01 - hanger sizing in caesar ii

Hanger SizingDavid Diehl

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CAESAR II

Hanger Sizing Algorithm in CAESAR II

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Variable Supports

Why are they required?

A spring support can carry deadweight load through some vertical travel.


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Selection Procedure –1: Collect Data

Calculate the “balancing load” at the specified locations This load will remove all pipe sag due to weight

This will be the design load for the operating position (the operating load)

(This load could also be chosen as the installed load.)

Calculate the required (vertical) travel at each location Determine the vertical travel to the operating position

but excluding weight sag

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Selection Procedure –1: How the Data is Collected

Calculate the “balancing load” at the specified locations Run a weight analysis with a rigid +Y restraint at each

hanger design location. [Assume “up” is +Y.]

The +Y restraint load is the “balancing load”.

Calculate the required (vertical) travel at each location Replace the added +Y support with vertical (up) force

equal to the “balancing load”. Run an operating analysis.

Collect the vertical travel. Remove the added forces.


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Selection Procedure –2: Find the Right Hanger

What hanger can carry 600 lbf after traveling up 1/3 inch?

Locate operating load

Find relative spring position

Move back to installed position

Read installed load

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Selection Procedure –3: Check Load Variation

Load Variation is defined as the change in load as a percentage of the operating load.

Oftentimes limited to 25%

Here: Change in load is about 100 lbf

Operating load is 600 lbf

Load Variation is 16%


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Selection Procedure –4: Identify the Hanger

What hanger can carry 600 lbf after traveling up 1/3 inch?

Size 8

Short range spring

Spring rate = 300 lbf/in

Operating load = 600 lbf

Change = 300*1/3

Installed load = 700 lbf

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Post Selection –5: Include Selection in the Model

The program may select a rigid restraint, a spring support or a constant effort support.

Selected supports are added to the model for all piping system analyses Rigid restraints are represented as a rigid vertical

restraint

Springs are represented as a flexible vertical restraint (k=selected spring stiffness) AND a preload (equal to the calculated installed load).

Constant effort supports are represented as an upward force and are listed in Restraint Reports.


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It’s that Simple

Now, how do you get CAESAR II to do that?

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CAESAR II Hanger Input Data

There are four locations where different portions of hanger selection data can be specified CAESAR II Configuration Settings

Controls the current data folder in setting initial values

Piping Input – Hanger Design Control Data Sets general control and initial setting values for the current

job

Piping Input – Hanger Data (Checkbox) Sets selection parameters / specifies existing spring for the

job

Load Case Setup – Load Case Options Establishes how hangers are treated in each load case


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Data Folder –Configuration Settings (1/3)

Hanger Default Restraint Stiffness 1E12 by default; just like rigid stiffness

Default Spring Hanger Table We currently reference 33 tables

Hangers & Hanger CNode display (plot colors) Suggest using different color for hangers

with CNodes (to identify different boundary conditions)


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Ignore Spring Hanger Stiffness Used to match simpler, hand calculations (ignore

stiffness and apply only hot load)

NOT RECOMMENDED

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Include Spring Hanger Stiffness in Hanger OPE Travel Cases


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Include Spring Hanger Stiffness in Hanger OPE Travel Cases This can reduce the travel demand on the hanger

Sets Hanger Stiffness for “Operating for Hanger Travel” to “As Designed” (instead of “Ignore”)

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Include Spring Hanger Stiffness in Hanger OPE Travel Cases Renames Theoretical Cold Load as Field Installed

Load

Be careful. Confirm.


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Piping Input – SpecificHanger Design Control Data (1/2)

Specific Settings found only here:

Number of Hanger Design Operating Load Cases

Multiple Load Case Design Options

Calculate Actual Cold Loads


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Piping Input – Specific Hanger Design Control Data (1/2)

Number of Hanger Design Operating Load Cases Specifies the number of load cases to be considered

when designing spring hangers. This value may be between 1 and 9 and corresponds to the number of thermal load cases to be used in hanger design. If more than one operating case is to be considered in the hanger design then you must also select the Multiple Load Case Design Option to use.

This entry will control the number of analyses required to select the hangers.

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Multiple Load Case Design Options Whenever more than one thermal load case is used

in the hanger sizing algorithm, CAESAR II must know how you want to weigh the results from the different cases.

As thermal strain can affect support loads, both the hanger’s operating load and deflection can change.

