Structural Analysis of Piping And Pipeline Systems With Soil Pipe interaction Using Caesar II BY – DUSHYANT VARSHNEY
Dec 04, 2014
Structural Analysis of Piping And Pipeline Systems With Soil Pipe interaction Using Caesar II
BY DUSHYANT VARSHNEY
PRESENTATION
OUTLINE
MODULE-3 RESULTS INTERPRETATION MODULE-2 BURIED SYSTEM MODELING AND ANALYSIS Seminal concepts Documents required for analysis Data Collection and Extraction How to model soil pipe interaction Understanding the ALA guidelines Virtual Anchor Length A case study What to look at the report The code compliance The displacements and interference The lift off The loads at supports Nozzle evaluation
MODULE-1 GETTING STARTED
A quick run through with Caesar GUI Understanding Caesar Setup File Caesar modeling procedure a Video Tutorial
Module-1 GETTING STARTED WITH CAESAR
A QUICK RUN THROUGH-
CAESAR II GUI
1) To start Caeser double click on the icon located on the desktop and if you cant find the icon then navigate through the path C:\Programe Files\Intergraph CAS\Caesar II 5.30 and find the file named c2.exe, double click on it and the Caesar gets started 2) When Caesar starts you see the following screens one by one
3) Click on close to go on the Caesar Main Menu
3) Click on the menu File the following screen appears this is called Piping input spread sheet
5) Then click on the sub menu New, the following screen appears which asks for file name and path to save the FILE
6) When you are done with the file name and the path where to save it; a screen appears which shows the default English unit system of the Caesar. If you are accustomed to work in English units you can go on and start working but if you are not then need not to worry you can change the unit system any time. This being a new job we need to first ok and then exit the program to change the unit file.
7) To change the unit click on the menu Tools and then submenu configure /setup as shown in the following screen shot-
8) After clicking on configure /setup the following configuration editor window appears-
9) In this editor select the option database definitions on the left pane and on the right pane you see the current unit file which is at present the English file, refer the attached screenshot.
10)Click on the option button on the right pane and you find the various unit systems select the one which you are accustomed to use moreover you can make your own unit file with your working unit system.
Caesar II Main Menu Tool BarsStandard Tool Bar
Caesar II Piping Input Spread Sheet Tool BarsNavigation Tool Bar Input Tool Bar Caesar II Tool Bar Legends Tool Bar Reset and Refresh Tool Bar Standard Operators Tool Bar
Plot Tools BarStandard Views Tool Bar Display Options Tool Bar List Tool Bar Block Operations Tool Bar Standard Tool Bar Auxiliary Tools Tool Bar Edit Tools Tool Bar Edit Mode Tool Bar Wizard Tool Bar Organisation Tool Bar Markups Tool Bar Cutting Planes Tool Bar CADWorx Tool Bar
UNDERSTANDING THE
CAESAR SETUP FILE
The Caesar behavior depends upon a file named caesar.cfg. The configuration or setup file contains directives that dictate how CAESAR II will operate on a particular computer and how it will perform a particular analysis. Each time CAESAR II starts, the configuration file caesar.cfg is read from the current data directory. If this file is not found in the current data directory, the installation directory is searched for the configuration file. If the configuration file is not found, a fatal error will be generated and CAESAR II will terminate The caesar.cfg file is created with every new job The caesar.cfg file can be generated by selecting TOOLS/CONFIGURE/SETUP (or the Configure button from the toolbar) from the CAESAR II Main menu Important: The caesar.cfg file may vary from machine to machine and many of the setup directives modify the analysis. Do not expect the same input file to produce identical results between machines unless the setup files are identical. It is advised that a copy of the setup file be archived with input and output data so that identical reruns can be made. The units file, if modified by the user, would also need to be identical if the same results are to be produced.
