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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
1
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?
2
DNV GL © 2015
Confidential
09 February 2018
Types of FSRU moorings
3
▪ 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
DNV GL © 2015
Confidential
09 February 2018
Types of FSRU moorings
4
▪ Spread mooring
▪ Currently no FSRUs
with this mooring
alternative
DNV GL © 2015
Confidential
09 February 2018
Types of FSRU moorings
5
▪ 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
DNV GL © 2015
Confidential
09 February 2018
Types of FSRU moorings
6
▪ Current and wind directions
▪ Access to traffic lanes
▪ Emergency departure capability
▪ Impact of passing traffic
▪ Collision risk
DNV GL © 2015
Confidential
09 February 2018
What makes quayside & inshore moorings critical?
▪ Benign Environment!
▪ Accessibility!
7
DNV GL © 2015
Confidential
09 February 2018
How people tend to deal with quayside moorings?
8
DNV GL © 2015
Confidential
09 February 2018
Some examples of Gulliver getting loose!!!
9
DNV GL © 2015
Confidential
09 February 2018
Some examples of Gulliver getting loose!!!
10
DNV GL © 2015
Confidential
09 February 2018
Some examples of Gulliver getting loose!!!
11
▪ 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
DNV GL © 2015
Confidential
09 February 2018
Some examples of Gulliver getting loose!!!
12
DNV GL © 2015
Confidential
09 February 2018
Hull Damage
13
DNV GL © 2015
Confidential
09 February 2018
Hull Damage
14
DNV GL © 2015
Confidential
09 February 2018
Bollard Vertical Load
15
DNV GL © 2015
Confidential
09 February 2018
Failure Investigation Example - Lead Angles
16
Stern lines
Breast lines Breast lines
Spring lines Bow lines
▪ Typical Quayside Mooring Arrangement (OCIMF)
DNV GL © 2015
Confidential
09 February 2018
Failure Investigation Example - Lead Angles
17
Multiple Breast line failures, all on a rising tide
DNV GL © 2015
Confidential
09 February 2018
Failure Investigation Example - Lead Angles
18
Stern lines Breast lines Breast lines Bow linesSpring lines
Stern lines
Breast lines Breast lines
Spring lines Bow lines
Actual
OCIMF
DNV GL © 2015
Confidential
09 February 2018
Failure Investigation Example - Lead Angles
19
Spring, bow and stern line Breast line
70-90°
Vertical angles, if possible, should not exceed 25°
15-30°
DNV GL © 2015
Confidential
09 February 2018
Failure Investigation Example - Lead Angles
20
Tide, draught, swell, trim
etc.
1m tidal rise = 3 Te increase
1m tidal rise = 30 Te increase
DNV GL © 2015
Confidential
09 February 2018
Failure Investigation Example - Lead Angles
21
10 Tonne Force = 1m offset
10 Tonne Force = 2m offset
DNV GL © 2015
Confidential
09 February 2018
Bollard Vertical Load
22
DNV GL © 2015
Confidential
09 February 2018
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
23
DNV GL © 2015
Confidential
09 February 2018
Failure of a mooring line on board the LNG carrier Zarga
24
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.
DNV GL © 2015
Confidential
09 February 2018
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.”
25
DNV GL © 2015
Confidential
09 February 2018
Failure Investigation Example - Passing Traffic
26
10 min, falling tide
Slack line
30 Te
DNV GL © 2015
Confidential
09 February 2018
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
27
DNV GL © 2015
Confidential
09 February 2018
Mooring Line Failure Causes
28
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
DNV GL © 2015
Confidential
09 February 2018
What makes quayside & inshore moorings critical?
▪ 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
29
DNV GL © 2015
Confidential
09 February 2018
What makes quayside & inshore moorings critical?
▪ 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
30
DNV GL © 2015
Confidential
09 February 2018
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
31
DNV GL © 2015
Confidential
09 February 2018
How can DNV GL help?
32
THIRD PARTY REVIEW AND APPROVALS
SITE SPECIFIC
MOORING SOLUTIONS
▪ Click icon to add table
Sustainable & Reliable Mooring System
DNV GL © 2015
Confidential
09 February 2018
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
33
DNV GL © 2015
Confidential
09 February 2018
How can DNV GL help?
34
THIRD PARTY REVIEW AND APPROVALS
MATERIAL TESTING
SITE SPECIFIC
MOORING SOLUTIONS
▪ Click icon to add table
Sustainable & Reliable Mooring System
DNV GL © 2015
Confidential
09 February 2018
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
35
▪ Full-scale rope
testing – up to
25,000kN
▪ Sub rope testing –
up to 3,200kN
▪ Yarn testing and
soil ingress testing
DNV GL © 2015
Confidential
09 February 2018
How can DNV GL help?
36
THIRD PARTY REVIEW AND APPROVALS
MATERIAL TESTING
SITE SPECIFIC
MOORING SOLUTIONS
▪ Click icon to add table
Sustainable & Reliable Mooring System
ACCIDENT INVESTIGATION
DNV GL © 2015
Confidential
09 February 2018
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
37
DNV GL © 2015
Confidential
09 February 2018
How can DNV GL help?
38
THIRD PARTY REVIEW AND APPROVALS
MATERIAL TESTING
RULES & STANDARDS
SITE SPECIFIC
MOORING SOLUTIONS
▪ Click icon to add table
Sustainable & Reliable Mooring System
ACCIDENT INVESTIGATION
DNV GL © 2015
Confidential
09 February 2018
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
39
DNV GL © 2015
Confidential
09 February 2018
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
40
DNV GL © 2015
Confidential
09 February 2018
How can DNV GL help?
41
THIRD PARTY REVIEW AND APPROVALS
MATERIAL TESTING
RULES & STANDARDS
SITE SPECIFIC
MOORING SOLUTIONS
▪ Click icon to add table
Sustainable & Reliable Mooring System
ACCIDENT INVESTIGATION
MOORING INTEGRITY MANAGEMENT
DNV GL © 2015
Confidential
09 February 2018
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)
42
DNV GL © 2015
Confidential
09 February 2018
The Mooring Lifecycle
43
Manufacturing
Installation
In-service
Design
DNV GL © 2015
Confidential
09 February 2018
Preventing Manufacturing Defects
44
DNV GL © 2015
Confidential
09 February 2018
The Mooring Lifecycle
45
Manufacturing
Installation
In-service
Design
DNV GL © 2015
Confidential
09 February 2018
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
46
DNV GL © 2015
Confidential
09 February 2018
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
47
DNV GL © 2015
Confidential
09 February 2018
Integrity Management Process
48
DNV GL © 2015
Confidential
09 February 2018
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.
49
DNV GL © 2015
Confidential
09 February 2018
Smart Solutions to Complex Challenges
50
THIRD PARTY REVIEW AND APPROVALS
MATERIAL TESTING
RULES & STANDARDS
SITE SPECIFIC
MOORING SOLUTIONS
▪ Click icon to add table
Sustainable & Reliable Mooring System
ACCIDENT INVESTIGATION
MOORING INTEGRITY MANAGEMENT
DNV GL © 2015
Confidential
09 February 2018
SAFER, SMARTER, GREENER
www.dnvgl.com
Thank you
51
Aseem Dhingra, Senior Naval Architect
DNV GL Oil & Gas