Comments, Questions, and Answers
Items #1:
Both AutoPIPE and caesar perform the same task of providing the user with stress analysis results based on load cases applied to a geometric model of a piping system. However, there is a fundamental difference between both applications on how load combinations are combined. The following will provide insight into AutoPIPE's approach vs caesar's.
Start by thoroughly reviewing and understanding AutoPIPE's Load Sequencing knowledge base article here. Only after truly understanding AutoPIPE's Non-Linear Load Sequencing will a person be able to convert combinations back and forth between the applications.
While reviewing the article, one of the major fundamental differences between AutoPIPE and caesar, AutoPIPE's combinations results are based on using a load sequencing (Operational Condition) approach while caesar uses an load vector superposition (Algebraic Subtraction) approach (see reference article here). Thereby one of the main reason for the difference in results between these applications.
If you consider the following example of caesar combinations:
L1 W+P1+T1(OPE) – equivalent to AutoPIPE GRT1P1
L2 W+P1(SUS) – equivalent to AutoPIPE GR + Max P
L3 T1 (EXP) – thermal only, no mass etc, intermediate step for calculating hot sustained (L5) – no AutoPIPE equivalent
L4 L1-L2(EXP) – equivalent to the AutoPIPE T1 case
L5 L1-L3(SUS) – Hot sustained
Note that both L1 and L2 are operating conditions, and L4 is caesar's superposition method of adding load vectors to achieve an individual load case T1. Whereas in AutoPIPE, T1 is an individual load case added in a load sequence to correctly calculate the operating conditions.
Furthermore, understand that caesar needs intermediate equations like L3 to calculate equations like L5 - hot sustained. However, as you now know AutoPIPE load sequence approach does not need intermediate equations like that found in caesar. Thus reducing the complexity of load combinations and length of output report.
Question, what is the difference between L2 and L5, where:
L2 = W+P1
L5 = L1-L3 = (W+P1+T1) - T1 = W+P1
Appears that L2 = L5.
Question, what is the difference between L3 and L4, where:
L3 = T1
L4 = (W+P1+T1) – (W+P1) = T1
Appears that L3 = L4.
If one must compare an AutoPIPE model with caesar, highly recommend comparing true operating conditions (ex. L1 to GRT1P1, L2 to GR+MaxP) instead of all the individual load case (ex. L3 & L4 to T1) as the fundamental different approach of adding vectors / load cases use by the two programs may present dissimilar results for individual load cases and respective combinations where such individual load cases are used.
One final note, be sure check that all of AutoPIPE's Tools> Model Options> General, Edit, & Results settings match caesar's settings.
Note: see bottom of page for an equivalent AutoPIPE code combination to caesar code combination
Item #2:
Caesar CII has a ‘H’ load variable which represents the hanger pre-loads…AutoPIPE doesn't seem to have a hanger variable…does AutoPIPE somehow automatically incorporate the hanger pre-loads?
Answer:
When inserting a typical variable spring in AutoPIPE the user is asked to enter 3 key values: Cold Load, Spring rate, and number of hangers. These values are considered during the analysis.
Otherwise, the user can specify, by program settings, to use a Cold / Hot load for design consideration in automatically selecting spring size and type based on load and movement of the node point. Refer to AutoPIPE's help for " Hanger Selection Procedure".
Item #3:
CAESAR has a ‘D1’ load variable which represents the inclusion of a user-specified displacement….does AutoPIPE incorporate something similar?
Answer:
Yes, Insert> Xtra-Data> Imposed Support Displacement, see online help for complete details on this AutoPIPE option.
As mentioned in the AutoPIPE's help and apparent on the dialog screen, an imposed support displacement can be assigned to any number of load cases (GR, T1-T100, E1-E10, W1-W10, P1-P100, U1-U140, S1-S10) or configured to span a selection of load cases. When that load case is used in a code / non-code combination, the specified imposed support displacement will be taken into consideration accordingly.
Example, the following support displacement is applied to load case U1, and will only be applied when load case U1 is included in a combination.
Item #4:
Caesar has a ‘F1’ load variable which represents the inclusion of a user-specified external force…does AutoPIPE incorporate something similar?
Answer:
Yes, Insert> Xtra-Data> Concentrated Force, see AutoPIPE's help for complete details on this option.
As mentioned in the AutoPIPE's help and apparent on the dialog screen, an concentrated force can be assigned to any number of load cases (GR, T1-T100, E1-E10, W1-W10, P1-P100, U1-U140) or configured to span a selection of load cases. When that load case is used in a code / non-code combination, the specified concentrated force will be applied accordingly.
Example, the following concentrated force is applied to load cases U1-U4, and will only be applied when U1, U2, U3, or U4 is included in a combination.
Item #5:
What are equivalent code combinations between AutoPIPE and Caesar:
AutoPIPE |
Caesar |
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| Code Combination Name | Code Combination Details | Type of Stress | Code Combination Name | Code Combination Details |
| Gr+MaxP(1) |
Gr = Weight Max P(1) = max pressure amoung all pressure cases (ex. P1, P2, P3) (1) = Analysis set #1 |
Sustain |
L13 = W+P1 L14 = W+P2 L15 = W+P3 |
W = Weight P1 = Pressure 1 P2 = Pressure 2 P3 = Pressure 3 |
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Load sequence = Gr>P1> T1 Amb to T1(1) Amb to T2(1) Amb to T3(1) Max Range(1) |
Start with Load sequencing, Apply Gravity, then pressure, and temperature load case T1, repeat sequence for T2, and repeat sequence for T3 Amb to T1(1) = Thermal expansion from Ambient temp. to Temp 1 for load case 1 Amb to T2(1) = Thermal expansion from Ambient temp. to Temp 2 for load case 1 Amb to T3(1) = Thermal expansion from Ambient temp. to Temp 3 for load case 1 Max Range = The maximum difference between the temperatures T1, T2, and T3 of analysis set 1. |
Expansion |
Exp1 = L2-L13 Exp2 = L3-L14 Exp3 = L4-L15 |
L2 = W+D1+T1+P1 L13 = W+P1 L3 = W+D2+T2+P2 L14 = W+P L4 = W+D3+T3+P3 L15 = W+P3
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Static Earthquake directions E1(1) = x, y, z E2(1) = -x, y, z E3(1) = x, -y, z E4(1) = x, -y, -z
Combinations to be checked: Sus+E1(1) Sus+E2(1) Sus+E3(1) Sus+E4(1)
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Sus = Gr+MaxP(1) E1(1) = Results after initial case(s) to Occasional E1 has been analyzed for analysis set 1. E2(1) = Results after initial case(s) to Occasional E2 has been analyzed for analysis set 1. E3(1) = Results after initial case(s) to Occasional E3 has been analyzed for analysis set 1. |
Seismic Occasional Cases The combination is done by summation of absolute values of each term at the stress level |
U1 = x direction U2 = y direction U3 = z direction L5 = Op1+U1+U2 L6 = Op1-U1+U2 L7 = Op1-U2+U3 L8 = Op1-U2-U3 L20 = L5-L2 = U1+U2 L21 = L6-L2 = -U1+U2 L22 = L7-L2 = U2+U3 L23 = L8-L2 = U2-U3 Combinations to be checked: L13+L20 L13+L21 L13+L22 L13+L23
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U is for uniform load in g U1+U2 = E1 -U1+U2 = E2 U2+U3 = E3 U2-U3 = E4 OP1=Operating 1 The check has been done only for OP1.It should be repeated for OP2 and OP3 To be able to check the non linear effect of static earthquake ,a loading case OP1+static Earthquake has to be build and after this loading case minus the OP1, give us the non linear effect of the static earthquake which has to be added to the sustain in Absolute value. |
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Wind Load W1=Wind in X dir W2=Wind in -X dir W3=Wind in Z dir W4=Wind in -Z dir
To be checked: SUS+W1 SUS+W2 SUS+W3 SUS+W4 |
A User Profile is going to be given (a Pressure per elevation) | Wind Occasional Case |
Wind Load WIN1=Wind in X dir WIN2=Wind in Y dir WIN3=Wind in Z dir L16 = Op1+WIN1+WIN2 L17 = Op1-WIN1+WIN2 L18 = Op1-WIN2+WIN3 L19 = Op1-WIN2-WIN3 L24 = L16-L2 = WIN1+WIN2 L25 = L17-L2 = -WIN1+WIN2 L26 = L18-L2 = WIN2+WIN3 L27 = L19-L2 = WIN2-WIN3 Combinations to be checked: L13+L24 L13+L25 L13+L26 L13+L27 |
WIN is for uniform load in pressure WIN1+WIN2 = W1 -WIN1+WIN2 = W2 WIN2+WIN3 = W3 WIN2-WIN3 = W4 OP1=Operating 1 The check has been done only for OP1.It should be repeated for OP2 and OP3 To be able to check the non linear effect of Wind ,a loading case OP1+WIN has to be build and after this loading case minus the OP1, give us the non linear effect of the Wind which has to be added to the sustain in Absolute value. . |
AutoPIPE |
Caesar |
