Can Today s Fracture Mechanics address Future Pipelines Integrity?

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1 Can Today s Fracture Mechanics address Future Pipelines Integrity? Subsea Systems Integrity Conference Ali Sisan 18/11/ DNV GL /11/2014 SAFER, SMARTER, GREENER

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3 Global reach local competence ,000 years offices countries employees 3

4 Fracture Mechanics Applying physics of stress and strain, in particular the theories of elasticity and plasticity, to the microscopic defects found in real materials in order to predict the macroscopic mechanical failure of bodies Wikipedia Fracture mechanics was developed during World War I by English aeronautical engineer, A.A.Griffith, to explain the failure of brittle materials 4

5 Fracture Mechanics The general philosophy of fracture mechanics was developed almost 100 years ago. Fracture mechanics uses analytical and numerical approaches to study the material's resistance to fracture. Today it is common practice to carry out fracture assessment of pipelines using different codes and guidelines In the last 20 years a number of research projects have been carried out to extend the application of current approaches 5

6 Quality Materials Improved welding Technology Better Inspection tools New Applications Harsher Environment Pushing the design limits 6

7 Fracture Mechanics, Engineering Critical Assessment Defect Type Load Material Properties a 2c B B a B p 2a 2c 2c

8 Failure Assessment Diagram K r Unacceptable a i Acceptable Da a c L r 8

9 What inputs do we need. Type of defect Surface Embedded ligament height Type of loading Installation, Operation Stress-based or Strain-based Material Properties Fracture Toughens, Fatigue Properties, Tensile Properties H2S CO2 Applied stresses Primary and Secondary loading Stress concentrations Weld residual stresses 9

10 Standard and rules Modern fracture mechanics assessments standards/guidelines: BS 7910 Metallic Structure API / ASME FFS-1 R6 Nuclear Industry FITNET European 10

11 Local Collapse/ Global Collapse OMAE Nowadays pipeline girth welds generally have good fracture toughness and it can be argued that plastic collapse is the governing failure mode (Not sour ENV). The definition of plastic collapse can affect the determination of the Lr parameter and should be carefully chosen. 11

12 Procedure for ECA of Pipeline Appendix A of DNV-OS-F101 12

13 Numerical Analysis in Fracture Mechanics Using Finite Element commercial Software Used more than before, but spending more time on simulations than understanding the problem Applications HP/HT Buckling Validation of analytical Comparisons with experimental work Under matching, high strains Including residual stresses into account Pipe in Pipe Lined and Clad Pipes FFS of a specific defect/ damage 13

14 X80 pipes Strain Limits and Accuracy of FEA 14

15 Strain Based Condition How accurate is using stress based FAD for strain based Conditions? A number of research carried out by different organisations 15

16 Clad and Lined Pipe Clad and lined pipeline materials have been used in the oil and gas industry for more than 25 years. DNV JIP starting in 2005 aiming to gain a better understanding on how Clad and Lined pipes perform under different installation and service conditions, the Phase 4 of this JIP still on-going.. There are other companies studying Clad and lined pipes Partial undermatch condition (Is FEA the only option?) Fatigue (develop a general S-N curves??) 16

17 Probabilistic Approach Assessment of an embedded flaw in a pipeline- OMAE

18 Harsh Environment Avoidance of in-service crack growth in aggressive corroding environments Material Properties in sour environment Specimens size, crack depth, Env condition What is the relevant fracture toughness value to use Sour service fatigue crack growth testing (relevant factors) Different Companies may have different requirements 18

19 We know more about residual stress and not much how to take it into account. Residual stresses may be classified by the scale over which they are significant: Microscopic residual stresses operate over the grain scale or the atomic scale of the material Macroscopic residual stresses exist over large distances Residual stresses are sometimes classified according to their origin (e.g. thermal or elastic mismatch). Ref: P. J. Withers and H. K. D. H. Bhadeshia,

20 More to consider STRESS/ STRAIN PRESSURE TEMPERATURE FRACTURE LOADING H2S FATIGUE PROPERTIES ECA ENVIRONMENT CO2 TENSILE INSPECTION ARCTIC DEFECT DETECTION NDT WORKMANSHIP CRITERIA 20

21 The future of Fracture Mechanics for Pipelines Procedure Numerical Experimental New Applications Better accuracy Better guidelines Fatigue Clad and Lined Pipes Simpler to follow Competency Toughness HP/HT Strain based Condition Residual Stress Local properties Undermatch welds Probabilistic Approach Damage models Harsh Env High grade steel 21

22 Can Today s Fracture Mechanics address Future Pipelines Integrity? Experience from earlier projects Experience from operations to newbuild Challenge conservatism in codes New innovative technology and solutions Share experience with other companies New Build Operation Safe and most cost-efficient operation of subsea assets 22

23 Ali Sisan SAFER, SMARTER, GREENER 23