STATE OF THE ART

PIPELAY ANALYSIS

Paper presented by:

Herman Perera

ZEE Engineering Sdn

Bhd

In association with:

Tarun Rewari

Aryatech Marine &

Offshore Services Pt Ltd

IORS 2013 CONFERENCE 20TH ANNUAL

INDIA OIL & GAS REVIEW SUMMARY & INTERNATIONAL EXHIBITION

INTRODUCTION

• Demand for Submarine Pipelines are increasing, due to

• Increase in Energy requirements for domestic use and industrialization resulting in;

* New Lines

* Rehabilitation / Replacement of existing lines

* Marginal field development

INTRODUCTION (cont.)

• Transport lines (larger diameter and longer)

– Standard DLB needs to be used

• In-field lines and marginal field development (smaller diameter, shorter)

– Non traditional methods need to be considered

* Surface tow (Rentis)

* On/Off bottom tow

* Variance of above

• For both cases Installation is a major cost driver

INTRODUCTION (cont.)

• Installation costs depend on;

– Offshore spread

– Methodology adopted

• Optimization of Installation costs

– Reduction of facilities

* Tensioner

* Wincher, davits etc.

• Enables companies to have larger contractor base for competitive bidding

• Enables contracts saving of cost by using optimum facilities such as reduction in tension.

OBJECTIVE OF PAPER

- To present a software package verified by

• Model test

• Field data

- Software package presented, OrcaFlex

- Computer Simulation depends on Methodology

• Static

• Dynamic

• Pseda- Dynamic

- OrcaFlex carries out large deflection, non-linear time domain analysis

BACKGROUND

• 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 software packages

- Ansys - Pipeline

- Marcs - OrcaFlex

- Sesam - Offpipe

• We are not condemning or criticizing any software, merely sharing our experience.

• This presentation is based on our personal views

PIPELAY ANALYSIS

Submarine pipeline from mainland to Labuan island to supply fresh water.

EPCC Contractor

• Kencana/Lleighton Joint Venture (KLJV)

Line Description

• 26 inch diameter, approx. length 23.0km

• Wall thickness 9.5mm

• Steel API 5L x 52

• Weight Coating

– Concrete density of 2.4MT/m3

– Varying 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

Labuan Pipeline (Malaysia)

A Case Study

PIPELAY ANALYSIS (cont.)

Project was interesting as a number of lay methods were used

Installation Methods • Traditional “S” lay • Surface Tow (Rentis) • Shore Pull • Mid-point tie-in • Riser stack-in

- For all the methods single program OrcaFlex was used. • Single data file • QA/QC made easy.

A Case Study

PIPELAY ANALYSIS (cont.)

• 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.

- FAILURE

The second attempt by (KLJV)

• Tight Schedule

• Closely monitored by Ministry and Third Party

Consultants

• Was successfully concluded

A Case Study

- SUCCESS

- PRELIMINARY ACTION

• Pipeline was sandblasted for slippage at tensioner

• Establish pipeline stiffness

* Large diameter, thin walled line with 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

note practical.

* ZEE proposed to use ASME paper recommendations for pipeline

stiffness.

PIPELAY ANALYSIS (cont.)

A Case Study

- 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

PIPELAY ANALYSIS (cont.)

A Case Study

PRELIMINARY ACTION

- Analysis options:

* Stiffness of bare pipe + weight of concrete coating

* Stiffness of Composite Section + weight of concrete coating

* Stiffness as per ASME Paper + weight of concrete coating

- Preliminary Analysis

* Option 1: Touch down point close stresses very large

* Option 2: Touchdown point very far. Lessen Bending Moments, Large Tension

* Option 3: Acceptable results (our opinion)

- Action Adopted

* The effective stiffness was critical

* Decided to carry out model test for verification

PIPELAY ANALYSIS (cont.)

A Case Study

MODEL TEST • Theoretical

– 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 actual pipeline behaviour)

- MODEL TEST

* Full scale Model Test carried out

* Two pipeline joints with 125m,

concrete coat thickness were

field- welded

* 2 equal loads were applied

simultaneously

* Strain gauge incorporated at

center of model (field joint)

* Strain measurements were

recorded at each weight

increment

* Test was carried out to collapse

PIPELAY ANALYSIS (cont.)

