Encapsulating membrane provides a complete corrosion protection for flanges. Alice Jucquois reports
The plant had a 52in flange on a vessel connecting to outlet piping that needed corrosion protection. The flange was affected by crevice corrosion, a well-known damage mechanism in petrochemical facilities caused by the concentration of corrosive substances within a confined space.
The crevice between two adjoining flanges is the ideal environment for initiation of crevice corrosion and the corrosion rate is accelerated by the concentration of these corrosive substances in a confined area. Corrosion of the sealing area can lead to loss of containment and the potential to cause product release with catastrophic consequences.
To avoid corrosion between the flange faces, a previous protection solution consisting of a fibreglass system was used on other vessels in the unit. Fibreglass offers good corrosion resistance but these materials can however be time-consuming and expensive to apply.
If access to bolts is required for flange maintenance, fibreglass can be cut away, but it is difficult to remove and normally must be replaced with a new system to reinstate the protection.
In order to avoid these drawbacks, the client was looking for an alternative and more cost-effective protective solution that allows for a simple installation, is suitable for all flange sizes and shapes, and permits easy access for inspection purposes.
Belzona 3411 (Encapsulating Membrane) was recommended as the system provides a complete corrosion protection for flanges, fastenings and associated pipes, and can be easily applied and peeled back for maintenance purposes. The system offers full corrosion protection due to its use with a dual use corrosion inhibitor/release agent, Belzona 8411, and the high adhesive properties of Belzona 3411 excludes any moisture.
The application was carried out by the plant personnel in accordance with Belzona’s application procedures. All surfaces to which the Belzona 3411 system was to bond to were cleaned with Belzona 9111 (Cleaner/Degreaser) to remove all dirt, grease and surface contaminants. The bond areas also required surface preparation to ensure good adhesion. The minimum level of surface preparation for exposed/corroded steel is wired brushing to ISO 8501-1 St 2/SSPC SP-2.
As the surfaces had been previously painted, the bond area were thoroughly abraded with abrasive paper to remove all gloss and provide a good key for the coating system.
The gap between flange faces was sealed with a strip of bond breaker tape and the two bond areas were mashed off to protect these sections of pipe from accidental overspray of Belzona 8411, and hence impaired adhesion.
The system requires the use of Belzona 8411 to achieve the optimum level of corrosion protection and to allow access to bolts and flanges in the event of required maintenance.
Belzona 8411 can be simply spray or brush applied onto the flange, pipe and fastenings ensuring the film coverage is even and complete. Once Belzona 8411 was touch dry, the masking tape over the bond areas was removed and plastic caps fitted over the bolts.
Belzona 3411 is a two-coat system, comprising a grey and a beige layer. The mixed Belzona 3411 was applied over the area to be protected using a short bristle brush at a thickness between 30 and 40 mils (750 - 1000 microns). The entire content of a further unit of mixed Belzona 3411 in beige colour was brush applied onto the touch dry first coat to finish the application.
This encapsulating system can not only be used to provide an excellent corrosion protection for the flanges, fastenings and associated pipes but also as a preventive system which helps facilitating and improving monitoring and inspection of flange faces.
The customer saved several thousand dollars over the previous fibreglass system with easier installation. When the vessel has to be opened, the technician can use a box knife instead of a heat gun or grit blast equipment to remove the system.
Indeed, when maintenance or inspection is required, the system can be simply cut open by using a sharp knife to cut through the membrane in the gap between the flange faces around the circumference of the flange. The membrane will be then be peeled back, exposing bolts and flanges. Once the required maintenance has been completed, the membrane will fold back to its original position and can be sealed with a further quantity of Belzona 3411.
The unit was inspected 90 days after installation and it looked as good as it did on day one. The application was revisited in April 2015 and the protection was still a perfect condition. The client was very satisfied with the Belzona solution and is planning to use Belzona 3411 on other flanges in the plant.
Alice Jucquois is with Belzona Polymerics Ltd, Harrogate, UK. www.belzona.com