Feb-2024

Eight critical process vessel, tower and column corrosion mitigation projects

Integrated Global Services (IGS) discusses eight global process vessel, column, and tower corrosion mitigation projects. This paper explores innovative strategies, technologies, and best practices designed to protect various typed of industrial equipment from corrosion and erosion.

Integrated Global Services

Article Summary

Learn more about IGS’s proprietary High Velocity Thermal Spray (HVTS) technology which deposits high nobility metal alloys onto the substrate to achieve a corrosionresistant barrier that offers greater protection than weld overlay while negating the need for heat treatment and avoiding heat-affected zones (HAZ).

Proven alternative to weld overlay in a corroded fractionator tower
Corrosion emergency
Built in the late 1970s, this 126,000-bpd refinery is one of Saudi Arabia’s oldest grassroots refineries. It comes as no surprise that some of its existing equipment is now approaching the end of its life. During a 2014 shutdown, the fractionator tower was found to be suffering pitting corrosion and required urgent protection to prevent the loss of integrity and a need for replacement. The operator considered two alternatives: 1) Weld overlay/ weld build up 2) IGS HVTS (High Velocity Thermal Spray). Weld overlay would have come with a requirement for tower stabilisation and PWHT making it a less practical choice in terms of cost and time (with this being an emergency).

Problem
Unexpected pitting corrosion in a section of the fractionator tower at a Saudi Arabia refinery.

Solution
IGS HVTS was applied in 2014 to a 89m² area, from tray 47 to 56. In 2017, following positive inspection results, the scope has been extended to include the manway, lid and internals beneath tray 47, a 44m² area. In 2020, both IGS HVTS applications have been inspected and found to be in excellent condition.

IGS HVTS experience
“Thermal spray” is not new. IGS HVTS, however, is a different class of technology. The material, its conveyancing technology and the application procedure have all been optimised over some decades to make IGS HVTS fit for mission-critical equipment protection. IGS HVTS has been approved by the oil Company operating this and other refineries in the region prior to 2014. As a result, this technology has been chosen to address the corrosion problem in the fractionator tower.

IGS HVTS application in 2014
The HVTS application was completed in 84 hours. An additional 72 hours were utilised to set up, pull in and out of the vessel as well as complete other tasks such as blow down, inspection and sealing. A total of 10 days were spent on site, working within the critical path of the shutdown.

Extended scope in 2017
HVTS cladding applied in 2014 was inspected and found to be in good condition. Additional scope was identified during the initial outage inspections.
Working together with the shutdown team IGS mobilised equipment and personnel, completing the expanded scope within the required shutdown timeframe.

2020 inspection
The entire 132m2 area cladded with HVTS was inspected in 2020. The IGS HVTS cladding was found to be in good condition with minimal to no thickness loss and ready for service.

Caustic vessel protected after repeated failure
Caustic corrosion
Caustic conditions, within MEROX and other demercaptanisation processes can rapidly attack steel’s protective magnetite layer and cause material wastage. Following destruction of the protective magnetite layer, NaOH can additionally react with exposed elemental iron to form atomic hydrogen, leading to hydrogen embrittlement, decreased wall thickness, and caustic stress corrosion cracking (CSCC) or caustic embrittlement. These phenomena have led to multiple plant failures under different caustic conditions.

Problem
A caustic wash settler was suffering pitting corrosion and weld cracking caused by the corrosive caustic environment. An organic coating application had failed and a lasting solution was required.

Solution
Upon stripping the organic coating, IGS HVTS alloy cladding was applied to the vessel shell. Twenty nozzle inserts were also installed into small bore nozzles. Rigorous testing has been carried out to ensure HVTS will be fit for purpose and protect the vessel until the next shutdown in 2025/26.

Material selection
Material susceptibility to caustic corrosion and CSCC is heavily dependent on concentration, temperature, and alloy type. Carbon steel is the most common material used for infrastructure exposed to caustic environments and is susceptible to CSCC and general corrosion or pitting at elevated temperatures above 50-60°C and NaOH concentrations below 20 wt. %. Stainless steel provides more protection but is at risk of CSCC and aggressive corrosion above 120°C.