The chemical production with salt as raw material will produce strongly corrosive hydrochloric acid along with its process. Therefore, corresponding measures should be taken in the design of chemical equipment and pipelines. Shenyang Liaozhong chemical plant uses sandviksaf2205 steel for relevant equipment, and pure austenitic 12Cr1MoVG alloy seamless pipe is used for process pipeline between chemical equipment.
It is a new alloy material, which is rarely used in China’s petrochemical industry, and its welding process has not been reported. This paper briefly analyzes the of the seamless alloy pipe and introduces its welding process.
Alloy seamless pipe, i.e. asme673 In unsn08904 technical conditions for welded pipes in part B of asmeii volume, it is the welded pipe for corrosion-resistant process pipeline, and the supply state is solution treatment.
Alloy steel is a kind of high chromium nickel alloy steel with ultra-low carbon (MO) content. Due to the solution treatment, the metallographic structure is pure austenite and free ferrite.
Generally speaking, the intergranular corrosion of austenitic stainless steel is caused by the “poor chromium” at the grain boundary. The “culprit” of “chromium deficiency” is that the carbon content of austenite in steel exceeds the dissolved amount at room temperature (the carbon dissolved amount of austenite at room temperature is 0.02%). Therefore, the fundamental measure to solve intergranular corrosion is to control the carbon content in steel.
In order to increase the pitting resistance of austenitic stainless steel, the content of Cr and Mo) is generally appropriately increased. Cr is the main element forming the passive film. Increasing the Cr content will make the passive film more stable; The higher content of Mo) will make the surface of steel form moociz protective film in the medium with C1. Therefore, higher CR and Mo) content can make austenitic stainless steel have strong pitting corrosion resistance. The literature fly points out that austenitic steel with high nickel (~ 25% Ni) has the ability to resist stress corrosion fracture. From the overall ability, the single-phase structure is good. The carbon content of alloy steel is 0.02%, and the contents of Cr, Ni and m <) are as high as 19.0% – 23.0%, 23.8% ~ 28% and 4.0% ~ 5.0% respectively. Its metallographic structure is single-phase austenite. Therefore, theoretically, alloy steel has high resistance to intergranular corrosion, pitting corrosion and stress corrosion fracture. Compared with other austenitic stainless steels, due to the advantages of alloy steel in C, Cr, Ni, MC) content and metallographic structure, its corrosion resistance and stress corrosion fracture ability are obviously better than austenitic stainless steels such as 1Cr18Ni9Ti and oocr18ni9. Therefore, it is appropriate to select alloy steel as the process pipeline material with hydrochloric acid medium.
Post time: Jan-17-2022