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Epoxy coating temperature resistance in practice - knife gate valves

2010-11-09

Comments or examples on practical upper limit for application of epoxid coated knife-gate valves for liquid fluids?
Product datasheets give 120 deg centigrades for the (EPDM) sealings on the knifegate. However the epoxid layer of 200-250my thickness will have a lower limitation. The layer - electrostatic applied to preheated valve -  will after hardening have a product guarantee limitid by the two following criteria for liquids:
a) Test Limited by 14 days submerged (totally) in hot water 90 deg C for 14 days, and a 16MPa adeshion strength.
b) A temperature gradient from outer wall of housing to inner wall of housing not more than 70 degrees centigrade. (To be understood such that if the surrounding temperature is 10 deg C plus the fluid temperature is limited to 80 degree centigrade).For dry air the limitation is higher.
The general rule here is not to use epoxy coating above 120 dC. In practice we did not have big problems when we operated a few days at 125-135 dC. The epoxy still had a good bonding but the colour slowly got brownish.


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