Formation and prevention of stress corrosion crack in steel structure

First, the cause of the formation of stress corrosion cracks

(1) activation path stress corrosion

When the corrosion battery is a large cathode and a small anode, the dissolution of the anode appears as a concentrated corrosion damage. As long as the anode remains in front of the crack during the corrosion process, the crack tip is not passivated, and some parts (on both sides of the crack port) are passivated, so that the crack develops forward to fracture.

(2) Strain produces stress corrosion of active channels

The passivation film cracks under the action of stress, and the exposed metal at the crack becomes the active anode and dissolves. In the corrosion process, the passivation film is repaired at the same time of the rupture of the passivation film, and the repaired passivation film is damaged under the condition of continuous strain, so that the corrosion continues.

(3) hydrogen embrittlement stress corrosion

The corrosion battery is composed of a small cathode and a large anode, and the large anode dissolves, showing uniform corrosion. If hydrogen evolution occurs in the small cathode region, concentrated hydrogen infiltration of the metal in the cathode region will occur, resulting in brittle fracture under continuous load, and stress corrosion will develop smoothly. With the appearance of crack, the stress and strain concentration of crack makes hydrogen in metal close to the crack, resulting in stress corrosion fracture.

Second, stress corrosion crack prevention measures

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

(1) Material: duplex stainless steel material; Select the welding material that is basically consistent with the chemical composition and organization of the base material (equal composition principle);

(2) Medium: The possibility of corrosion of the medium to the base material must be specifically considered, in order to reduce stress corrosion in a specific environment, corrosion inhibitors can be added to the medium. Surface treatment technology can also be used to prepare sacrificial anode coatings or physical isolation coatings on the surface of the member.

(3) Stresses include:

① Select a reasonable joint form during welding to reduce the residual stress; ② Correct welding sequence; ③ Suitable heat input; ④ Stress removal can be carried out after welding