Riser and Gas release frequencies.pdf

Risk Assessment Data Directory

Report No. 434 – 4March 2010

I n t e r n a t i o n a l A s s o c i a t i o n o f O i l & G a s P r o d u c e r s

Riser & pipeline release

frequencies

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RADD – Riser & pipeline release frequencies

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contents

1.0 Scope and Definitions ........................................................... 1 1.1 Application ...................................................................................................... 1 1.2 Definitions ....................................................................................................... 1

2.0 Summary of Recommended Data ............................................ 2 3.0 Guidance on use of data ........................................................ 3 3.1 General validity ............................................................................................... 3 3.2 Uncertainties ................................................................................................... 3 3.3 Application of frequencies to specific pipelines ......................................... 3 3.3.1 Offshore pipelines...................................................................................................... 4 3.3.2 Onshore pipelines ...................................................................................................... 6 3.4 Application to pipelines conveying fluids other than hydrocarbons ........ 6 4.0 Review of data sources ......................................................... 6 4.1 Basis of data presented ................................................................................. 6 4.1.1 Risers and offshore pipelines ................................................................................... 6 4.1.2 Onshore gas pipelines............................................................................................... 8 4.1.3 Onshore oil pipelines................................................................................................. 9 4.2 Other data sources ....................................................................................... 10 5.0 Recommended data sources for further information ............ 11

6.0 References .......................................................................... 11 6.1 References for Sections 2.0 to 4.0 .............................................................. 11 6.2 References for other data sources.............................................................. 11


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Abbreviations: AGA American Gas Association ANSI American National Standards Institute API American Petroleum Institute ASME American Society of Mechanical Engineers CONCAWE Conservation of Clean Air and Water in Europe DNV Det Norske Veritas DOT (US) Department of Transportation EGIG European Gas Pipeline Incident Data Group ESDV Emergency Shutdown Valve PARLOC Pipeline And Riser Loss Of Containment UK HSE United Kingdom Health and Safety Executive UKOPA United Kingdom Pipeline Operators’ Association VIV Vortex Induced Vibration


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1.0 Scope and Definitions 1.1 Application This datasheet presents (Section 2.0) frequencies of riser and pipeline releases. Frequencies for offshore and onshore pipelines are included. The frequencies given are based on analysis for pipelines conveying hydrocarbons. They may be applied to pipelines conveying other fluids as discussed in Section 3.4.

1.2 Definitions The pipeline frequencies are given for four different sections as shown in Figure 1.1. Risers are considered to comprise three sections: • Above water (often taken to be the topsides section below the riser ESDV) • Splash zone (exposed to aggressive corrosion conditions and ship collisions) • Below water (to the flange connection with the pipeline or a spool piece)

Figure 1.1 Definition of Pipeline Sections

For offshore sections, frequencies are given for steel and flexible risers and pipelines. “Flexible” should be understood in the context of the source data (see Section 4.1.1), which is from the North Sea. It therefore includes risers from FPSOs, TLPs and semisubmersibles but would not include deepwater technologies such as steel catenary risers. These are a specialist and relatively new area, and the failure frequency analysis should accordingly be undertaken utilising suitable expertise.


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2.0 Summary of Recommended Data The recommended frequencies and associated data are presented as follows: • Table 2.1 Recommended Riser and Pipelines failure Frequencies • Table 2.2 Recommended Hole Size Distributions for Risers and Pipelines • Table 2.3 Release Location Distribution for Risers Note that separate failure frequencies are not given for Segment III, Landfall zone. This segment, representing the tidal zone, is defined as the area where the pipeline may be wet and dry at different times. This allows the anode system to function. Onshore pipelines are often more affected by corrosion than pipelines in the tidal zone. Hence frequencies for onshore pipelines should be used in tidal zones. A pipeline in the landfall zone may also be subject to increased risk of external impact, e.g. due to grounding ships. Such risks may have to be assessed separately.

