mtd-99.100

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HSEHealth & Safety

Executive

Transient vibration

guidlines for fast acting valves

screening assessment

Prepared byAcoustic Technology Limited

for the Health and Safety Executive

OFFSHORE TECHNOLOGY REPORT2002/028

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HSEHealth & Safety

Executive

Transient vibration

guidlines for fast acting valves

screening assessment

Acoustic Technology Limited36-38 The Avenue

Southampton

SO17 1XN

United Kingdom

HSE BOOKS

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Crown copyright 2002Applications for reproduction should be made in writing to:Copyright Unit, Her Majestys Stationery Office,St Clements House, 2-16 Colegate, Norwich NR3 1BQ

First published 2002

ISBN 0 7176 2511 7

All rights reserved. No part of this publication may bereproduced, stored in a retrieval system, or transmittedin any form or by any means (electronic, mechanical,photocopying, recording or otherwise) without the priorwritten permission of the copyright owner.

This report is made available by the Health and SafetyExecutive as part of a series of reports of work which hasbeen supported by funds provided by the Executive.Neither the Executive, nor the contractors concernedassume any liability for the reports nor do theynecessarily reflect the views or policy of the Executive.

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Summary

To avoid the hidden threat posed by transient excitation due to the rapid operation of valves on

process pipework, a screening methodology has been developed. This screening methodology has

been designed to fit the existing screening methods supplied in the MTD document Guidelines for theavoidance of vibration induced fatigue in process pipework.

This report sets out the theory and screening methods to assess piping local to fast acting gas, liquid

and multiphase valves. The output from the screening is a Likelihood of Failure (LOF) term that when

used in conjunction with the small bore screening assessment in the MTD Guidelines provides a risk

rating for a connection. The risk can then be mitigated against by applying the recommended

modifications outline in the MTD document.

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CONTENTS

1. INTRODUCTION

2. TRANSIENT EXCITATION DUE TO RAPID VALVE OPERATION

2.1 Nomenclature

2.2 Liquid or Multiphase Valve Closure

2.3 Liquid or Multiphase Valve Opening

2.4 Dry Gas Rapid Valve Operation

2.5 Transient Limits

3. TRANSIENT SCREENING

4. SMALL BORE CONNECTION REVIEW

5. CONCLUSIONS

REFERENCES

FIGURES

APPENDICES1. Support Arrangement Selection

2. MTD Small Bore Connection Assessment

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1

1. INTRODUCTION

Steady state vibration of process piping is becoming a better understood phenomenon with

publications such as the MTD Guidelines for the Avoidance of Vibration Induced Fatigue in

Process Pipework (Reference 1); steady state vibration is additionally more easily assessedas part of a vibration survey. Transient events can result in excess levels of vibration for a

short duration, and this can pose a threat to process piping which is not always evident.

A recent investigation into an offshore piping failure in the North Sea concluded that the

failure was due to fatigue damage of a small bore drain connection as a result of several

years of operation of a valve local to the drain connection. Although steady state vibration

levels were minimal at the failure location, the line was exposed to a transient kick each time

the adjacent automatic valve was operated.

As a result of the hidden threat of transient excitation to process piping the following

guidelines for the avoidance of piping failures have been developed. The objective of the

guidelines is to provide a first level screening assessment method, that could be carried out

using the minimum of readily available process or valve information.

Inherent in this technique are a number of worst case assumptions that could potentially

identify high risk systems, a more detailed surge analysis may be required to assess the

system in more detail. The assessment methodology has been developed to be consistent

with the MTD Guidelines by generating a risk ranking in the form of likelihood of failure (LOF)

value for each valve.

For transient events impacting piping there are two limiting acceptance criteria:

Exceedance of the line pressure rating

Force sufficient to induce fatigue damage to the piping

If exceedances of the line pressure rating are predicted a full surge analysis should be

considered. For the case where the piping could be potentially damaged by fatigue, the most

likely failure location is at a small bore connection. If the LOF value predicted for the valve is

assigned to the attached pipework, the system risk assessment can be carried out as per the

MTD guidelines. The MTD guidelines provide the LOF information for small bore connections

and provide the appropriate recommendations as to remedial modifications.

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2

2. TRANSIENT EXCITATION DUE TO RAPID VALVE OPERATION

The methodology for assessing the potential transient excitation due to rapid valve operation

(valve closure/opening in less than 30 seconds) can be split into the following cases:

(i) Liquid or multiphase valve closure;

(ii) liquid or multiphase valve opening;

(iii) dry gas valve operation.

Sections 2.2 to 2.5 describe the theory developed to screen process piping for potential

damage resulting from transient excitation.

2.1 Nomenclature

do - pipe outside diameter (m)

di - pipe inside diameter (m)

c - sonic velocity (m/s)

E - Youngs modulus (N/m2)

Fmax - peak force (kN)

Flim - limit force (kN)

K - fluid bulk modulus (N/m2)

L - pipe length (m)

- fluid mass flowrate (kg/s)

Mw - molecular weight

P0 - static pressure (Pa)

P - pressure difference (bar)

R - universal gas constant (8314 J/kmol.K)

T - temperature (K)

t - time (s)

tc - valve closure time (s)

wt - pipe wall thickness (m)

- ratio of specific heat capacities

- fluid velocity (m/s)

0 - steady state fluid velocity (m/s)

- fluid density (kg/m3)

- pipe wall thickness / schedule 40 wall thickness

LOF - likelihood of failure

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3


The transient force that effects liquid and multiphase piping systems when a fast acting valve

is closed is due to the pressure surge generated by the change of momentum of the fluid.

The maximum surge pressure for a rapid valve closure is given by the Joukowski equation(equation 1).

0max cvP Pascal(1)

The sonic velocity, c, takes into account the combined wave speed of the fluid and the

containing pipe, which for a thin walled pipe gives:

wtEd

K

c

o1

1

m/s(2)

This value is correct for a valve closure time that is less than (2L/c), where L is the effective

upstream pipe length. A closure time of less than (2L/c) is termed sudden, and defines the

condition where the fluid entering the upstream pipework is unaffected by the initial movement

of the valve. In Figure 1 below, the red line indicates the acoustic wave travelling at a speed

c over the pipe length L. For a valve closure to be sudden this wave does not have

sufficient time to travel the distance 2 x L. For typical liquid systems and a valve closure time

of 2 seconds, the upstream pipe length would have to be greater than 800 m for the closure to

be deemed sudden.

FIGURE 1: Acoustic path for valve closure

For slower valve closures the peak pressure is dependant on the rate of change of valve flow

area, initial flow conditions and upstream pipe length. The rate of change of valve flow area is

valve type dependant, however, the maximum rate of change of area is predominantly over

the last few percent of closure.

Vessel oralternativeflow path

Autovalve

L(m)

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4

The pressure at the valve can be estimated by solving a differential equation (see equations 3

& 4).

2

22

0

1

4

1

2PPsurge Pascal(3)

where

0

0 )(

P

tFdt

dLv

.(4)

If the valve is downstream of a pump the shut in head of the pump also needs to be included

for the assessment as to whether the piping pressure rating is exceeded.

0_ PPPP inshutsurgetotal Pascal(5)

The function )(tF is the function defining the flow area of the valve at a time t. If it assumed

that the peak surge pressure occurs at the point where the valve is closed, ie. t equals total

time to closure (tc). This simplifies the differential of )(tF such that a simple term based on

total valve closure time can be expressed, see Table 1. The following terms are valid for

valve closure times up to 30 seconds.

Valve Type

)(tFdt

d

Full bore ball27.0

281.1

ct

Reduced bore ball362.0

168.1

ct

Butterfly275.0

877.2

ct

Globe32.0

266.2

ct

Gate315.0

41.3

ct

TABLE 1: Valve closure functions

The maximum transient force due to the rapid closure of a valve in a liquid system is:

4000

2

max isurge

dPF kN(6)

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5


If a closed valve in a liquid or multiphase system can be depressurised on the downstream

side, there is the potential for cavitation or a phase instability problem when the valve isopened. The pressure profile with distance for a valve typically follows the form shown in

Figure 2. The horizontal scale goes from upstream (negative) to downstream (positive) of the

valve, which is located at zero. The minimum pressure occurs at the valves vena contracta,

there is then a pressure recovery zone resulting in a final pressure drop for the valve.

The values for maximum pressure drop and total pressure drop are dependent on fluid

density, fluid velocity and valve loss coefficient. The loss coefficient for a valve is the constant

that relates the pressure drop across the valve to the flow velocity.

