The integrity of the flange connection is critical to the delivery of fluid piping systems. Whether it is a piping system that transports chemical media (such as hydrocarbons) or a water supply line, flange connection leakage can cause serious environmental and economic impacts, and may even pose a huge safety hazard. If the flange is not protected, it can be exposed to corrosive environments or contaminated industrial atmospheres.
In addition, due to the complex geometry of the flange connection, crevice corrosion between the two flange faces and galvanic corrosion between different metals are highly likely to seriously damage the integrity of the pipeline system. This article describes several practical methods for solving flange corrosion.
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.
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 effective and feasible quality control and overhaul procedures, external corrosion protection of flanges and fasteners is critical.
It should take into account excellent corrosion protection performance and simple construction procedures, and should be suitable for flanges of various sizes and shapes, and it is convenient to operate the bolts during maintenance. Common solutions currently on the market include:
Maintenance paint solution
Maintenance paint is a hard film that can be bonded directly to a substrate, typically an epoxy or polyurethane coating. Flanges have many edges, and it is difficult for conventional paint systems to effectively cover the edges due to edge thinning effects. Although the thicker coating will solve the problem of edge protection, it will also seal the fasteners and will not be disassembled for subsequent repairs. In addition, the coating will be destroyed when the bolt is operated and must be repainted after repair.
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 all sizes.
Tape or semi-solid anti-corrosion tape solution
Roll-wrapped tape (such as petrol tape, wax or elastic polymer wrap) is protected by wrapping on the surface of the substrate. Due to the good water resistance of semi-solid polymers, this protection provides reliable corrosion protection.
However, if the flange is complex in shape, this material is not only time consuming but also difficult to construct. When the bolts need to be disassembled, the material is relatively soft and easy to cut, but it is difficult to reseal and restore the original protection after disassembly and assembly, and generally requires re-construction.
Hot melt plastic solution
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 hot work, professional equipment and construction services. Although it can be reused, it is not easy to open and seal during maintenance.
Polymer sealed bag solution
The sealed bag encloses the flange completely and 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, rather than a durable and effective mechanical bond. There is a large area of steam inside the bag, which is easy to collect a large amount of water, and the corrosion inhibitor will be consumed for a period of time.
Although the above scheme can play a certain role in anti-corrosion protection, there are still some defects in construction, inspection and maintenance. It is necessary to explore and develop effective solutions to provide long-term and comprehensive protection for the flange.
New peelable sealing membrane system
In response to the problem of flange corrosion, the company has developed a new peelable sealing film system that is tough and flexible enough to use the chemical action of the polymer. It can be peeled back backwards without tearing, and has rubber elasticity. It is completely free of isocyanate and toxic metal catalysts.
Designed to protect flanges, fasteners and associated piping, the system can be bonded to hand-treated substrates without the need for hot work, making construction safe and easy.
The system uses a corrosion inhibitor as a primer to provide overall corrosion protection, while the coating itself has a strong bond that removes all moisture from the system.
System corrosion resistance
The corrosion resistance of the system is tested by salt spray and the corrosion resistance of the coating is evaluated by continuously placing the sample in a salt spray environment. The salt spray box converts a sodium chloride solution of 5% mass fraction into a high temperature salt spray of 35 °C. The test specimens were assembled flanged joints with bare steel on one side and the sealing membrane system on one side.
The samples were exposed to a salt spray for 1000 h and no signs of corrosion were found under the sealing membrane system. In contrast, the bare steel portion on the other side of the flange is severely corroded.
System adhesion performance
In order to ensure that the port is permanently sealed and moisture is removed, the system requires excellent adhesion, especially in close adhesion to manually treated surfaces. Adhesion testing was performed on three different substrates that were manually surface treated according to ASTM D429 and ISO8510-1.
The results show that the sealing film fails on the three kinds of substrates without adhesion failure, that is, the adhesion on the substrate is greater than the gelation cohesion of the polymer material, which proves that the sealing film has excellent adhesion. performance.
System stripping performance and flexibility
Another feature of the system is that the constructor can easily operate the fasteners. When it is time to repair! Simply insert the blade into the sealing film between the flange faces and cut it along the circumference of the flange. Then divide the sealing film into two halves, or you can pull it back together with the plastic cap to expose the flange and bolt. After the repair is completed, the sealing film can be folded back to its original position.
In order to meet the peelable characteristics, the sealing system must be both strong and flexible. The tests for tensile strength, elongation strength and tear strength were carried out in strict accordance with ASTM D412 and ASTM D624.
The use of reinforcing strips at both ends of the coating finish on the pipe and at the circumference of the flange face can increase the strength of the polymer material in critical stress areas during the peeling and sealing process during the test, giving the system superior elasticity and Intensity.
When resealing is required, the circumference of the flange must be cleaned to remove all dust, grease and surface contaminants. Then use a sealing film to brush the circumference of the cut protection system for quick and easy repair protection.
For the flange anti-corrosion problem, although there are different solutions on the market, most of the solutions can not have excellent anti-corrosion protection, easy installation, suitable for various flange sizes and shapes, and easy maintenance. After careful development, the peelable sealing system provides complete protection for the flange and avoids the potential risk of flange leakage.
Source: China Flanges Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)