oil & gas challenges of nearshore and quayside fsru …€¦ · a vessel broke away from the...

DNV GL © 2015

Confidential

09 February 2018 SAFER, SMARTER, GREENERDNV GL © 2015

09 February 2018

Confidential

OIL & GAS

Challenges of nearshore and quayside FSRU moorings

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Aseem Dhingra

Senior Naval Architect, Noble Denton marine services

DNV GL © 2015

Confidential

09 February 2018

Contents

▪ Types of FSRU moorings

▪ What makes quayside & inshore moorings critical?

▪ Quayside mooring incidents

▪ Failure investigation examples

▪ How can DNV GL help?

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Types of FSRU moorings

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▪ Turret mooring (Single

point mooring)

➢ Weather-vaning

freely

➢ Heading control to

limit roll motions

➢ Export of natural

gas to the onshore

network through

turret or flexible

risers

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▪ Spread mooring

▪ Currently no FSRUs

with this mooring

alternative

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▪ Permanently moored to

a jetty

➢ Used in benign

water conditions

(protected

location)

➢ Export of natural

gas to onshore

network through

loading arms or

flexible hoses

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▪ Current and wind directions

▪ Access to traffic lanes

▪ Emergency departure capability

▪ Impact of passing traffic

▪ Collision risk

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What makes quayside & inshore moorings critical?

▪ Benign Environment!

▪ Accessibility!

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How people tend to deal with quayside moorings?

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Some examples of Gulliver getting loose!!!

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▪ Oil tanker crashed

into the Mildred

Long Bridge

▪ Caused by a failure

of the ship’s

mooring system

▪ Lucky! Only $3.5m

in damages to

bridge and ship

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Hull Damage

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Hull Damage

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Bollard Vertical Load

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Failure Investigation Example - Lead Angles

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Stern lines

Breast lines Breast lines

Spring lines Bow lines

▪ Typical Quayside Mooring Arrangement (OCIMF)

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Multiple Breast line failures, all on a rising tide

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Stern lines Breast lines Breast lines Bow linesSpring lines

Stern lines

Breast lines Breast lines

Spring lines Bow lines

Actual

OCIMF

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Spring, bow and stern line Breast line

70-90°

Vertical angles, if possible, should not exceed 25°

15-30°

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Tide, draught, swell, trim

etc.

1m tidal rise = 3 Te increase

1m tidal rise = 30 Te increase

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10 Tonne Force = 1m offset

10 Tonne Force = 2m offset

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Bollard Vertical Load

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Winch Failure

▪ A vessel broke away from the berth under the influence of a strong ebb tide

▪ 2 spring, 1 breast and 1 stern line failed and the remaining lines ran off the winches. The

winches were found to be ineffective in holding the vessel in position and the vessel ran

aground in the channel

▪ This incident highlights the potential for serious consequences to result from a mooring

incident

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Failure of a mooring line on board the LNG carrier Zarga

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A deck officer suffered severe head injuries when he was struck by a parted HMPE mooring rope during a berthing operation at South Hook LNG terminal, Milford Haven on 2 March 2015.

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HMPE Rope Degradation – Zarga (MAIB Report 13/2017)

▪ HMPE appears to be a special case with a particularly high rate of failure

▪ Causes of HMPE failure has been explored in depth in the Zarga MAIB report:

– 50% of rope failures occurred at <16% of MBL for the general population of HMPE ropes

used on LNG vessels

– Axial compression fatigue was identified as the primary cause of the rope failure at much

less than MBL

– The rope jacket restrains the internal filaments, which allow them to form kinks. The fibre

can fail at the kink points, which reduces the rope residual strength.

– Bending around a small diameter fairlead relative to the rope diameter could cause kink

formation. Kinks were also found to be formed in the rope core during the manufacturing

process

– The report concludes: “Ropes to be used in his application need to be designed more

robustly....need to be subject to a rigorous test programme and manufacturers should be

able to demonstrate this to vessel operators and ports.”

