A failure in a Precipitation Hardened (PH) Nickel alloy component used as part of a Tubing Retrievable Safety Valve (TRSV) assembly occurred in an offshore gas well. The partial pressures of H2S and CO2 at the TRSV were estimated to be 333 and 534 psia, respectively. The well also produced 0.1 lb/MMSCF of elemental sulfur. The failed component was manufactured using grade UNS N07716 PH Nickel alloy heat treated to 140 ksi (965 MPa) Specified Minimum Yield Strength (SMYS) and 43 HRC max hardness in compliance to NACE MR0175/ISO 15156-3 standard.1 The well was completed and had been in production for approximately five years with no major issues before it was shut-in to service wellhead equipment. A few months after shut-in of the well for service, a rapid increase in the tubing-casing annulus (TCA) pressure was observed which resulted in the need to workover the downhole completion. During workover operations, the TRSV was found to have parted at a major body component of the TRSV assembly, resulting in only the upper portion of the Top Sub being initially retrieved. Fishing operations later successfully retrieved the remainder of the TRSV. Failure analysis of the component indicated brittle fracture due to Hydrogen Embrittlement (HE) as the cause of the failure. The failure initiated at a high stress location in a box thread of the component and propagated through the component's cross-section resulting in complete separation of the component into two portions. This paper provides the details of the environment conditions, analysis of the failed component, including metallurgical and engineering analysis, and results of HE testing conducted as part of analysis.

Subject
Test methods, Materials, Secondary cracks, Photography, Microscopy, Microstructure, Valves, Nickel based alloys, Raw material, Fracture surfaces, Mechanical failure, Fracture, Hydrogen
Keywords:
Precipitation Hardened Nickel Alloy, UNS N07716, Hydrogen Embrittlement (HE), Hydrogen Assisted Cracking (HAC), Hydrogen Induced Stress Cracking (HISC), Tubing Retrievable Safety Valve, H2S, NACE MR0175/ISO 15156
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2022
Association for Materials Protection and Performance (AMPP)
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