Refinery experienced in-service failure of their Sour Water Stripper column. During this unplanned shutdown, various sections of the column were cut and replaced. Other areas, found to be below minimum thickness spec, were repaired with weld metal build-up. The refinery also needed a long-term strategy to protect the rest of the exposed shell against sour water corrosion with a corrosion resistant alloy.
IGS was contracted to apply a High-Velocity Thermal Spray (HVTS) Alloy Cladding to prevent further sour water corrosion attack on the column shell. The material applied is a high Nickel Chrome alloy with Molybdenum content for pitting resistance and some trace elements to reduce stress and oxide formation.
Unplanned Shutdown of the Sour Water Stripper Column
During December 2017, a US Refinery experienced in-service failure of their Sour Water Stripper column. This was an unplanned shutdown, consequently causing other equipment to be shut down, compounding the effect of this outage. The inspection of the column revealed corrosion on the shell between the first and seventh tray. Extensive corrosion was also found behind vertical downcomers.
Corrosion Mitigation Options
The refinery was looking for a robust corrosion resistant alloy which would resist sour water corrosion and facilitate the column’s quick return to service. Welding repair would have required post weld heat treatment. Organic coating application was not feasible as it would have taken days to cure due to low ambient temperatures (50°F / 10°C).
Agile Corrosion Resistant Alloy Protection
IGS Alloy Cladding was applied utilizing a High-Velocity Thermal Spray (HVTS) process. HVTS exhibits very high bond strength and does not require a bond coat. The bond interface is mechanical and does not create any heat affected zones (HAZ), therefore there is no need for post weld heat treatment.
1003ft² (93m²) area of the sour water stripper column was protected in 2 ½ days in 5 shifts. The project was executed in accordance with the IGS Safety Program. Safety is Integrated Global Services’ first and highest priority. IGS performed work per the approved QCP/ITP on a 24hr basis by having a dayshift and nightshift crew on site.
Sour Water Corrosion Problem Area
The area behind downcomers was showing extensive signs of sour water corrosion.
Weld Metal Build-Up (WMBU) was applied behind the downcomers, in areas found to be below minimum thickness spec.
HVTS Corrosion Resistant Alloy Protection
IGS High Velocity Thermal Spray (HVTS) Alloy Cladding was applied to protect the shell and WMBU.
Sour Water Stripper Column Protection | Schedule and Completion
The scope area started from Tray 7 (Chimney tray) up to Tray 1, including the dome, two manways and an 8” nozzle in the elliptical head. Other areas included downcomers, obstructions, and tray rings. The total area protected with a corrosion resistant alloy was 1003ft² (93m²). Operators performed grit blasting and cladding activities for five twelve-hour shifts in the unit during dayshift and nightshift.
Refinery personnel provided IGS with a hole/fire watch for the duration of the sour water corrosion mitigation project. IGS executed the project successfully and handed the Sour Water Stripper column back to the client within the allocated time. IGS expects a significant extension in the life of this vessel.
IGS has a program that allows us to mobilize personnel to this and similar refineries very effectively, by pre-qualifying and pre-training personnel and maintaining a roster of eligible staff, readily available for rapid future mobilization.
Sour Water Stripper Column – First Inspection
Hydrogen flux monitoring inspection has since been completed to verify the performance of HVTS protection. All readings were found to be acceptable, within IGS recommendations, and did not indicate any signs of corrosion.
Inspection During 2020 Shutdown
The HVTS cladding was found to be in as-sprayed condition. There was no sign of defects, blisters, cracks, or spalling. During the inspection, close attention was paid to the areas behind the down comers as well as the weld buildup sections. These areas were all in good condition and within thickness specification.
HVTS cladding applied to previously pitted and corroded areas was closely inspected and cladding was found to be in good condition in all the observed areas.
Random thickness readings were taken throughout the scope area and all thicknesses measured within as-applied thickness range.
It can be concluded that the cladding has successfully protected the substrate from any further corrosion attack.
IGS Experience and Expertise
IGS stops corrosion mechanisms such as pitting, crevice corrosion, flow enhanced corrosion and general corrosion loss in amine vessels, knockout drums, crude desalters and other process vessels, towers, and columns. We use High Velocity Thermal Spray (HVTS) applied Alloy Cladding of high nobility Corrosion Resistant Alloys (CRAs) in-situ to protect existing columns during turnarounds.
Since 2001, IGS has protected ~100 of amine units for upstream and downstream operations, internally cladding more than 3000 m² of steel. HVTS is faster than welding, with no heat affected zones and no need for PWHT.
Unlike organic coating systems, HVTS metal claddings are robust, long-term and durable with high mechanical toughness, abrasion resistance and wide service temperature and pressure ranges, resistant to vessel steam-out and cleaning processes. We utilize our equipment and technology to apply corrosion resistant alloys almost anywhere in the world.
IGS carefully controls and monitors our application standards through strict QA/QC protocols. IGS generates an electronic thickness record on a defined reference grid across the clad area. This record is used for future inspection and verification of the internal cladding integrity. We have also developed inspection technologies for external, on-line verification of the cladding condition.