pressure tmin for thick piping
pressure tmin for thick piping
(OP)
Hi all,
I have to calculate the tmin for a 1/2 inch XS pipe at 150 psi and 100F. I'm using ASME b31.3 however my t is greater than D/6 indicating that I need to use an equation for thick wall I believe.
Now in the code there is a provision to calculate the coefficient Y for t > D/6. Does that imply that I am to use the same equation for thin wall piping or use Lame's equations ?
The line is just a branch connection going to an analyzer so there aren't any thermal stresses or fatigue to generally heavy loads on it.
Using the thin wall equation, I get t would be 0.003 inches + corrosion allowance of 0.05 inches = 0.053 inch.
I have to calculate the tmin for a 1/2 inch XS pipe at 150 psi and 100F. I'm using ASME b31.3 however my t is greater than D/6 indicating that I need to use an equation for thick wall I believe.
Now in the code there is a provision to calculate the coefficient Y for t > D/6. Does that imply that I am to use the same equation for thin wall piping or use Lame's equations ?
The line is just a branch connection going to an analyzer so there aren't any thermal stresses or fatigue to generally heavy loads on it.
Using the thin wall equation, I get t would be 0.003 inches + corrosion allowance of 0.05 inches = 0.053 inch.





RE: pressure tmin for thick piping
Now, invert the problem, you have a low temperature system 100F, right?
You have a specified pressure (150 psig), right?
What is the calculated wall thickness?
Does a 1/2 dia XS carbon steel pipe meet or exceed that wall thickness you calculated?
RE: pressure tmin for thick piping
All you have to do is make sure that your t min is < t of a 1/2" XS pipe.
1/2" XS is 0.147" thick. You've calculated 0.053". You're good to go. The thin wall equation normally gives a bigger, but seeing as this is 0.003", then I think you're OK.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: pressure tmin for thick piping
I was mainly asking as I was trying to figure out the plant designer's reasoning for using schedule XS for a 1/2 inch piping of such low pressure and temperature. As XS is around 0.15 inches i.e. 50 x tmin.
As this line is just a branch going to an instrument, there wouldn't be any excessive bending or cantilever sections, so I was wondering if a different thickness equation was required.
RE: pressure tmin for thick piping
And sometimes, it is because they didn't think.
RE: pressure tmin for thick piping
Hence many designers will simply use XS or sched 80 (same thing at 1/2") as a minimum for strength purposes.
Sure, in theory you only need a paper thin piece of pie, but it would collapse as soon as you tried to lift it, clamp it, attach anything or blow on it.
The thickness is pretty low ( 3.7mm). there's simply no long term benefit to reducing it any further.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: pressure tmin for thick piping
RE: pressure tmin for thick piping
There is a corrosion allowance of 0.05 inches specified by the plant designer based on the service.
RE: pressure tmin for thick piping
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: pressure tmin for thick piping
What I meant is that normally when doing something like calculating the remaining life based on some corrosion rate, if you calculate a structural thickness requirement as more than the thickness due to pressure, the structural one becomes the tmin.
But I am guessing that for these things, the pressure t-min is sufficient.
Also ultra-pipe produces a structural tmin which just subtracts the corrosion allowance and mill tolerance from the nominal thickness of the piping that you input.