Failure frequency guidance

PROCESS EQUIPMENT LEAK FREQUENCY DATA FOR USE IN QRA

failure frequency guidance

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02 I PROCESS INDUSTRY I quantified risk assessment I

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I quantified risk assessment I PROCESS INDUSTRY I 03

CONTENTS

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THE POWER TO GENERATE RESULTS

04 1. Introduction05 2. Background on HCRD06 3. Application of Data08 4. Methodology

12 5. Calculating Release Rate16 6. Leak Frequency Datasheets38 7. References


Frequency estimates are recognised as one of the largest sources of uncertainty in Quantitative Risk Assessment studies.

1. INTRODUCTION

There are a few sources of data for failure frequency data for

process equipment loss of containment: Netherlands and

Belgium have issued two different onshore frequency data-

sets for use in Seveso Directive risk assessments, and some

companies and consultants have their own data. In many

cases the provenance of these data is uncertain and exam-

ples exist of frequencies that are too low and do not match

historical accident frequencies. It is detrimental to QRA

methodology that such old or inconsistent data is routinely

used. DNV is therefore publishing this booklet in order to

put best practice process equipment leak frequency data

into the public domain.

DNV’s data is derived from the Hydrocarbon Release

Database (HCRD) which has been compiled by the UK

Health and Safety Executive (HSE) over a 20 year period.

The database [2] contains details of over 4000 leak events at

oil and gas installations in the UK Continental Shelf. It

identifies 78 different types and size categories of process

equipment, and records the quantity of the release and the

release hole size. This is considered the most extensive

dataset of its type and superior to current published datasets

which often have much smaller and older data which do not

reflect current integrity management programs. DNV has

assessed this data for several years on behalf of a major oper-

ator. While the data is ‘noisy’, typical for real data, DNV has

applied a smoothing function to cover all leak sizes. Leaks

are differentiated for 17 equipment types. This analysis and

interpretation is complex: considerable effort is required to

obtain generic leak frequency data that are suitable for use

in Quantified Risk Assessment (QRA).

DNV believes that process industry will benefit from consist-

ent application of these generic leak frequencies in QRA,

and is therefore publishing its preferred dataset in order to

encourage standardisation across different users.

The booklet describes DNV’s methods for interpreting the

HCRD and describes its application to offshore, onshore

and LNG plant. The booklet also presents tabulations of

generic leak frequency data for different equipment types.

The booklet compares the DNV dataset against some alter-

native sources of leak frequency data and describes some

important reasons why the DNV interpretation of the HCRD

should be preferred.

DNV was commissioned by Statoil to define the model pre-

sented in this document, involving contractors Scandpower

and Safetec in the work.


The Piper Alpha incident occurred in 1988 and resulted in 167 people losing their lives. As a result of this disaster Lord Cullen conducted an inquiry [1].

2. BACKGROUND ON HCRD

The inquiry made 106 recommendations including the

requirement to report leaks to the HSE through the report-

ing of injuries, diseases and dangerous occurrences regula-

tions (RIDDOR). The HSE organises this data and makes it

publically available through the Hydrocarbon Release

Database (HCRD). The database started to be compiled in

October 1992 and now contains 20 years of experience in

hydrocarbon releases from the UK Continental Shelf.

Figure 1 shows the number of recorded leaks per year since

1992. (For each bar in the graph, the reporting period for

leaks is between April 1st and March 31st in the following

year. The first bar contains data for a six month period 1st of

October 1992 and the 31st of March 1993).

Figure 2 shows the breakdown of these leaks into three

categories as defined by HSE: minor, significant and major.

The average number of minor leaks per year between April

1st 1993 and March 31st 1998 is 82, whereas there were an

average of 109 minor leaks per year between April 1st 2006

and March 31st 2010. This increase may be due to an actual

increase in minor leaks or an improvement in the reporting

of these leaks. Detection of smaller leaks may also have

improved. The number of significant and major leaks has

decreased over the period, particularly major leaks which

have decreased by a factor of 12. In 2010 in the UK the oil

and industry committed to reducing its number of hydrocar-

bon emissions by 50% in 3 years. Two years into the three

year programme there has been a 40% reduction in the

number of leaks [1].

Determining the number of leaks that have occurred off-

shore provides only one part of the data that is required to

calculate leak frequency. The number of different types of

equipment offshore has also been recorded and quantified

since 1992, although HSE has recorded no change in the

equipment count since 2003 (Regarding system and equip-

ment population data, HSE notes that the responsibility for

maintaining the currency of this data rests with duty holders.

The population data in HCRD is provided by duty holders

on a voluntary database and it is not HSE’s role to update,

or verify this particular data. Use of this population data

would need to be made with caution). It is questionable that

the amount of equipment has remained the same offshore

since 2003. Maintaining an accurate equipment count is not

straightforward, for example the count of equipment on

mobile rigs would require the database operators to keep

track of the position of MOUs and their movements. The

equipment count on the UKCS is provided by the operators

on a voluntary database and it is not part of HSE’s role to

monitor or verify the equipment count. Therefore there are

uncertainties associated with the equipment count.

200

250

300

350

No. of

Leaks

Year

150

100

50

0

1993 1995 1997 1999 2001 2003 2005 2007 2009

1994 1996 1998 2000 2002 2004 2006 2008 2010

200

250

150

100

50

0

1993 1995 1997 1999 2001 2003 2005 2007 2009

1994 1996 1998 2000 2002 2004 2006 2008 2010

Minor Significant Major

Figure 1 Number of Leaks per year Figure 2 Number of leaks per leak category per year


3. APPLICATION OF DATA

3.1 OFFSHORE

The data in this booklet is based upon data from the UK

sector of the North Sea which has been collected by the HSE

in the hydrocarbon release database (HCRD). The data is

based on approximately 4000 recorded leaks recorded

between October 1992 and March 2010. This database has

been analysed by DNV to produce generic leak frequencies

applicable for use with offshore installations that are oper-

ated to UK North Sea standards. The methodology of DNVs

approach is presented in the 2009 HAZARDS XXI�

Conference [4].

3.2 ONSHORE

DNV normally also use these data for QRA at onshore facili-

ties. In general, the HSE data set gives higher leak frequen-

cies than most of the onshore sources of data. There are

several possible explanations for this.

Process equipment on offshore installations might experi-

ence higher leak frequencies than on onshore plants.

Possible reasons might be extra external corrosion from

salt-water spray, internal erosion from entrained sand, or

impacts resulting from the more compact equipment lay-

outs. However, offshore installations have safety manage-

ment systems that would be expected to counter such evi-

dent hazards. The HSE data set on leak causes shows that

corrosion/erosion is a minor contributor, with operational/

procedural faults and mechanical defects being the primary

causes. Table 1 indicates the causes of leaks offshore

between the 1st October 1992 to the 31st of March 2002.