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| Non - Code Combination Name | Non - Code Combination Details | Note | Non - Code Combination Name | Non - Code Combination Details |
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Gr1(1) |
Gravity weigh for load set 1 |
Individual load case Gravity |
W+P1 |
W = Weight P1 = Pressure |
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T1(1) |
Temperature 1 load case for load set 1 |
Individual load case for Thermal |
T1+D1 |
T1 = Temperature 1 D1 = Displacement by T1 |
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Initial load to Occ = Gr E1(1) |
Load dues to occasional Earthquake 1 load case for load set 1 after all the initial GR load has been sequenced. |
Individual load case Static Earthquake |
U1 |
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Initial load to Occ = Op1 (GrP1T1) W1(1) |
Load due to occasional Wind 1 load case for load set 1 after all the initial loads, Gr> P1> T1) have been sequenced. |
Individual load case Wind |
WIN1 |
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GT1(1) = Gr(1)+T1(1) GT2(1) = Gr(1)+T2(1) GT3(1) = Gr(1)+T3(1) |
Gr = Weight T1(1) = Temperature 1 for analysis set (1) T2(1) = Temperature 2 for analysis set (1) T3(1) = Temperature 3 for analysis set (1) |
Operating loading case checking the forces and moments |
L2 = W+D1+T1+P1 L3 = W+D2+T2+P2 L4 = W+D3+T3+P3 |
W = Weight T1 = Temperature 1 T2 = Temperature 2 T3 = Temperature 3 D1 = Displacement by T1 D2 = Displacement by T2 D3 = Displacement by T3 |
Additional information:
AutoPIPE |
Caesar |
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AUTOPIPE is performing analyses for load increments. It is important to note that in an AUTOPIPE analysis, each load case is an increment of load, not a total load. For a linear analysis, the results for each load case are obtained all at once. By linear analysis, the “Gaps/Friction/Soil" option has to be disabled. For a nonlinear analysis the results are obtained sequentially. If analyses are performed for load increments ,The steps are:
GR->P1->T1 The “Static analysis set” is set under Static Analysis Sets (Analysis > Setup > Static Analysis Sets)
Analysis set options “Ignore Friction E” and “Ignore Friction GR” have to be removed because by caesar the friction is always acting First the analysis has to be done for the code stresses and once it is done, you can create your own non-code combinations. It is used to create your operating case or compare some loading case to define the maximum forces and moments on nozzles from the equipment. By AUTOPIPE , The code combinations are done automatically and users can define as many analysis set as we want and combine the results as needed. For instance, the hydrotest is a linear analysis so that we can define a 2nd analysis set to define this case.
AutoPIPE has to define operating 1 + Wind1 by the non-code combination to define the maximum forces and moments on supports.
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That means that CAESAR II is throwing every item (Weight, displacements, Temperature and so on) in a basket and adds everything together regardless when it happens. If analyses are performed for total loads, the steps are:
The loading cases will look like:
To sum up ,you can find following annotations
To obtain non linear analysis in Caesar II, you have always to create a loading case operating, then operating + wind or +earthquake, then subtract the operating + wind or + earthquake from operating alone. Then this occasional load will be added to the sustained stresses and compare to 1.33 Sh for instance by ASME B31.3 By the load case editor, you can define the type of loading. To notice that the basic allowable stresses taken are set by the stress type:
It is important to notice that first the basic loading cases are defined, then their combinations
In the load case options, define the
With example having 4 loading cases in Static earthquake and 4 wind directions,we end up having already 36 loading cases defined with the friction on.As the friction is not always acting,we should do the same loading cases without friction. Caesar II loading became quite complicated For the wind load, we define the wind pressure per elevation or use other codes.
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