Can Today’s Fracture Mechanics address Future Pipelines ... · Can Today’s Fracture Mechanics...
Transcript of Can Today’s Fracture Mechanics address Future Pipelines ... · Can Today’s Fracture Mechanics...
DNV GL © 2014 18/11/2014 SAFER, SMARTER, GREENER DNV GL © 2014
18/11/2014
Ali Sisan
Can Today’s Fracture Mechanics address Future Pipelines Integrity?
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Subsea Systems Integrity Conference
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Global reach – local competence
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400 offices
100 countries
16,000 employees
150 years
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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
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Fracture mechanics was developed during World War I by English
aeronautical engineer, A.A.Griffith, to explain the failure of brittle
materials
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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
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Quality Materials
Improved welding Technology
Better Inspection tools
New Applications
Harsher Environment
Pushing the design limits
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Fracture Mechanics, Engineering Critical Assessment
Defect Type
Material Properties
Load
2c
B a
2c
a B B
2c
p 2a
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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
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Standard and rules
Modern fracture mechanics assessments standards/guidelines:
– BS 7910
– Metallic Structure
– API 579-1 / ASME FFS-1
– R6
– Nuclear Industry
– FITNET
– European
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Local Collapse/ Global Collapse OMAE2013-11500
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.
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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
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Strain Based Condition
How accurate is using stress based FAD for strain based Conditions?
A number of research carried out by different organisations…
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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
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There are other companies studying Clad and lined pipes
Partial undermatch condition (Is FEA the only option?)
Fatigue (develop a general S-N curves??)
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Probabilistic Approach Assessment of an embedded flaw in a pipeline- OMAE 2011
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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
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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, 2001
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More to consider…
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STRESS/ STRAIN PRESSURE
TEMPERATURE
FRACTURE LOADING H2S
FATIGUE PROPERTIES ECA ENVIRONMENT CO2
TENSILE INSPECTION ARCTIC
DEFECT
DETECTION NDT
WORKMANSHIP
CRITERIA
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The future of Fracture Mechanics for Pipelines
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Procedure
Better accuracy
Simpler to follow
Strain based Condition
Probabilistic Approach
Numerical
Better guidelines
Competency
Residual Stress
Damage models
Experimental
Fatigue
Toughness
Local properties
Harsh Env
New Applications
Clad and Lined Pipes
HP/HT
Undermatch welds
High grade steel
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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
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Operation New Build
Safe and most cost-efficient operation of subsea assets
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www.dnvgl.com
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Ali Sisan
020 7716 6698