Table 2.1 Recommended Riser and Pipelines failure Frequencies

Pipeline Category Failure frequency

Unit

Well stream pipeline and other small pipelines containing unprocessed fluid

5.0 × 10-4

per km-year

Processed oil or gas, pipeline diameter ≤ 24 inch

5.1 × 10-5 per km-year

Subsea pipeline: in open sea

Processed oil or gas, pipeline diameter > 24 inch


Diameter ≤ 16 inch 7.9 × 10-4 per year Subsea pipeline: external loads causing damage in safety zone Diameter > 16 inch 1.9 × 10-4 per year

Flexible pipelines: subsea

All 2.3 × 10-3 per km-year

Steel - diameter ≤ 16 inch 9.1 × 10-4 per year Steel – diameter > 16 inch 1.2 × 10-4 per year

Risers

Flexible 6.0 × 10-3 per year Diameter < 8 inch 1.0 × 10-3 per km-year 8 inch ≤ diameter ≤ 14 inch 8.0 × 10-4 per km-year 16 inch ≤ diameter ≤ 22 inch 1.2 × 10-4 per km-year 24 inch ≤ diameter ≤ 28 inch 2.5 × 10-4 per km-year

Oil pipelines onshore

Diameter > 28 inch 2.5 × 10-4 per km-year Wall thickness ≤ 5 mm 4.0 × 10-4 per km-year 5 mm < wall thickness ≤ 10 mm 1.7 × 10-4 per km-year 10 mm < wall thickness ≤ 15 mm


Gas pipelines onshore

Wall thickness > 15 mm 4.1 × 10-5 per km-year


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Table 2.2 Recommended Hole Size Distributions for Risers and Pipelines

Onshore pipeline Hole size Subsea pipeline Gas Oil

Riser

Small (< 20 mm) 74% 50% 23% 60% Medium (20 to 80 mm) 16% 18% 33% 15% Large (> 80 mm) 2% 18% 15% Full rupture 8% 14% 29%

25%

Table 2.3 Release Location Distribution for Risers

Release location Distribution Above water 20% Splash zone 50% Subsea 30%

3.0 Guidance on use of data 3.1 General validity The frequencies given are based on analysis for pipelines conveying hydrocarbons. They may be applied to pipelines conveying other fluids as discussed in Section 3.4. There is an implicit assumption that the pipelines are built to a recognized international standard such as ANSI/ASME B31.4/8 [1,2] or (for subsea pipelines) DNV-OS-F101 [3].

3.2 Uncertainties In addition to the known causes of fluid release from transport pipelines, as discussed in Section 4.0, new or unforeseen factors may cause shutdown of pipelines. It is impossible to estimate the contribution from such incidents to the release frequencies, neither is it possible to state that it is more likely that some pipelines will sustain failure before others. Accordingly, unknown factors cannot be used either to identify pipelines which are especially exposed to the possibility of leakage or to prioritize risk mitigation measures.

3.3 Application of frequencies to specific pipelines In Table 2.1, most frequencies are given per km-year as they are dependent on the length of the pipeline. For a typical pipeline of length ℓ (km) with release frequency fkm, the release frequency F along the full length of the pipeline is simply given by:

F = ℓ × fkm per year: There are several causes that can result in the release frequency for a specific pipeline, or for a section of a pipeline, being different from that obtained simply using the Section 2.0 frequencies.


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In general there are two main groups of causes causing pipeline failures. The first group is related to loads exceeding pipeline critical loads, usually resulting in an isolated incident. The second group is related to effects gradually weakening the pipeline over a period of time. Those considered here are: Isolated incidents – offshore Mechanisms acting over time – offshore • Loads from trawl boards • Corrosion • Ship anchor / sinking ship • Open spans causing fatigue • Subsea landslide • Buckling Isolated incidents – onshore Mechanisms acting over time – onshore • External interference e.g. digging • Construction defect • Hot-tap made by error • Material failure • Ground movement e.g. landslide • Ground movement e.g. mining • Corrosion These are discussed further in Sections 3.3.1 (offshore pipelines) and 3.3.2 (onshore pipelines), with some guidance given on modifying the Section 2.0 frequencies. However, in situations where several of these causes pertain or critical decisions are dependent on the analysis results, a detailed analysis should be carried out utilising appropriate expertise and data specific to the situation. Such analysis is beyond the scope of this datasheet. 3.3.1 Offshore pipelines

