The Chad Risk Assessment
.pdf
Public Disclosure Authorized
Public Disclosure Authorized
Egypti n Natural Gas Company |
TheChad |
Prepared by:
Abo Homos-Nubaria
Natural Gas Pipeline,
EgyptChad
QUANTITATIVE RISK ASSESSMENT
July 2011
Abo Homos-Nubaria Pipeline QRA
|
|
|
TABLE OF CONTENTS |
|
1 |
Executive Summary.................................................................................................................. |
3 |
||
2 |
Introduction .............................................................................................................................. |
7 |
||
3 |
Technical Definitions ............................................................................................................... |
8 |
||
4 |
Project Description ................................................................................................................. |
10 |
||
|
Pipeline Route................................................................................................................................................... |
10 |
||
|
Pipeline Design Criteria................................................................................................................................... |
10 |
||
|
Valve Room Locations..................................................................................................................................... |
11 |
||
|
Major Crossings................................................................................................................................................ |
12 |
||
|
Design Gas Composition and Flow Rate .......................................................................................... |
12 |
||
5 |
Assessment of Risks ............................................................................................................... |
14 |
||
6 |
Methodology........................................................................................................................... |
15 |
||
7 |
Plan of Work........................................................................................................................... |
17 |
||
8 Operation of the Pipeline........................................................................................................ |
17 |
|||
9 |
Emergency Plan ...................................................................................................................... |
18 |
||
10 |
Weather Data....................................................................................................................... |
19 |
||
11 |
Release Scenarios ................................................................................................................ |
26 |
||
12 |
Impairment Criteria ............................................................................................................. |
28 |
||
13 |
Flammability Assessment ................................................................................................... |
29 |
||
|
13.1 |
|
General ...................................................................................................................................... |
29 |
|
13.2 |
|
Process Hydrocarbons ............................................................................................................... |
31 |
14 |
Consequence Modelling Input Data.................................................................................... |
32 |
||
15 |
Sensitivity Analysis............................................................................................................. |
35 |
||
16 |
Ignited Release Scenario ..................................................................................................... |
37 |
||
|
16.1 |
|
Generic Causes of Release ........................................................................................................ |
37 |
|
16.2 |
|
Generic Causes of Ignition........................................................................................................ |
37 |
17 |
Typical Fire Consequence Analysis .................................................................................... |
39 |
||
|
17.1 |
|
Hydrocarbon Releases............................................................................................................... |
39 |
|
17.1.1 |
Gaseous Release ............................................................................................................................. |
39 |
|
|
17.1.2 |
Liquid Release .................................................................................................................................. |
40 |
|
|
17.1.3 |
Toxic Gas release............................................................................................................................. |
42 |
|
|
17.2 |
|
Fire ............................................................................................................................................ |
42 |
|
17.2.1 |
Flash Fire........................................................................................................................................... |
44 |
|
|
17.2.2 |
Unobstructed Jet Fires..................................................................................................................... |
45 |
|
|
17.2.3 |
Obstructed Jet Fires......................................................................................................................... |
46 |
|
18 |
Release Scenarios ................................................................................................................ |
47 |
||
19 |
Consequence Modelling Results ......................................................................................... |
49 |
||
|
19.1 |
|
70Bar - Full Bore Rupture [32 Inch] - Vertical Release - Gas Dispersion ..................... |
52 |
|
19.2 |
|
70Bar - Full Bore Rupture [32 Inch] - Vertical Release - Jet Fire ................................... |
53 |
|
19.3 |
|
70Bar - Major Leak [16 Inch] - Vertical Release - Gas Dispersion ................................. |
54 |
|
19.4 |
|
70Bar - Major Leak [16 Inch] - Vertical Release - Jet Fire............................................... |
55 |
|
19.5 |
|
70Bar - Minor Leak [1 Inch] - Vertical Release - Gas Dispersion ................................... |
56 |
|
19.6 |
|
70Bar - Minor Leak [1 Inch] - Vertical Release - Jet Fire ................................................. |
57 |
|
19.7 |
|
70Bar - Depressurization Case [10 Inch Vent at 10 Meter Height]................................. |
58 |
|
19.8 |
|
Explosion Case....................................................................................................................... |
59 |
20 |
Likelihood Data................................................................................................................... |
59 |
||
|
20.1 |
|
Process Release ......................................................................................................................... |
59 |
|
|
|
1 |
|
Abo Homos-Nubaria Pipeline QRA |
|
||
20.2 |
Ignition Probability ................................................................................................................... |
59 |
|
21 |
Risk Assessment.................................................................................................................. |
60 |
|
21.1 |
Risk Assessment Basis.............................................................................................................. |
60 |
|
21.2 |
Risk Assessment for Buried Underground Pipeline.................................................................. |
60 |
|
21.3 |
Risk Assessment for Aboveground Pipeline ............................................................................. |
60 |
|
22 |
Risk Evaluation ................................................................................................................... |
61 |
|
23 |
Risk Reduction Measures (Recommendations) .................................................................. |
62 |
|
24 |
Uncertainty Analysis ........................................................................................................... |
63 |
|
25 |
References ........................................................................................................................... |
64 |
|
26 |
Appendix-1 FRED Simulation Cases for PRS.................................................................... |
65 |
|
26.2 |
Table of Contents ...................................................................................................................... |
65 |
|
26.3 |
70Bar - Full Bore Rupture [32 Inch] - Vertical Release ........................................................... |
65 |
|
|
26.3.1 |
Scenario Summary .............................................................................................................................. |
65 |
|
26.3.2 |
Jet Fire................................................................................................................................................. |
67 |
|
26.3.3 |
Pool Chart ........................................................................................................................................... |
69 |
|
26.3.4 |
Dispersion ........................................................................................................................................... |
70 |
|
26.3.5 |
Warnings ............................................................................................................................................. |
71 |
26.4 |
70Bar - Half Bore Rupture [16 Inch] - Vertical Release........................................................... |
72 |
|
|
67.4.1 |
Scenario Summary .............................................................................................................................. |
72 |
|
67.4.2 |
Jet Fire................................................................................................................................................. |
74 |
|
67.4.3 |
Pool Chart ........................................................................................................................................... |
76 |
|
67.4.4 |
Dispersion ........................................................................................................................................... |
77 |
|
67.4.5 |
Warnings ............................................................................................................................................. |
78 |
26.5 |
70Bar - Minor Leak [1 Inch] - Vertical Release ....................................................................... |
79 |
|
|
26.5.1 |
Scenario Summary .............................................................................................................................. |
79 |
|
26.5.2 |
Jet Fire................................................................................................................................................. |
81 |
|
26.5.3 |
Pool Chart ........................................................................................................................................... |
83 |
|
26.5.4 |
Dispersion ........................................................................................................................................... |
84 |
|
26.5.5 |
Warnings ............................................................................................................................................. |
85 |
26.6 |
70Bar - Depressurization [10 Inch] - Vertical Release ............................................................. |
86 |
|
|
26.6.1 |
Scenario Summary .............................................................................................................................. |
86 |
|
26.6.2 |
Jet Fire................................................................................................................................................. |
88 |
|
26.6.3 |
Pool Chart ........................................................................................................................................... |
90 |
|
26.6.4 |
Dispersion ........................................................................................................................................... |
92 |
|
26.6.5 |
Warnings ............................................................................................................................................. |
93 |
26.7 |
Explosion [Confined space] ...................................................................................................... |
93 |
|
|
26.7.1 |
Scenario Summary .............................................................................................................................. |
93 |
|
26.7.2 Pressure Decay with Distance Chart ................................................................................................... |
94 |
|
|
26.7.3 |
Warnings ............................................................................................................................................. |
94 |
2
Abo Homos-Nubaria Pipeline QRA
Executive Summary
Quantitative risk assessment study (QRA) has been performed for the Abo Homos-Nubaria Gas Pipeline 32" Gas Pipeline for the Egyptian natural Gas Company (GASCO).
The scope of this quantitative risk assessment (QRA) study is to perform consequence modelling analysis and risk assessment of the overall pipeline, while the pipeline inlet and outlet facilities are outside the scope of this study.
In order to perform consequence modelling analysis of the potential hazardous scenarios resulting from loss of containment of the pipeline, some assumptions and design basis have been proposed.
the pipeline release orientation have been proposed to be a vertical release, which is considered for buried underground pipeline releasing the entrapped materials in the vertical direction upwards (represents the actual release scenario). Other release orientations represent the exaggerated release scenario.
For the pipeline leak scenario, the release rate has been simulated based on 3-hole sizes as follows:
•Full bore rupture (32-inchs);
•Half bore rupture (16-inches);
•Pin hole leak (1-inch).
The first leak size is a full bore rupture of the pipeline (32 inch leak), which presents a hole diameter equivalent to the pipeline diameter. This scenario presents the worst case scenario for maximum release rate in order to represent a catastrophic release scenario.
The second leak size is a half bore rupture of the pipeline (16 inch leak), which presents a hole diameter equivalent to half the pipeline diameter. This scenario presents the severe case scenario for a reduced release rate in order to represent a major release scenario.
The third leak size is a one inch hole in the pipeline (1 inch leak), which presents a pin hole in the pipeline wall or small deformation equivalent to the one inch hole in diameter. This scenario presents the mild case scenario for a reduced release rate in order to represent a minor release scenario.
FRED has been selected for the consequence modeling of different types of hazardous consequences modeling presented as follows:
•Jet fires (resulting from immediate ignition).
•Gas clouds and Flash fires (resulting from delayed ignition),
Weather conditions have been selected based on wind speed and stability class for the greater Cairo area detailed weather statistics.
3
Abo Homos-Nubaria Pipeline QRA
The worst case weather conditions have been selected for consequence modelling represented by wind speed of 10 m/s and stability class "D" representing prevailing weather conditions, in order to obtain conservative results.
The gas dispersion distances have been calculated in meters in concentration terms of Lower Flammability Limits (LFL) and Upper Flammability Limits (UFL) presented by Part Per Million (PPM) concentrations in order to represent the flammability range of the released gas cloud; however the extent of damage is presented by LFL only.
The heat radiation from flash fires will not significantly affect humans, equipment or structures outside the 12.5 (Kw/m2) heat radiation envelopes due to the short duration of flash fires [in terms of milliseconds].
Since the jet fire is originally a high momentum directed jet release, hence the effects of wind direction, wind speed or atmospheric stability on the jet flame are minimal.
The jet fire (flame length) and heat radiation distances are measured in meters.
The extent of harmful effects on humans is presented by the distance to the heat radiation contour of 12.5 (Kw/m2) and the extent of damage for equipment is presented by the flame length (frustum).
Fire consequence analysis has been described in details in fire consequence effects section, which details the hazardous effects from different types of fires.
For the purposes of the hazard analysis and consequence modelling, a number of representative release scenarios and physical impact cases are defined in as per Table below.
