FF Spectacle Blind mating RF Flanges

[cjabhijit]

I have query regarding RF Flange to FF Spec blind or Spade in the approved Piping Material Specification.
As per me this should not be done & RF Flange should always connect to RF Spec Blind/Spade.

I have also compared the same issue with other project’s PMS & found that my understanding is right.

Could you pls advice on this pls? I want to raise a flag to our Material Engineer for this but before that I just want to make sure my understanding is right.

What I heard is this difference though not ideal but works without any issues ..but I am not satisfied with it.

Need an expert’s advice. Is it done to save on cost or something & it may work okay & saves cost??

 

[LittleInch]

cjab,

Normally you're correct and especially when the FF flange is Cast Iron.

However take a look at Asme B 16.48 - line blanks. In there they show both flat face and also RF "as an option", i.e. default is a flat face blind.

ring joint is different of course, but normal RF spectacle joint can be either flat face or RF.

Can't see any difference myself between one or the other.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[cjabhijit]

Thanks for the response littleinch but I suspect suspect an issue with mating surfaces RF TO FF so the leakage possibility.

Will see 16.48 for the same but any more info is welcome.

Thanks & Regards,
Abhijit

 

[europipe]

Most spades and spect. blinds have od the same as od raised face,
so how would you get a raised face in spades and spect. blinds ?

 

[gerhardl]

In practical use this would of course also be a question of outer form of the blind for correct positioning, material compatibility and form and how and which type of sealing is used, the whole package compressed and hold in place, correct bolting and tightening etc.

You will find this done with many variations for many different piping-specs around the world, without actually breaking any codes, at least for lower and normal pressure classes and dimensions.

Of course special care should be taken for larger dimensions and for larger dimensions. What this is will often be given by an estimate of cost and consequences and general risk analysis.

You do not mention any particulars regarding pressure and dimensions, making it more difficult to comment further.

 

[MickMc]

As mentioned blinds/spacers according to ASME B16.48 can be FF or RF with the facing finish as per applicable code e.g. ASME B16.5. However the OD of blinds/spacers whether FF or RF are same and will fit inside the flange bolt holes therefore care has to be taken when torqueing if flange material is cast/ductile iron or similar as over torqueing can damage flanges and lead to leakages. Normally the Flat/Full face gasket will as implied cover the entire face are with holes cut for bolt insertion and no gap at outside bolt area that can cause damage but not the case when blind/spacers inserted as gap equal to thickness will occur.

 

[cjabhijit]

Thanks a lot for so much of help. Found in ASME B 16.48 that -choice of RF face type is kept to the purchaser means is an option hence default choice is FF as per my understanding & seems no issues there.

Regards,
Abhijit

Thanks & Regards,
Abhijit