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Using raised face flange with flat face

Using raised face flange with flat face

Using raised face flange with flat face

(OP)
To save time and money is there a safe way to bolt a 150# rf flg to a 125# ff. The service is cooling water and chill water, bolting an instrument to a valve, less than 100degF and 80psig operating parameter. Is there somewhere that it is written that I could go too to print out. I have heard of double gaskets and changing bolting material.

RE: Using raised face flange with flat face

Your application won't hit the thresholds to get involved with pressure piping codes anyway, but if it did, you're supposed to remove the raised face from the 150# flange, and use a full face gasket. This leaves no gap for the relatively thin and brittle 125# flange to get sprung into when the bolts are tightened. A307 bolts & matching nuts are supposed to be used with 125# flanges. These have both a min and max tensile strength specified. They'll twist off before the flange cracks if they're over-tightened.

RE: Using raised face flange with flat face

Priest,

The way I have always done it is to have the raised face of the 150# flange ground off so that the mating surfaces are flush.  It is quite a bit of work.  Sometimes is is easier and cheaper (depending of pipe size) to match the 150# flange with a 150# flange.  I am guessing that your instrument has the 150# flange.  In the case of non-ASME code water piping, it has always seemed easier to me to direct the contractor to match whatever flange he needs to match.  

If you are connecting to a cooling tower, the balancing valves and the outlet connection usually need a flat faced flange.  Another cheap solution in these pressures and temperatures is an angle face ring and ductile iron back up flange.  They are cheap and require a full face gasket!

RE: Using raised face flange with flat face

If we know in advance that we've got a 150# raised face being mated to a 125# flat face, we get the raised face taken off at a machine shop prior to the flanges being delivered to the job site. (Some of our suppliers will provide this service for us, for a marginal cost.) It's very cost effective when compared to dealing with it in the field.

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