Shutdowns in the industries cost millions… even when planned properly. Shutdowns are significantly impacted by the operating costs due to damaged parts, including flange face imperfections, gasket failure, or general corrosion. A leak may occur when corrosive media meets the sealing surfaces of facing flanges. It is why flange maintenance is a crucial step that helps to prevent leakage.
Types of corrosion
Flanges may go through two types of corrosion in their lifetime. These include aperture and pitting.
Pitting occurs on the flange face and often appears in groups or clusters. The type of corrosion may result in small cavities or pits that form at the material’s surface. Proper alloy selection is one of the best-recommended ways to prevent pitting corrosion.
Crevice creep occurs when there is a buildup in the concentrated substance between the two adjoining flanges. It is the type of corrosion that can be very damaging because it is not easy to inspect the area of its occurrence.
Currently, monitoring the flange damage is to disassemble the joint and visually inspect the surfaces. It is not ideal due to the down cost and time. There has been some development using some non-destructive techniques to examine the amount of corrosion to the flanges.
Maintenance of paints is one of the most common methods that help to prevent corrosion. Maintenance paints are commonly urethane or epoxy-based coatings. Most maintenance paints bond directly to the substrate as a hard coating. With the use of maintenance paints, a perfect amount must be applied. If the paint is too thin, the area will be ineffective; however, if the paint is too thick, it will lead to seizing the fastenings.
There have been a lot of different flange shapes and angles, and you may not be able to coat the whole area. After the flange inspection, another layer of coating needs to be applied. A benefit of using maintenance paints is that they do not require specialist equipment or hot work.
Mechanical solutions are usually clamp encapsulated or rigid, covering the flange or the void between the flanges. These clamps or covers are made from plastic or stainless steel and incorporate a rubber seal.
The next solution is the usage of tapes, be it semi-solid or full. Tapes can be composed of viscoelastic polymers, wax, petrolatum embedded into the fabric for wrapping. These are useful specifically for their water-repellent nature of semi-solid polymers, although they may be less common in high-pressure applications.
All the preventative methods have some pros and cons—no solution can help prevent the corrosion from happening entirely. However, regular inspections and maintenance can help to prevent rapid corrosion and general upkeep is encouraged.
Ways to repair corroded flanges
There are three main ways you can use to repair the corroded flanges:
. Adding a polymer composite to rebuild the flange face.
. Add material to ring grove or sealing face and then machine within flange tolerance.
. Remove the damaged flange and weld a new one (safest choice).
Factors that influence flange corrosion resistance during the operating conditions
Three prominent factors influence flange corrosion resistance during the operation conditions. These are:
. The temperature of the corrosive agent
. Purity of corrosive agent
. Corrosive agent concentration
Few flange materials are subject to stress corrosion cracking given the general volume of applications that do not operate under heavy media stress. However, it is a fact that needs consideration while selecting the material and gasket type. When you choose a proper gasket, it can help prevent corrosion from aggressive chemicals.
There are also different flange faces, and gaskets must adhere to the proper type of flange face. When dealing with chemical oxidizers/HF acid, it is crucial to select a robust gasket that can help to prevent corrosion.
If you want to learn more about flange corrosion, visit our website today!