ILI of small diameter ethylene pipeline network

Inspection (ILI) of an ethylene pipeline network in the south of France posed several unusual challenges. Geometric and metal loss inspections were required.

Challenges included: small diameter lines combined with rather long sections, the presence of a number of ID restrictions and the requirement to perform all pigging in a gas (N2) medium. Magnets and metallic components remained in the pipelines from a previous unsuccessful attempt at inspection. The gaseous medium meant the potential for substantial speed excursions. Special procedures and customised tool for both cleaning and ILI were developed. Several mobilisations imposed additional logistical requirements.

Planning for ILI had begun already in 2011, with focus on performing pigging operations while the lines were temporarily de-commissioned.

First pigging operations began mid-2013 with another vendor – unknown to 3P Services. During the runs serious problems were encountered and the project ran into difficulties with damaged and stuck tools. Several factors were identified as causing the problems: the sections were too long, the N2 pressure was not high enough and the presence of heavy wall tee-pieces at valve stations. Since several attempts had been made using the same operational settings, it was decided to bring another ILI vendor to the project.

Pigging method

After consultation, the operator agreed with 3P Services to split the lines into shorter sections and increase pressure to achieve controlled tool runs. Several special pigging procedures as well as pipeline specific pumping procedures were developed with focus to achieve tool speeds as constant as possible. Customised cleaning tools were designed and built to recover the magnets and metallic components remaining in the lines.

The method, while seemingly complicated and laborious on site, did achieve the desired speed profile. Accelerations at the valve stations were unavoidable, but substantially mitigated and the distances where inspection data was impacted were reduced.

Results and experience

Timing was of critical importance due to plant shutdown periods and all inspections were successfully completed during the planned operational windows. While some cleaning issues were occasionally encountered, all ILI data was complete and good quality.

Mechanical parts collected during magnet hunter tool run

Even though the inspections were done at the specified high pressures, the tools stopped in front of and within valve stations at thick wall tee-pieces. Speed excursions resulted when tools exited the tees. The pigging method with temporary stops to shorten section length proved effective to reduce the length of the excursions and affected ILI data.

Physical performance of the tools was good. Only negligible and normal wear was observed on the PU components and tools could practically immediately be made ready for another run.

Already after the first pigging campaign, the operator performed some field investigations together with the responsible authority, which validated the findings of the inspection reports.