The following screen shot shows the Caesar setup editor
The various options which can be changed to control the Caesar behavior are discussed up next Computational ControlConvergence TolerancesDecomposition Singularity Tolerance Friction Angle Variation Friction Normal Force Variation Friction Slide Multiplier Friction Stiffness Rod Incremental (Degrees) Rod Tolerance (Degrees)
Input Spreadsheet DefaultsAlpha Tolerance Coefficient of Friction Default Rotational Restraint Stiffness Default Translational Restraint Stiffness Hanger Default Restraint Stiffness Minimum Wall Mill Tolerance New Job Ambient Temperature New Job Bourdon Pressure
MiscellaneousBend Axial Shape Ignore Spring Hanger Stiffness Include Insulation In Hydro Test Include Spring Hanger Stiffness In Hanger OPE Travel Case Incore Numerical Check Missing Mass ZPA Use Pressure Stiffening On Bends WRC-107 Interpolation Method WRC-107 Version
Database DefinitionsDatabasesAlternate Caesar II Distributed Data Path Default Spring Hanger Table Expansion Joints Load Case Templates Piping Size Specification Structural Data Base Units File Name User Material Database File Name Valve/ Flange File Location Valves And Flanges
ODBC SettingsAppend Rerun To Existing Data Enable Data Export To ODBS Compliant Databases ODBC Database Filename
FRP PropertiesMaterial PropertiesAxial Modulus Of Elasticity Axial Strain FRP Alpha FRP Density FRP Laminate Type FRP Property Data File Ratio Shear Modulus
SettingsBS 7159 Pressure Stiffening Exclude X2 From UKODA Bending Stress Use FRP Flexibilities Use FRP SIFs
Geometry Directives
BendsBend Length Attachment Percent Maximum Allowable Bend Angle Minimum Allowable Bend Angle Minimum Angle To Adjacent Bend Point
Input ItemsAuto Node Number Increment Connect Geometry Through C-node Horizontal Thermal Bowing Tolerance Loop Closure Tolerance Z-axis Vertical
Miscellaneous Options Input ItemsAuto Save Time Interval Disable File/Open Graphic Thumbnail Disable Undo/Redo Ability Dynamic Example Input Text Enable Auto Save Prompted Auto Save
Output ItemsDisplacements Report Sorted By Nodes Output Reports By Load Cases Output Table Of Contents Time History Animation
System Level ItemsCompress Caesar Ii Files Memory Allocated User ID
SIFs and Stresses Advanced SettingsClass 1 Branch Flexibility Use Schinder Use WRC 329
Code Specific SettingsB31.1 Reduced Z Fixed B31.1/B31.3 Verified Welding/ Contour Tees B31.3 Sec 319.2.3c Saxial B31.3 Sustained SIF Multiplier EN 13480/CODETI Use In-plane/Out-plane SIF
Module-2 BURIED SYSTEM MODELING AND ANALYSIS
SEMINAL
CONCEPTS
What is stress ! Quantitatively, Stress is a measure of the average force per unit area of a surface within the body on which
forces act, the same as pressure However there is a basic difference between stress and pressure STRESS is a measure of the internal forces acting within a deformed body. These internal forces arise as a reaction to external forces applied on the body. The reaction to the deformation is based on the elasticity of the material. Stress =Strain X Modulus of Elasticity (E) Thus stress is based on material property unlike pressure and will occur only when there will be resistance to strain
What is strain !STRAIN is a measure of deformation representing the displacement between particles in the body relative to a reference length. It is expressed as the ratio of total deformation to the initial dimension of the material body in which the forces are being applied. e= L/L STRAIN may occur due to Direct application of External force Change of Temperature Nature of induced stress
The code divides the system into the following two types Restrained system The system in which soil or supports prevent axial displacement of flexure at bends is restrained. Restrained system may include the following
(1) Straight sections of buried piping(2) Bends and adjacent piping buried in stiff or consolidate soil (3) sections of aboveground piping on rigid supports Unrestrained system Piping that is freed to displace axially or flex at bends is unrestrained. Unrestrained system may include the following (1) Aboveground piping that is configured to accommodate thermal expansion or anchor movements through flexibility Code requirements The ASME B31.8 essentially limits the stresses as following
B31.8Longitudinal stresses
(a) The longitudinal stress due to internal pressure in restrained pipelines is Sp =0.3SH (b) The longitudinal stress due to internal pressure in unrestrained pipeline is Sp =0.5SH (c) The longitudinal stress due to thermal expansion in restrained pipe is ST = E(T1 T2)
(d) The bending stress due to weight or other external loads isSB = M/Z The net longitudinal stresses in restrained pipe are SL = S P + S T + S X + S B Where SX is stress due to any other external force The maximum permitted value of |SL| is 0.9ST Where S is the specified minimum yield strength and T is the temperature de rating factorExpansion stress
SE = ME/Z ME = [(iiMi)2 + (ioMo)2 + Mt2]1/2 SA = f [1.25 (Sc + Sh) SL] And SE> SA
DOCUMENTS REQUIRED
FOR ANALYSIS
To start the analysis we need to have the following documents to extract the desired information Piping/Pipeline design basis Piping/Pipeline Material specification Piping process line list Alignment sheet Station layout (GAD) Approach drawing Station ISOs Geotechnical investigation report Equipment data sheet
DATA COLLECTION
AND EXTRACTION
So we all set to start the analysis but for that the data collection and extraction is very necessary. So where to look at for the data; in the previous slide we went through the documents necessary for analysis. We shall scan each document one by one for what data can we extract from these Piping/Pipeline design basis To extract the pipeline/ piping system analysis parameters like pressure, temperature, WT etc.
Piping/Pipeline Material specification To extract the MoC of the pipeline/piping system
Piping process line list This document gives all the details of piping system line wise like design pressure, temperature, operating pressure and temperature fluid density etc.