A Case Study

- MODEL TEST

* 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 were identical to the actual test.

PIPELAY ANALYSIS (cont.)

A Case Study

COMPUTER MODEL OF PIPELINE FOR STIFFNESS EVALUATION

- MODEL TEST

- Results (Model Test) & Computer Simulation * Strains vs Stiffness graph * Very close match * Observations

– Initial stiffness of composite section solely 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 to that of bare pipe.

PIPELAY ANALYSIS (cont.)

A Case Study

- MODEL TEST

* Stiffness is proportional to the bend Radius.

* For absolute accuracy the pipelay computer model should be incorporated with

varying 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.

* STIFFNESS AT PIPELAY

PIPELAY ANALYSIS (cont.)

A Case Study

* As per DnV (1981) the criteria

set for pipelay at sag bend is 85%

SMYS.

* It was decided to adopt stiffness

value at maximum bending range

just before the cracking of the

weight coat.

* The stiffness value is approximately

equal to 145% of bare pipe

* The stiffness is as per ASME paper

recommendation

RECOMMENDED PIPELINE STIFFNESS

- MODEL TEST

PIPELAY ANALYSIS (cont.)

A Case Study

PRELIMINARY ANALYSIS

• Two analyses were carried out to check

– Accuracy

– Simulation Time

• FE MODELS

PRELIMINARY ANALYSIS

• For both cases standard pipelay analysis was carried out the following were taken into consideration:

* Physical properties of bare pipe * Weight of concrete coating * Buoyancy * Hydrodynamic properties

• Full dynamic simulations were carried out with: * Tension of 750km * Maximum water depth * Waves and current heading 0.0 deg * Buoyancy bags not considered.

PIPELAY ANALYSIS (cont.)

A Case Study

- PRELIMINARY ANALYSIS

* Detailed simulation gave least stresses in the

pipeline system spiking at field joint locations.

This is realistic.

* Standard simulation produced higher stress

values but with a smoother curve.

* Detailed simulation took 600% of computer time

of standard simulation.

* Considering 8 stimulations 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)

Max SB

Stress

(MPa)

Touch down

Point (m)

Standard 695.4 453.2 238.5

Detailed 412.0 399.6 172.5

COMPARISON OF RESULTS

PIPELAY ANALYSIS (cont.)

A Case Study

- 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.

PIPELAY ANALYSIS (cont.)

A Case Study

- COMPARISON OF RESULTS

* Analysis vs Field measurements

* Field measurements only carried out for:

– Water depth

– Touchdown point

PIPELAY ANALYSIS (cont.)

A Case Study

COMPARISON OF RESULTS

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

PIPELAY ANALYSIS (cont.)

A Case Study

- COMPARISON OF RESULTS

• Deviations 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

- OBSERVATIONS

CONCLUSIONS

• Orcaflex program results closer to – Model Test – Field Measurements

PIPELAY ANALYSIS (cont.)

A Case Study

ADVANTAGES OF USING ORCAFLEX

• Many Advantages

- Limited time to go through

• Main Advantage

- Continuous Simulation

- Speed of vessel

- Optimization of forces on jacket/ dead Anchor

ORCAFLEX SIMULATIONS

Installation Bowline Davit Lift Installation Bowline

Stress Profile

Davit Lift Stress

Profile

Laydown Laydown Stress

Profile

RAPID RESPONSE

• Shore to SPM, through Reef • Pipelay delay • Commencement of Monsoon • Waves 4-5 meter height, designed for max 2m • Pipeline buckling at each joint • Field measurement were sent to office • Within 2 days accurate models were compiled & solution given • Pipeline successfully laid.

SRI LANKA CPC MUTHURAJAWELA PROJECT

Worst Case Solution

INNOVATIVE ENGINEERING

- RENTIS LINE

Towed 65 Miles and Installed between 2 Platform

Pipeline Bundle 8” concrete coated + 4” Fabricated onshore

INNOVATIVE ENGINEERING (cont.)

- EUROSPIRAL PIPELAY

Spiral Pipelay

Stress Profile

FUN ORCAFLEX DEMO

Boy Scout

FUN ORCAFLEX DEMO

Trampoline

FUN ORCAFLEX DEMO

Surfing Dog

FUN ORCAFLEX DEMO

Tire

THANK YOU