vst ® 05-Nov-2017 18:40

Report on the Effects of Fire on LNG Carrier Containment Systems


Year: 2009
Language: english
Author: SIGTTO
Genre: Handbook
Publisher: SIGTTO
Edition: First Edition
Format: PDF
Quality: eBook
Number of pages: 232
Description: In 2004, SIGTTO was approached by Professor Havens of the University of Arkansas who expressed concern about
the vulnerability of LNG carrier tanks that are insulated with non-fire-resistant materials such as polystyrenes or
polyurethanes.
Current practice provides for pressure relief systems, designed with credit for the tank’s insulation, to prevent LNG cargo
pressurisation due to boil-off and fire (IMO IGC Code 8.5). However, it is uncertain to what extent any degradation of
insulation, in a fire situation, is taken into account in the design of PRV systems. As foam plastic insulation materials are
subject to possible melting, degradation and/or ignition at temperatures lower than might be achieved during such fire
exposure, there is concern that the PRV systems may not be capable of relieving the vapour flows that would result from the
increased boil-off due to partial or total insulation failure.
Following considerable dialogue between SIGTTO members, the LNGC containment system designers, the USCG and the
major classification societies, at their April 2006 meeting the SIGTTO GPC sanctioned the formation of a working group to
thoroughly investigate the subject and produce a detailed report on the possible effects and any mitigation measures that
may be necessary.

Description (continued)

During the progression of the working group studies, it became clear that, for this complex issue of how a large fire scenario
may a) emit heat to a high sided vessel and b) affect the internal materials and structure of an LNG carrier, there were many
areas of uncertainty. The studies presented above capture both steady state and time based calculations, the basis of which
rely on knowledge of, or assumptions for, fire scenario conditions.
Given the uncertainty existing within the industry over large pool fire surface emissive powers, and how these are likely to
impact a carrier structure, it was not possible to gain unanimous agreement in all respects. However, the vast majority came
to agree with the conclusions and recommendations made in chapters 10 and 11.
Steady state conditions indicate that, in the extreme case of losing the entire insulation layer, then assuming that the factors
included in the IGC Code for sizing the relief valves, the valves are capable of relieving the anticipated vapour albeit at
raised tank pressures that can be withstood by the cargo tanks. Additionally, this relief valve capability can, as well as loss
of insulation, also comfortably accommodate the further extreme case of complete loss of the weather cover of a Moss type
LNG carrier.
For time based scenarios and studies, heat transfer and CFD calculations were performed, a review of previous studies on
insulation tests was undertaken and further insulation heat tests were performed. A range of times for complete degradation
of insulation were indicated through the various studies and tests such that definitive time could not be arrived at due to the
conflicting evidence and, therefore, differing views of the working group members. For this reason, Recommendation 2 is
made.

Additional info

Notice of Terms of Use
While the recommendations and advice given in this guide have been based on information made available to the Society of International Gas
Tanker & Terminal Operators (SIGTTO), no responsibility is accepted by SIGTTO or by any person, firm, corporation or organisation who or which
has been in any way concerned with the furnishing of information or data, the compilation, publication or any translation, supply or sale of this
guide for the accuracy of any information or advice given herein or for any omissions herefrom or for any consequences whatsoever resulting
directly or indirectly from compliance with or adoption of any of the recommendations or guidance contained herein even if caused by a failure
to exercise reasonable care.
Any queries or comments relating to these guidelines should be addressed to The General Manager, Society of International Gas Tanker & Terminal
Operators Limited, 17 St. Helens Place, London EC3A 6DE.

