Recently transmission pipeline operators have started designing pipe spools with manufactured cracks of very precise size and orientation for the purposes of qualifying measurement technologies.  The manufactured cracks are very similar to naturally occurring cracks and can be made to have varied profiles and off-planar shapes (like hook cracks).  The manufactured spools are installed on a transmission pipeline at either the pipe launcher, the receiver or in-line such that an ILI tool passes through it during a field run on a transmission pipeline.  This produces excellent data to evaluate measurement performance because the crack sizes are precisely known, crack morphologies are similar to realistic cracks and the ILI tool is tested in field conditions.  This paper describes the effect on the estimated ILI tool measurement performance for various combinations of manufactured cracks in a pipe spool.  The cases described include varying the number of manufactured cracks in the spool (the value of each additional crack), varying the distribution of sizes used (the value of large vs small cracks), and varying the number of measurements made on each crack (the value back-to-back ILIs). 

Traditionally, inline inspection tools have been evaluated based on field measurements.  However, since field measurements are subject to measurement errors, a larger data set is required to have confidence in the estimated ILI measurement performance.  In addition, a bias in both the ILI and the field measurements is difficult to ascertain without knowing the true sizes of a few cracks.  The model used to asses the effects of manufactured cracks simultaneously solves for the bias, slope, standard deviation error, linearity and probability of detection performance using a Markov Chain Monte Carlo simulation of a hierarchical Bayesian model.  Each parameter is described by its mean performance and 95% credible intervals and plotted as a full distribution which are compared to evaluate the performance of each case. 

Manufactured cracks are a new technology and present an interesting opportunity gain better insights into key measurement technologies that help integrity engineers maintain reliable transmission pipeline networks.


Manufactured Cracks in Pipe Used to Evaluate ILI Measurement Performance

Division / Sponsors: 
Pipeline Systems Division

Paper Proceedings: https://asmedigitalcollection.asme.org/IPC/IPC2020/volume/84447

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