Abu Dhabi, UAE – October 3, 2023: ADNOC and Occidental announced, today, an agreement to undertake a joint preliminary engineering study for the construction of the first megaton-scale direct air capture (DAC) facility outside the United States (US). The agreement is the first project to reach the technical feasibility stage since the two companies signed a strategic collaboration agreement, in 2023, to explore carbon capture, utilization and storage (CCUS) projects in the UAE and the US. The study will assess the proposed one million tonnes per annum (mtpa) DAC facility to be connected to ADNOC’s carbon dioxide (CO2) infrastructure for injection and permanent storage into saline reservoirs not used for oil and gas production. ADNOC is in the testing phase of the world’s first full sequestered CO2 injection well in a carbonate saline aquifer in Abu Dhabi.

 In simple terms, sour service refers to any oil & gas environment where hydrogen sulfide (H₂S) is present in process streams. Even trace levels of H₂S can be lethal, aggressively corrode steels, and cause brittle fractures—making it a top-priority risk for engineers, operators, and asset managers alike. 

Why “Sour” Demands Attention

Safety & Environment: H₂S is instantly toxic at just a few dozen ppm. Failing to control or detect sour gas can lead to catastrophic equipment failures, HSE incidents, and environmental liabilities. Corrosion & Cracking: Sour conditions accelerate sulfide stress cracking (SSC), hydrogen-induced cracking (HIC), and rapid general/localized corrosion. Overlooking these mechanisms during design or operation invites unplanned shutdowns and costly repairs. Regulatory Compliance: Standards like NACE MR0175/ISO 15156, API 5L/6A, and ISO 21457 exist precisely because sour-service failures have historically led to severe incidents. Non-compliance can result in fines, de-rating of equipment, or insurance denials. 

Key Takeaways for Engineering Teams

1. Lifecycle Challenges: From material procurement through fabrication, commissioning, and day-to-day operation, every step must account for H₂S’s aggressive nature. Material traceability, weld procedures, hardness control, and strict inspection regimes are non-negotiable.
2. Standards & Testing:  NACE MR0175/ISO 15156 dictates allowable H₂S partial pressures, maximum hardness (HRC 22), and required lab tests (TM0177 Methods B & C, HIC, SOHIC). API 5L/6A add further sour-service criteria for line pipe, valves, and wellhead equipment—ensuring components survive in H₂S-rich conditions.
3. Materials & Design: 

• Carbon Steel: Only in very mild sour environments (dry gas, < 4 ppm H₂S, low temperature) with hardness ≤ HRC 22.
• Duplex & Super-Duplex Stainless (2205, 2507): Excellent for moderate sour (higher H₂S, moderate temperature, elevated chlorides).
• Nickel Alloys (Inconel 625, Incoloy 825, Hastelloy C276): Ideal for severe sour (pH₂S > 0.1 MPa, T > 100 °C, high chloride).
• Cladding & Linings: Weld overlays of CRA or protective coatings can extend carbon-steel vessel life in sour feed conditions.

Operational Protocols

• Chemical Inhibition & Scavengers: Film-forming inhibitors and H₂S scavengers help keep metal surfaces protected.
• Gas Sweetening & Dehydration: Lower aqueous H₂S reduces acidity and corrosion.
• Monitoring & Pigging: Regular inline inspections, pig runs to remove iron sulfide scales, and real-time corrosion probes catch issues before they become failures.

Have you managed a sour-service project recently? Share your experiences or best practices in the comments—and let’s build safer, more reliable assets in H₂S-rich environments!

Pipeum’s Perspective