Austenitic stainless steel elbow causes of cracking has the following three points:
1, about the material, 1 cr18ni9ti casing heat exchanger pipe material, it is easy to produce stress corrosion in chloride environment, and generally been transgranular fracture.
2, corrosion environment, in the main medium of casing heat exchanger pipe for liquid titanium tetrachloride, still contain among them ferric chloride, sodium chloride, etc. As there is no purge, drain pipe heat exchanger, in a long time into the air and water droplets in the process of parking, gathered in the pipe of the hydrolysis of titanium tetrachloride pipeline, and because of chloride contains certain ability to make the material corrosion of chlorine ion, led to the acceleration of corrosion.
3, residual stress, the elbow did not eliminate the residual stress, the stress in addition to the working stress generated by the load, more of the residual stress is produced from the manufacturing process. Casing pressure and thermal stress, heat exchanger pipe bending, and the effect of welding residual stress and so on, will have a certain level of tensile stress conditions.
Control measures for the following three points:
1, selection of stress corrosion resistant material, in recent years developed a variety of stress corrosion resistance of stainless steel, austenitic steel, chromium nickel high purity high silicon austenitic nickel chrome steel, high chromium iron ferrite steel and ferrite, austenite dual phase steel. Among them, - austenite to ferrite dual phase steel stress corrosion resistance of the best.
2, the control stress, through solid solution after stabilizing treatment, can eliminate stress, also can obviously improve material chloride cracking resistance, but when considering using the method of this part to eliminate stress should be a good balance by sensitizing may cause problems.
3, strictly abide by the operation procedures and process operation and process conditions on the corrosion of austenitic stainless steel has a huge impact. Therefore, must be strictly controlled medium composition, flow velocity, medium technology indexes such as temperature, pressure, pH value. Within the scope of the process conditions allow adding corrosion inhibitor.
4, maintenance and management, in order to ensure the long-term safe operation of casing heat exchanger, must be strictly implemented on heat exchanger in aspects of the rules and regulations, and the defects of must be in the process of reviewing defects in its operation in a timely manner to master the development of the situation, take the appropriate measures to reduce the corrosion of the equipment.