Another possible explanation could be differences in data

quality. The HSE offshore data set is a high-quality database,

collected recently, covering a large population, with well-

defined hole sizes, comprehensive equipment counts, and

open for scrutiny by the operators and their consultants. Most

of the available onshore leak frequencies come from small

sample sizes. In fact in the case of onshore pipe leak frequen-

cies it is concluded that the most widely accepted data set is of

eight leaks in U.S. nuclear plants in 1972, or earlier collec-

tions whose size and origin are now unknown. [3].

A third factor affecting the comparison is that the HSE

offshore data set includes some leaks that occurred while

the equipment was depressurised, and others that were

quickly isolated. The onshore frequencies are applicable to

holes with process fluid at the full operating pressure. The

frequencies based on HCRD data should be used with out-

flow models that take account of the variation in operating

circumstances at the time of the leak.

A further complicating factor is that onshore and offshore

management systems in the UK must address different regu-

latory requirements. The Offshore Safety Case requirements

are more onerous than those required of onshore refineries

(e.g. offshore requirements for identification of safety criti-

cal elements, performance standards and written schemes,

plus the rigorous leak reporting requirements).

Overall, it is considered that the HSE offshore data provides

the best available estimate of leak frequencies for both

Category Causation Factor Instances Category Totals

Design fault – 321 321

Equipment Fault Corrosion/Erosion 277

1362

Mechanical Defect 920

Material Defect 76

Other 89

Operational Fault Incorrectly fitted 267

1116

Improper Operation 495

Dropped/Impact 36

Left Open/Opened 237

Other 81

Procedural Fault Noncompliance 231

588

Deficient Procedure 323

Other 34

Table 1: Causation factors in HSE offshore data [2]


onshore and offshore process equipment. However, it does

require that the outflow model should take account of the

possibility of the equipment being depressurised or quickly

isolated at the time of the leak.

3.3 LNG FACILITIES

The main risk drivers on an LNG site are events that are

unlikely to be within the direct experience of individual

plants and terminals. Establishing the frequency of such

events is difficult, precisely because of their rarity. It requires

systematic data collection, for leaks and the exposed equip-

ment population, over many plants for many years. Such

data collection is time-consuming and hence unusual.

Alternative methods such as fault tree analysis are possible

for plant-specific applications, but have not yet delivered

generic leak frequencies suitable for routine use in QRA

studies.

Data sets exist that attempt to provide failure rates for cryo-

genic pipework, or for LNG-specific operating experience in

general, but these are not considered to be sufficiently

robust to justify any modification to the generic data derived

from the HCRD. That is, any argument that offshore data

such as the HCRD is not relevant to LNG facilities is consid-

ered to be compensated for by the weight of statistical data

supporting the derived failure rates for specific equipment

items, compared to the very limited data supporting any

specific cryogenic / LNG failures that have occurred.

Given the perceived risks associated with LNG it is often the

case that fully welded pipelines and connections are

employed, at least for the cryogenic part of the facility.

Hence, where QRA of a ‘typical’ facility would assume that

all valves are flanged (even where not shown on the P&IDs)

this may not be the case for LNG facilities. It is important to

confirm the extent to which this applies for any given facility

– the default should be to assume flanged connections.

A common aspect of uncertainty in QRA is associated with

the frequency of inter-unit pipework / pipeline releases. It is

widely accepted that the application of process pipework

failure data will tend to give overly conservative values with

respect to longer inter-unit pipe segments. This can be of

particular relevance to LNG facilities, where the loading

lines are often several kilometers long. In the course of

conducting a large number of QRA studies, DNV has had

the opportunity to draw on the experience of a range of

operators. On the basis of these discussions, it is considered

appropriate to apply a factor of 10 reductions in the pipe-

work failure frequency for inter-unit piping. It should be

recognised that this is an engineering judgement assump-

tion, based on acknowledging operational experience that

inter-unit pipework fails very rarely (in comparison to the

process pipework within the main process areas). This

revised basis can be of particular relevance to loading lines,

although should not substitute for consideration of all

potential loads (and hence potential frequency modification

factors) that may apply to a particular facility, or particular

loading line.

In summary:

■■ The DNV analysis of HCRD is recommended as the basis

for the process and pipework failure data – as per all QRA

studies.

■■ There is no statistically sound basis for modifying the

source failure data to account for cryogenic or LNG-

specific application.

■■ It is considered justifiable – albeit by engineering judge-

ment – to reduce the process pipework failure rates by a

factor of 10 for inter-unit piping.

■■ It should not be assumed that valves are flanged but this is

an area where LNG applications may have the opportu-

nity to reduce the parts count and hence the calculated

leak frequency.


4. METHODOLOGY

4.1 GENERAL

This booklet provides hole size frequency data for use in

Quantified Risks Assessment (QRA) of process facilities. The

methodology shown in this document was developed as in

conjunction with Statoil and was presented in the 2009

HAZARDS XXI conference. The frequency data highlighted

in this document uses the same methodology but uses data

up to 2010 from the database. The booklet contains generic

leak frequencies for each of the following process equip-

ment types:

1. Compressors

•Centrifugalcompressors •Reciprocatingcompressors2. Filters

3. Flanges

4. Heat Exchangers (Including Coolers, Heaters

and condensers)

•AirCooledHeatExchangers •Plateheatexchangers •Shellsideheatexchangers •Tubesideheatexchangers

5. Pig traps

6. Process Pipes

7. Pumps

•Centrifugalpumps •Reciprocatingpumps8. Instruments

9. Valves

•Actuatedvalves •Manualvalves10. Pressurized process vessels

11. Atmospheric storage tanks

This analysis represents the leak size distribution by an ana-

lytical frequency function, which ensures non-zero leak

frequencies for all holes size ranges between 1 mm and the

diameter of the inlet pipe to the equipment. In the follow-

ing paragraphs a short presentation of the analysis is given.

The methodology for obtaining leak frequencies from

HCRD consists of three main steps:

■■ Grouping data for different types and sizes of equipment,

where there is insufficient experience to show significant

differences between them.

■■ Fitting analytical leak frequency functions to the data, in order

to obtain a smooth variation of leak frequency with equip-

ment and hole size.

■■ Splitting the leak frequencies into different leak scenarios, in

order to promote compatibility with different approaches

to outflow modelling in the QRA.

Grouping data

The DNV analysis covers 17 different types of process equip-

ment. Wellhead equipment, drilling equipment, pipelines

and risers are all excluded from the analysis, since other

more extensive data sources are available for these types of

equipment. The remaining types of equipment are charac-

terized as “process equipment”.

The HCRD and the Statistics Report [2] allow 78 separate

types and sizes of process equipment to be distinguished.

In some cases, there is relatively little leak experience, and

differences in leak frequencies between certain types and

sizes of process equipment have no statistical significance.

Analysis of results where there are only few reported results

may be misleading. To avoid this, it is desirable to combine

equipment types and sizes with relatively little leak

experience.

