Cause Analysis of Hydrogen Induced Crack by LSAW Steel Pipe

LSAW steel pipe due to the use of different conditions and environments, and changes with time and objective conditions, coupled with the intrinsic defect, within a certain time there will be different forms of damage. Such as welded steel pipe containing hydrogen, cracking occurs at a sufficiently high applied stress or residual stress, this form of destruction, often referred to hydrogen induced cracking. Welded steel hydrogen induced cracking is due to hydrogen diffusion inside the metal matrix to form a solid solution in the presence or in the form of metal hydrides, which led to the pipe brittle fracture. It is a source of potential damage to the pipe. When the pipe for underground, buried deep under higher stress or pressure, and sometimes even a few days can occur in a few weeks hydrogen induced cracking.

Pipe hydrogen induced cracking due to contact with hydrogen or cathodic corrosion reaction, thus resulting in a hydrogen atom into the interior of the pipe metal tissue, so that the pipe material brittle. However, the pipe material will not necessarily lose ductility cracking. If the production of pipe weld pipe and tube mother online or offline proper heat treatment, hydrogen is expelled from the interior of the pipe base material, so that the material will restore the original strength.

In welded steel pipe hydride type hydrogen induced cracking, mainly after generation of hydrogen atoms diffuse into the pipe due to the corresponding result of brittle hydrides. Form hydrides, hydrogen induced cracking impact will be as flaky hydride having greater sensitivity, because such hydride prone to stress concentration. A characteristic of hydrogen induced cracking pipe having hydrogen induced cracking susceptibility pipe under applied stress, cracks have appeared before a lag time, so pipe hydrogen induced cracking incidents often occur after a period of time before the pipe under stress. Independent of the length of the applied stress magnitude latency, but with the increase of hydrogen concentration in the tube shortened. Lag time indicates hydrogen diffusion into the core of the region near the crack, and the time to reach the required concentration of hydrogen cracking required. Such as the mechanism of interaction between hydrogen and dislocations said, pipe in the process of hydrogen induced cracking, crack propagation is not continuous, but the first plastic deformation, then hydrogen generation gap, atom diffusion into the defect area caused by the deformation, resulting in pipe welding a partial hardening of the joints, so that the crack extended forward, resulting in hydride hydrogen induced cracking.