Hello,

Can anybody help me in finding out why operating cases are not getting stress checked for B31.4 code by CARSAR II.It is showing allowable as 0.

Ambient temperature is 30 deg.C. This is metering skid where there will be one stream always at ambient temperature whereas others strems will be at 55 deg.C.

Program was calculating stresses initially when ambient was 0.

Thanks .

Regards,
Anant

It depends on whether the particular pipe element is "restrained" or "unrestrained", and the specific load case. The Code doesn't address all condtions.

Sorry Sir but I couldnt understand your point.Would it be possible to expalin in specific the cause of this error.

This is not an error. The Code does not define a stress or an allowable for both restrained and unrestrained for every load case. Check the Quick Reference Guide for the equations.

For Underground pipe modelling ocurr the same. Could you pls help us?

Because you need yo fill the Fac field as appropiate (1 or 0.001).

Fac

B31.4. Amount the pipeline may be considered under complete axial restraint, i.e. long and buried. This option is used primarily when the user is adding bending stresses to the stresses already developed in the pipeline due to its buried restraint. This condition occurs when, for example a branch is tieing into a long buried header and the soil supports are not modeled. The equation for stress in CAESAR II is:

Stress = (Fac) x abs[ Ea(T2-T1) + (1-n) Shoop ] + (SE + SL)(1-Fac)

Where:

E = elastic modulus
a = thermal expansion coefficient per degree
T2 = operating temperature
T1 = ambient temperature
n = Poisson's ratio
Shoop = hoop stress in the pipe.
SE = expansion stress due to bending
SL = sustained stress due to pressure.

Fac should be a number between zero and one. One, when the pipe is fully restrained, i.e. buried for a long distance. Zero when the pipe is subject to no buried axial restraint. The default value for Fac is 0.0. Note that when Fac is 0.001, this indicates to CAESAR II that the pipe is buried but that the soil supports have been modeled. This will cause the hoop stress component, rather than the longitudinal stress, to be added to the operating stresses, conforming to the spirit of the restrained line stress calculation above.