注意事项 Precautions for ammonia tank
(1) In terms of material selection: Practice has proved that the higher the material strength, the greater the possibility of stress corrosion. However, the minimum strength limit where stress corrosion does not occur is related to factors such as impurity content and characteristics, stress magnitude, and operating speed. In order to prevent stress corrosion, under the comprehensive consideration of operating pressure, residual stress, and safety and economy, low-strength steel should be selected as much as possible.
(2) For new storage tanks before being put into use, the air in them should be completely removed; during filling, discharging and maintenance, certain measures should be taken to avoid bringing in any air. For large storage tanks, ammonia vapor should be condensed continuously, and most of the non-condensable gas is air, which should be discharged. Use smaller pumps or transpiration to remove air from the tank. In short, eliminating air pollution inside the storage tank can effectively prevent stress corrosion.
(3) Adopt reasonable structure and welding process. Stress concentration caused by excessive welds, excessive concentration, asymmetric welds, weld crossings and unreasonable welding sequences should be avoided on the structure. Strong assembly welding should be avoided during manufacturing to prevent defects such as undercuts and misalignments, and to ensure that the surface in contact with the medium is as smooth as possible. After manufacturing, annealing heat treatment should be performed to remove residual thermal stress after welding. The correct post-weld heat treatment can greatly reduce the residual stress in the manufacturing process, and can reduce the peak hardness of the welding heat affected zone.