Is it normal to have Butt weld end connections on lower class  butterfly valves. Specifically an ANSI class 150 300mm valve. I was lead to believe the point of welding them in was for higher pressure thicker pipelines. Butterfly weld connections can be used for several reasons: 1) To save weight and/or money due to lower weight. Here you are right. For low class valves the difference is relatively small. 2) To ensure leaktight connections. Flange connections may leak and especially with toxic media this can be dangerous. 3) To save maintenance costs. In case a valve does not require maintenance you do not have to inspect the flange connections. (Also interesting for buried valves).

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