Service life of synthetic fibre ropesin deepwater lifting operations
The 15th North Sea Offshore Cranes & Lifting ConferenceAshley Nuttall
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Fibre ropes for deepwater liftingFibre ropes offer the following advantages• Lightweight construction is self-buoyant
• Easy to handle
• Possibility to make easy repairs with splices
However• Fibre ropes for dynamic lifting operations are a
relatively new development in the offshoreindustry
• Greater operational risks for lifting than formooring
• Little practical experience to base the design oflifting equipment on, thus implementation presentsvarious engineering challenges
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Deep water potential of fibre ropes
Example: Offshore Mast Crane• Single fall 200 ton capacity on the surface
• 92 mm steel wire rope• Submerged rope weight 36 kg/m
• At 3000 m water depth the rope weight is 108 ton
• Effective capacity at 3000 m is 92 ton
With a steel wire rope the crane capacity morethan halves at 3000 m depthA fibre rope with Dyneema® is self-buoyant thustheoretically the crane retains its 200 ton capacity
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Engineering challenges
• Service life• Discard criterion
• Safety factors
• Certification• Drum spooling
• Abrasive wear
Fibre ropes show large potential for deep water liftingoperationHowever for implementation questions have arisen ondifferent issues like
+ = ?
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Combined research activity
Huisman Equipment and DSM Dyneema are working together totackle these challenges
Goals• Develop deep water lifting equipment that can work with
synthetic fibre ropes
• Create a rope manual that can be used for the design of deepwater lifting equipment
Current focus on• Bend-over-sheave fatigue• Abrasion
• Winch design
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Service life and bend-over-sheave fatigue
Bend-over-sheave fatigue depends on• Rope construction• Rope diameter• Line pull• Sheave diameter• Groove radius and shape• Fleet angle• Load frequency• Temperature
Bend fatigue life prediction requires aconsistent set of measurement data
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Bend fatigue test data
• Target rope: fibre rope with Dyneema®, 12x1 braidedconstruction and DSM Dyneema coating
• Rope diameters: 8, 20, 50 and 80 mm
• Line pull: safety factors ranging between 2 to 10• Sheave diameter: D/d of 10, 20 and 30
• Groove radius: r/d of 0.5 and 0.53
• Low load frequency or cooled rope
Setup a model to predict rope life time within the given rangeof input parameters
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Bend-over-sheave fatigue model
drlogadloga
dD
dFloga
dDloga
dFloga
dFloga
dFlogaaNlog 762542
332
22210
Single bendsto failure
Influence of: Safety factor Sheave diameter Rope diameterGroove radius‘Life factor’
For steel wire ropes the Feyrer equation is commonly used
Modified version for synthetic fibre rope with Dyneema®
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Tuning of model with test data
100
F/d² [N/mm²]
Nfa
il[S
ingl
e be
nds] d = 8 mm, D/d = 10, r/d = 0.53
d = 8 mm, D/d = 20, r/d = 0.53
d = 8 mm, D/d = 30, r/d = 0.53
d = 20 mm, D/d = 20, r/d = 0.50
d = 80 mm, D/d =30, r/d = 0.50
300 50080
Model serves as input forrope service life estimation
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50 mm tests with Huisman’s test machine
Driven sheave End connections Rope pathwith counter bending
Rope pathwithout counter bending
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50 mm bend fatigue test results
34000
3030
9070
28440
0
5000
10000
15000
20000
25000
30000
35000
40000
Trefil complast 9 Rope withDyneema®
Dry test
Rope withDyneema®
Wet test
Rope with Dyneema®Bend optimised
Wet test
Num
ber o
f mac
hine
cyc
les
[-]
Optimization of fibreconstruction and
coating
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Abrasion due to spooling
• Spooling of a rope to and from a winch can lead to abrasion andlimit the rope’s service life
• Abrasion results from rope-to-rope and rope-to-flange contact
• This abrasion is similar to drum crushing of steel wire ropes
This effect was investigatedin a combined effort with• Huisman
• DSM• Jumbo Offshore
Rotterdam
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Winch spooling test installation
16 m
24 m
Winches supplied by Jumbo- 36 mm rope- Line pull 400 kN up to 6 layers- Lebus grooved shells- Filler pieces to reduce width
Winch test tower- Direct winch-to-winch spooling- Winch 1 regulates tension- Winch 2 regulates speed
Virtually any lifting scenariocan be simulated
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Abrasive spool test
• Continuous spooling and unspooling of 4 windings• Varying linepull to create slippage between layers
• Test locations at the center of the 1st and 3rd layer and at theflange from the 1st to the 2nd layer
• Residual strength determinedafter spooling test
Most abrasive wear occursbetween adjacent layers
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Residual strength measurements
0
0.2
0.4
0.6
0.8
1
Machine cycles [-]
Res
idua
l str
engt
h [-]
Winch 1 centre of layer 1 Winch 2 centre of layer 3
Effect of the number of cycles on the residual rope strength afterabrasion test
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Estimation of rope service life
0 1 2 3 4 5 n-5 n-4 n-3 n-2 n-1 nFline pull Fline pull
s1 s2 s20s19s18s3
s1 s2 s20s19s18s3
Hoisting
Winch
Winch Dead end
Dead end
half
bend
reve
rsal
full
bend
reve
rsal
half
bend
reve
rsal
Quay Crane atHuisman for inservice testing
Identification ofsystem points
3
5
6
9
10
13
15
17
14
1
2
4
8
12
11
7
1618
19
20
Administration of rope movementand occurring bends
n: number of nodess: rope section
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 100 200 300 400 5000
0.01
0.02
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0.05
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0.08
0.09
0 100 200 300 400 500
Rope length [m]
Estimation of rope service life
Radius
0 1 2 3 4 5 6 7Step
Hookload
Hookheight
Load cycle diagram
0
5
10
15
20
0 5 10 15 20 25 30 35 40Load [mt]
Cyc
les/
day
[-]
Load spectrum
Rope condition along rope
Heaviest loaded rope section determinesrope service life
Identification of critical sections aids ropeinspection
Dam
age
inde
x [-]
n
1i iifailure
i
)d,D,S(NNindexdamage
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Conclusions
• Synthetic fibre ropes with Dyneema® show potential for deepwater lifting operations
• Collaboration helps to fill the knowledge gaps and increasesconfidence
• Consistent bend and abrasion fatigue data makes service lifepredictions possible
• Combined with a rope monitoring system a bend fatigue andabrasion model can aid rope inspections
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Questions
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