Plate heat exchanger is liquid - liquid, liquid - steam for the ideal heat exchange equipment. It is a certain corrugated shape of a number of columns of metal sheet stack made of a new type of efficient heat exchanger.
1, electrochemical protection method
The stress corrosion fracture is the anodic dissolution process under stress. Therefore, it can be controlled by electrochemical protection. Metal or alloy stress corrosion fracture and potential, and some systems there is a critical rupture potential, higher than this value will produce corrosion fracture. More systems have a range of sensitive potentials, which are usually in the passivation region, and by electrochemical polarization the metal potential can leave the sensitive potential range.
The electrochemical protection method not only prevents stress corrosion cracking, but also prevents the expansion even if cracks are generated under the condition that the protection parameters are properly selected. The use of sacrificial anode protection or surface coating corrosion-resistant metal method, and sometimes can receive good results.
2, reasonable process design
In order to avoid residual liquid and sediment retention, welding as much as possible using double-sided butt welding and continuous welding, to avoid lap welding and spot welding.
As the plate is very thin, welding after welding less welding wire, easy to cause poor weld formation, welding process should be 100% to fill the wire to ensure that the weld is well formed.
3, reduce the residual stress
According to practical experience, the stress caused by stress corrosion cracking is mainly residual stress, and the residual stress is mainly composed of cold work and internal stress caused by welding. Heat treatment of cold workpieces and weldments helps to eliminate residual stresses and thus helps prevent stress corrosion. Therefore, the welding operation must strictly comply with the relevant welding procedures. When the heat treatment temperature control should be appropriate, to avoid the heat treatment to produce residual stress.
However, the use of heat treatment to eliminate residual stress is not only costly, but also some shortcomings, such as deformation, carbide precipitation along the grain boundary, the formation of scale and the elimination of internal stress and so on. Therefore, in the welding plate heat exchanger manufacturing process, should be based on the actual situation to consider in order to decide whether to take the stress relief annealing heat treatment to eliminate residual stress. Other methods of eliminating residual stresses, such as hydrostatic tests, vibration aging, shot peening and hammering, may also be used.
4, reduce the erosion of the media
The medium has different effects on different corrosion systems. For example, austenitic stainless steels are prone to stress corrosion in neutral chloride solutions, but stress corrosion does not occur as long as the mass concentration of oxygen in the medium is less than 1.3 mg / m3.
Thus, stress corrosion can be controlled by removing dissolved oxygen and oxidizing agents in the medium. Reducing the mass concentration of Cl- in the medium and strictly controlling the mass concentration of sulfur in the medium is also an effective measure to control the stress corrosion.http://www.forwon.com/
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