A two-pump installation where only one pump operates at a time is a good application for multiple load case hanger design.

This option can be (re)set as part of the individual hanger specification


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Multiple Load Case Design Options (13 in all) Design based on a single Load Case (#1 - #9)

Design for the maximum operating load

Design for maximum travel

Design for the average load and the average travel

Design for the maximum load and the maximum travel

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For example:

Design for LC1

Design for LC2

Operating Case 1 (LC1) Operating Case 2 (LC2)


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Here, set the Hanger Design Control Data: Number of Hanger Design

Operating Load Cases = 2

Multiple Load Case Design Options = Operating Case 1

In model input, reset the right spring: Multiple Load Case Design Option = Operating Case 2

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Piping Input – SpecificHanger Design Control Data (1/2)

Calculate Actual Cold Loads Indicates that CAESAR II makes one additional

analysis after hanger selection is complete and the supports are included in the model. This analysis will determine the actual installed loads that should be used when the hangers are first activated (unblocked).

This calculation tends to be important in the following situations: The stiffness of the piping system is small.

The stiffness of the hanger selected is high.

The hanger travel is large. This is usually more important in smaller diameter piping systems that are spring supported away from equipment nozzles.


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Piping Input – GeneralHanger Design Control Data (2/2)

Default settings for new entries AND unspecified settings for existing hanger locations. Entries here do not replace existing data.

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Allow Short Range Springs Turn this switch off if you do not wish to select short

range springs

Allowable Load Variation (%) Load Variation is defined as the change in hanger

load divided by the hot load.

Load Variation should not exceed 25% by specification (B31.1 & MSS SP-69)

Reduce load variation near sensitive equipment (e.g. constant effort hangers have a load variation of less than 6%)


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Rigid Support Displacement Criteria If the vertical growth at the hanger location is less

than this value, CAESAR II will select a rigid rod (a Y restraint)

Maximum Allowed Travel Limit If operating deflection exceeds this value, CAESAR II

will select a constant effort support

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Hanger Table Select one of the 33 manufacturer’s data sets

Check boxes (more later)

Extended Range – go beyond the “recommended” range

Cold Load – size spring to balance the cold load; useful in aligning equipment

Hot Load Centered – try to select a ”better” spring


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Piping Input –Hanger Data

Selecting a hanger

Specifying a hanger

Locating a hanger


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Piping Input –Node Data (1/3)

Node / CNode Node: You define where the support should be

located.

CNode: Think of the CNode as the other end of the hanger (which may have vertical growth to be included in the selection).

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Piping Input –Design Data (2/3)


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Hanger Table CAESAR II provides 33 hanger manufacturer catalogues

All have 3 spring sizes (e.g. short, mid & long range)

Some have a fourth (extra long) size

Hanger Manufacturers in CAESAR II

Anvil Bergen Power

Power Piping NPS Industries Lisega Fronek

Piping Technology

Capitol Piping Services Basic Engineers Inoflex E. Myatt

SINOPEC BHEL Flexider Carpenter & Paterson

Pipe Supports Ltd. Witzenmann

Sarathi Myricks China Power Pipe Supports USA Quality Pipe Supports

PiHASA

Binder Gradior NHK PSSI GmbH Seonghwa Mitsubishi

Yamashita Sanwa Tekki Techno Industrie

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Three check boxes can be used in combination Extended Range

Historically, manufacturers assume the calculated weights are incorrect. Accordingly, they design away from the top and bottom of travel to allow proper field adjustment. CAESAR II will permit design based on total available hanger travel.

Cold Load

This switch will select a spring which balances the dead load in the installed (rather than operating) position. Useful in aligning equipment.

Hot Load Centered

If the next size larger spring operates closer to the center of total travel, it – a more dependable spring – will be selected .


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Available Space Specifies the amount of room above or below the pipe where

you can install the hanger or can. If the value is negative, then CAESAR II assumes that a can is to be installed.

CAESAR II will select the spring only if its basic hanger/can length is below the entered value.

