Objective In the context of the “dual carbon” goals, liquid ammonia is anticipated to serve as an efficient and safe hydrogen storage carrier. However, during long-distance pipeline transportation of liquid ammonia, stress corrosion cracking may occur in the pipes, leading to leakage and compromising the intrinsic safety of the pipeline operation. Therefore, it is crucial to investigate the susceptibility of pipeline steel to stress corrosion from liquid ammonia to ensure pipeline safety.
Methods To analyze the stress corrosion behavior of X80 pipeline steel in a liquid ammonia environment with impurities, C-ring stress corrosion tests were conducted under varying levels of water, oxygen, and stress. The coupled effects of these impurities and stress on the corrosion behavior were quantitatively assessed using weight loss and control variable methods. This study clarified the evolution and internal mechanisms of liquid ammonia stress corrosion in pipeline steel based on corrosion rates, micro-morphology, and corrosion products.
Results In anhydrous liquid ammonia environment, the corrosion rate of pipeline steel increased with higher oxygen content and rose sharply with increased stress. When water with a mass fraction of 0.20％ was added to oxygen-containing liquid ammonia, the corrosion rates of pipeline steel decreased within the studied range of oxygen concentrations. The coupled effect of oxygen concentration and stress can lead to the formation of corrosion products on the surface of pipeline steel. At 100％ of yield strength, corrosion products appeared as granular deposits, and cracks began to initiate and propagate. As stress increased to 125％ and 150％ of yield strength, additional cracks formed on the surface of the pipeline steel, partially connecting with one another, while the corrosion morphology shifted to cementitious deposits accompanied by crack formation. When adding water with mass fractions of 0.20％ and 1.00％, respectively, only a few microcracks and corrosion products appeared on the surface of pipeline steel, even under high stress, indicating that a certain amount of water can inhibit liquid ammonia stress corrosion cracking in pipeline steel.
Conclusion During the design, construction, and operation of liquid ammonia pipelines, it is essential to consider the influence of factors such as the mixing of oxygen impurity, the high stress resistance of pipes, and residual strain from construction on liquid ammonia stress corrosion cracking. If necessary, adding a small amount of water can mitigate the risk of corrosion and enhance the safety of high-grade steel pipelines.
DownLoad: