Turning the Tables on Valve Corrosion

Why is Valve Corrosion a Problem?

Corrosion is a persistent threat to valve manufacturers and their customers. If valves reach the end user in a corroded condition, the result can be customer dissatisfaction, complaints and added costs for rust claims and interrupted schedules. However, this problem can begin during manufacturing, long before the valve reaches its final destination. The necessary evil of cleaning valve components and letting them sit between stages of manufacturing and assembly leaves the freshly cleaned metal surfaces susceptible to flash corrosion. The same is true for hydrostatic testing, which must be done to check for leaks once the valves are assembled. Despite the valves being drained and dried, moisture may remain in the complex valve internals, allowing corrosion to fester as the valve passes time in storage or shipping.

Another potential corrosion issue faces valve users. Valves are commonly found in boilers, piping systems and other infrastructure at industrial plants and facilities. Valves are often critical parts that should be backed up by spares. However, if spares are not properly protected, they may corrode during months or years of storage. If a replacement is suddenly needed, the corroded spare valve will only compound the problem, resulting in additional downtime while the valve is restored or a new one is ordered.

Sometimes, preservation of parts and equipment at an entire facility is needed while a plant temporarily shuts down or before it is brought online. This is especially common in large-scale oil, gas and power operations plagued by unstable markets. Frequently during plant construction, critical parts must be stored in an open yard where they are exposed to harsh outdoor elements that could accelerate corrosion and compromise the valves before they are ever installed. Alternately, if a plant is laid up because of a market downturn, the out-of-service valves and equipment may decline in value and not be ready for immediate recommissioning if inadequately protected from corrosion. In either case, it is important to implement effective preservation methods that will require as little cleaning or restoration as possible to bring the system back online.

Where Do Traditional Treatments Fail?

Often, traditional methods of protecting valves and equipment from corrosion are insufficient and rely on environmentally hazardous material that is cumbersome to remove or dispose. For example, during manufacturing, valve components are typically cleaned and left to sit in temporary storage until they are moved to the next stage in the process. This puts the freshly cleaned metal surface at risk for flash corrosion due to moisture and oxygen exposure. If a traditional rust preventative is applied at this point, the valve may be protected but will need an extra step of cleaning before moving to the next stage of manufacturing. After final assembly, the valve is hydrostatically tested and drained, further exposing the internal valve surfaces to moisture. Before shipment, the manufacturer typically sprays a contact corrosion inhibitor (often petroleum- or wax-based) on the valve internals and flange faces. The manufacturer then bolts a rubber protective covering on the flange face to protect it from physical damage and places it in a crate for shipping, hoping for sufficient protection.

Because of the complex valve interior, it is nearly impossible to ensure thorough application of the traditional corrosion inhibitor on all surfaces. Since contact corrosion inhibitors only protect those surfaces they are directly touching, any part of the valve that personnel cannot see or touch will go unprotected. The same problem can occur for valves stored onsite, sometimes in harsh outdoor conditions. Even if known to thoroughly cover and protect all surfaces, typical petroleum- or wax-based inhibitors may require extra labor to clean the valve before installation and extra disposal costs for products categorized as hazardous waste.

Alternative Strategies

Major progress in the protection of valves has been made by the introduction of in-process flash corrosion inhibitors and VCIs into the manufacturing, shipping and layup process. By implementing flash corrosion inhibitors directly into the cleaning of individual components, manufacturers can protect the components against flash rust for a week to several months indoors between manufacturing steps. This also reduces cycle time by adding the corrosion inhibitor directly into the cleaning step. Once the components are assembled, a combination of contact corrosion inhibitors and VCIs can be added to the hydrostatic test water. This helps protect the internals of the valve long-term even after hydrostatic testing has exposed the valve to the corrosive forces of moisture.

VCIs have a unique advantage over traditional corrosion inhibitors and rust preventatives because they do not need to be applied directly to the surfaces they protect. VCIs are able to vaporize from a source material, disperse throughout an enclosed space, and condense on metal surfaces, even in intricate, hard-to-reach areas. This is an important solution to the problem of complex valve geometry, because it removes the challenge of thoroughly applying a corrosion inhibitor to all metal surfaces inside the valve. If a hard-to-reach surface is missed during the application of a VCI carrier, it will still be protected as the VCI molecules diffuse throughout the space to reach all surfaces.

VCI can be applied in many forms, but it often works well to fog the interior of a valve with a waterborne VCI that does not need to be removed before using the valve. Valve flanges and rubber guards can be put on as normal before the valve is crated. The entire valve can be wrapped with a recyclable film containing VCI. The film serves the double purpose of providing extra VCI protection as well as trapping the waterborne VCI inside the valve. When the valve is shipped, it will remain protected with VCI until it is unwrapped at its destination. A similar method of protection can be performed onsite at facilities where valves or valve-containing systems need to be laid up or stored for replacement use. For valves that must be stored outside, a tough weather-resistant VCI film is an excellent option combined with a waterborne VCI fogging treatment or VCI-impregnated foam pads.

Any exposed machine surfaces such as flanges and stems can be protected with a water-based corrosion inhibiting rust preventative or protective coating if needed. Often these non-hazardous rust preventatives can simply be left on the valve during installation. For example, water-based coatings containing VCI have shown significant ability to effectively protect at low dry film thickness, making them a minimally invasive option for exterior valve surfaces.

An important advantage of these protection strategies is that they not only keep the valves or systems more thoroughly protected, but they keep the valves ready for immediate use whether a spare is needed or a facility or plant is ready to come online. Product removal time is minimal and often only requires unwrapping and recycling the VCI film, removing the flange protectors and installing the valve where it is needed.

Conclusion

Successfully protecting valves from corrosion has traditionally been a challenge due to the complex geometry of valve internals and their necessary exposure to moisture from cleaning and hydrostatic testing. Some methods of protection can be cumbersome, inadequate and include hazardous waste disposal costs. In contrast, implementing non-hazardous flash corrosion inhibitors and VCIs into the cleaning, hydrostatic testing and packaging processes provides more effective protection with easier removal that allows for speedy installation or commissioning of the valve or system.

Julie Holmquist is marketing content writer at Cortec Corporation. Valve preservation information was provided by Jim Holden, PE, technical director, energy & engineered solutions and technical review was provided by Eric Uutala, technical service manager at Cortec. Photos are copyright Cortec Corporation.