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Hydrogen Induced Stress Cracking of Swaged 25Cr Super Duplex Stainless Steel Subsea End-Fittings

In 2018 the apparent failure of two subsea jumper end-fittings was detected by remotely operated vehicle (ROV) inspection prompting their retrieval from the seabed for analysis. The components were manufactured from UNS S32760 a 25 wt% Cr super duplex stainless steel (SDSS) and connected to the flexible pipe by swaging. The end fittings were exposed to the cathodic protection system presenting extensive accumulation of calcareous deposits upon inspection. A single longitudinal crack was observed on each end-fitting propagating from end-to-end of the ferrule i.e. the swaged section of the part. The visual appearance of the fracture surface suggested at first glance cleavage fracture and thus the possibility of hydrogen induced stress cracking (HISC).This paper summarizes the results of an extensive investigation aimed at elucidating the root-cause of the failure. Given the suspicion of a hydrogen embrittlement phenomenon the scope of the work was designed to address the three HISC causative factors namely a susceptible alloy microstructure a critical tensile stress level and the presence of atomic hydrogen. The experimental techniques included scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) electron backscatter diffraction (EBSD) analysis mechanical and corrosion examinations as well as slow strain rate testing (SSRT).

Product Number: 51319-12963-SG
Author: Mariano Iannuzzi
Publication Date: 2019
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