Fitness-For-Service Assessment and Failure Analysis of Hydrogen-Induced Cracking in a Pipeline Steel

During inspection of an 11-km-long pipeline made of API X60 steel carrying hydrocarbons containing wet H2S, hydrogen-induced cracking (HIC) was found at different locations along the pipeline length. Microstructural investigations by scanning electron microscopy (SEM) showed stepwise cracking (SWC) as the result of the presence of MnS inclusions. Fitness-for-service (FFS) assessment based on API579-1/ASME FFS-1 was performed to decide on the pipeline serviceability. The finite element analysis (FEA) results showed that the HIC-damaged pipeline was acceptable per level-3 FFS requirements and the pipeline understudy was fit for service. The remaining life of the damaged pipeline should also be periodically monitored using failure assessment diagram (FAD).