|
|
Table 1.1: Representative Release Cases |
|
|||
Release |
Hole Size / |
Hole Size |
Press. |
Hazardous |
Case Identification |
|
Orientation |
Leak Type |
(Inch) |
(Bar) |
Scenario |
||
|
||||||
Full Bore |
Gas |
70Bar - Full Bore Rupture [12 Inch] - |
Dispersion |
Vertical Release - Gas Dispersion |
|
Rupture |
32 Inch |
70 |
|
70Bar - Full Bore Rupture [12 |
|
|
(Catastrophic |
|
|
Jet Fire |
Inch] - Vertical Release - Jet |
|
|
Failure) |
|
|
|||
|
|
|
|
Fire |
||
|
|
|
|
|
||
|
|
|
|
Gas |
70Bar - Half Bore Rupture [6 Inch] - |
|
1.0 |
Half Bore |
|
|
Dispersion |
Vertical Release - Gas Dispersion |
|
16 Inch |
70 |
|
70Bar - Half Bore Rupture [6 |
|||
Rupture |
|
|||||
Vertical Release |
(Major Leak) |
|
|
Jet Fire |
Inch] - Vertical Release - Jet |
|
Orientation |
|
|
||||
|
|
|
|
Fire |
||
|
|
|
|
|
||
|
|
|
|
Gas |
70Bar - Pin Hole leak [1 Inch] - |
|
|
|
|
|
Dispersion |
Vertical Release - Gas Dispersion |
|
|
Pin Hole |
1 Inch |
70 |
Jet Fire |
70Bar - Pin Hole leak [1 Inch] - |
|
|
(Minor Leak) |
Vertical Release - Jet Fire |
||||
|
|
|
|
|||
|
|
|
|
Jet Fire |
70Bar - Pin Hole leak [1 Inch] - |
|
|
|
|
|
Horizontal Release - Jet Fire |
||
|
|
|
|
|
||
2.0 |
Planned |
|
|
Gas |
70Bar - Depressurization [10 Inch] - |
|
Depressurizatio |
10 Inch |
70 |
||||
Depressurization |
Dispersion |
Vertical Release - Gas Dispersion |
||||
n |
|
|
||||
|
|
|
|
|
4
Abo Homos-Nubaria Pipeline QRA |
|
|
|
|
||
|
|
Table 1.1: Representative Release Cases |
||||
Release |
Hole Size / |
Hole Size |
Press. |
Hazardous |
Case Identification |
|
Orientation |
Leak Type |
(Inch) |
(Bar) |
Scenario |
||
|
||||||
3.0 |
N/A |
N/A |
N/A |
Explosion |
Explosion scenario |
|
Explosion |
||||||
|
|
|
|
|
||
Pipeline release generic failure frequencies and ignition probabilities have then been identified for the detailed quantitative risk assessment (QRA) purposes from E&P Forum, UKOPA and EGIG.
The failure rate of buried underground pipelines is lower than aboveground pipelines due to the protection from third parties impacts and adverse atmospheric conditions.
On the other hand, the probability of occurrence of a pipeline full bore leak (catastrophic failure) is deemed to be much lower than a half bore leak.
Quantitative risk assessment (QRA) has been performed to all types of the modelled hazardous events (flash fires and jet fires).
The risks have been assessed for the industrial workers and general public representing the two types of risk namely the "Individual Risk" and "Societal Risk".
From the risk assessment and the international risk acceptance criteria the risk evaluation for individual and societal risk presented in the following table.
Table 1.2 Buried Underground Pipeline Orientation Risk Evaluation Summary Table
No |
Risk Type |
Calculated Risk |
ALARP Limits |
Risk Acceptance |
1.0 |
Individual Risk |
64.60E-08 |
1.0E-03 to 1.0E-05 |
Acceptable ( ) |
2.0 |
Societal Risk |
65.60E-07 |
1.0E-04 to 1.0E-06 |
Acceptable ( ) |
It has been concluded that the risk falls within the Acceptable limits for the individual risk to workers and public for the pipeline. However, the following measures (recommendations) should be adhered:
•Ensure pipeline design, commissioning, start-up, construction and operation is complying with code requirements (ASME B31.8 Gas Transmission and Distribution Piping Systems).
•Ensure Signs or markers shall be installed where it is considered necessary to indicate the presence of a pipeline at road, highway, railroad, and stream crossings. Additional signs and markers shall be installed along the remainder of the pipeline at locations where there is a probability of damage or interference (ASME B31.8 requirement).