FIGURE 2: Typical Static Pressure profile across valve.

For a liquid, if the pressure drop across the valve is such that pressure downstream of the

pressure recovery zone is below the vapour pressure for the liquid, a large increase in the

vapour fraction (flashing) can occur. The downstream pipework causes the system to be

semi-bounded, this results in a situation where the rapid increase in specific volume due to

the phase change from liquid to vapour can cause a localised pressure increase which results

in a reversal of the phase change. The resulting forces from large bubbles forming and then

collapsing can be sufficient to cause excessive vibration.

In the case where:

a) the static pressure at the valves vena contracta is less than the liquids vapour pressure

and

-4 0 4 8 12 16

Length/diameter

Staticpressure

max dp

Total dp

flow

Pressurerecovery zone

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6

b) the static pressure after pressure recovery (ie. 5 to 6 diameters downstream of the valve),

is greater than the vapour pressure then cavitation will occur.

Cavitation is a more localised effect than the flashing described above. Small bubbles are

formed at the vena contracta, these bubbles then collapse in the pressure recovery region.This effect commonly occurs on fire water and water injection overboard dump lines. As the

opening of a valve is a transient event and the maximum pressure drop is changing with valve

position, there can be cavitation for a short duration. Typically, the dynamic forces due to

cavitation are not as extreme as those for flashing, but are still capable of causing pipework

failures.

The calculation for the pressure at the vena contracta for various valve types is ongoing.

Initial indications are that ball valves are unlikely to have a cavitation problem, whereas with

globe, butterfly and gate valves cavitation is possible. A conservative estimate for the

pressure at the vena contracta would be to take the downstream pressure minus 20% of the

pressure across the valve.

If neither flashing nor cavitation are likely to occur, there is still the possibility of high dynamic

forces due to the rapid change in momentum. The force in kN due to the change in fluid

momentum can be calculated using equation 7.

PMF 58.11

max kN (7)


For a dry gas any potential surge pressure due to a rapid closure is taken up via compression

of the gas, hence the likelihood of failure due to a gas valve closing is negligible.

For a rapid opening of a gas valve the transient forces are due to the sudden change in

momentum.

vMF max (8)

where can be expressed as the choking velocity, to give the peak force in kN by:

MwTRMF

)1(2

1000max

kN..(9)

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8

3. TRANSIENT SCREENING

The assessment methodology is shown in flowchart format in Figures 1 to 3.


Step 1: Is4000

2

0idcv > 1 kN

If Yes proceed to step 2

If No then LOF = 0

Step 2: Use equations 3 to 5 to attain maximum pressure

Step 3: If maximum pressure exceeds line pressure rating detailed surge analysis required

Step 4: Use equations 6 to attain maximum force

Step 5: Use equations 10 and 11 to find force limit and LOF

Step 6: Proceed to small bore connection review if required


Step 1: Is the fluid vapour pressure at upstream conditions > static downstream pressure

If Yes then flashing will occur LOF = 1.0 go to Step 5

If No go to Step 2

Step 2: Is vapour pressure at upstream conditions > static pressure at vena contracta for any

valve position

If Yes then cavitiation will occur LOF = 0.7 go to Step 5

If No go to Step 3

Step 3: Predict maximum force by equation 7




Step 1: If valve closing LOF = 0.

Step 2: Predict maximum force using equation 9.



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9

4. SMALL BORE REVIEW

The LOF value predicted from the transient screening is equivalent to an LOF predicted due

to flow induced turbulence or the other excitation sources considered in the MTD Guidelines.

For lines with an LOF, predicted from the transient screening, greater than 0.3 a review of the

small bore connections shall be assessed according to Appendix 2. For a small bore

connection to be at risk there needs to be both an excitation and a poor small bore connection

design.

The likelihood of failure of the small bore connection is the minimum of:

the Process LOF (i.e. from Transient Screening), see Figure A2.1

the small bore connection LOF (SBC LOF) from Appendix 2, see Figure A2.2

The minimum of the two inputs is required because both a badly placed/designed small bore

connection and an excitation source need to be present for the small bore connection to have

a higher likelihood of failure. This gives a Total LOF value, as shown in Figure A2.3.

The following are recommended actions as a result of the detailed screening of small bore

connection analysis.

