RiskAssessmentofFishingTrawlActivitiestoSubseaPipelinesof … · 2020. 7. 23. · A number of studies have been conducted on the in-teraction between trawl gear and subsea pipelines

Research ArticleRisk Assessment of Fishing Trawl Activities to Subsea Pipelines ofSabah and Labuan Waters

Ahmad Faizal Ahmad Fuad 1 Mohd Hafizi Said 1 Khalid Samo2

Mohd Asamudin A Rahman 2 Mohd Hairil Mohd 2 and Ismail Zainol 3

1Nautical Science Program Faculty of Maritime Studies Universiti Malaysia Terengganu Kuala Nerus 21030Terengganu Malaysia2Maritime Technology Program Faculty of Ocean Engineering Technology and Informatics Universiti Malaysia TerengganuKuala Nerus 21030 Terengganu Malaysia3Universiti Kuala Lumpur Institute of Marine Engineering Technology Dataran Industri Teknologi Kejuruteraan MarinBandar Teknologi Maritim Jalan Pantai Remis Lumut 32200 Perak Malaysia

Correspondence should be addressed to Ahmad Faizal Ahmad Fuad faizalfuad75gmailcom

Received 7 May 2020 Accepted 17 June 2020 Published 23 July 2020

Academic Editor Joatildeo Pedro Barreiros

Copyright copy 2020 Ahmad Faizal Ahmad Fuad et al is is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in anymedium provided the original work isproperly cited

Introduction Trawling is a method of catching fish in a large volume where fish nets are pulled through water using one or twoboats Bottom trawling is where the nets are pulled over on the seabede gear of the bottom trawling would impact the exposedsubsea pipeline on the seabed Subsea pipelines transport crude oil and gas from the offshore platform to shore facility is studyassesses the risk of fish trawling activities to the subsea pipelines at Sabah and Labuan offshore e specification of trawlequipment used by local trawlers in Sabah was determined by the on-site survey e frequency of a fish trawler crossing over thepipelines was calculated based interview on operation and site survey e calculation of the pull-over load of the otter board wascalculated using the DNVGL algorithm e severity and frequency index of the risk matrix was developed based on literaturereview Results showed that the pull-over load of the otter board would not damage the pipelinese risk posed by the fish trawleractivity to the pipelines is low and moderate

1 Introduction

Sabah is known for its fresh sea catches Seas of SuluSulawesi and South China which surround Sabah con-tribute to 418 in marine fish catches in Malaysia Sabahfisheries and aquaculture industries produce nearly 200000metric tons of fish annually and contribute to Sabahrsquos annualGross Domestic Product by 28emarine capture fisheryis the major contributor which accounts for about 80 ofthe statistics is is a catalyst by various fishing gearmethods used by the fisherman in Sabah e main fishingmethod that contributes to the total catches is the trawl netTrawling is a method of fishing where fish nets are pulledthrough water using one or two boats Trawl can be split intobottom trawling and midwater trawling [1] Apart from

fisheries and aquaculture industries Sabah has an oil and gasindustries with a reservoir that consist of West Sabah BasinNorthwest Sabah Basin and Northeast Sabah deep-waterarea Most oil and gas come from the West Basin namelyErbWest Tembungo and Kababangan oil fields as shown inFigure 1

However the existing subsea pipelines connecting oilfield to shore are affected by fishing activities especiallythe bottom-trawling e interaction may cause damageto the subsea pipelines which eventually leak and causemarine pollution is interaction is considered as athird-party impact due to the human activity at sea ethird-party impact is the impact caused by external ac-tivities such as trawling anchoring and dropped objects[3]

Hindawie Scientific World JournalVolume 2020 Article ID 6957171 9 pageshttpsdoiorg10115520206957171

A number of studies have been conducted on the in-teraction between trawl gear and subsea pipelines [4ndash8]DNV had introduced the algorithm to calculate the pull-overload and hooking of trawl gear on the subsea pipelines [9]e behaviour of X65 pipeline during impact has beenstudied by Kristoffersen et al [10] Longva et al [11] hadconducted a load test of fishing gear on subsea pipelinesestudy had identified the friction of board pipe the tension ofwire between the board and trawl net the towing line dragproperties and the direction of over-trawling that pro-foundly influenced the impactrsquos load Wu et al [12] hadproposed a new approach to quantify the probability of thetrawl board hooking by using simulation tools and statisticaldata DNV had updated their recommended practice oninterference between trawl gear and pipelines in 2017 [9]

