8.gresnigt

Pressurized pipes under concentrated lateral loads

e.g. excavators hitting buried pipelines

Static and impact loading

1Eurosteel 2005

Nol Gresnigt - Spyros Karamanos

Concentrated lateral loads on pipes

May occur:

• In buried pipelines e.g. due to

• an excavator

• settlement of the pipeline causing contact with e.g. a sheet pile wall

2COST C26 – October 2007

• In tubular structures due to lateral loads from cross beams or supports

• In columns due to collisions

• etc

Denting and scratching due to a rough excavator tooth

3COST C26 – October 2007

Dent in transverse direction with scratch in longitudinal direction

Dent in longitudinal direction

Safety against burst

Research carried out for pipeline companies to determine wall thickness such that “standard” excavator would not puncture / cause burst

4COST C26 – October 2007

Safety against burst depends on

• the depth and shape of the dent

• the material damage in the scratch

• the ductility of the steel

• the internal pressure

Test set up denting

5COST C26 – October 2007

Test set up denting and scratching

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Dent in transverse direction with scratch in longitudinal direction

Analytical model for load deformation

7COST C26 – October 2007

Analytical model for load deformation

• Elastic part Fe• Plastic part Fp• Membrane part Fm

P = 0

8COST C26 – October 2007

p = internal pressure

p0 = 2σ0t/D, fully plastic pressure

q = p/p0

Analytical model for load deformation

• Elastic part

1.33eB R R t b= +

30.149e e

rr

EIF B

Rd

a=

( )rr cr crp p pa = +

d = indentation dept (=2w)

EI = bending stiffness of the wall

Be = effective width

arr = reduction for internal pressure p or increase for external pressure (- sign)

pcr = collapse pressure (external)

9COST C26 – October 2007

( )rr cr cr

33crp EI R=

3

2,4,6,...

cos(0, ) 1.117 e

n n

F R t nw

R AREIR

t

ϕϕ

∞

=

=

∑

Based on modelling with Fourier series and thin shell analysis

Analytical model for load deformation

• Plastic part:

Fmθ

w0

ββR

R

Fpi

Fpi

w0

ββR

R

Fpi

Fpi

• Membrane part:

10COST C26 – October 2007

02 3

1.664

mF l t SR t

ds

d=

+

P = 0,6 PoFST FST

θ

θδ

l

deformed shape

of top generator

Analytical model for load deformation

Effect of internal pressure

11COST C26 – October 2007

Impact load (excavator)

Energy indenter = energy taken by the pipe

12COST C26 – October 2007

Finite Element Simulation

• Program ABAQUS – standard.

• Large-strain finite element formulation.

• J2-flow theory of plasticity.

• Material curve from coupon

13COST C26 – October 2007

• Material curve from coupon tests.

• Four-node shell elements (S4R).

• Rigid body denting tool.

• Capped-ends for pressure cases.

Finite Element Simulation

• Two denting tools:

– rounded (A)

– rectangular (B)

Type B

14COST C26 – October 2007

d=15mm

b

Boundary conditions FEA

F

Fixed endFixed end

15COST C26 – October 2007

F

FCE

Capped end Capped end

Finite Element Simulation

40

60

80

100indentation force F [KN]

16COST C26 – October 2007

0

20

40

0 8 16 24 32 40 48 56

indentation displacement d [mm]

indentation force F [KN]

FEM

TEST A2

Finite Element Simulation

40

60

80

100

indentation force F [KN]

17COST C26 – October 2007

0

20

0 4 8 12 16 20 24 28 32 36

indentation displacement d [mm]

indentation force F [KN]

FEM

TEST A3

Effect of internal pressure on shape of dent

18COST C26 – October 2007

No pressure Internal pressure gives a more

localised deformation.

Capped strains and Von Mises stresses

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Conclusions

• Analytical model for local loads fits well with test results

• Finite element results fit well with test results and provide strain distributions

• Analytical model gives quick estimate of load deformation behaviour

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• Fracture mechanics to asses the damage / risk for burst

• Safety (distance) from pipelines dependent on the type of gas, the pressure, the size of the crack, ….

• More details in COST26 Prague book

21COST C26 – October 2007

Exceptional load cases for buried pipelines

1 Pressurized pipes under concentrated lateral

loads e.g. excavators

2 Safety distance for natural gas pipelines

22Eurosteel 2005

Nol Gresnigt - Spyros Karamanos