As part of a sub-contract with a long-term client, we recently worked on a project to repair and coat a main cooling water pump impeller, which we had previously coated 15 years ago; when the impeller was brand new and first put in to service.
The pump was returned for maintenance and repair, and despite 15 years of service operating in water with high sand content, the damage to the impeller was impressively minimal, with just a few areas of mechanical damage, and slight water damage and discolouration along the vein tips and edges.
To begin, the impeller was flash blasted with fine grade abrasive. A fine grade was selected to avoid damaging the original coating, which had remained in excellent condition. Once clean, the surface was 100% spark tested to identify any damaged areas. DFT’s were taken all around and found to be around 1.5mm, which was the original specified thickness.
There were 8 small damaged areas in total, which were blasted back to Sa 2½ cleanliness and a surface profile of 50 microns. They were then repaired with Corroglass 600 series, using 632 to prime the bare steel, and then 602 was applied in multiple coats to build up to the required thickness and re-profile to the existing coating. On completion of the Spark/DFT inspection, a topcoat of 652 white was applied to the full impeller.
Impeller before repair Impeller after repair
Also, following the blasting process, the ring element of the pump was found to be severely damaged. In order to address this, the impeller was returned to the contractor and a new stainless steel ring was applied to add additional protection to this part of the component and limit future damage. The impeller was then sent back to our workshop to be coated with Corroglass 600 series.
Ring element before repair Ring Element after repair