REPORT
434-01
RISK ASSESSMENT DATA DIRECTORY
Process Release Frequencies
responsible
equipment
SEPTEMBER
2019
Acknowledgements
Safety Committee
Photography used with permission courtesy of
©Opla/iStockphoto and ©Rumo/iStockphoto (Front cover)
©Photo_Concepts/iStockphoto (Back cover)
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REPORT
434-01
RISK ASSESSMENT DATA DIRECTORY
Process Release Frequencies
Revision history
VERSION
DATE
AMENDMENTS
1.0
September 2019
First release
SEPTEMBER
2019
Process Release Frequencies
Contents
Abbreviations
5
1. Scope and definitions
6
1.1 Equipment
6
1.2 Changes From Previous Version of This Document
7
1.3 Application of Data
8
2. Summary of recommended data
9
2.1 Offshore and Onshore Installations, Petrochemical Plants and Refineries
9
2.2 Datasheets
11
2.3 LNG Facilities
43
3. Guidance on use of data
45
3.1 General validity
45
3.2 Uncertainties
46
3.3 Modification of frequencies for factors specific to plant conditions
46
4. Review of data sources
50
4.1 Basis of data presented
50
4.2 PLOFAM2 Model
54
4.3 OREDA
56
4.4 Other data sources
56
5. Recommended data sources for further information
57
6. References
58
6.1 References for Sections 2 to 4
58
6.2 References for other data sources
59
4
Process Release Frequencies
Abbreviations
ANSI
American National Standards Institute
API
American Petroleum Institute
DNV
Det Norske Veritas
ESD
Emergency Shutdown
ESDV
Emergency Shutdown Valve
FRT
Failure Rate Table
GFF
Generic Failure Frequency
HC
Hydrocarbon
HCRD
Hydrocarbon Release Database
HSE
(UK) Health and Safety Executive
LNG
Liquefied Natural gas
OGUK
Oil and Gas UK
OREDA
Offshore Reliability Data
PHMSA
Pipeline and Hazardous Materials Safety Association
PSM
Process Safety Management
QRA
Quantitative Risk Assessment (sometimes Analysis)
SSIV
Sub-sea Isolation Valve
UKCS
United Kingdom Continental Shelf
5
Process Release Frequencies
1. Scope and definitions
1.1
Equipment
This datasheet presents (Section 2) frequencies of releases from the following process
equipment types. They are intended to be applied to process equipment on the topsides of
offshore installations and on onshore facilities handling hydrocarbons but are not restricted
to releases of hydrocarbons.
1)
Steel process pipes
13) Heat exchangers: Plate
2)
Flanged Joints
14) Heat exchangers: Air-cooled
3)
Manual valves
15) Filters
4)
Actuated valves
16) Pig traps (launchers/receivers)
5)
Instrument connections
17) Flexible Pipes
6)
Process (pressure) vessels
18) Pressure Vessels (Other)
7)
Pumps: Centrifugal
19) Degassers
8)
Pumps: Reciprocating
20) Expanders
9)
Compressors: Centrifugal
21) Xmas Trees
10) Compressors: Reciprocating
22) Turbines
11) Heat exchangers: Shell & Tube, shell
side HC
23) Pipeline ESVDs
12) Heat exchangers: Shell & Tube, tube
side HC
24) SSIV Assemblies
The precise definition of each equipment type is given with the data in Section 2.
Besides the equipment defined in the above list, the equipment types listed in Table 1-1 are
also covered by the data given in Section 2.
Table 1-1: Other Equipment Types Covered
Equipment Type
See Datasheet
Equipment Type
See Datasheet
Absorbers
6
Grayloc flanges
2
Clamp connections
2
Knock-out drums
6
Columns
6
Pipe connections
2
Distillation columns
6
Printed Circuit Heat Exchangers
13
ESD valves
4
Reactors
6
Fin-fan coolers
14
Scrubbers
6
Fittings (small-bore)
5
Separators
6
Gaskets
2
6
Process Release Frequencies
1.2
Changes From Previous Version of This Document
The previous version of this document presented leak frequencies in three categories:
• Full releases: consistent with flow through the defined hole, beginning at the normal
operating pressure, and continuing until controlled by emergency shut-down and
blowdown (if present and operable) or inventory exhaustion.
• Limited releases: cases where the system pressure is not zero but the quantity
released is much less than from a full release. This may be because the release is
isolated locally by human intervention (e.g., closing an inadvertently opened valve),
or by a restriction in the flow from the system inventory (e.g., releases of fluid
accumulated between pump shaft seals).
• Zero pressure releases: cases where pressure inside the leaking equipment is
virtually zero (0.01 barg or less). This may be because the equipment has been
depressurised for maintenance.
In this revision, all sets of data are given as a single category. This is the combination
of the “full releases” and “limited releases” as defined above. This excludes “Zero
pressure releases” which would have negligible consequences relative to releases at the
normal system pressure. Consideration of releases of this type would require separate
consequence methodology which is not normally used in Quantitative Risk Assessments.
The full release and limited release categories have been combined in this document
because it is difficult in practice to draw a clear boundary between the two cases given
the levels of uncertainty of the input parameters used in making such a judgement. This
also makes it difficult to judge how limited releases should be treated in determining their
consequences. The use of a single category to model the release of the available inventory
is conservative and simplifies the analysis.
The values presented in the previous document were based on an analysis of the UK HSE’s
Hydrocarbon Release Database (HCRD) from its inception in October 1992 until March
2006. The values in this revision are based on data up until December 2015. The number
of incidents recorded per year in the database has been steadily decreasing and it may be
considered appropriate to base the frequency on more recent data on the assumption that
this is more representative of what will occur in the future. For this reason, two sets of data
are presented for each equipment type:
• Recommended frequencies based on the frequency of data in the last 10 years (2006
– 2015 inclusive)1
• For comparison purposes, e.g., sensitivity analysis, frequencies based on the whole
period (1992-2015) of the data base (23¼ years).
In both cases the hole size distribution based on the whole period of the database is used.
The analysis also takes into account improved estimates of the amount of process
equipment in service over this period and a better understanding of those incidents which
could be regarded as being of the type assessed in QRAs and compatible with the available
population data. More details are provided in section 4.1.2.
1 In cases where less than 10 incidents have been recorded in the 10 year period a modified approach is taken as discussed in Section 4.1.2.
7
Process Release Frequencies
1.3
Application of Data
The revised data leads to an overall reduction in leak frequencies compared with the
previous version of the datasheet. This should not be seen as invalidating the findings from
previous studies. However, these new data can be used to improve decision making based
on the results of QRA.
Although the datasheets are based on experience from offshore installation is the UKCS, it
may be applied in other locations and also for onshore installations. This is because of the
absence of comparable datasets based on the experience for those types of installations.
Where these data are applied, a check should be made on whether the overall leak
frequency is broadly comparable with the recorded experience for that installation or group
of similar installations. Where this is found not to be the case, a suitable scaling factor
should be applied. More robust justification is required for applying factors which reduce
the calculated leak frequency than are required for increasing it.
8
Process Release Frequencies
2. Summary of recommended data
2.1
Offshore and Onshore Installations, Petrochemical Plants and
Refineries
A datasheet is given below for each of the equipment types listed in Section 1.1. The
definitions given of the equipment types are consistent with those used by the UK HSE.
2.1.1 Format of Tables
Data sheets (1) to (4) and (17) present correlation parameters and frequencies for different
equipment sizes since there is sufficient information available to determine these. Data
Sheets (5) to (16) and (17) to (24) are based on the same size independent correlations
and only differ in that the higher hole size ranges may not have values if the size of the
equipment is smaller than the lower bound of that range.
For each equipment type, two tables are presented. The first are the recommended values
based on experience in the period 2006-2015 inclusive with the exception that if there have been
less than 10 incidents within that time, the time period is extended backwards until 10 relevant
incidents are available. These data are labelled as “2006-2015” for consistency even when there
has been a need to base them on a longer period. In some cases, such as reciprocating
pumps and air-cooled heat exchangers, there are less than 10 incidents in the database.
The second table provides the frequencies based on the whole period of the database. For
reciprocating pumps and air-cooled heat exchangers these would be the same as the first
table so only one table is presented. These second tables may be used if an estimate based
on a larger data set is required. With a few exceptions, these will provide higher estimates.
In many cases there are a significant differences.
Frequency exceedance plots are provided for “2006 – 2015” data from which frequencies for
other size ranges may be obtained.
2.1.2 Selection of Representative Hole Size
In carrying out risk analysis it will be necessary to select a representative hole size associated
with each range for the purposes of evaluating the consequences of the release. Selection of
this hole size has a direct bearing on the calculated risks. Various alternatives are available:
1)
Upper limit of range or full bore; this is the most conservative approach. For the
10 – 50 mm range the representative hole size would be 50 mm.
2)
Arithmetic Mean Hole Diameter: For the 10 – 50 mm range the representative hole
size would be 30 mm.
3)
Arithmetic Mean Hole Area: For the 10 – 50 mm range the representative hole size
would be 36 mm.
4)
Geometric Mean Diameter or Area: These produce the same result. For the 10 – 50 mm
range the representative hole size would be 22.3 mm; √(10 x 50) = 22.36.
9
Process Release Frequencies
With the exception of the highest range, the historic probabilistic distribution and modelled
correlations of hole sizes is heavily weighted towards the lower end of the range, i.e. most
leaks will be smaller than the arithmetic mean. An examination of average consequence, in
terms of fatalities, of holes over a given range was found to be best represented by a hole
size which was close to the geometric mean for that range [1]. Hence, the geometric mean
approach is recommended for use in most risk analyses. Use of the other approaches will
generally give conservative estimates of the risk. There may be particular cases where
the consequences are sensitive to a small change in the hole size, e.g., escalation and
associated increased fatalities occur for hole sizes above a certain critical value, but this
effect will normally be small in the context of a study considering multiple cases.
For the highest hole size range the representative value should be limited to the size of
the equipment or the largest connecting pipe as appropriate. In many cases the scenario
being modelled will be for a release from a section of the process equipment involving
many types and sizes of equipment so the representative hole size should be limited to the
largest of these.
Note that full bore ruptures in the context of a major piece of equipment should refer to the
size of the largest connecting pipe.
Figure 2-1 shows the proportion of holes within 5% bands of ratio of hole size to equipment
size for incidents in the HCRD where both dimensions are available. This indicates that
6.6% of incidents fall within the 95% - 100% band and be considered as ruptures whereas
the proportion in bands below this top band, but above half the equipment size, are much
smaller. The “rupture” category accounts for 62% of all incidents where the hole diameter
is greater than 50% of the equipment diameter. This suggests that, irrespective of the
approach used for lower hole size bands, that the largest category should use the full bore
release for the equipment concerned.
0.7
0.6
Portion In Range
0.5
0.4
0.3
0.2
0.1
0.95 - 1.00
0.90 - 0.95
0.85 - 0.90
0.80 - 0.85
0.75 - 0.80
0.70 - 0.75
0.65 - 0.70
0.60 - 0.65
0.55 - 0.60
0.50 - 0.55
0.45 - 0.50
0.40 - 0.45
0.35 - 0.40
0.30 - 0.35
0.25 - 0.30
0.20 - 0.25
0.15 - 0.20
0.10 - 0.15
0.05 - 0.10
0.00 - 0.05
0
Hole Size to Equipment Size Ratio
Figure 2-1: Proportion of Holes Falling Within 5% Bands of Hole Size to Equipment Size Ratio2
2 Analysis based on incidents which are “QRA significant” (as discussed in Section 4.1.2) and compatible with the available population
data and for which hole size and equipment diameter is available.
