PIPE STRESS ANALYSIS WORKBy: Tengku SyahdilanSenior Piping Mechanical EngineerPT KBR Engineers Indonesia

AGENDAWhy Do We Perform Pipe Stress Analysis?.Pipe Stress Engineer Scope of Work.Theory of Pipe Stress Analysis.Pipe Supports.Applicable Codes.Pipe Stress Analysis using Caesar II 5.20.Code Compliances and Nozzle Evaluation.Designer Responsibilities Related to Stress Engineering Work.

1. Why Do We Perform Pipe Stress Analysis?To keep stresses in the pipe and fittings within code allowable.To keep nozzle loadings on attached equipment within allowable of manufacturers or recognized standards (API 661, API 650 etc)To calculate design loads for sizing supports and restraints.To determine piping displacements for interference checks.To solve dynamic problems in piping, i.e.: mechanical and acoustic vibration, fluid hammer, pulsation, transient flow and relief valve discharge.To optimize piping design.To prevent flange leakage joint.

2. Pipe Stress Engineer Scope of Work

Pipe Stress Analysis CategoryMethod of Analysis:Category 3Using computer program such as: Caesar II (Coade), Autopipe (Bentley), PIPANL-3 (SSD) etc.

2. Category 4Using approximate methods such as: the Kellogg, Grinnell or Tube Turn methods.

3. Category 5Visual inspection with or without the aid of guided cantilever chart or similar short cut methods.

Ref: KBR Design Manual Subject No: 4100

3. Theory of Pipe Stress Analysis3. 1. Stress-Strain CurveWhere: = Stress (kg/cm2) = StrainE = Youngs Modulus (kg/cm2) Allowable stress is the yield strength divided by safety factor.I.E : Carbon Steel Pipe below creep range commonly has allowable stress is 2/3* y or * u. For detail see Table A-1 in B31.3

3. 2. Basic Stress ConceptsStress due to axial force = F / AF = Axial force acting on cross section (kg)A = Cross-sectional of pipe (mm2)

Stress due to bending and torsionb = Mb / Zt = Mt / 2ZMb = Bending moment (kg-mm)Mt = Torsional moment (kg-mm)Z = Section modulus of pipe (mm3)

Stress due to internal pressureH = PDi / 2t (Hoop)L = PDi / 4t (Longitudinal)P = Design pressure (kg/mm2)Di = Inner diameter (mm)t = Thickness of pipe (mm)

3. 3. Thermal EffectThermal Expansion = T x x L ; (mm) Carbon Steel +/- 1 mm/m for 100oC Stainless Steel +/- 1.35 mm/m for 100oC

Thermal Stress = x = /L x E = T x x E

Reaction ForceF = x A

Example: 1meter length of 8 NPS CS Pipe STD at 100oC. T ambient = 20oC1. = (100-20)x12x10-6x1000 = 0.96 mm2. = (100-20)x12x10-6x20000 = 19.2 kg/mm23. F = 19.2 x x (2192-2032)/4 = 27.6 ton

Damage

4. Pipe Support

5. Applicable Codes5.1. Piping Design CodeASME B31.1 Power PipingASME B31.3 Process PipingASME B31.4 Pipeline (Hydrocarbon)ASME B31.8 Pipeline (Gas)ASME Section III Nuclear Component Design

5.2. Related Code for Nozzle EvaluationAPI Std 610 Centrifugal PumpAPI Std 611 Steam TurbinesAPI Std 617 Centrifugal CompressorAPI Std 618 Reciprocating CompressorAPI Std 650 Welded Steel TanksAPI Std 560 Fired Heaters (Furnace)API STD 661 Air-Cooled Heat Exchangers (AFC)NEMA SM23 Steam TurbinesASME SEC VIII Pressure VesselWRC 107, WRC 297 Local Stress on Nozzles

ASME: The American Society of Mechanical EngineersAPI: American Petroleum InstituteNEMA: National Electrical Manufacturers AssociationWRC: Welding Research Council

6. Pipe Stress Analysis using Caesar II 4.506.1. Required Data:Piping Configuration complete with dimension.Material Spec. :Size, Thickness, Material Properties, method of bracing, etc.LDT (Line Designation Table): Pressure, Temperature, Insulation Thickness, Density etc.Equipment Drawing to determine nozzle movement. Wind and earthquake loading.Standard valve and flange weight.Number of operating cycles if any.Misc. item drawing such as silencer etc.6.2. Item need to be concerned:Boundary Condition.Operating Case, i.e: pump, run or stand-by.Friction.

7. Code Compliances and Nozzle EvaluationPrimary Load Characteristics:Primary loads are usually force driven (gravity, pressure, spring force, relief valve, fluid hammer etc).Primary loads are not self-limiting.Primary Loads are typically not cyclic in nature.Allowable limits for primary stress are related to the material yield stress, the ultimate strength or time-dependent stress rupture due to sustained load.Excessive load causes plastic deformation and rupture.

7.1 Primary vs. Secondary LoadsSecondary Load Characteristics:Secondary loads are usually displacement driven (thermal exp, anchor movement, settlement, vibration etc).Secondary loads are almost self-limiting.Secondary Loads are typically cyclic in nature except settlement.Allowable limits for secondary stress are based upon cyclic and fatigue failure modes.A single application of load never produce failure.

7.2. Code Stress Equations7.2.1. B31.1 Power Piping7.2.2. B31.3 Process Piping

7.3. Nozzle Evaluation7.3.1. Pump (API Std 610)

7.3.2. AFC (API Std 661)

7.3.3. Pressure Vessel/Heat Exchanger (KBR Specification)Note: For detail see Halliburton KBR Specification Doc. No: 308-7080-ST-54-101

7.3.4. Furnace (API Std 560)

7.3.5. Compressor and Turbines (NEMA SM23)

7.3.6. Tanks (API Std 650)

8. Designer Responsibilities Related to Stress Analysis WorkTo prepare stress sketch/isometric drawing based on critical line list from stress engineer.To prepare piping loading information for Civil and Equipment Department and Stress Engineer shall indicate the loads.To utilize the span table for horizontal support (guide) and vertical support (resting).To select a proper pipe support based on pipe support selection criteria and stress sketch from stress engineer.To inform the clearance for spring support installation.To prepare misc. support drawing as needed and then shall be verified by Stress Engineer.Etc.

8.1. Piping Loading Information to Equipment

8.2. Around PumpAdjustable SupportItems to be concerned:Shortest suction line shall be planned to minimize pressure loss.Adjustable supports shall be installed for suction and discharge line for pump maintenance and alignment and the location as close as possible to the nozzle.Care shall be taken in thermal stress calculations because the entire piping does not always have the same temperature, depend on operation plan.To relieve reaction force and moment due to thermal stress on the piping, expansion loops and restraint supports such as anchor, stopper, guide, resting and spring support shall be used.

Sway Brace

Re-strutAdjustable GuideVesselCompressorRe-strutCompressorAdjustable GuideRe-strut

Items to be concerned:Support arrangement of piping manifold shall be prepared to make it simple and economic.Piping route shall be flexible to prevent excessive forces and moments on the AFC nozzle.Piping support around AFC shall be selected to eliminate the vibration and excessive forces and moments to the AFC nozzle due to thermal stress. Stopper type support shall be installed as close as possible from the center of piping manifold.Vibration due to slug force can be eliminated by install properly stopper and guide support.

VesselAFCStopper8.5. Around AFC

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