Hitherto no study has been conducted on the fishtrawlers activities to subsea pipelines particularly at Sabahoffshore erefore the objective of this research is to de-termine the impact of the pull-over load of trawlers to thesubsea pipelines from Sabah and Labuan offshore to shoregas and crude terminal respectively

2 Methods

In this research several methods were used to achieve themain objective e overall research activities are shown inFigure 2 e explanation of each process is given in thefollowing paragraphs

e first step of the research is to obtain information onoil and gas pipelines from offshore fields to shore facilities atSabah and Labuane data were obtained from the relevantMAL chart series produced by the Malaysia National Hy-drographic Centre e electronic navigation chart series areavailable from C-Map and Navionics e pipelines datawere also obtained from the oil and gas company that ownsthe pipelines

e second step is to determine the frequency of crossingby trawlers on the pipelines According to the Sabah Fish-eries Department less than 30 of fishing vessels in Sabah isfitted with the Automatic Identification System (AIS) usthe AIS data for trawlers were not available To determinethe number of crossings on pipelines an alternative way wasdeveloped

e first method of the second step was to determinethe typical operation of trawlers in Sabah e informationwas gathered by conducting a survey on the three operatorfish trawlers at Kota Kinabalu fish jetty e informationwas the location of fishing ground speed and duration tothe fishing ground trawling speed and duration thenumber of trawling per day duration of fishing speed andduration to return to fish landing jetty duration of transfercargo to jetty and replenishment before going back tofishing e second method of the second step is to do a siteverification survey by boating along the route of thepipelines e course speed name and type of fishingvessels detected on-site were recordede third method ofthe second step is to determine the density of fishingtrawler per area of fishing ground is step was started byidentifying fishing grounds in Sabah waters e area foreach fishing ground was marked and measured by using theGoogle Earth application

e third step was to identify the specification of thetrawl gear and otter board used by trawlers e sitesurvey was conducted to fishing trawlers at the KotaKinabalu fishing port and shipyard at Sepanggar BayDuring the survey the dimension of the otter board wasmeasured and the thickness of the warp line wasmeasured

e fourth step was to calculate the force of the pull-overload by using equations (1)ndash(4) developed by DNV [9] epull-over load is the horizontal and vertical forces from thetrawl boards acting towards the subsea pipeline It shall beapplied as single point load to the pipeline under consid-eration [13]

e equation for the pull-over load of an otter board ortrawl door is given below [9]

Figure 1 Oil fields and subsea pipelines at Sabah West Basin(Source Navionics [2])

Obtain sabah offshorepipeline information

Determine frequency ofcrossing by trawlers

Identify specification oftrawl gear

Risk analysis

Result of risk matrix

Calculate pull-over load

Figure 2 Overall research activities

2 e Scientific World Journal

FP CFV mtkw( 111385712 (1)

where FP is the pull-over load of an otter boardtrawl doorkw is the warp line stiffness V is the trawling velocity mt isthe steel mass of boardbeam with shoes and CF is anempirical coefficient

CF is determined by

CF 80 middot 1 minus eminus08H

1113874 1113875 (2)

where H is a dimensionless height and is determined by

H Hsp + OD2 + 02

B (3)

where Hsp is the span height (negatively for the partly buriedtrenched pipeline) OD is the pipeline outer diameter in-cluding coating B is half of the trawl board height

e warp stiffness kw is assumed as

kw 35107

LW

(4)

where LW is the length of warp line in metere fifth step was to conduct the risk analysis which

consists of the frequency index severity index and riskmatrix e frequency index and severity index will bedeveloped based on DNV GL and ISO publications

e frequency index developed in this study is shown inTable 1 e table is a 9-point scale ranging from 0 to 8100frequencies with an increment of 900 between categoriese table is developed based on the DNV GL report onrecommended failure rates for pipelines by adapting tablecriteria for score assessment threats related to shipping lossemergency anchoring and dragged anchors from anchoredships [14]e table has 3 scores as follows 0 1 and 2 for thenumber of crossing less than 90000 between 90000 and180000 and above 180000 respectivelye adaptation wasby taking 1 of the scores of each category from the DNVGL table and developed the ratings in 9 scales is adap-tation would increase the impact probability to 100 per centwhich is due to the impact of trawl gear on the pipeline oneach crossing

e severity index in Table 2 was developed based onresearch conducted by Kristoffersen et al [10] However noresults of the calculated force are shown in the table in thissection e test conducted in the research is in accordancewith DNV-RP-F111 interference between trawl gear andpipelines [9] Results from the research were used to de-termine themagnitude of the force that resulted in the extentof damage to the pipeline which also subjects to thethickness of the pipeline A pipelinersquos load resistance againstexternal interference primarily depends on the pipelinediameter and wall thickness Tests have shown that the mostcommonly used excavators and construction equipment donot exercise enough load to cause leaks or rupture topipelines with a wall thickness larger than 11-12mm [14]e index number and meaning of the index of severity inTable 2 is developed based on ISO 17776 Risk Matrix withindex number starting from 0 to 4 [15]

Table 3 is the Risk Matrix Table for fishing activities onpipeline which is used to determine the result of the riskindex Table 3 combined the severity index and frequencyindex in one table and was used to calculate the summationbetween the frequency and severity index for a particularpipeline e result of the summation and the corre-sponding level of risk are shown in Table 4 ere are fivelevels of risk matrix shown in Table 4 from very low to veryhigh risk

3 Results and Discussion

ere were four pipelines that were identified in the studyPipelines ID85 and ID80 cross from Erb West oil field toSabah Gas Terminal Kota Kinabalu (SBGAST) and toLabuan Gas Terminal (LGAST) respectively (Table 5)Pipelines ID107 and 144A from Semarang oil field to LGASTare shown in Figures 3 and 4

31 -e Density of Fishing Trawler in Sabah WatersAccording to Kristoffersen et al [10] there are four mainfishing grounds of Sabah as shown in Figure 5 Fishingground A is located between Erb West oil field and KotaKinabalu mainland Fishing ground B is located at TelukKimanis Fishing ground C is located between MantaniIsland and the mainland and fishing ground D is locatedbetween Semarang oil field and Labuan mainland

e area of fishing ground A is 488 nm2 Results of sitesurvey at ground A show that twelve trawlers were found asshown in Figure 6 (the positions depicted by camera icon)e density of fishing trawlers in an area was obtained bydividing the area measured with the number of fishingtrawlers found thus the density of fishing trawler in area Ais 407 nm2 per trawl Fishing ground A is used as thebenchmark for density of trawler because it has the highestnumber of fishing trawlers registered at its coast (Kota

Table 1 Frequency index of fishing vessel crossing

Index Meaning Range0 Extremely low 0ndash9001 Very low 901ndash18002 Low 1801ndash27003 Slightly low 2701ndash36004 Moderate 3601ndash45005 Slightly high 4501ndash54006 High 5401ndash63007 Very high 6301ndash72008 Extremely high 7201ndash8100

Table 2 Severity index of the pull-over forceload

Index Meaning Calculated force (Fp)0 No damage No data1 Slight damage No data2 Minor damage No data3 Local damage No data4 Major damage No data

e Scientific World Journal 3

Kinabalu) compared to other fishing ground and it is alsothe biggest fishing ground in Sabah By using the result fromground A the density of trawler for fishing ground B C andD is calculated e area for ground B C and D is 157 nm2213 nm2 and 156 nm2 respectively e density of trawlerfor ground B C and D is 4 5 and 4 respectively

32TypicalOperationofFishingTrawlers inSabahWatersandFrequency of Crossing An interview with three skippers offishing trawler had identified the typical operation of thefishing trawlers in Sabah waters e information of theoperation is applied to fishing ground A an area betweenErb West oil field and the coast of Kota Kinabalu to Kar-ambunai Sabah (Figure 4) e result for fishing ground A isas follows

(i) e duration of one cycle of fishing trawl operationis 10 days which consists of 05 days going to afishing ground 7 days of trawling 05 days to returnto fish landing jetty and 2 days for discharge cargoand replenishment

(ii) e trawling operation is conducted 5 times perday where the duration for each trawling operationis 4 hours namely 1 hour to deploy and retrieve netand 3 hours to tow net

(iii) e trawl distance per day is 45 nm which resultedfrom 5 times trawl per day multiply 3 hours du-ration per trawl and multiply speed 3 knots

(iv) e distance of the fishing area is 28 nm which ismeasured from pipeline Erb WestndashLabuan GasTerminal to pipeline Erb WestndashSabah Gas Ter-minal in Figure 2 For a trawler that makes aU-turn after 28 nm trawling to make a new trawlleg with a trawling distance of 45 nm a vesselwould cross 1 pipeline twice and 1 pipeline onceHowever by taking into consideration theslight increase of speed lesser time in deploymentand retrieval of trawl gear it is assumed that atrawler may cross these two pipelines 2 times perday

