Mitigating risk: Navigate the complexities of sour gas plants
When working with highly corrosive and toxic substances such as hydrogen sulfide (H₂S) and carbon dioxide (CO₂), asset integrity is paramount. Without a robust inspection plan in place, sour gas plants can quickly become hazardous, with leaks and failures posing a significant risk to personnel and the environment.
Both colorless and flammable, H₂S is a highly corrosive substance that can rapidly degrade infrastructure, pipelines and equipment. As the result of a prolonged leak, H₂S can cause serious injury to personnel, varying from dizziness to complete paralysis of the respiratory system. Following a 6-yr study into workplace fatalities, the U.S. Bureau of Labor Statistics (BLS) reported 46 deaths related to H₂S poisoning. In addition, if not managed properly, it can be unintentionally released into the atmosphere, impacting air quality and polluting water and soil. In extreme cases, it can photo-oxidize into sulfuric acid, a major contributor to acid rain.
Despite the inherent risks of H₂S, sour gas facilities have been safely processing natural gas since 1951. Today, approximately 40% of onshore and offshore facilities operate under sour service conditions. Ensuring the reliability and safety of these plants relies heavily on regular inspections that combine preventive strategies with ongoing monitoring to identify and mitigate potential hazards.
While corrosion coupons are useful for tracking general corrosion and environmental conditions, the early detection of sulfide stress cracking (SSC) demands more advanced techniques. These include the use of stress-loaded specimens—such as U-bend or C-ring samples—tested in accordance with NACE standards TM0177 or TM0284, as well as hydrogen monitoring and adherence to material selection guidelines outlined in NACE MR0175/ISO 15156. Together, these approaches offer a more accurate evaluation of SSC risks, supporting safe operation under higher pressures, potential asset life extension and alignment with regulatory compliance requirements.
The author’s company supports some of the sector’s most complex projects with its inspection and integrity management services. As part of this service, the company recently completed an asset integrity management (AIM) and risk-based inspection (RBI) assessment for a major client, enhancing the safety, reliability and long-term performance of a European sour gas plant.
CASE STUDY
The author’s company was engaged to assess a facility that had previously reduced its operating pressure from the original design range of 60 barg–72 barg to 13 barg–40 barg. This pressure reduction enabled the owner to extract additional gas from aging, declining fields without the need for further compression at the oilfield facilities. The process streams contained both H₂S and CO₂. With plans now underway to tie in new fields, the owner was considering increasing the operating pressure back to near the plant’s original nameplate rating. Consequently, the author’s company was tasked with conducting a remaining life assessment (RLA) of the facility, with an operational outlook extending to the year 2040.
To forecast the fitness-for-service to 2040, the author’s company aimed to evaluate the plant’s ability to operate under increased pressures and assess the potential for life extension while ensuring compliance with industry best practices.
Beginning with the overall integrity management system, the author’s company’s inspectors conducted a thorough review of the plant’s existing RBI plans, inspection histories [including ultrasonic testing (UT) and corrosion coupons] and maintenance philosophies. A detailed RLA for equipment and piping was then conducted using corrosion rate data and thickness measurements. This two-part service scope enabled the author’s company to classify equipment and piping into three categories: fit until 2040, borderline or critical.
As assets age, a proactive approach is crucial to addressing issues like safety hazards, production downtime, environmental concerns and financial risks. Work scopes like this present significant challenges such as limited accessibility due to insulation, outdated RBI systems, corrosion-related fatigue and incomplete dead-leg registers. This project was an example of how these challenges can be addressed through the evaluation of aging infrastructure with complex service histories.
The author’s company’s inspectors completed a comprehensive multi-disciplinary site audit in collaboration with the plant’s inspection, process and chemistry departments. Together, they completed thorough documentation reviews and applied engineering expertise to evaluate asset conditions where direct data was limited. This approach enabled the inspectors to use logical extrapolation from past inspections to identify areas that could benefit from additional improvements to support the life expectancy of specific equipment.
Aligning with local regulations, the inspectors developed a system that would enable the plant to conduct inspection intervals in 72-mos cycles, as opposed to the typical 36 mos often seen in other countries. To ensure this inspection schedule could be adhered to without additional risk, the author’s company devised a systemic risk-based classification system. This system focuses on assets with high corrosion rates or limited lifespans. This new process utilizes quantitative corrosion rates to label assets—e.g., critical items with less than 5 yrs of remaining life.
In addition to the classification system, the author’s company provided in-depth recommendations for the equipment with high corrosion rates or that had been categorized as ‘high risk’ within the existing RBI system. Furthermore, improved sampling and analysis routines were generated, especially for the amine systems, and incorporated analysis for volatile fatty acids.
Thanks to this solution, the client can now conduct inspections every 72 mos as per in-country regulations and maintain asset integrity, mitigating unexpected downtime and optimizing the long-term reliability of the plant.
As the infrastructure of a sour gas plant continues to age, maintaining its long-term integrity presents significant challenges. Although a key aspect of this project was local regulations, the results offer valuable guidance for energy stakeholders maintaining aging assets:
- Data integration: Combining inspection data—such as UT, coupons and probes—with modeling and statutory requirements allows for defensible life-extension decisions.
- Risk prioritization: The use of corrosion rate thresholds and remaining life forecasting helps identify critical components much earlier than traditional methods alone.
- Proactive maintenance: In countries where inspection cycles are longer, it is imperative that inspection plans reflect proactive maintenance opportunities. These opportunities should account for insulation-related risks and H₂S cracking and should incorporate any previously unmonitored components.
- Digital challenges: Streamlined RBI data management and improved documentation practices significantly reduce errors and oversight.
This case study is an example of how an in-depth understanding of local and international standards supports the continued safe operations of hazardous environments. The guidance and recommendations now in place will enable continous operations through to 2040 and help protect personnel from unexpected leaks and failures.
Held to the highest standards of safety, the author’s company's methodology reflects its understanding of sour service degradation mechanisms and its capability to translate complex corrosion data into actionable integrity management strategies. When operating in high H₂S and CO₂ environments, where corrosion and cracking mechanisms are severe, bridging engineering assessments with practical field limitations enables the delivery of both diagnostic reviews and critical life-extension strategies. Life-extension strategies can range from coatings and material selection to competency training and maintenance schedules: ensuring an unbiased, in-depth assessment is in place is essential for optimizing the future of the plant’s equipment and pipelines.
By understanding the hazards of sour gas and the complexities of local regulations, the author’s company helps operators navigate the challenges of asset integrity management, ensuring optimized operations and safety for years to come.
ABOUT THE AUTHOR
Usman Afzal is a certified asset integrity management professional with more than 12 yrs of experience across the oil, gas and energy sectors. Starting his career as a piping engineer, he has held key roles, including Asset Integrity Engineer, RBI Specialist and Project Team Lead. He currently serves as Technical Lead for Fulkrum’s global asset integrity division, where he oversees critical projects related to AIM. Afzal has worked extensively across Pakistan, Saudi Arabia, the UAE and the UK, delivering integrity solutions for major international clients.
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