How To Solve Valve Corrosion
Here are a few techniques for making valves resistant to corrosion.
1. Materials resistant to corrosion can be selected based on the medium
In actual production, the medium's corrosion is highly complex. If there are variations in the concentration, temperature, and pressure of the medium, the material corrosion will not occur in the same way even when the same medium is employed with the same valve material. Every 10 °C rise in media temperature resulted in a one to three-fold increase in corrosion rate. The concentration of media on the corrosion of the valve material has a major effect. There is little corrosion if the lead is in a small sulfuric acid concentration. Additionally, corrosion will increase significantly at concentrations higher than 96%. On the other hand, carbon steel rusts most quickly at a sulphuric acid concentration of roughly 50%. There occurs corrosion rather than a sudden drop when the concentration hits 6%. Another example is aluminum, which corrodes at medium and moderate concentrations of nitric acid but nevertheless becomes seriously corroded at concentrations of more than 80% of the concentrated acid. Even though diluted nitric acid has an extremely high corrosion resistance in stainless steel, corrosion accelerated in more than 95% of the concentrated nitric acid.
Based on the aforementioned instances, the appropriate selection of valve materials should be determined by considering particular conditions, analyzing different aspects that contribute to corrosion, and selecting materials in accordance with the applicable anti-corrosion handbook.
2. Use of non-metallic materials
It has outstanding resistance to non-metallic corrosion. The valve can stop corrosion and preserve precious metals as long as it uses pressure and temperature that meet the needs of non-metallic materials. Commonly utilized non-metallic materials include the valve body, valve cover, liner, sealing surface, etc. The gasket is primarily a packing composed of non-metallic materials.For valve linings, we utilize rubber such as nitrile, neoprene, and natural rubber as well as polymers like PTFE and chlorinated polyether. Carbon steel and cast iron are typically used for the valve and cover bodies. It guarantees the valve's robustness and protects it from corrosion.The exceptional corrosion resistance and change performance of rubber is also taken into consideration in the construction of the clamp valve. With the increasing use of nylon, polytetrafluoroethylene, and other plastics, natural and synthetic rubber are now available for use in a variety of sealing rings and surfaces. They are applied to various kinds of valves as well. Not only do these non-metallic materials function well as sealing surfaces, but they also resist corrosion well. They work very well with media that contains particles. Naturally, they have a limited range of applications and poor strength and heat resistance. Conversely, the introduction of flexible graphite has allowed non-metals into the high-temperature field. It is an excellent high-temperature lubricant that also fixes the long-standing issue of fillers and gaskets leaking.
3. Spray paint
On valve items, paint serves as both an identifying mark and a crucial anti-corrosion element. Another non-metallic substance is paint. Typically, synthetic resin, rubber slurry, vegetable oil, solvent, etc. are used in its preparation. It can accomplish the goal of preventing corrosion by isolating the medium and atmosphere and covering the metal surface. The paint is mostly utilized in environments—such as water, salt water, ocean, and the atmosphere—where corrosion is not as severe. Anti-corrosion paint is frequently applied to the inside cavity of valves to stop them from corroding when exposed to water, air, and other substances. To show which material was used to make the valve, the paint is blended with various hues.
4. Add corrosion inhibitor
The rate of metal corrosion can be significantly reduced by introducing a tiny amount of specific other chemicals in the corrosive medium and corrosive substances. The term "corrosion inhibitor" refers to this special substance.
The mechanism via which corrosion inhibitors limit corrosion is by encouraging battery polarization. The two main applications for corrosion inhibitors are as fillers and media. To slow down equipment and valve corrosion, corrosion inhibitors are introduced to the medium. Stainless steel with chromium and nickel will get pyrophoric in a wide range of solubility when exposed to non-oxygenated sulfuric acid. More severe rusting results from this. Nevertheless, we can alter the dull state of stainless steel by adding a tiny quantity of copper sulfate, nitric acid, and other oxidants. To stop the medium from leaking through, its surface will produce a barrier layer. Titanium can be protected from corrosion by adding a little amount of oxidizing agent to hydrochloric acid. Test pressure of the medium, which is frequently used to measure valve corrosion, is typically measured using a valve test pressure. The valve can be shielded from corrosion by a little addition of sodium nitrite to the water. The corrosion of the valve stem is excellent, and asbestos packing includes chloride. Let's say the amount of chloride can be decreased by using a steam-distilled water washing procedure. However, this approach can only be recommended for specific needs due to its implementation's numerous challenges.
