Civil/Structural Engineers need to know how difficult to design pipe support with a safe & economical design to support the piping loads, especially when final piping drawings are not available. ...
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Pipe
Piping Stress Analysis
Stress Analysis
Overview
What is Flexibility Analysis ?
Fundamentals of Primary & Secondary stresses
Analytical Method to calculate Displacement & Stresses
Checking Flexibility using Nomographs
Guidelines for lines connected to Critical Equipment
Stress Analysis using CAESAR-II
Various Load Cases
Spring Supports
Expansion Joints
Stress Analysis- Responsibilities & Methodology
Fundamentals of Buried Pipe Analysis
Stress Analysis
Flexibility What is Flexibility of the Piping System? Ability to absorb thermal growth of the piping system Temperature
Not Flexible HO T
COLD
Flexible
More Flexible
Stress Analysis
Overview
What is Flexibility of the Piping System? Ability to absorb thermal growth of the piping system How to provide Flexibility in the Piping system ? By change in direction using BENDS, utilising Expansion joints
What code states about Flexibility in the Piping system ?
“ Piping system shall be designed to have sufficient flexibility to prevent pipe movements from causing failure from overstress, leakage at joints or detrimental distortion of connected equipment resulting from excessive thrusts and moments “
HOW to conclude whether system is Flexible or not ?
Stress Analysis Acceptability Criteria Piping
system- flexible and safe only IF following criteria are satisfied
Criteria Thermal stresses <= Allowable Stress Range Sustained (Primary) Stresses <= SH or SC Max Thermal Displacement- Axial / Lateral Pipe Sagging Flange Leakage Support Loading Nozzle Loading Vessels and Heat Exchangers Centrifugal Pumps Centrifugal Compressors Reciprocating Compressors Air Cooled Exchangers Steam Turbines
Stress Loading type - CYCLIC Failure type - FATIGUE Failure time - Number of Cycle
Conclusion ?
Stress Analysis
Allowable Stress Range Yield Stress ( Sy )
=1.5 x Allowable Tensile Stress ( Sc or Sh)
Allowable Stress Range ( Sa) = (1.5 x Sh) + (1.5 x Sc) = 1.5 ( Sc +Sh ) Reduced allowable = 1.25 ( Sc + Sh)
To account for simplification in calcn.
Provision of Primary stresses = Sh
To account for localised stresses
Allowable Stress Range ( Sa) = (1.25 Sc + 0.25 Sh ) x f
f HOT COLD
= = = = = = =
Stress reduction factor 1 For life cycle up to 7000 0.9 For life cycle 7001 ~ 14000 0.8 For life cycle 14001 ~ 22000 0.7 For life cycle 22001 ~ 45000 0.6 For life cycle 45001 ~ 100000 0.5 For life cycle 100001 & over
Stress Analysis
Stress Evaluation Linear Coef of thermal expn.
Temperature
( Ref. B31.3, Table C-1 )
L
=
x L
Young Modulus of Elasticity ( Ref. B31.3, Table C-6 )
HOT COLD
Stress = Strain x E Force = Stress x Area Guided Cantilever Method = 48 (L)2 S / E D S
=
E D / 48 (L)2
Stress Analysis
Stress Evaluation-In & Out Plan Bending, SIF Mt
Sb = ( Ii x Mi )2+ ( Io x Mo )2
Mo Mi
Z
Ii Io
= SIF factor- In Plane B 31.3 Table D-1 = Sif factor- Out Plane
Z
= Sectional Modulus of Elasticity = 3.142 x ( Do3 - Di3 ) / 32
St
= Mt / ( 2 x Z )
Se =
Sb2 + 4 x St2
For safe design Se < = Sa
Stress Analysis
Simplified method to check piping system flexibility Basis - Code B 31.3 para 319.4.1 D x
IF
(L - U)
2
<=
K
Then Piping is Flexible
D = Pipe OD
( mm )
= Resultant Displacement ( mm ) U HOT
L
COLD
L = Developed Length
( mtrs )
U = Anchor Distance
( mtrs )
K = 208.3 Limitations
Only two point of fixation
No change in pipe size
No intermediate restraint
Stress Analysis
Other Methods to check the flexibility Using
Nomographs
To perform quick flexibility check To estimate preliminary anchor loading for civil structural design To do preliminary exp.. loop sizing on pipe rack at early stage of the job To review visual analysis lines to avoid expensive CAESAR analysis Using
Computer application - CAESAR-II
Highly versatile application program Based on Finite Element Analysis Method Results are acceptable to world wide Engineering companies
Stress Analysis General Working Procedures Initial
Review
Review Piping Specification Review Piping Study Drawing around critical equipment Identify critical civil structural requirements Review all applicable project standards Quick check using Excel spreadsheet for Pipe Wall and Br. Reinf. Calculation Prepare Preliminary Stress Critical Line List Review Pipe-Rack study layout- Establish preliminary exp.. loop location Establish preliminary Pipe-rack loading for structural design Detailed
Review
Identify CAESAR Stress Models- Include group of lines in single model Perform detailed stress analysis based on issued stress critical line list Analyse visual check lines using simplified manual techniques Communicate with civil, Vessel and Mechanical groups for loading Final
Approval
Freeze the stress model based on final isometrics Documentation of Input and Output Reports
Stress Analysis General Working Procedures
Identify Stress
Review
Critical LinesStress Critical Line List
Stress Isometric
Acceptable ? ?
