A B S T R A C T Despite decades of research, the mechanisms of near-neutral pH stress corrosion cracking of pipeline steel are still not fully understood. This investigation was aimed to understand the effect of minor cycles with very high R ratios (minimum stress/maximum stress) on crack growth in air and in near-neutral pH environments. It has been demonstrated that the minor cycle, even with an R ratio as high as 0.9, could significantly contribute to the crack growth of pipeline steels in the presence of a large underload cycle with a low R ratio of 0.5 in near-neutral pH environment. Comparing with constant amplitude tests, an increase of crack growth rate by a factor of 3 and 5 was observed when some non-propagating minor cycles were combined with an underload cycle for tests in air and in near-neutral pH solution, respectively. Based on the test results, the crack growth mechanisms during minor cycle loading in near-neutral pH environments were discussed and practical strategies aimed to minimise crack growth during pipeline operation were also proposed.Keywords pipeline steel; near-neutral pH stress corrosion cracking; corrosion fatigue; variable amplitude cyclic loading; underloads; number of minor cycles. N O M E N C L A T U R Ea = crack length CT = compact tension da/dN = fatigue crack growth rate K = stress intensity factor K max = maximum stress intensity factor n = number of minor cycles per block NNpHSCC = near-neutral pH stress corrosion cracking R ratio = stress ratio SCC = stress corrosion cracking SEM = scanning electron microscope SMYS = specified minimum yield strength γ = acceleration factor Δa = crack growth increment ΔK = stress intensity factor range I N T R O D U C T I O NEngineering components are often operated under variable amplitude cyclic loadings. Underload and overload are two common features of variable amplitude cyclic loading, which could accelerate and retard subsequent fatigue crack growth, respectively. 1,2 These effects are seen when compared with the crack growth predicted by a linear summation of damage of constant amplitude cyclic loading, with magnitudes equal to the variable amplitude load history.