Titanium sponge production process often used stainless steel tube cooler for cooling four titanium tetrachloride, and four titanium tetrachloride contact material for austenitic stainless steel (1Cr18Ni9Ti), and the cooling medium contact material for Q235A steel. The hot side of the casing pipe cooler is welded by 180 degrees stainless steel elbow.
In the production process, the casing pipe cooler is often blocked. When removing the cleaning and dredging, it is found that there are many cracks in the inner side of the inner edge of the stainless steel elbow.
Causes of cracking:
1, residual stress: stainless steel elbow residual stress is not eliminated, stress in addition to the working stress generated by the load, the residual stress is more from the manufacturing process. Under the action of internal pressure and thermal stress and welding residual stress, the casing tube heat exchanger will have a certain level of tensile stress condition.
2, corrosion environment: in the casing for titanium tetrachloride liquid heat exchanger pipeline, the major media, which also contains ferric chloride, sodium chloride. Due to the double pipe heat exchanger without blowing and discharging device, in the long term parking cause into the air and water droplets, lead to pipeline gathered in the hydrolysis of titanium tetrachloride and blockage of the pipeline, the lower and because chloride containing chloride ions of the material corrosion resistance, led to the acceleration of corrosion.
3, material: tube plate’s pipe material for the 1Cr18Ni9Ti, in the chloride environment is easy to produce stress corrosion, and generally wear crystal fracture.
1, the choice of high stress corrosion material: in recent years for the development of a variety of should endure the stress corrosion of stainless steel: high purity austenitic chromium nickel steel, high silicon austenitic chromium nickel steel, high chromium iron prime steel and iron ferrite – austenite dual phase steel. Among them, the resistance to stress corrosion resistance of ferrite austenite dual phase steel is the best.
2, the control of stress: by stabilization after solid solution treatment can eliminate stress, also can obviously improve the material resistance to chloride cracking performance, but consider adopting this method to eliminate the stress should be a good trade-off by sensitization may cause all sorts of problems.
3, strictly comply with the operating procedures: process operation, process conditions on the corrosion of austenitic stainless steel has a huge impact. Therefore, it is necessary to strictly control the media composition, flow rate, temperature, pressure, pH value and other technical indicators. Adding corrosion inhibitor to the range of process conditions.
4, maintenance and management: to ensure the long-term safe operation of the heat exchanger casing type heat exchanger should be strict implementation of regulations and laws and regulations related to heat exchanger, the defects must be reexamined, timely grasp the operation of defects in the development of the situation, take appropriate measures, reduce equipment corrosion.
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)