10323 Mechanical and Electrochemical Evaluation of HCRAs for Oil and Gas Applications in Sour Environments

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Product Number: 51300-10323-SG

ISBN: 10323 2010 CP

Author: W. Kovacs III, H. Tsaprailis, J. R. Tuggle, S. A. Waters & L. F. Garfias-Mesias

Publication Date: 2010

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Increasingly, new systems are installed and used in harsh conditions such as installations with high expected ground movements, reeled offshore pipe lays, high pressure/high temperature (HPHT) service conditions and pipelines with occasional pressure spikes above the material yield strength. As a result of these demanding applications, the utility and necessity of strain-based design (SBD) has increased. To evaluate SBD components, testing methodologies need to correlate real material performance data to calculated design limits. One realistic test method for simulating the corrosion/mechanical failure conditions of SBD components is the cyclic slow strain rate test (CSSRT), alternatively named the ripple strain rate test (RSRT).

This paper documents the RSRT evaluation of UNS N06625 weld overlay material applied to low grade carbon steel for potential applications in an SBD oil and gas production situation containing high H2S and CO2 partial pressures as well as very oxidizing environments. The test methods (involving liquid H2S loading) are discussed in more detail. In addition, RSRT results will be compared with electrochemical testing in highly oxidizing environments containing ferric chloride at high temperatures (critical pitting and crevice temperatures following a modified version of the ASTM G48). Overall, the goal is to develop a rapid pre-screening, ranking and suitability process for Highly Corrosion Resistant Alloy (HCRA) or HCRA-clad materials that can take into consideration their corrosion resistance to highly corrosive environments and include mechanical strength testing of the desired material.

KEY WORDS: material qualification for oil and gas, highly corrosion resistant alloys (HCRAs), sour service, strainbased design (SBD), ripple strain rate test (RSRT), H2S testing, weld-overlay, laser welding, critical pitting temperature (CPT), critical crevice temperature (CCT)