Article by John Butterfield

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.

Thinning surface wall
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.
This extended for 185 m2 and was mostly located in the upper section of the column. The thinning was the result of frequent exposure to particularly harsh substances, such as highly corrosive salts formed by amine-based H2S scavengers. The Italian refinery contacted Sulzer, a company specialised in field services for refineries with over forty 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, weld overlay was identified 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.
Automated weld overlay
As a variety of cladding solutions is available, Sulzer’s 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 was determined. To prepare the column for the cladding, the internals, sumps and trays were removed and scaffolding installed. Subsequently, the column shell was pre-treated by conducting grit blasting. The 180 m2 damaged area in the column was repaired by applying a layer of 317L stainless steel using Sulzer’s CladFuse™ technology for automated weld overlay. Sulzer mobilised multiple systems to weld different areas simultaneously, minimising the repair time. The remaining 5 m2of corroded surface, located on the top dish and the nozzle, was in a narrow space and not easily accessible. Therefore, it was clad manually with an alloy of nickel and copper. Finally, internals and other elements were reinstalled, and nondestructive testing NDT) was conducted on the repair.
All’s well that ends weld
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. The refinery is expected to benefit from approximately 20 years of added service life to its ADU as a result of the repair.
About Sulzer
Sulzer is a global fluid engineering company specialised in pumping, agitation, mixing, separation and application technologies for fluids of all types. Sulzer has been headquartered in Winterthur, Switzerland, since 1834 and has 16,500 employees.).