DNV equipment type HCRD equipment types

Steel pipes Piping, steel (3 sizes)

Flanged joints Flanges (3 sizes)

Manual valves Valve, manual (10 types & sizes)

Actuated valves Valve, actuated (18 types & sizes)

Instruments Instruments (including connect-ing tubing, valves and flanges)

Process vessels Pressure vessel (14 types)

Atmospheric vessels Vessels at atmospheric pressure

Centrifugal pumps Pumps, centrifugal (2 seal types)

Reciprocating pumps Pumps, reciprocating (2 seal types)

Centrifugal compressors Compressors, centrifugal

Reciprocating compressors Compressors, reciprocating

Shell side heat exchangers Heat exchangers, HC in shell

Tube side heat exchangers Heat exchangers, HC in tube

Plate heat exchangers Heat exchangers, plate

Air cooled heat exchangers Fin fan coolers

Filters Filters

Pig traps Pig launchers & pig receivers (4 sizes)

Table 2: Equipment Type Groups


Most HCRD equipment types have been used as defined by

HSE, but some, with relatively little leak experience, have

been combined into the following groups:

■■ All types of manual valves (bleed, block, check and

choke).

■■ All other types of non-pipeline actuated valves (block,

blowdown, choke, control, ESDV and relief, but not pipe-

line ESDV and SSIV).

■■ All types of pressure vessel (horizontal/vertical adsorber,

KO drum, other, reboiler, scrubber, stabiliser, separator

and stabiliser).

Leak frequency function

HCRD data, being real data, is very noisy as can be seen in

Figure 3. DNV overlays a realistic distribution function that

fits the data to obtain average leak frequencies. In raw data

there are gaps (e.g. a particular equipment dimension may

have zero leak events, but we would not predict zero for its

actual leak likelihood) forcing a distribution of results in

realistic predictions.

A feature of the distribution function is that it allows any

hole size distribution to be employed without biasing the

result. In early coarse risk assessments we may only choose

two hole sizes – small and large, whereas in detailed studies

we may choose to employ 5 hole sizes for greater resolu-

tion. The equations allow any number of hole sizes to be

selected and the total release frequency will always stay the

same. The actual hole size feeds the consequence mod-

eling and the more sizes used the greater the computa-

tional effort.

The analysis represents the variation of leak frequency with

equipment and hole size by the following general leak fre-

quency function:

F(d) = f(D)dm + Frup for d = 1 mm to D Eqn 1

where:

F(d) = frequency (per year) of holes exceeding size d

f(D) = function representing the variation of leak

frequency with D

D = equipment diameter (mm)

d = hole diameter (mm)

m = slope parameter

Frup = additional rupture frequency (per year)

Hence the frequency of holes within any range d1 to d2 is:

F(d1) – F(d2) = f(D)(d1m – d2

m) for d = 1 mm to D Eqn 2

The frequency of full-bore ruptures, i.e. holes with diameter

D, is:

F(D) = f(D) Dm + Frup Eqn 3

For pipes, flanges, valves and pig traps, HCRD provides data

for different equipment size groups. Analysis of these

showed significant variations in leak frequency with equip-

ment size for pipes, flanges valves, whereas the population

was too small to show any significant variation of leak fre-

quency with equipment size for pig traps. Size dependence

is represented in the leak frequency function using the

following general form:

f(D) = C(1 + aDn) Eqn 4

where:

C, a, n = constants for each equipment type

The HCRD provides sufficient data to determine estimates

for the a and n parameters for f(D) for pipes, flanges, man-

ual valves and actuated valves. For the other equipment

types, f(D) is equal to the constant C.

It is important to be aware that the leak frequency form is

imposed on the data and that this is a mathematical repre-

sentation of historical data. The data itself does not directly

support a separate frequency for ruptures. The historical

data related to releases from large hole sizes is very limited

and the uncertainty related to estimation of such leaks is

therefore considerable The additional rupture frequency

Frup and the slope parameter m are assumed to be constants,

i.e. not to be dependent on equipment size, for any equip-

ment type.

The function is used to calculate separate hole size frequen-

cies for three types of leak scenario:

■■ Total leak frequency

■■ Full pressure leak frequency

■■ Zero pressure leak frequency

using separate parameters for C, a, n, m and Frup. These

variables are used in DNVs software LEAK to produce the

leak frequencies that are presented in the datasheets of this

report.

4.2 LEAK SCENARIOS

Analysis of the HCRD reveals a large number of scenarios

with a significant difference between the recorded released

mass and the mass that would be estimated by using a

standard QRA methodology based on the recorded inci-

dent data. The HCRD includes many leaks that have

occurred at very low system pressures. In order to account

for this the analysis divides the leaks in HCRD into 2 main

scenario categories: “full pressure leaks” and “zero pressure

leaks”.


Full pressure leaks

This scenario category is intended to be consistent

with QRA models that assume a leak through the defined

hole, beginning at the normal operating pressure, until

controlled by isolation and blowdown, with a probability

of isolation/blowdown failure. This is subdivided as

follows:

■■ Full leaks which are intended to be consistent with QRA

models that assume a leak through the defined hole,

beginning at the normal operating pressure, until con-

trolled by ESD1 and blowdown, with a small probability of

ESD/blowdown failure. These are subdivided as follows

– ESD isolated leaks, which are defined as cases where the

outflow quantity is comparable with that predicted for

a leak at the operational pressure.

– Late isolated leaks, presumed to be cases where there is

no effective ESD of the leaking system, resulting in a

greater outflow quantity. Late isolated leaks are defined

as cases where the outflow is greater than predicted for

a leak at the operational pressure controlled by the

slowest credible ESD and no blowdown.

■■ Limited leaks, presumed to be cases where the outflow

quantity is significantly less than from a leak at the opera-

tional pressure controlled by the quickest credible ESD

(after 30 seconds) and blowdown (according to API)

initiated 60 seconds later. This is presumed to be cases

where there exist restrictions in the flow from the system

inventory, as a result of local isolation valves initiated by

human intervention or process safety systems other that

ESD and blowdown.

Normally a quantitative risk assessment will assume that all

leaks are full leaks because these have the potential of devel-

oping into serious events endangering personnel and criti-

cal safety functions. From these leak frequencies the analyst

can use a standard event tree approach for the subsequent

consequence assessment. This includes probabilities for ESD

and BD failure.

Limited leaks may be of as much concern for personnel risk

as full leaks in the period immediately following the start of

the release, but they will have a shorter duration. Hence the

potential for them developing into any major concern for

other safety functions, such as structural integrity, evacua-

tion means, escalation, etc. Any consequence calculations

should be modelled as for ESD and late isolated leaks, but

reflect that these events involve reduced release mass and

durations.

Zero pressure leaks

This scenario includes all leaks where the pressure inside

the leaking equipment is virtually zero (0.01 barg or less).

This may be because the equipment has a normal operating

pressure of zero (e.g. open drains), or because the equip-

ment has been depressurised for maintenance, but not

de-inventoried.

These leaks may typically be very small gas releases, short

lasting oil spills, or liquid releases from atmospheric tanks.