Contents

Introduction ...........................................................................................................................................................1
1 Previous Incidents .............................................................................................................................................5
1.1 ‘Yuyo Maru’ No.10.....................................................................................................................................................7
1.2 ‘Gaz Fountain’ ...........................................................................................................................................................8
1.3 25,000 dwt Single Hull Product Carrier ........................................................................................................................9
1.4 ‘Val Rosandra’ Propylene Fire......................................................................................................................................9
2 The origins of the IGC-Code............................................................................................................................11
2.1 Introduction ..............................................................................................................................................................13
2.2 Review of the IGC-Code Requirements........................................................................................................................13
2.3 Relation between Volume Flow of Free Air and Heat Flux into the Tank..........................................................................14
2.4 Origins of Section the 8.5 of the IGC-Code.................................................................................................................14
2.5 Other Standards .......................................................................................................................................................16
2.6 Evaluating the Criteria...............................................................................................................................................16
2.6.1 Heat flux q from the fire............................................................................................................................... 17
2.6.2 Affected tank area A................................................................................................................................... 17
2.6.3 Fire factor F................................................................................................................................................ 17
2.6.4 Literature for this section .............................................................................................................................. 18
3 Fire Scenarios.................................................................................................................................................19
3.1 Summary of Documentation Review............................................................................................................................22
3.1.1 Guidance on risk analysis and safety implications of a large Liquefied Natural Gas (LNG)
spill over water – Document No. 1 ............................................................................................................... 22
3.1.2 Key results extracted ................................................................................................................................... 22
3.1.3 Cloud fire experiments................................................................................................................................. 23
3.1.4 Pool fire experiments................................................................................................................................... 23
3.1.5 Overall summary of results of experiments – pool fire & vapour cloud studies .................................................. 24
3.1.6 Results of 40 m3 LNG spills on water – Document No. 2................................................................................. 24
3.1.7 Consequence assessment methods for incidents involving releases from liquefied natural gas
carriers – Document No. 4........................................................................................................................... 24
3.1.8 Consequences of LNG marine incidents – Document No. 5 ............................................................................ 25
3.1.9 Consequence modelling of LNG marine incidents – Document No. 6 .............................................................. 25
3.1.10 Potential for BLEVE associated with marine LNG vessel fires – Document No. 7................................................ 25
3.1.11 Input to modelling work of other members of the working group..................................................................... 25
3.1.12 Large hydrocarbon fuel pool fires: physical characteristics and thermal emission variations
with height – Document No. 9...................................................................................................................... 26
3.1.13 Large hydrocarbon fuel pool fires: physical characteristics and thermal emission variations
with height – Document No. 11.................................................................................................................... 26
3.1.14 LNG properties & hazards – understanding LNG rapid phase transitions (RPT) – Document No. 12 .................. 26
3.1.15 LNG pool fire simulations – Document No. 14............................................................................................... 26
3.1.16 LNG decisions making approaches compared – Document No. 13................................................................. 27
3.1.17 Thermal response of gas carriers to hydrocarbon fires – Document No. 15...................................................... 27
3.1.18 Maplin sands experiments 1980 – dispersion results from continuous releases of refrigerated
liquid propane & LNG – Document No. 18................................................................................................... 28
3.1.19 Maplin sands experiments 1980 – dispersion & combustion behaviour of gas clouds resulting
from large spillages of LNG & LPG on the sea – Document No. 19 ................................................................. 28
3.2 Results......................................................................................................................................................................29
3.2.1 Results of documentation review................................................................................................................... 29
3.2.2 Summary ................................................................................................................................................... 29
This book has been released for free by SIGTTO in electronic formatviii
4 LNG Carrier Pressure relief Systems ................................................................................................................31
4.1 Functional Requirements............................................................................................................................................33
4.1.1 Cargo tanks to have an emergency over-pressure system which shall .............................................................. 33
4.1.2 Cargo tanks to have an emergency under-pressure system which shall............................................................ 33
4.1.3 Cargo tanks to have a pressure control system .............................................................................................. 33
4.2 Design Requirements.................................................................................................................................................33
4.2.1 Pressure Relief Valve (PRV) function .............................................................................................................. 33
4.2.2 Pilot design................................................................................................................................................. 34
4.2 Pressure Settings .......................................................................................................................................................35
5 Simplified reapplication of the Code for Loss of Insulation................................................................................37
5.1 Study 1 ....................................................................................................................................................................39
5.1.1 IGC code Pressure Relief Valve (PRV) sizing................................................................................................... 39
5.1.2 Moss rosenberg LNGC relief valve sizing considering pure methane conditions ............................................... 39
5.1.3 IGC code PRV required capacity .................................................................................................................. 41
5.1.4 Physical sizing of pilot-operated, Pressure Relief Valves (PRV) ......................................................................... 41
5.1.5 Choked flow ............................................................................................................................................... 42
5.1.6 Extrapolating fire conditions against PRV valve sizing .................................................................................... 42