(v) Monthly crossing for 3 fishing trips at 7 days actualtrawling operation the trawling days is 21 daysEach trawler would cross 42 times on each pipeline(21 days trawling per month x 2 times crossing perday)

(vi) Annual crossing assuming 11 months annualoperation (one month reserved for maintenanceand repair) each trawler would cross one pipeline462 times (42 times crossmonth x 11 months)

(vii) e density of fishing trawler for the area is 12erefore the number of annual crossing is esti-mated at about 5544 crossings (ie 12 trawlers x 462crossed per vessel) for each pipeline in area A

e results of fishing ground D are as follows

(i) 10 days per cycle of operation (05 days to fishinggrounds 7 days trawling 05 back to port and 2days to land fish and replenish fuel and supply)

(ii) Trawler density 407 nm2 area density per trawlerat area A is applied to other areas in Sabah andLabuan erefore for area D with 156 nm2 thedensity of trawlers for the area at one time is 4trawlers (156 nm2407 nm2)

(iii) Trawling distance of a trawler per day is 45 nm (5times trawl per day x 3-hour trawl x 3 knots)

(iv) Length of fishing area 13 nm (From Semar-angndashLabuan LGAST ID 107 and ID 144)(Figures 4 and 5)

(v) A trawler would make a U-turn after a distance of13 nm for new trawl leg (Figure 7)

(vi) With a distance of 45 nm trawl distance a vesselwould cross 2 pipelines (ID 107 and ID 144) 4times crossing per day (Figure 5)

(vii) Monthly crossings 84 crossingstrawlerpipeline(at three 7-day fishing tripsmonth) ie 7 days x 3trips x 4 times crossing per day

Table 3 Risk matrix table for fishing activities on pipeline

Severity 0 1 2 3 4

Freq

uenc

y

No

dam

age

Slig

htda

mag

e

Min

orda

mag

e

Loca

lda

mag

e

Maj

orda

mag

e

0 Extremelylow 0 1 2 3 4

1 Very low 1 2 3 4 5

2 Low 2 3 4 5 6

3 Slight low 3 4 5 6 7

4 Moderate 4 5 6 7 8

5 Slighthigh 5 6 7 8 9

6 High 6 7 8 9 10

7 Very high 7 8 9 10 11

8 Extremelyhigh 8 9 10 11 12

Table 4 Risk matrix table of fishing activities impact on pipeline

Meaning

Very low risk (VL)

Low risk (L)

Moderate (M)

High risk (H)

Very high risk (VH)

Risk matrix

0ndash3

4ndash5

6ndash7

8ndash10

11ndash12

Colour


Figure 4 Pipeline ID107 and ID144A Route Semarang to Labuan Gas Terminal (LGAST) (red line) Coordinates pipeline ID144A from seato shore is 5deg 3300primeN 114deg 57922primeE and 5deg16584prime N 115deg 8730primeE respectively

Figure 3 Pipeline ID 85 Erb West to SBGAST (red dotted line right) and ID80 Erb West to LGAST (red dotted line left) Coordinatespipeline ID85 from sea to shore is 6deg 15126primeN 115deg 50156primeE and 6deg 9730primeN 116deg 7189primeE respectively

Table 5 Pipelines information

Pipeline name Pipe length (km) Pipe diameter (inchcm) Design code WT (mm) Yield strength kNm2

ID85 Erb West to SBGST 604 16406 API 5L X60 159 42times105 60 ksiID80 Erb West to LGAST 1404 14355 API 5L X42 953 29times105 42 ksiID107 Semarang to LGAST 46 14355 API 5L X52 953 355times105 52 ksiID144A Semarang to LGAST 4771 20508 API 5L X65 111 45times105 65 ksi


(viii) Annual crossings 924 crossingstrawleryear (as-suming 11months operation less than 1month formaintenance and repair) ie 84 crossings x 11months

(ix) Based on the density of fishing trawler for the areawhich is 4 (see above assumption) the totalnumber of annual crossing 3696 (4 trawlers x924 crossings)

e frequency index table for the number of crossing ona pipeline by trawlers in a year is developed based on theassumed frequency of trawlers passing on the pipelines isfrequency is developed based on the assumption of the vessel

speed route taken distance travelled and commonlypracticed by the fishermen e frequency developed had tobe developed based on the assumption because accurateinformation leading to the frequency was not available