1.0 > Likelihood of Failure > 0.7

Modify the connection at the design stage or brace the small bore connection by means of

suitable support. Remove unnecessary or redundant small bore connections. Further

possible design solutions are contained in the MTD Guidelines (Reference 1) Section 4.3

(Design solutions for small bore connections).

0.7 > Likelihood of Failure > 0.4

Monitoring is required during commissioning to determine if bracing is required. In the event

of bracing being required, design solutions are itemised in Section 4.3 of the MTD Guidelines

(Design solutions for small bore connections). Alternatively modify the connection at the

design stage, as above.

Likelihood of Failure < 0.4

To ensure that design features of small bore connections are acceptable, a visual survey

should be conducted.

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10

5. CONCLUSIONS

A methodology has been proposed for assessing the vibration induced in pipework due to

operation of fast acting gas, liquid or multiphase valves. The likelihood of failure (LOF)

predicted for each valve should be applied to the attached pipework and then combined withthe small bore connection modifier LOFs to determine what vibration control measures, if any,

are required.

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REFERENCES

1. Guidelines for the avoidance of vibration induced fatigue in process pipework; MTD

Publication 99/100.

2. Handbook of Industrial Pipework Engineering; Holmes E; McGraw Hill (1973).

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FIGURE 1: FAST ACTING VALVE ANALYSIS

Start

Process

Operation

Peak Force

Assessment

OK

Calculate

Main Line LOF

(Eqs 10 & 11)

Operation

List of Lines

With Fast

Acting Valves

Detailed

Assessment

(Figure 3)

-c-v

Assessme

(Eqs 1 & 2

Force

Detailed

Assessme

(Figure 2

OPENING OPENING

FORCE > 1

CLOSING CLOSING

LIQUIDGAS

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FIGURE 2: DETAILED ASSESSMENT OF LIQUID SYSTEMS FOR VALVE CLOSI

Start

Liquid System

Valve WithHigh Peak

Force

Peak ForcePrediction

Predict

Force

(Eqs 3 & 6)

Calculate

Main Line LOF

(Eqs 10 & 11)

Valve Type

Upstream

Pipe Length

Process

Data

Valve

Closing

Time

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FIGURE 3: DETAILED ASSESSMENT OF LIQUID SYSTEMS FOR VALVE OP

Start

Liquid System

Opening Valves

Upstream VapourPressure > Downstream

Pressure?

Upstream Vapour

Pressure > Vena ContractaPressure?

Main LineLOF = 1

Main Line

LOF = 0.7

Predict Maximum Force

and Main Pipe LOF(Eqs 7, 10 & 11)

NO

NO

YES

YES

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Appendix 1: Support Arrangement Selection

The screening method is designed for four support arrangements; stiff, medium stiff, medium and

flexible, as detailed below. The principal response of the pipe to low frequency flow induced

turbulence is associated with the low frequency bending modes of piping spans, either between

supports or, if the supports are poorly designed, the supports should also be included.

Stiff Support Arrangement: applicable to piping systems which are well supported (as per

recommendations given in Reference 2). The fundamental natural frequency of the piping span is

approximately 14 to 16 Hz.

Medium Stiff Support Arrangement: applicable to piping systems which are well supported. The

fundamental natural frequency of the piping span is approximately 7 Hz.

Medium Support Arrangement: applicable to piping systems which are well supported. The

fundamental natural frequency of the piping span is approximately 4 Hz.

Flexible Support Arrangement: applicable to piping systems where long unsupported spans are

encountered and the fundamental natural frequency of the piping span is approximately 1 Hz. An

example of such a system is a wellhead flowline where increased flexibility is required to

accommodate riser movement.

The selection of support arrangement can be simplified as follows (Figure A1.1):

Support Arrangement Span Length Criteria Typical Natural

Frequency

Stiff 0563.202.010*2346.1 25 DDL 14 to 16 Hz

Medium Stiff

3601.3025262.010*1886.1

0563.202.010*2346.1

25

25

DDL

DDL

7 Hz

Medium

429.4033583.010*5968.1

3601.3025262.010*1886.1

25

25

DDL

DDL

4 Hz

Flexible 429.4033583.010*5968.1 25 DDL 1 Hz

(mm)diameteroutsideactual(m),lengthspanwhere DL

Table A1.1 Support Arrangement

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Figure A1.1Different support arrangements as a function of span length and outside diameter

