Study On Stress Corrosion Cracking Of 304 Stainless Steel Thin Wall Welded Pipe

304 stainless steel is a basic type of 18-8 series stainless steel, which possesses properties of high toughness, easy processing, excellent weldability and strong corrosion resistance.304 stainless steel thin wall pipe is widely used in heat exchangers, condensers, heaters, water pipes of building and nuclear power plant pipes. However, corrosion failure of 304 stainless steel thin wall welded pipe caused a large number of economic losses and casualties in practical application process, the majority of which is stress corrosion damage. According to the characteristic of stainless steel thin wall pipes, the author focused on the following area research: residual stress measurement, heat treatment of stress relief, stress corrosion testing, metallographic analysis and mechanics performance testing. The study determined heat treatment process to eliminate the surface residual tensile stress in steel pipes, thereby enhancing the stainless steel thin-walled pipe stress corrosion resistance.The study and results of this research include:1.Study of residual stresses of 304 stainless steel thin wall pipe. Utilize the method of X-ray diffraction to determinate surface residual stress of steel pipe. Determine the X-ray stress measurement method forΦ25×0.5mm 304 stainless steel thin-walled pipe. There are large tensile residual stresses in the surface of stainless steel pipe. This is the main reason due to stress corrosion cracking of steel pipes in the practical application.2.Study of stress relief heat treatment. The surface tensile residual stress transform into compressive residual stress by the heat treatment. It is helpful to improve the anticorrosion property of stainless steel pipes.3.The study of stress corrosion testing. According to the standard GB4334-84"Stainless Steel 42%MgCl2 Solution Stress Corrosion Method", the stress corrosion testing of 304 stainless steel thin wall welded pipes were determined, and designed the devices of test. Stress corrosion testing was done by put the pipes in boiling 42%MgCl2 solution before and after they were heat treated. The testing proves that the untreated pipes have bad anticorrosion property, and stress relief heat treatment improves the anticorrosion property of the stainless steel pipes.4. Metallographic analysis of the material and Mechanics Performance Testing. It is determined that the method of making austenitic stainless steel metallographic by comparing of different corrodents. It is found that the carbide inadequate solution to austenitic structure before heat treatment, and carbide could not completely dissolve in the austenite by heat treatment. The mechanics performance of heat treated 304 stainless steel thin wall welded pipe Meet national standards.