33 Specification of Trawl Gear e type of trawl gear usedin Sabah is the typical otter trawl gear which is using thepolyvalent or rectangular board is type of trawl gearconsists of a pair of otter boards warp line and net ereare two types of otter board used by trawlers in Sabahnamely the steel otter board and the steel-reinforced woodenotter board as shown in Figure 8

A

B

C

D

Figure 5 Fishing ground in west coast Sabah and Labuan e coordinates for area B are a4 5deg52prime1062PrimeN 115deg53prime966PrimeE a5 5deg49prime510PrimeN115deg56prime5814PrimeE a9 5deg33prime4032PrimeN 115deg46prime5244PrimeE and a10 5deg35prime1885PrimeN 115deg40prime3949PrimeE Coordinates for area C are c1 6deg51prime2820PrimeN116deg17prime5982PrimeE c3 7deg 5prime2437PrimeN 116deg37prime846PrimeE c5 6deg59prime3408PrimeN 116deg40prime2226PrimeE and c7 6deg45prime5184PrimeN 116deg25prime438PrimeE

A

B

E

D

C

2

13

54 67 8

9

Figure 6 Trawling area that involves Erb West to Labuan Gas Terminal pipeline (blue dotted line) and Erb West to Sabah Gas Terminalpipeline (green dotted line)e positions of the trawling area as follows A 6deg 2617primeN116deg 1076prime E B 6deg 2250primeN116deg 1653prime E C 6deg 655primeN116deg 169prime E D 6deg 198primeN 115deg 3244prime E and E 6deg 921primeN 115deg 3175prime Ee area is 488 nm squaree camera icon depicts the position of 10trawlers e nature of seabed in this area is mud


e types and dimension of the otter board are shown inTable 6 e category of fish trawlers that are using theseotter boards must have sufficient power to tow the heavyfishing gear at 3 knots erefore the engine horsepower is350 HP and aboveemajority of engine used in the fishingtrawlers have horsepower between 350 hp to 500 hp ediameter of the warp line used is 25 cm

34 Calculation of the Pull-Over Load e calculation of thepull-over load was done using equations (1)ndash(4) e inputsto the equations are trawl depth of 60 meters (Figure 2)trawling speed of 3 knots (154ms) 300 kg steel vee doorspecification (Tables 6 and 7) and span height on the seabedAll the pipelines are buried However by taking into con-sideration that the pipelines sit on the seabed the spanheight is zero [16]

Based on the calculation the result of the pull-over loadof a trawl board on Erb West to Labuan Gas Terminal is2401 kN and on ErbWest to Sabah Gas Terminal is 2598 kN(Table 8) ese results were compared with the yieldstrength of the pipelines in Table 7 ese results show thatthe trawl boardrsquos pull-over load on Erb West to Labuan GasTerminal and Erb West to Sabah Gas Terminal pipelines isfar lower than the yield strength of both pipelines epercentage of the pull-over load over yield strength of Erb

West to Labuan Gas Terminal and Erb West to Sabah GasTerminal pipelines are 78 and 45 respectively ere-fore the force of the pull-over load of the trawl boards wouldnot give a significant impact to damage the pipelinesHowever due to age factor and corrosion the yield strengthof the pipelines should be lower than new condition [14]

35 Calculation of the Frequency Index Severity Index andRisk Matrix for Fishing Activities Both severity index forpipeline ErbWest to the Labuan Gas Terminal and ErbWestto the Sabah Gas Terminal is zero because the impact forcefrom the otter board resulted in no damage to the pipelinese risk matrix results for both pipelines depend on thefrequency of crossing as shown in Table 9

Based on the observation of fishing trawl operating inSabah (Area A) and Labuan (Area D) the fish trawl skippersare aware that they were operating within the area withoffshore pipelines but do not know the exact location of thepipelinese reason that they fish in the area is that the yieldfrom the catch was good and the seabed is flat and suitablefor trawl operation According to Rouse et al [17] snaggingmay damage fishing gear disrupt the fishing operation andmay cause injuries to crew However no fish trawlers in thestudy area (Sabah and Labuan) had snagged their fishinggear with the pipelines is may be due to the pipelines

Figure 7 e width distance of area D (Labuan) fishing ground e nature seabed in this area is sand and mud e coordinates for areaLabuan D are as follows L1 5deg32prime474PrimeN 115deg 4prime5454PrimeE L2 5deg24prime3798PrimeN 115deg10prime276PrimeE L3 5deg17prime4518PrimeN 115deg 6prime996PrimeE and L55deg27prime5268PrimeN 114deg47prime5922PrimeE (Figure 5)

(a) (b)

Figure 8 Steel vee door (a) and common flat wooden door (b) used by trawlers in Sabah


buried in the muddy seabed erefore the fishermen didnot consider the pipelines as a snagging hazard

4 Conclusion

e trawling method used in Sabah waters is the bottomotter trawl is type of trawling would cause contact be-tween the trawl boards with subsea pipelines Based on thespecification of the trawl board and the subsea pipeline of thestudy area the impact force of the trawl boardrsquos pull-overload is lower that the force would cause slight damage to thepipelines e interaction between the otter boards and

subsea pipelines in West Sabah area and Labuan waterswould not damage the subsea pipelines However the fre-quency of the crossing in Labuan and Sabah (Kota Kinabalu)waters are moderate and high respectively Based on theseverity index and frequency index the risk of fishing ac-tivities Labuan and Sabah (Kota Kinabalu) waters are lowrisk and moderate risk respectively

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Table 7 Subsea pipeline Erb West oil field to Labuan data

Pipeline name Pipe length (km) Pipe diameter(inchcm) Design code WT (mm) Yield strength (kNm2) Pull-over load (kN)

ID80 Erb West to LGAST 1404 14355 API 5L X42 953 29times105 42 ksi 2401ID85 Erb West to SBGST 604 16406 API 5L X60 159 42times105 60 ksi 2598ID107 Semarang to LGAST 46 14355 API 5L X52 953 355times105 52 ksi 2819ID144A Semarang to LGAST 4771 20508 API 5L X65 111 45times105 65 ksi 38183

Table 8 Level of damage according to force of impact

Pipeline name ickness (mm) Extent of damage Force (kN) Yield strength (kNm2) Pull-over load Fp (kN)

ID80 Erb WestLGAST 953

Major 172011

29times105 at 42 ksi 2401Local 127067Minor 72946Slight 47062

ID85 Erb WestSBGST 159

Major 286985


ID107 SemarangLGAST 953

Major 172011


ID144A SemarangLGAST 111

Major 200348


Table 9 Calculated risk matrix

ID ampname Frequency crossing Frequency index Pull-over load (kN) Severity index Risk matrixID80 Erb WestLGAST 3696 4 2401 0 4 (low risk)ID85 Erb WestSBGST 5544 6 2598 0 6 (moderate)ID107 SemarangLGAST 3696 4 2819 0 4 (low risk)ID144A SemarangLGAST 3696 4 38183 0 4 (low risk)

Table 6 Types of fish trawl otter board used in Sabah and Labuan

Trawler categories Types of otter boards Dimensions in cm (LtimesWtimesT) Material used Weight (kg) of one otter board350 HP and above Steel vee door 190times106times 65 Steel 300350 HP and above Common flat wooden door 230times115times 5 Steel frame and wood 250350 HP and above Steel vee door 165times110times 5 Steel 210


Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors would like to thank Petronas for sharing thepipeline data

References

[1] Seafish ldquoBasic fishing methodsrdquo 2015 httpwwwseafishorg

[2] Navionics (2018) Sabah Marine Chart[3] E Pratiwi K Buda Artan A A B Dinariyana I M Ariana

D Widhi Hand and F Indrayuni ldquoRisk assessment of subseagas pipeline due to port development located at narrowchannelrdquo Asian Journal of Scientific Research vol 12 no 1pp 137ndash150 2019

[4] Y Bai and Q Bai Subsea Pipelines and Risers pp 173ndash194Elsevier Ltd Oxford UK 2005

[5] M R U Kawsar S A Youssef M Faisal A Kumar J K Seoand J K Paik ldquoAssessment of dropped object risk on corrodedsubsea pipelinerdquoOcean Engineering vol 106 pp 329ndash340 2015

[6] O Fyrileiv D Askheim R Verley and H RolsdorphldquoPipeline-trawl interaction effect of trawl clump weightsrdquo inProceedings of the 25th International Conference on offshoreMechanics and Arctic engineering pp 95ndash102vol 4 TerryJones Pipeline Technology Ocean Space Utilization CFD andVIV Symposium Hamburg Germany June 2006

[7] M Soslashrheim and Y Bai ldquoRisk analysis applied to subseapipeline engineeringrdquo in Procedings of the OMAErsquo99 StJohnrsquos Canada 1999

[8] J Willcocks and Y Bai ldquoRisk based inspection and integritymanagement of pipeline systemsrdquo in Proceedings ofISOPErsquo2000 Seattle WA USA 2000