We take the problem of stem corrosion resistance very seriously. We frequently employ surface treatment procedures including nitriding, boriding, chrome plating, and nickel plating because we have a wealth of production experience. It can increase resistance to wear and abrasion as well as corrosion. Various surface treatments ought to be appropriate for various stem materials and operational settings. Hard chrome plating and gas nitriding can be applied on asbestos packing contact stems and water vapor media in the atmosphere (ion nitriding should not be used on stainless steel). Higher phosphorus nickel electroplating performs better as a protective coating in the hydrogen sulfide atmosphere valve. While harsh chrome plating should be avoided, 38CrMoAlA material can be made to be corrosion resistant by ion and gas nitriding. Ammonia corrosion may not be able to penetrate 2Cr13 material after it has aged. Gas-nitrided carbon steel also prevents corrosion from ammonia. Furthermore, ammonia corrosion can affect any phosphor-nickel plating.
Handwheels and valve bodies with small diameters are frequently chrome-plated as well. It can adorn the valve and enhance its corrosion resistance capabilities.
5. Thermal spraying
One of the newest technologies for protecting the surface of materials is thermal spraying, a technique square for coating preparation. It's a major nationwide promotion initiative. It involves heating and melting metal or non-metallic elements in the form of an atomized spray to the basic surface by pretreatment using a high energy density heat source (gas combustion flame, electric arc, plasma arc, electric heat, gas combustion explosion, etc.). This leads to the production of a sprayed layer, or a surface strengthening process technique in which a sprayed weld layer is generated, and the simultaneous heating of the basic surface so that the coating is again molten on the surface of the substrate. The majority of metals and their alloys, metal oxide ceramics, metal-ceramic complexes, and hard metal compounds can be coated on a metallic or non-metallic substrate using one or more thermal spraying techniques.
Thermal spraying increases the resilience of their surfaces to heat, wear, and corrosion while also extending their service life. Special features of the one-of-a-kind functional coating created by thermal spraying include heat insulation, insulation (or isoelectricity), self-lubrication, abradable sealing, thermal radiation, and electromagnetic shielding. As a result, we may fix parts using thermal spraying.
6.Manage the environment that is corrosive.
The so-called environment is divided into two senses: wide and narrow. The installation of valves surrounding the environment and its internal circulation medium are referred to as the general sense of the environment. Most settings are out of our control, and we are powerless to arbitrarily alter manufacturing procedures. We can utilize the environment control method only if there is no damage to the product, process, etc. For instance, during the oil refining process, the boiler water is deoxygenated and the PH level is corrected using household alkali. According to this perspective, the inclusion of corrosion inhibitors, electrochemical protection, and other elements is also included in the process of managing the corrosive environment.
Particularly in the production environment, the atmosphere is heavy with fumes, water vapor, and dirt.such as brine and smoke, machinery that releases harmful gasses, and powdered grit, all of which can cause varying degrees of corrosion on the valve. In order to effectively prevent environmental corrosion, the operator should clean and purge the valve as directed by the operating instructions and refill on a regular basis. There are several ways to stop the erosion of a valve that contains corrosive materials, such as using a stem installation protection cover, a ground valve set ground well, valve surface spray paint, etc. The equipment and valves' corrosion will be accelerated if the surrounding temperature rises and there is air pollution, particularly in the closed environment of the equipment. To reduce the rate of environmental corrosion, we should employ open plants, ventilation, and cooling techniques.
7. Development of machining procedures and shapes for valve construction
Protection against valve corrosion caused by problem design, sound structural design, and appropriate technology for valve goods.
As a result, the manufacturing and design departments should be in charge of those structural designs that are unreasonable, improperly executed processes, and easily caused to enhance component corrosion. and adapt it to different working environments while adhering to the specifications.
The oxygen concentration difference cell is prone to corrosion in the gap at the valve connection.
As a result, the valve stem and the connection closure should, to the greatest extent feasible, not utilize a threaded connection form. Applications for valve welding, continuous welding, and double-sided butt welding are appropriate. Corrosion is frequently caused by spot and lap welds. thread connection of the valve and raw polytetrafluoroethylene pad and tape are used. It can stop corrosion in addition to having a good seal. Media that clog valves due to poor flow tend to erode the valve. When manufacturing valve parts, in addition to making sure the valve is not mounted backward and paying attention to the discharge of deposited media, we should attempt to avoid a free-of-depression structure. Additionally, we ought to attempt to install drainage holes for the valve.
Anodic metal corrosion can occur when various metals come into contact with one another and form a point pair. Avoid coming into touch with metals that cannot form a passivation coating and have a wide potential difference when selecting materials. We should focus on enhancing processing techniques during the fabrication and processing phases, particularly during the heat treatment and welding processes that create stress corrosion. We ought to make an effort to apply appropriate preventative measures, including annealing treatment, after welding. Both the valve stem machining and the surface roughness of the other valve components require improvement. Its corrosion resistance increases with surface roughness degree. The manufacture and processing of gaskets and packing need to be improved. Flexible graphite and plastic packaging, as well as stick-on flexible graphite gaskets and PTFE-wrapped gaskets, are all options. All of them enhance sealing performance and lessen flange sealing surface and ground stem corrosion.
