1 thickness for 2 standards??? 2

[2ndchild]

hi,

I have two wall thickness formula's for piping:
- The 1st one is according to the ASME B31.3 i.e.
t = f(working pressure P, external diameter D, design stress S, weld factor z); S,D,P and z are given.
-The 2nd one is according to the EN 13480-3 i.e.
t = f(allowable pressure Ps, outside or inside diameter Do or Di, allowable stress f and weld factor z)

The question is:
How can I use the data given by the first formula for the calculation of the thickness according to the 2nd formula?
(I have not any data or document conserning the Euro Standards)
If in the answer, you refer to an other formula, please quote it.

regards,

 

[FIF99]

You can't, and why should you.

For comparisson, checking which one is more conservative, you should note that design stresses should be determined according to the design code to which you make your calcs.

It's not allowed to use the design stress of ASME B31.3 within the EuroNorm or the other way around. In other words, mixing of codes is prohibited.

Regards.

 

[2ndchild]

I know that I cannot mixing two standards,
but what can I do? I must calculate the thickness according to EN 13480-3 but I have not the max. allow. pressure, and for calculating the max. allow. pressure, I need the thickness!
I need some help
thanks in advance for any help
regards,

 

[FIF99]

I assume you do have process conditions such as a system pressure and temperature, out of equipment (e.g. pump) or an existing piping system.

Out of that we normally verify/determine a pressure temperature rating out of the ASME B16.5. A flange connection is the weakest part of a piping system.

Using the ASME B16.5 limits as parameters for the wall calculation we assess the minimum required wall for pipe, e.g. according ASME B31.3. Off course we use the Stress values as specified in ASME B31.3.
Than we determine a standard commercial wall thickness for piping(ASME B36.10/ASME B36.19/ or API 5L).
Out of that we determine the MAWP (maximum allowable working pressure).

I think you would only need the ASME B16.5 limits!
Do you have system conditions and/or type of process application?
Do you have the grade of material?
Thats what you need as a minimum before you get started.

Regards.

 

[2ndchild]

-Pipework material: the grades/types used are:
ASTM A106 gr B/ A333 gr 6 carbon steel pipes
-the pressure formula is:
P = (20*f*z*e)/D (for 20C and 100C) or,
P = (20*f*z)/(D/e + z - 2) (for T>120C)
I think i can apply the formula for carbon steel pipes (it's not specify in the EN13480-3)
you said I cannot mixing two standards, so why I have to use the ASME B16.5 limits as parameters for the wall calculation?
what do you mean by "system conditions"?
thank you very much for your help
regards

 

[FIF99]

ASME B31.3 and ASME B16.5 are both ASME codes, so there is no mixing.
ASME B16.5 is specifying maximum allowable pressures for flange connections per rating, as applicable in piping systems designed according ASME B31.3.
You should not calculate the system pressure from the wall thickness formula. The MAWP can be made however, but will be used to verify a system for suitability (extra check).

In your situation material group 1.1 applies (see the tables in ASME B16.5). Do you have flanges in your system? If so, which pressure rating (150#, 300#, 6003 or higher)? E.g. for 150# the maximum pressure is 19.7 at room temp., you do not need to calculate the max. pressure.

With system condition I mean; is there a pump pressure, is a safety valve installed with a set pressure, is it connected to an existing piping system with a design pressure etc.?
From there it's pretty easy to assess the minimum required wall thickness?

Succes.

 

[2ndchild]

hi,
I use a pipework composed of a piping body and two kinds of connectors:
- a connector using a hammer union wing nut
- a clamp connector
for the first one, for example, two situations exist:
1/ low pressure hammer union pipework: we use A106grB/A333gr6, min. design stress is 20,000 psi
2/ High pressure hammer union pipework: we use AISI 4130 with the min. design stress is 48,000 psi

API 6A flanges, seal rings...are also used
-the temp. class is: -20F to 350F (-30C to 180C)

so, I can use the design stress given. isn't it?
but how can I calculate the max. allowable pressure without using the thickness formula?
thanks

 

[StressGuy]

2ndchild,

I'm not personally familiar with the EN standard, but I think you are getting mixed up by your pressure equation and your thickness equation.

You either need to have a design pressure as a known, or a wall thickness as a known. Typically, as in the case of the B31.3 wall thickness equation, the design pressure must be given to solve the equation. A process/chemical engineer typically determines this information. I think this is what you need to seek out (along with the design temperature, which should also come from the process engineer).

As for the pressure equation, again I don't know the EN code specifically, typically, you would use such an equation to determine the maximum pressure allowable when you know the wall thickness and design temperature of the pipe in quesion. I don't think you need to be using the pressure equation for what you are trying to do.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.