Using raised face flange with flat face

[Priest]

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.

 

[TBP]

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.

 

[UtilityLouie]

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!

 

[TBP]

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.