DET NORSKE VERITAS TM

Transcription

1 DET NORSKE VERITAS TM APPENDIX D - LEAK FREQUENCIES ANALYSIS SKANGASS AS REPORT NO./DNV REG NO.: / 17TLT29-3 REV 1,

2 Table of Contents Page 1 LEAK FREQUENCY ANALYSIS Equipment of LNG bunkering installation LNG loading arm failure Leak Frequency RESULTS DISCUSSION REFERENCES... 6 ANNEX 1 P&IDS , SHEETS TA01/TB01/TC Date : Page i of i

3 1 LEAK FREQUENCY ANALYSIS The frequency analysis determines the annual release of hazardous materials (flammable) from process equipment for LNG bunkering of Fjordline at Risavika harbour. The frequency analysis is critical to the analysis as the frequencies and hole size distribution are the fundamental assumptions which the consequence and risk estimates are based upon. The generic failure frequencies for valves, flanges and pipes are based on HCRD 2010 database and DNV report rev 4 dated 22nd of December 2010, ref. /1/. This database is viewed as the most comprehensive collection of leak frequency data currently available in any industry. 1.1 Equipment of LNG bunkering installation The frequencies detailed parts count of the system was using the available P&ID s (cf. Annex 1) together with estimates of line lengths from plot plans. The P&ID s used in this assessment are as close as possible to the final version. The frequency have been calculated using the DNV software LEAK v3.3 to produce release frequencies based on a defined hole size distributions, ref. Table D1. The LNG bunkering system has been divided into five main sections and subdivided into LNG line and Vapour Return line: Equipment for LNG ferry bunkering located inside the LNG plant area (including pump, flowmeter, LNG line and vapour return line) Pipeline section under ground between LNG plant and LNG ferry bunkering station (LNG line and Vapour return line) LNG ferry bunkering station upstream ESD valve on jetty LNG ferry bunkering downstream ESD valve on jetty LNG loading arm Welded connections have a lower leak frequency than flanges connections. It has been assumed that the flanges are welded, with the exception of the flanges present in the different P&IDs (cf. Annex 1) that have been taken into account. Note that the size of leak large covers two leak size, large and full bore rupture. Table D1 Hole size distribution Size of Leak Range [mm] Small 1 10 Medium Large > LNG loading arm failure Loading arm leak frequency is calculated separately and based on ACDS data covering both connection failures and ranging failures (leading to disconnection), ref. /2/. The ACDS data is Date : Page 1 of 11

4 considered to be the most representative data for liquefied gas loading arms, although it can be considered a conservative estimate for LNG loading arms. The generic loading arm frequency applied is 7.6E-05 per visit/transfer for all failure contributors, ref. Assumption no 3-C in Appendix A. The frequency is per bunkering operation for an LNG tanker. Assuming a typical LNG tanker bunkering operation will last for minimum 18 hours, whereas the bunkering of the Fjordline ferries lasts 1 hour (LNG transfer), the frequency is reduced with a factor 1/18. For ranging/disconnection failure (i.e. mooring and striking by passing ships) 100% of the total frequency is defined as a large release: Ranging failures per year = 9E-07 (per visit) * 365 visits * 1/18 * 100% = 1.8E-05 For connection type failures (failure of arm, failure of quick release, failure of ship s pipework and operator error) the leak size distribution is defined as 70% small leaks, 25% medium leaks and 5% large release. Connection failure, small, per year = 7.5E-05 (per visit) * 365 visits * 1/18 * 70% = 1.1E-03 Connection failure, medium, per year = 7.5E-05 (per visit) * 365 visits * 1/18 * 25% = 3.8E-04 Connection failure, large, per year = 7.5E-05 (per visit) * 365 visits * 1/18 * 5% = 7.6E-05 Based on this a total frequency of 1.5E-03 per year is applied for the loading arm, where 9.4E-5 leaks are large leaks. It should be noted that, even with accounting for shorter bunkering time, the generic failure frequency is assumed to be conservative. The reason for this is twofold: The ferry terminal has an extremely sheltered location, minimizing the risk of collision with other ships. The ferry terminal is believed to provide a more reliable mooring system compared to LNG tankers, which ref. /2/ is based on. The above would give reason to reduce the ranging failure frequency further. This has not been done Date : Page 2 of 11

5 1.3 Leak Frequency Table D2 presents the basis for leak frequency calculation in LEAK. Table D2 Basis for leak frequency model Ferry bunkering Pressure (bara): 10 Equipment Line Size (inch) Number Gas/Liquid (%) New equipment for LNG ferry bunkering inside plant Small Bore fittings /100 Vapour Return Line /5 Flanges Actuated valve Vapour Return Line 1 1 0/ / / / / / / / / /100 Vapour Return Line / /100 LNG Pump Manual valve / / / / /100 Vapour Return Line / /5 Pump - 1 0/ m 0/ m 0/ m 0/100 Piping m 0/ m 0/ m 95/5 Vapour Return Line m 95/5 Flowmeter Small Bore fittings m 95/ /100 Vapour Return Line /5 Flanges 6 6 0/100 Date : Page 3 of 11

