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DET NORSKE VERITASTM

REPORT NO./DNV REG NO.: 2013-4091 / 17TLT29-3

REV 1, 11.06.2013

APPENDIX D - LEAK

FREQUENCIES ANALYSIS

SKANGASS AS

Det Norske Veritas

Report for Skangass AS

Appendix D - Leak Frequencies Analysis

MANAGING RISK

DNV Reg. No.: 17TLT29-3 Revision No.: 1

Date : 11.06.2013 Page i of i

Table of Contents Page

1 LEAK FREQUENCY ANALYSIS .................................................................................................... 1 1.1 Equipment of LNG bunkering installation ................................................................................... 1 1.2 LNG loading arm failure .............................................................................................................. 1 1.3 Leak Frequency ............................................................................................................................ 3

2 RESULTS DISCUSSION ................................................................................................................... 6

3 REFERENCES .................................................................................................................................... 6

ANNEX 1 P&IDS 1301-1100-100, SHEETS TA01/TB01/TC01 ........................................................... 7

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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 2008-1768 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&IDs (cf. Annex 1) together with estimates of line lengths from plot plans. The P&IDs 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 10 50

Large > 50

1.2 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

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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 ships 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

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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

LNG Pump

Small Bore fittings LNG Line 0.5 7 0/100

Vapour Return Line 0.5 4 95/5

Flanges

LNG Line

1 1 0/100

4 1 0/100

6 7 0/100

10 4 0/100

Vapour Return Line

1 3 95/5

2 2 95/5

4 1 95/5

Actuated valve LNG Line

2 1 0/100

4 1 0/100

6 1 0/100

Vapour Return Line 2 1 95/5

Manual valve

LNG Line

1 15 0/100

2 10 0/100

3 1 0/100

4 3 0/100

6 1 0/100

10 1 0/100


2 7 95/5

Pump LNG Line - 1 0/100

Piping

LNG Line

1 25 m 0/100

2 17.5 m 0/100

4 5 m 0/100

6 37.5 m 0/100

10 25 m 0/100

Vapour Return Line

1 12.5 m 95/5

2 17.5 m 95/5

6 37.5 m 95/5

Flowmeter Small Bore fittings

LNG Line 0.5 14 0/100

Vapour Return Line 0.5 1 95/5

Flanges LNG Line 6 6 0/100

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Ferry bunkering

Pressure (bara): 10


8 10 0/100


Actuated Valve LNG Line - - -

Vapour Return Line - - -

Manual Valve LNG Line

1 10 0/100

2 4 0/100

6 10 0/100


Piping

LNG Line

1 10 m 0/100

2 10 m 0/100

6 10 m 0/100

Vapour Return Line

1 10 m 95/5

2 10 m 95/5

4 10 m 95/5

Piping between LNG pump

and Flowmeter Piping

LNG Line 8 25 m 0/100

Vapour Return Line 4 25 m 95/5

Pipeline between LNG plant and ferry bunkering station

Underground pipelines

Flange LNG line 8 1 0/100

Piping section LNG Line 8 495m 0/100


Ferry bunkering station

Upstream up to ESD valve

Small Bore fittings LNG Line - -

Flange LNG Line - - -

Actuated valve LNG Line 6 1 0/100

Manual valve LNG Line

1 5 0/100

2 1 0/100

3 1 0/100

6 1 0/100


Piping section

LNG Line 1 3 m 0/100

6 3 m 0/100


4 3 m 95/5

Downstream ESD valve

(365 hours per year)

Small Bore fittings LNG Line 0.5 6 0/100


Flange LNG Line 6 2 0/100


Actuated valve LNG Line - - -

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Ferry bunkering

Pressure (bara): 10



Manual valve

LNG Line 1 5 0/100

2 3 0/100

Vapour Return Line

1 2 95/5

2 3 95/5

6 1 95/5

Piping section

LNG Line 1 4 m 0/100

6 4 m 0/100


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

LNG Line 1.3E-02 1.8E-03 6.6E-04 1.6E-02

Vapour Return Line1 2.1E-04 2.1E-05 2.2E-06 2.3E-04

Between plant and ferry bunkering station

LNG Line 5.0E-05 7.7E-06 3.0E-06 6.0E-05


Jetty area Upstream ESD valve

LNG Line 5.3E-04 5.3E-05 1.5E-05 5.9E-04


Jetty area Downstream ESD valve1

LNG Line1 6.6E-05 8.3E-06 4.1E-07 7.5E-05


Loading arms LNG Line 1.1E-03 3.8E-04 9.4E-05 1.6E-03

TOTAL 1.5E-02 2.3E-03 7.7E-04 1.8E-02

1Only in use during 365 hours per year.

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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:

- 108 % 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 2008-1768 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, 09.11.2011

/3/

QRA for Risavika Ferry Bunkering Station, Skangass AS, Report No./DNV Reg No.:

2012-4049/143MJ79-5; Rev. 0, 18.05.2012

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ANNEX 1 P&IDS 1301-1100-100, 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.

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