Most likely they represent a significantly reduced major

accident risk potential relative to a pressurised release

through the same hole size (although they do pose occupa-

tional safety issues) and the contribution to the overall risk

level as predicted in QRA studies is considered negligible.

4.3 UNCERTAINTIES

There are several significant uncertainties in fitting a curve

to the available leak data. Some uncertainties are due to the

way that leak data is reported to the HSE and the lack of

data for larger events. Other sources of uncertainty include

issues about an accurate population count and the accuracy

with which the operator records the data. The sources of

uncertainty are illustrated in Figure 3.

4.4 ALLOCATION OF LEAK EVENTS

The method of allocating leak records in HCRD into the

scenarios is as follows:

■■ Identify the zero pressure leak events in order to dis-

count them from the analysis

■■ Estimate the initial release rate Qo from the hole, based

on parameters recorded in HCRD,

■■ Estimate a range of plausible release quantities, REmin to

REmax, based on typical ESD and blowdown response

■■ Compare the recorded release quantity in HCRD to the

estimated release quantity range to determine the

scenario.

The scenario allocation criteria are (in order):

■■ Zero pressure leaks – actual pressure in HCRD < 0.01

barg.

■■ Limited leaks – recorded release quantity in HCRD <

REmin·/ D

■■ ESD isolated leaks – recorded release quantity in HCRD

in the range REmin / D to REmax·

■■ Late isolated leaks – recorded release quantity in HCRD

> REmax·

1 With the assumption that process shutdown (PSD) is the shutdown of a particular section rather than the whole platform the PSD system may have

the same effect as far as QRA modelling of release rates is concerned.


Figure 3 Uncertainties in applying curve to data

HCRD Leak(Total)

Full pressure leaks

Full leak

Zero pressure leaks

Limited leak

Late isolated

ESD isolated

3%

94%

49%

51%

93%

7%

6% 6%

43%

48%

Figure 4: Event Tree of Leak Scenarios [4]

Release Type Total GAS LEAK OIL LEAK CONDEN-SATE LEAK

2-PHASE LEAK

NON- PROCESS

Zero Pressure leak 6% 6% 7% 7% 2% 8%

Full pressure leak

Limited leak 48% 33% 75% 64% 67% 53%

Full leaks

ESD isolated 43% 57% 16% 27% 30% 36%

Late Isolated 3% 4% 2% 2% 1% 3%

Total 100% 100% 100% 100% 100% 100%

Table 3 Proportion Distribution of leak incidents in the HCRD database2 (%)3 [4]

2 The figures take account of HCRD data until March 2010.

3 The data that supports the distribution of 2-Phase leaks and condensate leaks are not very comprehensive and the uncertainty in these numbers is

therefore larger than for the other phases e.g. gas and oil leaks. The given distribution for 2-phase leaks and condensate leaks represents a best

estimate.

D is a disproportion factor. It is used to ensure that the clas-

sification of limited leaks is appropriate. The value given to D

is typically 4 and this is the value which has been used in the

calculation of the tables in this document.

As a simple indication of the relative importance of each leak

scenario using the methods and criteria above, Figure 4

shows the breakdown of all leaks in HCRD for the period

1992-2010. This shows that approximately 6% of leaks are at

zero pressure, and that 48% are

limited leaks. Of the remaining

46% leaks, 3% are consistent

with late isolation.

Figure 4 can be further sub-

divided to produce Table 3. This

indicates the effects that each

individual fluid has on the leak

type. Table 3 can be used in

conjunction with the data sheets

to obtain an estimate of the

frequencies of limited leaks.

1.E-03

Holes<1mm only reported since 2001

Holes1-2mm probably under reported

Exposed population declines as d approaches D

Holes >100mm not specified since 2001

Uncertainty increases for largest events probably under reported

Freq

uen

cy E

xceed

ing

(/y

ear)

Hole Diameter (mm)

1.E-04

1.E-05

1.E-06

1.E-07

0.1

All releases LEAK Function

1 10 100


In order to estimate the initial release rate Qo from the hole and a range of plausible release quantities REmin to REmax a series of equations are used.

5. CALCULATING RELEASE RATE

The phase of the fluid refers to the initial state of fluid in

the equipment before a leak.

For gas releases the initial release rate from high pressure

equipment is given by:

Eqn 5

Where:

Qg = initial gas release rate (kg/s)

CD = discharge coefficient

A = hole area (m2)

PO = initial pressure of gas (N/m2) absolute

M = molecular weight of gas

g = ratio of specific heats

R = universal gas constant = 8314 J/kg mol K

To = initial temperature of gas (K)

Rearranging the above and noting that gives:

Eqn 6

Approximating the gauge pressure to absolute pressure,

substituting g = 1.31, CD = 0.85, and converting the units of

pressure to bar and noting that the units of the diameter are

in mm we have:

Eqn 7

Where:


rg = initial density of gas (kg/m3)

Pg = initial pressure of gas (bar gauge)

For liquid releases, the initial release rate is given by:

Eqn 8

Where:

QL = initial liquid release rate (kg/s)

CD = discharge coefficient

A = hole area (m2)

rL = liquid density (kg/m3)

Po = initial pressure of liquid (N/m2) (absolute)

Pa = atmospheric pressure = 105 N/m2

g = acceleration due to gravity = 9.81 m/s2

h = height of liquid surface above hole (m)

By neglecting the liquid head, h, and replacing the pressure

term with the gauge pressure of the liquid this can be simpli-

fied to:

Eqn 9

As a simple approximation, substituting CD = 0.61 and

neglecting the liquid head h, the equation can be simplified

to:

Eqn 10

where:


rL = liquid density (kg/m3)

PL = initial pressure of liquid (bar gauge)

This equation may be used for oil, condensate and non-

process releases.

Two-phase releases are less amenable to simple approxima-

tion, but since they form a small proportion of HCRD, they

are represented by:

Eqn 11

where:

Qo = initial release rate (kg/s)

Qg = release rate (kg/s)

QL = release rate (kg/s)

GOR = gas oil ratio (kg gas per kg oil)

The initial release rate is assumed to continue at a constant

rate until the inventory is isolated. After isolation, the

release rate declines as the isolated section is depressurised

through the leak. Blowdown of isolated sections can then

further increase the rate at which the section is depressur-

ized and hence decrease the release rate through the hole.

!! = !!!!! !"!!! !!!! !+!!!!

Where:

γ

!!!! = !!!! !! = !! !!!! ! !!!! !+!!!! !! !!!!

γ

!! = 1.4 x 10!!!! !!!!ρ

!! = !!! 2!! !! − !! !!!ℎ

ρ

!! = !! !!!! 2 !!!!

!! = 2.1 x 10!!!! !!!!ρ

!! = !"#!"#!!!! !!"#!!!!

ρ

!! = !! !!!! 2 !!!!!! = 2.1 x 10!!!! !!!!

ρ

!! = !"#!"#!!!! !!"#!!!!

ρ

!! = !! !!!! 2 !!!!!! = 2.1 x 10!!!! !!!!ρ

!! = !"#!"#!!!! � !!"#!!!!

