The May issue of Offshore Magazine features an overview of Hess’ use of a computed tomography (CT) scanner during a recent subsea flowline inspection campaign to verify the integrity of locations that could potentially develop high levels of corrosion. The scanner allowed the company to verify integrity without interrupting production. Ultimately, this lowered finding, development, and acquisition costs and protected its continued license to operate.
The article was based on a technical presentation given by Hess Sr. Subsea Engineer Jason Harry at the Subsea Tieback Conference in March.
Only the second operator at the time to have successfully employed this technology globally, Hess found that employing CT scanning on the subsea flowline added value in multiple ways. Scanning the line without impacting production saved both time and money. The clarity of the scans made an accurate diagnosis of the problem possible, helping the company to identify the scale issue before it affected flow in the line. In addition, it confirmed that adding new, high-pressure wells to the brownfield flowline was a safe, value-adding decision.
Most commonly used in the medical field, CT scanning, also known as CAT scanning, is also applicable in the subsea environment. With the help of a remotely operated vehicle (ROV), a subsea scanner can wrap around a pipe up to 27-in. diameter and scan a 360°, 15-mm section using powerful gamma rays. These gamma rays penetrate the thick insulation surrounding the flowline and record the density distribution and wall thickness. The scanner then transmits a high-resolution (+/- 1 mm) image of the data to the offshore vessel executing the campaign. The image uses color coding to identify the densities of the materials present in the flowline. Unlike previous technologies, the subsea CT scanner’s non-invasive, highly accurate technique makes it possible to perform flowline inspections without interrupting production.
Hess’ inspection campaign took place in December 2014 at a single-well, 6-in. tieback in the Gulf of Mexico. The company had targeted the brownfield flowline for extended life based on the value of using its existing equipment; however, the flowline’s corrosion models were out of date. Hess had volumetric metal loss data for the flowline, but lacked clarity on wall thickness. To obtain this data, it decided to try the new, non-invasive CT scanning method.
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