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Stress Analysis

Method and Emphasis points

David Cohen – 29/09/14

• The Most important reason stress analysis is carried out is : SAFETY

• This is achieved by designing a Code Compliant System.

• There are also Financial Saving to be made:

• Correct pipe support spans

• Material sizes and thickness which are correctly specified.

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General

Ideal Flowchart

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Dangers

High pressure Flammable

Good practice engineering, Quality controls, Experienced engineers, and correct installation should avoid dangerous consequences

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Dangers

Buried Pipes : along roads and in civil areas.HIDDEN DANGERS should be considered seriously

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• Design and Analysis should take into account also construction feasibility

• The designer should run different analyses according to specifying steps.

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Codes

• Loading Codes:

• Seismic Loads: SI-413

• Wind Loads: SI-414

• Traffic and Earth Loads: ASCE-Guidelines for the design of buried steel pipe

& Geotechnical Report

• Piping Codes:

• ASME B31.3

• ASME B31.8

• SI-5664

• NEN 3650

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Sources for generation of stress in a Piping System:•Weight

•Internal/External Pressure

•Temperature change

•Occasional Loads due to wind, seismic disturbances, PSV discharge etc.

•Forces due to Vibration.1.Sustained Stresses are the stresses generated by sustained loads. (e.g. Pressure , Weight). These loads are present

continuously throughout plant life.

2.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.

3.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 joint strength reduction factor.

4.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).

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Seismic Load התאמת

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M.J. O’RourkeX. Liu

Seismic Load התאמת

Lateral Ground Disp

High Seismic area: Solutions

David Cohen

David Cohen11

The SI-414 is giving a very detailed method for calculating wind forces on round elements

WIND Load התאמת

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WIND Load התאמת

TRAFFIC Load התאמת

Soil-Pipe Interaction

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Soil-Pipe Interaction

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Supports Definition

The supports should be in accordance with actual structures, and not “in the air”

The supports should be placed correctly

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Coefficient of friction factor depending upon the supporting interface (i.e, junction between Top of Steel and Bottom of Pipe or Bottom of Shoe/Cradle) shall be applied at all vertical restraint (+Y or Y supports) locations as mentioned below.

Carbon Steel to Carbon Steel: 0.3Polished Stainless Steel to Polished Stainless Steel/Graphite: 0.15Teflon to Teflon/ Polished Stainless Steel: 0.10Concrete to Carbon Steel: 0.4Pipe to Roll Support: 0.01Teflon to Carbon Steel: 0.2

Supports Friction

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From Piping design to stress analysis, just check that any design problem will occur.

PIPING Redesign will generate a new stress analysis process.

Check the Model

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From Soil Report

Soil Data should be inserted according to soil report , pipe diameter and pipe depth.

Insert Data

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ALL Line Numbers should be writtenOnly on main lines (not for vents)

ALL Supports should be with different name , check duplicity (line stop should be the same support name)

Insert Data

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Analysis Settings

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Check the highest displacement value : DR

Insert Data

Check the highest Support/Anchor Reaction Global FR