Hydrogen degradation of steels under long-term in-service conditions

Abstract

This chapter investigates the hydrogen-induced changes of mechanical properties and microstructures of two low-alloy steels and C-Mn steel as a result of their exposure to hydrogenated atmospheres at ambient, and elevated temperatures. As-received steels and steels being in the service as components of a hydrocracking reactor, boiler steam pipe, and oil trunk line are tested. Fracture mechanics, microstructural, hydrogen content, and hydrogen-transport analyses are employed to characterize the hydrogen-induced degradation of steels. A simple method for evaluating the hydrogen-induced degradation of steels in a high-temperature hydrogen atmosphere is developed. This method consists of thermocycling specimens between ambient and working (elevated) temperatures. The change of equilibrium hydrogen solubility at low and high temperatures causes the supersaturation of steels by hydrogen when it is cooled, resulting in the accelerated degradation of steels. The threshold effective stress intensity factor range, allowing for evaluation of a crack–closure effect, is used as a mechanical parameter, sensitive to high-temperature hydrogen degradation of steels under both in-service and laboratory conditions. The differences between the mechanical properties, and microstructures of degraded, and as-received steels, usually used in laboratory tests, can result in an improper evaluation of the risk of failures under in-service conditions.