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Trying to calculate wall thickness

Trying to calculate wall thickness

Trying to calculate wall thickness

(OP)
for gas project. I knew which material to use in material specification, but process didn't specify final design temperature and pressure yet.
I got basis allowable stress for 31.3

I don't know where I can design pressure and temperature?

I want to full flange rating to do the calculation, is that means I will use 16.5 pressure-temperature rating table to calculate wall thickness?

thanks in advance for any input

cheers

RE: Trying to calculate wall thickness

yes.  However, most engineers just use a standard schedule for the pipe.  For example, on a 3 inch line, the calculations may come up .125 wall pipe on a ansi class 300 flange, but the pipe used will be sch40, .216 wall.  this is where engineering judgement comes in.

RE: Trying to calculate wall thickness

Wait for process to specify the design pressure and temperature!  Believe me, you don't want to be responsible for designing or buying pipe without those numbers.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Trying to calculate wall thickness

Seriously, the only thing you'll be able to specify without temp. and pressure is what material to use and maybe what size of pipe (if you know the flow rate).

Dan

www.eltronresearch.com
Dan's Blog

RE: Trying to calculate wall thickness

Generally speaking, you the engineer will select an appropriate design pressure and temperature for the system, always a value above worth case operational conditions.

Biginch, in my experience process engineering will give maximum operational pressures and temperatures. I then take these values and add to them using appropriate factors based on the values. I use the CASTI guidbook on B31.3 process piping as a guidline for selecting design pressures and temperatures above the worst operational conditions.

Just my two cents worth.

A question properly stated is a problem half solved.

Always remember, free advice is worth exactly what you pay for it!   

RE: Trying to calculate wall thickness

(OP)
I found one of my client specifications for weld neck flange materials say ASTM A105N design temperature is -20 to 425 C
I use this temperature to proceed my calculation, got all of the pipe2" and is standard wall which is acceptable, right

Below 2" for thread connection, use one level thicker pipe wall which is XS.

is this method ok?

thanks for your input...

RE: Trying to calculate wall thickness

As long as the design pressure doesn't cause a hoop stress higher than the allowable hoop stress and any combined stresses from bending by internal and external loads over the pipe spans and the axial stresses from thermal expansion are less than the allowable combined stress, as per the allowable stesses as given in B31.3 for the material at the design temperature (or range of temperatures) adjusted for fatigue if required, yes, it will be just fine.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Trying to calculate wall thickness

(OP)
Tp = PD/(2*(SEW+PY))  
Tr =  (Tp + CA) / (100-12.5)%          Where 12.5% is Manuf's  undertolerance (for pipes to 24")
I use these 2 equation to calculate how I will know hoop stress and thermal load stress....

need more calculation?

thanks  

RE: Trying to calculate wall thickness

Why not just look in the P/T tables for std. pipe and fittings and set the wall thk. and flg. ratings from the max. allowables in the tables based on the material spec.? No need to reinvent the wheel.  

RE: Trying to calculate wall thickness

Because they're only based on hoop stress.

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

RE: Trying to calculate wall thickness

(OP)
thanks

 

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