The ability to accurately image in-service cracks is of great practical interest to asset owners. Knowing the precise through-wall extent of a crack, for instance, allows for efficient scheduling of repairs, while a detailed image of a crack's morphology can help assess its criticality. High fidelity imaging of cracks can be achieved by advanced ultrasonic techniques such as Full Matrix Capture/Total Focusing Method (FMC/TFM), however, different features and/or regions of a crack may respond better to different imaging modes necessitating the analysis of multiple mode images (T-T, TT-TT, TT-T, etc). Attempts have been made to devise strategies to merge multiple TFM mode images by summation, maximum stacking and multiplication (among others) with mixed results. Difficulty in selecting the correct modes to combine, correcting their relative amplitudes prior to combining them and suppressing artefacts between modes each complicate the merging process. To address these issues, a novel imaging technique is proposed in which the different modes are essentially treated as additional element pairs and processed via the Delay and Sum (DaS) and Delay Multiply and Sum (DMaS) algorithms. The approach is shown to increase the level of detail in crack images matching more closely to destructive results compared with other merging technique - this is particularly true when only the phase information is retained for rendering (Phase Coherence Imaging).

During the assembly of plastic gas pipelines, various types of environmental contaminants (e.g. dust, grease, etc.) can be introduced into the fusion zone during the welding process. Contamination of the joint along with other weld defects (e.g. cold fusion) eventually lead to failure of the joint under normal operational loading. It is therefore critical to be able to assess the quality of welded joints during the installation process. Accordingly, there exists considerable interest amongst the gas utilities in the development of an automated Non-destructive Evaluation (NDE) system capable of flagging defective joints in need of repair such that NDE technicians need not be deployed with every pipeline installation crew. To this end, a new Phased Array Ultrasonic Testing (PAUT) Technique has been developed and validated on a large sample set of butt fusion joints featuring common joint flaws, namely, cold fusion, lack of fusion, oil/grease contamination, coarse particulate contamination and fine particulate contamination. The technique uses custom designed polymer wedges to achieve the high refraction angles needed to achieve joint coverage. Excellent detection of all categories of joint flaws has been demonstrated on 2" to 8" diameter High Density Polyethylene (HDPE) and Medium Density Polyethylene (MDPE) joints. The analysis process has been completely automated by extracting simple amplitude based metrics which are sensitive to different types of joint flaws. The normal variation of these metrics has been determined from unflawed joints, allowing a set of significance thresholds to be set which balances the detection and false call rate.