Where none of the additional causes listed in Section 3.3 that could exacerbate the likelihood of a release are present, the release frequency can be reduced by 50%. On pipeline sections where loads from trawl boards pose a threat, it is suggested that frequencies could be up to a factor of 5 higher (see Section 3.3.1.1). On pipeline sections where the other causes pose a threat, it is suggested that frequencies could be up to a factor of 2 higher (see Sections 3.3.1.2 to 3.3.1.5). 3.3.1.1 Loads from trawl boards Pipelines located in areas where trawling activity takes place may be damaged. Pipelines are normally dimensioned to withstand loads from a trawl, such as impacts, overdraw1 or hook up2. The pipe wall is normally covered by a concrete coating giving protection against local impact loads to the pipeline, and it gives the pipeline the necessary weight to gain stability. Overdraw and hook ups can initiate buckling of the pipeline. Free spans will exacerbate the effect of trawl impacts. A trawl can also catch other equipments such as exposed flanges and bolts, and a trawl hook up may cause pipeline fracture on smaller pipelines.

1 Overdraw is a situation where the trawl board comes in under the pipeline and is drawn over applying force sideways. 2 Hook up is a situation where the trawl board gets stuck beneath the pipeline. The pipeline may be damaged if the vessel tries to bring in the trawl.


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Trawling with lump weights is a relatively new practice and consequently most pipelines are not designed to tackle such loads. Even though no serious damage due to lump weights has yet been registered, it is still uncertain what consequences boom trawl and lump weights may cause. 3.3.1.2 Ship anchor / impact from sinking ships Pipelines located in areas with shipping traffic may be damaged by anchors getting hold of the pipeline, or a sinking ship hitting the line. The relevant factors include shipping traffic density, distance from shore or port, water depth, vessel traffic surveillance. 3.3.1.3 Material left behind from war years If a pipeline is laid through coastal areas that were mined during war years, there may still be material present that poses a threat to the pipeline even if these areas were cleared before installation of the pipeline. 3.3.1.4 Fatigue (mainly due to free spans) Free spans can result in fatigue if the span is excited by current, and the pipeline can fracture relatively quickly. Some spans develop as the soil beneath the pipeline is washed away, and an already existing span may evolve quickly since the free spans influence local currents near the pipeline. Only one example, from China, is known to be caused by free spans. The incident was caused by extreme climatic conditions (2 following cyclones) and the free span was longer than what the pipeline was designed for. Vortex Induced Vibration (VIV) has caused leakages in the past, but today’s pipelines are designed to resist the associated stress. 3.3.1.5 Buckling Buckling (bends) may occur if the pipeline is prevented from extension forced by pressure tension in the axial direction. This can cause buckling sideways or upwards. Some pipelines are designed to allow for a controlled buckling to relieve axial tension. It is important that the buckling takes place over a long distance. In extremely disadvantaged situations, when the buckling is very local, great strain may be placed on the pipeline. The consequence may be pipeline leakage and subsequent replacement. Buckling will normally occur during the first years of operation when temperatures are at their highest, but may occur if operational conditions are changed, new connections of pipeline or new compressor stations. 3.3.1.6 Material damage/failures If there are indications of pipelines being especially exposed to a specific type of failure, then corrections should be made utilising suitable engineering expertise. Typical correction factors would be in the range 2 to 3, applied to the contribution from the specific failure mechanism affected; expert engineering judgment should be used to determine a suitable factor.


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3.3.1.7 Fluid medium Both wet and dry gas should be properly processed to avoid corrosion or keep corrosion under control. For example, control and monitoring techniques of the pipelines operated by Norwegian companies is considered to be so good that wet gas pipelines do not have a higher probability of corrosion than the dry gas pipelines. The same applies to processed gas. Hence in general no correction need be applied for fluid medium. However, if it is known that the control techniques in place or planned do not meet current best practice, then a correction should be made in the same way as described for material damage/failures (Section 3.3.1.6). 3.3.2 Onshore pipelines The EGIG and CONCAWE reports [7,8] give breakdowns of release frequencies by cause and release size. These are partially reproduced in Sections 4.1.2 (gas pipelines) and 4.1.3 (oil pipelines), and further data are available in the EGIG and CONCAWE reports. These sources of information could be used to obtain more location specific estimates of the release frequencies. However, in situations where several of these causes pertain or critical decisions are dependent on the analysis results, a detailed analysis should be carried out utilising appropriate expertise and data specific to the situation. Such analysis is beyond the scope of this datasheet.

