What Is Explosive Decompression in O‑Rings (AED) and How to Prevent It

Explosive decompression, often abbreviated ED, is also known as rapid gas decompression or RGD. In the sealing world you will also see the term AED, which refers to anti‑explosive‑decompression grades of elastomers. Whatever name is used, the failure mode is the same. Gas under pressure dissolves into an elastomeric seal. If system pressure is relieved too quickly, the dissolved gas expands inside the polymer faster than it can diffuse out. Internal stresses build, the rubber ruptures from within, and the seal surface is left blistered, pitted or cracked. In high‑pressure gas service the result can be immediate leakage, unplanned downtime and safety risk.

This guide explains the physics that drive ED, the operating conditions that make it likely, how to identify damage, and a systematic approach to preventing it. It also links out to Canyon Components resources for oilfield applications, compliance and materials selection so you can specify the right solution the first time.

• Industry: explore our Oil Field page for severe‑service sealing environments: Oil and Gas Industry.
• Compliance: learn about materials qualified to key ED and sour‑gas standards: API 6A Materials, NORSOK M‑710 Materials, and NACE TM0297 Materials.
• Background reading: Canyon’s overview of AED elastomers and test concepts: Anti‑Explosive Decompression Elastomers & O‑Rings.
• Related products: heavy‑duty oilfield connections and extreme‑service sealing: Hammer Union Seals and Spring‑Energized Seals.

What Actually Happens Inside an Elastomer During ED

An elastomer is a cross‑linked polymer network with free volume between chains. When a gas is applied at pressure, molecules dissolve into that free volume according to a solubility relationship. Diffusion then carries gas inward following a concentration gradient. At steady state the seal is saturated with pressurized gas. If the external pressure drops quickly, the dissolved gas becomes supersaturated and nucleates internal bubbles. Those bubbles expand, coalesce and create local tensile stresses. If the local stress exceeds the network strength, micro‑tears form that radiate to the surface. The visible symptoms are blisters, pits, radial cracks, or chunks missing from the sealing line. Because the mechanical damage originates subsurface, the O‑ring can sometimes look acceptable until it is pressurized again and leaks.

Several fundamentals fall out of this physics:

• Smaller gas molecules such as hydrogen and helium permeate faster than larger molecules. While this does mean that these small molecules saturate the elastomer quickly, they fortunately also desaturate from the elastomer quickly. More problematic gasses, like CO2, saturate the elastomer slowly and desaturate from the elastomer slowly. This slow desaturation actually makes explosive decompression much more likely.
• Higher pressure and longer exposure drive more gas into the network, increasing stored energy.
• Higher temperature accelerates diffusion and solubility. Extremely low temperature can make the rubber brittle so the same internal pressure causes more cracking.
• Elastomer microstructure matters. A tighter network with strong cross‑links and optimized filler can resist crack growth better than a weak network with high plasticizer content.

Where ED Shows Up Most Often

Any duty cycle that combines high‑pressure gas exposure with the possibility of a sudden de‑pressurization is at risk. Typical examples include:

• High pressure CO2 applications.
• Surface and downhole oil and gas equipment where pressure steps, choke changes or emergency shutdowns occur. See our industry summary: Oil and Gas Industry.
• Hammer union connections that see repeated make‑up, break‑out and pressure cycling. See: Hammer Union Seals.
• High‑pressure compressors, pumps and gas sampling systems.
• Subsea control modules and hydraulic accumulators with dissolved gas exposure.
• Hydrogen and CNG systems, where very small molecules drive fast permeation.
• Cryogenic or wide‑temperature service where diffusion, brittleness and pressure changes interact. For highly dynamic extremes consider: Spring‑Energized Seals.

How to Recognize ED Damage

Inspect used seals under good lighting and magnification. Common indicators include:

• Holes or gaps in the cross section of the O-ring when cut.
• Surface blisters. Raised domes or bubbles where expanding gas ruptured the surface skin. Note that these visual indicators can sometimes disappear over time the longer the material has been depressurized.
• Pitting. Small craters that look like corrosion pits on metal.
• Radial or subsurface cracks. Fissures propagating from the inner body toward the OD or ID.
• Chunking. Missing pieces at the sealing line or corners of a square‑section gasket.
• Loss of elasticity. A seal that feels stiff or glassy compared to new stock.

Because ED is a subsurface phenomenon, damage can be intermittent. A seal might pass a quick air‑leak check at low pressure but fail when the system is returned to working pressure.