10
Process Release Frequencies
In the following tables it should be noted that values are given for the 50 mm – 150 mm range
for equipment of nominal size 2”. Full bore ruptures for equipment of this size will generally
be taken as having a diameter of 2” (50.8 mm) regardless of the fact that the internal diameter
will vary depending on the wall thickness. Hence, this frequency applies to diameters which will
necessarily be close to the lower limit of the range. Similarly, for equipment of 6” nominal size, the
> 150 mm range effectively applies to full bore ruptures and generally taken as being 152.4 mm.
2.1.3 Equipment Boundaries
To ensure a common understanding of the boundaries of each item of equipment some
definitions are given in the relevant data sheet. A general rule for determining the
boundaries is that no component consists of an aggregation of two otherwise defined
equipment items, e.g., flange joints are not counted as part of any of the other equipment
items, but as a separate equipment item. An exception to this is the definition of an
instrument connection which included the instrument itself plus up to 2 instrument valves,
4 flanged joints, 1 fitting and associated small-bore piping, usually 1” or less. Figure 2-2
illustrates the boundaries between equipment types in typical arrangements.
Figure 2-2: Boundaries of Equipment Types
2.2
Datasheets
The following data sheets present leak frequency data in a number of forms for the process
equipment types listed in section 1.1.
General Equation: The mathematical equation for the frequency exceeding a hole size, d,
is given. In the case of equipment types where the parameters are a function of equipment
size, these are presented in a table from which the values appropriate to a given equipment
size can be interpolated.
Tabulation: The frequency per year for leaks within given hole size ranges and for a series
of equipment sizes are given.
Graphical representation: Curves giving the frequency of exceeding a given hole size are
presented for a variety of equipment sizes. This is provided for frequencies based on 2006 –
2015 data only unless the analysis had to be based on the full period.
11
Process Release Frequencies
Equipment Type: (1) Steel process pipes
Definition:
Offshore: Includes pipes located on topsides (from facility boundary import ESDV or dry tree
wellhead to the export or storage boundary ESDV).
Onshore: Includes pipes within process units, but not inter-unit pipes or cross-country pipelines.
The scope includes welds but excludes all valves, flanges, and instruments.
Refer to section 3.3.3 for inter-unit pipes connecting process units onshore.
Steel Pipework per metre year by pipe diameter (based on 2006-2015 data)
General equation
F(d) = Cdm + B ,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Where the parameters C, m and B are dependent on the equipment size (D) as given in by
interpolation from the following table
Equipment Diameter (mm)
Parameter
0
170
508
C
2.99 x 10-5
1.39 x 10-5
1.87 x 10-5
m
-0.798
-0.872
-0.482
B
0
0
6.69 x 10-8
Values greater than 508 mm use the same value as for 508 mm
Tabulation
HOLE DIA
RANGE (mm)
2" DIA
(50 mm)
6” DIA
(150 mm)
12” DIA
(300 mm)
18” DIA
(450 mm)
24” DIA
(600 mm)
36” DIA
(900 mm)
1 to 3
1.5E-05
9.5E-06
8.6E-06
8.1E-06
7.7E-06
7.7E-06
3 to 10
6.4E-06
3.9E-06
4.2E-06
4.8E-06
4.9E-06
4.9E-06
10 to 50
2.8E-06
1.6E-06
2.1E-06
3.0E-06
3.3E-06
3.3E-06
50 to 150
1.0E-06
3.2E-07
5.2E-07
9.7E-07
1.2E-06
1.2E-06
>150
---
2.0E-07
4.6E-07
1.3E-06
1.7E-06
1.7E-06
TOTAL
2.5E-05
1.6E-05
1.6E-05
1.8E-05
1.9E-05
1.9E-05
Graphical Representation
Equipment Type: (1) Steel process pipes
12
Process Release Frequencies
Equipment Type: (1) Steel process pipes
Steel Pipework per metre year by pipe diameter (based on 1992-2015 data)
General equation
F(d) = Cdm + B ,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Where the parameters C, m and B are dependent on the equipment size (D) as given in by
interpolation from the following table
Equipment Diameter (mm)
Parameter
0
170
508
C
7.65 x 10-5
2.09 x 10-5
1.68 x 10-5
m
-0.798
-0.872
-0.482
B
0
0
7.12 x 10-8
Values greater than 508 mm use the same value as for 508 mm
Tabulation
HOLE DIA
RANGE (mm)
2" DIA
(50 mm)
6” DIA
(150 mm)
12” DIA
(300 mm)
18” DIA
(450 mm)
24” DIA
(600 mm)
36” DIA
(900 mm)
1 to 3
3.6E-05
1.6E-05
1.1E-05
7.8E-06
6.9E-06
6.9E-06
3 to 10
1.5E-05
6.7E-06
5.1E-06
4.6E-06
4.4E-06
4.4E-06
10 to 50
6.6E-06
2.7E-06
2.5E-06
2.9E-06
3.0E-06
3.0E-06
50 to 150
2.4E-06
5.6E-07
6.4E-07
9.4E-07
1.0E-06
1.0E-06
>150
---
3.5E-07
5.6E-07
1.2E-06
1.6E-06
1.6E-06
TOTAL
6.0E-05
2.7E-05
1.9E-05
1.7E-05
1.7E-05
1.7E-05
13
Process Release Frequencies
Equipment Type: (2) Flanged Joints
Definition:
The following frequencies refer to a flanged joint3, comprising two flange faces, a gasket (where
fitted), and two welds to the pipe4. Flange types include ring type joint, spiral wound, clamp
(Grayloc) and hammer union (Chicksan).
Spectacle blinds and orifice plates would be the equivalent of 1.5 flanged joints
Flanges per year by diameter (based on 2006-2015 data)
General equation
F(d) = Cdm + B ,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Where the parameters C, m and B are dependent on the equipment size (D) as given in by
interpolation from the following table
Equipment Diameter (mm)
Parameter
0
174
508
C
5.37 x 10-6
1.31 x 10-5
3.10 x 10-5
m
-0.775
-0.790
-1.071
B
-1.40 x 10
4.00 x 10
-7
2.05 x 10-6
-7
Values greater than 508 mm use the same value as for 508 mm
Tabulation
HOLE DIA
RANGE (mm)
2" DIA
(50 mm)
6” DIA
(150 mm)
12” DIA
(300 mm)
18” DIA
(450 mm)
24” DIA
(600 mm)
36” DIA
(900 mm)
1 to 3
4.4E-06
7.0E-06
1.3E-05
1.9E-05
2.1E-05
2.1E-05
3 to 10
2.0E-06
3.1E-06
5.0E-06
6.5E-06
6.9E-06
6.9E-06
10 to 50
9.1E-07
1.4E-06
1.9E-06
2.1E-06
2.2E-06
2.2E-06
50 to 150
3.8E-07
3.2E-07
3.7E-07
3.4E-07
3.3E-07
3.3E-07
>150
---
5.7E-07
1.3E-06
2.0E-06
2.2E-06
2.2E-06
TOTAL
7.7E-06
1.2E-05
2.1E-05
3.0E-05
3.3E-05
3.3E-05
Graphical Representation
Equipment Type: (2) Flanged Joints
14
Process Release Frequencies
Equipment Type: (2) Flanged Joints
Flanges per year by diameter (based on 1992-2015 data)
General equation
F(d) = Cdm + B ,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Where the parameters C, m and B are dependent on the equipment size (D) as given in by
interpolation from the following table
Equipment Diameter (mm)
Parameter
0
174
508
C
1.64 x 10-5
4.00 x 10-5
9.48 x 10-5
m
-0.775
-0.790
-1.071
B
-4.27 x 10-7
1.22 x 10-6
6.26 x 10-6
Values greater than 508 mm use the same value as for 508 mm
Tabulation
HOLE DIA
RANGE (mm)
2" DIA
(50 mm)
6” DIA
(150 mm)
12” DIA
(300 mm)
18” DIA
(450 mm)
24” DIA
(600 mm)
36” DIA
(900 mm)
1 to 3
1.3E-05
2.2E-05
3.9E-05
5.9E-05
6.6E-05
6.6E-05
3 to 10
6.0E-06
9.6E-06
1.5E-05
2.0E-05
2.1E-05
2.1E-05
10 to 50
2.8E-06
4.3E-06
5.9E-06
6.6E-06
6.6E-06
6.6E-06
50 to 150
1.2E-06
9.9E-07
1.1E-06
1.0E-06
9.9E-07
9.9E-07
>150
---
1.7E-06
3.9E-06
6.0E-06
6.7E-06
6.7E-06
TOTAL
2.3E-05
3.8E-05
6.5E-05
9.2E-05
1.0E-04
1.0E-04
3 In the HCRD flanges are counted as flange faces. Within the analysis supporting this table, the population was divided by 2 to estimate
the number of flanged joints.
4 It should be noted that counts of flanges in the HCRD relate to flange faces as opposed to flanged joints. These tables relate to flanged
joint and the supporting analysis has assumed that the number of flanged joints in service is half the recorded number of flange faces.
15
Process Release Frequencies
Equipment Type: (3) Manual valves
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.
A conventional double block and bleed arrangement will include 2 main valves, half a bleed valve
and 5 flange connections. For a mono double block and bleed this should be counted as 2 main
valves, half a bleed valve and 3 flange connections.
Manual valve release frequencies (per valve year) by valve diameter (based on 2006-2015 data)
General equation
F(d) = Cdm + B ,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Where the parameters C, m and B are dependent on the equipment size (D) as given in by
interpolation from the following table
Equipment Diameter (mm)
Parameter
0
165
508
C
3.01 x 10-5
3.06 x 10-5
9.38 x 10-5
m
-0.557
-0.765
-0.524
B
0
0
4.41 x 10-7
Values greater than 508 mm use the same value as for 508 mm
Tabulation
HOLE DIA
RANGE (mm)
2" DIA
(50 mm)
6” DIA
(150 mm)
12” DIA
(300 mm)
18” DIA
(450 mm)
24” DIA
(600 mm)
36” DIA
(900 mm)
1 to 3
1.5E-05
1.7E-05
2.9E-05
3.9E-05
4.1E-05
4.1E-05
3 to 10
8.0E-06
8.0E-06
1.5E-05
2.2E-05
2.5E-05
2.5E-05
10 to 50
4.6E-06
3.8E-06
8.0E-06
1.4E-05
1.6E-05
1.6E-05
50 to 150
2.7E-06
9.1E-07
2.2E-06
4.3E-06
5.3E-06
5.3E-06
>150
---
7.2E-07
2.2E-06
5.5E-06
7.2E-06
7.2E-06
TOTAL
3.0E-05
3.1E-05
5.7E-05
8.5E-05
9.4E-05
9.4E-05
Graphical Representation
Equipment Type: (3) Manual valves
16
Process Release Frequencies
Equipment Type: (3) Manual valves
Manual valve release frequencies (per valve year) by valve diameter (based on 1992-2015 data)
General equation
F(d) = Cdm + B ,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Where the parameters C, m and B are dependent on the equipment size (D) as given in by
interpolation from the following table
Equipment Diameter (mm)
Parameter
0
165
508
C
4.90 x 10-5
4.99 x 10-5
1.53 x 10-4
m
-0.557
-0.765
-0.524
B
0
0
7.18 x 10-7
Values greater than 508 mm use the same value as for 508 mm
Tabulation
HOLE DIA
RANGE (mm)
2" DIA
(50 mm)
6” DIA
(150 mm)
12” DIA
(300 mm)
18” DIA
(450 mm)
24” DIA
(600 mm)
36” DIA
(900 mm)
1 to 3
2.4E-05
2.8E-05
4.8E-05
6.3E-05
6.7E-05
6.7E-05
3 to 10
1.3E-05
1.3E-05
2.4E-05
3.6E-05
4.0E-05
4.0E-05
10 to 50
7.4E-06
6.2E-06
1.3E-05
2.3E-05
2.6E-05
2.6E-05
50 to 150
4.3E-06
1.5E-06
3.5E-06
7.1E-06
8.6E-06
8.6E-06
>150
---
1.2E-06
3.5E-06
9.0E-06
1.2E-05
1.2E-05
TOTAL
4.9E-05
5.0E-05
9.2E-05
1.4E-04
1.5E-04
1.5E-04
17
Process Release Frequencies
Equipment Type: (4) Actuated valves
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.
