evaluation system for corrosion defects in pipelines

Bay Zoltán Foundation for Applied ResearchInstitute for Logistics and Productgion Systems

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Evaluation system for corrosion defects in

pipelines

Dr. Gyöngyvér B. Lenkey, Dr. László Tóth, Zsolt Balogh


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Objectives of the work

Evaluation of the applicability of FEM for predicting the failure pressure and the safe operation pressure for corroded pipelines

Development of safety diagrams Development of evaluation system for

corrosion defects


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Previous projects

Development of FEM model with real defect geometry

Development of simplified defect geometries and comparative assessment

Comparison of FEM results with pressure tests and with engineering methods

Development of failure criteria for failure pressure


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Mapping the real 3D defect geometryMapping the real 3D defect geometry

Sample (negative)

Laser distance

measurment


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Boundary conditions for FEM modelBoundary conditions for FEM model

Modelling the pressure test: Quarter modell Increasing internal pressure Increasing axial tension (proportional with

the pressure)


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0

200

400

600

800

1000

1200

1400

0 0.5 1 1.5

-

M

Pa

Parameters of FEM calculationsParameters of FEM calculations Elastic-plastic material law (determined from tensile

tests, ReH=350 MPa, Rm=480 MPa)

Von-Mises yield criteria, isotropic hardening Large deformation option


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Transfer the real defect geometry Transfer the real defect geometry into the FEM modellinto the FEM modell


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Development of simplified defect Development of simplified defect geometriesgeometries

1 4 7

10 13 16 19 22

S1

S9

S17

0

0,5

1

1,5

2

2,5

3

3,5

4

1 3 5 7 9

11 13

15

17

19

21

S1

S6

S11

S16

S21

0

0,5

1

1,5

2

2,5

3

3,5

4

1 3 5 7 9

11 13

15

17

19

21

S1

S6

S11

S16

S21

0

0,5

1

1,5

2

2,5

3

3,5

4

Parabolic modell Rectangular modell 6th order surface modell


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Predicting the failure pressurePredicting the failure pressure

0

200

400

600

800

1000

1200

0 5 10 15 20 25

Pressure, MPa

Str

ess,

MP

a

Eq. stress Main stress SMYS SMYS+69 Rm'

ReH

Rm'

pF


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Criterion: eq = Rm '

0

5

10

15

20

25

0 1 2 3 4 5 6 7

Defect depth, mm

Pre

ssu

re, M

Pa

Real defect

Rectengular modell

Parabolic modell

Measured failure pres.

6th order modell

Validation of failure criterion and Validation of failure criterion and applicability of simplified geometriesapplicability of simplified geometries


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0

5

10

15

20

25

0 1 2 3 4 5 6 7

Hibamélység,mm

Nyo

más

,MP

a

ASME B31.G RSTRENG DNV RP-F 101 Battelle Shell-92 Mért tönkr. nyomás

Comparison of measured and Comparison of measured and predicted failure pressure values – predicted failure pressure values –

with engineering methodswith engineering methodsP

ress

ure

, MP

a

Defect depth, mm

Meas. fail. pres.


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Objectives of the present project

Performing large number of FEM calculations with simplified defect geometry (parabolic)

Development of safety diagrams and defect evaluation system


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Material Diameter (D), mm Thickness (t), mm

1 A52K 323,9 5

2 X52 323,9 6,3

3 X52 406,4 5,6

4 DX60 406,4 7,1

5 X52 609,6 10

6 DX60 609,6 8

7 DX52 406,4 7,1

8 DX52 406,4 8

Basic data for the FEM calculations

Different pipe geometry (diameter, wall thickness)

Different materials Different defect sizes (d, L, b)

Defect length, mm Defect width (circumferential), mm

Relative defect depth, d/t

12 6 0,25

24 18 0,5

48 42 0,62

150 60 0,72

282 0,85

402

498


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Definition of critical pressure values (pys, pyf, pF)

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400

600

800

1000

1200

0 5 10 15 20 25

Pressure, MPa

Str

ess,

MP

a

Eq. stress Main stress SMYS SMYS+69 Rm'

ReH

Rm'

pys pyf pF


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Development of safety diagrams

Different representation possibilities (as a function of L/D, d/t, L or d)

E.g. normalisation of critical pressure values:

for pF-flawless=2.Rm'.t/(D-t) ,

1. norm - pys= pys/ pF- flawless,

2. norm - pyf= pyf/ pF- flawless,

3. norm - pF= pF/ pF- flawless,

4. norm - pü= pü/ pF- flawless.


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Normalised pressure values vs. L/D –comparison with the operation pressure

b=42; d/t=0.25

0.0

0.2

0.4

0.6

0.8

1.0

0 0.5 1 1.5

L/D

no

rm-p

, M

Pa

norm-pF; t=8

norm-pYs; t=8

norm-pYf; t=8

norm-pF; t=7,1

norm-pYs; t=7,1

norm-pYf; t=7,1

norm-pü (t=8)

norm-pü (t=7.1)

b=42; d/t=0.85

0.0

0.2

0.4

0.6

0.8

1.0

0 0.5 1 1.5

L/D

no

rm-p

, M

Pa

norm-pF; t=8

norm-pYs; t=8

norm-pYf; t=8

norm-pF; t=7,1

norm-pYs; t=7,1

norm-pYf; t=7,1

norm-pü (t=8)

norm-pü (t=7.1)


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Final safety diagramsA52K; D=323,9mm; t=5mm; B=6mm

0

1

2

3

4

5

6

7

8

9

10

0 0.2 0.4 0.6 0.8 1

d/t

p, M

Pa

L=12mm, Pys

L=24mm, Pys

L=48mm, Pys

L=150mm,Pys

L=282mm,Pys

L=402mm,PysL=498mm,Pys

Pü

For Pys


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A52K; D=323,9mm; t=5mm; B=6mm

0

2

4

6

8

10

12

14

0 0.2 0.4 0.6 0.8 1

d/t

p, M

Pa

L=12mm, Pyf

L=24mm, Pyf

L=48mm, Pyf

L=150mm, Pyf

L=282mm, Pyf

L=402mm, Pyf

L=498mm, Pyf

Pü

For Pyf


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For PF

A52K; D=323,9mm; t=5mm; B=6mm

6

8

10

12

14

16

18

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

d/t

p, M

Pa

L=12mm, PF

L=24mm, PF

L=48mm, PF

L=150mm, PF

L=282mm, PF

L=402mm, PF

L=498mm, PF

Pü

PF-1-1

PF-1-2

PF-1L1

L2


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Definition of safety factors

For the critical pressure values:

– n1=Pys/Pü for the beginning of plastic deformation

– n2=Pyf/Pü for the localisation of the plastic deformation

(contraction)

– n3=PF/Pü for the failure (plastic instability)

Operational safety? – combination of n1, n2, n3 –

application possibility of risk based approaches –

owner’s responsibility!


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Summary and conclusionSummary and conclusion FEM calculations gave more accurate prediction for the

failure pressure than engineering methods. The predicted failure pressure (based on FEM calculations)

were in good agreement with the pressure test results. Simplified defect geometries could be applied for predicting

the failure pressure, so it gives opportunity to perform large number of FEM calculations and development of safety diagrams.

With the application of the safety diagrams a proper safety evaluation system can be developed together with the owner.

Possibility for more complex safety assessment system and application of risk based principles.


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evaluation system for corrosion defects in pipelines

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