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PETROWORLD INDIA 2013 CONFERENCE

“STATE OF THE ART PIPELAY ANALYSIS”

Paper presented by;

In Association with;

Herman PereraZee Engineering Sdn Bhd

Tarun RewariAryatech Marine & Offshore Services Pvt Ltd

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INTRODUCTION

• Installation is a Major cost driver in Submarine Pipelines.• Installation cost directly related to;

- Methodology adopted,- Required Offshore spreads.

• Methodology- To justify the cost effective methodology extensive computer simulations

need to be carried out.• Offshore Spreads

- Day rate for traditional DLB’s can range from 100$/day to 3000-4000$/dayor more.

- DLB Capacity (Tensioner) can be optimized using a reliable computerpackage.

• Curent trend in pipelines are increasing rapidly Demand in Energy Requirements for domestic consumption andindustrialization resulting in;- Rehabilitation/Replacement of existing lines,- New lines (infield flow and transportation lines)- Marginal field development.

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INTRODUCTION (CONT.)

• New lines (larger diameter and longer)Standard DLB need to be used

• In-field lines (smaller diameter, shorter)Minimum DLB or non traditional methods are cost effective.

• Marginal Field DevelopmentThe installation method is the cost driver. Minimum DLB or non traditionalmethods need to be adopted.

• Computer Simulation- According to latest codes dynamic simulation is mandertory.- Vigorous simulation (non linear/dynamic time domain) may result in

considerable reduction of costs.- Such as establishing the minimum tensioner requirement which willresult in type and capacity of the DLB.

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OBJECTIVE OF PAPER

• Computer Simulation- Depends on Methodology- Static- Dynamic- Pseudo-Dynamic- Results are theoretical hence accadamic

• Objective- To present a software with results varified by- Model test- Field data

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BACKGROUND• Zee Engineering

- Over 25 years experience in submarine pipeline design.- Completed nearly 250 pipelines.- Has developed pipeline installation software.- Has used a number of industry approved pipeline installation softwarepackages- Ansys- Marcs- Sesam- Pipeline- Offpipe- Orcaflex

• We humbly feel that we are qualified to carry out comparative studies on various pipeline installation software packages.

• We are not condemning or crilizing any software but sharing our experience.• The presentation is based on our personnell views.

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Project Description• PROJECT NAME : Labuan Pipeline (Malaysia)

Submarine pipeline from mainland to Labuan Island to supplyfresh water.

• EPCC contractor : Kencana/Lleighton Joint Venture (KLJV)• Line Description : 26 inch diameter, approx length 23.0 km

- Wall thickness 9.5mm- Steel API 5L x 52- Weight Coating

Concrete density of 2.4MT/m3Varying thickness of 125mm to 75mm

- Reinforcement 32nos 8mm steel rods will 8mm rings at 80mm CRS.

- Concrete cast in moulds and compacted- Water depths 26m to 1.0m

PIPELAY ANALYSIS

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PIPELAY ANALYSIS (CONT.)• Installation Methods

- Traditional “S” lay- Surface Tow (Rentis)- Shore Pull- Mid point tie in

• For all the methods single program Orcaflex was used.• Advantages

- Single data file.- QA/QC made easy.

Failure• The pipelay operation was attempted by a contractor and abandoned due to

buckling at each joint.• As the supply of water to Labuan (a tourist destination) was vital the project

became a political issue.• The second attempt by (KLJV) had a tight schedule and closely monitored

by the ministry and the third party consultant.

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PRELIMINARY ACTION• Pipeline was sand blasted for slipage at tensioner • Establish pipeline stiffness

- Large diameter, thin walled line unit large concrete weight - Lessons learned from earlier failure

• Pipeline stiffness - Consultant was of the opinion that the stiffness of the full composite section

should be considered. - Preliminary analysis showed the full composite section stiffness was not practicle. - Zee proposed to use ASME paper recomendations for pipeline stiffness.