6 Ferry bunkering Pressure (bara): 10 Equipment Line Size (inch) Number Gas/Liquid (%) /100 Vapour Return Line /5 Actuated Valve Manual Valve Vapour Return Line / / /100 Vapour Return Line m 0/ m 0/100 Piping 6 10 m 0/ m 95/5 Vapour Return Line 2 10 m 95/ m 95/5 Piping between LNG pump and Flowmeter Piping Pipeline between LNG plant and ferry bunkering station 8 25 m 0/100 Vapour Return Line 4 25 m 95/5 Underground pipelines Ferry bunkering station Flange LNG line 8 1 0/100 Piping section 8 495m 0/100 Vapour Return Line m 95/5 Small Bore fittings - - Flange Actuated valve 6 1 0/ /100 Upstream up to ESD valve Manual valve 2 1 0/ / /100 Vapour Return Line Piping section Vapour Return Line 1 3 m 0/ m 0/ m 95/5 4 3 m 95/5 Downstream ESD valve (365 hours per year) Small Bore fittings Flange /100 Vapour Return Line /100 Vapour Return Line /5 Actuated valve Date : Page 4 of 11

7 Ferry bunkering Pressure (bara): 10 Equipment Line Size (inch) Number Gas/Liquid (%) Vapour Return Line /5 Piping section Manual valve Vapour Return Line Vapour Return Line 1 5 0/ / / / /5 1 4 m 0/ m 0/ m 95/5 4 4 m 95/5 Even if it has been assessed that the equipment will be used with different durations, the leak frequencies presented in Table D3 are per year. The difference in usage duration has been taken into account into the Leak Frequency model as follows: - All the equipment on the LNG line up to the ESD valve will be filled with LNG the whole year; - Meanwhile the equipment on the LNG line downstream the ESD valve will be filled with LNG only during the bunkering operation let assumed 365 hours per year. - The same assumption is applicable to the vapour return line that is going to be used only for the bunkering operation, let 365 hours per year. Table D3 Leak frequency by section (per year) Frequencies (per year) Small Medium Large Total Equipment for LNG ferry bunkering inside plant Between plant and ferry bunkering station Jetty area Upstream ESD valve 1.3E E E E-02 Vapour Return Line 1 2.1E E E E E E E E-05 Vapour Return Line 1 1.9E E E E E E E E-04 Vapour Return Line 1 4.7E E E E E E E E-05 Vapour Return Line 1 2.3E E E E-05 Loading arms 1.1E E E E-03 TOTAL 1.5E E E E-02 1 Only in use during 365 hours per year. Date : Page 5 of 11

8 2 RESULTS DISCUSSION Since the previous update ref./3/, it has been assessed that the total leak frequency has increased by 42%. It is due to the new design that increased strongly the number of flanges and small bore fittings, both high contributor of leak frequency. The small leak frequency has increased by 54%, the medium leak frequency by 22% and the large leak frequency reduced by 34%. Compared to the previous design used in the previous QRA, the leak frequencies have evolved in the different sections as follows: % increase in the plant area; - 95 % reduction for the underground pipelines; - 70 % reduction for the jetty area. The leak frequencies are not distributed evenly between the different sections of the bunkering installation. Indeed, 87.5% of the total leak frequency is in the plant perimeter, 0.3 % in the underground section and the rest, 12.2 % is inside the jetty area. It has been assessed that the underground LNG pipeline represent a very low contribution to the leak frequency. It is due to the design retained for the underground pipeline (underground double wall full containment pipe with all the connections and extension welded) giving a very low probability of failure. On the other hand, the new design includes a vapour line return running from the jetty area to the plant. But due to the low pressure and the few hours in operation, the leak probability is low. The contribution of the vapour return line has been assessed to represent 1 % of the total leak frequency, meanwhile the LNG line do represent 99 % of the total leak frequency. 3 REFERENCES /1/ DNV report rev 4 Offshore QRA Standardised Hydrocarbon Leak Frequencies.; dated December 2010, Based upon HCRD 10/92 03/10) /2/ DNV Guideline 16, LNG QRA Guideline, rev 0, /3/ QRA for Risavika Ferry Bunkering Station, Skangass AS, Report No./DNV Reg No.: /143MJ79-5; Rev. 0, Date : Page 6 of 11

9 ANNEX 1 P&IDS , SHEETS TA01/TB01/TC01 These P&IDs served as basis for the counting of equipment. Note based on the request of Skangass AS, some equipment have been added to the inventory, even if they are not appearing on the drawings: - For each PSV loop, instead of the diameter redactor a valve has been added to the inventory; - One valve has been added to the underground LNG line. Date : Page 7 of 11

10 Date : Page 8 of 11

11 Date : Page 9 of 11

12 Date : Page 10 of 11

13 Date : Page 11 of 11

14 : DNV is a global provider of knowledge for managing risk. Today, safe and responsible business conduct is both a license to operate and a competitive advantage. Our core competence is to identify, assess, and advise on risk management, and so turn risks into rewards for our customers. From our leading position in certification, classification, verification, and training, we develop and apply standards and best practices. This helps our customers to safely and responsibly improve their business performance. Our technology expertise, industry knowledge, and risk management approach, has been used to successfully manage numerous high-profile projects around the world. DNV is an independent organisation with dedicated risk professionals in more than 100 countries. Our purpose is to safeguard life, property and the environment. DNV serves a range of industries, with a special focus on the maritime and energy sectors. Since 1864, DNV has balanced the needs of business and society based on our independence and integrity. Today, we have a global presence with a network of 300 offices in 100 countries, with headquarters in Oslo, Norway. Global impact for a safe and sustainable future: Learn more on