Actuated valve release frequencies (per valve year) by valve diameter (based on 2006-2015 data)
General equation
F(d) = Cdm + B ,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Where the parameters C, m and B are dependent on the equipment size (D) as given in by
interpolation from the following table
Equipment Diameter (mm)
Parameter
0
172
508
C
2.79 x 10-4
1.23 x 10-4
1.37 x 10-4
m
-0.957
-0.718
-0.912
B
-9.89 x 10-8
2.90 x 10-7
0
Values greater than 508 mm use the same value as for 508 mm
Tabulation
HOLE DIA
RANGE (mm)
2" DIA
(50 mm)
6” DIA
(150 mm)
12” DIA
(300 mm)
18” DIA
(450 mm)
24” DIA
(600 mm)
36” DIA
(900 mm)
1 to 3
1.4E-04
7.9E-05
7.5E-05
8.4E-05
8.6E-05
8.6E-05
3 to 10
5.8E-05
3.7E-05
3.3E-05
3.3E-05
3.3E-05
3.3E-05
10 to 50
2.3E-05
1.8E-05
1.5E-05
1.3E-05
1.3E-05
1.3E-05
50 to 150
7.3E-06
4.3E-06
3.3E-06
2.6E-06
2.4E-06
2.4E-06
>150
---
3.6E-06
2.6E-06
1.7E-06
1.4E-06
1.4E-06
TOTAL
2.3E-04
1.4E-04
1.3E-04
1.3E-04
1.4E-04
1.4E-04
Graphical Representation
Equipment Type: (4) Actuated valves
18
Process Release Frequencies
Equipment Type: (4) Actuated valves
Actuated valve release frequencies (per valve year) by valve diameter (based on 1992-2015 data)
General equation
F(d) = Cdm + B ,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Where the parameters C, m and B are dependent on the equipment size (D) as given in by
interpolation from the following table
Equipment Diameter (mm)
Parameter
0
172
508
C
4.67 x 10-4
2.06 x 10-4
2.29 x 10-4
m
-0.957
-0.718
-0.912
B
-1.66 x 10-7
4.87 x 10-7
0
Values greater than 508 mm use the same value as for 508 mm
Tabulation
HOLE DIA
RANGE (mm)
2" DIA
(50 mm)
6” DIA
(150 mm)
12” DIA
(300 mm)
18” DIA
(450 mm)
24” DIA
(600 mm)
36” DIA
(900 mm)
1 to 3
2.4E-04
1.3E-04
1.3E-04
1.4E-04
1.5E-04
1.5E-04
3 to 10
9.7E-05
6.2E-05
5.5E-05
5.6E-05
5.6E-05
5.6E-05
10 to 50
3.9E-05
3.0E-05
2.5E-05
2.2E-05
2.2E-05
2.2E-05
50 to 150
1.2E-05
7.2E-06
5.6E-06
4.4E-06
4.1E-06
4.1E-06
>150
---
6.1E-06
4.3E-06
2.8E-06
2.4E-06
2.4E-06
TOTAL
3.9E-04
2.4E-04
2.2E-04
2.3E-04
2.3E-04
2.3E-04
19
Process Release Frequencies
Equipment Type: (5) Instrument connections
Definition:
Includes small-bore connections for flow, pressure and temperature sensing. The scope
includes the instrument itself plus up to 2 instrument valves, 4 flanged joints, 1 fitting and
associated small-bore piping, usually 1” diameter or less.
Instrument connection release frequencies (per instrument connection year) by connection
diameter (based on 2006-2015 data)
General equation
F(d) = 1.99 × 10-4d-0.87,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Tabulation
HOLE DIA RANGE (mm)
1” DIA (25 mm)
2” DIA (50 mm)
1 to 3
1.2E-04
1.2E-04
3 to 10
5.0E-05
5.0E-05
10 to 50
2.7E-05
2.0E-05
50 to 150
---
6.6E-06
>150
---
---
TOTAL
2.0E-04
2.0E-04
Graphical Representation
Equipment Type: (5) Instrument connections
Instrument connection release frequencies (per instrument connection year) by connection
diameter (based on 1992-2015 data)
General equation
F(d) = 3.41 × 10-4d-0.87,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Tabulation
HOLE DIA RANGE (mm)
1” DIA (25 mm)
2” DIA (50 mm)
1 to 3
2.1E-04
2.1E-04
3 to 10
8.5E-05
8.5E-05
10 to 50
4.6E-05
3.5E-05
50 to 150
---
1.1E-05
>150
---
---
TOTAL
3.4E-04
3.4E-04
20
Process Release Frequencies
Equipment Type: (6) Process (pressure) vessels
Definition:
Offshore: Includes all types of pressure vessel; adsorber, knock-out drum, reboiler, scrubber,
separator and stabiliser, oriented either horizontally or vertically. It does not include the HCRD
categories “horizontal other” or “vertical other”, which are mainly associated with produced
water treatment systems.
Onshore: Includes process vessels and columns, but not storage vessels.
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.
No quantification of the likelihood of complete vessel failure is included here due to the lack of
incidents of this type in the HCRD. Some data for catastrophic structural vessel failures can be
found in [2].
Pressure vessel release frequencies per vessel year (Based on 2006-2015 data)
General equation
F(d) = 6.50 × 10-4d-0.66,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Tabulation
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
3.3E-04
3.3E-04
3 to 10
1.7E-04
1.7E-04
10 to 50
9.3E-05
9.3E-05
50 to 150
4.9E-05
2.5E-05
>150
---
2.4E-05
TOTAL
6.5E-04
6.5E-04
Graphical Representation
Equipment Type: (6) Process (pressure) vessels
21
Process Release Frequencies
Equipment Type: (6) Process (pressure) vessels
Instrument connection release frequencies (per instrument connection year) by connection
diameter (based on 1992-2015 data)
General equation
F(d) = 3.41 × 10-4d-0.87,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Tabulation
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
5.0E-04
5.0E-04
3 to 10
2.6E-04
2.6E-04
10 to 50
1.4E-04
1.4E-04
50 to 150
7.4E-05
3.8E-05
>150
---
3.6E-05
TOTAL
9.8E-04
9.8E-04
22
Process Release Frequencies
Equipment Type: (7) Pumps: Centrifugal
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.
* Analysis has shown that there is no statistical difference between single and double seal types for releases in the size range considered.
Centrifugal pump release frequencies per pump year (Based on 2006-2015 data)
General equation
F(d) = 3.50 × 10-3 d-1.35,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
2.7E-03
2.7E-03
3 to 10
6.4E-04
6.4E-04
10 to 50
1.4E-04
1.4E-04
50 to 150
1.8E-05
1.4E-05
>150
---
4.0E-06
TOTAL
3.5E-03
3.5E-03
Graphical Representation
Type: (7) Pumps: Centrifugal
CentrifugalEquipment
pump release
frequencies per pump year (Based on 1992-2015 data)
General equation
F(d) = 7.68 × 10-3 d-1.35,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
5.9E-03
5.9E-03
3 to 10
1.4E-03
1.4E-03
10 to 50
3.0E-04
3.0E-04
50 to 150
3.9E-05
3.0E-05
>150
---
8.9E-06
TOTAL
7.7E-03
7.7E-03
Note that the largest hole size recorded for centrifugal pumps is 25.4 mm (1”). The above model extrapolates frequencies for larger hole sizes and this
gives results which are consistent with there being no recorded incident prior to 2016. There may be valid reasons related to the manufacture of centrifugal
pumps which make them less prone to large leaks than this model would suggest. Lower values may be adopted providing robust justification is given.
23
Process Release Frequencies
Equipment Type: (8) Pumps: Reciprocating
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.
* Analysis has shown that there is no statistical difference between single and double seal types for releases in the size range considered.
Reciprocating pump release frequencies per pump year (Based on 1992-2015 data)
General equation
F(d) = 2.22 × 10-3 d-0.41,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Tabulation
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
8.1E-04
8.1E-04
3 to 10
5.5E-04
5.5E-04
10 to 50
4.2E-04
4.2E-04
50 to 150
4.4E-04
1.6E-04
>150
---
2.8E-04
TOTAL
2.2E-03
2.2E-03
Graphical Representation
Equipment Type: (8) Pumps: Reciprocating
Note: The number of incidents associated with reciprocating pumps is small; 9 selected incidents in the period 1992 – 2015. Frequencies based on
2006 – 2015 would have large uncertainties. Therefore only results based on the 1992 – 2015 period are presented.
24
Process Release Frequencies
Equipment Type: (9) Compressors: Centrifugal
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.
Note: One compressor comprises all stages on one shaft.
Centrifugal compressor release frequencies per compressor year (Based on 2006-2015 data)
General equation
F(d) = 5.80 × 10-3 d-0.80,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
3.4E-03
3.4E-03
3 to 10
1.5E-03
1.5E-03
10 to 50
6.7E-04
6.7E-04
50 to 150
2.5E-04
1.5E-04
>150
---
1.1E-04
TOTAL
5.8E-03
5.8E-03
Graphical Representation
Type: (9) Compressors: Centrifugal
CentrifugalEquipment
compressor
release frequencies per compressor year (Based on 1992-2015 data)
General equation
F(d) = 6.27 × 10-3 d-0.80,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
3.7E-03
3.7E-03
3 to 10
1.6E-03
1.6E-03
10 to 50
7.2E-04
7.2E-04
50 to 150
2.7E-04
1.6E-04
>150
---
1.1E-04
TOTAL
6.3E-03
6.3E-03
Note that the largest hole size recorded for centrifugal compressors is less than 50 mm. The above model extrapolates frequencies for larger hole
sizes and this gives results which are consistent with there being no recorded incident prior to 2016. There may be valid reasons related to the
manufacture of centrifugal compressors which make them less prone to large leaks than this model would suggest. Lower values may be adopted
providing robust justification is given.
25
Process Release Frequencies
Equipment Type: (10) Compressors: Reciprocating
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.
