Accurate sizing and classification of cracks continues to present significant challenges to the pipeline and non-destructive testing (NDT) industries. This case study highlights the importance of a combination of technology, expertise and experience for the quality of the results.
ROSEN performed a combined UTCD and EMAT in-line inspection (ILI) on a 20 inch crude oil pipeline. After the inspection, the customer hired a local contractor who was not able to identify any indications in the first three anomalies previously reported by ILI. As a result, the customer was convinced that the pipeline did not have any associated crack-like indications and that the tool was not performing within its specification.
ROSEN technicians underwent an assessment process at the operator's facility, ensuring their competence was validated through blind trials on a number of validation spools. This process proved high confidence not only in the technicians capabilities but also in their precision regarding sizing tolerance.
The customized solution yielded substantial savings of cost and effort for the operator. Furthermore, it significantly reduced the risk of the operation by rendering any subsea work obsolete.
All requested inspection data was delivered in one run with outstanding
reliability and accuracy. Based on these high-quality results, the operator was able to execute a corrosion growth assessment and a pipeline lifetime calculation. All this was valuable input for a detailed repair plan and an integrity management plan, including required inspection cycles.
The customer asked the ROSEN field verification team to visit the site to validate the findings of the tool and to provide a second opinion to the local contractor they had chosen.
ROSEN was asked to perform three verifications during this visit. The first feature identified by ILI was an internal 2.4 mm deep internal long seam anomaly. Having scanned the area with an encoded Phased Array Ultrasonic Testing (PAUT) device, the local contractor was unable to identify the feature and again reported “no indications present.” After repeating the scan using its own equipment and setups, ROSEN confirmed the results of the initial inspection, stating that PAUT could not identify any significant defects.
As part of the verification process, ROSEN also performed a Time of Flight Diffraction (ToFD) inspection, which can identify defects not visible in the PAUT inspection by looking for tip diffractions. The ToFD data indicated a significant defect in the weld toe on the internal surface within the ILI indication location. It was recommended that the weld cap be ground flush to allow detailed examination and to improve the sizing accuracy of the ToFD. A planar, 2.2-mm-deep feature was identified at the toe of the weld by both ToFDs and verified by a focused PAUT inspection.
The local contractors were competent on paper, had all relevant qualifications, used high-quality equipment and produced high-quality reports, but they did not have the experience to understand the implications of ILI tool validation compared to conventional non-destructive testing (NDT). This is one of several in-field verifications that demonstrate the importance of competence in ILI validation.
As a result of this validation, the client accepted that there was a potential cracking issue and began to plan the next ILI campaign, which would include a crack inspection, support with the integrity management framework for cracking and additional in-field support from ROSEN.
Field data collected by ROSEN provides a number of benefits that lead to the fair representation of the ILI system and long-term improvement of the ILI service: