Relationship between hydrogen-induced additive stress and threshold cracking stress for a pipeline steel

Tensile specimen of X-80 pipeline steel was strained to over 1% plastic deformation in air. The strained specimen was charged with hydrogen, and the charged specimen was strained in air. The flow stress and yield stress of the charged specimens are different from the uncharged. The difference is the hydrogen-induced additive stress, which can help the external stress to enhance the plastic deformation. The hydrogen-induced additive stress, sigma(ad), increases linearly with the hydrogen concentration, i.e, sigma(ad) = -14.1 + 3.89C(0). On the other hand, fracture stress during dynamically charging with hydrogen decreases linearly with hydrogen concentration in slow stain rate tests, i.e, sigma(F)(H) = 675 - 6.1C(0). The threshold stress decreases linearly with the logarithm of hydrogen concentration for the samples in constant load tests, i.e, sigma(HIC) = 669 - 124 ln C-0.