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Failure Investigation Example - Passing Traffic

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10 min, falling tide

Slack line

30 Te

Video 2.avi

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Failure Investigation Example - Degradation

▪ Failures much below MBL

▪ Degradation

– Internal abrasion (iron ore particles could be a factor)

– Fatigue (flex fatigue due to bending around fairlead)

– Temperature

– UV damage

– Cutting & chafing

– Creep

– Twists, kinks and hockles

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Mooring Line Failure Causes

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LoadResistance

▪ UV damage

▪ Abrasion

▪ Fatigue

▪ Fairlead design

▪ …

▪ Passing traffic

▪ Tide

▪ Current

▪ Wind

▪ Line tension

adjustment

▪ Lead angles

▪ …

MBL=100 Te Design load=20-50 Te

Degraded

capacity

Actual load

FAILURE

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▪ Short taut lines which can lead to very high tensions with even very small

magnitude of motions

▪ Sensitivity to the stiffness of mooring lines

▪ Uncertainty in the calculation of environmental forces due to wind shear effects

and shallow water blockage effects

▪ Potential for failures due to chafe points and abrasion

▪ Potential for failures due to degraded components and /or connection points on

the vessel and shore

▪ Multiple connections - multiple modes of failure - different levels of reliability

▪ Potential limitations on the ability to adjust moorings and balance the line

tensions in adverse weather conditions

▪ High consequence of failure given the proximity to shore, other assets and limited

response time

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▪ FSRU

– LNG Carrier mooring to FSRU

– Hydrodynamic interaction

– Waves from passing ships

– 100 year return design environment

– Tsunami

– Remain or depart in extreme environmental events

– Effect of line failure on operation

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Failure statistics

▪ Qmax and Qflex vessels in the LNG industry have a reported failure rate of 1.5%

per vessel visit (Ref Zarga MAIB report)

▪ Marine Accident Investigation Branch (MAIB): The MAIB investigates marine

accidents involving UK vessels worldwide and all vessels in UK territorial waters.

https://www.gov.uk/government/organisations/marine-accident-investigation-

branch

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https://www.gov.uk/government/organisations/marine-accident-investigation-branch

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How can DNV GL help?

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THIRD PARTY REVIEW AND APPROVALS

SITE SPECIFIC

MOORING SOLUTIONS

▪ Click icon to add table

Sustainable & Reliable Mooring System

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Designing for Long Term Integrity

▪ Environment: appropriate averaging and return periods

▪ Vessel vertical motions, e.g. due to tide variations and waves from passing

vessels

▪ Shallow water effects

▪ Line make-up – stiffness, pretensions

▪ Redundancy

▪ Hydrodynamic interaction

▪ Multiple connections – multiple modes of failure - different levels of reliability

▪ Suitability & compatibility of the components

▪ Fendering

▪ Storm surges (positive and negative), Seiche (wind induced wave effects close to

shore), Waves/Swell (exposed berths), Tsunami

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MATERIAL TESTING

SITE SPECIFIC

MOORING SOLUTIONS



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Materials testing and qualification

▪ DNV GL operates 14 laboratories across 3 continents

▪ Some of the most important and progressive laboratories and test facilities in the

industry.

▪ Materials testing and qualification

▪ Failure analysis and failure investigation

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▪ Full-scale rope

testing – up to

25,000kN

▪ Sub rope testing –

up to 3,200kN

▪ Yarn testing and

soil ingress testing

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MATERIAL TESTING

SITE SPECIFIC

MOORING SOLUTIONS



ACCIDENT INVESTIGATION

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Failure Investigations - Typical solutions

▪ LOAD REDUCTION

– Develop standard mooring arrangements for each berth and vessel size

– Passing traffic speed and distance limits

– Tailor tension limits to specific berths and mooring lines

– Enforce line tending frequency and minimum crew manning/competence

▪ CAPACITY INCREASE / MAINTENENCE

– Line type recommendations (e.g. specific material and strength required)

– Service Life and Inspection and maintenance philosophy

– Damage assessment and line replacement philosophy

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MATERIAL TESTING

RULES & STANDARDS

SITE SPECIFIC

MOORING SOLUTIONS




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DNV GL Guidelines on Moorings

