ASME B16.36 Flange tap size 1

[svi]

The note 1 (please see the interpretation link in the attachment) is misleading. It says other tap sizes may be used. A further interpretation says that there is no validation for the P-T ratings of the flange, if a tapping size other than in the table is used.

 

[nickelkid]

Okay, so what are you trying to do?

 

[svi]

So if I use a 3/4" or 1" tapping, even if the tap fits the flange thickness, there is no guarantee that the flange rating is intact. In which case why did ASME have to say this as an interpretation. Would it not have been better that they said as they do for B16.5 and B16.47, that the deviations from the stated dimensions will invaidate the conformance to the standard. It is for the user to re-validate each such case by elaborate calculations.

 

[nickelkid]

I think you have answered your question and believe the interpretation lead you there.
Not much of an issue if you would be using a 3/8 NPT or some other ½ thread the way I read it.

 

[svi]

A Gasco standard requires to have 3/4" tapping instaed of the 1/2". I am inclined to believe that this is not correct.

 

[nickelkid]

Not sure of your application, but I just did a couple of orifice plate metering runs using tapped flanges. ISO 5167-2 requires the taps to be less then 13mm..

 

[svi]

This forum is about the ASME Code related problems. I thought you were familiar with the B16.36 when you responded. It is a dimensional standard for the Orifice flange component, unlike the ISO 5167-2. I wouldn't think that the ISO covers the aspect on the flange derating as a result of the drilling of the orifice tap on to the flange edge.

 

[nickelkid]

Svi, apparently I am misunderstanding your issue, which appears to be the Gasco standard, not the code. The code is clear and you have a requirement that does not fall within its ratings. My reference to the iso standard was simply to illustrate that the application should be taken into consideration to understand why a deviation from the published ratings are required. Perhaps taps larger than ½” are not required, maybe they are…

 

[svi]

Robin, If one were only reading the ASME B16.36 standard alone and not the interpretation. Which is the normal case. I would start looking for an interpretation when I see a problem with what is there in the standard. Now the standard calls for 1/2" size tapping. This is fine, except that it says (as it does in the reproduction of the standard in the attached vendor's catalogue), in note 1 that other sizes may also be furnished. It does not warn or inform the reader that by using a larger size that one may be invalidating the flange rating. This is what has happend in the Gasco standard which calls for 3/4" size tapping for the orifice tap.

 

[nickelkid]

Svi, my perspective on this is a result of my last exercise of specifying this very connection. Others preferred ¾, but it was not necessary and I campaigned for adherence to the standard without change. Personally I was not very accommodating to the reducing in thickness with the larger tap – also unaware of the addenda you provided. I looked at B16.11 – which does not apply – for a reference of wall thickness and decided it was not worth pursuing, but advised if desired p/t ratings could most likely be justified with additional hours, but no guarantee.
Sure the standard could be clearer, but I can honestly say that it is a pitfall that has been avoided with the data at hand.