Variables That Drive ED Risk

Successful prevention starts with an honest accounting of the operating envelope. The following variables have the largest influence on risk:

1. Operating pressure. Higher differential pressures load more gas into the elastomer and raise stored energy.
2. Elastomer durometer, permeability, and strength. AED formulations use polymer selection, cure system and filler to reduce permeability and improve resistance to crack growth.
3. Gas composition. CO2 is the most likely to cause explosive decompression due to it's molecular structure. Hydrogen and helium permeate fastest. Sour‑gas environments add chemical attack. Reference: NACE TM0297 Materials.
4. Decompression rate. The single most controllable variable. Faster pressure drop equals higher risk.
5. Temperature. Elevated temperature increases diffusion rate and can weaken the network. Very low temperature reduces toughness.
6. Exposure time. Long soaks at pressure allow the seal to reach near‑equilibrium gas content.
7. Geometry and squeeze. Thin cross‑sections vent faster than thick sections. Excess squeeze raises stress concentrations and can accelerate cracking.
8. Dynamic motion. Sliding or vibrating interfaces disturb the sealing line during a pressure step and turn internal flaws into active leaks.

Standards and Qualification Testing

Several industry standards describe methods to screen materials for ED resistance. Canyon Components supplies compounds and finished seals that have been validated to these frameworks when specified.

• API 6A Materials. API 6A is the core specification for wellhead and Christmas tree equipment. Material annexes reference ED‑relevant properties and hydrocarbon and sour‑gas service expectations. Operators often specify API 6A equipment combined with a dedicated RGD validation protocol.
• NORSOK M‑710 Materials. Defines test conditions for nonmetallic sealing materials, including multiple pressure and temperature cycles in relevant gases. Post‑test seals are dissected and rated for internal cracking and blistering.
• NACE TM0297 Materials. Focuses on rapid gas decompression of elastomers, establishing procedures to expose O‑rings to gas at pressure and temperature then decompress, followed by dissection and damage scoring.

These protocols do not guarantee immunity in every field scenario. They are comparative filters that help you choose better materials and set realistic decompression limits.

Elastomer Materials That Resist ED

No elastomer is completely immune to rapid decompression, but several families offer significantly better resistance when compounded for AED performance.

• AED FKM. Fluorocarbon compounds with optimized cure systems and fillers. Good choice for hydrocarbon gases and mixed‑service oilfield environments. Strong high‑temperature capability and chemical resistance.
• AED HNBR. Hydrogenated nitrile blends designed for toughness and ED resistance. Often preferred for sour‑gas exposure and when better low‑temperature performance than FKM is needed.
• AED FFKM. Perfluoroelastomers like Canrez® and Kalrez® at the top end of chemical and thermal resistance. Used where process purity, high temperature and severe decompression combine. Higher cost but best‑in‑class ED resistance when formulated for RGD.
• Aflas (TFE/P). Useful for amines and steam plus sour‑gas environments. Can be considered where ED risk and chemical attack coincide.

When you are selecting materials for oilfield service, pair the compound choice with the compliance framework. See the overviews for API 6A Materials, NORSOK M‑710 Materials and NACE TM0297 Materials.

Backup rings and hybrid solutions

ED rarely occurs in isolation. The same duty cycles that create decompression events also push extrusion limits. Use PTFE or PEEK backup rings to control extrusion clearances. In extremes, a jacketed or metallic solution may be more robust. See: Spring‑Energized Seals.

Design Practices That Reduce ED Risk

Good design narrows the window in which ED can occur.

• Choose a sensible cross‑section. Larger cross‑sections hold more dissolved gas and vent more slowly. If the envelope allows, consider thinner sections or vented geometries to shorten internal diffusion paths.
• Use correct squeeze. Excessive squeeze raises internal stresses and makes crack growth more likely. Follow proven gland designs with attention to stretch, compression and gland fill. Avoid sharp corners and discontinuities that serve as crack starters.
• Add backup rings. On pressure‑energized seals, backup rings support the O‑ring and reduce extrusion during the transient when the O‑ring is weakened by internal gas pressure.
• Consider double‑seal arrangements. Two seals with a vented cavity between them allow staged pressure equalization during shutdowns.
• Manage surface finish. A moderate, uniform finish helps maintain a continuous sealing line and reduces micro‑leak paths that can evolve during decompression events.

Operating Practices That Prevent ED

Even the best elastomeric material can be damaged if the system is vented carelessly. Establish procedures and hardware that keep decompression within safe limits.