No space provided for hardware.

true

CAESAR II

CAESAR II value for hangers

CAESAR II value for

cans

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Allowable Load Variation The general default value (specified in general Hanger

Control Data) can be modified here; as near pumps

Rigid Support Displacement Criteria Often used on flexible, horizontal runs away from risers, this

setting will select a rigid rod if the vertical growth at the hanger node is less than the entered value

Max. Allowed Travel Limit CAESAR II will select a constant effort support if no spring

can be properly sized. This switch will force a constant support selection if the vertical growth at the hanger node exceeds the entered value


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No. Hangers at Location Specify where a single hanger is not practical, e.g. on risers

where two or more hangers would be required

Note that CAESAR II will divide the total design load to be carried between this count

Allow Short Range Springs A local switch for controlling use of (more expensive or less

available) short range springs

Operating Load (Total at Location) Usually specified after reviewing initial results, this entry

overrides the calculated design (typically, operating) load for the hanger. Useful in fine tuning supports around sensitive equipment

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Hanger Hardware Weight Hardware weight between the pipe and spring (e.g. long rods

on light springs) may alter the installed and operating spring loads

The entered value will be added to the design load but it will not appear in the program’s restraint listings

Multiple Load Case Design Option Discussed earlier, use this option when the piping must

operate at more than one operating condition.

Specify a specific operating case (e.g. Operating Case #1), or use average/maximum values for travel/load based on the number of hanger design operating load cases.


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Free Restraint at Node (2 entries allowed) The initial weight analysis will distribute load to each boundary

condition based on system stiffness

The purpose of selecting a spring may be to unload a system boundary. For example, a support at the top of a riser off a pump should carry most of the riser weight with little load on the pump below.

Restraints for this initial weight analysis can be excluded for this load case only to relocate load to the hangers

Displacement sets are treated as restraints here.

Free Code (used with “Free Restraint at Node”, above) Indicate the direction of freedom (up, up & X, up & other

horizontal, all translation, all 6 DOF).

Up is suggested and only when hanger is above this restraint.

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Piping Input –Predefined Hanger Data (3/3)


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Piping Input –Predefined Hanger Data (3/3)

Used to specify an existing support Spring Rate AND Theoretical Cold (Installation) Load

A calculated value, Theoretical Cold Load = operating load + (pipe growth times)*(spring stiffness)

-or-

Constant Effort Support Load Unlike an applied load (e.g. F1), this support load is treated

as a sustained load component and included in the restraint table output.

Note that if a Theoretical Cold Load is not entered, CAESAR II will select a new spring but first attempt to use the existing spring with recalculated loads

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Hanger Display

Whether entered explicitly or specified for design, CAESAR II shows these hangers in the plot.

If “Available Space” is negative, a different symbol will be displayed.


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Required Analyses for Hanger Sizing

With hanger selection indicated, CAESAR II will display a note during error check stating the load cases required for Hanger Selection:

Note the extra case if Actual Installed Loads are requested

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Load Case Setup – Load Case Options Establishes how hangers are treated in each load case


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Load Case Setup –Load Case Editor

Recommended Load Cases Estimate hanger operating load L1

Estimate hanger travel L2

Select supports and preloads from a catalog

Calculate actual installed loads (if requested) L3

Run additional load cases with selected supports and preloads L4+

Note “StressType”

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Load Case Setup –Load Case Options

Output Status General results for Load Cases with Stress Type of

HGR are suppressed

As these results do not include the selected hangers, it is unwise to activate their display (i.e. “Keep”)


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Load Case Setup –Load Case Options

Hanger Stiffness (Rigid, Ignore, As Designed) The initial weight case includes rigid +Y restraints.

The operating travel for the spring (L2) has no stiffness for the hangers. Deadweight sag is eliminated by including the calculated (up) force from L1.

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Load Case Setup –Multiple Hanger Design Cases

Similar action when there are multiple operating cases for hanger sizing. Here, two operating cases are defined:

Error Check:

Load Case Editor:


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CAESAR II Hanger Output

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CAESAR II Hanger Results


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CAESAR II Hanger Results

Hanger Table:

Hanger Tablewith Text:

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Output (1/3)

Hanger Table or Hanger Table W/ Text

2. Calculated in initial operating analysis

1. Calculated in initial weight analysis

3. Here’s the spring rate that works

4. Back-calculated installed load = Hot Load

+ (k*vertical move.)

5. A single Anvil Figure 82 (short)

size 7 spring selected at node 68.


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Output (1/3)

Hanger Table or Hanger Table W/ Text

6. Load Variation shows the change in load as a percentage of the

design load

7. The actual installed load was not calculated

8. Check horizontal displacement for rod

swing

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Output (3/3)

Hanger Table with Text Identifies other useful data:

9. Spring size

10. Minimum & Maximum Spring Loads

are used to check spring position

11. Clearance required for

hanger/can body


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Verify Program’s Selection

You must confirm the spring selection Hanger Report:

Is the spring working near its load limits?

