Service temperatures, maximum quoted

Over the years many attempts have been made to provide some measure of the maximum service temperature which a material will be able to withstand without thermal degradation rendering it unfit for service. Quite clearly any figure will depend on the time the material is likely to be exposed to elevated temperatures. One assessment that is being increasingly quoted is the UL 746B Relative Temperature Index Test of the Underwriters Laboratories (previously known as the Continuous Use Temperature Rating or Index). 

Service Temperature - the maximum temperature at which the cured adhesive can be used continuously. At higher temperatures, adhesives progressively lose strength. For this reason test specifications normally define this as the temperature at which a certain level of Lap Shear Strength (LSS) is maintained, usually (and for the purposes of this book) this strength figure is 6.9 MPa (1000 psi). Service temperatures may also be quoted as a range. Most adhesives have a lower service temperature below 0°C. For joints in very cold applications (below >55 C) the choice of adhesive is very much reduced. 

Data quoted by Hull for Aflas 150P in 35% wet sour gas at 200°C (Table 15) indicate a somewhat better performance profile for this polymer type. It may be that hot sour oil (Table 14 and Fig. 6) has a more aggressive effect on TFE/propylene polymer than sour gas. Suffice it to say that both fluoroelastomers and TFE polypropylene rubbers are likely to give much better service in sour conditions than nitrile rubber, regardless of temperature. As is the case with corrosion inhibitors, perfluoroelastomer will give maximum resistance to sour conditions. 

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