Pipe Thickness 3

[yanuarsaja]

Hi,
i found in some calculation procedure/criteria from various spec to calculate thickness of piping:
1.
a. For Class 150 and 300 systems: The maximum pressure rating in accordance to the
Temperature- Pressure Rating Tables in ASME B16.5 is used.
b. For Class 600 and above: Design Pressure based on the Temperature-Pressure range
for each piping material class.

and

2.
Wall thickness calculations shall be based on the following:
(a) For 12” and smaller: To use TEMPERATURE-PRESSURE RANGE of each piping material class
specified in ASME B16.5.
(b) For 14” and larger: To use most severe condition of each line.

the both methode are different, 1 based on rating, and the other based on size, (both are comply with 31.3)

what is normally used in the Industry to determine thickness?
thankyou.

Yanuar

 

[racookpe1978]

Use the appropriate formula and Code, based on the required pressure and temperature, service conditions and material selected. Add in corrosion allowance and margins.

Then you buy what is available larger than the minimum.

 

[LittleInch]

Yanuar,

There is no "normal", that's why design engineers exist.

Both of these procedures you list are a crude attempt to provide design guidance.

In reality for piping (B 31.3) using standard flanges ratings (B 16.5) smaller pipes (<12") and lower pressure rated pipes (#300 and lower), when you calculate the wall thickness you can get ridiculously thin pipe if, say, you used a design pressure of 3 barg instead of the max class rating of 19 barg. Hence the pipe needs to be thicker in order to be practical. Some companies decide that rather than having multiple different thicknesses of the same size pipe leading to potential for delay if the right size isn't there or using thinner pipe than you should, they will just specify all pipes to be capable of the maximum flange rating for whichever class of piping you have. They therefore pay more than they should for many pipes whose design pressure is less than the maximum flange rating, but decide that that price is worth it and if things change later on then the pipe is good enough for the max flange rating.

The alternative often used is to have a rather thick piping manual which has multiple different pipe classes for the same pressure rating, but calls up different wall thicknesses for different duties and temperatures. Some will have CA added, some will be CRA material, some high temperature, some low temp, some one design pressure, the other a different design pressure - depends on the complexity of the plant you're designing.

There is no standard for this and it will depend on how big your plant is, what the design philosophy is for piping and whether you're in a competitive situation or not.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[MJCronin]

Good explanation LittleInch.... Kudos to you !

Perhaps this would be a good time to introduce to the OP the concept of "Piping Line Class" and how it is to be used.

MJCronin
Sr. Process Engineer

 

[yanuarsaja]

Hi LittleInch,
Thank you for a great explanation.

Yes MJCronin.. This will be a good start for me to understand about pipe class development.

Thanks all.
Yanuar.

 

[MickMc]

Yanuar,

As touched on by littleInch typically client piping class standards in my experience may stipulate that wall thickness is calculated to B16.5 P/T ratings up to maybe Class 900/1500 and pipes purchased to the nearest standardised wall thickness above the calculated as per ASME B36.10/19. With higher pressures you may be outwith these standardised ranges and/or it is more economical to calculate to design pressure and in all likelyhood to have thinner wall than the maximum as per Class 2500 or 1000 PSI etc. Also again for economical reasons wall thickness of say NPS 24 and above will also be calculated based on design pressure.