0

5

10

15

20

25

0 100 200 300 400 500 600 700 800 900

Actual Outside Diameter - D - (mm)

Flexible Support

Arrangement

Medium Stiff

Support Arrangement

Stiff Support

Arrangement

L = -1.2346*10-5D2+ 0.02D + 2.0563

L = -1.1886*10-5

D2+ 0.025262D + 3.3601 Medium Support

Arrangement

L = -1.5968*10-5

D2+ 0.033583D +4.429

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Appendix 2: Small Bore Connections Screening

1.0 Small Bore Connection Modifier

The calculation of the small bore connection modifier is categorised into two parts:

Likelihood of failure in branch due to branch geometry

Likelihood of failure due to main pipe geometry.

These are combined to give the small bore connection modifier. The small bore connection modifier

is the minimum of the likelihood of failure in branch due to branch geometry and the likelihood of

failure due to main pipe geometry.

2.0 Likelihood of Failure due to the Branch Geometry

The factors governing the likelihood of failure of the branch are:

type of fitting;

overall length of branch;

number and size of valves;

main pipe schedule;

small bore pipe diameter.

The various factors are combined as shown in Figure A2.1 to give an overall probability of failure in

the small bore branch connection.

2.1 Type of Fitting

A weldolet involves two welds and hence (in comparison to a contoured body fitting or short

contoured body fitting) has double the number of sites at welds for potential fatigue failures.

Additionally contoured body fittings and short contoured body fitting have higher natural frequencies

than weldolets.

Fitting Likelihood of Failure (LOF)

Weldolet 0.9

Contoured body fitting 0.6

Short contoured body fitting 0.4

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2.2 Overall Length of Branch

The length also determines the natural frequency. Again a longer unsupported branch results in

lower natural frequencies and hence greater likelihood of failure. Length is measured from the main

pipe wall to the end of the branch assembly (including valve(s) if fitted).

Length Likelihood of Failure (LOF)

over 600mm 0.9

up to 600mm 0.7

up to 400mm 0.3

up to 200mm 0.1

2.3 Number and Size of Valves

This is the element of likelihood of failure associated with the unsupported mass. Higher mass results

in lower natural frequencies and hence greater likelihood of failure.

Number of Valves Likelihood of Failure (LOF)

2 or more 0.9

1 or integral double block and bleed valve 0.5

0 0.2

2.4 Main Pipe Schedule

Thin walled main pipe is at higher likelihood of failure than the heavier schedules as its lower stiffness

results in low natural frequencies and high levels of stress at the joint between the small bore branch

and the main pipe.

Schedule Likelihood of Failure (LOF)

10S 0.9

20 0.8

40 0.7

80 0.5

160 0.3

>160 0.3

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2.5 Small Bore Pipe Diameter

As the diameter of the small bore fitting increases the natural frequency will also increase and hence

likelihood of failure will be reduced.

Fitting Diameter (Nominal Bore)

Inches DN (mm) Likelihood of Failure (LOF)

0.5 15 0.9

0.75 20 0.8

1 25 0.7

1.5 40 0.6

2 50 0.5

3.0 Likelihood of Failure due to Location on the Parent Pipe

The likelihood of failure of a connection due to the geometry of the main pipe is dependent on:

pipe schedule;

location of the connection on the main pipe.

3.1 Main Pipe Schedule

Thin walled main pipe has a higher likelihood of failure than the heavier schedules as its lower

stiffness results in low natural frequencies and high levels of stress at the joint between the small bore

branch and the main pipe.

ScheduleLikelihood of Failure (LOF)

10S 0.9

20 0.8

40 0.7

80 0.5

160 0.3

>160 0.3

3.2 Location on Main Pipe

A small bore connection located at rigid supports for the main pipe is unlikely to vibrate as the support

will force a node of vibration on the main pipe and as a result no forcing for the small bore branch.

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Conversely small bore branches located near bends, reducers or valves are more likely to experience

high levels of excitation and therefore a higher likelihood of failure.

Location Likelihood of Failure (LOF)

Valve 0.9

Reducer0.9

Bend 0.9

Mid span 0.7

Partially Fixed Support * 0.4

Fixed support** 0.1

* Braced in one direction : (1 translational degree of freedom perpendicular to the axis of the small

bore is fixed and the remaining degrees of freedom are free)

** Braced in two directions : (two translational degrees of freedom perpendicular to the axis of the

small bore are fixed (braced in two directions), please note this means no allowance for movement).

