Indranil Roy

Surface Property Enhancement of UNS N07718 and G41400 by Ultrasonic Impact Treatment

Ultrasonic impact treatment is a relatively new surface modification process that may be potentially applied to impart compressive residual stresses onto oilfield parts experiencing wear, fatigue, and possibly environmentally-assisted cracking. Through severe plastic deformation, ultrasonic impact treatment is herein investigated to surface harden two oilfield alloys, UNS N07718, a premium alloy with satisfactory oilfield performance but occasionally lacking surface hardness and abrasive wear resistance, and UNS G41400, a comparatively low-cost alloy restricted by its corrosion fatigue limit in oilfield rotating equipment. For comparison purposes, the two studied alloys were ultrasonic impact treated under identical conditions and carefully selected to exhibit similar yield strengths (900 MPa). Results from microstructural examinations, micro-hardness indentations, and residual stress measurements all indicate that ultrasonically treated surfaces exhibit superior properties that create opportunities for implementing this new surface modification process in selected oilfield applications.

Comparative Performance of Three High-Strength Ni-Cr-Mo Alloys in Oilfield Simulated H2S Environment

Three Ni-Cr-Mo alloys with 140ksi minimum yield strength, namely 625Plus, 718, and 945X were tested in selected sour environments to evaluate and rank their environmentally-assisted cracking susceptibility. The testing revealed that none of the alloys, stressed to 90% of their actual yield point, cracked as a result of an agressive 30-day NACE level VII-modified environment (401 ± 9 oF, 500 psia H2S, 500 psia CO2 and 151,700 mg/liter chlorides). In a complementary attempt to rank the alloy cracking susceptiblity, quasi-static strain rate (SSR) tests per NACE TM0198-2004 were conducted in a modified H2S-saturated NACE TM0177 Solution A. Following a critical analysis of parameters such as time-to-failure (TTF), percentage reduction in ductility (%ε), percentage reduction of cross-sectional area (% RA) and fractomicrographs, 625Plus was confirmed to outperform its counterparts while some evidence of hydrogen embrittlement was found on 945X.