•Signs or markers and the surrounding right-of way shall be maintained so markers can be easily read and are not obscured (ASME B31.8 requirement).
•The signs or markers shall include the words “Gas" (or name of gas transported) Pipeline,” the name of the operating company, and the telephone number (including area code) where the operating company can be contacted (ASME B31.8 requirement).
5
Abo Homos-Nubaria Pipeline QRA
•Ensure Overpressure protection is provided by a device or equipment installed in a gas piping system that prevents the pressure in the system or part of the system from exceeding a predetermined value (ASME B31.8 requirement).
•Emergency Response plan (ERP) to include means for detection pipeline leak or rupture also, means for safe and quick isolation of the damaged section of the pipeline.
Finally, uncertainty analysis has been performed in order to verify and ensure that certainty of the results obtained from the consequence modelling analysis and quantitative risk assessment are certain and none of the scenarios or input factors have been neglected or underestimated.
Hence, the risk shall be within the acceptable and tolerable limits, if the pipeline is buried underground and all safe design precautions have been considered and strictly followed in the design, construction and operation of the Pipeline.
6
Abo Homos-Nubaria Pipeline QRA
Introduction
This report represents the Quantitative risk assessment study (QRA) performed for the Abo Homos-Nubaria Gas Pipeline 32" Gas Pipeline for the Egyptian natural Gas Company (GASCO).
The scope of this quantitative risk assessment (QRA) study is to perform consequence modelling analysis and risk assessment of the overall pipeline, while the pipeline inlet and outlet facilities are outside the scope of this study.
Objectives:
The primary objective is to perform a quantitative risk assessment to identify the major risk issues and contributors with a “best estimate” of the associated levels of risk for the pipeline and its boundaries and crossings.
In general the work will cover, but not necessarily be limited to, the following:
o Define data to be provided,
o Review key project data,
o Perform physical survey of the pipeline route to identify possible ‘hot spots’,
o Define possible accident scenarios and events,
o Conduct a full consequence analysis in relation to gas leaks and fire scenarios,
o Perform quantitative risk assessment,
o Conduct ALARP risk reduction/mitigation review,
o Define possible risk elimination/reduction measures,
o Propose residual risk control measures.
7
Abo Homos-Nubaria Pipeline QRA
Technical Definitions
Confinement |
A qualitative or quantitative measure of the enclosure or partial enclosure areas |
|
where vapors cloud may be contained. |
Congestion |
A qualitative or quantitative measure of the physical layout, spacing, and |
|
obstructions within a facility that promote development of a vapor cloud |
|
explosion. |
EERA |
Escape, Evacuation and Rescue Assessment |
ESD |
Emergency Shut Down |
FRA |
Fire Risk Assessment |
Gas cloud |
Gas cloud air dilution naturally reduces the concentration to below the LEL or |
dispersion |
no longer considered ignitable (typically defined as 50% of the LEL). |
Hazard |
An inherent physical or chemical characteristic (flammability, toxicity, |
|
corrosivity, stored chemical or mechanical energy) or set of conditions that has |
|
the potential for causing harm to people, property, or the environment. |
Individual risk |
The risk to a single person inside a particular building. Maximum individual risk |
|
is the risk to the most-exposed person and assumes that the person is |
|
exposed. |
QRA |
Quantitative Risk Assessment |
Risk |
Relates to the probability of exposure to a hazard, which could result in harm to |
|
personnel, the environment or general public. Risk is a measure of potential for |
|
human injury or economic loss in terms of both the incident likelihood and the |
|
magnitude of the injury or loss. |
Risk |
The identification and analysis, either qualitative or quantitative, of the likelihood |
assessment |
and outcome of specific events or scenarios with judgments of probability and |
|
consequences. |
8
Abo Homos-Nubaria Pipeline QRA
Vapor cloud |
An explosion in air of a flammable material cloud |
explosion |
|
(VCE) |
|
9