The integrity of flanged connections is critical to containing fluids in piping systems. Loss of containment, whether in chemical or water distribution lines, will have an environmental, operational and commercial impact, and could pose a serious safety risk. Flanges present a unique corrosion protection challenge because solutions must both prevent corrosion and allow access to fastenings for inspection or maintenance. In addition, due to the complex geometry of a flanged connection, problems such as crevice corrosion found within the void between the two flange faces, and galvanic corrosion found where dissimilar metals are used, are common and can prove detrimental to the integrity of the piping system.
Effective monitoring and inspection techniques are required to minimise unscheduled shutdowns due to leakage in order to meet ever demanding production requirements. Usually, leakages occurring between the flange faces are the primary concern, leaving fastenings and pipe external protection unaddressed, leading to potential problems especially under adverse conditions. Insufficient external protection can lead to rapid and more extensive damage to the flanges and fastenings which will in turn accelerate the deterioration of the sealing system as a whole. The consequences of such a situation are not easy to predict since they are dependent upon prevailing conditions: depending on the severity of these there may, at best, be a slow continuous degradation of the substrate. However, under extreme conditions, the external corrosion process may rapidly reach a point where the structural integrity of the system is adversely affected, resulting in a catastrophic loss of containment. Since visual inspection of the sealing faces of flanged connections can only be done during a system shutdown, it is vital that this process is made as simple as possible and therefore elimination of external corrosion must be a high priority. Alternatively, if shutdown is not an option, ultrasonic techniques can be used for the inspection, but this process can be more complex and inaccurate if external corrosion is not controlled.
Due to the complexity of flange geometry, it has become a challenge to design efficient solutions to protect flanges against corrosion. The most common solutions available on the market are maintenance paints and mechanical solutions. Maintenance paints are epoxy- or urethane-based hard coatings bonded directly to the substrate. As flanges involve lots of edges, paint systems will struggle to coat effectively due to thinning when applied over an edge: thicker layers may address the issue, but it may also lead to seizing of fastenings. In addition, accessing the bolt will be difficult without cracking the coating, therefore necessitating re-application after the inspection. Mechanical solutions such as covers and clamps encapsulate the flange or the void between the flange faces. Constructed from stainless steel or plastic, and incorporating a rubber seal, this protection is rigid and requires having the correct cover or clamp size in stock to cater for each size of flange. Another solution is to use semi-solid tapes, for example Petrolatum tape. Supplied on a roll, they are wrapped around the surface to be protected and provide reliable corrosion protection, thanks to their water-repellent nature.
However, these materials can be time-consuming and difficult to apply to complex shapes. If access to bolts is required, these relatively soft materials can be cut away, but cannot be easily resealed and normally must be replaced. Hot-melt thermoplastics are relatively new: they are wax-like meltable polymers which are heated to high temperatures and then sprayed onto the surface with specialist hot-melt equipment. The main advantage is that the coating can be melted and recycled, which offers a cost effective solution. However, it requires specialist equipment and contract application, and while the coating can be reused it cannot be easily opened and resealed to facilitate inspection. (NB. Belzona has developed a new liquid-applied flange protection system that can be peeled and resealed.)
Another relatively new form of flange protection are polymer bags, containing vapor corrosion inhibitors (VCI), which entirely cover the flanges and are 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 method. The large vapour space inside the bag means that a relatively large amount of moisture may be trapped inside the system and the VCI’s are consumed over a period of time.
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
Application of Belzona 8411
Application of Belzona 3411
Belzona 3411 is a moisture cured system, therefore to ensure cure is not retarded and the correct overcoat times are observed, the temperature and relative humidity must be measured before application of Belzona 3411 begins ensuring the relative humidity is above 30% and the temperature is above 5°C.
Prepare strips of Belzona 9311 (Reinforcement sheet) as follows:
Empty the entire contents of the Belzona 3411 Base container into the mixing bowl provided. Pour the contents of the Solidifier container over the Base and mix immediately.
NOTE: It is recommended that the first coat of Belzona 3411 is beige to provide a contrast with the substrate.
|1||Tensile strength (Adhesion)||ASTM D412||Unreinforced 290 psi/2.0 Mpa|
|Reinforced with belzona 9311 520 psi/ 3.6 Mpa|
|2||Tear strength||ASTM D 624||Unreinforced 22pli/3.9 N/mm|
|Reinforced with belzona 9311 69Pli/12.1 N/mm|
|3||Corrosion resistance||ASTM B117||No corrosion after 1000 hours exposure to a salt-fog atmosphere at 33 °C|
|4||Elongation Strength||ASTM D412||Unreinforced : 69 %
Reinforced with Belzona 9311 :31%
|5||90 °C Peel adhesion||ASTM D429||Manually Prepared solvent- borne polyurethane paint: ?6.4 psi / 1.12 Mpa|