▪ DNV GL offshore standard, Position mooring, DNVGL-OS-E301

– Primarily for design of offshore moorings

▪ DNV GL offshore standard, Marine operations and marine warranty, DNVGL-ST-

N001

– Amalgamation of legacy DNV-OS-H### series and legacy Noble Denton

Guidelines

– Provides comprehensive guidance on quayside and inshore moorings

– Cover long term moorings, but is mostly focussed on relatively short term

moorings of O&G structures

▪ Offshore Technical Guidance, Guidance for near shore mooring systems, DNVGL-

OTG –18

– Focussed on permanent moorings

– Expected to be released in April 2018

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Other DNV GL Guidelines on Moorings

▪ DNV GL offshore standards (OS)

– Offshore mooring chain, DNVGL-OS-E302

– Offshore fibre ropes, DNVGL-OS-E303

– Offshore mooring steel wire ropes, DNVGL-OS-E304

▪ DNV GL class programmes (CP)

– Type approval: Synthetic fibre ropes for towing, mooring and anchoring,

DNVGL-CP-0100

– Approval of manufacturers: Wire ropes, DNVGL-CP-0255

▪ DNV GL recommended practices (RP)

– Damage assessment of fibre ropes for offshore mooring, DNVGL-RP-E304

– Design, testing and analysis of offshore fibre ropes, DNVGL-RP-E305

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MATERIAL TESTING

RULES & STANDARDS

SITE SPECIFIC

MOORING SOLUTIONS




MOORING INTEGRITY MANAGEMENT

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MOORING INTEGRITY MANAGEMENT (MIM)

▪ Though originally devised for offshore permanent mooring systems, the process

can bring significant benefits for the long term nearshore and quayside moorings

▪ It is a continuous process to assure mooring system remains reliable and

managed cost effectively and safely for full lifecycle.

▪ MIM follows the lifecycle of a mooring system from design to operation.

– During design, failure modes are identified, risks evaluated and control

measures defined considering the long term mooring integrity (e.g. Suitability &

compatibility of the components)

– Manufacturing (e.g. Procurement process, vendor selection),

– Installation (e.g. equipment handling, pre-tensioning, pre/post-installation

survey, procedures),

– Operation (e.g. monitoring & inspection, maintenance, failure response)

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The Mooring Lifecycle

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Manufacturing

Installation

In-service

Design

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The Mooring Lifecycle

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Manufacturing

Installation

In-service

Design

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Operational considerations

▪ Operating procedures should detail and quantify, where applicable,

– mooring tension monitoring, & inspection

– mooring line tending arrangements

– emergency response arrangements, including spare equipment and availability

of tugs and shore-based manpower

▪ LNG Carrier Berthing – direction & magnitude of current, no. of tugs and

configuration, potential whiplash/snap back zones

▪ Disconnection philosophy

▪ Inspection and Maintenance of Mooring Systems- Risk Based Inspection

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Inspection and Maintenance of Mooring Systems (Risk Based Inspection)

▪ Establishment of inspection regime – based on redundancy of the system,

calculated safety factors, type of mooring lines, variation in loads and locations

vulnerable to damage.

▪ Process should be:

– determine feasible failure modes for each component

– mitigate against failure by design if possible

– for residual risk, implement a monitoring, inspection and maintenance strategy

to cover likely failure modes for each component

▪ Chafe points.

▪ Wear, UV exposure and other environmental influences

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MOORING INTEGRITY MANAGEMENT (MIM)

▪ MIM provides a basis for enhancing or reducing inspection frequency and scope

depending on the failure risk of the component.

▪ This enables reliability, availability and safety of complex systems to be increased,

whilst having the potential to reduce inspection costs over the life-cycle of an

asset.

▪ A risk based approach to mooring integrity management is well fitted to FSRU

since conditions and configurations are possibly changing and so should the

integrity management planning.

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Smart Solutions to Complex Challenges

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MATERIAL TESTING

RULES & STANDARDS

SITE SPECIFIC

MOORING SOLUTIONS




MOORING INTEGRITY MANAGEMENT

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09 February 2018

SAFER, SMARTER, GREENER

www.dnvgl.com

Thank you

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Aseem Dhingra, Senior Naval Architect

DNV GL Oil & Gas

[email protected]

oil & gas challenges of nearshore and quayside fsru …€¦ · a vessel broke away from the...

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