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

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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.

Product Number: 51322-17766-SG
Author: Arshad B. Gavanluei, Ramgopal Thodla, Manuel Marya, Alexis Simon, Vipul Shinde, Stanley Gregory
Publication Date: 2022
Industries: Corrosion Monitoring and Control , Coatings and Linings , Coatings
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A thorough characterization of nickel-based UNS N09955 was performed in a simulated sour production wellbore environment for high-pressure, high-temperature (HPHT) subsea applications. The test environment chemistry was 1.14 mol% of carbon dioxide (CO2), 0.4-psia fugacity of hydrogen sulfide (H2S), 240,000 mg/L of chlorides, dissolved oxygen less than 10 ppb, and a pH of 4.2, at 400 °F (204 °C) temperature. Environmentally assisted cracking (EAC) susceptibility was evaluated by fracture toughness (FT) test using compact tension test specimens and rising displacement method. Fatigue crack growth rate (FCGR) and static crack growth rate (SCGR) were studied in the HPHT environment. FT testing indicated a moderate reduction in the initiation FT value of the alloy in HPHT condition compared with the in-air value. FCGR testing was performed at different frequencies and at maximum stress intensity factor (Kmax) (or stress intensity range [ΔK]) values. At a Kmax value of 55 MPam, FCGR increased at low frequencies, which may have been associated with the crack front sampling the susceptible orientation. However, at Kmax values of 66, 75, and 85 MPam, there was no or little evidence of an increase in FCGR at low frequencies. Additionally, no evidence of a stable SCGR was observed over a range of Kmax values from 55 to 85 MPam, supporting the fact that the threshold stress intensity factor (Kth) of Alloy 955 is greater than 85 MPam in the tested environment. Finally, scanning electron microscopy (SEM) was used to characterize the fracture surface morphology and crack-growth behavior of Alloy 955. Ductile features for in air FT test and evidence of dislocation slip band cracking and fatigue striations were observed for environmental tests.

A thorough characterization of nickel-based UNS N09955 was performed in a simulated sour production wellbore environment for high-pressure, high-temperature (HPHT) subsea applications. The test environment chemistry was 1.14 mol% of carbon dioxide (CO2), 0.4-psia fugacity of hydrogen sulfide (H2S), 240,000 mg/L of chlorides, dissolved oxygen less than 10 ppb, and a pH of 4.2, at 400 °F (204 °C) temperature. Environmentally assisted cracking (EAC) susceptibility was evaluated by fracture toughness (FT) test using compact tension test specimens and rising displacement method. Fatigue crack growth rate (FCGR) and static crack growth rate (SCGR) were studied in the HPHT environment. FT testing indicated a moderate reduction in the initiation FT value of the alloy in HPHT condition compared with the in-air value. FCGR testing was performed at different frequencies and at maximum stress intensity factor (Kmax) (or stress intensity range [ΔK]) values. At a Kmax value of 55 MPam, FCGR increased at low frequencies, which may have been associated with the crack front sampling the susceptible orientation. However, at Kmax values of 66, 75, and 85 MPam, there was no or little evidence of an increase in FCGR at low frequencies. Additionally, no evidence of a stable SCGR was observed over a range of Kmax values from 55 to 85 MPam, supporting the fact that the threshold stress intensity factor (Kth) of Alloy 955 is greater than 85 MPam in the tested environment. Finally, scanning electron microscopy (SEM) was used to characterize the fracture surface morphology and crack-growth behavior of Alloy 955. Ductile features for in air FT test and evidence of dislocation slip band cracking and fatigue striations were observed for environmental tests.

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

Product Number: 51322-17768-SG
Author: Arshad B Gavanluei, Vipul Shinde, Manuel Marya, Ramgopal Thodla, Alexis Simon, Stanley Gregory
Publication Date: 2022
$20.00

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.
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Hydrogen Embrittlement of High Strength Precipitation Hardenable Nickel Alloys

Product Number: 51319-13161-SG
Author: Michael Dodge
Publication Date: 2019
$20.00

The high strength and corrosion resistance of nickel-chromium alloys such as Alloy 718 and nickel-iron-chromium alloys such as Alloys 945 and 945X make them particularly good candidates for use in demanding environments in the upstream oil and gas industry. These materials generally perform well where resistance to sulphide stress cracking and chloride stress corrosion cracking is required. However whilst these alloys are considered ‘NACE compliant' environmentally-assisted failures can still occur.It is generally accepted that for hydrogen cracks to initiate there must be a critical combination of stress susceptible microstructure and hydrogen concentration. In this project the effect of microstructure is explored by heat treating Alloy 718 945 and 945X to standard and non-standard conditions. Tensile specimens were slow-strain-rate-tested in air and under CP to explore sensitivity to hydrogen embrittlement. Finally the effect of a severe stress concentration in the form of a sharp notch was used to determine whether there is an enhanced susceptibility to hydrogen embrittlement due to the presence of local stress raisers. The results are compared with tests undertaken by other authors under various hydrogen-charging conditions.
Evaluation of Hydrogen Embrittlement of Nickel-Based Alloys in Cesium Formate with H2S/CO2
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Evaluation Of Hydrogen Embrittlement Of Nickel-Based Alloys In Cesium Formate With H2S/CO2

Product Number: 51322-18024-SG
Author: Xiaoji Li, Ramgopal Thodla
Publication Date: 2022
$20.00

Cesium formate (CsFo) brines have been used as the drilling and/or completion fluids in oil and gas wells in need of high-density fluids.1,2 Multiple studies on corrosion of steels and corrosion resistance alloys (CRA) in formate environments have been reported in the literature.2-8 It was known that the formate brines could undergo significant decomposition to form hydrogen when in contact with catalytic surfaces which CRA can act as. Therefore, there have been concerns that the CRA may catalyze the decomposition of formate brines to accelerate the generation of hydrogen which in turn may embrittle certain CRAs and endanger the relevant well equipment.
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