API-6A BX ring grooves 1

[mr0426]

We recently encountered an issue we were not previously aware of.

When a BX159 ring was inserted into a BX159 groove, we found that it only contacted on the outer edge. There was a gap on the inner edge of approx 0.8mm (0.030").

I drew (AutoCAD) the groove and ring to scale using the sizes in API-6A table B52 and found the same mismatch.

Is this mismatch intended? Has anyone else found this?
Any advice or comments appreciated.

Regards,
Mike Riach

 

[carthago]

API 6A:

I have always understood that these rings will be Plastically = Permanently deformed when seated...
------------
Further if you look to for instance API 6A , Appendic C
(Determination of bolt length) you will notice on the sketch for Ring Type BX
That the clearance between face of flanges= S =0
-----------
For the type b , S > 0

 

[EagleKnee]

I have worked with these high pressure seal grooves for several years and yes they are designed to seal when pressured up.The pressure should protrude over the ID of the groove wall to expand the ring against the outer wall.So in fact there is only a seal on the outer wall of the groove.Hense the tighter tolerance on the OD of the groove only.

Hope that helps.