!! = !!!!! !"!!! !!!! !+!!!!

γ

!!!! = !!!! !! = !! !!!! ! !!!! !+!!!! !! !!!!

Approximating the gauge pressure to absolute pressure, substituting γ

!! = 1.4 x 10!!!! !!!!ρ

!! = !!! 2!! !! − !! !!!ℎ

!! = !!!!! !"!!! !!!! !+!!!!

γ

!!!! = !!!! !! = !! !!!! ! !!!! !+!!!! !! !!!!

γ

!! = 1.4 x 10!!!! !!!!

Where:

ρ

!! = !!! 2!! !! − !! !!!ℎ

!! = !!!!! !"!!! !!!! !+!!!!

γ

!!!! = !!!! !! = !! !!!! ! !!!! !+!!!! !! !!!!

γ

!! = 1.4 x 10!!!! !!!!ρ

!! = !!! 2!! !! − !! � !!!ℎ

!! = !!!!! !"!!! !!!! !+!!!!

γ

!!!! = !!!! gives:

!! = !! !!!! ! !!!! !+!!!! !! !!!!γ

!! = 1.4 x 10!!!! !!!!ρ

!! = !!! 2!! !! − !! !!!ℎ


Rele

ase

Rate

Time

Isolation

Leak Flow

Blowdown

QT

QO

QB

t I tB

HPSectionScrubber

HP GasCompressor

Cooler

KEY

Manual Valve

Actuated Valve

Flange

Small Bore Fitting

Figure 5 Decline of release rate with timeTable 4 Parts Count of Isolatable System

The expected release quantity is calculated as follows:

Eqn 12

Where:

Eqn 13

Eqn 14

Eqn 15

QB = release rate through leak when blowdown starts

(kg/s)

QT = total release rate through leak and blowdown

valve when blowdown starts ( kg/s)

I = inventory in isolated section (kg)

MB = mass remaining when blowdown starts

t = time from start of leak (s)

tI = time from start of leak to isolation (s)

tB = time from start of leak to blowdown (s)

rd = density factor

RE = expected ESD-limited outflow (kg)

b = blowdown valve diameter

The density factor is set to 1 for gas and 2-phase releases,

but for liquid releases the following formula is used:

Eqn 16

Where:

f = density number (0.5)

rg = gas density (kg/m3)

rl = liquid density (kg/m3)

Once the frequency of a hole size occurring is determined

the release rate for that particular diameter of hole can be

calculated thereby finding the frequency of that release rate.

5.1 SAMPLE CALCULATION

Figure 6 shows a sample isolated section and Table 4 displays

the part count for this simplified system. Process pipe is

length in metres, not number of pipes. There are 2 pipe

sizes in the system. The 6” pipe connects the scrubber to the

compressor and on to the cooler. The remaining pipework

is 8”. The leak analysis is being conducted on a gas stream.

There are a number of assumptions that are made in count-

ing the parts:

■■ For parts that are independent of equipment size (all

items except for valves, pipe and flanges) the largest pipe

diameter that is connected to the piece of equipment is

taken to be the size.

■■ Only half the scrubber is counted since only the top half

is in contact with gas under normal operating conditions.

(The lower half of the scrubber is included in a separate

count for the liquid stream).

Equipment No. Size

Process Vessel 0.5 8”

Centripetal Compressor 1 6”

Shell and Tube Heat Exchanger 1 6”

Flange 11 8”

Flange 5 6”

Actuated Valve 2 8”

Small Bore Fittings 2 ½”

Manual Valve 3 8”

Process Pipe 10 8”

Process Pipe 5 6”

!! = !!!! � I 1− !!!! �!! !!!!

Where: !! = !!exp !!! !!!!!I!! = I !!!!!!!! = !!!!!!!!!

ρ

!! = ! !!!!

ρρ

!! = !!!! I 1− !!!! !! !!!! !! = !!exp !!! !!!!!I

!! = I !!!!

!!!! = !!!!!!!!!

ρ

!! = ! !!!!

ρρ

!! = !!!! + I 1− !!!! +!! !!!!!! = !!exp !!! !!!!!I

!! = I !!!!

!!!! = !!!!!!!!!

ρ

!! = ! !!!!

ρρ

!! = !!!! + I 1− !!!! +!! !!!!!! = !!exp !!! !!!!!I!! = I !!!!

!!!! = !!!!!!!!!

Q = release rate through leak when blowdown starts (kg/s)

ρ

!! = ! !!!!

ρρ

!! = !!!! + I 1− !!!! +!! !!!!!! = !!exp !!! !!!!!I!! = I !!!!!!!! = !!!!!!!!!

ρ

!! = ! !!!!

Where:

ρρ

Figure 6: Sample Isolatable Section


■■ Two flanges are counted on each valve. (The base leak

frequency of the valve does not account for flange

connections).

■■ The actuated valves at the boundaries of the system are

ESDVs. These isolate the section. Only half these valves

are counted and one flange connection.

The results are shown in Table 3.

Then by applying Eqn 1 to each type of equipment, the

contribution of each hole size can be examined.

Equipment No. Size Frequency [ /equipment year] Total [Leaks/year]

Process Vessel 0.5 8” 2.155 x 10-3 1.077 x 10-3

Centrifugal Compressor 1 6” 1.061 x 10-2 1.061 x 10-2

Shell and Tube Heat Exchanger 1 6” 3.446 x 10-3 3.446 x 10-3

Flange 11 8” 1.286 x 10-4 1.414 x 10-3

Flange 5 6” 1.117 x 10-4 5.585 x 10-4

Actuated Valve 2 8” 5.921 x 10-4 1.184 x 10-3

Small Bore Fittings 2 ½” 5.894 x 10-4 1.178 x 10-3

Manual Valve 3 8” 1.437 x 10-4 4.311 x 10-4

Process Pipe 10 8” 6.945 x 10-5 6.945 x 10-4

Process Pipe 5 6” 7.349 x 10-5 3.674 x 10-4

Total 0.021

Table 5 Sample Calculation

5.2 ALTERNATIVE SOURCES OF LEAK FREQUENCY

DATA

The leak frequency data and methodology presented in this

document are based on analysis and application of data in

the HSE Hydrocarbon Release Database. A number of other

data sources and methodologies have been published, but

DNV considers the HSE database to be the best available for

most QRA applications.

Other available databases include the handbook for failure

frequencies which was developed by the Flemish (Belgian)

Government [5], and the Reference Manual Bevi Risk

Assessments which was developed by the Dutch National

Institute of Public Health and the Environment[5] [6].

DNV has compared the leak frequency result from these

sources against the DNV methodology. A comparison of

results based on the sample isolatable section is shown in

Table 4.

The comparison of results shows that the leak frequency

estimated using DNV’s method for this case is greater than

that obtained by the Dutch and Belgian methodologies. The

Belgian and Dutch methodologies present leak frequency

data for equipment systems; and omit any explicit counts of

the flanges, valves and instruments associated with major

equipment items. This is the main reason why the Dutch

and Belgian methodologies produce lower estimate of leak

frequency.

