Research Papers: Piper and Riser Technology

Mechanical Behavior of Dented Steel Pipes Subjected to Bending and Pressure Loading

[+] Author and Article Information
Aglaia E. Pournara

Department of Mechanical Engineering,
University of Thessaly,
Volos 38334, Greece
e-mail: agpourna@uth.gr

Theocharis Papatheocharis

Department of Civil Engineering,
University of Thessaly,
Volos 38334, Greece
e-mail: th_papath@yahoo.gr

Spyros A. Karamanos

Department of Mechanical Engineering,
University of Thessaly,
Volos 38334, Greece;
Institute of Infrastructure and Environment,
School of Engineering,
The University of Edinburgh,
Edinburgh EH9 3FG, UK
e-mail: skara@mie.uth.gr

Philip C. Perdikaris

Department of Civil Engineering,
University of Thessaly,
Volos 38334, Greece
e-mail: filperd@uth.gr

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received October 10, 2017; final manuscript received July 6, 2018; published online August 13, 2018. Assoc. Editor: Theodoro Antoun Netto.

J. Offshore Mech. Arct. Eng 141(1), 011702 (Aug 13, 2018) (16 pages) Paper No: OMAE-17-1183; doi: 10.1115/1.4040835 History: Received October 10, 2017; Revised July 06, 2018

The presence of dents on steel pipeline wall may constitute a threat for pipeline structural safety. Experimental testing results supported by numerical simulations are reported, in an attempt to assess the structural integrity of smoothly dented (nongauged) steel pipes. Ten experiments on 6 in diameter X52 steel pipes are reported, where dented steel pipes are subjected to bending and pressure loading, in order to estimate their residual strength and remaining fatigue life. Six specimens were subjected to cyclic bending loading, whereas four dented pipe specimens, following cyclic pressure loading, have been pressurized to burst to determine their ultimate pressure capacity. Numerical simulation of the testing procedure and, in particular, the loading pattern of each specimen (denting and cyclic loading) has also been performed so that local stress and strain distributions at the dented region are calculated accurately. Based on the finite element results, a simple and efficient fatigue assessment methodology is adopted, to estimate the remaining fatigue life and the predictions were found to compare with the experimental results. Finally, following a parametric numerical study, strain concentration factors (SNCFs) for dented pipes subjected to bending are calculated, to be used in fatigue life assessment.

Copyright © 2019 by ASME
Topics: Pressure , Pipes , Steel , Stress
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Fig. 1

6 in diameter 1 m long X52 pipe specimens: (a) pipe with 4.78 mm thickness and (b) machined pipe at 2.8 mm thickness

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Fig. 2

(a) Wedge-shaped denting tool and wooden base to support pipe specimens during denting and (b) pipe denting process configuration

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Fig. 3

Schematic view of the strain gages implemented at the denting region: (a) SP5d specimen, (b) SP6d specimen, and (c) strain gages attached to the dent ridges of SP5d pipe specimen after denting

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Fig. 4

Four-point bending test setup: (a) schematic overall experimental configuration, (b) side view of bent specimen and the cross-beam, and (c) hinged end support of specimen and wooden clamp for load application

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Fig. 5

Pressure valve and manometer for low-level internal pressure measurement during cyclic bending

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Fig. 6

Application of internal pressure on pipe specimen SP2d

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Fig. 7

Pipe material stress–strain curve (X52 steel grade)

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Fig. 8

(a) Thickness measurements on ∅168.3/4.78 pipe specimens using an ultrasonic device and (b) marked ∅165/3 specimens

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Fig. 9

Load–displacement (stroke) diagrams during the denting procedure, for specimens: (a) SP1d and SP3d, (b) SP5d and SP6d, and (c) SP9d and SP10d

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Fig. 10

Load–displacement diagrams during the denting procedure of the SP10d specimen and comparison of the displacement values from the LVDTs and the applied stroke of the hydraulic actuator

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Fig. 11

Evolution of longitudinal and hoop strains during denting for specimens (d/D = 12%): (a) SP5d and (b) SP10d

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Fig. 12

Load versus displacement diagrams of the wooden base top surface during denting of the SP3d and SP1d pipe specimens

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Fig. 13

Normalized experimental moment–curvature diagrams for specimens SP5d and SP6d under monotonic and cyclic bending

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Fig. 14

Dented specimen SP5d subjected to cyclic four-point bending: (a) general configuration of dented specimen and (b) pipe wall rupture at dent ridge

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Fig. 15

Moment–curvature diagram for specimen SP1d subjected to reverse and cyclic bending

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Fig. 16

Moment–curvature diagram for specimen SP3d subjected to reverse and cyclic bending

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Fig. 17

(a) Dented specimen SP1d and (b) detail of buckle development at the opposite side of the dent during reverse and cyclic four-point bending

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Fig. 18

Moment–curvature diagrams for specimens: (a) SP9d and (b) SP10d

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Fig. 19

Pipe wall rupture of specimen SP9d due to cyclic bending loading at the dent “ridge”

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Fig. 20

(a) Rupture of specimen SP2d (∅168.3/4.78), (b) detail of crack opening in specimen SP2d, and (c) ruptured (burst) pipe specimen SP7d (∅165/3) due to increased internal pressure

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Fig. 21

Pipe wall rupture of SP8d pipe specimen (∅165/3) due to fatigue loading (cyclic internal pressure); wall rupture occurred at the “ridge” of the dented region

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Fig. 22

Finite element model: (a) different parts of the model and (b) shell finite element mesh of the dented specimen

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Fig. 23

Deformed geometry and distribution of Von Mises stress in MPa obtained from finite element simulations after the removal of denting load: (a) specimen SP1d (d/D= 6%) and (b) specimen SP5d (d/D= 12%)

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Fig. 24

Load–displacement curves for (a) SP6d and (b) SP3d models during denting in comparison with the corresponding experimental curves

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Fig. 25

Strain evolution in terms of (a) denting load and (b) denting tool displacement, during the denting process of SP5d specimen (for strain gages refer to Fig. 3)

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Fig. 26

Schematic representation of the loading pattern in the finite element model employed for cyclic bending on dented pipes

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Fig. 27

Moment–curvature bending diagram for specimen SP3d (reverse and cyclic bending) obtained from finite element analysis and comparison with the corresponding experimental results

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Fig. 28

Moment–curvature diagrams from experimental and finite element results for specimen SP5d

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Fig. 29

Deformed shapes of specimen SP5d: (a) finite element model and (b) deformed shape from experiment

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Fig. 30

Deformed shapes of SP3d specimen subjected to reverse and cyclic bending: (a) finite element model and (b) experiment

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Fig. 31

Local curvatures of pipe wall surface for estimating strains in smooth dents, as specified in Ref. [11]

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Fig. 32

Dent geometry for d/D= 6%: (a) before the application of internal pressure and (b) after the application of internal pressure

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Fig. 33

“Smoothening” of the dent profile with the increase of internal pressure (in MPa) for pipe specimen SP2d

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Fig. 34

Comparison of API 579 fatigue curve [11] with X52 fatigue curve of pipe material [17]

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Fig. 35

Normalized moment–curvature diagrams for dented pipes with d/D= 1.2% and 14.3% subjected to bending (maximum curvature kmax/kc= 1)

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Fig. 36

Strain concentration factor values in terms of the normalized dent depth (d/D) for kmax/kc ratios ranging from 0.1 to 1

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Fig. 37

Strain concentration factor values in terms of kmax/kc ratio for four levels of dent depth ratio values (d/D ranging from 1.2% to 14.3%)



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