The most practical solution to flange corrosion

　　The integrity of flange connection is very important for fluid pipeline system. Whether it is the pipeline system conveying chemical medium (such as hydrocarbon) or the water supply pipeline, the flange connection leakage will cause serious environmental and economic impact, and may even bring huge security risks. If the flange is not protected, the corrosion rate will be very fast if it is exposed to corrosive environment or polluted industrial atmosphere.

　　In addition, due to the complex geometry of the flange connection, the gap corrosion between two flange faces and galvanic corrosion between different metals are very easy to occur, which will seriously damage the integrity of the pipeline system. This paper introduces several practical methods to solve the flange corrosion.

　　In order to meet the harsh production needs and reduce the sudden shutdown caused by leakage, effective monitoring and detection is essential. Usually, technicians are more concerned about the leakage between flange surfaces, and ignore the protection of fasteners and the outside of the pipeline, which may cause extremely serious consequences in the harsh external environment. Insufficient external protection will accelerate and expand the damage of flange and fastener, accelerate the deterioration of the whole sealing system, and may quickly damage the structural integrity of the system, resulting in seal failure.

　　Since the visual inspection of flange connection sealing surface can only be carried out when the whole system is shut down, the inspection procedure should be as simple as possible, so the external corrosion should be eliminated first. If the machine can not be shut down, ultrasonic technology can only be used for detection. In the case of external corrosion can not be controlled, the process will be more complex and accurate test results can not be obtained. Therefore, in order to monitor the whole system and provide effective and feasible quality control and maintenance procedures, the external corrosion protection of flange and fastener is very important.

　　The ideal solution should take into account the excellent anti-corrosion protection performance and simple construction procedures, and should be suitable for flange of various sizes and shapes, and can easily operate the bolts during maintenance. At present, the common solutions in the market include:

　　1. Maintenance paint solutions

　　Maintenance paint is a hard coating that can be directly bonded to the substrate, usually epoxy or polyurethane coatings. There are many edges and corners in the flange. Due to the edge thinning effect, it is difficult for the conventional paint system to cover the edges effectively. Although the thickened coating can solve the problem of edge protection, it can also seal the fasteners, which can not be removed in subsequent maintenance. In addition, the coating will be damaged when the bolt is operated, and it must be repainted after maintenance.

　　2. Mechanical solutions

　　Flange and flange surface clearance are mainly sealed by protective cover and clamp, which are usually made of stainless steel or plastic material and equipped with rubber sealing strip. The flexibility of this protection method is poor, so it is necessary to store the cover or clamp that completely matches the flange of various sizes.

　　3. Solution of adhesive tape or semi solid anticorrosive tape

　　Rolled tape (such as petrolatum tape, waxy or elastic polymer tape) is wrapped on the surface of the substrate for protection. 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, this material is not only time-consuming but also difficult to construct. When the bolt needs to be disassembled, the material is relatively soft and easy to cut, but it is difficult to re seal and restore the original protection after disassembly, so it is generally necessary to re construct.

　　4. Hot melt plastic solutions

　　In fact, hot melt plastic is a kind of waxy fusible polymer heated at high temperature, which is sprayed on the surface of substrate by professional hot melt equipment. The advantage of this protection method is that it can be remelted and reused, saving cost. But this method also needs hot work, professional equipment and construction services. Although it can be reused, it is not easy to open and seal during maintenance.

　　5. Polymer sealed bag solution

　　The sealing bag can completely wrap the flange, which is composed of low permeability polymer, corrosion inhibitor steam and desiccant. It's easy to install, but the ends of the bag are only sealed with tape instead of long-lasting and effective mechanical bonding. There is a large area of steam space inside the bag, which is easy to accumulate a lot of water, and the corrosion inhibitor will be consumed in a period of time.