Cable tray, trunking and their supports and hangers shall be made of corrosion-resistant rigid materials when they are used in corrosive environment.Or take anti-corrosion treatment, which shall meet the requirements of engineering environment and durability.Aluminum alloy cable tray should be used in places with high requirements for corrosion resistance or cleanliness.

   With the progress of science and technology, as well as the deepening of people’s understanding of steel structure, steel structure, a new type of building structure, has been adopted more and more.Due to the different technical level and processing technology of manufacturers or installers, the quality of steel structure is also very different. Xuzhou Sifang will introduce the formation of stress corrosion crack of steel structure and preventive measures.

1、 Causes of stress corrosion cracking

(1) Activation pathway stress corrosion

When the corrosion cell is a large cathode and a small anode, the dissolution of the anode shows concentrated corrosion damage.As long as in the corrosion process, the anode is always at the forefront of the crack, the crack tip is in an active state without passivation, and other parts (both sides of the crack end) are passivated, so that the crack develops to fracture. 

(2) Stress corrosion of active channel caused by strain

The passivation film breaks under the action of stress, and the metal exposed in the crack becomes the active anode and dissolves.In the process of corrosion, when the passivation film breaks, it will be repaired at the same time. Under the condition of continuous strain, the repaired passivation film will be damaged again, so that the corrosion will continue.

(3) Hydrogen embrittlement stress corrosion

The corrosion cell is composed of a small cathode and a large anode. The large anode dissolves, showing uniform corrosion.If hydrogen evolution occurs in the small cathode area, concentrated hydrogen permeation will occur in the metal in the cathode area, which will lead to brittle fracture under continuous load, and stress corrosion will develop smoothly.With the appearance of cracks, the concentration of stress and strain at the crack tip promotes the accumulation of hydrogen in the metal towards the crack tip, which eventually leads to stress corrosion fracture.

2、 Prevention measures of stress corrosion crack 

The formation of stress corrosion must have three factors at the same time, that is, material, medium and tensile stress.Therefore, we should start from three factors, from product structure design, installation and construction to production management.

(1) Material: adopt duplex stainless steel material; select welding material (equal composition principle) which is basically consistent with chemical composition and structure of base metal;

(2) Medium: the possibility of medium corrosion to base metal must be specifically considered. In order to reduce or eliminate stress corrosion in specific environment, corrosion inhibitor can be added to the medium.Surface treatment technology can also be used to prepare sacrificial anode coating or physical isolation coating on the surface of components.

(3) Stresses include:

① In the process of welding, choose reasonable joint form to reduce residual stress; ② correct welding sequence; ③ appropriate heat input; ④ stress relief treatment can be carried out after welding