Prewelding of LSAW Steel Pipe
Date:2018-01-29 View:942 Tag:Prewelding of LSAW Steel Pipe
Longitudinal submerged arc welded pipe due to the use of different environmental conditions, and the objective conditions of change over time, coupled with the inherent defects in a certain period of time there will be different forms of damage. Such as hydrogen-containing welded steel pipe, in the high enough stress or residual stress cracking occurs, the form of such damage is commonly referred to as hydrogen induced cracking. Hydrogen-induced cracking of welded steel is due to the diffusion of hydrogen in the metal matrix, forming solid solutions in the form of metal hydrides or metal hydrides, resulting in brittle fracture of the pipe. It is a source of potential pipeline damage. Hydrogen induced cracking can occur in a few weeks even at high stresses or pressures when buried underground.
Hydrogen induced cracking of the pipe is due to contact with hydrogen or cathodic corrosion reactions, resulting in the hydrogen atoms entering the metal structure of the pipe to make the pipe brittle. However, the ductile material does not necessarily lose ductile cracking. Hydrogen is the substrate that is discharged from the inside of the pipe to make the material return to its original strength, if the pipe and pipe production pipe are properly heat-treated on-line or off-line.
Hydrogen induced cracking of the welded steel pipe caused hydrogen atoms to diffuse into the pipe mainly due to the consequent hydrogen embrittlement. Morphohydrides, hydrogen induced cracking will be flake hydrides with higher sensitivity because of the tendency of such hydrides to cause stress concentrations. Hydrogen induced cracking tube under the action of stress, with the characteristics of hydrogen-induced cracking of the tube, cracks occur before the lag time, the stress caused by hydrogen cracking after a period of time often occur. It has nothing to do with the applied stress amplitude latency, but shortens with the increase of hydrogen concentration in the tube. The lag time indicates hydrogen diffusing to the core near the crack and the time required to reach the desired hydrogen cracking concentration. For example, the mechanism of interaction between hydrogen and dislocations indicates that the cracking caused by the hydrogen process tube is not continuous, but the first plastic deformation, and then the hydrogen generation gap, atoms diffuse to the defect site caused by the deformation, This results in localized hardening of the welded pipe joints, causing the cracks to extend forward, causing hydride hydrogen cracking.