Reciprocating compressor release frequencies per compressor year (Based on 2006-2015 data)
General equation
F(d) = 1.19 × 10-2 d-0.78,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
6.8E-03
6.8E-03
3 to 10
3.1E-03
3.1E-03
10 to 50
1.4E-03
1.4E-03
50 to 150
5.6E-04
3.2E-04
>150
---
2.4E-04
TOTAL
1.2E-02
1.2E-02
Graphical Representation
Equipment Type: (10) Compressors: Reciprocating
Reciprocating compressor release frequencies per compressor year (Based on 1992-2015 data)
General equation
F(d) = 2.73 × 10-2 d-0.78,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
1.6E-02
1.6E-02
3 to 10
7.1E-03
7.1E-03
10 to 50
3.2E-03
3.2E-03
50 to 150
1.3E-03
7.4E-04
>150
---
5.5E-04
TOTAL
2.7E-02
2.7E-02
Note that the largest hole size recorded for reciprocating compressors is 25.5 mm. The above model extrapolates frequencies for larger hole sizes and
this gives results which are consistent with there being no recorded incident prior to 2016. There may be valid reasons related to the manufacture of
reciprocating compressors which make them less prone to large leaks than this model would suggest. Lower values may be adopted providing robust
justification is given.
26
Process Release Frequencies
Equipment Type: (11) Heat exchangers: Shell & Tube, shell side HC
Definition:
Shell and 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.
Heat exchanger release frequencies per heat exchanger year (Based on 2006-2015 data)
General equation
F(d) = 1.64 × 10-3 d-0.72,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
9.0E-04
9.0E-04
3 to 10
4.3E-04
4.3E-04
10 to 50
2.1E-04
2.1E-04
50 to 150
9.7E-05
5.3E-05
>150
---
4.4E-05
TOTAL
1.6E-03
1.6E-03
Graphical Representation
Equipment Type: (11) Heat exchangers: Shell & Tube, shell side HC
Heat exchanger release frequencies per heat exchanger year (Based on 1992-2015 data)
General equation
F(d) = 2.27 × 10-3 d-0.72,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
1.2E-03
1.2E-03
3 to 10
6.0E-04
6.0E-04
10 to 50
3.0E-04
3.0E-04
50 to 150
1.3E-04
7.4E-05
>150
---
6.1E-05
TOTAL
2.3E-03
2.3E-03
27
Process Release Frequencies
Equipment Type: (12) Heat exchangers: Shell & Tube, tube side HC
Definition:
Shell and 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.
Note that loss of containment in this context refers to the release of hydrocarbons to the atmosphere. i.e. internal leakage is excluded
Heat exchanger release frequencies per heat exchanger year (Based on 2006-2015 data)
General equation
F(d) = 8.83 × 10-4 d-0.53,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
3.9E-04
3.9E-04
3 to 10
2.3E-04
2.3E-04
10 to 50
1.5E-04
1.5E-04
50 to 150
1.1E-04
4.9E-05
>150
---
6.2E-05
TOTAL
8.8E-04
8.8E-04
Graphical Representation
Equipment Type: (12) Heat exchangers: Shell & Tube, tube side HC
Heat exchanger
release frequencies per heat exchanger year (Based on 1992-2015 data)
General equation
F(d) = 1.09 × 10-3 d-0.53,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
4.8E-04
4.8E-04
3 to 10
2.9E-04
2.9E-04
10 to 50
1.8E-04
1.8E-04
50 to 150
1.4E-04
6.1E-05
>150
---
7.7E-05
TOTAL
1.1E-03
1.1E-03
28
Process Release Frequencies
Equipment Type: (13): Heat Exchangers: Plate
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 itself is also excluded.
This category is also considered to be applicable to printed circuit heat exchangers.
Heat exchanger release frequencies per heat exchanger year (Based on 2006-2015 data)
General equation
F(d) = 8.42 × 10-3 d-0.99,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
5.6E-03
5.6E-03
3 to 10
2.0E-03
2.0E-03
10 to 50
6.8E-04
6.8E-04
50 to 150
1.7E-04
1.1E-04
>150
---
5.8E-05
TOTAL
8.4E-03
8.4E-03
Graphical Representation
Equipment Type: (13): Heat Exchangers: Plate
Heat exchanger release frequencies per heat exchanger year (Based on 1992-2015 data)
General equation
F(d) = 1.02 × 10-2 d-0.99,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
7.2E-03
7.2E-03
3 to 10
2.5E-03
2.5E-03
10 to 50
8.7E-04
8.7E-04
50 to 150
2.2E-04
1.5E-04
>150
---
7.4E-05
TOTAL
1.1E-02
1.1E-02
29
Process Release Frequencies
Equipment Type: (14) Heat exchangers: Air-cooled
Definition:
Often referred to as fin-fan coolers but in principle includes all air-cooled type heat exchangers.
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.
Heat exchanger release frequencies per heat exchanger year (Based on 1992-2015 data)
General equation
F(d) = 1.34 × 10-3 d-0.993,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
8.9E-04
8.9E-04
3 to 10
3.1E-04
3.1E-04
10 to 50
1.1E-04
1.1E-04
50 to 150
2.8E-05
1.8E-05
>150
---
9.3E-06
TOTAL
1.3E-03
1.3E-03
Graphical Representation
Equipment Type: (14) Heat exchangers: Air-cooled
There are only 6 recorded incidents of releases from air-cooled heat exchangers in the HCRD.
Of these only 1 is selected as being QRA significant.The above table has been generated based
on the frequency of this single event and the hole size distribution obtained by scaling the
values for plate heaters.The frequencies presented have a high degree of uncertainty.
30
Process Release Frequencies
Equipment Type: (15) Filters
Definition:
The scope includes the filter body 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.
Filter release frequencies per filter year (Based on 2006-2015 data)
General equation
F(d) = 1.86 × 10-3 d-0.988,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
1.2E-03
1.2E-03
3 to 10
4.4E-04
4.4E-04
10 to 50
1.5E-04
1.5E-04
50 to 150
3.9E-05
2.6E-05
>150
---
1.3E-05
TOTAL
1.9E-03
1.9E-03
Graphical Representation
Equipment Type: (15) Filters
Filter release frequencies per filter year (Based on 1992-2015 data)
General equation
F(d) = 3.53 × 10-3 d-0.988,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
2.3E-03
2.3E-03
3 to 10
8.3E-04
8.3E-04
10 to 50
2.9E-04
2.9E-04
50 to 150
7.4E-05
4.9E-05
>150
---
2.5E-05
TOTAL
3.5E-03
3.5E-03
31
Process Release Frequencies
Equipment Type: (16) Pig traps
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.
Note that these frequencies are based on experience from pig traps in service which will be depressurised for a large proportion of the
time. The frequencies may be reduced/increased if the equipment in question is believed to be pressurised for a smaller/greater proportion
of the year than might be considered average based on the number of operations.
Pig trap release frequencies per pig trap year (Based on 2006-2015 data)
General equation
F(d) = 2.80 × 10-3 d-0.648,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
1.4E-03
1.4E-03
3 to 10
7.4E-04
7.4E-04
10 to 50
4.1E-04
4.1E-04
50 to 150
2.2E-04
1.1E-04
>150
---
1.1E-04
TOTAL
2.8E-03
2.8E-03
Graphical Representation
Equipment Type: (16) Pig traps
Pig trap release frequencies per pig trap year (Based on 1992-2015 data)
General equation
F(d) = 3.63 × 10-3 d-0.648,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Inlets 50 to 150 mm diameter
Inlets >150 mm diameter
1 to 3
1.8E-03
1.8E-03
3 to 10
9.6E-04
9.6E-04
10 to 50
5.3E-04
5.3E-04
50 to 150
2.9E-04
1.5E-04
>150
---
1.4E-04
TOTAL
3.6E-03
3.6E-03
32
Process Release Frequencies
Equipment Type: (17) Flexible Piping
Definition:
Offshore: Includes pipes located on topsides (from facility boundary import ESDV or dry tree
wellhead to the export or storage boundary ESDV).
Onshore: Includes pipes within process units, but not inter-unit pipes.
The scope excludes all valves, flanges, and instruments.
Flexible pipework release frequencies per metre year by pipe diameter (based on 2006-2015 data)
General equation
F(d) = Cdm + B ,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Where the parameters C, m and B are dependent on the equipment size (D) as given in by
interpolation from the following table
Equipment Diameter (mm)
Parameter
0
170
C
1.59 x 10
9.70 x 10
1.82 x 10-5
m
-0.748
-0.405
-0.176
B
0
0
0
-3
508
-5
Values greater than 508 mm use the same value as for 508 mm
Tabulation
HOLE DIA
RANGE (mm)
2" DIA
(50 mm)
6” DIA
(150 mm)
12” DIA
(300 mm)
18” DIA
(450 mm)
24” DIA
(600 mm)
36” DIA
(900 mm)
1 to 3
5.8E-04
9.7E-05
1.9E-05
6.2E-06
3.2E-06
3.2E-06
3 to 10
3.0E-04
6.4E-05
1.5E-05
5.3E-06
2.9E-06
2.9E-06
10 to 50
1.7E-04
4.6E-05
1.3E-05
5.3E-06
3.0E-06
3.0E-06
50 to 150
9.2E-05
1.7E-05
5.6E-06
2.7E-06
1.6E-06
1.6E-06
>150
---
2.8E-05
1.4E-05
1.0E-05
7.5E-06
7.5E-06
TOTAL
1.1E-03
2.5E-04
6.6E-05
3.0E-05
1.8E-05
1.8E-05
Graphical Representation
Equipment Type: (17) Flexible Piping
33
Process Release Frequencies
Equipment Type: (17) Flexible Piping
Flexible pipework release frequencies per metre year by pipe diameter (based on 1992-2015 data)
General equation
F(d) = Cdm + B ,
F(d) = 0 ,
1 mm < d ≤ D
d>D
Where the parameters C, m and B are dependent on the equipment size (D) as given in by
interpolation from the following table
Equipment Diameter (mm)
Parameter
0
170
508
C
2.77 x 10-3
1.69 x 10-4
1.68 x 10-5
m
-0.748
-0.405
-0.176
B
0
0
0
Values greater than 508 mm use the same value as for 508 mm
Tabulation
HOLE DIA
RANGE (mm)
2" DIA
(50 mm)
6” DIA
(150 mm)
12” DIA
(300 mm)
18” DIA
(450 mm)
24” DIA
(600 mm)
36” DIA
(900 mm)
1 to 3
1.0E-03
1.7E-04
3.3E-05
1.1E-05
5.6E-06
5.6E-06
3 to 10
5.3E-04
1.1E-04
2.5E-05
9.3E-06
5.0E-06
5.0E-06
10 to 50
2.9E-04
8.1E-05
2.2E-05
9.2E-06
5.2E-06
5.2E-06
50 to 150
1.6E-04
3.0E-05
9.7E-06
4.7E-06
2.8E-06
2.8E-06
>150
---
4.8E-05
2.4E-05
1.8E-05
1.3E-05
1.3E-05
TOTAL
2.0E-03
4.4E-04
1.1E-04
5.2E-05
3.2E-05
3.2E-05
34
Process Release Frequencies
Equipment Type: (18) Process (pressure) vessels (Other)
Definition:
Offshore: Pressure vessels covered by the HCRD categories “horizontal other” or “vertical
other”, which are mainly associated with produced water treatment systems. These are distinct
from adsorbers, knock-out drums, reboilers, scrubbers, separators and stabilisers, which are
covered by equipment category “Process (pressure) vessels”.
Onshore: Includes process vessels and columns other than those covered by the category
“Process (pressure) vessels”, but not storage vessels.
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.
No quantification of the likelihood of complete vessel failure is included here due to the lack of
incidents of this type in the HCRD. Some data for catastrophic structural vessel failures can be
found in [2].
