The retained coating system inside the pressure filters had delaminated. The coating system had suffered a 100% failure due to issues surrounding the inter coat adhesion characteristics of the material. The project required the complete removal of the existing coating system through dry abrasive blast cleaning.
Each pressure filter has a plenum floor within the vessel. Each plenum floor exhibited signs of stress cracking within the coating system. It is believed the stress cracking was due to over application of the coating system The stress cracking had resulted in areas of localised corrosion. Moisture had been able to migrate freely to the steel substrate due the failures within the coating system.
SPG operatives used mechanical tools to remove the existing coating system from the holes across the plenum floor. Mechanical preparation was also undertaken across the plenum floor prior to dry abrasive blast cleaning. This resulted in less blast media being required to achieve the visual surface preparation standard.
Removal of the retained coating system by mechanical means indicated that no surface preparation had been undertaken prior to the application of the existing coating system. Mill scale was evident across the plenum floor.
This view shows the thickness of the existing coating. Visual assessment measured at 5mm thick. The coating system had also been applied in several layers. Adhesion between the coating layers was poor, indicating that further preparation of the coating system had not been undertaken prior to the application of the subsequent coating layer.
The specified requirements for this project included BS EN ISO 8501-1SA2.5 This was consistently achieved. Elcometer grit comparator (serial No. Gi6771) used to monitor visual standard/surface profile and Elcometer surface profile needle gauger (serial No.E224C-BS) being used to monitor surface profile.
All seven pressure filter vessels are in commsioning at the Wessex Water, Codford site. SPG succssfully applied the internal, potable water lining system along with the application of an external protective coating system.