5.1.7 Total relieving capacity of cargo containment system...................................................................................... 43
5.1.8 PRV capacity at maximum back pressure ...................................................................................................... 45
5.1.9 Moss type LNG carrier – response to over-pressure conditions........................................................................ 46
5.2 Study 2 ....................................................................................................................................................................47
5.2.1 Résumé ...................................................................................................................................................... 47
5.2.2 Selected relief valve..................................................................................................................................... 47
5.2.3 Cargo ........................................................................................................................................................ 48
5.2.4 Maximum cargo tank size............................................................................................................................ 48
5.2.5 Over pressurization of cargo tank due to fire ................................................................................................ 49
5.2.6 Increase in relief valve capacity due to over pressurization............................................................................. 49
5.2.7 Existing ship ............................................................................................................................................... 50
5.2.8 Results........................................................................................................................................................ 50
6 Heat Transfer Into the tank ..............................................................................................................................53
6.1 Fire Scenario............................................................................................................................................................55
6.2 Limit for Heat Flux into LNG and Possibility of Tank Collapse ........................................................................................55
6.2.1 Heat flux into the weather cover ................................................................................................................... 55
6.2.2 Possibility of film boiling .............................................................................................................................. 56
6.3 Burning of the Insulation or Explosion of Combustible Mixtures ....................................................................................57
6.3.1 Burning of insulation ................................................................................................................................... 57
6.3.2 Explosion within the cargo hold.................................................................................................................... 57
6.4 CFD Evaluation of the Tank Fire Problem.....................................................................................................................58
6.4.1 CFD calculation .......................................................................................................................................... 58
6.5 Heating up of the Weather Cover and the Insulation ....................................................................................................60
6.6 Heat Transport into the Insulation ...............................................................................................................................62
6.7 Relation of CFD Calculation Results to Pool Fire Burning Duration According SANDIA Report .........................................63
6.7.1 Melting of insulation and leak size................................................................................................................ 63
6.7.2 Heating up of weather cover and leak size.................................................................................................... 64
6.8 Temperature in Skirt Area..........................................................................................................................................65
6.9 Literature for this Section ...........................................................................................................................................67
7 Time Based Heat Transfer................................................................................................................................69
7.1 One-Dimensional, Transient, Heat Transfer Analysis.....................................................................................................71
7.1.1 Initial conditions.......................................................................................................................................... 71
7.1.2 Boundary conditions ................................................................................................................................... 72
7.1.3 Results........................................................................................................................................................ 72
This book has been released for free by SIGTTO in electronic formatix
7.2 Predicted Component Failure Commencement Times....................................................................................................74
7.2.1 Metal failure............................................................................................................................................... 74
7.2.2 Insulation failure ......................................................................................................................................... 74
7.2.3 Insulation combustion .................................................................................................................................. 74
7.3 Update on Issues Remaining – Appropriate Values of the Environmental Factor FI to Account for Radiation
Shielding by the Tank Cover.......................................................................................................................................75
7.4 Critical Update on Issues Remaining – Thermal Degradation Properties of Polystyrene Foam: New Results for the
Estimated Time for Insulation Failure...........................................................................................................................76
8 response of Insulation Materials to Heat..........................................................................................................79
8.1 Thermal Loads on Insulation.......................................................................................................................................81
8.2 Thermal Effects on the Insulation.................................................................................................................................82
8.3 Outline of DNV Test Programme.................................................................................................................................83
8.3.1 Results........................................................................................................................................................ 84
9 Discussion ......................................................................................................................................................85
9.1 Steady State Conditions.............................................................................................................................................87
9.2 Time Based Conditions ..............................................................................................................................................87
9.3 Decisions and Agreement of the Working Group.........................................................................................................87
10 Conclusions ....................................................................................................................................................89
11 recommendations...........................................................................................................................................93
appendix 1 – Moss tank cover response to heat ....................................................................................................95
appendix 2 – Thermodynamic boundary condition..............................................................................................133
appendix 3 – CFD Modelling of the heat input to an LNG tank .............................................................................161
appendix 4 – JHM paper, Fire performance of LNG carriers insulated with polystyrene foam ................................177
appendix 5 – Thermodynamic boundary condition..............................................................................................187
appendix 6 – Insulation heating comparison .......................................................................................................203
appendix 7 – Polyurethane heat tests..................................................................................................................207

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