Process (pressure) vessels (Other) by vessel year (based on 2006-2015 data)
General equation
F(d) = 4.09 × 10-3 d-0.51,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
Pressure vessel release frequencies per vessel year (Based on 2006-2015 data)
HOLE DIA RANGE (mm)
Connections 50 to 150 mm diameter
Connections >150 mm diameter
1 to 3
1.7E-03
1.7E-03
3 to 10
1.1E-03
1.1E-03
10 to 50
7.1E-04
7.1E-04
50 to 150
5.6E-04
2.4E-04
>150
---
3.2E-04
TOTAL
4.1E-03
4.1E-03
Graphical Representation
Equipment Type: (18) Process (pressure) vessels (Other)
35
Process Release Frequencies
Equipment Type: (18) Process (pressure) vessels (Other)
Pressure vessel (Other) release frequencies per vessel year (Based on 1992-2015 data)
General equation
F(d) = 4.38 × 10-3 d-0.51,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Connections 50 to 150 mm diameter
Connections >150 mm diameter
1 to 3
1.9E-03
1.9E-03
3 to 10
1.1E-03
1.1E-03
10 to 50
7.6E-04
7.6E-04
50 to 150
6.0E-04
2.6E-04
>150
---
3.4E-04
TOTAL
4.4E-03
4.4E-03
36
Process Release Frequencies
Equipment Type: (19) Degassers
Definition:
The scope includes the degasser vessel itself, but excludes all attached valves, piping, flanges,
instruments and fittings beyond the first flange. The first flange itself is also excluded.
Degassers release frequencies per vessel year (based on 1992-2015 data)
General equation
F(d) = 2.14 × 10-3 d-0.474,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Connections 50 to 150 mm diameter
Connections >150 mm diameter
1 to 3
8.7E-04
8.7E-04
3 to 10
5.5E-04
5.5E-04
10 to 50
3.8E-04
3.8E-04
50 to 150
3.4E-04
1.4E-04
>150
---
2.0E-04
TOTAL
2.1E-03
2.1E-03
Graphical Representation
Equipment Type: (19) Degassers
There are only 3 recorded incidents of releases from degassers in the HCRD. Of these only 2
are selected as being QRA significant. These were relatively large (10.7 mm and 26.2 mm). The
above table has been generated using a best fit routine where it was also assumed a frequency
of exceeding a hole size of 2 mm was twice that of the historical frequency. The frequencies
presented have a high degree of uncertainty.
37
Process Release Frequencies
Equipment Type: (20) Expanders
Definition:
The scope includes the expander itself, but excludes all attached valves, piping, flanges,
instruments and fittings beyond the first flange. The first flange itself is also excluded.
Expander release frequencies per equipment year (based on 1992-2015 data)
General equation
F(d) = 3.88 × 10-3 d-0.8,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Connections 50 to 150 mm diameter
Connections >150 mm diameter
1 to 3
2.3E-03
2.3E-03
3 to 10
1.0E-03
1.0E-03
10 to 50
4.5E-04
4.5E-04
50 to 150
1.7E-04
9.9E-05
>150
---
7.0E-05
TOTAL
3.9E-03
3.9E-03
Graphical Representation
Equipment Type: (20) Expanders
There are only 2 recorded incidents of releases from expanders in the HCRD. Of these only
1 is selected as being QRA significant and this had a hole size of 1 mm. The above table has
been generated based on the frequency of this single event and the hole size distribution
obtained by scaling the values for centrifugal compressors. The frequencies presented have a
high degree of uncertainty.
38
Process Release Frequencies
Equipment Type: (21) Xmas Trees
Definition:
The scope includes the entire unit including valves, flanges, rams, etc. down to the wellhead
connection and up to the first flange, but excluding all piping, valves and fittings beyond the first
flange, e.g., flow line or choke/kill connection. The first flange itself is also excluded.
Xmas tree release frequencies per equipment year (based on 2006-2015 data)
General equation
F(d) = 4.01 × 10-4 d-0.822,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Connections 50 to 150 mm diameter
Connections >150 mm diameter
1 to 3
2.4E-04
2.4E-04
3 to 10
1.0E-04
1.0E-04
10 to 50
4.4E-05
4.4E-05
50 to 150
1.6E-05
9.6E-06
>150
---
6.5E-06
TOTAL
4.0E-04
4.0E-04
Graphical Representation
Equipment Type: (21) Xmas Trees
Xmas trees release frequencies per equipment year (Based on 1992-2015 data)
General equation
F(d) = 1.38 × 10-3 d-0.822,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Connections 50 to 150 mm diameter
Connections >150 mm diameter
1 to 3
8.2E-04
8.2E-04
3 to 10
3.5E-04
3.5E-04
10 to 50
1.5E-04
1.5E-04
50 to 150
5.5E-05
3.3E-05
>150
---
2.2E-05
TOTAL
1.4E-03
1.4E-03
39
Process Release Frequencies
Equipment Type: (22) Turbines
Definition:
The scope includes the turbine itself, but excludes all attached valves, piping, flanges,
instruments and fittings beyond the first flange. The first flange itself is also excluded.
Turbines release frequencies per equipment year (based on 2006-2015 data)
General equation
F(d) = 1.02 × 10-2 d-1.017 + 1.51 × 10-4,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
Pressure vessel release frequencies per vessel year (Based on 2006-2015 data)
HOLE DIA RANGE (mm)
Connections 50 to 150 mm diameter
Connections >150 mm diameter
1 to 3
6.9E-03
6.9E-03
3 to 10
2.4E-03
2.4E-03
10 to 50
7.9E-04
7.9E-04
50 to 150
3.4E-04
1.3E-04
>150
---
2.1E-04
TOTAL
1.0E-02
1.0E-02
Graphical Representation
Equipment Type: (22) Turbines
Turbine release
frequencies per equipment year (Based on 1992-2015 data)
General equation
F(d) = 1.02 × 10-2 d-1.017 + 1.51 × 10-4,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Connections 50 to 150 mm diameter
Connections >150 mm diameter
1 to 3
6.9E-03
6.9E-03
3 to 10
2.4E-03
2.4E-03
10 to 50
7.9E-04
7.9E-04
50 to 150
3.4E-04
1.3E-04
>150
---
2.1E-04
TOTAL
1.0E-02
1.0E-02
Note that the overall frequencies based on 1992-2005 are very close to those for the last 10 year period (2006-2015) such that the results quoted in this
datasheet are the same when expressed to two significant figures.
40
Process Release Frequencies
Equipment Type: (23) Pipeline ESVDs
Definition:
Emergency Shutdown Valves on pipelines beyond the riser ESDV. The scope includes the valve
body, stem and packer, but excludes flanges, controls and instrumentation.
Note that the definition of Pipeline ESDVs is not well defined to distinguish them from riser ESDVs or SSIV assemblies reporting under this
category may therefore be inconsistent. An acceptable approach would be to neglect this equipment type and use data for actuated valves
or SSIVs as appropriate.
Pipeline ESDV release frequencies per valve year (based on 2006-2015 data)
General equation
F(d) = 6.63 × 10-4 d-0.635 + 1.68 × 10-5,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Connections 50 to 150 mm diameter
Connections >150 mm diameter
1 to 3
3.3E-04
3.3E-04
3 to 10
1.8E-04
1.8E-04
10 to 50
9.8E-05
9.8E-05
50 to 150
7.2E-05
2.8E-05
>150
---
4.4E-05
TOTAL
6.8E-04
6.8E-04
Graphical Representation
Equipment Type: (23) Pipeline ESVDs
Pipeline ESDV release frequencies per valve year (Based on 1992-2015 data)
General equation
F(d) = 7.93 × 10-4 d-0.635 + 2.01 × 10-5,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
HOLE DIA RANGE (mm)
Connections 50 to 150 mm diameter
Connections >150 mm diameter
1 to 3
1.2E-03
1.2E-03
3 to 10
6.0E-04
6.0E-04
10 to 50
3.0E-04
3.0E-04
50 to 150
1.3E-04
7.4E-05
>150
---
6.1E-05
TOTAL
2.3E-03
2.3E-03
41
Process Release Frequencies
Equipment Type: (24) SSIV Assemblies
Definition:
The scope includes the SSIV body, stem and packer, but excludes flanges, controls and
instrumentation.
SSIV Assembly release frequencies per assembly (based on 2006-2015 data)
General equation
F(d) = 1.022 × 10-3 d-0.635 + 3.10 × 10-5,
Tabulation
F(d) = 0 ,
1 mm < d ≤ D
d>D
Pressure vessel release frequencies per vessel year (Based on 2006-2015 data)
HOLE DIA RANGE (mm)
Connections 50 to 150 mm diameter
Connections >150 mm diameter
1 to 3
6.2E-04
6.2E-04
3 to 10
3.3E-04
3.3E-04
10 to 50
1.8E-04
1.8E-04
50 to 150
1.3E-04
5.1E-05
>150
---
8.2E-05
TOTAL
1.3E-03
1.3E-03
Graphical Representation
Equipment Type: (24) SSIV Assemblies
There are only 2 recorded incidents of releases from SSIV Assemblies in the HCRD. Of these
only 1 is selected as being QRA significant and this had a hole size of 15 mm. The above table
has been generated based on the frequency of this single event and the hole size distribution
obtained by scaling the values for Pipeline ESDVs. The frequencies presented have a high degree
of uncertainty.
42
Process Release Frequencies
2.3
LNG Facilities
Failure frequencies for LNG process equipment have been provided by PHMSA in its LNG
Failure Rate Table (FRT) and are reported in a study by the Gas Technology Institute’s [2] which
considered refinements to the values provided. Table 2-1 presents the failure frequencies
as given in the report. Reference [3] was a review of published failure frequency information
covering all industries with very little LNG specific information being available. The table was
derived by expert judgement of this industry from available information and is not necessarily
LNG specific. For further information, it is recommended to consult [3]. It should be noted
that Appendix B in [3] summarises recommend modifications to some of these values.
Table 2-1: Nominal Failure Rates Specified in the LNG FRT From [3]
Nominal Failure Rate
per Year of Operation
Equipment
Type of Failure
Cryogenic Storage
Tanks (General)
Rupture of Storage Tank Outlet/Withdrawal Line
3 x 10-5
Catastrophic Failure, Release to Atmosphere
5 x 10-6 per tank
Catastrophic Failure of Tank Roof
1 x 10-4 per tank
Release from hole in inner tank with effective diameter of 1 m (~3 ft)
8 x 10-5 per tank
Release from hole in inner tank with effective diameter of 0.3 m (~1 ft)
2 x 10-4 per tank
Release from hole in inner tank with effective diameter of 0.01 m (0.4”)
1 x 10-4 per tank
Catastrophic Failure, Release to Atmosphere
5 x 10-7 per tank
Catastrophic Failure of Tank Roof
1 x 10-4 per tank
Release from hole in inner tank with effective diameter of 1 m (~3 ft)
1 x 10-5 per tank
Release from hole in inner tank with effective diameter of 0.3 m (~1 ft)
3 x 10-5 per tank
Release from hole in inner tank with effective diameter of 0.01 m (0.4”)
1 x 10-4 per tank
Catastrophic Failure, Release to Atmosphere
1 x 10-8 per tank
Catastrophic Failure of Tank Roof
4 x 10-5 per tank
Release from hole in inner tank with effective diameter of 1 m (~3 ft)
1 x 10-6 per tank
Release from hole in inner tank with effective diameter of 0.3 m (~1 ft)
3 x 10-6 per tank
Release from hole in inner tank with effective diameter of 0.01 m (0.4”)
1 x 10-4 per tank
Catastrophic Failure (Rupture)
5 x 10-6 per vessel
Release from hole in inner tank with effective diameter of 0.01 m (0.4”)
1 x 10-4 per vessel
Rupture of transfer arm
3 x 10-4 per transfer
arm
Release from a hole in transfer arm with effective diameter of 10%
transfer arm diameter with maximum of 50 mm (2”)
3 x 10-3 per transfer
arm
Rupture of transfer hose
4 x 10-2 per transfer
hose
Release from a hole in transfer hose with effective diameter of 10%
transfer arm diameter with maximum of 50 mm (2”)
4 x 10-1 per transfer
hose
Single Containment
Atmospheric Storage
Tanks5
Double Containment
Atmospheric Storage
Tanks
Full Containment
Atmospheric Storage
Tanks
Process Vessels,
Distillation Columns,
Heat Exchangers and
Condensers
Truck Transfer
5 Note that the outer wall of a single containment atmospheric storage tank will not normally be designed to contain cryogenic material.
A release from the inner tank should conservatively be assumed to result in a release to atmosphere.
43
Process Release Frequencies
Equipment
Ship Transfer
Piping (General)
Piping: d < 50 mm (2”)
Piping: 50 mm (2”)
<= d < 150 mm (6”)
Piping: 150 mm (6”)
<= d < 300 mm (12”)
Piping: 300 mm (12”)
<= d < 500 mm (20”)
Piping: 500 mm (20”)
<= d < 1000 mm (40”)
Type of Failure
Nominal Failure Rate
per Year of Operation
Rupture of transfer arm
2 x 10-5 per transfer
arm
Release from a hole in transfer arm with effective diameter of 10%
transfer arm diameter with maximum of 50 mm (2”)
2 x 10-4 per transfer
arm
Rupture at Valve
9 x 10-6 per valve
Rupture at Joint
4 x 10-3 per expansion
joint
Failure of Gasket
3 x 10-2 per gasket
Catastrophic Rupture
1 x 10-6 per metre
Release from a hole with effective diameter of 25 mm (1”)
5 x 10-6 per metre
Catastrophic Rupture
5 x 10-7 per metre
Release from a hole with effective diameter of 25 mm (1”)
2 x 10-6 per metre
Catastrophic Rupture
2 x 10-7 per metre
Release from a hole with effective diameter of 1/3 of pipe diameter
4 x 10-7 per metre
Release from a hole with effective diameter of 25 mm (1”)
7 x 10-7 per metre
Catastrophic Rupture
7 x 10-8 per metre
Release from a hole with effective diameter of 1/3 of pipe diameter
2 x 10-7 per metre
Release from a hole with effective diameter of 10% pipe diameter, up
to 50 mm (2”)
4 x 10-7 per metre
Release from a hole with effective diameter of 25 mm (1”)
5 x 10-7 per metre
Catastrophic Rupture
2 x 10-8 per metre
Release from a hole with effective diameter of 1/3 of pipe diameter
1 x 10-7 per metre
Release from a hole with effective diameter of 10% pipe diameter, up
to 50 mm (2”)
2 x 10-7 per metre
Release from a hole with effective diameter of 25 mm (1”)
4 x 10-7 per metre
In 2006, DNV compared failure rate data for equipment in LNG facilities with those
derived from the HCRD. The comparison indicated that LNG failure frequencies could
have been around 40% to 65% of the equivalent equipment on offshore installations. It
may be assumed that leak frequencies for LNG facilities have reduced over the period
since the study was conducted in a similar way to those for offshore facilities in the UKCS.
However, this has not been verified and the data for LNG installations is relatively sparse.
It is therefore recommended that, as an alternative to using the values in Table 2-1 or
for equipment that is not listed there, the frequencies given in section 2 are used. A 50%
reduction could be considered as a sensitivity but decisions based on this would need to be
fully justified.
44
Process Release Frequencies
3. Guidance on use of data
3.1
General validity
The data presented in Section 2 can be used for process equipment on the topsides of
offshore installations and for onshore facilities handling hydrocarbons6, and could also be
used as appropriate for subsea completions.
The release frequencies given in Section 2 are valid for holes of diameter (d) from 1 mm
to the diameter of the equipment (D). Frequencies of smaller holes may be estimated
by extrapolation of the frequencies to smaller hole sizes, but this is beyond the range of
the HSE data (see Section 4) and in any event are unlikely to ignite unless under specific
conditions such as high system pressure coupled with discharge into an area with low
ventilation. Extrapolation to large hole sizes is acceptable given the lack of alternative
information from other data sources. However, the levels of uncertainty are greater for
larger hole sizes because they are based on relatively few incidents. The data presented
in section 2 includes frequencies for incidents in hole size ranges which may not yet
have been experienced in the UKCS for a given equipment type. These frequencies will
normally be lower than the frequency which would be calculated from a single incident
for the exposure population. It is possible that there are physical reasons why a given type
of equipment is less likely to have a release with a large hole size than predicted in the
correlations. However, until sufficient experience is available to demonstrate otherwise, it is
assumed that extrapolation of the correlations between the largest recorded hole size and
the equipment size is the most appropriate approach.
The release frequencies are valid for equipment diameters (D) within the normal range of
offshore equipment. This is not precisely defined in the available equipment population data.
Using judgment based on the trends of the estimated diameter dependence and the average
diameters of the available data groups, the following ranges of validity are suggested:
• Pipes:
20 to 1000 mm
• Actuated valves:
10 to 1000 mm
• Flanges:
10 to 1000 mm
• Instruments:
10 to 100 mm
• Manual valves:
10 to 1000 mm
• Pig traps: 100 to 1000 mm
• All other equipment:
40 to 400 mm
With lesser confidence, the datasheets in Section 2 can be used to estimate frequencies
over larger ranges, but they should be subject to sensitivity testing.The frequencies are not
recommended for equipment outside this range.
6 The justification for using offshore data for onshore facilities is two-fold. First, no public domain dataset for onshore facilities is available
that is comparable to HCRD, considering both the equipment population and completeness of recording releases. Second, although
offshore facilities operate in a more challenging (e.g., more corrosive) environment, this is compensated for in the design, inspection
and maintenance. Hence there is no apparent reason why onshore and offshore release frequencies should differ significantly. However,
some environmental factors are considered in Sections 3.3.1 and 3.3.2. The standard of the safety management system is also believed
to have a major influence on release frequencies, regardless of operating environment, as also discussed in Section 3.3.2.
45
Process Release Frequencies
3.2
Uncertainties
The sources of uncertainties in the estimated release frequencies are discussed in Section 4.1.3.
The uncertainty in the release frequencies presented in Section 2 tends to be greatest for
large hole sizes, for equipment sizes far from the centres of the ranges of validity given in
Section 3.1, and for equipment types where fewer releases have been recorded (see Section
4.1.1). While there is greater uncertainty in these situations, it is considered that the
approach taken in deriving these frequencies is conservative.
No quantitative representations of the uncertainty in the release frequency results have
yet been derived. Frequencies for hole sizes in the range 2 mm – 10 mm are judged to be
accurate within a factor of 2, higher or lower. However, this may increase to an order of
magnitude for holes in the region of 100 mm.
3.3
Modification of frequencies for factors specific to plant
conditions
3.3.1 General considerations
The frequencies tabulated in Section 2 are generic frequencies for installations designed
and operating to “typical” European/North American standards. A large number of possible
factors may suggest that these generic frequencies ought to be modified to make them
specific to the local conditions. These factors include the physical characteristics of the
equipment, the operating conditions, and characteristics of the management system in
place. Factors related to the physical characteristics and operating conditions could include:
• Design code
• Equipment age
• Operating environment
• Welds
• Process continuity
• Operating pressure
• Material of construction
• Seismic activity
• Cold or hot weather
• Radiography
• Stress cycling
• Operating temperature
• Fluid inside equipment
• Integrity status
Many of these are addressed in API 581 [4] which is discussed in Section 3.3.2. along with
the influence of safety management. Some more specific factors relating to inter-unit
piping are presented in Section 3.3.3. and flanges in section 3.3.4 .
3.3.2 API 581 Approach
API 581 [4] presents a set of generic failure frequencies (GFFs) which can then be adjusted
through the application of a damage factor and management safety factor. These are
primarily aimed at determining inspection priorities and optimising inspection efforts
rather than frequency analysis within QRA.
46
Process Release Frequencies
The basic function of the damage factor is to statistically evaluate the amount of damage
that may be present as a function of time in service and the effectiveness of an inspection
activity. Damage factors are not intended to reflect the actual probability of failure
but to reflect a relative level of concern about a given component based on the stated
assumptions in each of the applicable sections of the document. Damage factor estimates
are provided for the following damage mechanisms:
• Thinning
• Stress Corrosion Cracking
• External Damage
• High Temperature Hydrogen Attack
• Mechanical Fatigue (Piping Only), and
• Brittle Fracture
These can be combined to provide an overall multiplying factor for the equipment.
A management systems factor is used to adjust generic failure frequencies for differences
in process safety management systems. This factor is derived from the results of an
evaluation of a facility or operating unit’s management systems that affect plant risk.
Within any one study, the management systems factor should be the same and the factor is
applied equally to all components. The management systems factor can have a significant
effect on the overall leak frequency for a facility. The management systems evaluation
covers all areas of a plant’s PSM system that impact directly or indirectly on the mechanical
integrity of process equipment.
The methodology includes an evaluation tool to assess the portions of the facility’s
management system that most directly impact the probability of failure of a component.
This consists of a series of interviews with plant management, operations, inspection,
maintenance, engineering, training, and safety personnel.It comprises numerous
questions, most of which have multiple parts. Each possible answer to each question is
given a weight, depending upon the appropriateness of the answer and the importance of
the topic.
The scale recommended for converting a management systems evaluation score to a
management systems factor is based on the assumption that the “average” plant would
score 50% on the management systems evaluation. A 100% score would equate to a one
order-of magnitude reduction in risk while a score of zero would equate to a one order of
magnitude increase in the risk.
The overall process is complex and it is not usual for damage factors and management
system factors to be included in a QRA to determine modified loss of containment
frequencies. The GFFs to which the factors are applied are not directly derived from the
HCRD so it would be inappropriate for them to applied without care. The standard of
management systems within operators of North Sea installations may be relatively high
and so on average score more than 50% on the API 581 tool.It is noted in [5], commenting
on the 2nd edition of API 581, that “overall, the observed tendency towards very low MF
scores for average good sites today may bias the results and lead to underestimates of leak
frequencies and thus this aspect of the API 581 method is not recommended. In fact, very few
sites implementing risk-based inspection use this management system correction factor”.
47
Process Release Frequencies
While application of modification factors to support significant reductions in estimates
for leak frequencies is not recommended, situations where there is an expectation that
standards are lower than those from which the generic data is derived should be subjected
to a modification factor greater than 1. Preferably this should be based on the frequency of
recorded leaks on the installation in question, provided the data is statistically significant,
in comparison with the value estimated from unfactored application of the generic data.
Alternatively, the assessment can be based on data collected from installations considered
to be comparable.
If it is believed that higher frequencies are applicable, then a factor should be applied.
However, a factor to reduce the frequencies should not be applied.