[9] DNVGL DNVGL-RP-F111 Interference between Trawl Gearand Pipelines Health and Safety Executive London UK 2017a

[10] M Kristoffersen T Boslashrvik I Westermann M Langseth andO S Hopperstad ldquoImpact against X65 steel pipesmdashan ex-perimental investigationrdquo International Journal of Solids andStructures vol 50 no 20-21 pp 3430ndash3445 2013

[11] V Longva S Saeligvik E Levold and H Ilstad ldquoDynamicsimulation of subsea pipeline and trawl board pull-over in-teractionrdquo Marine Structures vol 34 pp 156ndash184 2013

[12] X Wu V Longva S Saeligvik and T Moan ldquoA Simplifiedapproach to estimate the probability of otter board hooking atpipelinesrdquo Journal of Offshore Mechanics and Arctic Engi-neering vol 137 no 6 Article ID 061702 2015

[13] B Yohannes Trawl Gear Interaction with Subsea PipelinesUniversity of Stavanger Stavanger Norway 2012

[14] DNVGL ldquoRecommended failure Rates for pipelinesrdquo 2017[15] DNV ldquoMarine risk assessmentrdquo Offshore Technology Report

vol 2001063 pp 1ndash68 Health and Safety Executive LondonUK 2001

[16] E S Taghizadeh and E Pedram ldquoAccidental limit state ofsubmarine pipeline trawl gears pull-over loads and effect offree spanrdquo International Journal of Maritime Technologyvol 8 no 1 pp 47ndash58 2017

[17] S Rouse A Kafas P Hayes and T AWilding ldquoDevelopmentof data layers to show the fishing intensity associated withindividual pipeline sections as an aid for decommissioningdecision-makingrdquo Underwater Technology vol 34 no 4pp 171ndash178 2017


A number of studies have been conducted on the in-teraction between trawl gear and subsea pipelines [4ndash8]DNV had introduced the algorithm to calculate the pull-overload and hooking of trawl gear on the subsea pipelines [9]e behaviour of X65 pipeline during impact has beenstudied by Kristoffersen et al [10] Longva et al [11] hadconducted a load test of fishing gear on subsea pipelinesestudy had identified the friction of board pipe the tension ofwire between the board and trawl net the towing line dragproperties and the direction of over-trawling that pro-foundly influenced the impactrsquos load Wu et al [12] hadproposed a new approach to quantify the probability of thetrawl board hooking by using simulation tools and statisticaldata DNV had updated their recommended practice oninterference between trawl gear and pipelines in 2017 [9]

Hitherto no study has been conducted on the fishtrawlers activities to subsea pipelines particularly at Sabahoffshore erefore the objective of this research is to de-termine the impact of the pull-over load of trawlers to thesubsea pipelines from Sabah and Labuan offshore to shoregas and crude terminal respectively

2 Methods

In this research several methods were used to achieve themain objective e overall research activities are shown inFigure 2 e explanation of each process is given in thefollowing paragraphs

e first step of the research is to obtain information onoil and gas pipelines from offshore fields to shore facilities atSabah and Labuane data were obtained from the relevantMAL chart series produced by the Malaysia National Hy-drographic Centre e electronic navigation chart series areavailable from C-Map and Navionics e pipelines datawere also obtained from the oil and gas company that ownsthe pipelines

e second step is to determine the frequency of crossingby trawlers on the pipelines According to the Sabah Fish-eries Department less than 30 of fishing vessels in Sabah isfitted with the Automatic Identification System (AIS) usthe AIS data for trawlers were not available To determinethe number of crossings on pipelines an alternative way wasdeveloped

e first method of the second step was to determinethe typical operation of trawlers in Sabah e informationwas gathered by conducting a survey on the three operatorfish trawlers at Kota Kinabalu fish jetty e informationwas the location of fishing ground speed and duration tothe fishing ground trawling speed and duration thenumber of trawling per day duration of fishing speed andduration to return to fish landing jetty duration of transfercargo to jetty and replenishment before going back tofishing e second method of the second step is to do a siteverification survey by boating along the route of thepipelines e course speed name and type of fishingvessels detected on-site were recordede third method ofthe second step is to determine the density of fishingtrawler per area of fishing ground is step was started byidentifying fishing grounds in Sabah waters e area foreach fishing ground was marked and measured by using theGoogle Earth application

e third step was to identify the specification of thetrawl gear and otter board used by trawlers e sitesurvey was conducted to fishing trawlers at the KotaKinabalu fishing port and shipyard at Sepanggar BayDuring the survey the dimension of the otter board wasmeasured and the thickness of the warp line wasmeasured

e fourth step was to calculate the force of the pull-overload by using equations (1)ndash(4) developed by DNV [9] epull-over load is the horizontal and vertical forces from thetrawl boards acting towards the subsea pipeline It shall beapplied as single point load to the pipeline under consid-eration [13]

e equation for the pull-over load of an otter board ortrawl door is given below [9]

