Hi, I have some doubts regarding the way Caesar II computes the code stress.
According with the Quick Reference Guide:

1) If FAC = 1.0 (fully restrained pipe)
FAC*abs(E a dT - uShoop) + Shoop < 0.9(Syield) (OPE)

2) If FAC = 0.001 (buried, but soil restraints modeled)
Fax/A - uShoop + Sb + Shoop < 0.9(Syield) (OPE)

3) If FAC = 0 (fully above ground)
Slp + Fax/A +Sb + Shoop < 0.9(Syield) (OPE)

The formula in 1) is the same shown in the code, but i don´t understand how is derived the formula in point 2).
Also i can´t see from wich part of the code is derived formula in point 3). Furthermore, I'm performing a stress analysis of a scraper trap line, and the code stress computed for above ground pipe is: Slp+Sb and the allowables are zero.
Also allowables are zero for under ground pipe with soil restraints modeled.

I hope anyone can clarify this.

Best Regards.

Diego Lorenzo

The Codes provide an equation for the longitudinal stress of fully restrained lines: Sl = E * alpha * (t2-t1) – v * Shoop
For a given pressure, temperatures, and material characteristics, this produces a constant value of Sl. The geometry, soil properties, and other characteristics of the piping system are irrelevant, as long as the system is “fully restrained”.

The Codes also state that “the net longitudinal stress becomes compressive for moderate increases of t2 and that according to the commonly used maximum shear theory of failure, this compressive stress adds directly to the hoop stress to increase the equivalent tensile stress available to cause yielding. As specified in paragraph 402.3.2(c), this equivalent tensile stress shall not be allowed to exceed 90% of yield”. This leads to the first equation found in the CAESAR II Quick Reference Guide for B31.4 and Z662 [note that adding “E * alpha * (t2-t1) – v * Shoop” to “Shoop” makes the equation “Sl = E * alpha * (t2-t1) + (1 – v) * Shoop”].

The equation provided in the “Help System” for FAC is a summarization of what happens in the pipe, for less than 100% restraint (if that is possible). In that case we “blend” the “restrained” calculation with the “unrestrained” calculation, according to the degree of restraint (indicated by “FAC”). For unrestrained pipe (i.e., FAC = 0.0) the first term (discussed in 1 above) disappears, while for restrained pipe (FAC = 1.0) the second term goes to zero. If the user wants, for some reason, to indicate less than 100% restraint then we suspect that some bending stresses will come into play (however we do not recommend doing such a thing).

Note that there is a special case (FAC = 0.001) that indicates that the model has passed through the buried pipe modeler, so degree of restraint will be less than 100%, and based upon the stiffness of soil restraints. In this case there will be a combination of axial and bending stresses – CAESAR II will calculate stresses and allowable in a form similar to that described in (1) above whenever the net axial force is compression (which is the underlying intent of the restrained equation).

Richard, first of all thank you four your quick reply. I wanto to apologize for posting the same thread two times, that was due to internet problems.
Let me confirm if i understood your explanation:

-If FAC = 1.0, then:

E*alpha*(T2-T1)+(1-v)*Shoop < 0.9 Syield

-If FAC = 0.0, then:

Slp + Fax/A + Sb < 0.9 Syield , (if Slp + Fax/A is compressive).

This means that if this stress is not compressive the allowables are zero?

I'm still confused about the case when the model is buried. I call the stress extended report and I´m looking at the Static Output Processor - Stress Extended Report and can´t find the way to combine the stress in order to obtain the code stress computed by Caesar.

Another question..supose that part of the line under analysis is buried and the soil is modeled. Do i have to indicate the value FAC = 1.0 where i consider the line fully restrained?

In general, you cannot take the component stresses (axial, bending, etc) and determine the Code Stress.

Actually if you use the "buried modeler", you want to leave FAC set to 0.0001 so that CAESAR II determines restrained versus unrestrained. However, if you want to force the issue, yes you can reset the value of FAC. Just be aware this is a "duplicated" value just like everything else on the "Allowable Stress" dialog.