ANSI B16.5 flanges; reduced length through hub

[Oldliar]

Hi there,

I have a supplier of a component with 4" WN ANSI B16.5 600# RJ flanges. In order to reduce the overall lenght of the component, they reduce the lenght through the hub from stated 4 inch to 3.15 inch, thus saving a total of 1.7 inch on the lenght. The machine new welding ends, seems to be in line with the standard. But what about the lenght? Is it okay to reduce it without any notes or 'special considerations'?

Regards

 

[SnTMan]

Oldliar, I don't see how it can be considered a B16.5 flange any longer, as to P & T ratings. Perhaps there is a Code Case or interp that permits this.

Regards,

Mike

 

[11echo]

I don't see a problem! Code does not stipulate a mandatory dimension, only the ability to stand up to a certain design temp/press. The dimensional standard is just for covenants of construction, as long as you/client are happy with the "new" flange, there should be no issue. My $0.02 anyway, Good Luck!

 

[SnTMan]

11echo, so you alter the flange from B16.5 dimensions. How are you assured it meets the B16.5, or any, temp and pressure ratings, short of treating it as an Appendix 2 flange, or some equivalent for Codes other than Sec VIII, Div 1?

Just curious.

Regards,

Mike

 

[TGS4]

I'm with SnTMan on this - it's not a B16.5 flange unless it fully complies with ALL of the requirements, including dimensions, of ASME B16.5. If the hub length is shorter, how do you know that it will meet the P&T ratings!

 

[TBP]

In addition to possible code issues, is there any real reason to leave this nifty little dimensional time-bomb for the maintenance crew to find by surprise 10 years from now? I used to be in maintenance. Please, use fittings with standard dimensions.

 

[jte]

as long as you/client are happy with the "new" flange, there should be no issue.

Guys, you're being a bit harsh. Note that 11echo stated that as long as you/client are happy. So either I, as the client, don't care about liability due to use of nonstandard components or I've satisfied myself that the design can meet some other generally recognized and accepted engineering standard. We don't know whether this flange has been qualified by burst testing or anything else... Either way, as long as I'm happy... And why should I let a maintenance issue 10 years from now worry me?

jt

 

[TBP]

"And why should I let a maintenance issue 10 years from now worry me?"

So it's not that you're incapable of designing something that's maintainable - you just don't care?

 

[jte]

TBP-

Ummm... ok, you don't know me well... Let me make it loud and clear: That was a huge dose of sarcasm. Believe me, I'm the one harassing project engineers to put in 24" manways instead of saving $100 by putting in an 18".

jt

 

[gr2vessels]

I cannot accept the use of modified "B16.5" flanges due to dimensional non-conformance with the "prescriptive" dimensions allowed by the B16.5.
However, the diameter "X" is the fixed dimension of the hub. The taper of the hub varies between 1:3 and 1:4, continued by the straight portion of the hub. If you can control the machining precision of your machining centre, then make all the hubs of 1:3 taper and make the weld prep at the end of taper, without the straight portion, as allowed by the ASME code. This will shorten the standard flange without modifying or altering the strength of the flange. How much saving, you work it out.
Also, you might need to advise the vessel fabricator to provide extra welding up on the hub taper to generate the required transition of 1:4 taper. You old liar, have you deviced this all by yourself, testing the limits of the conservative people, or intend to propose a fine change to the old cookbook?
Cheers,
gr2vessels

 

[dcasto]

So how do we use Graylock flanges guys? If you can prove through design and test that the flange meets the requirments, then go for it..

 

[TGS4]

dcasto - the issue is not whether or not the flange is acceptable, just whether it meets the standard. There are many proprietary bolted connections out there, but you should note that a Graylock does not purport to be a B16.5 flange.

 

[gr2vessels]

Nice polemic,
Perhaps we should take it a bit further.
1. The shortened flange geometry resembles the B16.5 shape, but does not conform to the standard requirements.
2. The lengh of the hub, beyond the joint of the taper with the cylindrical end, has nothing to do with the rating. I have requested a FEA analysis for both shapes;- I'll keep you informed as soon as I have the results.
3. The question, in my opinion, is beyond the compliance with the B16.5 requirements. The oldliar seems to be confused by a flange most likely passing the P&T requirements for the equivalent B16.5 flange, despite of some geometric non-conformance. The B16.5 / B16.47 is still under constant review and open for improvement. Perhaps the "short" flange supplier took a little too early step selling them, but is stepping likely in the right direction. Obviously, he will have trouble convincing people to accept his short flanges, without proper backing from the code or other sources.
Any other opinion?
gr2vessels

 

[MJCronin]

gr2, Old, et al..

Hopefully, these are not those damned Chinese flanges ...... or are they ?

That is a topic for another forum..

MJC

 

[RossABQ]

How often do you replace flanges as a maintenance item? I can't think of a single case outside of very high pressure steam systems, where the steam cut the RF.

If you make these flanges a little shorter still, don't they essentially become slip-on flanges?

 

[Oldliar]

Gents,

My question is only if it's allowed by code to do modifications. In my opinion it's not. And for gods sake, I don't machine these flanges in my garage (or in China for that sake). It's a sub-supplier having some clever idea that he's struggling to give me some good support on.

 

[jte]

OldLiar-

I think the bottom line is that a modified B16.5 flange is no longer B16.5. It may be safe, it may even be legal (with the proper backup in the form of testing and/or calc's). But it isn't a B16.5 flange. When my wife's boss put a Chevy V-8 into his Volvo wagon (as I found out, not as uncommon as you might think...), you wouldn't expect him to drive in to a Volvo dealer and expect them to cover the engine under warranty... But it is legal, and probably even safe...

jt

 

[LSThill]

jte (Mechanical)

jte (Mechanical) Good point.

Now Modified to ASME CODE: Section VIII, Division 1 Replace Flange by Appendix 2 Flanges; Or ASME CODE: Section VIII, Division 2 Add Appendix 3 Flange. This would be legal, and safe.

 

[ijzer]

The flange rating can not be used anymore. You have to calculate the flange per ASME VIII-1 with the new dimensions. Could still be good.