No
Revise the Piping study & Isometric
Yes
Freeze
Approve
Nozzle
Supporting arrangement
the Stress Isometric
loading & Civil Loading
Stress Analysis Responsibilities of Stress Engineers Stress Lead Engineer
R e s p o n s i b i l i t i e s
Nominated by Chief Piping Engineer Responsible for all Stress and Support related activities
Ensure work carried out per Procedures and Design Basis
Establish the Contract Design Data and Design Philosophy
Issue Stress and Support Design Note
Establish Stress Critical Line List
Stress Group Progress Reporting, Man-hours allocation and Forecast
Raise the Change order to reflect additional work
Supervise Stress and Support activities
Review Piping Specification for Pipe wall thickness and Branch Calc
Job close-out report for stress and support group
Stress Engineer
R e s p o n s i b i l i t i e s
Stress Analysis Responsibilities of Stress Engineers
Nominated by Chief Piping Engineer/Lead Stress Engineer
Carry out Flexibility analysis
Identify all the load cases to be considered in analysis
Review Study Drawing to ensure sufficient flexibility in critical piping
Identify and review all critical piping supports
Summarise Equipment Nozzle Loading communicate to others
Perform flange leakage calculation for high pressure piping
Communicate critical support loading to Civil
Prepare Spring Schedule/Bellow Specification for procurement
Identify requirement of reinforcement pad due to stress consideration
Decide on position of Fixed saddle of horizontal Heat Exch.. and Vessels
Review Vendor data regarding nozzle loading etc..
Documentation of Analysis Reports
Stress Analysis
SPRING Supports Spring
Hangers/ supports
Why required ? ? ?
Types of Spring supports
Variable Type
Principle of working
Terminology
Constant Force Type
Cold Load Hot Load Spring Rate
Technical Specification
Instruction for Field Installations
Travel
Stress Analysis
Expansion Bellows
Why to use ? ? ?
Why NOT to use ? ? ?
Material of Construction
Metallic Bellow
Non- Metallic ( Rubber / Fabric )
Types of Metallic Bellows
Axial Hinged
Universal Gimbal
Swing Tied Pressure Balanced
Back Thrust of Un-tied bellow
Selection Criteria
Technical Specification
Instruction for Field Installations
Piping Supports
Pipe Supports Overview
Purpose of Support
Type of Supports
Pipe support Standard
Pipe support Instructions and Design Guide
Pipe Support - Span Table
Pipe Support - Trunnion Calculation
Pipe Supports
Purpose of Pipe supports Purpose
To Support dead weight of Piping system
To minimise Pipe Sagging
To take Expansion load in the Piping system
To absorb wind load and Seismic load
To absorb Vibration in the Piping system
To Suppress the Noise level in the Pulsating Piping systems
To absorb Hydraulic Thrust in the Piping system
To absorb the Pressure Thrust of Bellow
To Support the system during Shut down/ Maintenance Cond.
Pipe Supports
Types of Pipe supports Based
on Functions
Loose or Resting supports Longitudinal Guide Supports Transverse Guide Supports Welded Type Anchor Supports Non- Welded Type Limit Stops
