STATE OF THE ART PIPELAY ANALYSIS

Transcription

1 IORS 2013 CONFERENCE 20 TH ANNUAL INDIA OIL & GAS REVIEW SUMMARY & INTERNATIONAL EXHIBITION STATE OF THE ART PIPELAY ANALYSIS Paper presented by: In association with: Herman Perera ZEE Engineering Sdn Bhd Tarun Rewari Aryatech Marine & Offshore Services Pt Ltd

2 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

3 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

4 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.

5 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

6 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

7 PIPELAY ANALYSIS A Case Study Labuan Pipeline (Malaysia) 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

8 PIPELAY ANALYSIS (cont.) A Case Study 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.

9 PIPELAY ANALYSIS (cont.) A Case Study - 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. - SUCCESS The second attempt by (KLJV) Tight Schedule Closely monitored by Ministry and Third Party Consultants Was successfully concluded

10 PIPELAY ANALYSIS (cont.) A Case Study - 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.

11 PIPELAY ANALYSIS (cont.) A Case Study - The stiffness related to the pipeline are: Source Stiffness (mm4) % of Bare Pipe Bare Pipe 1.029E Full Composite 4.318E ASME Paper 1.520E

12 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

13 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)

14 PIPELAY ANALYSIS (cont.) A Case Study - 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

15 PIPELAY ANALYSIS (cont.) A Case Study - MODEL TEST COMPUTER MODEL OF PIPELINE FOR STIFFNESS EVALUATION * 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.

16 PIPELAY ANALYSIS (cont.) A Case Study - 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.

17 PIPELAY ANALYSIS (cont.) A Case Study - MODEL TEST * STIFFNESS AT PIPELAY * 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.

18 PIPELAY ANALYSIS (cont.) A Case Study - MODEL TEST RECOMMENDED PIPELINE STIFFNESS * 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

19 PRELIMINARY ANALYSIS Two analyses were carried out to check Accuracy Simulation Time FE MODELS

20 PIPELAY ANALYSIS (cont.) A Case Study 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.

21 PIPELAY ANALYSIS (cont.) A Case Study - PRELIMINARY ANALYSIS COMPARISON OF RESULTS * 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 Detailed

22 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.

23 PIPELAY ANALYSIS (cont.) A Case Study - COMPARISON OF RESULTS * Analysis vs Field measurements * Field measurements only carried out for: Water depth Touchdown point

24 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

25 PIPELAY ANALYSIS (cont.) A Case Study - COMPARISON OF RESULTS - OBSERVATIONS 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 CONCLUSIONS Orcaflex program results closer to Model Test Field Measurements

26 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

27 ORCAFLEX SIMULATIONS Installation Bowline Installation Bowline Davit Lift Davit Lift Stress Stress Profile Profile Laydown Laydown Stress Profile

28 RAPID RESPONSE SRI LANKA CPC MUTHURAJAWELA PROJECT 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. Worst Case Solution

29 INNOVATIVE ENGINEERING - RENTIS LINE Pipeline Bundle 8 concrete coated + 4 Fabricated onshore Towed 65 Miles and Installed between 2 Platform

30 INNOVATIVE ENGINEERING (cont.) - EUROSPIRAL PIPELAY Spiral Pipelay Stress Profile

31 FUN ORCAFLEX DEMO Boy Scout

32 FUN ORCAFLEX DEMO Trampoline

33 FUN ORCAFLEX DEMO Surfing Dog

34 FUN ORCAFLEX DEMO Tire

35 THANK YOU