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Research Papers: NDE

# Ultrasonic Circumferential Guided Wave for Pitting-Type Corrosion Imaging at Inaccessible Pipe-Support Locations

[+] Author and Article Information
K. Shivaraj, Krishnan Balasubramaniam, C. V. Krishnamurthy

Centre for Nondestructive Evaluation, and Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600 036, India

Bharath Petroleum Corporation Limited, Mumbai 400 074, India

J. Pressure Vessel Technol 130(2), 021502 (Mar 17, 2008) (11 pages) doi:10.1115/1.2892031 History: Received January 28, 2007; Revised September 30, 2007; Published March 17, 2008

## Abstract

A higher order cylindrically guided ultrasonic wave was used for the detection and sizing of hidden pitting-type corrosion in the hidden crevice regions (between the pipe and the pipe supports) without lifting or disturbing the structural layout arrangement of the pipelines. The higher order circumferential guided waves were generated using a piezoelectric crystal based transducer, located at the accessible top region of the pipes, in a pulse-echo mode. By studying the experimental parameters such as dispersion, particle displacement, and wavelength of the ultrasonic guided wave modes, an appropriate higher order mode was selected for excitation using an appropriately designed acrylic angle wedge that conforms to the pipe’s outer curvature. A manual pipe crawler was designed with a provision for holding the wedge, and the essential hardware such as data acquisition card, encoder, etc., was integrated with the system so that the corrosion was mapped in real time during the scanning of the pipes. The system was validated on pipes ranging from $6in.to24in.$ outer diameters of wall thicknesses up to $12mm$, by mapping defects as small as $1.5mm$ diameter and 25% penetration wall thickness. A 2D finite element model using ABAQUS ® was used to understand the wave propagation in pipe wall and its interaction with pinhole-type defects.

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## Figures

Figure 1

Phase velocity and group velocity dispersion curves for 168mm diameter and 10.5mm wall thickness steel pipe

Figure 2

Particle displacement across pipe wall thickness for selected guided wave mode at 1MHz frequency

Figure 3

Acrylic wedge with corrugations on the top and side walls

Figure 4

Experimental layout of the circumferential guided wave inspection system

Figure 5

CAD model of the pipe crawler

Figure 6

Experimental setup with the data acquisition system

Figure 7

Screenshot of the real-time imaging software GUI

Figure 8

Mild steel sample pipe (168mm diameter, 10.5mm wall thickness) with drilled pinhole-type defects of 75mm pitch

Figure 9

A-scan of pipe in a defect-free region

Figure 10

A-scan corresponding to (a) 100% deep defect, (b) 80% deep defect, (c) 60% deep defect, (d) 40% deep defect, (e) 20% deep defect, and (f) defect-free region of calibration pipe shown in Fig. 9. Region between the dotted lines indicates the reflection of wave from the hidden portion of the pipe support region.

Figure 11

B-scan image indicating percentage metal losses in the sample pipe

Figure 12

Mapped image of the corroded region in a sample pipe taken out of service

Figure 13

Energy plot for different sized defect and depth in calibration pipe

Figure 14

(a) Reflection energy parameter (ξ) for different defect cross-sectional areas of defect and (b) plot between the squared defect depth and energy reflection parameter (ξ) for a 168mm diameter steel pipe with 10.5mm wall thickness

Figure 15

FEM 2D model of the wedge and pipe

Figure 16

Snapshots of the wave propagation in pipe at various time instants

Figure 17

A-scan from FEA simulation corresponding to (a) defect free, (b) 20% deep defect, (c) 40% deep defect, (d) 60% deep defect, and (e) 80% deep defect of 6mm wide in a pipe of 168.5mm diameter and 10.5mm wall thickness

Figure 18

Comparison of simulation and experimental results for the reflection energy parameter versus percentage defect depth

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