1、RECOMMENDED PRACTICEDNV-RP-F111INTERFERENCE BETWEEN TRAWL GEAR AND PIPELINESOCTOBER 2006Since issued in print (October 2006), this booklet has been amended, latest in April 2007. See the reference to “Amendments and Corrections” on the next page. DET NORSKE VERITASFOREWORDDET NORSKE VERITAS (DNV) is
2、 an autonomous and independent foundation with the objectives of safeguarding life, prop-erty and the environment, at sea and onshore. DNV undertakes classification, certification, and other verification and consultancyservices relating to quality of ships, offshore units and installations, and onsh
3、ore industries worldwide, and carries out researchin relation to these functions.DNV Offshore Codes consist of a three level hierarchy of documents: Offshore Service Specifications. Provide principles and procedures of DNV classification, certification, verification and con-sultancy services. Offsho
4、re Standards. Provide technical provisions and acceptance criteria for general use by the offshore industry as well asthe technical basis for DNV offshore services. Recommended Practices. Provide proven technology and sound engineering practice as well as guidance for the higher levelOffshore Servic
5、e Specifications and Offshore Standards.DNV Offshore Codes are offered within the following areas:A) Qualification, Quality and Safety MethodologyB) Materials TechnologyC) StructuresD) SystemsE) Special FacilitiesF) Pipelines and RisersG) Asset OperationH) Marine OperationsJ) Wind TurbinesAmendments
6、 and Corrections This document is valid until superseded by a new revision. Minor amendments and corrections will be published in a separatedocument normally updated twice per year (April and October). For a complete listing of the changes, see the “Amendments and Corrections” document located at: h
7、ttp:/ under category “Offshore Codes”.The electronic web-versions of the DNV Offshore Codes will be regularly updated to include these amendments and corrections.Comments may be sent by e-mail to For subscription orders or information about subscription terms, please use Comprehensive information ab
8、out DNV services, research and publications can be found at http:/, or can be obtained from DNV, Veritas-veien 1, NO-1322 Hvik, Norway; Tel +47 67 57 99 00, Fax +47 67 57 99 11. Det Norske Veritas. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by an
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10、s, then Det Norske Veritas shall pay compensation to such personfor his proved direct loss or damage. However, the compensation shall not exceed an amount equal to ten times the fee charged for the service in question, provided that the maximum compen-sation shall never exceed USD 2 million.In this
11、provision Det Norske Veritas shall mean the Foundation Det Norske Veritas as well as all its subsidiaries, directors, officers, employees, agents and any other acting on behalf of DetNorske Veritas.Recommended Practice DNV-RP-F111, October 2006Introduction Page 3IntroductionDNV-RP-F111 is issued as
12、an update to DNV Guidelines No.13 Interference between trawl gear and pipelines issued in1997. This RP replaces DNV Guideline No. 13, which will bewithdrawn. Trawl equipment has developed since 1997, and new typesof equipment (i.e. clump weights) are being used in theNorth Sea and the Norwegian Sea.
13、 The new DNV-RP-F111 includes these changes. As part of the qualification of new pipelines in the Norwe-gian Sea (Kristin, Snhvit and Ormen Lange), severalstudies and model tests of clump weight interference withpipelines have been performed. Results from these studieshave also been included in this
14、 RP.Main changesThe main changes are: Harmonisation of the design format and acceptance crite-ria with other DNV Offshore Codes. Includes increased sizes and new trawl equipment (in par-ticular clump weights used in twin trawling). Utilization of new know-how from recent pipelineprojects designing f
15、or clump weights.AcknowledgementsThe following companies sponsored this JIP: Hydro ASA Statoil DNV.The following organisations have made major contributions tothe hearing process: Reinertsen Engineering Subsea 7.DNV is grateful for the valuable input, including test results,cooperation and discussio
16、ns with these companies. DET NORSKE VERITASRecommended Practice DNV-RP-F111, October 2006Page 4 IntroductionDET NORSKE VERITASAmended April 2007 Recommended Practice DNV-RP-F111, October 2006see note on front cover Page 5CONTENTS1. GENERAL . 71.1 Introduction .71.2 Trawling aspects .71.3 Scope and a
17、pplication .81.4 Limitations .91.5 Relationship to other rules.91.6 References .91.7 Trawl-pipeline interaction phases.91.8 Units.101.9 Symbols and abbreviations.112. TRAWL DESIGN DATA . 122.1 Types of trawl gear.122.2 Basic data requirements .122.3 Most critical trawl gear.132.4 Trawl gear impact f
18、requency .133. IMPACT. 133.1 Introduction .133.2 Impact energy .133.3 Energy dissipation .133.4 Simplified response calculations .154. PULL-OVER . 174.1 Introduction .174.2 Structural modelling .174.3 Pull-over loads for trawl boards and beam trawls .174.4 Pull-over loads for clump weights.184.5 Pul
19、l-over duration Trawl boards and beam trawls .194.6 Pull-over duration - clump weight. 194.7 Response calculations . 205. HOOKING. 205.1 Introduction. 205.2 Structural model . 215.3 Snagging. 215.4 Critical span height. 215.5 Part penetration . 215.6 Wedged. 215.7 Maximum warp line force . 215.8 Res
20、ponse calculations . 216. ACCEPTANCE CRITERIA. 226.1 General. 226.2 Pipe shell - impact . 226.3 Coating - impact. 226.4 Pull-over. 236.5 Hooking. 247. COATING IMPACT TESTING. 247.1 General. 247.2 Specimens. 247.3 Test equipment . 257.4 Test procedure. 267.5 Test-rig calibration . 268. BIBLIOGRAPHY .