3.4 Application to pipelines conveying fluids other than hydrocarbons Certain non hydrocarbon fluids can increase the likelihood of failure through specific mechanisms. For example, under certain circumstances ammonia may cause stress corrosion cracking, increasing the contributions from internal and external corrosion. In the first European Benchmark Study, DNV [5] estimated a factor-of-3 increase in these contributions to the overall failure frequency. As already discussed in Section 3.3.1, the factor should be estimated using expert engineering judgment.

4.0 Review of data sources 4.1 Basis of data presented 4.1.1 Risers and offshore pipelines The frequencies and distributions presented in Section 2.0 for risers and offshore pipelines are derived from DNV’s re-analysis [6] of the data presented in PARLOC 2001 [4]. The re-analysis was performed because of recognised errors in the frequencies given in PARLOC 2001 itself. Table 4.1 presents the data used as the basis of the analysis. Allocation of failures to failure mechanisms vary according to source. Table 4.2 indicates how much different mechanisms contribute to the overall failure frequency. This can be used to determine how specific features of the pipeline design may affect the frequency. Section 3.3 provides some general guidance that is not dependent on failure mechanism. Expert judgment should be used where the likelihood of failure by a specific mechanism is affected by specific features of the pipeline design (see Section 3.3.1).


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Table 4.1 Incident and Population Data for Offshore Pipelines from [4]

Pipeline description No. of releases

Exposure time

Well stream pipelines and other small pipelines containing unprocessed fluid, diameter ≤ 16 inch

30 60033 km-years 10576 pipe-years

Well stream pipelines and other small pipelines containing unprocessed fluid, diameter > 16 inch

3 36925 km-years (pipe-years not available)

Processed oil or gas pipeline, diameter ≤ 24 inch 3 59003 km-years

4320 pipe-years Processed oil or gas pipeline, diameter > 24 inch 2 147608 km-years

2949 pipe-years External load causing pipeline damage1, diameter ≤ 24 inch 7 8836 years

External load causing pipeline damage1, diameter > 24 inch 0.72 3734 years

Steel riser, diameter< 16 inch 10 10979 riser-years Flexible pipeline 11 3447 km-years

3898 pipe-years Steel riser, diameter > 16 inch 0.72 5937 riser-years Flexible riser 5 5 riser-years

Notes 1. Applies to near platform zone 2. No releases to date; estimate using standard statistical techniques.

Table 4.2: Allocation of Failure Mechanisms from [4]: Offshore Pipelines,

All Diameters

Failure mechanism Distribution Corrosion 36% Material 13% External loads causing damage 38% Construction damage 2% Other 11%

Note: This is a summary. The distribution varies between hole sizes. For further information refer to the source report [4].

Table 4.3: Hole Size Distribution for Offshore Pipelines from [4]

Number of releases Hole size Pipelines Risers

Small (< 20 mm) 37 9 Medium (20 to 80 mm) 8 2 Large (> 80 mm) 1 4


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Full rupture 4 Total 50 15

4.1.2 Onshore gas pipelines The frequencies presented in Section 2.0 for onshore gas pipelines are based on data from EGIG’s most recently available report [7]. The EGIG database spans the period 1970-2004; it includes 1123 incidents on pipelines with a total exposure of approximately 2.77 million km-years. It shows an average incident frequency over this period of 4.1 × 10-4 per km-year and an average over the period 2000-2004 of 1.7 × 10-4 per km-year. Table 4.4 reproduces the breakdown of failures by cause given in the EGIG report [7].

