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


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


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


Test set up denting and scratching


Dent in transverse direction with scratch in longitudinal direction

Analytical model for load deformation



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

P = 0


p = internal pressure

p0 = 2σ0t/D, fully plastic pressure

q = p/p0


• 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)


( )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


• Plastic part:

Fmθ

w0

ββR

R

Fpi

Fpi

w0

ββR

R

Fpi

Fpi

• Membrane part:


02 3

1.664

mF l t SR t

ds

d=

+

P = 0,6 PoFST FST

θ

θδ

l

deformed shape

of top generator


Effect of internal pressure


Impact load (excavator)

Energy indenter = energy taken by the pipe


Finite Element Simulation

• Program ABAQUS – standard.

• Large-strain finite element formulation.

• J2-flow theory of plasticity.

• Material curve from coupon


• Material curve from coupon tests.

• Four-node shell elements (S4R).

• Rigid body denting tool.

• Capped-ends for pressure cases.


• Two denting tools:

– rounded (A)

– rectangular (B)

Type B


d=15mm

b

Boundary conditions FEA

F

Fixed endFixed end


F

FCE

Capped end Capped end


40

60

80

100indentation force F [KN]


0

20

40

0 8 16 24 32 40 48 56

indentation displacement d [mm]

indentation force F [KN]

FEM

TEST A2


40

60

80

100



0

20

0 4 8 12 16 20 24 28 32 36

indentation displacement d [mm]


FEM

TEST A3

Effect of internal pressure on shape of dent


No pressure Internal pressure gives a more

localised deformation.

Capped strains and Von Mises stresses


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


• 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

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

8.gresnigt

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