Effect of corrosion medium composition on rate of crack growth in X70 pipeline steel

Application of SSRT to estimate the effect of corrosive medium on the liability of X70 pipe steel to stress corrosion cracking

“…The chemical composition of the steel is provided elsewhere [8]. The steel has a yield point of  0.2 = 538 MPa and a tensile strength of  В = 622 MPa.…”

“…However, the citrate buffer solution used in [8] as the reference corrosive medium does not represent the composition of the sub-film electrolyte. Furthermore, the crack growth rate (~10 -7 mm/s) measured under specimen strain values within the kinetic curve plateau is about an order of magnitude higher than the crack growth rates most commonly observed on the outside walls of gas transmission pipelines [9].…”

“…The effect of a number of soil electrolyte components on the growth rate of corrosion cracks in X70 pipe steel in weakly-acidic (pH 5.5) citrate solution at static specimen straining has been studied [8]. It has been shown that the presence of sulfides and carbonates in a corrosive medium increases the crack growth rate, which is due to the stimulating effect of these additives on the anodic dissolution of steel in the potential region in the vicinity of the corrosion potential.…”

“…In those places where crevices are found on the outside pipe walls, the liquid under delaminated isolating coating (sub-film electrolyte) is a dilute aqueous solution of inorganic salts (mainly carbonates) and organic acids [6,7,8]. The sub-film electrolyte may contain dissolved hydrogen sulfide and bisulfide ions that are products of sulfatereducing bacteria life activity [6,8].…”

“…The sub-film electrolyte may contain dissolved hydrogen sulfide and bisulfide ions that are products of sulfatereducing bacteria life activity [6,8].…”