Six Solutions for Flange Corrosion
The integrity of flange connection is very important for the pipeline system of conveying fluid. Whether it is the pipeline system for transporting chemical media (such as hydrocarbons) or the water supply pipeline, the leakage of flange connection will cause serious environmental and economic impact, and even may 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. This paper introduces several practical methods to solve flange corrosion.
In order to meet the harsh production needs and reduce sudden shutdown caused by leakage, effective monitoring and detection is essential. Usually technicians are more concerned about the leakage between flange surfaces, but neglect the protection of fasteners and pipeline exterior, which may cause extremely serious consequences in harsh external environment. Insufficient external protection will accelerate and expand the damage of flanges and fasteners, accelerate the deterioration of the whole sealing system, and may quickly destroy the structural integrity of the system, resulting in seal failure.
|Corrosion Problems and Detection of Flanges||Six Solutions for Flange Corrosion|
Because the visual inspection of the sealing surface of flange connection can only be carried out when the whole system shuts 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, only ultrasonic technology can be used to detect. When external corrosion is uncontrollable, 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, external corrosion protection of flanges and fasteners is very important.
Flange is an important part of pipeline system. In order to meet the harsh production needs and reduce sudden shutdown caused by leakage, effective monitoring and detection technology is essential. Generally speaking, people are more concerned about the leakage between flange surfaces, and neglect the protection of fasteners and pipeline exterior. In harsh external environment, this may cause extremely serious consequences.
Insufficient external protection will accelerate and expand the damage of flanges and fasteners, which will accelerate the deterioration of the entire sealing system. The consequences of this situation are unpredictable beforehand, because it depends entirely on the specific operating conditions and environment. In extremely harsh environment, external corrosion may quickly destroy the structural integrity of the system, resulting in catastrophic seal failure.
Because the visual inspection of flange connection sealing surface can only be carried out when the whole system is down, the inspection procedure should be as simple as possible, so the external corrosion should be eliminated first. If it can’t shut down, it can only be detected by ultrasonic technology. In the case of uncontrollable external corrosion, this process will be more complex and can’t get accurate test results.
Therefore, in order to monitor the whole system and provide effective and feasible quality control and maintenance procedures, external corrosion protection of flanges and fasteners is very important.
Excellent anticorrosion protection performance and simple construction procedure should be taken into account, and flanges of various sizes and shapes should be suitable, and bolts can be easily operated during overhaul. The solutions commonly used in the market at present include:
Maintenance Paint Solution
Maintenance paint is a kind of hard film which can be directly bonded to the base material. It is usually epoxy or polyurethane coatings. There are many edges and corners in flange. Because of edge thinning effect, it is difficult for conventional paint system to cover edges effectively. Thickening the coating will solve the problem of edge protection, but at the same time, 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.
Sealing flange and flange clearance mainly through protective cover and fixture, usually stainless steel or plastic material with rubber sealing strip. This kind of protection is less flexible, and needs to store the cover or fixture that matches all kinds of flanges.
Solution of Rubber Belt or Semi-solid Anticorrosive 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, this material 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. Generally, it needs to be re-constructed.
Solutions for Hot Melt Plastics
Hot-melt plastic is essentially a waxy meltable polymer heated at high temperature, which is sprayed onto the surface of the substrate by professional hot-melt equipment. The advantage of this protection method is that it can be remelted, reused and cost-saving. But this method also needs fire operation, professional equipment and construction services. Although it can be reused, it is not easy to open and seal during overhaul.
Solution of Polymer Sealing Bag
The flange can be completely wrapped in a sealed bag consisting of a low permeability polymer, a corrosion inhibitor vapor and a desiccant. It is easy to install, but the ends of the bag are sealed only with tape, not with durable and effective mechanical bonding. There is a large area of steam space inside the bag, which is easy to accumulate a large amount of water, and the corrosion inhibitor will be consumed in 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 flanges.
New Peelable Sealing Membrane System
In order to solve the problem of flange corrosion, some companies have developed a new type of peelable sealing film system, which is tough and elastic enough. It can be peeled back by force without tearing, has elasticity of rubber, and does not contain isocyanate and toxic metal catalyst at all.
The system is specially designed to protect flanges, fasteners and related pipes. It can be bonded to the base material handled by hand without fire operation, but it 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 strong cohesion, which can eliminate all moisture in the system.
Corrosion resistance of system
The corrosion resistance of the system was tested by salt spray test, and the corrosion resistance of the coating was evaluated by placing the samples in the salt spray environment continuously. The sodium chloride solution with 5% mass fraction was converted into high temperature salt fog at 35 C in the salt fog chamber. The test sample is assembled flange connection, one side is bare steel, the other side is coated with the sealing film system.
The samples were exposed to salt fog for 1000 hours without any corrosion under the sealing film system. In contrast, the bare steel part on the other side of the flange is seriously corroded.
Adhesion performance of the system
In order to ensure that the port is permanently sealed and moisture is removed, the system needs to have excellent adhesion, especially to be tightly adhered to the manually treated surface. According to ASTM D429 and ISO8510-1, the adhesion force of three different substrates after manual surface treatment was tested.
The results show that the cementitious cohesion of the sealant film on all three substrates is not the failure of the adhesive force, that is, the adhesive force on the substrates is greater than the cementitious cohesion of the polymer material itself, which proves that the sealant film has superior adhesion performance.
Defilm Performance and Elasticity of the System
Another feature of the system is that the fasteners can be easily operated by the constructors. When it needs repairing! Just insert the blade into the sealing film between the voids of the flange surface and cut along the circumference of the flange. Then the sealing film is divided into two halves. It can also be pulled back with the plastic cap to expose the flange and bolt. After repair, the sealing film can be folded back to its original position.
In order to satisfy the peelable characteristics, the sealing system must be both strong and flexible. Tensile strength, elongation strength and tear strength were tested strictly according to ASTM D412 and ASTM D624.
Using reinforcing bands at both ends of the coating end and the circumference of the flange surface can increase the strength of the polymer material in the critical stress area during the peeling and sealing process, so that the system has better elasticity and strength.
When re-sealing is required, the flange circumference must be cleaned to remove all dust, grease and surface contaminants. Then the seal film brush is applied on the circumference of the cut protection system for simple and quick repair and protection.
Source: China Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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