Can your seals fail in pressurized gas environments? Critical component failure in the Energy, Oil, & Gas Industry (EOG) can have disastrous consequences. Elastomeric seals provide the necessary barrier between your process and the environment. Leakage can occur when a seal is compromised, leading to unscheduled maintenance. At the worst, leakage can harm personnel or the environment. Identifying and preventing seal failure is critical to minimizing downtime and keeping the environment, health, and safety a top priority.
What is RGD?
Rapid Gas Decompression (RGD), also sometimes referred to as explosive decompression (ED), is one of the most common failure modes that affects seals in EOG applications. RGD is a phenomena related to pressurized gas applications. While in service, gas begins to permeate and diffuse through the free volume of the elastomer. At high pressures, the gas is in a compressed state. When a significant pressure drop occurs in the system, the compressed gas expands and tries to escape as quickly as possible, putting stress on the elastomer. When the stress exceeds the strength of the elastomer, tears, fissures, and cracks are created which compromise the integrity of the seal. As the system is re-pressurized this could lead to a leak.
Identifying RGD before it occurs
Being able to identify the conditions which lead to RGD can help prevent a failure from occurring. Parker has three application guidelines for determining whether RGD may occur in your system:
1. Is the application seeing gas service above 750 psi?
2. Does depressurization occur at a rate greater than 200 psi/min?
3. Are there multiple pressurization/depressurization cycles throughout the seal life?
If you've answered yes to any of the three questions above, then RGD could be an area of concern for your application. Other factors which can impact a compound's RGD resistance include temperature, max pressure, gas composition, seal size, gland design, and length of service.
A Parker Application Engineer can assess your situation and help you determine the proper compound choice to minimize the occurrence of RGD related damage.
Assessing seals affected by RGD
Knowing and documenting the cause of a leak is the best way to prevent the failure from reoccurring. Visual inspection is the best method for determining whether RGD occurred. In cases of severe RGD, the o-ring can appear torn apart with splits and fractures on the surface similar to the photos shown below:
Sometimes the splits do not tear open, and appear as blisters on the surface as shown below:
In other situations, the outside of the seal does not appear impacted by RGD. The o-ring must be cut into sections so that the cross-section can be examined. RGD can be identified by splits and fissures, which if significant enough, can cause the elastomer to lose its sealing capability.
How can I prevent RGD?
The easiest and quickest solution to limiting exposure to RGD failure is by using a material which is certified and proven to work in EOG environments. Parker Engineered Materials Group understands the concern that RGD poses to customers operating in the EOG market, which is why we have focused our state of the art compounding on creating more RGD resistant compounds across all types of rubber, including Hydrogenated Nitrile (HNBR), Fluorocarbon (FKM), AFLAS® (FEPM), and Perfluoroelastomer (FFKM). These materials are tested to the most pertinent industry standards including ISO 23936-2, Norsok M-710, and Total GS EP PVV142. Using Parker compounds certified for RGD can help give your company the peace of mind you need to operate safely and successfully in the EOG marketplace.
For further information on NORSOK, ISO, and API approvals refer to our bulletin ORD 5774.
This article was contributed by Eric Uehlein, Applications Engineer, Parker Hannifin O-Ring Division
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