Manufacturing of welded joints with realistic defects

Intentional weld defect or flaw specimens can be required for training purposes, developing new non-destructive testing techniques, qualifying non-destructive testing procedures, obtaining mechanical property data and in support of safety cases. The single most important criterion in producing defects or imperfections is that they must accurately simulate the flaws that can occur in welded components and structures. For this reason, in certain applications, saw cuts or machined slots, which are more easily detected, may not be considered acceptable as planar imperfections/defects for the purpose of NDT training or validation. Therefore, TWI has developed techniques for producing realistic imperfections/defects and, in the case of cracks, the desired morphology, including roughness and angles of tilt and skew to the surface.

This paper describes the techniques used to obtain the abovementioned defects and, for the most commonly required defect types, the qualification procedure used by TWI. This consists of inspecting by surface NDT methods, ultrasonic or radiographic inspection and/or sectioning to demonstrate that the dimensional tolerance of the simulated imperfections (ie actual size of the imperfection versus required size) can be generally guaranteed to within ±0.5 mm in through-wall extent and ±1 mm in length.