3.3.3 Inter-unit piping
A confidential study performed by Technica in 1983 on the causes of piping failure and
another performed by DNVTechnica 1993 on the application to this analysis of judgemental
modifications to account for the differences in inter-unit and transfer pipes, indicated that
the following release frequency modification factors can be applied:
• Inter-unit pipe:
0.9
• Transfer pipe:
0.8
These were relevant to the assessed offshore process leak frequencies at the time the
analysis was carried out in 1989 and 1993.The ratio may be assumed to still be applicable to
the values given in section 2.
Note that these two confidential studies were quoted in the previous version of this report
(434-01, March 2010) but have not been available for authors of this update to review,
therefore this section of this report remains unchanged from the previous version.
3.3.4 Flanges
Studies [8] and [9] of the effect of flange type on flange failure frequency developed
modification factors to the frequencies presented in the previous version of the datasheet
and recommended their application when performing detailed risk analyses where the
flange types are known or alternatively as decision input to design when flange types are to
be decided. The flange types considered were:
• ANSI Ring Joint
• ANSI Raised faced
• Compact flange
• Grayloc flange
The ANSI Ring Joint, historically the most common flange type in the UK offshore industry, was
assumed to be represented by the HCRD data for flanges based on 1992-2006 data. Factors for
the other types generally indicated an order of magnitude reduction in leak frequency for holes
in the range 1 mm - 50 mm but comparable for hole sizes larger than this.
48
Process Release Frequencies
Given the significant reduction in the observed frequency of leaks from flanges in the period
2006-2015 compared with previous experience and the absence of a comparable study
on modification factors it is not recommend to apply modification factors to the values
presented in section 2.
Although it is not recommended, it may be permissible to introduce a factor to increase
or reduce the frequency of leaks from flanges provided that there is sufficient specific
evidence available to the QRA sponsor to support the use of that factor.
The PLOFAM study [10] concluded that the leak frequency for compact flanges may be an
order of magnitude lower than standard flanges but this is based on a very small sample.
It is also considered that while compact flanges may have a reduced probability of leaking
when first in use, the advantage may be reduced following maintenance involving rebolting.
49
Process Release Frequencies
4. Review of data sources
4.1
Basis of data presented
The release frequencies for the main process equipment items presented in Section 2
are based on an analysis of the HSE hydrocarbon release database (HCRD) for 1992-2015
[11], [12] and [13] according to a methodology described in section 1.1. An overview of this
methodology is given in Section 4.1.2.
The HSE hydrocarbon release database (HCRD) has become the standard source of
release frequencies for offshore QRA and provides a large, high-quality collection of
release experience. Reporting of offshore incidents is required in the UK by various pieces
of legislation including the Reporting of Injuries, Diseases and Dangerous Occurrences
Regulations 2013 (RIDDOR) [14]. Additionally, European Commission Implementing
Regulation (EU) No 1112/2014 [15] now applies in the UK and creates legal obligations to
report certain types of incident. However, this has not affected the reporting of incidents in
the time period considered here. The database contains reports of 4664 releases up until 31
December 2015, of which 3551 relate to the equipment types addressed in this datasheet.
The database is considered to be the best available source of data for offshore process
leaks given that it collects data from over 300 offshore installations since October 1992
and is believed to include a very high proportion of leaks with an equivalent hole diameter
of more than 1 mm. The population data is based on information collected in an extensive
study in the 1990s which was updated in the following years. A review in 2015 identified that
data from many recent platforms had not been included and not all process systems had
their equipment counted. The population data was adjusted and revised estimates issued
[13]. These estimates relate only to fixed production installations since insufficient records
of the time which mobile units were operating in UKCS waters are available. Despite this
issue the HCRD is considered the most comprehensive collection of data available. Hence it
has been selected in preference to other data sources discussed in Section 4.4.
4.11
Summary of release statistics
Table 4-1 summarises the number of releases and exposure (population) for each
equipment type represented in the HSE HCRD.
50
Process Release Frequencies
Table 4-1: Summary of Release Statistics for HSE HCRD 1992-2015
Equipment type
All Releases
Selected* Releases
Exposure
1. Steel process pipes
1019
333
11,109,032 pipe metre years
2. Flanged Joints
434
242
6,581,236 flange joint years
3. Manual valves
309
165
3,585,211 valve years
4. Actuated valves
406
203
667,643 valve years
5. Instrument connections
780
397
1,559,992 instrument years
6. Process (pressure) vessels
52
20
37,388 vessel years
7. Pumps: Centrifugal
172
75
22,197 pump years
8. Pumps: Reciprocating
32
9
4,863 pump years
9. Compressors: Centrifugal
70
38
6,835 compressor years
10. Compressors: Reciprocating
67
41
1,439 compressor years
11. Heat exchangers: Shell & Tube, shell side
29
16
7,127 exchanger years
12. Heat exchangers: Shell & Tube, tube side
30
18
12,643 exchanger years
13. Heat exchanges: Plate
51
38
6,390 exchanger years
14. Heat exchangers: Air-cooled
6
1
1,933 exchanger years
15. Filters
73
40
18,589 filter years
16. Pig traps
47
26
7,824 pig trap years
17. Flexible pipes
139
46
167,529 pipe metre years
18. Pressure Vessels (Other)
49
25
5,415 vessel years
19. Degassers
3
2
2614 degasser years
20. Expanders
2
1
258 expander years
21. Xmas Trees
108
68
47,261 xmas tree years
22. Turbines
146
26
3,077 turbine years
23. Pipeline ESVDs
31
14
21,240 pipeline ESDV years
24. SSIV Assemblies
2
1
4,016 SSIV assembly years
*See section 4.1.2 for selection criteria
4.12
Methodology for obtaining release frequencies
The method of obtaining release frequencies from HCRD consists of a number of steps:
• Selection of data which is “QRA significant” and compatible with the available
population data. Details of the criteria applied are given in [16]. In summary, incidents
which met one or more of the following criteria were excluded:
– Incidents which occurred on other than fixed production installations.
– Incidents which occurred in systems for which population data was not available.
– Incidents with an equivalent hole size of 1 mm or less.
– Incidents that occurred at low pressure (<=0.01 barg) indicating that the process
system was not in operation at the time and the resulting inventory released did
not pose a threat of the type considered in QRAs.
51
Process Release Frequencies
– Deliberate releases which were accidentally ignited, i.e. incidents which would
not have been included had they not ignited.
– Releases which do not comply with the current OGUK reporting criteria [17].
The majority of incidents in the HCRD become excluded in this process. The number
of remaining “selected” incident is 1965 of which 1662 relate to the equipment types
addressed in this datasheet.
• Grouping data for different types and sizes of equipment where there is insufficient
experience to show significant differences between them.
• Redistribution of incidents for which equipment types were not recorded.
Redistribution was proportional to the fraction of each equipment type for which an
equipment code was assigned.
• Determination of frequencies: this was undertaken using two criteria:
1)
Frequency based on selected incidents in the most recent 10 year period or 10
incidents if there were less than this number in the 10 year period.
2)
Frequency based on all selected incidents up until 31st December 2015.
• Determination of hole size distributions using all selected data available in the HCRD.
• Fitting analytical frequency functions to the data, in order to obtain a smooth variation
of release frequency varying with equipment type and hole size. For some equipment
types the influence of equipment size can also be inferred.
• Generation of tabulated data for hole size ranges using the analytical frequency
functions.
The release size distribution is represented by an analytical frequency function, which
ensures non-zero release frequencies for all holes sizes between 1 mm and the diameter
of the inlet pipe.
F(d) = Cdm + B ,
F(d) = 0 ,
1 mm < d ≤ D
d>D
where:
F(d)
is the frequency per year of releases exceeding size d (mm)
d
is the equivalent hole diameter
D
is the equipment size
C, m and B
are constants specific to the equipment type and release scenario
For four types of equipment there are sufficient data in each of the equipment size subcategories to establish size specific parameters. These are: steel process pipes, flanges,
manual valves and actuated valves (non-pipeline). Based on these, interpolation functions
can be developed to model the effect of variation in equipment size on the C, m and B
parameters with equipment size. For all other equipment types the same function is applied
irrespective of equipment size other than the hole size is limited to the size of the equipment.
The function can then be used to calculate the frequency of a release in any size range (such
as the ranges used in Section 2). The frequency of leak in the range d1 to d2 is F(d1) – F(d2).
52
Process Release Frequencies
The parameters C, m and B referred to above are derived by a combination of an automated
curve fitting process and judgment. As an example, Figure 4-1 shows the curve fitted to the
historical hole size versus exceedance frequency distributions for 3” – 11” flanges.
Figure 4-1
Figure 4-1: Mathematical Correlation Fitted to Historical Data for Flanges 3” - 11”
4.1.3 Uncertainties in release frequencies
Uncertainties in the estimated release frequencies arise from three main sources:
• Incorrect information in HCRD about the releases that have occurred. This includes
the possibility of under-reporting of small releases, errors in measuring the
equivalent hole diameter or estimating it based on other quantities such the amount
of hydrocarbon released and the duration. Although the data in HCRD is considered
the best available, the possibility of systematic bias or other errors is recognised.
• Inaccurate assessment of equipment populations. The calculated frequency is
dependent on the exposure for a particular equipment category as well as the number
of incidents recorded for it. A review of the equipment data in 2016 identified that
equipment counts from a significant number of installations were omitted from
the HCRD. Also, even when there were records for an installation, not all of their
process systems had equipment counts. As a short term, partial solution to this issue,
additional equipment was added to the overall HCRD population counts in two ways:
– Installations with no-equipment counts were matched with an installation of
similar type and assigned a proportion, based on judgement, of the equipment
from that surrogate installation.
– Process systems with no equipment counts were assigned the average
equipment count for the systems counted on other installations.
While this has improved the accuracy of the overall equipment counts the amounts
added are subject to significant uncertainties. The initial counts of the equipment are
also subject to uncertainties.
53
Process Release Frequencies
• Selection of relevant incidents. The process for selection of relevant incidents has a
degree of subjectivity. There will be incidents which have been incorrectly included
or excluded from the analysis. However, these incidents will predominantly be those
which have small hole sizes (less than 2 mm) whereas the frequency distributions are
primarily influenced by the larger hole size incidents (2mm and above).
• Inappropriate representation of the release frequency distributions by the fitted
correlations. The uncertainty in the correlations are largely dependent on the number
of relevant incidents available upon which to base the analysis. The simplifications
inherent in the chosen functions, and their use to extrapolate frequencies for sizes
where no releases have yet been recorded is a further factor.
4.1.4 Conclusions
Others have also analysed the HCRD and obtained different functional forms for the release
frequencies. However, the process outlined above provides:
• An analysis of the most recent incident data for which final information is available.
• Inclusion of the currently accepted best estimate of the process equipment.
• Frequencies derived from a process of fitting correlations which provide a smooth
variation for hole sizes.
• A model that is consistent with recent experience.
On this basis, the tabulations in Section 2 are presented as the best available analysis of
the best available data.
4.2
PLOFAM2 Model
A recent study involving a number of operators and consulting organisation in Norway has
proposed an alternative approach for deriving frequency estimates. The study resulted
in the Process Leak for Offshore Installations Frequency Assessment Model (PLOFAM2)
[10]. The model is mainly validated against available data of leaks that has occurred at
installations on the Norwegian Continental Shelf (NCS), but also takes account of data
from the HCRD where data material for NCS is scarce. Leak frequencies are based on
experience in the period 2006-2017 while the whole period (2001-2017) is used for the
relative leak rate distribution.