21、 27APP. A ADVANCED IMPACT CALCULATION METHOD . 28APP. B EXAMPLE. 31DET NORSKE VERITASRecommended Practice DNV-RP-F111, October 2006 Amended April 2007Page 6 see note on front coverDET NORSKE VERITASAmended April 2007 Recommended Practice DNV-RP-F111, October 2006see note on front cover Page 71. Gene
22、ral1.1 IntroductionFishing activities such as bottom trawling shall be consideredfor offshore pipelines for two main reasons: possible hazard and inconvenience to the fishermen incase of trawl gear hooking to the pipeline, and possible hazard to the integrity of the pipeline due to loadsfrom the tra
23、wl gear.This Recommended Practice (RP) covers the aspects of pipe-line integrity and not the potential hazard for fishermen in par-ticular.Equipment used for bottom trawling can expose a pipeline tosubstantial loads that may damage it. Such load is associatedwith the instantaneous impact and the sub
24、sequent pull-over asthe trawl gear hits and is dragged over the pipeline. In addition,hooking of trawl equipment may impose considerable loadingto the pipeline.Typical trawl gears are illustrated in Figures 1-1 to 1-3.Figure 1-1Typical otter trawl gear crossing a pipelineFigure 1-1 shows a typical o
25、tter trawl. The otter trawl boardholds the trawl net open by hydrodynamic forces. Such trawlboards are dragged along the seabed and may represent a haz-ard to the pipeline. Figure 1-2Typical beam trawl gear crossing a pipelineIn beam trawling, a transverse steel beam is used to keep thenet open as s
26、hown in Figure 1-2. Beam shoes are mounted ateach end of the beam and represent a substantial hazard topipelines due to their sharp edges and large kinetic energy.In twin trawling the clump weight shown in Figure 1-3 has amass typically in the range of 2 to 9 tonnes, and can causelarger impact energ
27、y and pull-over loads than trawl boards.Several designs are used, ranging from a clump of chain tospherical or cylindrical rollers. Twin trawling with clumpweight is currently not used for industrial trawling, and isFigure 1-3Typical twin trawling with clump-weight.Traditionally, pipelines are prote
28、cted against trawl impact bycoating, gravel or burial. As such protection is expensive; thereis a need for improvement with respect to design methods andrules for trawl gear interference. This RP gives information ondesign methods such that unnecessary conservatism may beavoided. At the same time it
29、 intends to give a more uniformsafety level for the potential failure modes.1.2 Trawling aspectsThe authority requirements with respect to interferencebetween trawl gear and pipeline/ subsea structures vary fromcountry to country. In the Norwegian sector, it is required thatall subsea installations
30、shall not unnecessarily or to an unrea-sonable extent impede or obstruct fishing activities, whereas inother countries the authorities allow non-overtrawlable struc-tures (i.e. by applying safety zones and restricted areas onmaps, or by using guard vessels).Subsea installations attract fish, and hen
31、ce fishing activity. Agood dialog between the fishing and offshore industries isimportant in order to ensure safe and cost effective operationfor all parties. Examples of elements important to communi-cate are: pipelines preferably to be routed outside fishing bankswhenever practical, and thus, desi
32、gners need importantinformation about such; the offshore industry needs information on trawl equip-ment used, to design for appropriate loads and to reducerisk of hooking; new trawling equipment should be designed to minimizerisk of hooking pipelines, subsea structures and other sea-bed obstructions
33、; and development of new trawl equipment may have impact onexisting pipeline designs. Trawl velocity and pattern is mainly governed by fish move-ment pattern, sort of fish to catch (swimming speed), and eco-nomic speed of trawl vessels. Therefore, it is not likely that thetrawling velocity will incr
34、ease significantly in the future.Trawling for prawns is typically performed at 2 - 3 knots (1-1.5m/s), whereas trawling for fish is performed at up to 5 - 6 knots(2.8 m/s average).Presently (2005), the heaviest twin trawl equipment has a typ-ical mass up to 9-10 tonnes and is used in the Barents Sea
35、 andoutside Greenland - mainly trawling for prawn in areas withoutoffshore activities. However, trawlers operating in these areasmay also use the same heavy equipment in the North Sea or theNorwegian Sea (i.e. to avoid having two sets of equipment).The weight of the clump weights used is typically 6
36、0 - 70 % ofthe total weight of the trawl doors. Trawling along a curved path may cause the trawl equipmentpath to be considerably different from the path of the vessel.Figure 1-4 illustrates a potential scenario where the trawl ves-sel turns around a 500 m radius safety zone and causes thetrawl equi
37、pment to follow a path well within the restrictedzone, 9. It should be noted that trawling inside the safetyzones is not allowed. However experience shows that this maySweeplineTrawl boardTrawl netWarplineTrawl netWarplineBeamBeam Shoe150 - 350mClump WeightDET NORSKE VERITAShence only relevant in co
38、nsumption trawl areas. occur and should be considered in the design. Recommended Practice DNV-RP-F111, October 2006 Amended April 2007Page 8 see note on front coverFigure 1-4Possible trawl vessel and bottom trawl gear positions when fish-ing around platform safety zone.Trawl interference with pipeli
39、ne rock-berm and trenches aswell as cuttings deposited during well drilling operations andleft after removal of installations may represent considerableloading (and potential hooking) to trawl equipment. Theseaspects are not covered by this RP.1.3 Scope and applicationThe objective of this RP is to
40、provide rational criteria and guid-ance on design methods for pipelines subjected to interferencefrom trawling gear; including the impact, pull-over and possi-ble hooking phases. Design criteria are given as well as guid-ance on applicable calculation methods.For pipelines subjected to global buckling, such as:1) pipelines with release of effective, compressive axial force(buckling) prior to trawling, or 2) pipelines with release of effective, compressive axial forcesimultaneously with trawling, i.e. the trawl load triggersglobal buckling.Global buckling pipeline
