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

0.03

0.04

0.05

0.06

0.07

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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