The experience base of the Dutch and Belgian methodolo-

gies does not match the large experience of leaks contained

in the HCRD; leak frequencies derived from the HCRD are

more accurate primarily because HCRD is the largest data-

base with information for over 70 different sizes and types of

equipment, collected systematically over the last 20 years.

DNV notes that the absence of separate frequencies for

flanges, valves and instruments in the Belgian and Dutch

methodologies also means that risk assessments performed

using these methods are insensitive to some design deci-

sions, such as the benefits of all-welded designs.

Figures 7 and 8 illustrate these points. They show the ratios

of frequencies for each type of equipment obtained by divid-

ing the DNV frequency by the Dutch/Belgian frequency for

each type of equipment. The figures show for the majority

of equipment types the DNV methodology quotes higher

frequencies. The figures highlight the large difference

between the frequencies. The explanations of the differ-

ences are as discussed in Section 3.2.

Data source & methodology Leak frequency (per year)

HCRD (DNV) 0.021

Dutch government 0.006

Belgian government 0.012

Table 6: Comparison of Estimated Leak Frequencies


Figure 7: Ratio of frequencies - DNV data to Belgium tabulation

Figure 8: Ratio of frequencies - DNV data to Netherlands tabulation

0.1 1

Storage Vessel

Centrifugal Compressor

Heat Exchanger Plate

Heat Exchanger (HC in tube)

Heat Exchanger (HC in shell)

Recipricating Compressors

Centrifugal Pump

Process Vessel

20(in.), Im in LengthProcess Pipeline



10 100 1000

Storage Vessel

Centrifugal Compressor

Recipricating Pump

Recipricating Compressors

Centrifugal Pump

Process Vessel




0.01 10.1 10 100 1000


6. LEAK FREQUENCY DATASHEETS

The following pages include leak frequency data for 17 types

of process equipment. These process equipment types are

split into two categories:

■■ Diameter Dependent

■■ Diameter Independent

As explained in section 4.1 there is enough information in

the HCRD to determine all the constants of the leak fre-

quency data equation for the diameter dependent equip-

ment types (Process pipe, Flanges, Manual and Actuated

Valves). Leak frequencies for other types of equipment are

considered to be independent of equipment size. For equip-

ment considered independent of equipment size the leak

frequencies are quoted to an equipment size of 6 inches.

This is because the leak frequencies remain the same for the

larger diameters.

Typically the parts count is multiplied by the total leaks to

determine the overall leak frequency. For a more in-depth

analysis the parts count may be multiplied by the values in

the full, limited and zero pressure leak columns, but for

most purposes it will be sufficient to use only the “full” leak

frequencies. The frequency of limited leaks can be obtained

using data in Table 3. It may be noted that the sum of fre-

quencies for full, limited and zero pressure leaks do not

necessarily equal the total leaks. The small difference is due

to total, full and zero pressure leaks being determined using

different equations.

The tables presented in this section have been gener-

ated using commercially available DNV LEAK software

which implements the methodology described in this

document.


Process Equipment Leak Frequencies

Rev.: 1

Date: 26/9/2012

Equipment Type: Centrifugal Compressors Source: HCRD 10/92 – 03/10

Definition: The scope includes the compressor itself, but excludes all attached valves, piping, flanges, instruments and fittings beyond the first flange. The first flange itself is also excluded.

Frequency Data: Equipment Size Category Total Full Pressure Zero Pressure

0.5 in

1 ‐ 3 mm 5.802E‐03 5.583E‐03 1.324E‐04 3 ‐ 10 mm 2.462E‐03 2.316E‐03 1.052E‐04 10 ‐ 50 mm 1.435E‐03 1.300E‐03 2.624E‐04 50 ‐ 150 mm 0.000E+00 0.000E+00 0.000E+00 > 150 mm 0.000E+00 0.000E+00 0.000E+00

Total 9.699E‐03 9.199E‐03 5.000E‐04

1 in


Total 9.699E‐03 9.199E‐03 5.000E‐04

2 in

1 ‐ 3 mm 5.802E‐03 5.583E‐03 1.324E‐04 3 ‐ 10 mm 2.462E‐03 2.316E‐03 1.052E‐04 10 ‐ 50 mm 1.057E‐03 9.686E‐04 9.519E‐05 50 ‐ 150 mm 3.772E‐04 3.309E‐04 1.672E‐04 > 150 mm 0.000E+00 0.000E+00 0.000E+00

Total 9.699E‐03 9.199E‐03 5.000E‐04

4 in


Total 9.699E‐03 9.199E‐03 5.000E‐04

6 in

1 ‐ 3 mm 5.802E‐03 5.583E‐03 1.324E‐04 3 ‐ 10 mm 2.462E‐03 2.316E‐03 1.052E‐04 10 ‐ 50 mm 1.057E‐03 9.686E‐04 9.519E‐05 50 ‐ 150 mm 2.257E‐04 2.008E‐04 4.428E‐05 > 150 mm 1.516E‐04 1.300E‐04 1.229E‐04

Total 9.699E‐03 9.199E‐03 5.000E‐04



Rev.: 1

Date: 26/9/2012

Equipment Type: Reciprocating Compressors Source: HCRD 10/92 – 03/10

Definition: The scope includes the compressor itself, but excludes all attached valves, piping, flanges, instruments and fittings beyond the first flange. The first flange itself is also excluded.


0.5 in

1 ‐ 3 mm 3.641E‐02 3.685E‐02 0.000E+00 3 ‐ 10 mm 1.581E‐02 1.512E‐02 0.000E+00 10 ‐ 50 mm 9.572E‐03 8.324E‐03 0.000E+00 50 ‐ 150 mm 0.000E+00 0.000E+00 0.000E+00 > 150 mm 0.000E+00 0.000E+00 0.000E+00

Total 6.179E‐02 6.029E‐02 0.000E+00

1 in


Total 6.179E‐02 6.029E‐02 0.000E+00

2 in

1 ‐ 3 mm 3.641E‐02 3.685E‐02 0.000E+00 3 ‐ 10 mm 1.581E‐02 1.512E‐02 0.000E+00 10 ‐ 50 mm 6.973E‐03 6.238E‐03 0.000E+00 50 ‐ 150 mm 2.599E‐03 2.085E‐03 0.000E+00 > 150 mm 0.000E+00 0.000E+00 0.000E+00

Total 6.179E‐02 6.029E‐02 0.000E+00

4 in


Total 6.179E‐02 6.029E‐02 0.000E+00

6 in

1 ‐ 3 mm 3.641E‐02 3.685E‐02 0.000E+00 3 ‐ 10 mm 1.581E‐02 1.512E‐02 0.000E+00 10 ‐ 50 mm 6.973E‐03 6.238E‐03 0.000E+00 50 ‐ 150 mm 1.532E‐03 1.275E‐03 0.000E+00 > 150 mm 1.067E‐03 8.107E‐04 0.000E+00

