Abstract
Bolts and stud bolts produced from UNS N07718 are used for subsea applications in the oil and gas industry. These components are commonly connected to cathodic protection systems to avoid corrosion degradation, but it can result in free hydrogen formation on the metal surface, and its subsequent adsorption and diffusion may lead to premature fracture. The present study investigated the influence of different UNS N07718 microstructures, obtained according to the API 6A CRA and ASTM B637 standards, on the hydrogen embrittlement susceptibility. For this purpose, a modified Incremental Step Load (ISL) test method (ASTM F1624) were carried out with 80 µm and 250 µm specimen notch radii and an increased step time (10/5/7,14). The results have shown that the ISL test succeeded in evaluate the UNS N07718 HES, and regardless of the notch radius the invariant limiting force (Pth) of the hydrogen permeation tests were less than 50% of the in-air fracture load, with the smaller notch radius reducing the Pth value more significantly. In addition to this, the API 6ACRA heat treatments (HTA and HTB) that had δ phase precipitation at the grain boundaries showed increased susceptibility to hydrogen embrittlement as compared to the ASTM B639 heat treatment (HTC).