Basics Of Pipe Stress Analysis 5w1s1i

BASICS OF PIPE STRESS ANALYSIS: A PRESENTATIONPart 1 of 2 BASICS OF PIPE STRESS ANALYSIS: A PRESENTATION Contents 

Objectives of Pipe Stress Analysis

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Governing Codes and Standards

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Stresses in a Piping System

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Reducing Piping Stresses

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Basic Allowable Stress

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Loads on a Piping System

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Work Flow Diagram

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Stress Criticality & Analysis Method

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Piping Stress Analysis using Software Caesar II

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Type of s

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Questionnaire

Objectives of Pipe Stress Analysis: Structural Integrity: 

Design adequacy for the pressure of the carrying fluid.

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Failure against various loading in the life cycle . Limiting stresses below code allowable.

Operational Integrity: 

Limiting nozzle loads of the connected equipment within allowable values.

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Avoiding leakage at ts.

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Limiting sagging & displacement within allowable values.

Optimal Design:

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Avoiding excessive flexibility and also high loads on ing structures. Aim towards an optimal design for both piping and structure.

Governing Codes and Standards: 

Codes and Standards specify minimum requirements for safe design and construction (i. e. provides material, design, fabrication, installation and inspection requirements.)

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Following are the codes and standards used for Refinery Piping:

1. ASME B31.3: Process piping Code 2. ASME B31.1: Power Piping Code 3. Centrifugal Pumps: API 610 4. Positive Displacement Pumps: API 676 5. Centrifugal Compressors: API 617 6. Reciprocating Compressors: API 618 7. Steam Turbines: NEMA SM23/ API 612 8. Air Cooled Heat Exchanger: API 661 9. Fired Heaters: API 560 10. Flat Bottom Welded Storage Tanks: API 650 11. Heat Exchangers: TEMA/ Vendor Specific. 12. Vessel/Column: Vendor Specific Stresses in a Piping System: 

Sources for generation of stress in a Piping System:

1. Weight 2. Internal/External Pressure 3. Temperature change 4. Occasional Loads due to wind, seismic disturbances, PSV discharge etc. 5. Forces due to Vibration.

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Sustained Stresses are the stresses generated by sustained loads. (e.g. Pressure , Weight). These loads are present continuously throughout plant life.

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Resistive force arising out of sustained stresses balance the external forces keeping the system in equilibrium. Exceeding sustain allowable stress value causes catastrophic failure of the system.

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As per ASME B 31.3, (clause 302.3.5) “ The sum of the longitudinal stresses, SL, in any component in a piping system, due to sustained loads such as pressure and weight, shall not exceed the product Sh x W ”. Where, Sh=Basic allowable stress at maximum metal temperature expected during the displacement cycle and W=weld t strength reduction factor.

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Pressure Stresses are taken care of by calculating and selecting proper pipe thickness. The pressure thickness (t) of a straight pipe can be obtained as per ASME B31.3 from the equation (Clause 304.1.2) mentioned in Fig.1: