The Use of Drag Embedment Anchors in Offshore Applications

8/17/2019 The Use of Drag Embedment Anchors in Offshore Applications

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OTEO International Conference on Offshore Renewable Energy, 10-12 May

2012, Porto

The use of drag embedment anchorsin offshore applications

by

Senol OzmutluVryhof Anchors BV – Netherlands


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The use of drag embedment anchors in offshore applications; by Senol Ozmutlu,

Offshore Renewable Energy, 10-12 May 2012, Porto

Contents

• Introduction

• Mooring systems

• Offshore foundations: Anchors

• Fluke anchors (Stevpris, Stevshark) and Plate anchors (Stevmanta VLA)

– Design

– Installation

• Real time tracking of anchor parameters (Stevtrack)

• Selected project examples and reliability levels• Conclusions


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The vryhof scope:

• design, manufacturing and supply of High Holding Power (HHP) anchors and

tensioning equipment

• selection and supply of fit-to-purpose mooring line components and connectors

on behalf of clients

• operating an alliance of leading manufacturers of mooring line components

• Installation assistance

• Engineering services


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Company milestones:

• 1972 incorporation and Stevin anchor introduction

• 1982 Stevpris anchor introduction

• 1990 vryhof group diversification program

• 1992 introduction of the mooring specialists alliance

• 1996 Stevmanta VLA concept introduction

• 1998 Stevmanta proven and operational offshore Brazil

• 2000 introduction of “Deeprope”

Stevin®, Stevpris®, Stevshark®, Stevmanta®, Stevtensioner®, Stevtrack®…….

HQ and R&D is near Rotterdam with fabrication at Rotterdam Port

Offices: Mooreast (Singapore) - Moorwest (Houston) - Vryhof do Brazil - Vryhof Russia


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Many offshore units around the world are floating structures and are moored

OIL & GAS


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RENEWABLE ENERGY & OFFSHORE CONSTRUCTION


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Projects in Renewable Energy Sector

Completed projects

• Mooring of Wave Energy devices – Offshore Scotland

• Mooring of Spar type Floating windmill HYWIND – Offshore Norway

• Mooring of Semi-sub type Floating windmill WINDFLOAT – Offshore Portugal

• Other small scale test units for wind, wave, tidal, and current devices – Europe

Projects currently running with installation targeted at 2012 – 2014

• 1 Floating windmill offshore Spain

• 2 Floating windmills offshore southern France

• 2 Floating windmills offshore Japan

• 1 floating windmill USA

• Several wind, tidal, wave, and current devices planned in Europe, Africa, Asia,Japan


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Mooring systems in general : Catenary mooring

• chain

• wire rope

• drag embedment anchor


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Mooring systems in general: Taut leg mooring

• synthetic rope

• wire rope

• vertical loaded anchor (VLA)


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MOORED OBJECT

15 mT StevprisMk5 Anchor

84 mm x 500 m

ORQ chain

Pearlink

SwivelPearlink

ShackleThimble

133 mm x 1000 m(or 1500 m)polyester rope

90 mm rig wire

SEA LEVEL

SEABED

Thimble

Shackle Pearlink

PearlinkSwivel

Mooring system elements

Mooring systems are

•Either pre-installed•or installed when the unit arrives at the location


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gravity anchorsuction pilepile

drag embedment anchor

Anchoring options

Gravity installed: DPA, torpedo, etc


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A drag embedment anchor is pulled in (dragged in) to the subseabed. Thecapacity and performance is a function of anchor type/size and the in-situ

geotechical conditions.


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Majority of the moored structures around the world uses drag anchors;

Vryhof only over 9000 anchors - about 1600 anchors on permanent systems

Stevin

Stevmanta VLA

Stevpris Mk3, Mk5 Stevshark Mk3, Mk5

Stevpris Mk6


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Installation records: project distribution world-wide


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Only a special category of drag embedment anchors is suitable for offshore use

A Class anchors


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Anchor holding capacity in medium dense silica SAND

10

100

1000

10000

1 10 100

Anchor s ize [ton] -->

T y p i c a l U l t i m a

t e H o l d i n g C a p a

c i t y [ t o n ] - -

Stevpris Mk6 Bruce FFTS Flipper Delta Moorfast Stockless


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DESIGN PROCESS : requirements / specs

Client specifies

Mooring / metocean conditions

Type of mooring system

Spread or single pointCatenary or taut or semi-taut

Type of moored object

Permanent (FPSO, FSO, FPI)

Temporary (MODU, barge, etc)

Mooring line characteristics

Anchor loads (quasi-static / dynamic)

intact

damaged

transientSpecifications and applicable codes

Site conditions

Location (maps)

Bathymetry

Geophysical data

GeohazardsGeological data

Geotechnical data

Suitable anchortype & size

fluke/shank angle setting

Drag + Penetration

Inverse catenary of forerunner

Installation requirements

Installation performanceLong term performance

Client may provide

Client requires


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• soil conditions,

• anchor type,

• anchor size

• Fluke/shank angle setting

ANCHOR HOLDING CAPACITY & ANCHOR STABILITY

is a function of

ANCHOR CAPACITY & STABILITY

is not dependent on the dead weight / dry weight of the anchor but on

the design / geometry of the anchor!!

Our designs meets the requirements of the all classifications societies or regulatory

authorities. We have working experience will all classification societies worldwide.


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Utilising results from anchor tests: Soft models

d W

d A

m

UHC

insF

drag Anchor

pW

pd A

UHC

insF n penetratio Anchor

nW

c AUHC Anchor

][** _

][** _

* _

⎥⎥⎦

⎤

⎢⎢⎣

⎡=

⎥⎥⎦

⎤

⎢⎢⎣

⎡=

=

Empirical

CBR & KBR– 9000 anchors, thousands of documented installation

Numerical, constitutive


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A simple anchor sizing exercise for generic soils

• soil : very soft clay : silica SAND

• forerunner : chain : chain

• required UHC : 400 t : 400 t

• pre-tension load : 250 t : 250 t

Stevpris Mk6 size : 10 t 5 t


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Small, middle and large fluke/shank angles.

Fluke/shank angles


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Mounting and changing fluke-shank angle is simple and quick 25 – 40 min

fluke

shank front pintle

rear pintle

sand angle mud angle


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Numerous Installation means and methods are applicable

See our anchor manual or visit www.vryhof.com

Stevpris® /Stevshark® handling/deployment with chaser


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Stevpris® /Stevshark® can be retrieved by

•using mooring line itself •PCP

•Recovery pennant

•Recovery bridle


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STEVMANTA VLA: anchor of choice for semi-taut and taut legmoorings with very high vertical and horizontal loads

Permanent moorings Temporary moorings, MODUs

Angle adjuster

Fluke plate

Wire shank

Angle adjuster

Shear pin

Chain shank

Recovery socket

Streamlined fluke plate


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Characteristics of the Stevmanta VLA

• Deep penetrating anchor in soft soils

• Suitable for supporting large vertical and horizontal loads

• Optimal choice for semi-taut and taut leg moorings

• Easy installation: installed like a conventional drag embedment anchor

• After installation, loading at any angle (0 to 90 degrees)

• Loading in all directions possible

• V/H ratio : 2.5 to 3.5

• Easy anchor recovery


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Stevmanta VLA is suitable for

high mooring loads with 0 to 90 uplift angle at the mudline AND

loading directions with 360 degrees freedom (weathervaning systems)


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Installation options: various methods are possible for details please refer toVryhof Anchor manual or www.vryhof.com/ammanual.htm

Single line installation: shear pin - angle adjuster

Option 1: Single line installation with one AHV


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Stevmanta VLA recovery

1) With tail 2) With special sockets

3) pull-back the installation line:

double line and fixed angleadjuster option


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Other installation options for drag embedment anchors are to use surface or

subsea tensioning methods

•High horizontal loads with vertical pull in the order of 40%

to 50% of the required tension

•Use of small installation vessels

•Real-time measurement and record of tension data

•Less sensitive to sea state


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Load, anchor penetration and drag can be measured

At the field by simple means


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As well as using advanced tools like Stevtrack

with the real time measurement of load at the anchor and anchor

positions/orientations


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EUROPE – NORTH SEA

•Both permanent and temporary/mobile units

•Stevpris/Stevshark common

• Anchors installed and proof tension tested 150 – 500 tons and at/above 820 tons

•Stevmanta VLA in congested areas

Stevpris®, Stevshark®, and Stevmanta® anchors have a long successful track record


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Middle East – Arabian gulf

• Permanent and temporary moorings with Stevpris / Stevshark Mk5 anchors

• 11 to 31 tons installed at 200 to 600 tons in cemented carbonate soils



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South East Asia - Australia

•Over 200 permanent projects where Vryhof anchors are being used

•Many FPSOs, FSOs, SPMs, CALM buoys etc. anchored with Stevpris & Stevshark anchors

•Many MODUs operating in the region are using Stevpris & Stevshark anchors

• Stevmanta VLAs used: MODU moorings and marine/civil construction

• Stevshark Mk5 is the anchor for Australian carbonate settings: cemented soils, calcarenite,

calcilutite, etc.

•25 mT Stevpris anchors installed and proof tension tested above 725 tons

•Stevtensioner: commonly used



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The use of drag embedment anchors in offshore applications; by Senol Ozmutlu,Offshore Renewable Energy, 10-12 May 2012, Porto

Mediterranean & AFRICA

• Stevpris and Stevshark anchors installed in record times

• MODU, SPM, FSO and FPSO moorings

• MODUs moored with Stevmanta VLAs at water depths of ~2000 m

• Single point / weatherwaning moorings with Stevmanta VLAs over 1300 m water depth

• Anchors installed and proof tension tested above 760 tons



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Brazil

• Stevpris and Stevshark are used for MODUs and permanent moorings

• 3 FPSO + 3 FPU moored with Stevmanta VLAs & Several MODUs with Stevmanta VLAs

• Water depths where Stevmanta VLAs used have reached over 2150 meters

• Design UPC level has reached over 1200 tons

• Polyester common

• 2 to 4 anchor legs are completed per day



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Central America

• Stevpris and Stevshark on MODU and permanent mooring systems

• 36 mT Stevpris Mk5 anchors in extremely soft organic soil

• Anchors proof tension tested at 688 tons



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GOM

Stevpris / Stevshark is common

Several MODUs using Stevmanta VLAs

Water depths over 1600 meters Polyester and wire rope systems

Smaller AHVs, yet 3 to 4 anchor legs per day



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Canada - Alaska

• Stevpris – Stevshark on MODUs and

permanent units

• Very dense or hard soils

• Arctic conditions

• 60 mT (15mT) Stevshark Mk5 anchors

installed at 836 tons (5-15 m drag)



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•Drag Embedment Anchors (DEA) are simple but robust offshore foundations

•Design is based on soil mechanics principles

•Requires less soil data (i.e. huge cost savings in site investigation campaigns)•Well tested and proven technology

•Large track record worldwide; Vryhof only over 9000 anchors

•Anchor capacity, penetration, drag, and long term behavior are well predicted

•DEAs are field load tested; reliability level is verified before put in service

•Simple installation methods: the installation does not require special vessels

•DEAs are recoverable and re-usable

•DEAs are cheaper than other offshore foundations; less offshore installation budget

CONCLUSIONS

The Use of Drag Embedment Anchors in Offshore Applications

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