Identifying and sizing axial seam weld flaws in ERW pipe seams and SCC in the pipe body using ultrasonic imaging


    Originally published in 11th Iternational Pipeline Conference 2016, November 10th (Volume 1 Pipeline and Facilities Integrity)

    A significant portion of global energy pipeline infrastructure is constructed with pipe materials manufactured using the Electric Resistance Weld (ERW) process. The longitudinal seam of these ERW pipelines may contain manufacturing flaws and anomalies that can grow over time through pressure cycle fatigue, resulting in a pipeline integrity failure. These flaws can be present in both vintage pipe (generally pre-1970) manufactured using a low frequency ERW process, and more modern pipe manufactured using a high frequency ERW process. Such ERW seam anomalies are difficult for current in-line inspection and in-ditch non-destructive testing (NDT) inspection technologies to detect, differentiate, and size. This is driving the industry to better understand current inspection performance and to develop new technologies for ERW seam anomaly.

    Ultrasonic (UT) imaging using inverse wave field extrapolation (IWEX) is an emerging NDT technique that is being applied to improve differentiation and sizing of anomalies in pipelines. This paper describes the developing use of IWEX, the challenges related to seam weld integrity and assessment and stress corrosion cracking (SCC) assessment, and the results of studies to evaluate performance. UT imaging is also compared to current state-of-the-art techniques, such as UT phased array (PA). A goal of the project is to produce images capable of distinguishing between cold welds, surface-breaking hook cracks, non-surface breaking upturned fibre indications, poor trim, offset plate edges and anomalies with fatigue cracking.
    The goal is to size all of the cracks in an SCC colony and produce a 3-D map of the area. In mapping these anomalies, however, the sizing needs to be sufficiently accurate to qualify in-line inspection tools for crack inspection.
    UT imaging technologies involve full waveform capture and inversion to provide an image of anomalies − similar to existing technologies in other fields, such as medical ultrasound imaging and seismic imaging.
    UT imaging is used to generate a cross-sectional view of the ERW seam, showing the dimensions and orientation of indicators in the seam.
    Multi-mode imaging is used for samples of known thickness. UT imaging using arrays is based on capturing the full waveform of data received at the individual array elements, often called full matrix capture (FMC) data. An image is produced from this data by assembling a collection of A-scans, using all of the pairs of array elements as sources and receivers. In contrast to beam forming (as used by phased array inspection), imaging approaches allow for each point in an area of interest to be focused on individually.
    This paper describes efforts to assess the detection, characterisation and sizing performance of IWEX by comparing it to metallographic chilled forced fracture along a 3 defect surface, metallographic section across defects in the circumferential direction, and various other NDT technologies, such as phased array (PA) and time of flight diffraction (ToFD). The goal is to significantly improve detection, characterisation and sizing, compared to the methods currently available.
    Using IWEX UT images, the location, shape and orientation of the detected anomaly are used to identify the anomaly type, in a bid to improve differentiation between different types of seam defects. Once identified, the edges of the anomaly are used to size the defect. The objective here is to improve sizing to the point where in-ditch measurements could soon be used to qualify in-line inspection tools for crack detection and sizing. Read more.

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