Abstract

The qualification of materials in accordance with NACE MR0175/ISO 15156 is commonly performed by subjecting candidate materials to stress corrosion testing under an applied load in either a standard test solution (e.g. NACE solution A or B) or a test environment simulating service conditions. The exposure times for standard NACE solution A or B can vary from a few days up to a month (720 hours), whilst the exposure time for simulated service conditions is typically one month. This is widely accepted in the Oil & Gas industry and supported by good field experience with alloys such as martensitic and duplex stainless steels, suggesting that this duration is sufficient for those materials.

A similar approach has also been employed in the past for precipitation hardening (PH) nickel alloys, which are being increasingly used in the Oil & Gas Industry. However, field failures of some NACE MR0175/ISO 15156 qualified PH nickel alloys have raised questions over the suitability of the exposure times and test methods that were used.

The present work focused on PH nickel alloys exposed to the NACE Level VI and VII environmental conditions described in NACE MR0175/ISO 15156 for up to 1 year exposure time, to evaluate their performance using both ‘conventional’ and ‘accelerated’ testing techniques. The results indicate that the ‘conventional’ qualification methodology might not be suitable to ensure continuous safe operation for the materials investigated even with extended testing periods (up to one year). However, the approach used in the present work was not fully reproducible and needs further improvement.

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