Reasons for cracking:
1. Residual stress
The residual stress of the elbow is not eliminated. In addition to the working stress caused by the load, the stress is more from the residual stress generated by the manufacturing process. Under the influence of internal pressure, thermal stress, welding residual stress, etc., the bent tube of the tube heat exchanger will have a certain level of tensile stress.
2. Corrosive environment
The main medium in the tube of the tube heat exchanger is titanium tetrachloride liquid, which also contains chlorides such as ferric chloride and sodium chloride. Since the tube heat exchanger has no purge and discharge device, it will cause air and water droplets during long-term shutdown, which will cause the titanium tetrachloride accumulated in the pipeline to hydrolyze and block the pipeline. The corrosion resistance of the material is reduced, resulting in accelerated corrosion.
3. Material
The pipe material of the casing heat exchanger is 1Cr18Ni9Ti, which is prone to stress corrosion in the chloride ion environment, and generally shows transcrystalline fracture.
The control measures are:
Through the stabilization treatment after solid solution, part of the stress can be eliminated, and the material's resistance to chloride cracking can be significantly improved, but when considering the use of this partial stress relief method, it is necessary to weigh well the various possible causes of sensitization. problem.
Strictly follow the operation regulations
Process operation and process conditions have a huge impact on the corrosion of stainless steel. Therefore, it is necessary to strictly control the process parameters such as medium composition, flow rate, medium temperature, pressure, and pH value. Add corrosion inhibitor within the allowable range of process conditions.
Maintenance and management
In order to ensure the long-term safe operation of the tube-type heat exchanger, the rules and regulations concerning the heat exchanger should be strictly implemented, the existing defects must be reviewed, and the development of the defects in the operation must be timely grasped, and appropriate measures should be taken to reduce Corrosion of equipment.
