Crude oil contaminants contain a large volume of corrosive species, such as acids, chlorides and saline solutions. When they come into contact with the metallic structures of atmospheric columns and other crude distillation overhead systems during operation, they can affect the structural integrity and performance of these key pieces of equipment.

To avoid failures and extend the service life of crude distillation overhead systems, plant operators need to conduct regular inspections to evaluate the level of corrosion and plan suitable mitigation strategies. During one of its regular assessments, a major Italian refinery noticed extensive corrosion on the column shell of one of its largest atmospheric distillation units (ADUs).

The main damage to the structure consisted of substantial thinning of the vessel’s surface, which extended for 185 m2, and was mostly located in the upper section of the column. This was the result of frequent exposure to particularly harsh substances, such as highly corrosive salts formed by amine-based H2S scavengers.

The advantages of full-service providers

Keen on partnering up with a reliable and experienced full-service provider of mass transfer equipment and service solutions, the Italian refinery contacted Sulzer. The company is specialized in field services for refineries with over 40 years of experience in tower, drum and vessel maintenance, repair and revamps.

By closely evaluating all the technical documentation on the column and inspecting the damaged areas, Sulzer identified weld overlay as the most suitable repair method. This consists of applying layers of alloys onto the damaged surfaces to restore shell thickness, ensuring sound structural and mechanical integrity. As a variety of cladding solutions is available, Sulzer’s expert engineering teams conducted extensive finite element analysis (FEA) to simulate different procedures as well as the resulting residual stresses and distortions. In this way, the most suitable strategy for the refinery’s ADU could be determined.

To prepare the column for the cladding, the internals, sumps and trays would be removed and scaffolding installed. Subsequently, the column shell would be pre-treated by conducting grit blasting. The 180 m2 damaged area in the column would then be repaired by applying a layer of 317L stainless steel using Sulzer’s CladFuse™ technology for automated weld overlay. Sulzer mobilized multiple systems to weld different areas simultaneously, minimizing the repair time.

The remaining 5 m2 of corroded surface, located on the top dish and the nozzle, was in a narrow space and not easily accessible. Therefore, it would be cladded manually with an alloy of nickel and copper. Finally, internals and other elements were reinstalled and non-destructive testing (NDT) was conducted on the repair.

All's well that ends weld

Thanks to the extensive expertise of Sulzer’s teams, the repair project was successfully completed in a narrow timeframe of only 32 days. This meant that the refinery could restart its processing activities with minimal downtime. The column, now fully operational, passed positive material identification (PMI), ultrasonic thickness gauge (UTG), dye penetrant inspection (DPI) and Out of Roundness (OoR) NDT. As a result of the repair, the refinery is expected to benefit from approximately 20 years of added service life to its ADU.

Sulzer’s Tower Field Service specialists were crucial to the successful completion of this challenging project. Thanks to their comprehensive capabilities in maintenance and repair of mass transfer components, the teams were able to support the customer restart its operations in a timely manner.

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