Restraint (Summary) Report: Is the spring carrying a proper load near equipment?

What is the overall maximum & minimum load? (CAESAR II does not “bottom out” or “lift off”, automatically.)

Displacement Report: Is there too much horizontal deflection?

Perhaps you can do better.

Don’t say “CAESAR II told me to buy that spring”

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Is the spring doing it’s job? Input:


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Is the spring doing it’s job? Results: No, a bigger spring would pull more load off the pump!

Pump load

Hanger load

Spring:

Anvil Fig. 82 Size 6

Hot Load=390

k=168

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Is the spring doing it’s job? Fix:


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Is the spring doing it’s job? Results: Much better!

Pump load

Hanger load

Spring:

Anvil Fig. 82 Size 7

Hot Load=558

k=224

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Is the spring doing it’s job? Fine Tuning:

Pump load ranges from +41 (cold) to -124 (hot)

If spring carries an additional 42, pump is +83 (cold) to -82 (hot)

New hot spring load = 558+42


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Is the spring doing it’s job? Results:

“Balanced” Pump Load

Specified HGR Load

Same spring, different set load

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Odds & Ends


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Zero Load

Review hanger locations when CAESAR II notes that hangers are not carrying weight. During Solution

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Zero Load

Review hanger locations when CAESAR II notes that hangers are not carrying weight. In the Solver

In the Hanger Table


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Zero Load

Investigate by replicating the weight case

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Hot Load Centered

Many designers prefer that the hot load be as close as possible to the middle of the spring table. This provides as much variability as possible in both directions.

The CAESAR II design algorithm will move to a higher size spring if the design load is closer to the middle of the larger spring's range.

CAESAR II attempts to move the hot load to the next higher spring (of the same type) when it is within 10% of the maximum travel range for the spring.


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Hot Load Centered

Hot Load Centered – Inactive

Hot Load within 10%

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Hot Load Centered

Hot Load = 653 lbf; Vertical Growth = -0.35 in

653

574

10%

653

548


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Hot Load Centered

Hot Load Centered – Active

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Two springs

Read the number!

If a single, large spring is too big to fit in the available space, CAESAR II may select two smaller springs.

(Also a hanger selection specification.)


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Actual Cold Load

Why calculate “Actual” Cold Load? A hanger designed to balance the operating load is

out of balance in the installed position. Using the “Theoretical Cold Load” as the installed spring set point may prevent easy removal of blocks to place the hanger in service.

Field adjustments to set hanger cold position to this “Theoretical Cold Load” may move the pipe rather than compress the spring – so operating load will be off.

Better to provide “Hot Load” and “Actual Cold Load” when ordering the spring.

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Actual Cold Load

Variation between “Theoretical Cold Load” & “Actual Cold Load” is caused by: Relative stiffness between piping system and the

spring

Large load variation with a flexible line

Available dead load when springs are unblocked (e.g. adjusting a spring to carry fluid weight while the pipe is empty)


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Actual Cold Load

At times, accounting for this difference (between actual and theoretical) cold load may reduce the required spring travel. Perhaps allowing the use of a shorter range spring

Try using the “Include Spring Hanger Stiffness in Hanger OPE Travel Cases” switch or set the Load Case Option.

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Actual Cold Load

Default selection

Include spring stiffness in initial operating analysis


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Actual Cold Load

Groups of springs can cause additional issues

Here there many hangers selected for a flexible run. The combined load differential (installed v. operating) along with the added spring stiffness pulls the line more than necessary. And the selected hangers show this.

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Actual Cold Load

Default Selection Include Stiffness

Same (Total) Loads

Different Travels

Different Springs!


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Springs Loads Change as Pipe Moves Vertically

One balance position with springs That’s our design load

Default is operating (“hot”) but can be set to installed (“Cold Load Design”)

Other positions are out of balance Limited by Load Variation (default limit is 25%)

Usually this is acceptable

You will see this out of balance by (minor) spring deflection in the installed (SUS) analysis

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Questions? Comments?

01 - hanger sizing in caesar ii

Documents

operating load

balancing load

design load

installed load intergraph

deadweight load

y restraint load

lbf load variation

calculated installed