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Technical Brief

Detecting Loosening of Bolted Connections in a Pipeline Using Changes in Natural Frequencies

[+] Author and Article Information
K. He

Graduate Research Assistant
Department of Mechanical Engineering,
University of Maryland–Baltimore County,
1000 Hilltop Circle,
Baltimore, MD 21250
Structural Analyst Engineer,
Vermeer Corporation,
Pella, IA 50219

W. D. Zhu

Professor
ASME Fellow
Department of Mechanical Engineering,
University of Maryland–Baltimore County,
1000 Hilltop Circle,
Baltimore, MD 21250

1Corresponding author.

Contributed by the Design Engineering Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received November 30, 2012; final manuscript received January 14, 2014; published online April 1, 2014. Assoc. Editor: Bogdan I. Epureanu.

J. Vib. Acoust 136(3), 034503 (Apr 01, 2014) (8 pages) Paper No: VIB-12-1334; doi: 10.1115/1.4026973 History: Received November 30, 2012; Revised January 14, 2014

Loosening of bolted connections in a structure can significantly reduce its load-bearing capacity. Detecting loosening of bolted connections at an early stage can prevent failure of the structure. Due to the complex geometry of a bolted connection and material discontinuity between clamped components, it is difficult to detect loosening of a bolted connection using conventional nondestructive test methods. A vibration-based method that uses changes in natural frequencies of a structure to detect locations and extent of damage can be used to detect loosening of bolted connections since the method focuses on detecting a stiffness reduction, which can result from loosening of bolted connections. Experimental and numerical damage detection was conducted to detect loosening of bolted connections in a full-size steel pipeline with bolted flanges using the vibration-based method. With the recent development of a modeling technique for bolted connections in thin-walled structures, an accurate physics-based finite element model of the pipeline that is required by the vibration-based damage detection method is developed. A trust-region search strategy is employed to improve the damage detection method so that global convergence of the damage detection algorithm can be ensured for underdetermined systems, and robustness of the algorithm can be enhanced when relatively large modeling error and measurement noise are present. The location and extent of loosened bolted connections were successfully detected in experimental damage detection using changes in natural frequencies of the first several elastic modes of the pipeline; the exact location and extent of the loosened bolted connections can be detected in numerical simulation where there are no modeling error and measurement noise.

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Figures

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Fig. 1

A steel pipeline on two airbeds, with enlarged views of bolted flanges and the placement of accelerometers

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Fig. 2

Schematic of a cantilever beam whose stiffness is represented by a set of nondimensional stiffness parameters G

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Fig. 3

Flowchart of the damage detection algorithm using the L–M method

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Fig. 4

An enlarged view of the accelerometer that is placed along the circumferential direction of the pipeline through a steel bracket

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Fig. 5

Calculated pressure distribution in a clamped component of an isolated bolted connection

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Fig. 6

(a) FE model of the pipeline in Fig. 1 and (b) an expanded view of the bolted flanges

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Fig. 7

Frequency response functions of the pipeline in Fig. 1 measured in a reciprocity test

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Fig. 8

Groups in the FE model of the pipeline in Fig. 1

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Fig. 9

(a)–(c) Experimental and (d) numerical damage detection results for detecting the loosening of the bolted connections in the pipeline in Fig. 1

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