Location

La Jolla ,CA

Start Date

1-1-1989 12:00 AM

Description

High quality heavy plates have to be free of any defects. The UT-inspection for internal defects is introduced as a standard. However, until now the inspection for surface defects is limited to visual inspection, magnetic stray flux — or eddy current inspection. The most sensitive technique is the magnetic stray-flux technique, but it is very time consuming because of the necessity to scan the whole surface. Using Rayleigh waves the inspection can be automated and performed at rolling speed. The sensitivity of frequency optimized Rayleigh waves is sufficient to detect a 0.3 mm deep model defect at a distance of 300 mm. The use of piezoelectric probes is limited by coupling problems. These problems are overcome by the use of EMAT’s, which have been optimized with respect to probe size, sensitivity and wear resistance. For the automated inspection the ALOK-system has been adapted in a laboratory system to the surface inspection of heavy plates by Rayleigh waves. This equipment consists of an ultrasonic hardware device for fast data-acquisition and -preprocessing (essential data reduction) according to the ALOK-algorithm, and a computer to realize noise- and ghost — elimination as well as defect imaging and -reconstruction.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

8A

Chapter

Chapter 5: Systems and Instrumentation

Pages

1127-1135

DOI

10.1007/978-1-4613-0817-1_142

Language

en

File Format

application/pdf

Share

COinS
 
Jan 1st, 12:00 AM

Alok-Imaging and -Reconstruction of Surface Defects on Heavy Plates with E.M.A.-Rayleigh Wave Transducers

La Jolla ,CA

High quality heavy plates have to be free of any defects. The UT-inspection for internal defects is introduced as a standard. However, until now the inspection for surface defects is limited to visual inspection, magnetic stray flux — or eddy current inspection. The most sensitive technique is the magnetic stray-flux technique, but it is very time consuming because of the necessity to scan the whole surface. Using Rayleigh waves the inspection can be automated and performed at rolling speed. The sensitivity of frequency optimized Rayleigh waves is sufficient to detect a 0.3 mm deep model defect at a distance of 300 mm. The use of piezoelectric probes is limited by coupling problems. These problems are overcome by the use of EMAT’s, which have been optimized with respect to probe size, sensitivity and wear resistance. For the automated inspection the ALOK-system has been adapted in a laboratory system to the surface inspection of heavy plates by Rayleigh waves. This equipment consists of an ultrasonic hardware device for fast data-acquisition and -preprocessing (essential data reduction) according to the ALOK-algorithm, and a computer to realize noise- and ghost — elimination as well as defect imaging and -reconstruction.