This paper describes an innovative apparatus and method that has been developed to volumetrically examine dielectric materials, including high density  polyethylene piping weldments. The method employs a first of a kind apparatus that is based on the creation of an image using electromagnetic energy in the microwave frequency range. The results of comprehensive laboratory testing and actual field inspection of HDPE thermal fusion welds using the microwave method and apparatus are presented. The specimens examined included both sound thermal welds and those that included different types of internal flaws that commonly occur in industrial application. Through this research and field application, the apparatus has been shown capable of detecting the presence of internal flaws, such as lack of fusion (i.e. – cold fusion) welds and weld inclusions. Also, thickness changes and voids in the HDPE pipe base material were detected and imaged. The results of the NDE technique are compared to mechanical pull test validation. Finally, the scan images of the PE pipe thermal welds are compared to theoretical weld microstructure. Relationships between the HDPE weld images and the basic weld microstructure are developed.