In-line inspection (ILI) is often used to estimate failure pressure from anomalies as part of the integrity management of pipelines. The goal of this project is to improve failure pressure estimates of stress corrosion cracking (SCC) colonies by advancing field measurements and comparing ILI tool data. Electromagnetic acoustic transducer (EMAT) ILI technologies have made significant strides in providing crack depth measurements for SCC colonies, and emerging technologies such as ultrasonic testing (UT) imaging are providing more accurate in-ditch validation data. For new ILI technologies,...
In-line inspection (ILI) is often used to estimate failure pressure from anomalies as part of the integrity management of pipelines. The goal of this project is to improve failure pressure estimates of stress corrosion cracking (SCC) colonies by advancing field measurements and comparing ILI tool data. Electromagnetic acoustic transducer (EMAT) ILI technologies have made significant strides in providing crack depth measurements for SCC colonies, and emerging technologies such as ultrasonic testing (UT) imaging are providing more accurate in-ditch validation data. For new ILI technologies, feeding back accurate field measurements to vendors is an essential part of the process for improving ILI estimates of failure pressure.
This project was designed to improve failure pressure estimates with three tasks spanning three years. Year 1 (Task 1) included the development of ultrasonic imaging processes and procedures for gathering accurate in-ditch measurements of depth, length and separation for SCC. Year 2 (Task 2) comprised field trials of the ultrasonic imaging and collection and analysis of EMAT data. Validation was performed and improvements to signal analysis for crack sizing and interaction criteria were made. Year 3 (Task 3) work included validation by means of burst tests to evaluate the performance of the model that predicts failure pressure based on ultrasonic imaging measurements.
The main focus of Year 1 was comparing the dimensions of SCC colonies measured by X-ray computed tomography (XCT) to IWEX ultrasound imaging for thirty 4-inch (10 cm) wide plates containing SCC colonies. For truth data, two of these samples were destructively evaluated by breaking open cracks frozen in liquid nitrogen and sectioning through multiple parallel cracks with subsequent polishing of samples. Comparisons of the XCT and IWEX to the freeze break sample results are presented in this report across profiles of cracks in an SCC colony. The details of the work are documented in the first report for this project and summarized in this report.
Year 2 focused on collecting data in the field with the IWEX system based on EMAT inspection results. A process was developed to facilitate comparisons between IWEX and EMAT data to allow an in-ditch verification of the axial cracking. Due to the technology differences between ILI and IWEX, the ILI recorded data/signals show less detail and do not allow for discrimination of the individual flaws the same way that IWEX does. Even with the differences in sampling and resolution between the techniques, it is possible to establish parameters for burst pressure calculations. A second goal of Year 2 was to select samples for Year 3 pressure testing.
Year 3 focused on pressure testing of four samples to improve and verify failure pressure predictions calculated from field NDE and ILI measurements of SCC crack colony dimensions. Also examined was the potential of the recently developed intelligent interaction criteria (PRCI SIA-1-5) to predict failure pressure using IWEX results. The application of traditional interaction criteria produced mixed results. For the intelligent interaction criteria, the comparison between experimentally determined and predicted failure pressures was excellent, with a 3% average overestimation of predicted values and tight error distribution with a 3% standard deviation.
Along with the specific results, this project successfully demonstrated a general approach for improving crack ILI technology using field NDE methods.