Alignment sheet Station layout (GAD) Approach drawing All these drawings help to have the geometry of the system
ISOs This is used for node numbering and dimensioning for stress analysis
Geotechnical investigation report This report is used to extract various soil features to model the soil pipe interaction
Equipment data sheet To extract the dimensional and geometrical features to model the system
PIPE SOIL
INTERACTION
What is Pipe-Soil Interaction? Behavior of buried pipeline in the surrounding soil Pipe and soil together form an engineered system
How to undertake this scenario? We can do it by modeling the pipe soil interaction mathematically
How to model the scenario?We can take up this scenario by any two of the following industry accepted methods ALA guidelines Pengs Method
ALA Method Vs Peng Method ALA METHOD PENGs METHOD
Based on laboratory and field Based on theoretical soil experimental investigations mechanics Advanced estimation Advanced Caesar II Widely applied soil modeler Preliminary estimation in Basic Soil Caesar II Modeler in
recognized
and Not so widely recognized and applied
What can happen if not taken correctly? Pipe soil interaction estimation is very important in onshore/offshore pipeline design if not taken up well this may lead to serious problems as shown below
Upheaval buckle of 1020 mm pipeline in Uzbekistan
A pipeline moved transversely
Actual Soil Pipe system Vs Analytical discrete Soil Pipe system
ALA Or PENG
UNDERSTANDING THE
ALA GUIDE LINES
Assumptions of ALA Guidelines The soil resistance is idealized as elastic perfectly plastic springs The soil bed which acts as a continuous support is idealized as distributed soil resistance and is modeled as Winkler foundation i.e. the soil support is modeled as a series of discrete springs which provide a specified resistance per unit length of pipe The guidelines equations are based on buried pipelines in uniform soil conditions The guidelines assume that the force exerted by the soil on the pipe line is constant once it reaches the maximum value Cautions Caution shall be taken while applying these guidelines for offshore design Types of Soil restraints
Actual Vs Ideal behavior
Actual behavior of pipe- soil system
Idealized ElastoPlastic behavior of pipe- soil system
Axial Soil Spring
K k00 1 Sin b 1 sin
Lateral Soil Spring
Vertical Uplift Soil Spring
Vertical Bearing Soil Spring
Data Required for soil restraints calculation Pipe Diameter(OD) Soil cover to top of pipe Soil cohesion Unit weight of soil Angle of internal friction of soil Friction between soil and pipe coating Values of a, b, c, d and e corresponding to angle of internal friction (ALA, 2001, Appendix B)
VIRTUAL ANCHOR
LENGTH
Defining a boundary condition is must while analyzing the pipeline/piping systems. In piping we can have a real physical boundary to isolate the systems but in case of pipelines which are of 1000 miles long a real physical boundary to appear is less prone. Sometimes we could have an anchor block due to some practical reasons but most of the times we dont have such boundary When we dont have real boundary then we take help of virtual boundary This virtual boundary is called virtual anchor And the straight length which gives this virtual anchor is called as virtual anchor length
Virtual Anchor Length Calculation Anchor force = A S Where A is the cross sectional area of the pipe and S being the stress generated = A e E = A E T 2 T 1 0.5 S HP Virtual Anchor Length La =A E T 2 T 1 0.5 S HP f
Where f is the soil resistance force per unit length
A CASE
STUDY
Pipeline Mechanical Properties Description : Sweet Gas Pipeline Line No(s) : 30-GP-61-7931-C06L Start Location : ARAB-D (Launcher) End Location : Up to virtual Anchor after Hot Induction Bends In Burial Dia. Nomin. : 30 Wall Thickness : 14.3/11.9 Design Factor : 00.6/0.72 OD : 762.0 Line type : LSAW Product : Sweet Gas Design pressure : 74.5 Bar-g MOP : 58 Bar-g Hydro Test Press : 1.5 x DP Des. Temp. : 85 C Ope. Temp. : 57.0 63.4 C Min. Des. Temp. : -29 C Install. Temp. : 21 C Material : CS API X65, PSL2 Corr. Allow. : 3.0 mm Fluid Spe. Gravity : 44.5 Kg/m3
Friction Coefficient Soil Density Buried Depth to Top of Pipe Friction Angle Overburden Compaction Multiplier Yield Displacement Factor(>0) Therm. Exp. Coeff. (L/L/deg C ) Temp. Change, Install-Operating
: : : : : : : :
0.57 1650 kg/m3 0.6 to 2.0 m 36 7.6 0.015 (Caesar II Default Value) 11.21 42
RESULTS
INTERPRETATION
What to look at the report So now we have Caesar reports but how to claim the structural integrity of the system. To predict the integrity of the system we look at the following reports of the Caesar output The code compliance The very first thing that we need to check is the code compliance if this this is satisfied then it implies that the system has the stresses which are lower than the allowed by the code The displacements and interference This report gives us the displacement under various load conditions and we have to scan this report for any unaccepted displacements The lift off Sometimes in the operating case the weight taking support which was engaged in the sustained case to the pipe may disengage in the operating case and thus increasing the stresses so this condition must be avoided by either relocating or trying to fix it in the moving direction also The loads at supports Supports at loads are used to design the support system if these support loads are within he allowable limit then its OK otherwise try to reduce the loads if possible
Nozzle evaluation The nozzles of an equipment are very delicate part of the overall system and that is why we check the loadings on the nozzles if this equipment is covered under any standard like API 610 etc then we compare the nozzle loads as per the allowable limits otherwise we can take help of WRC bulletins