Will help you understand and appreciate need of stress analysis

1. Walk-Through Pipe Stress
By
Ashish Shrivastava

2. 3 Questions?
Walk-Through Pipe Stress

3. Why Pipe Stress Analysis?

4. Why Pipe Stress Analysis?
Piping systems are network of piping, valves and fittings and
process equipment to carry fluids. These are subjected to many
kinds of loads in different scenarios. Different kinds of loads are:
Walk-Through Pipe Stress
Sustained Loads (dead
weight)
• Piping system have
self weight, valve
and fittings weight
fluid weight,
insulation weight

5. Thermal Loads
• All piping systems are required to carry fluid at
some pressure and temperature. Pressure and
temperature results in displacement of pipe as
pipes thermally expand or contract.
• If these pipes are left free, there will be no
force and stress in pipes but these are
connected to some equipment nozzle or other
pipes.
• This results in thermal forces and hence in
stresses.
Walk-Through Pipe Stress
Why Pipe Stress Analysis?

6. Occasional Loads
• Piping systems are also subjected to
Wind/Seismic/Snow/PSV Loads.
Dynamic Loads
• Vibrations/pulsation
• PSV
• Water hammer (Surge)
All these individually or in combination generate stresses, loads
on equipment nozzle & civil structures and displacements in
pipes.
Walk-Through Pipe Stress
Why Pipe Stress Analysis?

7. Consequences:
a) Pipe rapture, Pipe falling out of
supports, deformation of pipes, flange
leak, equipment and structural damage.
b) Can lead to Plant shutdown
c) Fire accidents
d) Loss of Personnel and Property.
e) Financial losses
Walk-Through Pipe Stress
Why Pipe Stress Analysis?

8. To optimize the piping systems and ensure that stresses,
nozzle/structural loads, displacement due to (self weight,
thermal, pressure, wind/seismic, foundation settlement,
pulsation & water hammer etc.) are within the safe limit and
to maintain the structural integrity of piping systems for its
designed life (generally 20 years),
“PIPE STRESS ANALYSIS IS REQUIRED”.
Walk-Through Pipe Stress
Why Pipe Stress Analysis?

9. Pipe Failure- Really?
Pipe stress analysis shows failure but
pipeline runs without failure for years
1. Failure does not mean catastrophic-
excess movement/stress/loads than
allowable is called failure.
2. Allowable is always lower than yield
strength example for ASME B 31.3
(2/3 of yield).
3. Even movement/stress/loads
exceeds yield, plastic deformation
and subsequent fracture point still
are additional margin.
Walk-Through Pipe Stress

10. Do all piping system require
stress analysis-NO
Depends on companies
standards based on permutation
and combination of three:
• Line size (2” and above)
• Temperature
• Connected equipment type (2”
and above for all reciprocating
equipment)
Walk-Through Pipe Stress
Why Pipe Stress Analysis?

11. What to do in Pipe Stress Analysis?

12.  Ensure Stresses in piping systems
are within the code allowable limit
 All equipment nozzles loads are
within the allowable limit provided
by vendors
 Structural loads due to piping are
uniformly distributed
What to do in Pipe Stress Analysis?

13.  Prepare datasheets for
spring hangers, sway
braces, struts and
expansion joints
 Ensure that piping
systems are adequately
supported during
operations and
maintenance
What to do in Pipe Stress Analysis?

14.  Maintain the overall
structural integrity
of piping systems
for its designed
life.
What to do in Pipe Stress Analysis?

15. Acceptance Criteria
Stresses : Applicable Codes like ASME B31.3 (Process piping), B
31.1 (Power Piping) etc.
Equipment nozzles : Standards like API 610 (Pumps), API 661
(Air fin fan coolers), API 650 tanks or vendor provided
allowable limits.
Structural loads : Project Guidelines
Pipe movement : Project Guidelines
Walk-Through Pipe Stress
What we do in Pipe Stress Analysis?

16. Other important parameters
Consistency : Stress Analysis shall be consistence with globally
acceptable methods
Aesthetic look: Stress analysis shall be also aesthetic, identical piping
systems shall have typical layout and supports.
O&M : Plant has to run designed life, stress analysis shall be inline
and supportive of operation and maintenance requirement.
Walk-Through Pipe Stress
What to do in Pipe Stress Analysis?

