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Subject: Deformed ring grooves after make-up and break-out

Question:

We have a job in process using 7-1/16” 5M flanges and RX-46 ring gaskets. We have made-up connections, applying 722 ft-lbs torque (using Easyrun 100 as a lubricant). Upon dismantling of the connections we have observed metal deformation around the whole of the outer sealing surface of the ring groove. We have not seen this before. Can we accept this condition, and should we consider the condition as normal?

Answer:

The phenomenon you have observed does frequently occur. We do not know the make-up tension you produced in the bolts using the combination of lubricant and torque you mention, as we do not know the lubricant’s characteristics. The tension in the bolts ultimately determines everything about a bolted connection. Despite its common use, bolt torque serves as a poor predictor of bolt tension.

With this said, the answer to your question should come from a practical test. Assuming the deformation appears slight, we at WOODCO USA believe a repeat make-up and test of a typical portion of your assembly will demonstrate that the condition does not get worse to a degree that might cause leakage. The number of make-up and test repetitions should approximate the number you might expect in the field during the reasonable expected useful life of the equipment.

If your testing produces disappointing results, you may want to consider the following information.

API weld neck flanges made of 45K yield strength material may have a hardness as low as 140 HBW. API integral flanges made of 60K yield strength material may have a minimum 174 HBW hardness, for “sour service” these flanges would have a specified maximum hardness of 237 HBW. Standard service equipment has no specified maximum hardness.

RX ring gasket design produces a specific “self sealing” characteristic. Without explaining all the details ( see http://www.woodcousa.com/field_appr.htm ), this factor of design contributes to your problem. The RX gasket profile intends the gasket to seal only on its’ O.D. The wide surface on its’ I.D. bears over more surface of the ring groove in the flange, and as the flanges come together and compress the ring gasket, this wider surface engagement on the I.D. causes the great majority of the “coining” force to bear on the narrower O.D. of the gasket (and the O.D. of the groove).

API specifies hardness maximums for ring gaskets specifically to reduce the problem you have experienced. Ring gaskets without an API Monogram may not have this hardness control. Even with controlled hardness ring gaskets, repeated make-up will slightly deform the ring groove of flanges that fall within the hardness limits required for “sour service” applications.

If your situation involves using weld neck flanges made from 45K yield strength material, you can expect this problem to continue. Substitution of higher strength material for weld neck flanges will improve the situation in regard to deformation of the ring groove, but will increase problems in welding.

At WOODCO USA, we have found this problem limited to appearance. Repeated make-up and test has not produced connection leakage, even when ring groove distortion on 6B test rack flanges that seal with R or RX ring gaskets has reached a point of widening the ring groove beyond allowable tolerance.

WOODCO USA
P.O. Box 1261
Houston, Texas 77251-1261
Phone: 713-672-9491
USA and Canada: 1-800-496-6326
Fax:  713-672-8768
www.woodcousa.com