The Six Most Practical Solutions for Forged Steel Flange Corrosion
The integrity of forged steel flange connections is critical to the fluid delivery piping system. Whether it is a pipeline system that carries chemical media (such as hydrocarbons) or a water supply pipeline, the leakage of forged steel flange connections will cause serious environmental and economic impacts and may even bring huge potential safety hazards. If forged steel flange is exposed to corrosive environment or polluted industrial atmosphere without protective measures, corrosion rate can be rapid.
In addition, due to the complex geometry of the forged steel flange connection, the gap corrosion between two forged steel flange faces and the galvanic corrosion between different metals are extremely easy to occur, which will seriously damage the integrity of pipeline system. This article introduces several practical methods to solve the corrosion of forged steel flange.
In order to meet the demanding production needs and reduce the sudden shutdown caused by leakage, effective monitoring and detection is essential. Generally, technicians are more concerned about the leakage problem between forged steel flange faces, but neglect the protection of fasteners and the outside of pipelines, which may cause extremely serious consequences in the harsh external environment. Insufficient external protection will accelerate and expand the damage of forged steel flanges and fasteners, deteriorate the whole sealing system quickly, which may rapidly spoil the structural integrity of the system and cause sealing failure.
Since the visual inspection of the sealing surface of forged steel flange connection 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 the machine cannot be stopped, only ultrasonic technology can be used for detection. In the case that external corrosion cannot be controlled, the process will be more complex and accurate test results cannot be obtained. Therefore, in order to monitor the whole system, and provide effective and feasible quality control and maintenance procedures, it’s crucial to take the external corrosion protection measures for forged steel flanges and fasteners.
Existing solutions for corrosion of forged steel flange
The ideal solution should give consideration to excellent corrosion protection and simple construction procedure, and should be suitable for all sizes and shapes of forged steel flange, and bolts can be easily operated during maintenance. Common market solutions include:
1. Maintenance paint
Maintenance paint is a hard film that can be bonded directly to the substrate, usually epoxy or polyurethane paint. Forged steel valve flange has many edges and corners, which is difficult to be effectively covered by conventional paint systems due to edge thinning effect. Although the thickening coating solves the problem of edge protection, it will also seal the fasteners so that they cannot be removed during subsequent maintenance. In addition, the operation of bolts will damage the coating, so after maintenance the forged steel flange must be re-painted.
The gap between the forged steel flange and the forged steel flange surface is sealed mainly by the protective cover and fixture which is usually made of stainless steel or plastic with rubber sealing strip. This type of protection is less flexible and requires storage of enclosures or fixtures that are perfectly compatible with forged steel flanges of all sizes.
3. Tape or Semi-solid anticorrosive tape
Roll-wrapped tape (such as petrolatum tape, waxy or elastomeric tape) protects the surface of the substrate by wrapping it. Due to the good water resistance of semisolid polymer, this protection method can provide reliable anticorrosive protection. However, if the shape of forged steel flange is complex, this material is difficult to construct and time-consuming. When the bolt needs to be dismantled, the material is relatively soft and easy to cut, but it is difficult to re-seal and restore the original protection after the dismantling, so it generally needs to be re-constructed.
4. Hot-melt plastic
Hot-melt plastics is essentially a high-temperature heating meltable waxy polymer, sprayed onto the substrate surface by a hot melt specialized equipment. The advantage of this approach is remelting, recycling and cost savings. However, this approach also requires hot work, professional equipment and construction services. It can be re-used, but difficult to be opened and sealed in maintenance.
5. Sealed bag of polymer
Forged steel flange can be completely wrapped by sealed bag that is consistent of low permeability polymer, corrosion inhibit vapor and desiccant. It is easy to install, but the ends of the bag only sealed by tape, rather than lasting and effective mechanical bonding. There is a large area of steam space inside the bag, which is easy to collect a large amount of moisture, so corrosion inhibitors will be used up over a period of time.
The above scheme can play a role in anti-corrosion protection to some extent, but there are still some defects in the construction, maintenance. It’s necessary to explore an effective solution that provides long-term, comprehensive protection for forged steel flange.
6. New type separable sealed film system for corrosion of forged steel flange
In order to solve the corrosion problem of forged steel flange, some companies have developed a new type separable sealed film system that is both tough and elastic enough by using the chemical effect of polymer. It can be forcefully peeled off backward without tearing with the elasticity of rubber, and is completely free of isocyanate and toxic metal catalyst.
This system is specially designed for the protection of forged steel flanges, fasteners and related pipes. It can be bonded on the manually processed substrates without hot work, but makes the construction safe and simple. The system uses corrosion inhibitor as the base adhesive to provide overall corrosion protection. At the same time, the coating itself has a strong adhesion, which can remove all the moisture in the system.
1) Corrosion resistance of the system
The corrosion resistance of the system has passed the salt spray test, and the corrosion resistance of the coating is evaluated by continuously placing the sample in a salt spray environment. The salt spray chamber converts the mass fraction of 5% sodium chloride solution to 35 ℃ salt spray with high temperature. The test sample is assembled forged steel flange connection, which one side is bare steel, and the other side is coated with the sealed film system. The samples were exposed to salt spray for 1000 hours without any sign of corrosion under the sealed film system. In contrast, the bare steel part of the forged steel flange is severely corroded.
2) Adhesion property of the system
To ensure that the port can be permanently sealed and exclude moisture, the system needs to have excellent adhesion, in particular, be closely adhered with the artificially treated surface. According to ASTM D429 and ISO8510-1, adhesion test performed on three different substrates after manual surface treatment, the result shows that the sealed film on three kinds of substrates has gelling cohesion failure rather than the adhesion failure. That means adhesion on the substrate is greater than the gelling cohesion of the polymers, and proves that the sealed film has superior adhesive properties.
3) Stripping resilience of the system
Another feature of the system is that the constructor can easily operate the fasteners. When forged steel flange needs maintenance, simply insert the blade into the sealed film between the gaps of the forged steel flange face and draw along the circumference. Then cut the sealed film in half or push back together with the plastic cap to reveal the forged steel flange and bolts. After completing the maintenance, the sealed film can be retraced to the original position.
In order to meet the characteristics of stripping, the sealing system must be both strong and elastic, and the tensile strength, elongation strength and tear strength are tested strictly according to ASTM D412 and ASTM D624.
The use of reinforcing bands at both ends of the coating on the pipe and at the circumference of the forged steel flange surface can increase the strength of the polymer in the key stress area during the peeling and sealing process of test, so that the system has superior elasticity and strength.
When forged steel flange requires resealing, its circumference must be cleaned to remove all dirt, grease and surface contaminants. Then the sealed film brushes on the circumference of the cutting protection system for simple and quick repair and protection.
For the corrosion protection of forged steel valve flange, there are different solutions in the market, but most of them don't have excellent corrosion protection, simple installation, convenient maintenance and other properties, and are not suitable
for every size and shape of forged steel flange. After precise research and development, the separable sealed system can provide comprehensive protection and avoid the potential risk of leakage of forged steel flange.