The study identified leaks which were relevant to leak scenarios which would be expected
to be modelled in risk assessments. The model distinguishes two types of leak which are
defined as “significant” and “marginal”. Marginal leaks are those where the total quantity
leaked is less than or equal to 10 kg.
Only the significant leak scenario is relevant for detailed modelling of consequences and
dimensioning accidental loads in a formal QRA. The marginal leak scenario is only relevant
with regard to immediate exposure of personnel in the close vicinity of the release or for
small poorly ventilated enclosures.
Various levels of filtering are applied to the incidents in the HCRD. From this process 1053
are identified as being “significant” leaks and a further 534 are “marginal” leaks. This is a
smaller number than used in the analysis from which the values in section 2 are derived.
54
Process Release Frequencies
This is partly because the PLOFAM study did not have access to the details of the incidents
between 1st April and 31st December 2015 but mostly because of differences in the
selection criteria.
The PLOFAM study derived a series of mathematical equations to represent the hole size
frequency distribution. The general form is
F(d,D) = [F0(D) - α FD (D)] dm(D) + α FD (D),
F(d,D) = 0 ,
Where
1 mm < d ≤ D
d>D
F(d,D) is the hole size frequency distribution per year per equipment item
F0 is the total leak frequency per year per equipment item, F0 = F(d=1,D)
FD is the total full bore hole frequency per year per equipment item,
FD = F(d=D,D)
D is the equipment diameter in millimetres
d is the hole diameter in millimetres
m(D) is the slope parameter, and
α is a dimensionless parameter
The equation describes a power law relation that is valid for hole sizes less than the
equipment diameter. The total leak frequency F0 and the full bore hole fraction FD are
modelled using the following relations.
F0 (D) = Fhist (A0 DM0)
FD (D) = F0 (D) (AD DMD) + BD)
Where,
F(d, D) is the hole size frequency distribution
Fhist is the average leak frequency (independent of equipment diameter) for
the relevant equipment item per year per equipment item. The subscripts
“significant” and “marginal” are used to denote the historical frequency of
significant leaks and, where relevant, marginal leaks respectively, and
A0, M0, AD, MD and BD are parameters in the total hole and full bore hole
frequency equations
The slope parameter m(D), follows from the assumption of a power law relation and the
values for F0, FD and D:
m(D) = log(FD - α FD) - log(F0 - α FD)
log(D)
For several equipment types, many of the parameters have a value 0 or 1, resulting in a
simpler formulation for that equipment type.
Parameters were derived for 20 different equipment types as shown in Table 4-2.
55
Process Release Frequencies
Table 4-2: PLOFAM2 model Parameters From [10]
Equipment type
A0
m0
AD
mD
BD
α
Fℎist,Significant
Fℎist,Marginal
Air-cooled heat exchanger
1.00
0
0
0
3.0E-2
0
5.00E-4
0
Atmospheric vessel
1.00
0
0
0
1.0E-1
0
5.00E-4
0
Centrifugal compressor
1.00
0
0
0
6.0E-3
0
1.30E-3
0
Centrifugal pump
1.00
0
0
0
3.0E-5
0
3.00E-3
0
Compact flange
1.00
0
0
0
1.0E-3
0.9
3.00E-6
0
Filter
1.00
0
0
0
8.0E-4
0
2.30E-3
0
Flexible pipe
1.00
0
0
0
4.0E-1
0.75
1.40E-4
0
Gas lift well
1.00
0
0
0
2.5E-2
0
1.00E-4
1.00E-04
Hose
1.00
0
0
0
4.0E-1
0.75
6.00E-5
1.00E-05
Instrument
1.00
0
0
0
1.5E-1
0
1.30E-4
0
Pig trap
1.00
0
0
0
2.0E-2
0
1.70E-3
0
Plate heat exchanger
1.00
0
0
0
1.0E-3
0
3.50E-4
0
Process vessel
1.00
0
0
0
6.0E-4
0
5.00E-4
0
Producing well
1.00
0
0
0
2.0E-2
0
2.00E-5
1.30E-05
Reciprocating compressor
1.00
0
0
0
1.0E-2
0
5.00E-3
-
Reciprocating pump
1.00
0
0
0
3.0E-5
0
3.00E-3
-
Shell and tube heat
exchanger exchanger
1.00
0
0
0
7.5E-3
0
3.30E-4
-
Standard flange
1.00
0
18.0
-1.45
5.0E-3
0.5
2.50E-5
5.00E-06
Steel pipe
4.20
-0.30
17.6
-1.75
1.0E-3
0.9
1.40E-5
2.00E-06
Valve
1.11
-0.10
16.0
-1.70
1.0E-3
0.5
2.15E-4
3.50E-05
Values denoted by “-“ should be taken as zero.
4.3
OREDA
OREDA [18] gives the number of incidents of external leakage of process medium from
subsea equipment together with the corresponding exposure data in terms of hours of
operation. This includes, wellheads & xmas trees, flowlines, manifolds, pipelines and
risers. If frequencies derived from theses are used, it should be noted that these are
based on only a small number of incidents and so are subject to statistical uncertainty. It
is suggested that use of onshore/topsides failure frequencies, e.g., the frequencies for the
corresponding equipment types from nos. 1 to 16 above, is preferable.
4.4
Other data sources
A large number of other data sources and analyses of process release frequencies
were analysed previously. These are listed in section 6.2. Not all of these address all the
equipment types for which frequencies are given in Section 2.
56
Process Release Frequencies
5. Recommended data sources for
further information
For further information, the data sources used to develop the release frequencies
presented in Section 2 and discussed in Sections 3 and 4 should be consulted.
57
Process Release Frequencies
6. References
6.1
References for Sections 2 to 4
[1]
Brian Bain et. al, Modelling of Accidental Hydrocarbon Releases in QRAs: Hole Size Versus
Initial Release Rate Basis, Hazards 24 Symposium, 2014.
[2]
HSE, Failure Rate and Event Data for use within Risk Assessments, Issued 28/6/2012.
[3]
Gas Technology Institute, Statistical Review and Gap Analysis of LNG Failure Rate Table, GTI
Project Number 21873, January 2017 available at https://primis.phmsa.dot.gov/matrix/FilGet.
rdm?fil=11074
[4]
API, 2016. Risk-Based Inspection Methodology, API recommended Practice 581, 3rd ed.
[5]
Robin Pitblado, R et. al., Frequency Data and Modification Factors Used in QRA Studies”,
Journal of Loss Prevention in the Process Industries, Volume 24 Issue 3, May 2011.
[6]
Technica, 1989. Confidential Report for UK HSE.
[7]
DNV Technica, 1993. Confidential Report.
[8]
DNV, 1997. Reliability Evaluation of SPO Compact Flange System, DNV Technical Report 97-3547,
rev. 2, for Steel products Offshore A/S.
[9]
DNV, 2005. Decision model for choosing flange or weld connection, DNV Technical Report (in
Norwegian) 2005-0462, rev. 2.
[10]
Lloyd’s Register Consulting, Process Leak for Offshore Installations Frequency Assessment
model – PLOFAM(2). Report No. 1007566/R1 Rev: Final, December 2018.
[11]
HSE, Spreadsheet entitled “Offshore Hydrocarbon Releases 1992 – 2016” available from
http://www.hse.gov.uk/offshore/statistics.htm
[12]
HSE Spreadsheet entitled “Offshore Hydrocarbon Releases 2015 – 2016” available from
http://www.hse.gov.uk/offshore/statistics.htm
[13]
HSE Spreadsheet entitled “Offshore Hydrocarbon Population Data 2015 – 2016” available from
http://www.hse.gov.uk/offshore/statistics.htm
[14]
HM Stationary Office, 2013. The Reporting of Injuries, Diseases and Dangerous Occurrences,
Statutory Instruments 2013 No. 1471.
[15]
European Union, 2014, “Commission Implementing Regulation (EU) No. 1112/2014.
[16]
Bain, B, “Updated Leak Frequency Modelling Based on the UK Hydrocarbon Release
Database, Hazards 27 Symposium, 2017.
[17]
Oil & Gas UK. Supplementary Guidance on the Reporting of Hydrocarbon Releases, Issue 3,
2015
[18]
SINTEF, 2015 (OREDA 2015). Offshore Reliability Data, 6th. ed., Volume 2 – Subsea Equipment.
58
Process Release Frequencies
6.2
References for other data sources
ACDS, 1991. Major Hazard Aspects of the Transport of Dangerous Substances, Advisory Committee
on Dangerous Substances, Health & Safety Commission, HMSO.
AEA, 1998. Hydrocarbon Release Statistics Review, Report for UKOOA, AEA Technology.
AEA, 2000. A Preliminary Analysis of the HCR99 Data, Report for UKOOA, AEA Technology.
AME (1998), PARLOC 96: The Update of Loss of Containment Data for Offshore Pipelines, Offshore
Technology Report OTH 551, Health & Safety Executive.
Ames, S. & Crowhurst, D, 1988. Domestic Explosion Hazards from Small LPG Containers, J. Haz.
Mat., 19, 183-194.
Arulanatham, D.C. & Lees, F.P., 1981. Some Data on the Reliability of Pressure Equipment in the
Chemical Plant Environment, Int. J. Pres. Ves & Piping, 9, 327-338.
Aupied J.R., Le Coguiec, A. & Procaccia, H., 1983. Valves and Pumps Operating Experience in French
Nuclear Plants, Reliability Engineering, 6, 133-151.
Batstone, R.J. & Tomi, D.T., 1980. Hazard Analysis in Planning Industrial Developments, Loss
Prevention, 13, 7.
Baldock, P.J., 1980. Accidental Releases of Ammonia - An Analysis of Reported Incidents, Loss
Prevention, 13, 35-42.
Blything, K.W. & Reeves, A.B., 1988. An Initial Prediction of the BLEVE Frequency of a 100 te Butane
Storage Vessel, UKAEA, SRD R448.
Bush, S.H., 1978. Reliability of Piping in Light Water Reactors, Symposium on Application of Reliability
Technology to Nuclear Power Plants, International Atomic Energy Agency, vol. 1, IAEA-SM-218/11.
Bush, S.H., 1988. Statistics of Pressure Vessel and Piping Failures, J. Pressure Vessel Technology,
110/227.
Cox, A.W., Lees, F.P. & Ang, M.L., 1990. Classification of Hazardous Locations, Rugby, UK: Institution of
Chemical Engineers.
Crossthwaite, P.J., Fitzpatrick, R.D. & Hurst, N.W., 1988. Risk Assessment for the Siting of
Developments near Liquefied Petroleum Gas Installations, IChemE Symposium Series No 110.
Crerand, A, et al. 2014. Improvement in Release Frequencies for Quantitative Risk Assessment, Hazards
24 Symposium.
Data Engineering, 1998. Hydrocarbon Release Database, Population Data Statistics, OTO 98 158, Health
& Safety Executive, Offshore Safety Division.
Davenport, T.J., 1991. A Further Survey of Pressure Vessel Failures in the UK, Reliability 91, London.
E&P Forum, 1992. Hydrocarbon Leak and Ignition Database, Report 11.4/180.
Falck, A., Bain, B., & Rødsætre, L. K., Leak Frequency Modelling for Offshore QRA Based on the
Hydrocarbon Release Database. Hazards XXI Conference. Manchester, UK. 2009
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61
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This datasheet presents frequencies
of releases from the listed process
equipment types. They are intended
to be applied to process equipment
on the topsides of offshore
installations and on onshore
facilities handling hydrocarbons
but are not restricted to releases of
hydrocarbons.
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