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RECOMMENDED PRACTICE DNV-RP-F109

ON-BOTTOM STABILITY DESIGN OF SUBMARINE PIPELINESOCTOBER 2010

DET NORSKE VERITAS

FOREWORDDET NORSKE VERITAS (DNV) is an autonomous and independent foundation with the objectives of safeguarding life, property and the environment, at sea and onshore. DNV undertakes classification, certification, and other verification and consultancy services relating to quality of ships, offshore units and installations, and onshore industries worldwide, and carries out research in relation to these functions. DNV service documents consist of amongst other the following types of documents: Service Specifications. Procedual requirements. Standards. Technical requirements. Recommended Practices. Guidance. The Standards and Recommended Practices are offered within the following areas: A) Qualification, Quality and Safety Methodology B) Materials Technology C) Structures D) Systems E) Special Facilities F) Pipelines and Risers G) Asset Operation H) Marine Operations J) Cleaner Energy

O) Subsea Systems

The electronic pdf version of this document found through http://www.dnv.com is the officially binding version Det Norske Veritas Any comments may be sent by e-mail to rules@dnv.com For subscription orders or information about subscription terms, please use distribution@dnv.com Computer Typesetting (Adobe Frame Maker) by Det Norske Veritas

If any person suffers loss or damage which is proved to have been caused by any negligent act or omission of Det Norske Veritas, then Det Norske Veritas shall pay compensation to such person for 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 compensation shall never exceed USD 2 million. In this 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 Det Norske Veritas.

Recommended Practice DNV-RP-F109, October 2010 Changes Page 3

Acknowledgements The following companies are gratefully acknowledged for their contributions to this Recommended Practice: DHI Hydro Marintek PRCI Statoil Woodside DNV is grateful for the valuable cooperation and discussions with the individual personnel representing these companies. CHANGES General Main changes

As of October 2010 all DNV service documents are primarily published electronically. In order to ensure a practical transition from the print scheme to the electronic scheme, all documents having incorporated amendments and corrections more recent than the date of the latest printed issue, have been given the date October 2010. An overview of DNV service documents, their update status and historical amendments and corrections may be found through http://www.dnv.com/resources/rules_standards/.

Since the previous edition (October 2003), this document has been amended, most recently in April 2006. All changes have been incorporated and a new date (October 2010) has been given as explained under General.

DET NORSKE VERITAS

Recommended Practice DNV-RP-F109, October 2010 Page 4 Changes

DET NORSKE VERITAS

Recommended Practice DNV-RP-F109, October 2010 Contents Page 5

CONTENTS1. 1.1 1.2 1.3 1.4 1.5 GENERAL .............................................................. 7 Introduction .............................................................7 Objective...................................................................7 Relationships to other codes ...................................7 Safety philosophy.....................................................7 Symbols.....................................................................73.4.3 3.4.4 3.4.5 3.4.6 Short term wave conditions .............................................. 11 Wave directionality and spreading ................................... 12 Hydrodynamic loads......................................................... 13 Soil Resistance.................................................................. 14

3.53.5.1 3.5.2

Generalized lateral stability method ................... 15Introduction ...................................................................... 15 Design curves ................................................................... 15

1.5.1 1.5.2

Latin.................................................................................... 7 Greek................................................................................... 8

3.63.6.1 3.6.2 3.6.3 3.6.4 3.6.5

Absolute lateral static stability method............... 17Introduction ...................................................................... 17 Design criterion ................................................................ 17 Safety factors .................................................................... 17 Loads ................................................................................ 17 Resistance ......................................................................... 19

2. 2.1 2.2 2.3 2.4 2.5 3. 3.1 3.2 3.3 3.4

DESIGN................................................................... 8 Target failure probability .......................................8 Load combinations ..................................................8 Weight calculations .................................................8 Resistance calculations............................................8 Design criterion........................................................8 DESIGN METHODS ............................................. 9 Introduction .............................................................9 Vertical stability in water .......................................9 Vertical stability on and in soil...............................9 Dynamic lateral stability analysis ..........................9

4. 4.1 4.2 4.3 4.4 4.5 5.

MISCELLANEOUS............................................. 19 Free spans .............................................................. 19 Mitigating measures.............................................. 19 Curved laying ........................................................ 19 Seabed stability...................................................... 19 Soil liquefaction ..................................................... 20 REFERENCES..................................................... 20

APP. A STABILITY CURVES FOR CLAY ................. 21 APP. B CARBONATE SOILS........................................ 26

3.4.1 3.4.2

Introduction......................................................................... 9 Current Conditions............................................................ 10

DET NORSKE VERITAS

Recommended Practice DNV-RP-F109, October 2010 Page 6 Contents

DET NORSKE VERITAS

Recommended Practice DNV-RP-F109, October 2010 Page 7

1. General1.1 IntroductionThe present document considers on-bottom stability design for submarine pipelines subjected to wave and current loading. The premises of the document are based on technical development and experience. The basic principles applied in this document are in agreement with most recognised rules and reflect state-of-the-art industry practice and latest research. Other data and/or methods than those described herein may be used if a sufficient level of safety can be documented.

Gs FY FZ FR FC Hs H* Kb k kT kU kV K K*

Soil (sand) density parameter =

s' . g w

Horizontal hydrodynamic (drag and inertia) load. Vertical hydrodynamic (lift) load. Passive soil resistance, Ref. Eq. 3.23. Vertical contact force between pipe and soil, Ref. Eq. 3.24. Significant wave height during a sea state. Maximum wave height during a sea state. Equivalent sand roughness parameter = 2.5d50. Wave number given by2g = k tanh k d .

1.2 ObjectiveThe main objective of this document is to provide rational design criteria and guidance for assessment of pipeline on-bottom stability subjected to wave and current loading.

Ratio between period of single design oscillation and design spectrum = T * / Tu . Ratio between oscillatory velocity amplitude of single design oscillation and design spectrum = U * / U s . Ratio between steady velocity component applied with single design oscillation and with design spectrum. Significant Keulegan-Carpenter number = U s Tu / D . Keulegan-Carpenter number for single design oscillation = U * T * / D . Significant weight parameter =ws . 0.5 w D U s2

1.3 Relationships to other codesThis document formally supports and complies with the DNV Offshore Standard Submarine Pipeline Systems, DNV-OSF101, 2000 and is considered to be a supplement to relevant National Rules and Regulations. In case of conflict between requirements of this RP and a referenced DNV Offshore Code, the requirements of the code with the latest revision date shall prevail. In case of conflict between requirements of this code and a non DNV referenced document, the requirements of this code shall prevail.Guidance note: Any conflict is intended to be removed in next revision of that document.---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---

L L*

Weight parameter related to single design oscillation ws . = 2 0.5 w D U * + V *

(

)

M M* Mn

1.4 Safety philosophyThe safety philosophy adopted herein complies with section 2 in DNV-OS-F101. The design of submarine pipelines against excessive displacement due to hydrodynamic loads is ensured by use of a Load and Resistance Factors Design Format (LRFD). For the absolute stability criterion, the set of safety factors is calibrated to acceptable failure probabilities using reliabilitybased methods. For other design criteria, th