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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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$20.00
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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.
Picture for Environmentally Assisted Cracking of High Strength Nickel Based Alloys Under Cathodic Protection
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51318-10700-Environmentally Assisted Cracking of High Strength Nickel Based Alloys Under Cathodic Protection

Product Number: 51318-10700-SG
Author: Ramopal Thodla
Publication Date: 2018
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Environmentally assisted cracking of high strength nickle based alloys was investigated in 3.5wt% NaCl under cathodic protection.
Picture for Performance of Nickel Alloy UNS N06625 Welds in Supercritical H2S Environment
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51318-10938-Performance of Nickel Alloy UNS N06625 Welds in Supercritical H2S Environment

Product Number: 51318-10938-SG
Author: Henry Begg / Shiladitya Paul
Publication Date: 2018
$20.00

This paper presents environmental performance data on welded nickel alloy under high temperature, high pressure, ‘ultra-sour’ conditions. Welded coupons of nickel alloy UNS N06625 were subjected to three levels of nominal stress and tested for 30 days.
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