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Environmentally Assisted Cracking Of Nickel Based Alloy 955 In Saltwater With Cathodic Protection For HPHT Application

Environmentally Assisted Cracking Of Nickel Based Alloy 955 In Saltwater With Cathodic Protection For HPHT Application
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Precipitation hardened (PH) Ni-based alloys have been utilized in oil and gas industry for decades. Among them, UNS1 N07718 because of its performance in sour wellbore fluids and in hydrogen charging environments has received the most attention for multiple upstream applications such as tubing hangers, production stab, multi-phase flow meter bodies, valve stems, etc. It has been reported that the alloy performance is generally acceptable for many applications up to 175 °C (350 °F) – 204 °C (400 °F) in the exposed wellbore environments such as sour production fluid, completion brine, and depending on metallurgical processing and microstructure externally exposed to SWCP at the seabed temperature.

Product Number: 51322-17768-SG
Author: Arshad B Gavanluei, Vipul Shinde, Manuel Marya, Ramgopal Thodla, Alexis Simon, Stanley Gregory
Publication Date: 2022
Industries: Coatings and Linings , Corrosion Monitoring and Control , Coatings
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A thorough characterization of nickel-based UNS N09955 was performed in saltwater with cathodic protection (SWCP) environment for high-pressure high-temperature (HPHT) subsea applications. The test environment was deionized water with 3.5% NaCl, pH of 8.2, CP potential of –1,050 mV vs. saturated calomel electrode, and at 40 °F (4.4 °C).

Environmentally assisted cracking susceptibility of the alloy was evaluated by performing fracture toughness test using compact tension test specimen and rising displacement method in air and in SWCP as well as fatigue crack growth rate (FCGR) and static crack growth rate (SCGR) in SWCP. Fracture toughness test in SWCP conditions indicated a significant reduction in the initiation fracture toughness value of the alloy in SWCP versus in-air values. FCGR by performing frequency scan at various ΔK values and SCGR of the alloy was studied in SWCP condition. SCGR was obtained at different load holds of 55, 66, 75, and 99 MPam and various CP potentials of –1,050, 1,000, –950, and –900 mV. No crack growth was observed at 55 MPam, and a crack growth rate (CGR) of 2 × 107 mm/s was established at –1,050 mV CP potential. By changing the load and electrode potential, CGR was varied. The obtained results were also compared with other precipitation hardened nickel alloy behavior.

Finally, scanning and transmission electron microscopy (SEM and TEM) were used to characterize the fracture surface morphology, grain structure, and grain boundary precipitates, as well as the shape, size, and distribution of the precipitates.   

A thorough characterization of nickel-based UNS N09955 was performed in saltwater with cathodic protection (SWCP) environment for high-pressure high-temperature (HPHT) subsea applications. The test environment was deionized water with 3.5% NaCl, pH of 8.2, CP potential of –1,050 mV vs. saturated calomel electrode, and at 40 °F (4.4 °C).

Environmentally assisted cracking susceptibility of the alloy was evaluated by performing fracture toughness test using compact tension test specimen and rising displacement method in air and in SWCP as well as fatigue crack growth rate (FCGR) and static crack growth rate (SCGR) in SWCP. Fracture toughness test in SWCP conditions indicated a significant reduction in the initiation fracture toughness value of the alloy in SWCP versus in-air values. FCGR by performing frequency scan at various ΔK values and SCGR of the alloy was studied in SWCP condition. SCGR was obtained at different load holds of 55, 66, 75, and 99 MPam and various CP potentials of –1,050, 1,000, –950, and –900 mV. No crack growth was observed at 55 MPam, and a crack growth rate (CGR) of 2 × 107 mm/s was established at –1,050 mV CP potential. By changing the load and electrode potential, CGR was varied. The obtained results were also compared with other precipitation hardened nickel alloy behavior.

Finally, scanning and transmission electron microscopy (SEM and TEM) were used to characterize the fracture surface morphology, grain structure, and grain boundary precipitates, as well as the shape, size, and distribution of the precipitates.   

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Picture for Environmentally Assisted Cracking Susceptibility Of Nickel Based Alloy 955 In A Sour Wellbore Fluid For HPHT Application
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Environmentally Assisted Cracking Susceptibility Of Nickel Based Alloy 955 In A Sour Wellbore Fluid For HPHT Application

Product Number: 51322-17766-SG
Author: Arshad B. Gavanluei, Ramgopal Thodla, Manuel Marya, Alexis Simon, Vipul Shinde, Stanley Gregory
Publication Date: 2022
$20.00

Precipitation-hardened nickel-based alloys have been used for decades in the oil and gas industry. Among these alloys, UNS1 N07718 has received the most attention for use in upstream applications such as tubing hangers, production stab plate, multiphase flowmeter bodies, and valve stems because of its performance in sour wellbore fluids (SWFs) and hydrogen-charging environments.
Picture for On the Susceptibility of Precipitation Hardened Nickel Alloys to Hydrogen Assisted Cracking
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On the Susceptibility of Precipitation Hardened Nickel Alloys to Hydrogen Assisted Cracking

Product Number: 51319-12846-SG
Author: Roberto Morana
Publication Date: 2019
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Precipitation Hardened (PH) Nickel alloys have been widely used in the Oil & Gas Industry for decades as these materials offer high strength and outstanding corrosion resistance in aggressive environments. They are commonly used in high-strength components in downhole wellhead subsea and Christmas tree equipment. However high profile failures of equipment have occurred including tubing hangers cross-overs and subsea bolts with alloys such as UNS N07718 UNS N07716 or UNS N07725. In all these cases the mechanism identified was Hydrogen Assisted Cracking (HAC) as the result of the interaction between atomic hydrogen adsorbed by the alloy and its microstructure.PH Nickel alloys are all subject to precipitation of secondary and tertiary phases which if processed improperly (particularly during hot working and heat treatment) may adversely affect the material properties required for the intended application. Despite the number of scientific and technical contributions produced over the last years the interaction between these complex microstructural features and atomic hydrogen is still not understood and is further complicated by variations in testing approaches used to simulate severe hydrogen charging conditions. The present paper provides insights on the HAC failure mechanism for API 6ACRA PH Nickel alloys comparing findings from numerous studies. In addition implications for currently adopted standards and emerging specifications are also presented and discussed.
Picture for Hydrogen Embrittlement Failure Of Nickel Alloy UNS N07716-140 Tubing Retrievable Safety Valve Component Installed In A Sour Production Gas Well
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Hydrogen Embrittlement Failure Of Nickel Alloy UNS N07716-140 Tubing Retrievable Safety Valve Component Installed In A Sour Production Gas Well

Product Number: 51322-17709-SG
Author: Iyad Al-Buraiki, Qasem Alhassan, Karthik Krishnan, Wade Meaders
Publication Date: 2022
$20.00

A 9-5/8 inch (244.8 mm) Tubing Retrievable Safety Valve (TRSV), which is a type of Sub Surface Safety Valve (SSSV) governed by API Specification 14A, was found to have failed when retrieved during workover operations in a gas production well in June 2019. This TRSV was installed in the well in November 2013 and was in production service from 2015 until November 2018 when the well was shut in for maintenance of surface equipment. In March 2019, with the well still shut in for maintenance, a rapid increase in the tubing-casing annulus (TCA) pressure was observed.
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