Corrosion Resistance and Long-Term Reliability of Super-Austenitic Alloy 27-7MO for Use as Expandable Pipe

Abstract

Abstract In today's competitive oilfield environment, end-users are faced with choosing the lowest-cost material that meets the technical and environmental needs of the application. With field development expanding into deeper, more corrosive environments, corrosion-resistant alloys (CRAs) must be used. In this paper, the discussion will investigate CRAs and the added burden of maintaining economic efficiency in corrosive environments requiring sand control ― more specifically, materials for expandable sand-control systems. For expandable applications, materials must compete with existing non-expandable lower-cost commodity-type screen materials. 13Cr, for example, is the first choice CRA material for the base pipe in conventional sand screens. Although 13Cr is one of the least costly of the CRAs and provides the necessary corrosion resistance in mild H2S environments under a variety of chloride/temperature conditions, it lacks the ductility needed for 20 to 25% expansion as a solid-expandable. Austenitic stainless steels such as 316L (UNS S31603) have the needed ductility for expansion, but with their low resistance to Stress Corrosion Cracking (SCC) may be insufficient for severe-service applications. Thus, a need for an alloy that can be expanded while maintaining corrosion resistance is required. Furthermore, to prevail in this very competitive arena, the material must offer a cost-effective alternative to standard 13Cr and expanded S31603 pipe. The basis for this study involves measuring the SCC resistance and predicting the mechanical behavior of higher-strength corrosion-resistant super austenitic alloy 27-7Mo (UNS S31277). Slow strain rate (SSR) tests, pitting and corrosion tests, as well as U-bend tests are used to explore and compare environments where S31277 and S31603 can offer the most economical solution for expandable sand control products in corrosive conditions.