Abstract
The estimated service life for elastomeric seals exposed to degradative fluids is important to both facilities engineers, who need to keep equipment operating, and materials scientists who need to understand how and why elastomers deteriorate. In this investigation, four elastomers were evaluated for use in seawater / triethylene glycol service as heat exchanger gaskets. Physical properties were measured once a week for twelve weeks to determine the rate and severity of degradation as a function of time. In addition, O-rings of some of the heat exchanger gaskets were exposed to the TEG fluid in a seal life chamber in order to predict the service life of the gaskets.
The results showed that monitoring changes in the shore hardness of the elastomers can lead to improper conclusions; materials which are clearly deteriorating sometimes show no change in measured hardness. While it can be stated that a dramatic change in hardness is an indication of material deterioration, material deterioration does not always result in a change in shore hardness. Only by careful comparison of the complete physical properties of the elastomers (hardness, stress/strain curves, volume swell, etc.) can the relative degradation be qualitatively estimated.
It was also found that the seal life chamber is inadequate for this type of investigation due to the fact that the TEG fluid did not aggressively attack the elastomers so that failure did not occur at intermediate temperatures (300-350°F). At high temperatures, the TEG breaks down and thus the test is no longer valid. In general, any seal chamber testing in fluid service must be performed with some knowledge of the actual effect of the fluid on the elastomer, since simple swelling will not result in failure.
