High-pressure, high-temperature (HPHT) service has a famous reputation. It gets the headlines, the standards and the testing programmes. High-pressure, low-temperature (HPLT) is the same seal under pressure at the other end of the thermometer, and it fails in different ways.
What goes wrong in the cold
- Stiffening. As the rubber approaches its glass transition, modulus rises by orders of magnitude, and the seal no longer follows the surface it is meant to seal.
- Loss of recovery. A seal that has been squeezed in the cold may not spring back when the load changes. Low-temperature compression set tells you about it.
- Thermal contraction. Rubber shrinks much more than metal when cooled. A seal that fitted at room temperature can lose its squeeze.
- Plasticiser loss. Plasticisers that gave cold flexibility can crystallise, migrate or extract.
- Rapid cycling. A system that goes from hot service to cold shutdown cycles the seal across its whole range.
Why it needs its own design
The polymer choice, plasticiser strategy and network density that make a good hot seal are often not what a good cold seal needs. Fluorine content, which helps HPHT, raises Tg. Heavily reinforced compounds help tear strength and hurt cold flexibility.
How we handle it
- Specify the cold requirement as numbers: TR10, TR70, low-temperature compression set, brittleness and Tg.
- Choose the polymer family for the cold end first, then optimise for the hot end.
- Test at the real temperature, not at the nearest convenient one.
- Document the plasticiser and its behaviour.
Pascalor LT and ULT grades are built on that approach. If you have a cold-service seal that is giving trouble, send us the duty and we will start from the numbers.
About this article. It is original writing prepared from public sources, standards and general industry practice. It is not a copy of any book or standard and it is not engineering advice. Confirm values against the current edition of the standard and test in your own application. Only analyse material you own or are entitled to analyse.
