APPLICATION ENGINEERING



ARE YOU SEALING CHEMICALS AT LOW TEMPERATURE ?


Low temperature performance of elastomer seals is becoming more important with the commercialisation of oilfields in cold locations, such as in Alaska, the North Sea and Russia. Traditionally, FKM seals have not been recommended for low temperature dynamic applications below -30°C (-22°F). This is due to the Glass Transition Temperature (Tg) of most low temperature ED resistant FKM elastomer formulations. The Tg is the temperature at which an elastomer changes its physical pr...operties from elastic and pliable to rigid and brittle and, as a result, loses its sealing ability. Any movement of either the seals or the mating surfaces of the equipment at this temperature could result in damage to the seal surface in the form of cracking or splitting. High pressure has the apparent effect of increasing the Tg of an elastomer; as a general rule, for every 5 MPa (725 psi) bar increase in pressure, the Tg increases by 1°C. This has significant implications for engineers involved in the selection of elastomer seals. For example, an elastomer having a Tg of -30°C (-22°F) at atmospheric pressure, would in effect have a Tg of only -20°C (-4°F) when the pressure acting on the seal is increased to 50 MPa (7250 psi).