Abstract
Most non-magnetic drill collars (NMDC) used in directional, measurement-while-drilling and logging-while-drilling tools are manufactured using CrMn-austenitic stainless steels. These proprietary grades meet the demanding requirements in terms of mechanical, magnetic and corrosion resistance properties necessary for these applications. However, these grades might become susceptible to pitting corrosion and environmentally assisted cracking (EAC) when subjected to high chloride-containing water-based drilling fluids at elevated temperatures. Thermo-mechanical processing necessary to raise strength, as well as welding operations can lead to sensitization of these grades. Consequently, API Specification 7-1 includes requirements regarding intergranular corrosion resistance based on ASTM A262 Practice A. In addition, pitting corrosion requirements, most of them based on testing according to ASTM G48 Method A, have been recently added to API Specification 7-1. In this study, results from ASTM G48 Method A on several commercially available austenitic stainless steel grades commonly used in drilling tools are discussed to replace current pitting requirements in API Specification 7-1. In addition, electrochemical results were produced to support the provided conclusions.
