Crack growth behaviour and crack tip chemistry of X70 pipeline steel in near-neutral pH environment

In this paper, crack growth behaviour and the crack tip chemistry of X70 pipeline steel in the near-neutral pH environment were investigated using the in-situ measurements. The stress corrosion crack propagated forward under the cyclic load, with a mean crack growth rate (CGR) of 4.28 × 10–3 mm/cycle. The CGR da/dN obeys well with the stress corrosion fatigue mechanism. During the crack propagation, the crack tip environment differed significantly from the bulk solution. An aggressive electrolyte with low pH (about 4.0) and high concentration of Cl– (about 3.8 M) was produced near the crack tip. These results provided the direct evidence for simulating the crack tip solution and investigating the crack tip anodic dissolution.