FLANGE CORROSION PROBLEMS AND THE MOST PRACTICAL SOLUTIONS

The integrity of flange connection is very important for the pipeline system of conveying fluid. Whether it is a pipeline system for transporting chemical media (such as hydrocarbons) or a water supply pipeline, the leakage of flange connections will cause serious environmental and economic impact, and may even bring huge potential safety hazards. If flanges are exposed to corrosive environment or polluted industrial atmosphere without protective measures, the corrosion rate will be very fast.

 

In addition, because of the complex geometry of flange connection, it is easy to cause gap corrosion between two flange surfaces and galvanic corrosion between different metals, which will seriously damage the integrity of pipeline system.

 

In order to meet the demanding production needs and reduce the sudden shutdown caused by leakage, effective monitoring and inspection is essential. Often the technician is more concerned with the leakage problem between the flange faces, while ignoring the protection of the fasteners and the exterior of the pipe, which can have extremely serious consequences in a harsh external environment. Insufficient external protection accelerates and expands the damage to the flanges and fasteners, causing the entire seal system to accelerate and deteriorate, potentially damaging the structural integrity of the system and causing seal failure.

 

Since the visual inspection of the flanged sealing faces can only be carried out when the entire system is shut down, the inspection procedure should be as simple as possible and the external corrosion should first be eliminated. If it is not possible to stop the machine, it can only be detected by ultrasonic technology. In the case where external corrosion cannot be controlled, the process will be more complicated and accurate test results will not be obtained. Therefore, in order to monitor the entire system and provide an effective and feasible quality control and overhaul procedure, external corrosion protection of flanges and fasteners is critical.

Existing solutions

The ideal solution should combine excellent corrosion protection and simple construction procedures, and should be suitable for flanges of various sizes and shapes (such as threaded flanges, plate flanges, long weld neck flange, lap joint flanges and so on), and it is easy to operate the bolts during maintenance. Common solutions currently on the market include:

(1) Maintenance Paint Solution

Maintenance paint is a hard film that can be bonded directly to a substrate, typically an epoxy or polyurethane coating. There are many edges and corners in flanges, and it is difficult for conventional paint systems to effectively cover the edges due to edge thinning effects. Although thickening the coating will solve the problem of edge protection, it will seal the fastener and make it impossible to disassemble during subsequent maintenance. In addition, the coating will be destroyed when the bolt is operated, and it must be repainted after maintenance.

 

(2) Mechanical Solutions

The gap between the flange and the flange surface is mainly sealed by the protective cover and the clamp, and is usually made of stainless steel or plastic with a rubber sealing strip. This type of protection is less flexible and requires the storage of covers or clamps that are perfectly matched to flanges of various sizes.

 

(3) Solution of Tape or Semi-Solid Anti-Corrosion Belt

Roll-wrapped tapes (such as mineral resin tapes, waxy or elastic polymer bandages) are protected by wrapping around the surface of the substrate. Because the semi-solid polymer has good water resistance, this protection method can provide reliable anti-corrosion protection. However, if the flange shape is complex (such as blind flanges,slip on flanges, socket weld flanges and so on), this solution is not only time-consuming but also difficult to construct. When bolts need to be disassembled and assembled, the material is relatively soft and easy to cut. But it is difficult to re-seal and restore the original protection after disassembly and assembly.

 

(4) Solution of Hot Melt Plastics

The hot melt plastic is essentially a high temperature heated waxy fusible polymer that is sprayed onto the surface of the substrate by professional hot melt equipment. The advantage of this type of protection is that it can be remelted and reused, saving costs. However, this method also requires fire operation and professional equipment. Although it can be reused, it is not easy to open and seal during maintenance.

 

(5) Solution of Polymer Sealing Bag

The flange can be completely wrapped in a sealed bag, which consists of a low permeability polymer, a corrosion inhibitor vapor and a desiccant. It is easy to install, but the ends of the bag are only sealed with tape, not with durable and effective mechanical bonding. If there is a large area of steam inside the bag, which is easy to collect a large amount of water, the corrosion inhibitor will be consumed in a period of time.

 

(6) New Peelable Sealing Membrane System

In response to the problem of flange corrosion, a company has developed a new peelable sealing membrance system that is tough and flexible enough to use the chemical action of the polymer. It can be peeled back hard and not torn. It has rubber elasticity, no isocyanate and toxic metal catalysts. The system is specially designed to protect flanges, fasteners and related pipes. It can be bonded to the manually treated base material without any fire operation, which makes the construction safe and simple. The system uses corrosion inhibitor as primer to provide overall corrosion protection. At the same time, the coating itself has a strong bond that removes all moisture from the system.

For the flange anti-corrosion problem, although there are different solutions on the market, most of them can not simultaneously have excellent anticorrosion protection, simple installation, suitable for various flange sizes and shapes, convenient maintenance and other performance. After precise research and development, the strippable sealing system provides comprehensive protection for flanges and avoids the potential risk of flange leakage.