Research conducted in a high pressure polyethylene plant in Belgium, indicates that certain conventionally designed and scaled-up safety relief valves did not open consistently with ethylene at 300 barg and also at 250 barg. Comparative tests in the high capacity at the High Pressure Laboratory of a German safety relief valve manufacturer showed that the same conventionally designed and scaled-up safety relief valves tested at a set pressure of 250 barg had high lift fluctuations on air but did not open on water. It was also demonstrated that a safety relief valve designed by a German manufacturer, which opened reliably on air and on water at a set pressure of 250 barg also opened reliably on ethylene at a set pressure of 250 barg (i.e. supercritical condition). The comparative tests with ethylene in the polyethylene plant in Belgium showed also that the blow down values on that valve with ethylene are similar to the blow down values with water. Therefore it looks like the flow behavior in the safety relief valve with supercritical ethylene is similar as with a liquid. This plant testing on ethylene at 250 barg indicates that there are advantages to using the German manufacturer’s designed safety relief valves with the certified “one trim design” for liquid and gas.

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