts of tower, such as grille, tray, etc. This material has been used in distillation section of mother liquor distillation tower of ammonia-alkali in China, but it produces stress corrosion cracking after putting into operation. Analysis shows that the stress corrosion damage site is at the highest temperature. Although duplex stainless steel has better resistance to intercrystalline corrosion than austenitic stainless steel with equivalent carbon content, the chloride stress corrosion resistance of duplex stainless steel is superior to that of ordinary 18-8 austenitic stainless steel only under low stress, but it is not different or basically the same under high stress. Therefore, cracks appeared on the wall of mother liquor distillation tower made of this material after 2 years of use and leakage occurred. After 5 years of use, more than 30 leakage points appeared in each tower. Cracks and cracks mostly occur in the weld and heat-affected zone of the tower body. The cracks in the heat-affected zone of the girth weld are the most, and the serious cracks radiate outward, leading to internal and external perforation. The cracks in the heat-affected zone of the weld seam are concentrated, and the direction is parallel to the weld seam and the length corresponds to it. Point corrosion occurs in many parts of the base metal of the local cylinder body. It is considered that the main cause is the damage caused by stress corrosion of chloride. The main cause of stress corrosion cracking is the welding stress, especially the residual stress caused by repairing welding and the structural stress caused by equipment manufacturing. At the same time, the chloride ion medium is locally concentrated by scaling on the tower wall and alternating wetting and drying. The effect of quality leads to stress corrosion damage.

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