1. Determine the load and the total movement.
Total movement = design movement + over travel
Over travel = 20% of the design movement or 25mm whichever is higher.
2. Select the spring from the load chart keeping in mind that the spring selected must lie within the working range
3. Select the type and check the feasibility of the spring depending on space available and type of structure available.
4. The Spring box must be able to move freely without any restriction.
5. Stress Engineer must check the eccentricity (See Fig 1 below) of the spring load flange and the spring base plate while providing foundation information to civil.

Spring Selection procedure in Caesar II:
1. CAESAR-II Default Setting for Hanger Selection:
Before making input for spring selection it is always better to make a default Caesar setting for hanger design.

Caesar II Default hanger setting

2. CAESAR-II Auxiliary Spreadsheet setting for Hanger Selection
During spring selection at a particular node the following auxiliary spreadsheet appears. The setting of this spreadsheet is to be done as illustrated in below diagram.

Caesar II Auxiliary spreadsheet for hanger selection

NOTE-1:
Maximum Allowed Travel Limit:
This field is used to specify a limit on the amount of travel a variable support hanger may undergo. CAESAR will be forced to select a Constant Effort Spring if the movement exceeds the limit in this field, even though a variable effort spring would have fulfilled our purpose.
Constant effort hangers can be designed forcefully by inputting a very small number i.e. 0.001 in this field.

NOTE-2: Free Code:
Anchor or Restraints from equipment connections which are very near to the hangers are usually freed during the hanger design restrained weight run, so that loads normally going to the equipment nozzle are carried by the hanger.
The hanger can be designed to take almost the full weight of the pipe between the anchor and the hanger.
Using this field enter the node number & the direction in which free code is to be used.
Free Codes are:-
1. Free the anchor or restraint in the Y direction only.
2. Free the anchor or restraint in the Y and X directions only.
3. Free the anchor or restraint in the Y and Z directions only.
4. Free all translational degrees of freedom for the anchor or restraint. (X, Y and Z)
5. Free all translational and rotational degrees of freedom for the anchor or restraint. (X, Y, Z, RX, RY, and RZ). Refer Figure below.
The option 5 above usually results in the highest adjacent hanger loads, but should only be used when the horizontal distance between the hanger and the anchor is within about 4 pipe diameters as shown in below Figure

Maximum Spring distance for using Free Code

NOTE-3:
Number of hangers at location:
For better stability, the base type spring support of 24″ and larger is used with 2 spring cans.

Few important points to keep in mind while Spring selection:

•For can type springs the spring height should be kept minimum from stability point of view. If spring height is less the moment on spring will reduce and tilting of spring (below Figure) can be avoided or significantly minimized.
•The spring which has lower spring rate will have lower load variation.
•While designing the spring hanger the sustained sagging should be minimized within +/-(1 ~ 2) mm so that original piping system is not strained much.

Effect of Spring Height

Structural Analysis of Pipe Supports:

CAE Piping performs the Pipe Support Stress Analysis based on ASME and AISC codes . We perform the structural analyses based on ASME section VIII for the supporting structures of the piping systems evaluated by ASME B31 codes. We use ASME section III for the analysis of pipe supports of the nuclear piping systems.

Beside data provided in ASME codes and WRC's Bulletins, CAEP performs advanced finite element analysis to estimate the SIFs (Stress Intensification Factors) for different piping components like as tees, bends, etc.

Structural and Failure Analysis Conulting

CAE Piping offers structural and failure analyses consulting services: Performing structural analyses and mechanical failure analyses (Fatigue,ratcheting, shake down, limit load and fracture mechanics analyses and ...) for the welded components, pipelines and storage tanks, turbine blades, boiler components, aerospace and other mechanical components.

We specialize in examination of the fracture surfaces to determine the type and direction of the crack propagation, estimating the remain life of the cracked components and providing solutions to stop the crack propagation or designing the improved replacement part.

There exists a number of possible failure modes that we take into consideration in the design of piping systems and mechanical components. We provide the Root Cause Failure Analysis (RCFA), identifying the root causes of faults or problems in mechanical components, piping system and supporting structures, utilizing finite element analysis.

The failure analysis services are carried out in two steps:

First Step: Design by linear elastic analysis based on ASME Section III or Section VIII:

Limit on primary stress to prevent plastic deformation.
Limit on primary plus secondary stress to prevent excessive plastic deformation.
Limit on peak stress to prevent fatigue failure due to cyclic loading.