Table 4.4: Allocation of Failure Mechanisms from [7]: Onshore Gas Pipelines, All Diameters / Wall Thicknesses

Failure mechanism Distribution External interference 49.7% Construction defect / Material failure

16.7%

Corrosion 15.1% Ground movement 7.1% Hot-tap made in error 4.6% Other/unknown 6.7%

The report also presents a graph showing the frequencies by cause separately for three sizes of failure: • Pinhole/crack: diameter of hole ≤ 20 mm. • Hole: 20 mm ≤ diameter of hole ≤ pipeline diameter • Rupture: hole diameter > pipeline diameter The report presents more detailed frequencies for each of the causes listed above. Those showing the dependence of the frequencies of failure due to external interference and corrosion on pipeline wall thickness have been used to derive the frequencies presented in Section 2.0 for pipelines with a wall thickness up to 15 mm. For thicker walled pipes, it has been assumed that the frequency is 50% of that for pipelines with a wall thickness of 10 – 15 mm based on the trend with diameter. Wall thickness rather than pipeline diameter has been found to be the most significant factor in determining pipeline failure rates. To some extent it is dependent on diameter, so accordingly some dependence on diameter is implicit in the data presented. Based on the rolling 5-year average total frequencies presented in the report, it has been assumed that current frequencies are approximately 50% of the 1970-2004 average. The frequencies in Section 2.0 include this trend factor. The report contains more detailed analysis of pipeline failure rate dependencies than is presented here, addressing: • External interference: pipeline diameter, depth of cover and wall thickness


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• Construction defect / Material failure: year of construction • Corrosion: year of construction, type of coating and wall thickness • Ground movement: pipeline diameter • Hot-tap made by error: pipeline diameter • Other / unknown: main causes For more detailed analysis of these factors, reference should be made to the report directly. 4.1.3 Onshore oil pipelines The frequencies presented in Section 2.0 for onshore oil pipelines are based on data in CONCAWE [8]. The data include 379 failures on pipelines with a total exposure for pipelines containing crude oil and products of approximately 667,000 km-years. More detailed analysis has enabled the diameter specific frequencies presented in Section 2.0 to be derived. The CONCAWE report [8] includes a detailed breakdown of failure size and mechanism, partially reproduced in Table 4.5. Based on the definitions of the failure sizes in the CONCAWE report [8], the hole size distribution given in Table 2.2 has been derived as follows: • Pinhole + Fissure: Small (diameter of hole ≤ 20 mm.) • Hole: Medium (20 mm ≤ diameter of hole ≤ 80 mm) • Split: Large (diameter of hole > 80 mm) • Rupture: Rupture (pipeline diameter)

Table 4.5: Allocation of Failure Mechanisms from [8]: Onshore Oil Pipelines, All Diameters / Wall Thicknesses

Distribution Failure mechanism Pinhole Fissure Hole Split Rupture Overall Total no. of failures 20 21 58 27 50 1761 Percentage of total 12% 12% 34% 16% 29% 100% Mechanical failure 5% 19% 12% 22% 24% 17% Operational 0% 5% 2% 11% 4% 4% Corrosion 90% 33% 29% 30% 18% 34% Natural hazard 0% 5% 2% 11% 2% 3% Third party 5% 38% 55% 26% 52% 43%

Note 1: Hole size data was only available for 176 out of the 379 failures.


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4.2 Other data sources For risers and offshore pipelines, the PARLOC 2001 data [4] is regarded as the best source despite the shortcomings in the report noted in Section 4.1.1. It should be noted, however, that the previous cycle of 2-yearly revisions has lapsed. Other data sources from which onshore pipeline failure frequency data can be obtained included:- 1. US Department of Transportation. The US Department of Transportation Office

of Pipeline Safety maintains a database of leaks from hazardous liquid and gas pipelines, together with exposure data. The database covers 800,000 km of pipelines, and is the largest of its kind. An analysis of the gas transmission and gathering line data was prepared for several years for the American Gas Association (AGA) by Batelle (e.g. Jones & Eiber 1989). An analysis of liquid pipeline data was prepared for DOT and API by Keifner & Associates (Keifner et al 1999). The database itself can be obtained from the DOT website at ops.dot.gov/libindex.htm. It includes files of pipeline incidents for natural gas transmission/gathering and distribution lines and liquid lines. Each is split into 1984 to date and pre-1984, due to a change in inclusion criteria. Pipeline population data is available in separate files for each year for 1995-98 for gas transmission/gathering and distribution lines. Summary statistics, together with population data for liquid lines since 1986 are at ops.dot.gov/stats.htm.

