Dear members

I am working in a simulation of a buried system. I have some problems in two bends (buried) because of thermal expansion (195 F), I can’t change the pipe (24” SCH STD, API 5L X42) to solve my problem, I want to try using different soil properties, (another kind of soil) to avoid my over stresses bends, (It could happen, if the pipe have less restrictions in bends) but I don’t know where I can find the properties of more kinds of soils. Especially the properties that CAESAR needs:

FRICTION COEFFICIENT
SOIL DENSITY
FRICTION ANGLE

I really appreciate if you may help me.
Thanks a lot.

Gustavo Cuervo
Oxy. Occidental de Colombia, Inc.
Bogotá - Colombia

Dear Gustavo,

Go through Soil Mechanics text books.

Following books will help.

1.Soil Properties : Testing,Measurement and evaluation by Cheng Liu and Jack Evett

ISBN 0-13-0200069-7

Publisher : Prentice Hall

2.Soil Mechanics in Engineering Practice by Karl Terzaghi

Publisher : John Wiley & Sons

3.Essence of soil Soil Mechanics and Foundations : Basic Geotechnics by David F Mc Carthy .

Publisher : Prentice Hall.

I hope this helps.

Anindya Bhattacharya

Stress Analyst

Bechtel Corporation

If you have a specific site location for your system, you should have your Geotechnical group obtain soil borings, and through testing determine the necessary analysis parameters.

May be you have already worked on following lines. If not then I may suggest
1- If the bens are in the area near the AG/UG interface and there is soil resisting the horizontal displacement of the riser spool then check the possibility of freeing the riser spool from soil resistance enclosing it in an evacuated pit.
2- Place anchor before the bend to reduce expansion at the bend and thereby reducing soil resistance and stresses in bend
3- if the bend are field located then suggest to replace the bens with smooth field bends having radius of the order of 100-200 m


Also I have concern about the stiffness and ultimate load of Y restraints put by Caesar in buried model, if the soil model # is other than 1 (user defined stiffness). In this case Caesar does not differentiate between the downside and upside of a pipe buried horizontally and places a Y restraint (applicable to both downside and upside) with ultimate load and stiffness calculated from the equations given at pages 11-11 and 11-12 of the user guide. However in my opinion, for -y direction, if the pipe depth is not too much then the ultimate load will be weight of soil column above pipe + shear and friction force experienced by the soil column during upward lift. Due to this I prefer to specify user defined stiffness and ultimate load in buried pipe modeler.


Can anybody point out some reference to understand the equation for Transverse Ultimate Load given in user guide at page 11-11 specially the “Overburden Compaction Mul-tiplier”?

The CAESAR II Buried Pipe Modeler is based on the papers written by L. C. Peng, published in Pipe Line Industry, in 1978. The two articles are:

- Stress analysis methods for underground pipe lines, Part 1, April 1978.
- Stress analysis methods for underground pipe lines, Part 2, May 1978.

A recent study of the CAESAR II/Peng methodology compared to the B31.1 Appendix VII can be found in PVP2002-1271, by Robert Robleto.

American Lifelines Alliance
http://www.americanlifelinesalliance.org/Products.htm#Guidelines

Guideline for the Design of Buried Steel Pipe - July 2001

This guideline presents design provisions to evaluate the integrity of Buried steel pipe for a range of applied loads. It applies to new or existing buried pipe made of carbon or alloy steel; welded pipe; piping designed, fabricated, inspected and tested in accordance with an ASME B31 pressure piping code; and buried pipe and its interface with buildings and equipment.

Leonard@thill.biz
www.thill.biz

Please check the bend angle provided by you. try 5D bends, it may solve ur problem.

Estimado Gustavo Cuervo,
La fase critica de un analisis de flexibilidad de tuberia enterrada es la precisa identificación de las propiedades del suelo, por lo es recomendable realizar un analisis dentro de un rango variable de rigideses y fuerzas ultimas. Normalmente es conveniente obtener los datos del suelo y relleno actuales de un estudio geotecnico. Particularmente, para tu problema de expansion, prueba anclar la linea a una distancia del codo 20 veces el diametro. Tal como lo recomienda L.Peng en su articulo de 1978.

Actualmente tengo el problema de analisar un pipeline el cual posee codos con curvatura no estandar y que ademas estan soportados a lo largo de se curvatura, Como seria el input para este tipo de arreglo?