NDTnet 1998 Aug, Vol.3 No.8

Abstract

New developments on the field of x-ray line cameras for CT-applications up to 420 keV are suitable for automated scanning of weldments. A modified radiometric line camera was assembled together with an adapted US-manipulator and a mobil 225 keV x-ray tube. This device permits to scan a circumferential weld with a scan width of 100 mm. The pixel resolution amounts to 50pm for 2048 pixels per line. Corresponding to fig. 1 the camera and the x-ray tube are separated on the pipe by an angle of 180°. They are moved line by line around the circumference to acquire the radiometric image. The sensitivity of the camera was estimated to about 70% of the maximum sensitivity calculated for 100% photon absorption and quantum noise only.

Figure 1: Scheme of Automated Weld Inspection System

The applied principle of line scanning yields several advantages in comparison to the film radiography. The radiation direction corresponds to the central projection technique which always enables radial penetration. All radial flaws are detected with maximum contrast. The slit collimator of the camera reduces the intensity of the scattered radiation significantly. The well adjusted system yields therefore better image quality than film radiography for pipes with thick walls. The final image does not consist of several separated radiographs due to the required minimum number of exposures of the classical double wall technique corresponding to prEN1435. The inspector must interpret one image only for the total circumference. The system provides radiographic images with high image quality for a penetrated steel thickness of 4 - 46 mm (2 - 23 mm wall thickness) in a reasonable time. Due to the limited resolution of the applied camera of about 160 µm (measured with double wire IQI by EN 462-5) the optimum application range covers wall thicknesses of 10-20 mm from the present point of view Measured radiographs are presented.

The available scanner enables the modification of the radiation direction. It is possible to set up the system for a special inspection of side wall flaws. Scanning the weld under different angles provides multi angle projections which improve the probability of detection for flat inhomogeneities in the material like cracks and lack of fusion. It is demonstrated how tomosynthesis algorithms improve the image interpretation.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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