17. How to do Pipe Stress Analysis?

18. How to do Pipe Stress Analysis?
1. Get process and utilities P&IDs and Line List for all lines
2. Define Critical Line List as per design basis (sample below).
Highly Critical -C1 (Computer Analysis)
• 2” and above connected to reciprocating equipment
• 4” and above with temperature of 200C/-49C
• 4” and above connected to rotary equipment
• 16” and above 120C
Walk-Through Pipe Stress

19. Moderately Critical-C2 (Approximate method)
• 4” and above connected to static
equipment
• 4” and above connected to PSV lines
• 6” and above 120C to 200C
Low Critical –C3 (Visual check)
• 4” and below up to 200C
• 16” and below up to 120C
Walk-Through Pipe Stress
How to do Pipe Stress Analysis?

20. Moderately Critical-C2 (Approximate method)
For C2 category lines some hand calculations are performed for
approx. results
Walk-Through Pipe Stress
How to do Pipe Stress Analysis?

21. Low Critical-C3 (Visual method)
For C3 category lines are no formal analysis is required.
It is done on judgement basis of individual and past experience
1. Piping system is acceptable without formal analysis if it is compared
to identical system is previously analyzed.
2. Piping system is acceptable without formal analysis if a similar
system has run for designed life successfully
3. Piping system can be cleared on the individual experience and
accountability.
Walk-Through Pipe Stress
How to do Pipe Stress Analysis?

22. Design Basis may also define the acceptable values for
1. Applicable Code (ASME B31.3)
2. Stress (generally 90%)
3. Sagging (generally 10 mm)
4. Displacement (generally axial- 200mm on rack, lateral
50 mm)
5. Equipment nozzle loads in absence of vendor data
6. Maximum Pipe support loads limits (More than 5 tons)
7. Use of special supports like springs, expansion joints etc.
8. Assumptions
Walk-Through Pipe Stress
How to do Pipe Stress Analysis?

23. Pipe Stress Analysis for C1 (Computer Analysis) is done in 4 steps
1) Modelling 2) Load case
3) Analysis 4) Output
Walk-Through Pipe Stress
How to do Pipe Stress Analysis?

24. Inputs Required for Modelling:
• Isometrics
• LDT -(Design temp, pressure, Ope. Temp, Min. Temp, Fluid density,
Material, Line Size and thickness, Insulation thk and density,
Corrosion allowance etc)
• P&ID
• Equipment GA with allowable nozzle loads
• Piping Material Specification
• PSV/ Control Valve GA and Datasheet
• Soil Characteristics from civil for underground analysis
• Wind and Seismic data
• Plot Plan for finding HPP elevation and equipment orientation.
• Governing Code
Walk-Through Pipe Stress
How to do Pipe Stress Analysis?

25. Load Case Setup:
Load cases are setup for different operating scenarios by
combining different loads case.
1. Max & Min Design conditions (for nozzle/structural loads
and displacements)
2. Operating conditions ( for nozzle loads of rotary
equipment)
3. Sustain conditions (for dead weight)
4. Occasional conditions (wind/seismic/psv for stresses and
loads)
5. Expansion range (for stresses)
Walk-Through Pipe Stress
How to do Pipe Stress Analysis?

26. Analysis:
• Providing additional pipe supports like rest, guide, anchor, anti-
friction pads springs and Expansion joints.
• Make necessary layout changes (loops, perpendicular legs) to
ensure stresses, displacement, loads are within the allowable.
Walk-Through Pipe Stress
How to do Pipe Stress Analysis?

27. Final Stress report with following with
annexures.
• Project background
• Inputs
• Assumptions/Deviations/Notes
• Results
Walk-Through Pipe Stress
How to do Pipe Stress Analysis?

28. Final Stress report with following with annexures.
Annexures
a) Native software file
b) Stress mark up on isometrics with pipe supports
like rest, guide, anchor and springs details.
c) Input Echo
d) Stress summary
e) Restraint summary extended
f) Displacement summary
g) Data sheets of springs and expansion joints etc.
h) Nozzle load sheets
Walk-Through Pipe Stress
How to do Pipe Stress Analysis?

29. Summary
 In this Webinar, we learnt about:
 Why Pipe Stress Analysis
 What to do in Pipe Stress Analysis
 How to do Pipe Stress Analysis

30. Thank You!