CAESAR II STATIC LOAD CASE EDITOR

Loren Brown

Senior Engineer/Developer CADWorx & Analysis Solutions Intergraph Process, Power, & Marine

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TYPES OF LOADS

• • Primary Loads – Force driven, cause catastrophic failure.

– Weight, Pressure, Point Loads, Uniform Loads, Hanger Loads, Wind and Wave loads.

Secondary Loads – Strain based, cause fatigue failure.

– Temperature, Displacements.

AVAILABLE LOAD TYPES IN CAESAR II

• • • • • • • • W (Weight), WNC (Weight No Contents) WW (Water-filled Weight) P (Pressure), HP (Hydrotest Pressure) T (Temperature), D (Displacement) H (Hanger Pre-loads), F (Concentrated Loads) U (Uniform Loads) Win (Wind), Wav (Wave and Current) CS (Cut Short or Cut Long)

Available Stress Types in CAESAR II

• • • • • • • OPE – Operating SUS – Sustained EXP – Expansion OCC – Occasional HYD – Hydrotest HGR – Hanger Design FAT - Fatigue

Load Case Definition

• • • Operating case contains all loads in the system.

– L1 = W+P1+T1+H (OPE) this is called a basic load case Sustained Case contains only primary loads.

– L2 = W+P1+H (SUS) another basic load case Expansion Case is the difference between the operating and sustained cases.

– L3 = L1-L2 (EXP) this is called a combination load case

Combination Load Cases

• • • Used to add or subtract results from previously defined primitive load cases.

Necessary for proper EXP and OCC code stress definition.

Not used for restraint or equipment load definition, nor for displacement reporting.

Why subtract SUS from OPE?

• Why not simply use L3 = T1 (EXP)?

– Because the restraint configuration may result in an incorrect solution. – Nonlinear restraints drive the restraint configuration.

– Other loads in the system combine to change the restraint configuration.

Nonlinear Restraints

• • Stiffness of Restraint changes depending on position of pipe or forces on restraint.

Examples: – Uni-directional Restraints (+Y) – Gaps in restraints – Friction – Large-rotation rods – Bi-linear Restraints

Force vs. Distance in Nonlinear Restraints

Example 1: T1 (EXP)

L3 = T1 (EXP) This is how the line is modeled in Caesar II. The gaps are equal on both sides of the pipe. No loads are yet applied.

The thermal forces have closed the gap on the right side.

Total Displacement for T1 (EXP) = 1 x Gap

Example 2: L1 – L2 (EXP)

L2 = W+P1 (SUS) L1 = W+P1+T1 (OPE)

Weight has caused the pipe to close the gap to the left. This can happen when the pipe pivots about a different restraint.

Operating conditions have caused the pipe to close the gap to the right, even against the weight force trying to hold it on the left.

Example 2 (con’t)

• If we subtract the displacements of the SUS case from OPE we get: – Total Displacement for L1-L2 = 2 x Gap – In a linear system T1 (EXP) = L1 – L2 (EXP) – In a nonlinear system this is not guaranteed.

– This represents the effect of temperature in the presence of other loads.

– This is a displacement stress range, not starting from the neutral position.

Occasional Load Cases

• For most piping codes (not the offshore codes): – Set up an OPE case that includes the occasional load – Subtract the standard OPE case from the OPE that includes the occasional load. We call this the segregated occasional load case.

– Add the above load case results to the SUS load case results for the code stress check

Example 3: Occasional Load Cases

• Assume we have a uniform load representing a seismic load, U1.

– – L1 = W+P1+T1 L2 = W+P1 (OPE) standard operating (SUS) – – – L3 = W+P1+T1+U1 L4 = L1-L2 L5 = L3-L1 (OPE) operating with occasional load (EXP) (OCC) segregated occasional – L6 = L2+L5 (OCC) * occasional code stress case * use scalar combination method.

Combination Methods

• • Algebraic: – Used for subtracting two load cases.

– Takes the displacements from the referenced cases and subtracts them.

– Then computes forces, moments, and resultant stress from these displacements.

Scalar: – Used for adding two load cases.

– Adds the stresses from the two referenced load cases.

– Unlike algebraic the stresses are not recomputed from displacements.

Notes on combination methods

• • Don’t use algebraic for adding two load cases.

– You can’t take credit for occasional loads acting opposite to operating loads.

Don’t use scalar for subtracting two cases.

– This results in a lower code stress than actual.

Output Types

• • • Displacement – Usually reported only for basic load cases Force – Usually reported only for basic load cases Stress – Reported based on code requirements.

Example 4 – Restraint Loads

The algebraic difference between these two conditions will result in a positive force on the restraint. This is an impossible condition. But the EXP code stress is correctly computed for this condition.

What to report

• • • • Suppress the HGR cases and the segregated occasional load cases.

Report displacement, force for all primitive load cases.

Don’t report stress for the operating load cases.

– This is not true for offshore codes, nor FRP codes, nor buried pipe codes.

Report only stress for combination load cases.

Using the Hot Modulus of Elasticity

• • • It is required to use the cold modulus of elasticity for stress computation.

You can reduce restraint loads by use of the hot modulus of elasticity.

Create identical OPE cases, one with hot modulus for restraint loads, and one with cold modulus for use in the combination with SUS for determining EXP stress.

Using the Friction Multiplier

• • • • Friction Multiplier acts on the Mu value entered on each restraint in the model.

Input 0.0 for no friction and 1.0 for full friction.

Create identical load cases, but change the value of Friction Multiplier on one of them.

Compare the results in the Restraint Summary and report the worst-case results.