Dear Mr. Ay,

I am performing a stress analysis regarding a high-pressure large bore buried pipe (24” NPS, 225 bar internal pressure).
I am not an experienced Caesar software user. Most of the stress calculations I've accomplished using Pipe-Plus program. However, this program hasn't been designed for buried pipe analysis, so that in order to satisfy the client request, I have to use Caesar program for this special task.

Because Caesar Software Documentation refers to L.C. Peng article, entitled “Stress Analysis Methods for Underground Pipelines” (Pipe Line Industry – 1978), I've studied this paper and I've tried to perform a computer analysis for the basic example treated there.
I've noted significant differences between the article hand calculation results and the computer analysis results (performed with Caesar II). To be more specific, Caesar program run has provided significant lower forces, moments and stresses than there have been found in that paper. Under such circumstances, it would appear that Caesar software results underestimate the actual forces and stresses magnitude developed in the high-pressure large bore piping systems.
I've made further investigations and I've seen that the main reason of these differences is the internal pressure effect neglecting in connection with the forces and moments assessment.
It's true that Caesar takes into account the internal pressure effect for the pressure stresses calculation, but, unfortunately, the axial pressure force effect (the so called “pressure thrust” load) is neglected. In my opinion, this aspect could be an important drawback in connection with the anchor loads calculation, especially for high-pressure large bore pipe analyses.

I've seen that other Caesar program users are also interested in this problem (for instance, see the “Anchor” topic, posted on the 30th of November by P. Alvarez). I've noted also the opinion that, for a complicate piping system, the Pressure Trust load influences (developed at the elbows/bends level or wherever there is a change in direction) will be distributed among the pipe system components, depending on their relative stiffnesses and the suggestion to consider additionally applied pressure P*A (A being the internal pipe flow area) forces on the elbows, in order to estimate these influences.

However, I would like to know your pertinent opinion regarding this subject and, if it's possible, to get some further useful suggestions.

Thank you in advance,

Giorgio Frediani

General Electric – Nuovo Pignone
Florence Office - Italy

1) I believe it is necessary to turn on the <EM>Bourdon Option</em> to obtain the pressure effect you are after. (From the input spreadsheet, go to <em>Special Execution Options</em>, select Bourdon Option #1.)

2) It would be good to get a copy of the recent PVP paper by Robert Robleto discussing buried pipe and CAESAR II. The paper is PVP2002-1271.

RE: additionl reference

AmericanLifelinesAlliance

DESIGN AND REPAIR OF BURIED PIPE
... utility and transportation systems from natural hazards Seismic Design and Retrofit of Piping Systems July 2002

buried_pipe.pdf

americanlifelinesalliance.org