Autoclave Lining Repair at a Copper Facility

Introduction

This engineering case study presents an application of IGS Weld Metal Overlay (WMO) for an autoclave in operation at a copper facility in Africa. The autoclave is utilized in the leaching process, where base metal-rich solids are leached in high-pressure autoclaves and contacted with leach solution to yield separate valuable mineral streams. IGS carried out WMO to repair autoclave corrosion in 2016 and after successful installation, IGS has been providing solutions to this facility to solve other metal wastage problems, supporting their goal to improve up-time and reduce maintenance costs.

Background

Originally installed lead linings showed severe degradation due to the Pb linings not being able to withstand the in-service operating conditions, especially in the the vapour zone.

The main cause of failure was due to increased operating temperatures. At higher temperatures, the lead lining experienced creep failure, resulting in thinning of the lead lining in the vapour zone of the autoclave and in the worst cases even lead to the exposure of the carbon steel shell. The autoclave also experienced accelerated corrosion due to the presence of corrosive species, including sulphur and chlorides.

The plant was in a predicament where the lining needed to be repaired and/or replaced continuously, which lead to high maintenance costs and downtime impact.

Consideration of Maintenance

IGS engineered a solution for not only reducing corrosion attack on the autoclave shell and nozzles but also to reduce the maintenance schedule, as this was one of the plant’s main concerns. Weld overlay is a robust technology, but application time is generally slow. IGS recommended the installation of an Inconel lining that is designed to withstand the thermal, chemical, and physical attack of the aggressive process environment. The plant decided to carry out the recommended WMO as a solution, due to the upgrade of the surface and the reduced maintenance period.

Project Execution

IGS installed 80m2 of Inconel overlay on all the nozzles and around the nozzles of the Autoclave (bore weld and roof overlay). The project was executed on-site, and in-situ and the total duration of the project was 18 days.

Outcome and Benefits

IGS’s WMO cladding technology proved to be an effective solution, as evidenced by the condition of the existing WMO cladding applied. The cladding was inspected in 2018 and was found to be in excellent condition with no signs of failure / metal loss (NDT, visual). No further maintenance on the autoclave lining was required during the 2018 maintenance shutdown, reducing maintenance expenditure and schedule, resulting in significant cost savings for our client.

Return on Investment (ROI)

The same scope of work was completed in 2 additional autoclaves at this facility in 2018 and 2019, and inspected in 2020/21, delivering the same positive business results for the client. Due to the fact that the IGS WMO application has been installed three times and has been included in future maintenance planning, it has proved that the IGS solution is successful and indispensable for this plant. The overall business results are long-term cost savings and shortened turnaround impact, resulting in a significant ROI.

Conclusion

The introduction of IGS WMO in the autoclaves demonstrates innovative engineering with the application of superior technology, meticulous planning and effective execution. The utilization of a fit-for-service solution ensured that no additional repairs were needed after cladding installation and with a premium and proven solution of Inconel WMO in the vapor zone of the autoclaves, the plant has been able to strengthen their operations and save on costs.