Pressure rating of NPT Pipe Nipples

[Hutamaki]

How do i calculate the pressure rating of pipe nipples. ASME B31.3 says that i should subtract allowances for threading, where do i find this dimension (thread dimension for subtracting from pipe WT) in ASME B1.20.1?

If i had a 1" SCH 80 seamless nipple (threaded to ASME B1.20.1 NPT) made of A106 Gr B pipe and i want to use it at 20deg C - what would be the pressure rating as per B31.3?

 

[ScottPearson]

I've found that information on standard charts from pipe and fitting suppliers. I'm not sure where to find that on-line or in literature.

I've run across a problem related to this in the past and at the time found this site that details some of what you are asking.

Pipe Thread Link

When you remove pipe wall for threading, you are removing pipe wall thickness and may be below the pressure requirements of the service. A piping spec we were using had this very problem for 1" SCH 40 pipe. We have since switched to SCH 80 for these applications.

Sorry I can't help you on that one but I do know it is something that needs to be taken in to account

 

[TBP]

The "Piping Handbook" by Nayyar, along with some pipefitter's books like IPT's "Pipe Trades Handbook" list the thread depth allowances. For 1/2" & 3/4" pipe, it's 0.0571", for 1" through 2", it's 0.696", and for 2-12" & up, it's 0.1000". Nayyar's book recommends taking a further 0.015" for the tolerance on the dies.

 

[NozzleTwister]

Hutamaki,

I've always used the values in ASME B1.20.1 for thread allowances when doing wall thickness calculations.

Also, be sure to consider Mill Tolerance and Corrosion Allowance as well.

If you just want the pressure rating of a specific nipple diameter and wall thickness that's a simple calc. If you are selecting a nipple for an application, there are other considerations.

The required wall thickness for pressure only is pretty thin. Be sure you have some mechanical strength in the corroded condition. Nipples are often used in places that can see some abuse, for example, vent and drain valves on headers can easily be bumped.

It's not unusual to see sch. 160 or XXS nipples.

Regards,

NozzleTwister
Houston, Texas

 

[abbver98]

I don't think that you can made calculation. I made investigation on this subject and I find those limitations in ASME B31.1 Table 114.2.1 : (taper pipe threads)
3" max. pressure : 400 psi
2" max. pressure : 600 psi
1" max. pressure : 1200 psi
3/4 and smaller max. pressure : 1500 psi
No temperature limitation
if T> 925°F or P>1500 psi ---> seal weld

See also ASME B31.1 114

Hope it helps,
MA

 

[Hutamaki]

B1.20.1 has many drawings and descriptions. For my particular case "1" SCH 80 seamless nipple (threaded to ASME B1.20.1 NPT) made of A106 Gr B pipe " @ 20deg C - what would the pressure rating be from a B31.3 perspective.

Can you show me what values you use and where to find it in B1.20.1?

 

[NozzleTwister]

For the thread allowance, use "Height of Thread", "h", column 22, Table 2 in ASME B1.20.1.

NozzleTwister
Houston, Texas