Restoring Integrity: In-Situ Repair of Circumferential Weld Seams on a Vintage CO₂ Absorber

Why It Matters

The successful in‑situ weld repair safeguards ammonia catalyst performance, prevents costly shutdowns, and demonstrates a cost‑effective path to extend the life of legacy pressure vessels in petrochemical plants.

Key Takeaways

• 1964 absorber repaired without dismantling
• Circumferential welds inspected per ASME Section VIII
• In‑situ welding avoided stress‑corrosion risks
• Repair extended absorber service life by years
• Demonstrates cost‑effective asset integrity strategy

Pulse Analysis

CO₂ absorbers are a linchpin in ammonia production, removing carbon oxides that would otherwise poison the synthesis catalyst. The C‑208 unit at FFC’s Port Qasim plant is a 1964‑era Bechtel design, originally fabricated in the United States and later relocated to Pakistan. Its 181‑foot high‑pressure column, now operating with a packed‑bed configuration, must maintain strict integrity to sustain the Benfield absorption process, a challenge common to many aging petrochemical assets worldwide.

The in‑situ repair tackled two critical circumferential weld seams using heat‑treated filler material, adhering to ASME Section VIII Division I requirements. Detailed non‑destructive examinations, including ultrasonic and radiographic testing, verified weld quality before and after the procedure. By performing the work on‑site, the team eliminated the need for full column disassembly, reducing exposure to stress‑corrosion cracking and preserving the original post‑weld heat‑treatment condition. This approach showcases how modern inspection techniques can safely extend the service life of vintage pressure vessels.

From a business perspective, the successful rehabilitation avoided a multi‑million‑dollar shutdown and deferred capital‑intensive replacement. Extending the absorber’s operational window improves plant availability, stabilizes ammonia output, and enhances overall return on investment. The project serves as a blueprint for other facilities grappling with legacy equipment, illustrating that strategic, code‑compliant repairs can deliver significant cost savings while upholding safety and performance standards.

Restoring Integrity: In-Situ Repair of Circumferential Weld Seams on a Vintage CO₂ Absorber

By Sadiq Usman Khattak, Section Manager, Inspection at Fauji Fertilizer Company · Port Qasim Plant · Published in the November/December 2025 issue of Inspectioneering Journal

Introduction

This article details the in‑situ rehabilitation of two circumferential weld seams on a CO₂ absorber (C‑208) at the Fauji Fertilizer Company Limited (FFC) Port Qasim Plant, Karachi, Pakistan. The absorber, a 1964 Bechtel design, was commissioned at FFC Port Qasim in 1998 after being relocated from Lake Charles, Louisiana (USA). As a crucial component of the ammonia production process, it plays a vital role in ensuring the effective separation of CO₂ from synthesis gas. This article highlights the mechanical integrity evaluations, along with the comprehensive assessments and measures undertaken during the rehabilitation of these critical weld seams.

Overview of the CO₂ Absorber

The CO₂ Absorber (C‑208) operates as a high‑pressure column in the Benfield system, designed for CO₂ absorption using a potassium carbonate solution. The column was designed per the 1962 edition of the ASME Section VIII code, fabricated in 1965, and originally configured with internal sieve trays. However, during balancing, modernization, and replacement of the ammonia plant in 2006, the design of the column was changed to a packed bed to increase its reliability, energy efficiency, and production.

The overall length of the column is 181 feet 8 inches with a thickness of 2.3 inches in the lower 14‑foot ID section, 2.6 inches in the conical section, and 1.4 inches in the top 8‑foot ID section. The shell material and heads of the column are fabricated from C‑Mn steel (A‑212‑B FB Grade). As per mechanical requirements of ASME Section VIII Div I UCS 56, and in line with process licenser/manufacturer recommendations, the column was delivered in two halves, each fully post‑weld heat treated in a furnace. The final circumferential closing seam was welded on‑site during installation to avoid stress corrosion cracking in Benfield service.

The column comprises six packed beds that facilitate efficient counter‑current gas‑liquid interactions, reducing CO₂ concentrations in the synthesis gas. This separation process is essential to prevent carbon oxides from poisoning the ammonia converter catalyst, which is crucial for maintaining the efficiency of the ammonia synthesis process.

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About the Author

Sadiq Usman Khattak is an experienced inspection and reliability engineer with over 13 years in the fertilizer and petrochemical industries. He is currently leading a team focused on maintaining the mechanical integrity of FFC PQ’s 1964‑vintage ammonia plant, relocated from Lake Charles, USA. His expertise includes quality control, failure analysis, and strategic inspection.