A106 Pressure-Temperature Rating 1

[ryldbl]

Could someone do me a huge favor and verify my calculation of the pressure rating of A106 Gr. B threaded pipe as per ASME B31.3?

What I get for threaded 2" STD pipe @ 100F is P=1,122 PSI

for threaded 1" STD pipe @ 100F I get P=1,465 PSI

Do these numbers sound right? I am second guessing myself when I read pipe manufacturers tables who rate their PLAIN-END pipe at more than double these values.

Any help you could give would be great. Thanks

 

[metengr]

The specified minimum wall thickness (Tmin) per ASME B31.3 is based on the equation in 304.1.1., Tmin = t + c

t is from equation 3(a) in 304.1.2 and is the pressure design thickness excluding mechanical, corrosion and erosion allowances. These are allowances to compensate for loss of wall thickness in the case of threading or to provide for reinforcement.

You need to factor in your thread depth in addition to the calculated value of pressure design thickness. For example, 2" Sch 40 (standard) carbon steel piping, the design pressure from equation 3(a) at 100 deg F is approximately 2735 psi. This means that straight pipe, 2" Sch 40 under internal pressure can be safely used up to 2735 psi, assuming a nominal wall thickness of 0.154" (with no additional thickness to compensate for threads). You will need to add the depth of the thread to “t” to assure that the equation in 304.1.1 is satisfied for your specific application.


For 1" Sch 40 at 100 deg F, the design pressure is approximately 4402 psi. The same situation would apply, the specified minimum wall thickness equation in 304.1.1 will need to be satisfied, as well.

 

[ryldbl]

Yeah, that's exactly where I'm getting the calculations from. And those are the values I get for straight pipe. My problem is, I'm a manufacturer of fittings with threaded ends, and I'm trying to give pressure ratings. For the equation Tmin = t + c , the value that I am using for "c" is simply "h" from B1.20.1. Is this correct? The reason I'm second guessing my calculations is because the values I am getting are drastically lower than for straight pipe. Am I using the right value?

 

[metengr]

Yes, per ASME B31.1, see page 20, under definition of c.

 

[PAN]

metengr,
From your post on 12-07-05, in case of pipe 2"-Sch. 40, nominal thickness is 0.154". I understand that we also need to subtract with mill tolerance (minus 12.5%) of pipe. Therefore, the maximum design pressure should be decreased to 2,377 psig.

 

[metengr]

correct, PAN