Study of Field Failures Decodes Hydrogen Embrittlement in High-Strength Coiled Tubing
Authors: Carpenter Chris 
Published: June 2024

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 218327, “Decoding Hydrogen Embrittlement in High-Strength Coiled Tubing: Insights From Acid-Induced Failures, Field-Data Analysis, and Corrosion-Management Strategies,” by G. McClelland, SPE, Irma I. Galvan, and Genesis L. Mallanao, FET Global Tubing, et al. The paper has not been peer reviewed.

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Recent reports have highlighted hydrogen embrittlement of high-strength, quench-and-temper (Q&T) coiled tubing (CT) resulting from hydrochloric (HCl) acid usage in sour environments. HCl acid treatments expose CT surfaces to aggressive corrosion, often exacerbated by hydrogen sulfide (H2S) from formation fluids or as a chemical reaction. Helping the CT industry recognize the morphologies of damage when the tube is retired and re-evaluating CT grade selection and chemicals are vital for averting costly and dangerous CT failures. To achieve this goal, a summary of field failures was evaluated from diverse operational environments and locations.

Hydrogen Embrittlement: Failure Case Studies and Modes
Failure Case Studies.
The case studies conclude that failures are generally associated with an acid environment or acid stimulation jobs. In one case, citric acid was mixed with an oxygen scavenger and produced low levels of H2S, causing clear embrittlement and failures on the reel in multiple locations. In several other cases, logistical job delays caused extended acid exposure to the CT, or inhibitor depletion, which, consequently, allowed more hydrogen to enter the steel matrix. Another instance involved unintended H2S exposure in a well which was purportedly sweet. Other investigations indicated a variety of reasons, including recirculated fluids, lack of inhibition or improper use of inhibition, and increased levels of H2S beyond job-planning scenarios.
Another consistent variable in RCA is lack of pertinent, accurate field information, such as system pH, duration of exposure, timing for acid mixing, acid-decline curves, field consumption of inhibitor pills and timing, field consumption of injection fluids, temperature (surface ambient and downhole), and partial pressure of H2S.
Failure Modes.
Hydrogen embrittlement typically is characterized by intergranular cracking along the grain boundaries of the steel. Transgranular embrittlement may manifest itself in some cases. In the samples evaluated, the failure mechanism was observed on both outer-diameter (OD) and inner-diameter (ID) surfaces or was observed as hydrogen gas recombination, resulting in blistering both along the longitudinal weld and in the base Recent reports have highlighted hydrogen embrittlement of high-strength, quench-and-temper (Q&T) coiled tubing (CT) resulting from hydrochloric (HCl) acid usage in sour environments. HCl acid treatments expose CT surfaces to aggressive corrosion, often exacerbated by hydrogen sulfide (H2S) from formation fluids or as a chemical reaction. Helping the CT industry recognize the morphologies of damage when the tube is retired and re-evaluating CT grade selection and chemicals are vital for averting costly and dangerous CT failures. To achieve this goal, a summary of field failures was evaluated from diverse operational environments and locations.