Safety in the Plant
Therefore, external corrosion protection of flanges and fastenings is critical to be able to both monitor the system and provide more effective and realistic quality control and inspection procedures. Due to the complexity of the flange
geometry, it has become a challenge to design efficient solutions to protect flanges against corrosion. The ideal solution would be a system that combines excellent corrosion protection along with a simple installation procedure and is suitable for all flange sizes and shapes, in conjunction with easy bolt access for inspection purposes. The most common solutions
available on the market are maintenance paints and mechanical solutions. Maintenance paints are hard coatings that are bonded directly to the substrate, commonly epoxy or urethane based. As flanges involve lots of angles and edges, paint systems will struggle to coat effectively due to the thinning effect when paints are applied over an edge. Applying thicker layers may address the issue of edge protection, but it may also lead to seizing of fastenings, which prevents subsequent access. In addition, accessing the bolt will be difficult without cracking the coating and it will therefore be necessary to re-apply the coating after the inspection. Mechanical solutions such as covers
and clamps encapsulate the flange or the void between the flange faces and they are usually constructed from stainless steel or plastic and incorporate a rubber seal. This protection is rigid, not flexible and requires having the correct cover or clamp size in stock to cater for each size of flange. Another commercially available
solution is tapes or semi-solid tapes. These come in various forms, such as Petrolatum tape, wax or visco-elastic polymers embedded into fabric for wrapping. Tapes are supplied on a roll and are wrapped around the surface to be protected. They provide reliable corrosion protection, thanks to the water-repellent nature of these semi- solid polymers. However, these materials can be time-consuming and difficult to apply on complex shapes. If access to
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bolts is required, these relatively soft materials can be readily cut away, but cannot be easily resealed afterwards to reinstate the protection, and normally must be replaced with new. Hot-melt thermoplastics are
relatively new on the market. They are essentially wax-like meltable polymers that are heated to high temperatures and then spray applied onto the surface with specialist hot-melt equipment. The main advantage of using this solution is the fact that it can be re-melted and recycled, which offers a cost-effective solution for flange protection. However, it requires hot work as well as specialist equipment and contract application service, and while the coating can be reused it cannot be easily opened up and resealed to facilitate inspection. Another relatively new form of
flange protection is polymer bags containing vapour corrosion inhibitors (VCI), which entirely cover the flanges. The sealed bag is composed of a low permeability polymer with internal VCI film (and drying agents). They are quick and easy to install but the ends of the bag are sealed using normal adhesive tape – not the most durable or effective of bonding mechanisms. The large vapour space inside the bag means that a relatively large amount of moisture may be trapped inside the system and the VCIs are consumed over a period of time.
Peelable coating To offer an alternative answer to flange corrosion issues, Belzona has formulated a new peelable coating concept, Belzona
Fig. 3. Salt spray test showing no corrosion under the encapsulating system - close up.
Fig. 4 Encapsulating system being cut for inspection.
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