Plastic bearings in an inspection device for offshore drilling riser

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• What was needed: iglidur ® G plain bearing, drylin® N miniature guides, igubal ® rod end, igubal ® clevis joint
• Requirements: With high radial forces, the joints had to be mounted permanently, reliably and with as little friction as possible.
• Industry: Offshore, oil & gas
• Success for the customer: The bearings transmit the high radial centring forces with low friction and no stick-slip and minimise friction in the arm system thanks to their integrated start-up.

As the riser is exposed to aggressive media and high mechanical loads, safety and environmental protection aspects require regular inspection. A new device delivers reliable results here and replaces the conventional hand-held inspection devices. Plain bearings made of high-performance plastic play an amazing role in this high-tech application. The inspection device from Tuboscope Vetco Deutschland GmbH scans the entire inner surface of the extremely stressed riser main tube semi-automatically in just one operation. Driven centring units move, guide and centre the device in the tube. Highly sensitive special sensors record the condition of the pipe without contact. Downstream electronics and computers analyse their signals and document the inspection results. The device must be lightweight, low-maintenance and reliable. It should be robust and user-friendly and resist corrosion. In addition, it must not be affected by impurities such as corrosion products, residual liquid, sand, grease or oil. These requirements also apply to the machine elements used, such as the plastic plain bearings.

To ensure the required quality, igus® provided free bearing samples for the development and construction of a very first hand model. The prototype already met all the requirements, with the igus® products located in the centring and sensor system of the testing device.

Low friction and effective
The bolts of the articulated joints are mounted in GFM-0810-05 plastic plain bearings. These reliably transmit the high radial centring forces with low friction and no stick-slip and minimise friction in the arm system thanks to their integrated thrust collar. As a result, the entire centring system works very effectively. The representatives of the iglidur ® G product family are generally recommended when extremely high loads occur, at low to medium sliding speeds and when the bearing should be insensitive to dirt.

Highly sensitive individual sensors
The sensor system consists of many highly sensitive individual sensors that are evenly distributed around the circumference. Set at a specific distance from the pipe wall, they work completely contact-free. Their measuring accuracy is in the tenth of a millimetre range. A central synchronised adjustment enables precise, uniform and simultaneous positioning of the sensors during system calibration and when changing nominal widths. The guide system and track rods form the centrepiece. Each individual sensor sits on its own miniature guide system of type NK-02-27. In the extremely flat drylin® N-guidance in various widths, the guide carriages run without grease or oil in an anodised aluminium C-profile. The lightweight construction and low wear with a low coefficient of friction are particularly impressive. High speeds and accelerations are also possible. Adjustable track rods couple the sliding carriages to the central adjustment. They consist of igubal ® rod end with right-hand or left-hand thread, EBRM-05 and EBLM-05. igubal ® clevis joint GERMK-05 serve as counter bearings on both sides. The joint and clevis joint are set to run particularly smoothly with extremely low clearance. This means that all adjustments to the sensor system can be made smoothly and sensitively; the movements are low-friction and stick-slip-free.

Structure of the inspection device from Tuboscope Vetco Germany: 1) frame, 2) front centring, 3) rear centring, 4) sensor system, 5) electronics

Sensor system of the inspection device: 1) guide system, 2) track rod with counter bearing