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?

1

Subsea Systems Integrity Conference

DNV GL © 2014 18/11/2014

Global reach – local competence

3

400 offices

100 countries

16,000 employees

150 years

DNV GL © 2014 18/11/2014

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

4

Fracture mechanics was developed during World War I by English

aeronautical engineer, A.A.Griffith, to explain the failure of brittle

materials

DNV GL © 2014 18/11/2014

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

DNV GL © 2014 18/11/2014 6

Quality Materials

Improved welding Technology

Better Inspection tools

New Applications

Harsher Environment

Pushing the design limits

DNV GL © 2014 18/11/2014

Fracture Mechanics, Engineering Critical Assessment

Defect Type

Material Properties

Load

2c

B a

2c

a B B

2c

p 2a

DNV GL © 2014 18/11/2014

8

Failure Assessment Diagram

Lr

Kr

Acceptable

Unacceptable

ai

ac

Da

DNV GL © 2014 18/11/2014

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

DNV GL © 2014 18/11/2014

10

Standard and rules

Modern fracture mechanics assessments standards/guidelines:

– BS 7910

– Metallic Structure

– API 579-1 / ASME FFS-1

– R6

– Nuclear Industry

– FITNET

– European

DNV GL © 2014 18/11/2014

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.

11

DNV GL © 2014 18/11/2014

12

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

DNV GL © 2014 18/11/2014

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

DNV GL © 2014 18/11/2014

X80 pipes Strain Limits and Accuracy of FEA

14

DNV GL © 2014 18/11/2014

Strain Based Condition

How accurate is using stress based FAD for strain based Conditions?

A number of research carried out by different organisations…

15

DNV GL © 2014 18/11/2014

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

DNV GL © 2014 18/11/2014

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

DNV GL © 2014 18/11/2014

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, 2001

DNV GL © 2014 18/11/2014

More to consider…

20

STRESS/ STRAIN PRESSURE

TEMPERATURE

FRACTURE LOADING H2S

FATIGUE PROPERTIES ECA ENVIRONMENT CO2

TENSILE INSPECTION ARCTIC

DEFECT

DETECTION NDT

WORKMANSHIP

CRITERIA

DNV GL © 2014 18/11/2014

The future of Fracture Mechanics for Pipelines

21

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

DNV GL © 2014 18/11/2014

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

22

Operation New Build

Safe and most cost-efficient operation of subsea assets

Can Today’s Fracture Mechanics address Future Pipelines ... · Can Today’s Fracture Mechanics...

Documents

Transcript of Can Today’s Fracture Mechanics address Future Pipelines ... · Can Today’s Fracture Mechanics...