must have load cases for stress analysis of a typical piping system _ what is piping
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The main objectives of stress analy sis is to ensure
A. Structural Integrity (Design adequacy for the pressure of the carry ing fluid,Failure against
various loading in the life cy cle and Limiting stresses below code allowable.)
B. Operational Integrity (Limiting nozzle loads of the connected equipment within allowable
values, Avoiding leakage at joints, Limiting sagging & displacement within allowable values.)
C. Optimal Design (Avoiding
What is PipingAn attempt to explain process piping engineering basics in detail to help all the process
piping engineering professionals around the world.
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1 0th December 201 3 Anup Caesar II 4 Comments
Must have Load cases for stress analysis
of a typical piping system using Caesar
II
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excessive flexibility and also high
loads on supporting structures. Aim
towards an optimal design for both
piping and structure.)
To meet these objectives several
load cases are required during stress
analy sis. This article will guide all
the beginners with the methodology
to build several load cases which
will be required for stress analy sis.
In this article we will use following
notations for building load cases:
WW=water filled weight of piping sy stem,
HP=Hy drotest Pressure,
W=weight of pipe including content and insulation,
P1=Internal Design pressure,
T1=Operating temperature,
T2=Maximum temperature,
T3= Minimum temperature,
WIN1, WIN2, WIN3 AND WIN4: wind loads acting in some specific direction,
U1, U2, U3 AND U4: uniform (seismic) loads acting in some specific direction.
While analy sis at a minimum the stress check is required for the below mentioned cases:
a. Hy drotesting case: Pipelines are normally hy drotested before actual operation to
ensure absence of leakage. Water is used as the testing medium. So during this situation pipe
will be subjected to water weight and hy drotest pressure.
Accordingly our first load case in Caesar II will be as mentioned below
1. WW+HP HY D
b. Operating case: When operation starts working fluid will flow through the piping at a
temperature and pressure. So accordingly our operating load cases will be as mentioned
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below:
2. W+T1+P1 OPE for operating temperature case
3. W+T2+P1 OPE for maximum sy stem temperature case
4. W+T3+P1 OPE for minimum sy stem temperature case
c. Sustained Case: Sustained loads will ex ist throughout the plant operation. Weight and
pressure are known as sustained loads. So our sustained load case will be as follows:
5. W+P1 SUS
d. Occasional Cases: Piping may be subjected to occassional wind and seismic forces. So
to check stresses in those situations we have to build the
following load cases:
6. W+T1+P1+WIN1 OPE Considering wind from +X direction
7 . W+T1+P1+WIN2 OPE Considering wind from -X direction
8. W+T1+P1+WIN3 OPE Considering wind from +z direction
9. W+T1+P1+WIN4 OPE Considering wind from +z direction
10. W+T1+P1+U1 OPE Considering seismic from +X direction
11 . W+T1+P1-U1 OPE Considering seismic from +X direction
12 W+T1+P1+U2 OPE Considering seismic from +X direction
13 W+T1+P1-U2 OPE Considering seismic from +X direction
While stress analy sis the above load cases form load case 6 to load case 13 is generated only
to check loads at node points.
To find occasional stresses we need to add pure occassional cases with sustained load and
then compare with code allowable values. Following sets of load cases are built for that
purpose.
14. L6-L2 OCC Pure wind from +X direction
15. L7 -L2 OCC Pure wind from -X direction
16. L8-L2 OCC Pure wind from +z direction
17 . L9-L2 OCC Pure wind from -z direction
18. L10-L2 OCC Pure seismic from +X direction
19. L11-L2 OCC Pure seismic from -X direction
20. L12-L2 OCC Pure seismic from +z direction
21. L13-L2 OCC Pure seismic from -z direction
22. L14+L5 OCC Pure wind+Sustained
23. L15+L5 OCC Pure wind+Sustained
24. L16+L5 OCC Pure wind+Sustained
25. L17 +L5 OCC Pure wind+Sustained
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26. L18+L5 OCC Pure seismic+Sustained
27 . L19+L5 OCC Pure seismic+Sustained
28. L20+L5 OCC Pure seismic+Sustained
29. L21+L5 OCC Pure seismic+Sustained
Load cases from 22 to 29 will be used for checking occasional stresses with respect to code B
31.3 allowable (=1.33 times Sh value from code). Use scalar combination for load cases 22 to
29 above and algebraic combination for others as shown in figure attached below:
e. Expansion Case: Following load cases are required for checking expansion stress range
as per code
30. L2-L5 EXP
31. L3-L5 EXP
32. L4-L5 EXP
33. L3-L4 EXP for complete stress range
The above load cases (from 30 to 33) are used to check expansion stress
The above mentioned load cases are minimum required load cases to analy sis any stress
sy stem. Out of the above load cases the load cases mentioned in point number 1 , 5, and 22-
33 are used for stress check. And load cases mentioned in point number 1 to 13 are used for
checking restraint forces, displacements and nozzle load checking.
Few additional load cases may be required for PSV connected sy stems, Rotary equipment
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connected sy stems.
Seismic and Wind analy sis may not be required every time. So those load cases can be
deleted if the piping sy stem does not fall under the purv iew of seismic and wind analy sis by
project specification. However to perform wind and seismic analy sis proper related data
must have to be entered in Caesar II spreadsheet (Will be discussed in my future posts).
If the stress sy stem involves use of imposed displacements (D) and forces (F) then those
have to be added with the above load cases in the form of D1, D2 or F1 , F2 as applicable.
It is a better practice to keep
1. Hy dro and sustained stresses below 60% of code allowable
2. Expansion and occasional stresses below 80% of code allowable
3. Sustained sagging below 10 mm for process lines and below 3 mm for steam, two phase
and flare lines
4. Design/Maximum displacement below 7 5 mm for unit piping and below 200 mm in rack
piping.
Related posts:
1 . Case Study for Fatigue Analy sis in Caesar II for a ty pical piping sy stem
2. Points to consider while checking a stress sy stem using Caesar II
3. Alignment Check Methodology in Piping Stress Analy sis using Caesar II
4. Stess Analy sis of PSV connected Piping sy stems using Caesar II
5. Step by Step Methods for WRC 107 and WRC 297 Checking in Caesar II
6. Spring hanger selection and design guidelines for a Piping engineer using Caesar II
7 . Stress Analy sis of Pump Piping (Centrifugal) Sy stem using Caesar II
More In Caesar II
Case Study for Fatigue Analysis in Caesar II for a
typical piping system
I have taken up this topic to explain the fatigue analy sis (Click here to
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read the basic article on Fatigue Analy sis) methodology using caesar II…read more →
Points to consider while checking a stress system
using Caesar II
In most of the organization there is a 3 tier process for every stress sy stem for maintaining
quality of analy sed stress sy stems. Normally stress sy stem…read more →
Methods for flange leakage checking by Pressure
Equivalent Method using Caesar II
Few day s back I had published a post on Methods for checking flange
leakage. In that article the I had mentioned the theoritical
background (analy sis…read more →
This article has 4 comments
ddd
Wednesday 18 December 2013, 8:21 am
I couldn’t resist commenting. Exсeptionally well written!
Reply
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Friday 20 December 2013, 6:33 am
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Reply
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