In high-pressure gas, an elastomer absorbs gas. If the pressure falls fast, the dissolved gas expands inside the rubber and can leave blisters, splits or internal cracks. A seal can pass heat ageing and fluid immersion and still fail this way. Pressure-cycling duty is the reason our RGD grades exist, and why each one carries its decompression test plan.
What makes RGD worse
- High gas pressure and gases that dissolve readily (CO2 in particular).
- Fast depressurisation and many cycles.
- Soft, low-modulus compounds and thick cross-sections.
- Poor filler dispersion and voids, which give gas somewhere to collect.
What helps
Compounds for RGD duty usually have higher hardness and modulus, a tightly controlled filler system and good dispersion, and a cure that gives a stable network. Cross-section geometry and housing design matter too, and they are your side of the specification.
What to write in the specification
- The gas mixture and partial pressures, including CO2 and H2S if present.
- Maximum pressure, temperature and decompression rate.
- Number of cycles the seal must survive.
- Test method. ISO 23936-2 and NORSOK M-710 describe tests for non-metallic materials in oil and gas service, including RGD. Name the standard and the version you require.
- Acceptance criteria. Many specifications use a visual rating of the sectioned test ring and a limit on volume change, so state both.
- Specimen size. Results depend on cross-section, so say which O-ring size or slab the test uses.
- Reporting. Ask for photographs and rating of every specimen, not only a pass statement.
What a supplier should be able to show
Dispersion and density checks on the batch, hardness and modulus against limits, and RGD results on the same compound recipe, not a similar one. Our lot passport reports the release tests for each lot, so you can see consistency between the batch you tested and the batch you receive.
Limits of this note
RGD test programmes are costly and are run at specialist laboratories. Nothing here replaces the standard you are required to follow. Use it to write a clear request. Then start a requirement and we will respond with candidate compounds and a test plan.
