ASME B16.5 Raised Face Connection Bore Mismatch 2

[Peter R]

thread794-499953

The referenced thread has some discussion about ASME RF Bore ID mismatch between lapped flange and butt weld flange, what ASME allows. ASME does not mention this bore mismatch or the step it creates or if said step must be mitigated, therefore I assume this mismatch is allowed, although it would seem clear (without ASME comment) that the gasket would need to be sized for the larger ID joint and not the butt weld side. That said, paragraph 2.8.3 says "In no case shall the bore diameter exceed the bore of the same size and class lapped flange", which is an important caveat. Basically the lapped flange variant bore B is the max bore, no matter what the customer says. This was confusing because in the flange dimensional tables, this lapped bore B is denoted as "minimum", but paragraph 2.8.3 denotes it as "maximum", which is a discrepancy. The butt weld bore, despite that the code stipulates "to be specified by the purchaser" implying no ASME code requirement, does have some limitations that ASME imposes, and does it's best to make you go hunt for. If the bore is a continuous ID from face to butt weld, clearly it must be sufficiently less than butt weld OD H. But if the bore is tapered, which is not discussed in ASMEB16.5, but appears allowable, the face side OD must not exceed the lapped variant bore B. For the slip on flange, the bore appears to be able to vary between B for slip on flanges as a minimum and B for lapped flanges as a maximum. Lapped flange bores would appear to be specified as lapped bore B exactly with no allowance for tolerance. You would be forgiven for using your best engineering judgment and applying a reasonable +/- tolerance to lapped bore B.

 

[LittleInch]

That's a big block of text but is there a question??

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

 

[Peter R]

Since the referenced thread was closed, I had no way to add this comment, with the only option being to start a new thread. If you would like to respond, perhaps you could weigh in if this is a concern you have seen before, if you agree with my comment, etc.

 

[LittleInch]

I think you've misread that thread as I can't see any discussion about "ASME RF Bore ID mismatch between lapped flange and butt weld flange"

Think you need to add a sketch to see what your point is.

And please break your paragraphs up a bit - It's very difficult to follow your points in such a large block of text.



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

 

[Eric W]

Like the others, I'm having a tough time understanding the question or problem at hand.

The butt weld flange to which you refer is commonly called a weld neck flange and the bore of the flange can be specified at time of order so the flange bore matches the pipe bore. 6" 300# RFWN, A-105, ASME B16.5, sch 80 pipe bore.



If you can't fix it with a hammer, it's an electrical problem.

 

[Peter R]

Hello Eric, thanks for the reply. I am a valve manufacturer and so I sell custom designed valves into large systems. In a recent valve design, my customer is specifying RF flanges, the flanges will be machined integral to the valve body, and I must specify the bore that best meets my needs for the valve design and meets ASME. In this case, that means the bore will be all the way at the maximum allowed. In this case, as is typical, I do not have control of the flange that my valve will be connected to, that flange is on the client side. I assume it is a weld neck flange, and this weld neck bore diameter, unless it transitions to a larger diameter near the RF, would typically be less that the maximum allowed (which comes from 16.5 para 2.8.3). so in my case, we will likely have a small step between the client's piping flange bore and my valve flange bore, which will be slightly larger.

I was surprised to learn that this step, although clearly is a possible outcome, is not addressed in ASME, no comment about whether or not this step is allowed or what issues it may cause. After digging deeper, I also noticed the discrepancy I noted in my OP, that the lapped flange bore ID, denoted maximum in the tables, is also denoted as minimum in para 2.8.3, which is a clear conflict. We must always have a tolerance band for the dimensions we use to make machined parts, but in the case of the lapped flange bore ID, any deviation above or below the lapped flange bore ID specified in the tables would technically be non-conformant to ASME 16.5, hence my comment that people should just go ahead and use engineering judgement to assign a +/- tolerance to this dimension.

 

[moltenmetal]

Bore differences in any butt weld will interfere with radiographic inspection of the weld joint. But in this case, a visual inspection of the weld root should be possible. Will that be enough? Most of the time when butt welding one schedule of pipe to another, whether the "pipe" was a pipe spool or a fitting, we back-bored the pipe for ~ 5 wall thicknesses to the larger ID to ensure that the butt weld was easy to inspect by RT.

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