Welding Imperfections and Materials Inspection: Procedures and Techniques

Abstract

As the presence of imperfections in a welded joint may not render the component defective in the sense of being unsuitable for the intended application, the preferred term is imperfection rather than defect. For this reason, production quality for a component is defined in terms of a quality level in which the limits for the imperfections are clearly defined, for example Level B, C or D in accordance with the requirements of BS EN ISO 5817. For the American standards ASME IX and AWS D1.1, the acceptance levels are contained in the standards.

The application code will specify the quality levels which must be achieved for the various joints. Imperfections can be broadly classified into those produced on fabrication of the component or structure and those formed as result of adverse conditions during service. The principal types of imperfections are:

Fabrication: lack of fusion, lack of or incomplete penetration, cracks,porosity, inclusions, incorrect weld shape and size.

Service: brittle fracture, stress corrosion cracking, fatigue failure, Welding procedure, joint features and access and welder technique will have a direct effect on fabrication imperfections. Incorrect procedure or poor technique may produce imperfections leading to premature failure in service.

The primary reason to identify and prevent weld defects is the potential danger a poor-quality weld can pose since they are more likely to fail. The consequences of a weld failing might be merely the inconvenience of a pipe bursting in the bathroom. However, if the weld on a gas pipe should fail, the results could be catastrophic, including loss of life. The same is true of a structural weld in which a bad weld could injure or kill motorists crossing a bridge or workers in a high-rise office.

Keywords: Welding Imperfections, Materials Inspection, BS EN ISO 5817, lack of fusion