Pipe stress analysis is carried out to ensure the structural integrity of piping systems and predict stresses from various loads like pressure, temperature, weight, and seismic forces. It is important to analyze thermal loads at different operating conditions, sustained loads from pressure and weight, seismic loads, wind loads, pressure relief valve reaction forces, and slug forces. All types of load cases must be considered for accurate stress analysis to prevent piping system failure.

1. Important Pipe Stress Analysis
Load Cases

2. What is Pipe Stress Analysis ?

Analysis carried out on any piping design project to ensure structural and
operatonal integrity and optmal design.

Predicts stresses in piping and loads on equipment resultng rom various
actors like pressure, temperature, weight, seismic and other related actors.

An important actor in detailed piping engineering to ensure that the piping
system doesn’t ail under any sort o stresses and loads.

Governed by diferent codes and standards that speci y minimum
requirements or sa e design and constructon.
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3. Why Pipe Stress Analysis?

Any piping system is subjected to diferent kinds o loads during their
design li e cycle.

These loads result in the development o stresses in the piping system.

To analyze and measure these stresses, pipe stress analysis is carried
out.

Pipe stress engineers use reliable sofware like CAESAR II to analyze
stress in these systems and check whether they are under permissible
limits as defned by codes and standards.
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4. Loads Considered During Pipe Stress Analysis

Diferent types o loads considered during piping stress analysis
 Thermal Loads at Various Operatng Conditons
 Sustained Loads
 Seismic Loads
 Wind Loads
 PSV Reacton Force
 Slug Force
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5. Thermal Loads At Various Operatng Conditons

Pipes contract or expand due to the temperature change which
results in thermal load

To avoid ailure due to thermal load, the piping system must be
made fexible

Piping system must be analyzed or the design temperature and
operatng temperature

I design temperature o pipes > 80 deg C and diference between
operatng and design temperature > 25 deg C, then the
maximum/minimum operatng temperatures, as derived rom
Process Group, can be used in pipe stress analysis instead o
design temperature.

6. Sustained Loads

“Allowable stresses or sustained loads” have
been set by internatonal piping codes or the
axial stresses caused by dead-weight and
pressure to avoid ailure.

To achieve it, the piping system is required to
be supported vertcally.

These are the loads that exist throughout the plant
operaton.

Consists o loads due to internal pressure & dead-weight.

Dead-weights are to be considered as ollows
 Design pressure
 Weight o Pipe and associated components such as
Flanges, Valves, Strainer, Sight glass etc., mounted
on the Piping System.
 Weight o Fluid/contents in the piping
 Insulaton and cladding weight
 Hydro test loads, i applicable
 Snow load, i applicable

7. Seismic Loads

These are considered or piping system to be implemented in seismic zone.

Statc seismic analysis needs to be carried out to evaluate seismic stresses,
displacements and loads.

Seismic coefcient to be provided by client.

I not provided then, statc seismic coefcient is calculated using relevant codes
in terms o ‘g’ – as per project specifc in ormaton.

To be considered to be actng along the horizontal axes – along North, South,
East, and West directons but not actng at the same tme.

8. Occasional Loads

Loads imposed due to occasional events like wind, earthquake,
etc.

Wind loads - considered or lines with external diameter 14”
NB (including insulatonn or above and at elevaton 10 meters
or higher rom the ground level.

Lateral supports are atached to protect piping rom wind
efects

In case o earthquakes, some restng supports are constructed
as integral two way lateral and vertcal restraints.

Normal operatng temperature is used when analyzing
occasional loads.

Two concurrent occasional loads shouldn’t be considered in
stress analysis.

9. PSV Reacton Force

I the piping system uses pressure sa ety valves
(PSVn, then reacton orce due to PSV operaton is
applicable.

Dynamic Load Factor (DLFn o 2.0 must be applied
on valve reacton orce value.

For high reacton orce value, DLF calculated as per
appendix-II o ASME B31.1 should be used.

10. Slug Force

Considered when stress analysis or lines have slug fow regime. It is calculated as ollows:
 Fslug = (ρn (An (V2n [2(1 – cos θn]1/2 DLF
 Where,
 Fslug = Force due to slug in Newton.
 ρ = Density o the slug in Kg/m3
 A = Inside area o pipe cross secton in m2,
 V = Velocity o moving slug in m/sec.
 θ = inclusion angle at elbow or change o directon
 DLF = Dynamic Load Factor (DLFn equal to two shall be used, unless more accurate value is available.
 Faxial = (ρn (An (V2n DLF
 Forthogonal = (ρn (An (V2n DLF

Slug propertes can be obtained rom Process group.

11. Conclusion

All the types o load cases must be considered or stress analysis o any piping system. Ignoring any one o
them could result in the piping system ailure.

In spite o the best design tools and sophistcated sofware, any pipe stress analysis project is not complete
without clever engineering judgment, experience and oresight.

12. Thank You
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