Total 6.179E‐02 6.029E‐02 0.000E+00



Rev.: 1

Date: 26/9/2012

Equipment Type: Filters Source: HCRD 10/92 – 03/10

Definition:


0.5 in


Total 3.520E‐03 2.890E‐03 6.290E‐04

1 in


Total 3.520E‐03 2.890E‐03 6.290E‐04

2 in


Total 3.520E‐03 2.890E‐03 6.290E‐04

4 in


Total 3.520E‐03 2.890E‐03 6.290E‐04

6 in


Total 3.520E‐03 2.890E‐03 6.290E‐04



Rev.: 1

Date: 26/9/2012

Equipment Type: Flange Source: HCRD 10/92 – 03/10

Definition: The following frequencies refer to a flanged joint, comprising two flange faces, a gasket (where fitted), and two welds to the pipe. Flange types include ring type joint, spiral wound, clamp (Grayloc) and hammer union (Chicksan)


0.5 in


Total 6.316E‐05 5.808E‐05 4.400E‐06

1 in


Total 6.795E‐05 6.156E‐05 4.400E‐06

2 in


Total 7.701E‐05 6.844E‐05 4.403E‐06

4 in


Total 9.415E‐05 8.200E‐05 4.452E‐06

6 in


Total 1.106E‐04 9.542E‐05 4.687E‐06



Rev.: 1

Date: 26/9/2012

Equipment Type: Flange Source: HCRD 10/92 – 03/10


10 in


Total 1.423E‐04 1.220E‐04 6.856E‐06

14 in


Total 1.729E‐04 1.484E‐04 1.449E‐05

20 in


Total 2.176E‐04 1.877E‐04 4.955E‐05



Rev.: 1

Date: 26/9/2012

Equipment Type: Fin Fan Heat Exchanger Source: HCRD 10/92 – 03/10

Definition: The scope includes the heat exchanger itself, but excludes all attached valves, piping, flanges, instruments and fittings beyond the first flange. The first flange is also excluded.


0.5 in


Total 1.450E‐03 1.450E‐03 0.000E+00

1 in


Total 1.450E‐03 1.450E‐03 0.000E+00

2 in


Total 1.450E‐03 1.450E‐03 0.000E+00

4 in


Total 1.450E‐03 1.450E‐03 0.000E+00

6 in

1 ‐ 3 mm 7.997E‐04 7.997E‐04 0.000E+00 3 ‐ 10 mm 3.802E‐04 3.802E‐04 0.000E+00 10 ‐ 50 mm 1.866E‐04 1.866E‐04 0.000E+00 50 ‐ 150 mm 4.600E‐05 4.600E‐05 0.000E+00 > 150 mm 3.740E‐05 3.740E‐05 0.000E+00

Total 1.450E‐03 1.450E‐03 0.000E+00



Rev.: 1

Date: 26/9/2012

Equipment Type: Plate Heat Exchanger Source: HCRD 10/92 – 03/10

Definition: The scope includes the heat exchanger itself, but excludes all attached valves, piping, flanges, instruments and fittings beyond the first flange. The first flange is also excluded.


0.5 in


Total 1.070E‐02 1.050E‐02 3.800E‐04

1 in


Total 1.070E‐02 1.050E‐02 3.800E‐04

2 in


Total 1.070E‐02 1.050E‐02 3.800E‐04

4 in


Total 1.070E‐02 1.050E‐02 3.800E‐04

6 in


Total 1.070E‐02 1.050E‐02 3.800E‐04



Rev.: 1

Date: 26/9/2012

Equipment Type: Shell Side Heat Exchanger Source: HCRD 10/92 – 03/10

Definition: Shell & tube type heat exchangers with hydrocarbon in the shell side. The scope includes the heat exchanger itself, but excludes all attached valves, piping, flanges, instruments and fittings beyond the first flange. The first flange itself is also excluded


0.5 in


Total 3.900E‐03 3.700E‐03 4.000E‐04

1 in


Total 3.900E‐03 3.700E‐03 4.000E‐04

2 in


Total 3.900E‐03 3.700E‐03 4.000E‐04

4 in


Total 3.900E‐03 3.700E‐03 4.000E‐04

6 in


Total 3.900E‐03 3.700E‐03 4.000E‐04



Rev.: 1

Date: 26/9/2012

Equipment Type: Tube Side Heat Exchanger Source: HCRD 10/92 – 03/10

Definition: Shell & tube type heat exchangers with hydrocarbon in the tube side. The scope includes the heat exchanger itself, but excludes all attached valves, piping, flanges, instruments and fittings beyond the first flange. The first flange itself is also excluded.


0.5 in


Total 3.040E‐03 2.610E‐03 4.270E‐04

1 in


Total 3.040E‐03 2.610E‐03 4.270E‐04

2 in


Total 3.040E‐03 2.610E‐03 4.270E‐04

4 in


Total 3.040E‐03 2.610E‐03 4.270E‐04

6 in


Total 3.040E‐03 2.610E‐03 4.270E‐04



Rev.: 1

Date: 26/9/2012

Equipment Type: Pig Trap Source: HCRD 10/92 – 03/10

Definition: Includes pig launchers and pig receivers. The scope includes the pig trap itself, but excludes all attached valves, piping, flanges, instruments and fittings beyond the first flange. The first flange itself is also excluded.


0.5 in


Total 6.820E‐03 6.039E‐03 7.800E‐04

1 in


Total 6.820E‐03 6.039E‐03 7.800E‐04

2 in


Total 6.820E‐03 6.039E‐03 7.800E‐04

4 in


Total 6.820E‐03 6.039E‐03 7.800E‐04

6 in


Total 6.820E‐03 6.039E‐03 7.800E‐04



Rev.: 1

Date: 26/9/2012

Equipment Type: Process Pipe Source: HCRD 10/92 – 03/10

Definition: Includes pipes located on topsides (between well and riser) and subsea (between well and pipeline). The scope includes welds but excludes all valves, flanges, and instruments.


0.5 in


Total 1.428E‐03 1.414E‐03 2.371E‐05

1 in


Total 4.277E‐04 4.307E‐04 1.568E‐05

2 in


Total 1.596E‐04 1.578E‐04 1.219E‐05

4 in


Total 8.779E‐05 8.205E‐05 1.067E‐05

6 in


Total 7.366E‐05 6.672E‐05 1.022E‐05



Rev.: 1

Date: 26/9/2012

Equipment Type: Process Pipe Source: HCRD 10/92 – 03/10


10 in


Total 6.610E‐05 5.833E‐05 9.890E‐06

14 in


Total 6.475E‐05 5.680E‐05 9.813E‐06

20 in


Total 6.338E‐05 5.523E‐05 9.722E‐06



Rev.: 1

Date: 26/9/2012

Equipment Type: Centrifugal Pump Source: HCRD 10/92 – 03/10

Definition: Centrifugal pumps including single‐seal and double‐seal types. The scope includes the pump itself, but excludes all attached valves, piping, flanges, instruments and fittings beyond the first flange. The first flange itself is also excluded.