Figure 1 Oil fields and subsea pipelines at Sabah West Basin(Source Navionics [2])

Obtain sabah offshorepipeline information

Determine frequency ofcrossing by trawlers

Identify specification oftrawl gear

Risk analysis

Result of risk matrix

Calculate pull-over load

Figure 2 Overall research activities


FP CFV mtkw( 111385712 (1)


CF is determined by


1113874 1113875 (2)


H Hsp + OD2 + 02

B (3)



kw 35107

LW

(4)

































Severity 0 1 2 3 4

Freq

uenc

y

No

dam

age

Slig

htda

mag

e

Min

orda

mag

e

Loca

lda

mag

e

Maj

orda

mag

e


1 Very low 1 2 3 4 5

2 Low 2 3 4 5 6




6 High 6 7 8 9 10

7 Very high 7 8 9 10 11



Meaning

Very low risk (VL)

Low risk (L)

Moderate (M)

High risk (H)

Very high risk (VH)

Risk matrix

0ndash3

4ndash5

6ndash7

8ndash10

11ndash12

Colour













A

B

C

D


A

B

E

D

C

2

13

54 67 8

9










(a) (b)




4 Conclusion



Data Availability








Major 172011



Major 286985



Major 172011



Major 200348









Acknowledgments


References



















FP CFV mtkw( 111385712 (1)


CF is determined by


1113874 1113875 (2)


H Hsp + OD2 + 02

B (3)



kw 35107

LW

(4)

































Severity 0 1 2 3 4

Freq

uenc

y

No

dam

age

Slig

htda

mag

e

Min

orda

mag

e

Loca

lda

mag

e

Maj

orda

mag

e


1 Very low 1 2 3 4 5

2 Low 2 3 4 5 6




6 High 6 7 8 9 10

7 Very high 7 8 9 10 11



Meaning

Very low risk (VL)

Low risk (L)

Moderate (M)

High risk (H)

Very high risk (VH)

Risk matrix

0ndash3

4ndash5

6ndash7

8ndash10

11ndash12

Colour













A

B

C

D


A

B

E

D

C

2

13

54 67 8

9










(a) (b)




4 Conclusion



Data Availability








Major 172011



Major 286985



Major 172011



Major 200348









Acknowledgments


References





































Severity 0 1 2 3 4

Freq

uenc

y

No

dam

age

Slig

htda

mag

e

Min

orda

mag

e

Loca

lda

mag

e

Maj

orda

mag

e


1 Very low 1 2 3 4 5

2 Low 2 3 4 5 6




6 High 6 7 8 9 10

7 Very high 7 8 9 10 11



Meaning

Very low risk (VL)

Low risk (L)

Moderate (M)

High risk (H)

Very high risk (VH)

Risk matrix

0ndash3

4ndash5

6ndash7

8ndash10

11ndash12

Colour













A

B

C

D


A

B

E

D

C

2

13

54 67 8

9










(a) (b)




4 Conclusion



Data Availability








Major 172011



Major 286985



Major 172011



Major 200348









Acknowledgments


References






























A

B

C

D


A

B

E

D

C

2

13

54 67 8

9










(a) (b)




4 Conclusion



Data Availability








Major 172011



Major 286985



Major 172011



Major 200348









Acknowledgments


References
























A

B

C

D


A

B

E

D

C

2

13

54 67 8

9










(a) (b)




4 Conclusion



Data Availability








Major 172011



Major 286985



Major 172011



Major 200348









Acknowledgments


References


























(a) (b)




4 Conclusion



Data Availability








Major 172011



Major 286985



Major 172011



Major 200348









Acknowledgments


References




















4 Conclusion



Data Availability








Major 172011



Major 286985



Major 172011



Major 200348









Acknowledgments


References





















Acknowledgments


References



















Documents

RiskAssessmentofFishingTrawlActivitiestoSubseaPipelinesof … · 2020. 7. 23. · A number of studies have been conducted on the in-teraction between trawl gear and subsea pipelines