NDTnet 1998 Aug, Vol.3 No.8

Abstract

Among the numerous techniques of testing the containers welded joints for tightness the chemical methods are of great practical interest. The essence of these techniques consists in the following. To the external surface of a welded joint the indicating coating is applied which includes a part of components of a chemical indicating reaction and technological components. The other part of indicating reaction components is introduced into the chamber of an object under test. Then the conditions are created under which the testing substance penetrates through defects in an object wall to the indicating coating. As a result of reaction in the places of leaks on the coating the color spots appear whose dimensions and rate of growth depend on the amount of leak.

With the traditional chemical methods the acid-base or red-ox reactions are most often used. In doing so, the attained threshold of sensitivity does not exceed 10^-7 m³ Pa/s. The possibilities of its increase have been practically exhausted.We have proposed catalymetric chemical methods of the testing, with which the catalyst of an indicating reaction is used as a testing substance, while the complete set of of the components for this reaction is introduced into the indicating coating. The sensitivity actually reached with the use of the chemical catalymetric methods makes up 10^-10m³ Pa/s.

The search for new and perfection of known highly sensitive reactions, the study of the kinetics and mechanism of the specific catalytic reactions in the thin layer of an indicating coating on the surface of structural materials, and the study of the physical and chemical processes with the participation of testing substances in the thin ducts of simulated and actual through defects in the structural materials have been carried out.

The coatings for localization of the leaks have been developed in the form of pastes, films and film-producing liquids, which quickly polymerize on the testing surface.
For a number of special containers (lengthy pipeline hydraulic and gas fittings of small diameter, multi-layer pipes, etc.) as sources of testing gas have been proposed substances which at the moment of introduction into the chamber possess a negligible volume, then upon being initiated from outside they undergo gas-emitting reaction that leads to a sharp rise of gas phase pressure in the chamber. Some coordination compounds and adducts (e.g. complexes containing ammonia, freon, etc.), which can evolve the corresponding gases upon heating, have been proposed for this purpose.
Combination of pneumatic and/or hydraulic tests of containers with final testing of them for tightness have been suggested to improve the quality of the containers, pipelines and pipeline systems.

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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