• The stiffness related to the pipeline are;

Source Stiffness (mm4) % of Bare Pipe

Bare Pipe 1.029E + 09 100.00

Full Composite 4.318E + 09 419.631

ASME Paper 1.520E + 09 147.716

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PRELIMINARY ACTION (CONT.)• Analysis options;

1. Stiffness of bare pipe + weight of concrete coating 2. Stiffness of Composite Section + weight of concrete coating 3. Stiffness as per ASME Paper + weight of concrete coating

• Preliminary Analysis Option 1 : Touch down point close very large Option 2 : Touch down point very far. Lesser Bending Moments, Large

Tension Option 3 : Exceptable results (our opinion)

• Action adopted - The effective stiffness was critical - Decided to carry out model test for verification.

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MODEL TESTTheoretical• Test model was set up as recommended in the ASME paper.• Note that the centre of model is in bending with minimal shear (similar to

pipeline actual behaviour)

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• Test Model

• Full scale Model Test carried out• Two pipelines joints with 125mm concrete coat thickness were field welded• 2 equal loads were applied simultaneously • Strain gague incorporated at centre of model (field joint)• Strain measurements were recorded at each weight increment• Test was carried out to collapse

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MODEL TEST (CONT)

• Computer Model

• Physical measurements same as per Actual test.• Stiffness as per ASME Paper was adopted.• Finite Element model was segmented as per stiffness variations• Load increments and steps was identical to the actual test.

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MODEL TEST(CONT)

• Results (Model test) & Computer Simulation

• Strains Vs Stiffness graph• Very close matchObservations;- Initial stiffness of 2.074E+09mm4

Relates to composite section soley due to self weight

- As the load increased gradual debonding of reinforced bars and cracking of concrete. Resulting in reduction of stiffness.

- At collapse the effective stiffness was close that of bare pipe.

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MODEL TEST (CONT)

• Stiffness at pipelay

• Stiffness is propotional to the bend Rradius.• For absolute accuracy the pipelay computer model should be

incorporated with varrying stiffness along the line• This will result in a very complex F.E model requiring long computer

time for simulation/results.• It was decided to adopt a single pipeline stiffness.

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RECOMENDED PIPELINE STIFFNESS

• As per DnV (1981) the criteria set for pipelay at sag bend is 85% SMYS.

• Corresponding micro strain value is 1464.83 (units)Resulting stiffness is 1.05E+09mm4.

Approximately equal to 200% of bare pipe inertia.• It was decided to adopt stiffness value at

maximum bending range just before the cracking of the weight coat.

• The stiffness value at this range is 1.43E+09mm4

• Approximately equal to 145% of bare pipe• The stiffness as per ASME paper is

1.520E+09mm4

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PRELIMINARY ANALYSIS

• Two Analysis were carried out to check• Accuray• Simulation time• FE MODELS

• For both cases the following were taken into consideration- Physical properlise of bare pipe- Weight of concrete coating- Buoyancy- Hydrodynamic propertize• Full dynamic simulations were carried out with;- Tension of 750km- Maximum water depth- Waves and current heading 0.0 deg- Buoyancy bags not considered.

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PRELIMINARY ANALYSIS

COMPARISON OF RESULTS • Detailed simulation gave least stresses in the pipeline system spiking at field joint locations. This is realastic.

• Standard simulation produced higher stress values but with a smoother curve.

• Detailed simulation took 600% of computer time of standard simulation.

• Considering 8 simulations for each water depth, and actual time taken for each simulation, it was decided to adopt the standard model for study.

• This will give conservative results.Analysis Max

OB Stress (MPa)

MaxSB

Stress (MPa)

Touchdown Point

(m)

Standard 695.4 453.2 238.5

Detailed 412.0 399.6 172.5

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COMPUTER SIMULATION

• Coupled time domain dynamic simulation was carried out along the pipeline route considering;

- Water depth,- Weight coat Thickness.• The pipeline system was over stressed both in over and sagbend

locations.• Buoyancy system needed to be incorporated.• 2 ½ tan Buoyancy bags were used.• 8 directional analysis were carried out for each location• Typical buoyancy system.

