Evaluating performance and cost-effectiveness of corrosion-resistant alloys ‒ mechanically lined tubulars in geothermal wells

Geothermal energy is one of the main sustainable alternatives to fossil fuels; however, it poses material and economic challenges due to the corrosive nature of geothermal fluids. This study evaluates the long-term performance and cost-effectiveness of Corrosion-Resistant Alloy (CRA) used in Mechanically Lined Tubulars (MLTs) under the extreme conditions of the Salton Sea geothermal field. In CRA-MLTs, the MLTs feature UNS N06625 (Alloy 625) as an internal liner and UNS N06680 (Alloy 680) as the weld overlay at coupling interfaces and metal-to-metal seals. After 18 months of field exposure at temperatures reaching 360 °C, the CRAs-MLTs evaluated in this study exhibited no measurable corrosion, wall thinning, or microstructural degradation. Ultrasonic thickness measurements confirmed a stable liner thickness of 3.0 mm, while SEM, EDS and XRD analyses revealed intact oxide films and adherent CaCO₃ scaling without evidence of pitting or localized attack. Both alloys used met their respective standards ASTM B443 (2019) and ASME BPVC II.C (2023), confirming their chemical stability and compatibility with high-chloride, CO₂- and H₂S-rich fluids. An economic assessment comparing conventional carbon steel tubing, mechanically lined tubing and solid CRA tubing for a representative Middle Eastern oil well demonstrated that MLT offers the lowest total cost of ownership. Although MLTs involve 30–60% higher upfront cost than carbon steel, they eliminate most corrosion-related OPEX and achieve a net present value (NPV) advantage of approximately $1.5 million over a 20-year life cycle. These findings confirm that CRA-MLTs combine technical reliability with economic efficiency, thus providing durable and cost-effective protection for geothermal and sour-service wells. CRA-MLTs can also support the long-term sustainability of energy production.