Can I use different flanges as a pair? 3

[billbusy]

I was just think is there any rules for a pair of flanges.

Do they need to be same material? Same rating? Same type (like RFWN, RFSW, FFSO), or Just same bolt size and location?

Anybody can give me an explanation? Thanks.

3 years industry experience;
Oil & Gas industry in Canada.

 

[pennpiper]

Rules for a pair of flanges.
1.) Flanges must be the same nominal pipe size

2.) Flanges must be the same Rating (or Class)

3.) Flanges must have the same Face

4.) Flanges must have the Bolt size and Location

5.) Flanges do not need to be the same material but sometimes if they are of different material you must take special action (example: Cast Iron against Forged Steel)

6.) Flanges do not need to be the same type but sometimes if they are different types you must take special action (example: Weld Neck flange mated against a Slip-On flange the gasket type needs to be provided that will not fail through lack of retention support by the Slip-On Flange)

prognosis: Lead or Lag

 

[jtseng123]

If you have different materials, you are facing different thermal growth rates and selection of bolting becomes crucial to retain the tighteness. It does not mean that you can not do it.

 

[moltenmetal]

Flanges and their bolting are rarely the same material. Flanges and bolting with significantly different thermal expansion coefficients are commonplace, which makes gasket selection very important.

Thanks Pennpiper for reminding people about my favourite pet peeve amongst your otherwise comprehensive list. In fact you need to ensure that any spiral-wound gasket used with RFSOs has the correct dimensions (i.e. no winding past the ID of the raised face of the RFSO, which is slightly larger than the pipe OUTER diameter), whether or not they're mated to a different type of flange. Gaskets specified to use inner rings made from sch5Spipe will be a problem at all sizes, but standard gaskets from most manufacturers are only a problem below about 4" NPS.