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Piper and Riser Technology

Resonant Bending Fatigue Test Setup for Pipes With Optical Displacement Measuring System

[+] Author and Article Information
Jeroen Van Wittenberghe, Patrick De Baets, Wim De Waele, Wouter Ost, Matthias Verstraete

Stijn Hertelé

e-mail: Stijn.Hertele@UGent.be Ghent University, Laboratory Soete, St.-Pietersnieuwstraat 41, 9000 Gent, Belgium

J. Offshore Mech. Arct. Eng 134(3), 031702 (Feb 01, 2012) (6 pages) doi:10.1115/1.4005182 History: Received October 13, 2010; Revised August 02, 2011; Published February 01, 2012; Online February 01, 2012

Pipes and tubular members are used in offshore applications as structural elements, such as columns or in transport pipelines, risers, etc. When subjected to dynamic loads, weld defects or geometrical stress raisers can initiate fatigue cracks, causing the columns or pipelines to fail prematurely. In order to investigate the fatigue behavior of pipe joints, a resonant bending fatigue setup was designed, suitable for testing pipes within a diameter range from 6 in. to 20 in. In this setup, the pipe, filled with water, is subjected to a dynamic excitation force with a frequency close to the natural frequency of the filled pipe. The force is applied using a unique drive unit with excentric masses. The pipe is supported in the nodes of its natural wave-form, so that no dynamic forces are transmitted to the setup. The deformation of the pipe is measured at discrete locations using an optical 3D dynamic measuring system. Through-thickness fatigue cracks can be detected by pressurizing the water in the pipe and applying a pressure gauge. In this paper, some unique aspects of the design of the resonant bending fatigue setup are discussed by presenting the results of a semianalytical model used for calculating the deformation and bending stress in the excitated pipe and by comparing these results to the deformation measurements made by the dynamic measuring system. The working principles of the setup are illustrated by showing the preliminary test results for a 12 in. diameter X65 steel pipe with a wall thickness of 12.7 mm. It is demonstrated that the model predicts the behavior of the pipe in the setup very accurately.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Resonant bending fatigue setup

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Figure 2

View of the setup from the side with the compensating mass

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Figure 3

Setup with optical measurement system

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Figure 4

Model of a free floating pipe

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Figure 5

Boundary conditions at the free end (left)

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Figure 6

Boundary conditions at the right end with excenter force Fe

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Figure 7

First three eigenmodes of the free floating pipe

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Figure 8

Deflection and bending stress with forced vibration

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Figure 9

Influence of the pipe length on its natural frequency

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Figure 10

Model of the total setup

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Figure 11

Reaction forces in the supports

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Figure 12

Frequency response

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Figure 13

Markers as identified by the optical measuring system (arrows indicate stationary markers on the safety frame)

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Figure 14

Calculated and measured deformation shape

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Figure 15

Movement of the central point

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