• Control ramp‑down rate. Specify and enforce maximum allowable pressure drop per unit time. Train operators and automate where practical.
• Step‑decompress. Instead of one long vent, break the event into several stages with dwell periods to allow diffusion out of the elastomer.
• Temperature management. If the system allows, maintain a moderate temperature during decompression to promote diffusion without making the elastomer brittle. Avoid sudden chilling from Joule‑Thomson effects.
• Limit soak time at peak pressure when possible. Shorter exposure means less dissolved gas in the network.
• Service intervals. Proactively replace seals in high‑risk duty cycles before accumulated damage causes a leak.

Troubleshooting Checklist for Suspected ED

When you see leakage after a shutdown or a rapid vent, use this quick diagnostic list.

• Inspect the failed seal. Look for blisters, pits, radial cracks and missing chunks. Compare against a library of failure photos.
• Confirm the event history. Did pressure drop quickly or in steps. Were there temperature swings. Was the gas composition different from normal.
• Review materials. Was the compound an AED grade qualified under NORSOK M‑710 or NACE TM0297. Was there sour‑gas exposure.
• Check gland and backup hardware. Any extrusion marks or sharp edges that could have turned micro‑cracks into active leaks.
• Evaluate decompression practice. Are there written limits for ramp rate. Can the hardware meet those limits under upset conditions.

Document findings and adjust materials, design or procedures accordingly. If you need help interpreting the failure, contact Canyon’s engineering team and reference the resources listed below, including our overview post: Anti‑Explosive Decompression Elastomers & O‑Rings.

Example Scenario: Hammer Union Seal in Sour‑Gas Service

A production site used high pressure connections that routinely saw 10,000 psi gas service with H2S content. The connection was vented quickly during change‑outs. Standard FKM O‑rings lasted for several cycles but began to leak following rapid shutdowns. Forensics showed blistering and radial cracks. The team replaced the material with our AF90BK01 AED Aflas qualified per a NORSOK M‑710 protocol and added PTFE backup rings. Operations updated the procedure to require staged decompression with 5 minute dwells at two intermediate pressure levels. After the change, seals lasted through the planned maintenance interval with no ED damage. For similar use cases, see: Hammer Union Seals and our oilfield overview: Oil and Gas Industry.

How to Specify AED‑Resistant Seals

Use a concise data set to get fast, accurate recommendations.

• Application. Static or dynamic. Gas composition and contaminants. CO2 yes or no. Sour‑gas yes or no.
• Pressure profile. Peak pressure, typical dwell time at pressure, maximum allowed decompression rate.
• Temperature profile. Normal operating range and extremes. Any cold starts.
• Size and geometry. O‑ring standard size or custom gasket. Gland dimensions if available. Extrusion gaps.
• Compliance. State required frameworks up front. Link to your organization’s preference for API 6A Materials, NORSOK M‑710 Materials and NACE TM0297 Materials.

With this information Canyon Components can recommend an AED material family, durometer, backup strategy and decompression envelope that meets your risk profile.

Frequently Asked Questions

Is any elastomer immune to ED. No. AED‑rated compounds raise the threshold significantly but cannot remove all risk, especially in hydrogen service or extreme pressure steps. PTFE spring energized seals are significantly more resistant to AED than any elastomer, but there are limitations and installation complications that need to be taken into account.

Does higher durometer always help. A harder seal can resist crack growth better, but excessive hardness reduces conformability and increases leakage risk on imperfect surfaces. We balance hardness with groove design and backup rings.

Should I switch to a metallic or PTFE solution. In some extremes a jacketed or spring‑energized design outperforms an elastomer. See: Spring‑Energized Seals. For oilfield unions and similar connections, also see: Hammer Union Seals.

Are ED tests the same as sour‑gas tests. Not exactly. ED tests simulate decompression damage. Sour‑gas tests address chemical compatibility and blistering from H2S and associated fluids. Many projects require both. Reference the compliance pages for program details: API 6A Materials, NORSOK M‑710 Materials and NACE TM0297 Materials.

Summary and Next Steps

Explosive decompression is a physics problem that becomes a reliability problem. Gas dissolves in the elastomer at pressure. A rapid pressure drop turns that dissolved gas into expanding bubbles and internal cracks. The solution is a layered strategy. Choose AED materials that have been qualified under realistic standards. Design glands that support the seal and control extrusion. Operate equipment with controlled decompression and defined dwell steps. Inspect seals and update practices when you see early warning signs.

For severe‑service oilfield and high‑pressure gas applications, start with the pages below, then contact Canyon for an application review and quote.

• Industry context: Oil and Gas Industry
• Compliance and materials: API 6A Materials • NORSOK M‑710 Materials • NACE TM0297 Materials
• Background post: Anti‑Explosive Decompression Elastomers & O‑Rings
• Related products: Hammer Union Seals • Spring‑Energized Seals