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COMPARISON OF RESULTS

• Analysis Vs Field measurements• Field measurements only carried out for;- Water depth- Touchdown point

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COMPARISON OF RESULTS (CONT.)

KP

Water Depth Touch down Tensioner Stress(meter) (meter) (MT) % SYMS

Analysis Field Measurement Analysis Field

Measurement Analysis Field

Measurement Overbend Sagbend

46 18.64 15.6 188.7 194 60 55 61 62

45 18.64 17.7 188.7 230 60 65 67 89

44 24.14 19.2 177.5 - 207 191 80 78 77 84

43 24.14 20.2 177.5 - 207 183 80 80 77 84

42 24.14 20.6 177.5 - 207 187 80 80 77 84

41 24.14 20.4 177.5 - 207 176 80 80 77 84

40 24.14 20.2 177.5 - 207 183.7 80 80 77 84

39 24.14 18.2 177.5 - 207 187 80 80 77 84

38 24.14 18.5 177.5 - 207 176 80 75 77 84

37 24.14 17.9 177.5 - 207 181.2 80 75 77 84

36 24.14 17.3 177.5 - 207 205 80 77 77 84

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COMPARISON OF RESULTS (CONT.)

• Observations- Deviation of results within +10%. Close match- Except at kp 45 (possibly field measurement error)• Deviations possibly due to- Variance in water depths- Variance in Tensioner- Non consideration of waves and currents for field measurements• Conclusions

Orcaflex program results closer to- Model test- Field measurements

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ADVANTAGES USING ORCAFLEX PROGRAM• General- Carries out coupled, Non linear, large displacement

time domain Analysis.- Coupled- Analysis carried as a sytem including mooring lines

- UncoupledAnalysis carried for vessel, vessel displacements are introduced to the mooring system for line tension.

• Interactive user interface- Ease of input & developing models- Allow intermitent checking- Convenient for QA• Pipelay vessel components accurately modelled- Rollers- Stinger- Tensioner

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ADVANTAGES USING ORCAFLEX PROGRAM (CONT.)

• Restart facilities- Intermediate checking- Re-modelling (if required)• Graphical Results- Ease of interpretation of data

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PIPELAY ANALYSIS• Entire “Firing line”, rollers, supports and tensioner can be modelled

accurately.• Stinger configuration can be,- Sloping- Single curvature- Double curvature- Combination• Vertical and Horizontal Rollers are modelled accurately to simulate

touching (bearing) or lift off.

Pipelay

Stress Profile

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START-UP

• Can be + Dead Man Anchor• + Bow Line (various configuration)• + others• Continuos analysis includingh speed of vessel• Most programs analysis carried out in stages• + Man-hour intensive• + may not be accurate

• Tensioner and or speed of vessel can be optimized for controlled tension on jacket legs

Installation Bowline Stress Profile

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LAY DOWN

• Continuous Analysis• Tensioner and or vessel speed may be optimized for

minimal system stresses.

Laydown Stress Profile

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LIFT (Repair)

• Davits can be modelled accurately • Continuous operation• Flip over

Davit Lift Stress Profile

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SHORE APPROACH

• Continuous operation• Stop/Start Capability

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FLEXIBLE PIPELINE INSTALLATION & “J” TUBE PULL• Continuous operation• Modelled- Flexi Pipeline- Umblical- “J” Tube, bell mouth- Chute- Stinger & Deck Rollers

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RAPID RESPONSE

• Sri Lanka CPC Muthurajawela Project• Shore to SPM, Through Reef• Commencement of Mansion• Waves 4-5 meter height, Ddesigned for Max 2m• Pipeline Buckling at each joint• Field measurement were sent to office• Within 2 days accurate model were compiled & solution given• Pipeline succesfully laid.

Worst Case Solution

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FUN ORCAFLEX DEMO

THANK YOU FOR YOUR TIME

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