2. United Kingdom Onshore Pipeline Operators’ Association (UKOPA). UKOPA has issued a report (2005) that analyses pipeline product loss incidents in the UK over the period 1962-2004, covering about 21,700 pipeline km at the end of 2004 and 650,000 km-years pipeline exposure. Products covered are: natural gas (dry), natural gas liquid, ethane, ethylene, propane, propylene, LPG, butane, condensate and crude oil (spiked). Overall incident frequencies are calculated for 5-year periods. For the whole 43-year period the report presents frequencies by hole size (not related to pipeline diameter), and by cause and size of leak. There is further breakdown by hole size of the frequencies for external interference and corrosion as follows: External interference External corrosion • Pipeline diameter • Wall thickness class • Measured wall thickness • Year of construction • Area classification • External coating type • Type of backfill

3. UK HSE (1999). This study of the risk from UK gasoline pipelines collected data on events worldwide involving gasoline leaks from cross country pipelines. The data were used to determine the likelihood of events such as leaks and fires, and also to generate consequence models based on the available data. The report references CONCAWE and US DOT data.

4. UK HSE (2001). This study specifically addresses third party damage to onshore pipelines, comparing EGIG data and BG Transco’s incident database. The latter represents nearly 460,000 km-years exposure, with 32 third party incidents, 32 loss events, and 564 incidents altogether. The third part activity failure model takes into account such factors as: pipeline diameter, wall thickness and location; depth of cover; damage prevention measures in place.


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5.0 Recommended data sources for further information For further information, the data sources used to develop the release frequencies presented in Section 2.0 and discussed in Sections 0 and 4.0 should be consulted. These references are shown in bold in Section 6.0.

6.0 References 6.1 References for Sections 2.0 to 4.0 1. ANSI/ASME B31.4:2006. Pipeline Transportation Systems for Liquid Hydrocarbons and

other Liquids. 2. ANSI/ASME B31.8:2003. Gas Transmission and Distribution Piping Systems. 3. DNV-OS-F101 2000 amended Oct. 2005. Submarine pipeline systems, Offshore

Standard. 4. PARLOC 2001 – The Update of Loss of Containment Data for Offshore

Pipel ines , prepared by Mott McDonald for the UK HSE, UKOOA and IP, 2003. 5. DNV 1989. Phase 1 Report, CEC Benchmark Study – Project HH, Independent Risk

Analysis. 6. DNV 2006. Riser/Pipeline Leak Frequencies, Technical Note T7, rev. 02, unpublished

internal document. 7. EGIG 2005. 6th EGIG-report 1970-2004 Gas Pipel ine Incidents , 6 th report of

the European Gas Pipeline Incident Data Group, Doc. No. EGIG 05.R.0002.

8. CONCAWE 2002. Performance of crosscountry oi l pipel ines in Western Europe , Report No. 1/02.

6.2 References for other data sources (US) Department of Transportation. Refer ops.dot.gov/stats/stats.htm. ((UK) Health and Safety Executive 1999. Assessing the risk from gasoline pipelines in the United Kigdom based on a review of historical experience, Contract Research Report 210/1999, prepared by WS Atkins Safety & Reliability. http://www.hse.gov.uk/research/crr_pdf/1999/crr99210.pdf. (UK) Health and Safety Executive 2001. An assessment of measures in use for gas pipelines to mitigate against damage caused by third party activity, Contract Research Report 372/2001, prepared by WS Atkins Consultants Ltd. http://www.hse.gov.uk/research/crr_pdf/2001/crr01372.pdf. UKOPA 2005. Pipeline Product Loss Incidents (1962 - 2004), prepared by Advantica, Report Ref. R 8099, for UKOPA FDMG. http://www.ukopa.co.uk/.

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Riser and Gas release frequencies.pdf