RTJ Flange Bolting
RTJ Flange Bolting
(OP)
I have an application involving a special flange (based on ASME 16.5 1500lb) which has a spacer in the flange pair. There are ring type joints either side of the spacer. The problem I have is that very high bolt torques (and preloads) are required in order to achieve the 3mm offset at each ring as specified in B16.5. The bolts are now over stressed compared to the B31.3 allowable stresses as are the flanges based on an ASME VIII Div1 Appx 2 calculation. With "regular" bolt torque values each ring joint has an offset of approximately 5.5mm.
Can anyone shed any light? This is a common scenario for example wafer check valves with RTJ faces.
Secondary questions are:
A, Do B16.20 RTJ's deform plastically under gasket seating
B, Are the ASME VIII Div1 Appx2 seating stresses reliable?
C, Secondly are the B16.5 gaps typically attainable without using high torques?
Regards,
Tim
Can anyone shed any light? This is a common scenario for example wafer check valves with RTJ faces.
Secondary questions are:
A, Do B16.20 RTJ's deform plastically under gasket seating
B, Are the ASME VIII Div1 Appx2 seating stresses reliable?
C, Secondly are the B16.5 gaps typically attainable without using high torques?
Regards,
Tim





RE: RTJ Flange Bolting
If Im not mistaken, RTJ tend to strainharden after torqueing, especially when re-torqued over and over.
RE: RTJ Flange Bolting
Unless your bolts will exceed the proportionality limit, there's very little risk of failure...
RE: RTJ Flange Bolting
RE: RTJ Flange Bolting
The bolt pre-stress required was around 90ksi the flanges were well over-loaded. We have decided to use standard asme torques and target a larger gap in order to protect the non-standard Appx 2 flanges.
RE: RTJ Flange Bolting
This is a commonly used gap when working out piping distances, but doesn't mean that is what you work to when sealing. It's all about bolt torque/force and ring sealing forces, not distances. Nothing is that precise in the world of flanges and rings for dimensions.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: RTJ Flange Bolting
What's a "standard ASME torque"?
Have you read and understood Appendix S?
RE: RTJ Flange Bolting
Unless the center/spacer flange is threaded to hold the studs in place, normal bolt loads should suffice to energize both mating RTJ gaskets, it will just a little longer for the bolt loads to seat both gaskets. But your joint can successfully be joined using the normal bolt loads/toruqes. Dependent on bolting materials, flange materials, operating conditions, somewhere between 40% and 75% of bolt yield strength is usually acceptable for most applications.
To echo what was said earlier, please do read ASME Sec VIII, Appendix S. It relates specifically that design loads are just that, design, and are not sufficient in most cases to successfully seal a bolted joint in service conditions.
I am not familiar with the 3mm offset you are referring to, unless is a customer specific requirement? Pictures???
Rick
RE: RTJ Flange Bolting
I realize this isn't the code defined methodology. The equipment purchased is supposedly manufactured to a +/-1.5mm overall length. This length includes 4 RTJ joints so it was critical for us to achieve the design 3mm gap in each joint to meet the overall length for our package assembly. The 3mm gap comes from table 5 of ASME B16.5 (3 and 6 inch 1500lb flange).
The flanges were deemed overloaded based on running an appendix 2 calculation substituting the actual bolt pre-load for the code values. I made this decision in order to check the flange stresses in the non-standard flanges with the high bolt pre-load.
In truth I don't know what the standard "ASME" torques are. Our fitters stated that the required bolt torques were higher than what they typically use for standard ASME flanges.
I need to convince my company to purchase ASME VIII. It is a hard sell as we only design items to B31.3 at the moment.
RE: RTJ Flange Bolting
Next, read appendix O and K of PCC-1. Especially the 2013 edt which will be out soon contains some useful updates.
Also purchase ASME II part D (as you might need it for B31.3 work), and try to get a hold of some of W. Brown's papers presented by PVP conference proceedings; they present the latest design technology for BFJ's, esp. on this topic. Esp. last PVP conference in Paris contained some useful papers on this subject.
RE: RTJ Flange Bolting
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way