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During a Post Installation Mooring Inspection at Mississippi Canyon block 736, curious growths were noted on the chain which are evidence of Microbiologically Influenced Corrosion (MIC). These growths were also observed on subsea shipwrecks such as the Titanic and in some conditions corrode steel at a surprising rate. Though observation of these tubercles does not accelerate their growth rate, designers should consider corrosion rates in their design even at depths of 6000 feet below sea level. Corrosion can and does occur in an anoxic environment and designers should not relax their corrosion allowances for chains at depth.
Citation preview
OMAE2011-50298
Murphy Thunder Hawk:New Findings on Polyester and
Chain Mooring SystemsPresented by
Jonathon D. Miller P.E.
OMAE2011-50298
Murphy Thunder Hawk:New Findings on Polyester and
Chain Mooring SystemsPresented by
Jonathon D. Miller P.E.
OverviewOverviewOverview
• Thunder Hawk Platform• Inspection Findings• Conditions for Corrosion• Steel Corrosion Model• Bio-film formation• Rusticles – Composition• Rusticles – Structure• Rusticles – Other vessels• Conclusions • Acknowledgements
Thunder Hawk PlatformThunder HawkThunder Hawk PlatformPlatform
• 45,000 BOPD Oil• 70,000,000 CFPD Gas• 71 x 71 x 52 m hull• 10,250 tons operating wt• Murphy (37.5%) • ENI (25%)• StatOilHydro (25%)• Marubeni Oil (12.5%)
Thunder Hawk PlatformThunder Hawk Thunder Hawk PlatformPlatform
Thunder Hawk PlatformThunder Hawk Thunder Hawk PlatformPlatform
• Insert Drawing of Mooring Leg
Thunder Hawk PlatformThunder Hawk Thunder Hawk PlatformPlatform
Thunder Hawk PlatformThunder Hawk Thunder Hawk PlatformPlatform
Thunder Hawk PlatformThunder Hawk Thunder Hawk PlatformPlatform
~2m
~2.5m
Thunder Hawk PlatformThunder Hawk Thunder Hawk PlatformPlatform
Inspection FindingsInspection FindingsInspection Findings
• Top Chains – Twist Free• Fairleads – Intact• Fairlead Chains – Intact• Polyester Ropes – Intact• H-link hardware – Intact• Ground Chain – Intact • Ball-grab connectors – Not visible• Anchors – Intact
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Topside Chains +15m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Fairlead Chains – 26m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Upper Chain to Polyester H-Link – 117m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Polyester Insert – 142m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Upper Polyester to Polyester H-Link – 144m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Lower Polyester to Polyester H-Link – 147m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Upper Polyester Segment – 700m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Middle Polyester to Polyester H-Link – 960m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Lower Polyester Segment – 1462m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Lower Polyester to Chain H-link – 1717m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Lower Chain Segment – 1751m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Driven Piles – 1870m
Year 1 Inspection-Mooring LinesYear 1 InspectionYear 1 Inspection--Mooring LinesMooring Lines
• Marine Life Highlights
The Subsea Environment – ReinhartThe Subsea Environment The Subsea Environment –– ReinhartReinhart
Surface
300
600
900
1200
1500
1800
2100
6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2
33.0 33.2 33.4 33.6 33.8 34.0 34.2 34.4 34.6 34.8
0 1 2 3 4 5 6
0 2 4 6 8 10 12 14 16 18
pH
Salinity
(ppt)
Oxygen
(mL/L)Temperature
(°C)
Steel Corrosion Model – MelchersSteel Corrosion Model Steel Corrosion Model –– MelchersMelchers
Corrosion Loss
ra rs
ro
ca
cs
ta
Localized anaerobic conditions have developed
Exposure Period
Phase 0Phase 1
Phase 2Phase 3
Phase 4
Water Temperature Impact – MelchersWater Temperature Impact Water Temperature Impact –– MelchersMelchers
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
00 1 2 3 4 5 6
Exposure Period (years)
Cor
rosi
on L
oss
(mm
) 20°C28°C
10°C4°C
Bio-film Formation – DreeszenBioBio--film Formation film Formation –– DreeszenDreeszen
Bio-film Formation – BorensteinBioBio--film Formation film Formation –– BorensteinBorenstein
(1)= O2 + 2H2O + 4e- → 4OH- (cathodic)
(2)= Fe → Fe++ + 2e- (anodic)
(3)= 4Fe++ + O2 + 10H2O → 4Fe(OH)3 + 8H+
(tubercle formation)
Rusticles – Titanic - Droycon BioConcepts Inc.Rusticles – Titanic - Droycon BioConcepts Inc.
Rusticles – Composition – Pellegrino et. al.Rusticles Rusticles –– Composition Composition –– Pellegrino et. al.Pellegrino et. al.
• Titanic Rusticles – 20-35% Iron• Other Shipwrecks – 79.7-92.2% Iron
Rusticles – Structure – Cullimore et. al.Rusticles Rusticles –– StructureStructure –– CullimoreCullimore et. al.et. al.
Central Water Channel
Rusticles – Structure – Cullimore et. al.Rusticles Rusticles –– Structure Structure –– CullimoreCullimore et. al.et. al.
γFe3+O(OH)
αFe3+O(OH)
Rusticles – Structure – Frankel et. al.Rusticles Rusticles –– Structure Structure –– Frankel et. al.Frankel et. al.
What Do Rusticles Do? – Ray et. al.What Do Rusticles Do?What Do Rusticles Do? –– Ray et. al.Ray et. al.
(Pitting)
After
Before
• Corrosion occurs in a hypoxic environment?
ConclusionsConclusionsConclusions
• Does corrosion occur at 1800m depth?
• Is corrosion life predictable?
),,,( 2 pHvOTfr oo
•
• Rusticles evidence of steel corrosion?
• Should corrosion allowances be maintained?
• Synthetic Rope Moorings corrosion solution?
AcknowledgementsAcknowledgementsAcknowledgements
• Co-Authors– Luc Chabot– Jim Jenkins– Brett Warren
• Conference Reviewers and Administrators– Ron Riggs– René Huijsmans– Joel Witz– Johann Wichers
• American Society of Mechanical Engineers• Kivi Niria• OMAE 2011
E x p e c t M o r e . . . G e t M o o r .
QUESTIONS?QUESTIONS?