Explosive Decompression

Definition and Distinction

Explosive decompression describes a damage mode in elastomer seals when a gas under high pressure penetrates the material and the pressure is then released quickly. In sealing technology, this particularly concerns O-rings, sealing lips, and shaped seals in valves, fittings, compressors, or pressure couplings. The term “explosive” can be slightly misleading, because no chemical explosion is involved. What is meant is the rapid expansion of gas dissolved in the elastomer, which mechanically damages the material from within.

In many data sheets and standards, the term rapid gas decompression (RGD) is used for the same phenomenon. It describes more precisely what happens: rapid pressure release after prior gas absorption. ED (explosive decompression) and RGD are often used synonymously in everyday language, yet technically RGD is the clearer term.

ED/RGD is a different mechanism than extrusion. Extrusion means that elastomer is pushed under pressure into a gap, where it shears at edges or migrates out of the sealing gap. ED/RGD can promote extrusion, because a pre-damaged material tears more easily. Equally distinct is chemical attack — that is, a material change driven by media (e.g., swelling, hardness loss, or crack formation through reaction). In practice, combinations occur — for example, when a medium softens the elastomer and ED/RGD damage then grows faster.

Why Elastomer Seals Are Particularly Affected

Elastomers are partially permeable to many gases, meaning that gas can penetrate the polymer through diffusion. Under high pressure, the solubility of the gas in the material additionally rises; the elastomer charges with gas until a saturation state is reached. This gas absorption is the prerequisite for any strong internal expansion to occur during a rapid release.

Mechanism and Damage Pattern

The sequence can be described in a few steps. First, the seal stands under high-pressure gas, so that gas diffuses into the elastomer and dissolves there. Then a rapid pressure release follows — for example, through a fast valve opening or an emergency vent. The dissolved gas cannot diffuse out of the material quickly enough and expands inside. As a result, local overpressures arise that widen the elastomer and tear it internally.

The damage pattern ranges from blistering (bubble-like bulges) to cracking (crack formation) and flaking. What is critical is that damage can also occur purely internally. Such fissures (fine cracks) are sometimes barely visible from outside, yet they can significantly worsen the sealing effect. The consequence is often a creeping leakage, and in unfavorable cases a sudden failure when a crack runs through to the sealing surface.

Identification Features in Practice

ED/RGD frequently becomes apparent in connection with a specific operating event: the seal was stable under pressure, then quickly released, and a short time later leakage occurs. On disassembly, typical features then show up depending on severity.

Influencing Factors and Risk Drivers

Whether ED/RGD occurs depends on how much gas is absorbed and how strongly the release overburdens the system. In many applications, the risk rises with higher pressure, because more gas dissolves in the elastomer at higher pressure. Higher temperature often acts critically as well, because diffusion and solubility increase and because mechanical properties of the elastomer can change. The residence time under pressure is also relevant: the longer the seal sits at high pressure, the closer it gets to saturation.

The directly triggering factor is usually the decompression rate. When pressure drops very rapidly, gas cannot diffuse out in time. An internal gas pressure builds up that tears the material. In practice, the question “how quickly is pressure released?” is therefore often as important as “how high was the pressure?”.

The most important influencing factors can be summarized briefly:

• Pressure level: more gas absorption at higher pressure.
• Temperature: affects diffusion, solubility, and elastomer strength.
• Type of gas: determines how well the gas penetrates the elastomer and dissolves there.
• Time under pressure: longer time raises the saturation level.
• Pressure-release profile: rapid release raises internal stresses.

Why Some Gases Are More Critical (e.g., CO₂, H₂)

Gases differ in how strongly they dissolve in elastomers and how fast they diffuse. CO₂ is considered particularly critical in many applications, because it is highly soluble in numerous elastomers, which can lead to high gas contents in the material. Hydrogen (H₂) is also relevant in high-pressure applications, because rapid pressure changes and high pressures can promote the formation and growth of defects. For design, this means: the same sealing concept can work in air or nitrogen, yet show significantly higher ED/RGD risks in CO₂ or H₂ systems under similar pressure cycles.

Avoidance: Material, Design, Operation, and Testing

The most effective operational measure is often slower pressure release. A controlled release gives the gas time to diffuse out of the elastomer before it generates high internal stresses. When operations cannot avoid rapid releases, material selection and design must be more strongly tailored to ED/RGD.

On the material side, compounds with higher strength and higher elastic modulus (stiffness) often help, frequently together with higher hardness. These properties raise resistance against bubble growth and crack propagation. Nevertheless, RGD resistance always remains relative: a compound can withstand moderate conditions yet fail under harsher cycles. Therefore, transferring data-sheet values without a suitable test cycle is risky.

From a design perspective, a clean layout of the installation space (gland) is important. Excessively large gaps and unfavorable guidance raise the risk that a seal pre-damaged by ED/RGD additionally extrudes or tears at edges. Larger sealing cross-sections and well-supported geometries can help, because they reduce stresses and guide the material more stably — yet they must fit the application.

A compact measure logic:

Test and Assessment Logic (Standards Overview)

In practice, ED/RGD resistance is assessed through test cycles that define gas type, pressure, temperature, and a defined decompression profile. After repeated cycles, the damage is evaluated visually and often through cross-section images using a rating. This logic appears in widely used references such as ISO 23936-2 and NORSOK M-710. For CO₂-related decompression tests, NACE methods such as TM0297 are also referenced; depending on industry and application, additional NACE methods are discussed.

For interpretation, it is decisive that test conditions reflect the real application. A good rating in a mild cycle says little about a harsh release in the field. Therefore, the test plan should always be derived from the specific values: which gas is present, how high is the pressure, which temperatures occur, how long does the system stay under pressure, and how quickly is it released?

In the end, specialized consultation can be sensible when operating profile, gas mixture, and seal design deviate strongly from standard cases.