B16.11 Hex Head Plug Pressure rating 1

[anolan23]

Designing a vessel to Section VIII Div. 1 and I need to calculate the pressure rating of this component.

It says in B16.11 that the pressure rating shall be computed as straight seamless pipe of equivalent material.Straight pipe MAWP is calulated in Section VIII Div.1 under UG-27 where it breaks it down to Circumferential Joint and Longitudinal Joint.

I'm having trouble calculating the Longitudinal Joint maximum allowable pressure rating. The formaula is:

P=2SEt/R-0.4t

E= joint efficiency = 0.70
S=max allowable stress = 14020psi
t= minimum required thickness of shell = 0.301in
R=inside radius of shell = 0.119in

The value for P im getting is -4,220,020psi because the thickness is a little bigger than the inside radius. The plug is a 1/2" hex head 3000# F316 - SA-182 so I chose 0.84in for the OD for the equivalent pipe. Am I missing something? I'm trying to get the MAWP for this plug component.

 

[XL83NL]

I would consider the plug's rating (at least) equivalent to that of a half coupling in which it is screwed into, provided it has the same class rating (e.g. Cl. 3000).

For the half coupling calculation I'd use the formula for circ joints (because of the assumption of straight seamless pipe) to UG-27, calculated using the equivalent wall thickness from B16.11. When the limits of UG-27 are exceeded, use appendix 1.

 

[anolan23]

I meant to say that I'm having trouble with the circ. joint calculation as shown in the formula above. It's giving me a value of -4,220,020psi. The formula allows this because the denominator becomes negative and really small. How can I find the pressure rating if it's giving me this negative number?

 

[SnTMan]

anolan23, I assume what you are trying to do is calculate the MAWP of a straight piece of pipe, 1/2" NPS and let that represent the MAWP of the plug?

First, referring to B16.11 (which I found in about 2 mins on the net) there is no Class 3000 plug, they are Class 6000 only. See Note 1 to Table 1B.

Second the wall corresponding to Class 6000 is XXS, per Table 2, 0.294 inch.

Third, the minimum thickness of a threaded component is 0.31 inch, using the smaller values of Tables 5A and 6A. Since this is larger than XXS pipe, I'd just use that value, neglecting wall tolerance and threading allowance.

Fourth, using the allowable stress for a seamless product, E = 1.0, I'd calculate the MAWP of the 0.840 OD x 0.294 pipe, deducting corrosion allowance if applicable.

I mean, if I was going to do it at all.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

SnTMan, no calculation is required for plugs

See note (1) in Table 6:
Plugs and bushings are not identified by class designation. They may be used for ratings up through
Class 6000 designation.

Regards
r6155

 

[SnTMan]

r6155, see the first sentence of my post. Then see the last.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

Incorrect designation: NPS ½ hex head plug class 6000

Correct designation: NPS ½ hex head plug

Regards
r6155

 

[anolan23]

Thank you all for your help

Do I need the fitting to conform to B16.11 in order to use it on a Section VIII vessel? Or can this part qualify as a threaded rod or bar? The plug I have now is a solid piece.

I'm trying to avoid buying a B16.11 plug if I can

 

[SnTMan]

anolan23, I don't know what you have now, but if you use a plug not conforming to B16.11 it is on you to demonstrate it complies with Sec VIII, Div 1. See UG-11.

How much can a 1/2" B16.11 plug cost?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[anolan23]

SnTMan,

We sell a lot of instrumentation that is usually asked for B31.1 and B31.3, but recently we received our U and UM stamp certification.
Cost matters if you sell a bunch like we are. In fact, it may be cheaper for the B16.11 plug. If so, I'll look into it and make the B16.11 a standard across the board. The engineering dept here is dwindling with layoffs...

 

[SnTMan]

anolan23, I don't know if the piping codes have a section that corresponds to UG-44, but I'd be surprised if they don't. After all, they are the same parts.

That said, if you manufacture fittings that comply in all respects with B16.11, then they are B16.11 fittings and can be used as such.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand