PIPE STRESS ANALYSIS WORK

By: Tengku Syahdilan

Senior Piping Mechanical Engineer

PT KBR Engineers Indonesia

AGENDA

1. Why Do We Perform Pipe Stress Analysis?.

2. Pipe Stress Engineer Scope of Work.

3. Theory of Pipe Stress Analysis.

4. Pipe Supports.

5. Applicable Codes.

6. Pipe Stress Analysis using Caesar II 5.20.

7. Code Compliances and Nozzle Evaluation.

8. 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

-Depend on Client Specification.

Review andComment onConceptual

Studies

Review 3DModel and

Support Scheme

Review andApprove the

Stress Isometric

Develop Critical Lines List

Review StressIsometric

Revise the PipingLayout & Isometric

Acceptable?No

Yes

-Category 3 (Computer Analysis).

-Category 4 (Approximate Method).

-Category 5 (Visual Exam.).

-Modify pipe support type and location.

-Add elbow to increase

piping flexibility.

-Stresses are within allowable.

-Nozzle loads are within allowable.

-Anchor and guide support location are already fixed and already informed the loading values to Civil Department.

-To prepare pipe support selection.

-To select pipe support based on pipe support selection criteria.

-To check the 3D Model is comply with the latest stress calculation or not.

Pipe Stress Analysis Category

Method of Analysis:1. Category 3

Using computer program such as: Caesar II (Coade), Autopipe (Bentley), PIPANL-3 (SSD) etc.

2. Category 4

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

3. Category 5

Visual 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 Analysis

3. 1. Stress-Strain Curve

E x ε σ

Where:

σ = Stress (kg/cm2)

ε = Strain

E = Young’s 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* σy or ¼* σu. For detail see

Table A-1 in B31.3

3. 2. Basic Stress Concepts

Stress due to axial force σ = F / A

F = Axial force acting on cross section (kg)A = Cross-sectional of pipe (mm2)

Stress due to bending and torsion

σb = Mb / Z

σt = Mt / 2ZMb = Bending moment (kg-mm)

Mt = Torsional moment (kg-mm)Z = Section modulus of pipe (mm3)

Stress due to internal pressureσH = PDi / 2t (Hoop)

σL = PDi / 4t (Longitudinal)P = Design pressure (kg/mm2)

Di = Inner diameter (mm)t = Thickness of pipe (mm)

Mt

Mb

FF

σL σH P

3. 3. Thermal Effect

Thermal Expansion

δ = ΔT x α x L ; (mm) Carbon Steel +/- 1 mm/m for 100oC Stainless Steel +/- 1.35 mm/m for 100oC

Thermal Stressσ = ε x Ε = δ/L x E = ΔT x α x E

Reaction ForceF = σ x A

Example: 1meter length of 8” NPS CS Pipe STD at 100oC. T ambient = 20oC1. δ = (100-20)x12x10-6x1000 = 0.96 mm2. σ = (100-20)x12x10-6x20000 = 19.2 kg/mm2

3. F = 19.2 x π x (2192-2032)/4 = 27.6 ton

δ (Pushed)

ForceDamage

4. Pipe Support

4.1. Support Around Control Valve

Control ValveSliding Support

Tight Support Variable Spring Support Adjustable Guide

4.2. Spring and Adjustable Support

4.3. Hold Down Guide

Sliding Plate

4.4. Anchor

PadShoe

4.5. Spring Hanger Assembly

Eye Bolt

Spring Hanger

Turnbuckle

Pipe Clamp

Structure

4.6. Stopper

5. Applicable Codes

• 5.1. Piping Design Code ASME B31.1 Power Piping ASME B31.3 Process Piping ASME B31.4 Pipeline (Hydrocarbon) ASME B31.8 Pipeline (Gas) ASME Section III Nuclear Component

Design

• 5.2. Related Code for Nozzle Evaluation

API Std 610 Centrifugal Pump API Std 611 Steam Turbines API Std 617 Centrifugal Compressor API Std 618 Reciprocating Compressor API Std 650 Welded Steel Tanks API Std 560 Fired Heaters (Furnace) API STD 661 Air-Cooled Heat Exchangers

(AFC) NEMA SM23 Steam Turbines ASME SEC VIII Pressure Vessel WRC 107, WRC 297 Local Stress on

Nozzles

ASME: The American Society of Mechanical Engineers

API: American Petroleum Institute

NEMA: National Electrical Manufacturers Association

WRC: Welding Research Council

6. Pipe Stress Analysis using Caesar II 4.50

6.1. 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.

K-3301A

K-3301B

K-3301C

V-1001

V-1002Spring Hanger (Typ. 12ea)

Spring Support

Vertical Guide

Trunnion (Typ. 3ea)

Guide (Typ. 3ea)

7. Code Compliances and Nozzle Evaluation

Primary Load Characteristics:1. Primary loads are usually force

driven (gravity, pressure, spring force, relief valve, fluid hammer etc).

2. Primary loads are not self-limiting.

3. Primary Loads are typically not cyclic in nature.

4. Allowable limits for primary stress are related to the material yield stress, the ultimate strength or time-dependent stress rupture due to sustained load.

5. Excessive load causes plastic deformation and rupture.

7.1 Primary vs. Secondary Loads

Secondary Load Characteristics:1. Secondary loads are usually

displacement driven (thermal exp, anchor movement, settlement, vibration etc).

2. Secondary loads are almost self-limiting.

3. Secondary Loads are typically cyclic in nature except settlement.

4. Allowable limits for secondary stress are based upon cyclic and fatigue failure modes.

5. A single application of load never produce failure.

7.2. Code Stress Equations

• 7.2.1. B31.1 Power Piping 7.2.2. B31.3 Process Piping

HoA

sus St

Pd

Z

iM.S

4

750

)25.125.1( SUSHCAC

EXP SSSfSZ

iMS

HoBA

OCC kSt

Pd

Z

iM

Z

iMS

4

75.075.0

Where:

MA = Resultant moment due to sustained, kg-mm

SH = Allowable stress at operating temperature, kg/mm2

i = Intensification factor

Mc = Resultant moment due to expansion, kg-mm

SA = Allowable expansion stress, kg/mm2

MB = Resultant moment due to occasional, kg-mm

k = occasional factor

= 1.2 for loads occurring less than 1% of the time

= 1.15 for loads occurring less than 10% of the time

SC = Allowable stress at installation temperature, kg/mm2

Hoooii

m

axsus S

t

Pd

Z

MiMi

A

FS

4

])()[( 2/122

)25.125.1(]4)()[( 2/122

*2

*SUSHCA

TooiiEXP SSSfS

Z

MMiMiS

HlSUSOCC SSSS 33.1

Where:

Fax= Axial force due to sustained, kg

Mi = In-plane bending moment due to sustained, kg-mmMo = Out-plane bending moment due to sustained, kg-mm Mi* = Range of in-plane bending moment due to expansion, kg-mmMo* = Range of out-plane bending moment due to expansion, kg-mmSH = Allowable stress at operating temperature, kg/mm2

ii ,io = In-plane, out-plane intensification factorMT = Torsional moment due to expansion, kg-mmSA = Allowable expansion stress, kg/mm2

SC = Allowable stress at installation temperature, kg/mm2

Sl = Bending stress due to occasional loads such as wind/earthquake f = Stress range reduction factor

7.2.3. B31.4 Liquid Transportation Piping

Yieldblpsus x S. x .SSS 720750

YieldtbEXP SSSS 72.0)4( 2/122*

YieldSUSEXPHOPE SFSSSvTEaFS 9.0)1(

YieldblpOCC x k x S. x .SSS 720750**

Where:

Slp = Longitudinal pressure stress, kg/mm2

Sb = Bending stress due to sustained, kg/mm2

Sb* = Range of bending stress due to expansion, kg/mm2

St = Range of torsional stress due to expansion, kg/mm2

Sb** = Bending stress due occasional, kg/mm2

Syield = Specified minimum yield stress material, kg/mm2

F = 1 (under ground pipeline); 0 (above ground pipeline)

E = Modulus of Elasticity

a = Thermal expansion coefficient

ΔT = Temperature change of pipe from ambient

v = Poisson’s ratio

SH = Hoop stress kg/mm2

k = Occasional load factor

7.2.4. B31.8 Gas Transportation Piping

T S x F x .SSS blpsus 750

SSSS tbEXP 72.0)4( 2/122*

SSSS SUSEXPOPE

x T x k x S x F.SSS b**lpOCC 750

Where:

Slp = Longitudinal pressure stress, kg/mm2

Sb = Bending stress due to sustained, kg/mm2

Sb* = Range of bending stress due to expansion, kg/mm2

St = Range of torsional stress due to expansion, kg/mm2

Sb** = Bending stress due occasional, kg/mm2

S = Specified minimum yield stress material, kg/mm2

F = Construction type

T = Temperature derating factor

k = Occasional load factor

7.3. Nozzle Evaluation

7.3.1. 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)

eRR DMF 5003

eRR DMF 5003

Fx = 50 Dc

Fy = 125 Dc

Fz = 100 Dc

Mx = 250 Dc

My = 125 Dc

Mz = 125 Dc

Individual Forces and Moments

Total Resultant Forces and Moments

Combine Loads for Inlet and Outlet

eRR DMF 5003

CCC DMF 2502

7.3.6. Tanks (API Std 650)

Note:

Appendix P on API Std 650 shown that the nomogram is only applicable for tanks larger than 36 m in diameter.

If not we will use WRC297 to verify our piping loads are within allowable or not , but it will be better to ask Tank Department to verify our piping loads.

API Std 650 is not mention how to verify the nozzle loads at roof of tank.

8. Designer Responsibilities Related to Stress Analysis Work

• To 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

Plan View

8.2. Around Pump

Adjustable Support

Items to be concerned:

1. Shortest suction line shall be planned to minimize pressure loss.

2. 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.

3. Care shall be taken in thermal stress calculations because the entire piping does not always have the same temperature, depend on operation plan.

4. 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

Reactor

Fired Heater

Sway Brace

Adjustable Guide

Constant Hanger

Lift Off

Constant Hanger

Items to be concerned:

1. Piping shall be designed to have sufficient flexibility but it shall be arranged as short as possible.

2. Piping support around reactor shall be selected to eliminate the vibration and excessive forces and moments to the reactor nozzle due to thermal stress. Fixed type support shall be installed as close as possible from the nozzle.

3. Sway brace is vibration eliminator and identical to variable hanger in their resistance against thermal expansion, so should be installed at location where the thermal displacement is as smaller as possible.

8.3. Around Reactor and Fired Heater

Re-strut

Adjustable Guide

Vessel

Compressor

Re-strut

Items to be concerned:

1. Piping route shall be flexible to prevent excessive forces and moments on the compressor nozzle.

2. Piping support shall be installed well balanced so no excessive forces and moments on the compressor nozzle.

3. Piping connected to and from suction and discharge of compressor shall be equipped with vibration proof as required.

4. Vibration proof piping support shall allows piping movement caused by thermal expansion and prevent piping vibration caused by compressor.

5. Sleeper support shall be adopted to abate the vibration of piping and shall be not connected or closed to compressor shelter to prevent sleeper piping vibration is transmitted to shelter.

6. To check the natural frequency of piping system against compressor.

7. Expansion joint shall not be used for vibrating line which may cause damage.

8.4. Around Compressor

Compressor

Adjustable Guide

Re-strut

Items to be concerned:

1. Support arrangement of piping manifold shall be prepared to make it simple and economic.

2. Piping route shall be flexible to prevent excessive forces and moments on the AFC nozzle.

3. 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.

4. Vibration due to slug force can be eliminated by install properly stopper and guide support.

Vessel

AFC

Stopper

8.5. Around AFC

THE END