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.

1. OMAE2011-50298
Murphy Thunder Hawk:
New Findings on Polyester and
Chain Mooring Systems
Presented by
Jonathon D. Miller P.E.

2. Overview
• Thunder Hawk Platform
• Inspection Findings
• Conditions for Corrosion
• Steel Corrosion Model
• Bio-film formation
• Rusticles – Composition
• Rusticles – Structure
• Rusticles – Other vessels
• Conclusions
• Acknowledgements

3. Thunder Hawk Platform
• 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%)

4. Thunder Hawk Platform

5. Thunder Hawk Platform
• Insert Drawing of Mooring Leg

6. Thunder Hawk Platform

7. Thunder Hawk Platform

8. Thunder Hawk Platform
~2.5m
~2m

9. Thunder Hawk Platform

10. Inspection 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

11. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Topside Chains +15m

12. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Fairlead Chains – 26m

13. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Upper Chain to Polyester H-Link – 117m

14. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Polyester Insert – 142m

15. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Upper Polyester to Polyester H-Link – 144m

16. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Lower Polyester to Polyester H-Link – 147m

17. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Upper Polyester Segment – 700m

18. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Middle Polyester to Polyester H-Link – 960m

19. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Lower Polyester Segment – 1462m

20. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Lower Polyester to Chain H-link – 1717m

21. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Lower Chain Segment – 1751m

22. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Driven Piles – 1870m

23. Year 1 Inspection-Mooring Lines
Inspection-Mooring
• Marine Life Highlights

24. The Subsea Environment –– Reinhart
Reinhart
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
pH
Surface
Salinity
300
(ppt)
600
900
1200
1500
Oxygen
1800 (mL/L)
2100 Temperature
0 1 2 3 4 5 6
0 2 4 6 8 10 12 14 16 18 (°C)

25. Steel Corrosion Model –– Melchers
Melchers
Corrosion ra rs
Loss
Localized anaerobic
cs
conditions have
developed
ca
ro ta Exposure Period
Phase 4
Phase 3
Phase 2
Phase 1
Phase 0

26. Water Temperature Impact –– Melchers
Melchers
0.4
0.35 20°C
Corrosion Loss (mm)
28°C
0.3 10°C
4°C
0.25
0.2
0.15
0.1
0.05
0
0 1 2 3 4 5 6
Exposure Period (years)

27. Bio-film Formation –– Dreeszen
Bio-film Dreeszen

28. Bio-film Formation –– Borenstein
Bio-film Borenstein
(1)= O2 + 2H2O + 4e- → 4OH- (cathodic)
(2)= Fe → Fe++ + 2e- (anodic)
(3)= 4Fe++ + O2 + 10H2O → 4Fe(OH)3 + 8H+
(tubercle formation)

29. Rusticles – Titanic -- Droycon BioConcepts Inc.
Droycon BioConcepts Inc.

30. Rusticles – Composition –– Pellegrino et. al.
Pellegrino et. al.
• Titanic Rusticles – 20-35% Iron
• Other Shipwrecks – 79.7-92.2% Iron

31. Rusticles – Structure –– Cullimore et. al.
Cullimore et. al.
Central Water Channel

32. Rusticles – Structure –– Cullimore et. al.
Cullimore et. al.
γ
Fe3+O(OH)
α
Fe3+O(OH)

33. Rusticles – Structure –– Frankel et. al.
Frankel et. al.

34. What Do Rusticles Do? –– Ray et. al.
Ray et. al.
Before
After
(Pitting)

35. Conclusions
• Does corrosion occur at 1800m depth?
• Is corrosion life predictable?
• Should corrosion allowances be maintained?
• Corrosion occurs in a hypoxic environment?

• ro  f (T , O2 , vo , pH )
• Rusticles evidence of steel corrosion?
• Synthetic Rope Moorings corrosion solution?

36. Acknowledgements
• 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

37. QUESTIONS?
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