The electrolyte composition was shown to affect the crack growth rate in pipeline steel X70. Citrate
buffer (?? 5.5) and a mixture of NS4 solution with borate buffer (pH 7.0) were used as background
solutions under static and cyclic loading, respectively. Various substances were added to the citrate
buffer solution in order to affect anodic dissolution (AD) and hydrogen absorption (HA) of the metal. AD
inhibitors decrease the crack growth rate. Sulfide, carbonate and phosphate ions, which stimulate the
AD process, accelerate crack propagation in weakly-acidic solutions. Thiourea stimulates the ?D
process in buffered NS4 solution and accelerates the crack growth in this solution. The effects of HA
promoters may vary. Their influence on the crack propagation could be connected with the activating
effect of atomic hydrogen on the anodic dissolution of iron. The data obtained testify that anodic
dissolution of the metal is the governing mechanism in the SCC of pipe steel X70 in the vicinity of the
corrosion potential.
Key words: pipeline steel, near-neutral pH environment, crack propagation, electrolyte composition,
anodic dissolution, hydrogen absorption.