4.0 Small Bore Connection Modifier

The LOF values are combined as shown in Figure A2.2 to give the small bore connection modifier.

The LOF for the connection is defined as the minimum of the likelihood of failure in the branch due to

branch geometry and the likelihood of failure due to main pipe geometry; this is termed the SBC LOF.

As both an excitation and a poor small bore geometry are required for the connection to be at a high

risk; an overall LOF for the fitting is attained by taking the minimum of the SBC LOF and 1.42 times

the predicted process LOF, as shown in Figure A2.3.

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Figure A2.1 Process LOF Screening Flowchart

Stage 1

(yes/no)

FlowInduced

Turbulence

HighFrequen

cyAcoustic

MechanicalE

xcitation

Pulsation(Re

ciprocating

Compressor/Pump)

Pulsation(Ro

tatingStall)

Pulsation(FlowInduced

Excitation)

Stage 2

(LOF)

Maximum

of all inputs

Main PipeLOF

Is main pipeLOF>1.0?

Yes No

SBC=small bore connection

LOF=likelihood of failure

Assess all SBC's on problem system.Place Main Pipe LOF value in FigureA2.3.

Is main pipeLOF >=0.5 ?

Is main pipeLOF >=0.3?

Redesign as perSection 4.2 ofMTD Guidelines

Can system be redesigned orsupported as per Section 4.2 of the

MTD Guidelines?

Alternatively survey the main pipe asper Section 5.0 of MTD Guidelines.If above acceptance limit redesignas per Section 4.2 of MTDGuidelines

Check that thebasic design ofSBCs is sound(see guidance givenin Section 4.3 ofMTD Guidelines)

Yes

Yes

No

Yes

No

No

Project/Plant:

System:

Subsystem:

Assessed by:

Ref. No.

Line number:

Main Pipe LOF:

Actions:

Is detailed analysispossible?

No

LOF greater than 1.0 see Section4.2 of MTD Guidelines

Yes

TransientEx

citation

(Fastacting

valves)

Date:

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Likelihoodofsm

allbore

failureduetolocation

onparentpipe

Likelihoodofsmall

borefailuredueto

geometryofbranch

W

hatisthe

parentpipe

schedule?

Whereisthe

SBConthe

parentpipe?

Whatisthe

SBC

diame

ter?

Whatisthe

typeoffitting?

Whatisthe

numberand

sizeofvalv

es?

Whatisthe

overalllength

ofthebranch?

Minimum

ofbothinputs

Whatisthe

parentpipe

schedule?

L

OFValues

1

0S

0.9

2

0

0.8

4

0

0.7

8

0

0.5

1

60

0.3

>

160

0.3

LOFValues

DN150.5

DN200.75

DN251

DN401.5

DN502

LOFValues

>2

0.9

1

0.5

0

0.2

LOFValues

>600mm

0.9

pressure at valve vena contracta (6 20%x(10 - 6) = 5.2 bara) YES

Cavitation across the valve is likely therefore LOF is 0.7.

LOF is greater than 0.5 therefore check parent pipe support structure, and undertake a small bore

review of connections upstream and downstream of the valve (as per Appendix 2).

Example 3: Gas Valve Opening

This example predicts the dynamic forces due to a relief valve opening.

Flow rate for fully open valve 3 kg/sRatio of specific heat capacities 1.4Molecular weight 21

Upstream temperature 45 CMain line 8 Sch 40S (OD 0.2191 m, wt 0.0082 m, di 0.2027 m)Support type medium stiff

Step 1: Is this a valve closure scenario? - NO

Step 2: Predict force due to valve opening, eq(9).

kNMw

TRMF 15.1

2114.1

2734583144.12

1000

3

)1(

2

1000max

Step 3: Calculate LOF value, eqs(10 and 11)

Pipe is sch 40, hence 1 and pipe support medium stiff, hence = 2

kNddF io 00.84

25.257+525.67+1.8139-16.8132

23lim

14.08

15.1

lim

max

F

FLOF

LOF is less than 0.3, therefore line is OK.

Printed and published by the Health and Safety ExecutiveC0.50 06/02

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OTO 2002/028

ISBN 0-7176-2511-7

mtd-99.100

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