Careers Carbonate Wash Column Corrosion Mitigation During Turnaround
Introduction: Corrosion in Benfield Carbonate Process
Hot potassium carbonate process is licensed by Honeywell UOP as the “UOP Benfield™ Process.” Carbonate wash towers are essential for Carbon Dioxide removal in Syngas, ethylene production and other processes. However, caustic can attack the vessel shell, leading to Caustic Stress Corrosion Cracking, particularly under high applied or residual stress levels.
This case study looks at an IGS client which is a prominent oil & gas company in South Africa, and which is responsible for around 50% of the total domestic fuel and lubricants market, largely through its world-leading technologies. Therefore, great pressure has been applied to the unit production costs, product quality, and operational flexibility of the plant, and significant investment has been made in new technologies and ways of working.
Benfield Carbonate Wash Corrosion
The plant had experienced metal loss in its carbonate wash columns for many years, primarily driven by caustic corrosion conditions. The carbonate wash columns had extensive wall thickness loss in certain areas. The client selected IGS as its partner of choice, considering effective maintenance solutions for the columns to ensure safe and effective future operations.
IGS initially applied Weld Metal Overlay (WMO) in 2007 and subsequently upgraded it to High Velocity Thermal Spray (HVTS) in the Benfield carbonate wash columns. The initial request from the client, was to weld out the complete column/s but over the years as time constraints and costs became a significant issue, HVTS was considered and applied to reduce tight schedules and cost implications.
Equipment Information
The problem statement and equipment information are summarized in the following tables:
Table 1: Problem statement
| The problem | – Caustic Stress Corrosion Cracking– Hydrogen Induced Corrosion |
| The effects | – Material wastage/ thinning |
| The results of the problem | – Downtime (production losses)– Loss of efficiency
– High repair costs – Frequent maintenance |
| The benefits of a solution | – Reduce the risk of losing efficiency– Reduce downtime/production losses
– Long-term cost saving |
Table 2: Benfield Carbonate Wash Column Information
| Equipment process function | Carbonate wash column |
| Base metal composition | Carbon steel – SA516 Gr. 70 |
| Operating temperature | 109 ºC (145°C – design) |
| Operating pressure | 2795 kPa (3250 kPa – design) |
| Process material phase | Liquid |
| Process Material Composition | Caustic |