Non-destructive weld inspection during the welding process - possibilities and limitations of an inline monitoring approach

Welded joints are usually inspected by ultrasonic non-destructive testing (UT) after completion of the weld. However, such a conventional offline NDT approach is inefficient in case of complex welding techniques, large structural components or expensive materials. If structurally relevant defects are found, a repair is no longer possible and the whole component has to be rejected. For a better identification of defects during the welding process, a temperature-resistant inline monitoring approach is necessary. In the present contribution we describe a multi-method approach based on three different techniques: Phased Array Ultrasonic Testing (PAUT), Acoustic Process Monitoring (AE) and Laser Speckle Photometry (LSP). We present results of inline measurements during Laser-Multi-Pass-Narrow-Gap-Welding of Nickel super alloys and compare the results with posterior ultrasonic immersion testing and metallographic micrographs.