Pipe Support Stiffness - GMRC Project

7262019 Pipe Support Stiffness - GMRC Project

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Pipe Support Stiffness

(BETA Research project for the GMRC 2014)

1 Industry Challenge

Pipe supports are used to secure process piping and prevent harmful vibrations The goal of a well-

designed pipe support for vibratory service is to minimize vibration at the

support This mainly depends on the supportrsquos stiffness and location

The stiffness of a pipe support system depends on two things

bull The stiffness of the clamp itself and

bull The stiffness of the structure underneath the pipe (to which the pipe is

clamped)

See Figures 1 to 3 for examples of typical pipe support systems An accuratestiffness for the pipe clamp system is essential to determine the natural

frequency of piping which indicates a possibility of high vibrations The natural

frequency of piping varies with the spacing between supports and with the

stiffness of the supports themselves

Pipe supports also affect the results of a Piping Stress Analysis (also called a Piping Flexibility Study or

Thermal Analysis) The same stiffness value used to determine the natural

frequency of piping can also be used in a flexibility study to determine the piping

stress and deflection restraint reaction forces and nozzle loads on equipment

An industry-wide problem exists due to incorrect assumptions about pipesupport stiffness The current practice by many engineering firms is to assume a

pipe support is rigid (eg 1E12 lbin) In reality the clamp and support system

has some flexibility (eg 1E5 - 1E6 lbin) This means the piping engineerrsquos

assumptions can be over 1000000 times stiffer than the actual installation

Inaccurate stiffness assumptions create (expensive) consequences such as

bull Higher pipe natural frequencies than would be measured in the field

which may lead to high pipe vibration

bull Thermal loops that may not be required

bull Removal of pipe clamps (to solve thermal problems) which can result

in high pipe vibrationsbull Failed pipe clamps and equipment nozzles due to higher than expected

pipe deflections and loads

This problem exists because of these two issues

bull There is a lack of understanding and information on this issue and

bull The engineering firms do not have the experiencecapability to

determine the actual stiffness values For example specialized finite

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983137983150983140 983152983151983155983156983085983156983161983152983141 983155983157983152983152983151983154983156

Clamp

Support

Support

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983155983157983152983152983151983154983156

Support

Clamp

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Clamp

Support



Beta Machinery Analysis


element analysis (FEA) software is required (eg ANSYS) as well as an understanding of how to

properly model the stiffness

In an attempt to give the industry guidance as to what stiffness is required for a well-designed support

API 618 5th Edition has recommended a minimum stiffness However there are no published stiffness

values for the different types of clamp designs and different support structure designs (eg concrete pier

beam support or elevated post)

This project will investigate the stiffness of different types of clamps and support designs The sensitivity

of the stiffness calculation to installation variations and

sensitivity of piping natural frequency to support stiffness will be

briefly investigated during the analysis

2 Project Deliverables

There are two project deliverables

bull Best practices for evaluating and applying piping support

stiffness in new facilities with case studies examples

standard specifications and ldquodorsquos and donrsquotsrdquo so piping

engineers understand how to design an adequate system ndash

and not end up with poor designs like Figure 4

bull A table of stiffness values for 20 standard pipe supports

sizes in the NPS 2rdquo-40rdquo range The table will have axial

lateral vertical and torsional stiffness of the clampsupport

and can be used by Engineering Consultants (ECs) involved

in piping layout pipe stress analysis and mechanical

analysis

3 Industry Benefits

Many gas plants and compressor stations suffer from poorly designed pipe supports Incorrect

assumptions on pipe stiffness are often used which result in costly vibration and stress problems Having

access to accurate stiffnesses will greatly improve the piping system reliability

983110983145983143983157983154983141 983092983086 983120983151983151983154 983155983157983152983152983151983154983156 983140983141983155983145983143983150



Beta Machinery Analysis


element analysis (FEA) software is required (eg ANSYS) as well as an understanding of how to

properly model the stiffness

In an attempt to give the industry guidance as to what stiffness is required for a well-designed support

API 618 5th Edition has recommended a minimum stiffness However there are no published stiffness

values for the different types of clamp designs and different support structure designs (eg concrete pier

beam support or elevated post)

This project will investigate the stiffness of different types of clamps and support designs The sensitivity

of the stiffness calculation to installation variations and

sensitivity of piping natural frequency to support stiffness will be

briefly investigated during the analysis

2 Project Deliverables

There are two project deliverables

bull Best practices for evaluating and applying piping support

stiffness in new facilities with case studies examples

standard specifications and ldquodorsquos and donrsquotsrdquo so piping

engineers understand how to design an adequate system ndash

and not end up with poor designs like Figure 4

bull A table of stiffness values for 20 standard pipe supports

sizes in the NPS 2rdquo-40rdquo range The table will have axial

lateral vertical and torsional stiffness of the clampsupport

and can be used by Engineering Consultants (ECs) involved

in piping layout pipe stress analysis and mechanical

analysis

3 Industry Benefits

Many gas plants and compressor stations suffer from poorly designed pipe supports Incorrect

assumptions on pipe stiffness are often used which result in costly vibration and stress problems Having

access to accurate stiffnesses will greatly improve the piping system reliability

983110983145983143983157983154983141 983092983086 983120983151983151983154 983155983157983152983152983151983154983156 983140983141983155983145983143983150

Documents

Pipe Support Stiffness - GMRC Project