0.5 in


Total 6.529E‐03 6.099E‐03 4.320E‐04

1 in


Total 6.529E‐03 6.099E‐03 4.320E‐04

2 in


Total 6.529E‐03 6.099E‐03 4.320E‐04

4 in


Total 6.529E‐03 6.099E‐03 4.320E‐04

6 in


Total 6.529E‐03 6.099E‐03 4.320E‐04



Rev.: 1

Date: 26/9/2012

Equipment Type: Reciprocating Pump Source: HCRD 10/92 – 03/10

Definition: Reciprocating pumps including single‐seal and double‐seal types. The scope includes the pump itself, but excludes all attached valves, piping, flanges, instruments and fittings beyond the first flange. The first flange itself is also excluded.


0.5 in


Total 6.200E‐03 5.600E‐03 6.600E‐04

1 in


Total 6.200E‐03 5.600E‐03 6.600E‐04

2 in


Total 6.200E‐03 5.600E‐03 6.600E‐04

4 in


Total 6.200E‐03 5.600E‐03 6.600E‐04

6 in


Total 6.200E‐03 5.600E‐03 6.600E‐04



Rev.: 1

Date: 26/9/2012

Equipment Type: Small Bore Fittings Source: HCRD 10/92 – 03/10

Definition: Includes small‐bore connections for flow, pressure and temperature sensing. The scope includes the instrument itself plus up to 2 valves, 4 flanges, 1 fitting and associated small‐bore piping, usually 25mm diameter or less.


0.5 in


Total 5.330E‐04 5.050E‐04 2.800E‐05

1 in


Total 5.330E‐04 5.050E‐04 2.800E‐05

2 in


Total 5.330E‐04 5.050E‐04 2.800E‐05



Rev.: 1

Date: 26/9/2012

Equipment Type: Actuated Valves Source: HCRD 10/92 – 03/10

Definition: Includes all types of actuated valves (block, blowdown, choke, control, ESDV and relief), but not actuated pipeline valves (pipeline ESDV and SSIV). Valve types include gate, ball, plug, globe and needle. The scope includes the valve body, stem and packer, but excludes flanges, controls and instrumentation.


0.5 in


Total 8.105E‐04 7.804E‐04 1.809E‐05

1 in


Total 8.114E‐04 7.813E‐04 2.268E‐05

2 in


Total 8.138E‐04 7.837E‐04 2.891E‐05

4 in


Total 8.202E‐04 7.898E‐04 3.737E‐05

6 in


Total 8.281E‐04 7.974E‐04 4.365E‐05



Rev.: 1

Date: 26/9/2012

Equipment Type: Actuated Valves Source: HCRD 10/92 – 03/10


10 in


Total 8.471E‐04 8.157E‐04 5.334E‐05

14 in


Total 8.695E‐04 8.373E‐04 6.102E‐05

20 in


Total 9.081E‐04 8.745E‐04 7.050E‐05



Rev.: 1

Date: 26/9/2012

Equipment Type: Manual Valves Source: HCRD 10/92 – 03/10

Definition: Includes all types of manual valves (block, bleed, check and choke). Valve types gate, ball, plug, globe, needle and butterfly. The scope includes the valve body, stem and packer, but excludes flanges, controls and instrumentation.


0.5 in


Total 9.404E‐05 9.004E‐05 9.494E‐07

1 in


Total 9.428E‐05 9.027E‐05 1.829E‐06

2 in


Total 9.575E‐05 9.169E‐05 3.590E‐06

4 in


Total 1.046E‐04 1.003E‐04 7.110E‐06

6 in


Total 1.245E‐04 1.195E‐04 1.063E‐05



Rev.: 1

Date: 26/9/2012

Equipment Type: Manual Valves Source: HCRD 10/92 – 03/10


10 in


Total 2.092E‐04 2.014E‐04 1.767E‐05

14 in


Total 3.703E‐04 3.573E‐04 2.471E‐05

20 in


Total 7.924E‐04 7.656E‐04 3.527E‐05



Rev.: 1

Date: 26/9/2012

Equipment Type: Process Vessel Source: HCRD 10/92 – 03/10

Definition: Includes all types of pressure vessel (horizontal/vertical absorber, knock‐out drum, reboiler, scrubber, stabiliser, separator and stabiliser), but not the HCRD category “other”, which are mainly hydrocyclones. The scope includes the vessel itself and any nozzles or inspection openings, but excludes all attached valves, piping, flanges, instruments and fittings beyond the first flange. The first flange itself is also excluded.


0.5 in


Total 2.360E‐03 1.540E‐03 8.110E‐04

1 in


Total 2.360E‐03 1.540E‐03 8.110E‐04

2 in


Total 2.360E‐03 1.540E‐03 8.110E‐04

4 in


Total 2.360E‐03 1.540E‐03 8.110E‐04 1 ‐ 3 mm 8.884E‐04 7.859E‐04 1.600E‐04 3 ‐ 10 mm 5.946E‐04 4.093E‐04 1.393E‐04 10 ‐ 50 mm 4.379E‐04 2.236E‐04 1.408E‐04

6 in 50 ‐ 150 mm 1.652E‐04 6.181E‐05 7.316E‐05 > 150 mm 2.736E‐04 5.930E‐05 2.977E‐04 Total 2.360E‐03 1.540E‐03 8.110E‐04



Rev.: 1

Date: 26/9/2012

Equipment Type: Atmospheric Storage Vessel Source: HCRD 10/92 – 03/10

Definition: This datasheet applies to offshore atmospheric tanks. Includes types of vessel at atmospheric pressure (oil storage tanks). The scope includes the vessel itself and any nozzles or inspection openings, but excludes all attached valves, piping, flanges, instruments and fittings beyond the first flange. The first flange itself is also excluded.


0.5 in


Total 4.690E‐03 3.310E‐03 1.380E‐03

1 in


Total 4.690E‐03 3.310E‐03 1.380E‐03

2in


Total 4.690E‐03 3.310E‐03 1.380E‐03

4in


Total 4.690E‐03 3.310E‐03 1.380E‐03

6 in


Total 4.690E‐03 3.310E‐03 1.380E‐03


7. REFERENCES

1. Department of Energy, The Public Inquiry into the Piper

Alpha Disaster, 1990

2. Health and Safety Executive (HSE), Hydrocarbon release

reporting and statistics (www.hse.gov.uk/offshore/

hydrocarbon.htm) accessed 2012

3. Spouge, J. (2005), New generic leak frequencies for

process equipment, Process Safety Progress, 24, 4,

pp249-257

4. Falck, A., Bain, B., & Rødsætre, L. (2009) Leak frequency

modeling of offshore QRA based on the Hydrocarbon

Release Database, Hazards XXI Conference, IChemE,

Nov. 2009.

5. Flemish Government. (2009) Handbook Failure

Frequencies 2009 for drawing up a safety report. LNE

Department. Environment, Nature and Energy Policy

Unit. Safety Reporting Division.

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