NDTnet 1998 Aug, Vol.3 No.8

Abstract

Weld inspection on oil and gas pipelines as well as in chemical and petrochemical production plants has always been one of the most important areas of gamma radiography. Gammagraphic inspection is performed either in a double-wall single image technique using conventional portable gammagraphic equipment with the source located outside of the pipe. Alternatively, self-propelled pipeline crawlers have been designed travelling inside the pipe line.

Gammagraphic weld inspection in the lower range of steel thicknesses has been done with ¹²¹Iridium and ¹⁶⁹Ytterbium isotope sources throughout the past. The large majority of applications has been using 1 Iridium due to the unfavourable economical parameters of ¹⁶⁹Ytterbium, obviously with non-optimal results at thin wall inspections.

Recently we have made available the isotope ⁷⁵Selenium for non-destructive testing. These sources offer technical specifications as required by industrial applications and provide various advantages when compared with other radiation sources.

The paper presents the results from systematic comparison of contrast and resolution obtained with different types of radiation sources on steel thicknesses from 5 to 40 mm. These results have been taken into account with the definitions of the European standard for radiographic inspection of weldments (EN 1435) that is approved since 1997. Conclusions from practical investigations on pipe line sites, in petrochemical plants and in nuclear power stations will be discussed as well. Furthermore, the presentation will stipulate a variety of advantages obtained from the new source in terms of collimation and radiation protection.

For wall thicknesses of typically 2-30 mm of steel ⁷⁵Selenium has meanwhile become well accepted in international radiography with the clearly legible trend to be the preferential choice in the near future.

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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