MAWP for NPT fittings
MAWP for NPT fittings
(OP)
I have been trying to put this all together for a little while now and I could use you guys' help to get through this.
I am trying to figure out how to calculate the maximum allowable working pressure for NPT threaded fittings. I know the formula P=2St/(D-2yt) can give you the pressure but I am having trouble matching it exactly to some tables I am comparing it to. Let's take for example a 2000#, 1/2", API-5L-B seamless pipe which has an allowable stress of 20,000 psi, OD= .84, nominal thickness=.147, max thread depth of .05714, and assume no corrosion. I get 4680 for MWAP while the chart I am comparing it to comes out with 3678! the formula they use to find t is t=tn*(.875)-C-A where tn is nominal thickness C is corrosion allowance and A is additional thickness required for: threaded pipe=depth of thread. Please help me figure out what I else I need to fix this descrepancy. Thanks, Greg.
I am trying to figure out how to calculate the maximum allowable working pressure for NPT threaded fittings. I know the formula P=2St/(D-2yt) can give you the pressure but I am having trouble matching it exactly to some tables I am comparing it to. Let's take for example a 2000#, 1/2", API-5L-B seamless pipe which has an allowable stress of 20,000 psi, OD= .84, nominal thickness=.147, max thread depth of .05714, and assume no corrosion. I get 4680 for MWAP while the chart I am comparing it to comes out with 3678! the formula they use to find t is t=tn*(.875)-C-A where tn is nominal thickness C is corrosion allowance and A is additional thickness required for: threaded pipe=depth of thread. Please help me figure out what I else I need to fix this descrepancy. Thanks, Greg.





RE: MAWP for NPT fittings
Second, not seeing the table you're looking at, I don't know, but
Is it because you're using t = specified wall thickness - maximum thread depth, but they're calculating (?) the minimum wall thickness at 87.5% of the nominal thickness as mill tolerance and not deducting thread? Are they specifically deducting thread depth somewhere?
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RE: MAWP for NPT fittings
RE: MAWP for NPT fittings
p 304.1.2 Straight Pipe
t = P*D / (2 (Y*P + S*E))
t = (P*d+2c) / (2 (SE-P (1-Y))
Y = (d+2c)/(D+d+2c) for t>D/6
other conditions apply for t<D/6
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RE: MAWP for NPT fittings
RE: MAWP for NPT fittings
RE: MAWP for NPT fittings
Also, what about the pressure and wall thickness formulas found in B31.1 104.1?
RE: MAWP for NPT fittings
It is important to recognize that NO ASME CODE provides equations for determining the required thickness for fittings. Fittings are rated by proof tests and not by equations.
The B31 Code calculations for required wall thickness REALLY DO include allowances for erosion, corrosion, threading, and grooving (for using graylock type fittings). Also, mill tolerances are to be considered for seamless pipe.
Fittings and flanges are rated for coincident application of pressure and TEMPERATURE for various materials.
Regards, John.
RE: MAWP for NPT fittings
RE: MAWP for NPT fittings
The ASME B31 Pressure Piping Codes address pressure design for pipe and refer to other associated Codes and Standards for pressure design of fittings. If you are using a "Standard listed" fitting then the appropriate Standard details the methodology for the fitting's MANUFACTURER to pressure-rate the fitting.
If you were using the ASME B31.3, Process Piping Code you would go to table 326.1 and if the fitting is "listed" there you need do no further calculation - this is one of the reasons for "Standards". The fitting (if it is listed) will have a pressure-temperature rating and if that rating is appropriate for the service of the system you are designing you can use it in systems with the same P?T rating.
Regards, John.
RE: MAWP for NPT fittings
RE: MAWP for NPT fittings
RE: MAWP for NPT fittings
EJL
RE: MAWP for NPT fittings