Plastic bearings in an inspection device for offshore drilling riser

Profile

• What was needed: Miniature guide, plastic bearings and adjustable tie rods
• Requirements: Light, low-maintenance, reliably robust and user-friendly 
• Industry: Oil production
• Success for the customer: Lubrication-free guide carriages with low wear and low coefficient of friction.

 
When drilling for oil and gas in the offshore sector, so-called "drill risers" connect the drilling platform with the seabed. Many individual risers are flanged together as in an umbilical cord. They transport the media during the drilling process. They also protect and guide the drill pipes that run inside the riser main pipe.

Inspection device from Tuboscope Vetco Germany

Problem

Since the riser is exposed to aggressive media and high mechanical loads, safety and environmental protection aspects require regular inspection. A new device provides reliable results here and replaces the conventional hand-held testing 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 pipe semi-automatically in just one operation. Driven centring units move, guide and centre the device in the pipe. Highly sensitive special sensors detect the condition of the pipe without contact. Downstream electronics and computers evaluate their signals and document the inspection results. The device must be lightweight, low-maintenance and reliable. It should be robust, user-friendly and resistant to corrosion. Furthermore, it must not be affected by impurities such as corrosion products, residual liquid, sand, grease or oil.  These requirements also apply to the used machine elements, for example the plastic plain bearings.

Solution

To ensure the required quality, igus® provided free bearing samples for the development and construction of the very first hand model. Already the prototype fulfilled all requirements, whereby the products from igus® are located in the centring and sensor system of the test device.
 
Low-friction and effective
The pins of the joint connections are mounted in plastic plain bearings "GFM-0810-05". These transmit the high radial centring forces reliably with low friction and without stick-slip, and minimise friction in the arm system thanks to their integrated thrust collar. This makes the entire centring system work very effectively. The representatives of the iglidur® G product family are generally recommended for extremely high loads, low to medium surface 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. Adjusted to a certain distance from the pipe wall, they operate completely contact-free. Their measuring accuracy is in the tenth of a millimetre range. A central synchronous adjustment enables the exact, even and simultaneous positioning of the sensors during system calibration and when changing the nominal width. Guide systems and tie rods form the core of the system. Each individual sensor is mounted on its own miniature guide system of type "NK-02-27". In the extremely flat drylin® N guides in various widths, the guide carriages run without grease or oil in an anodised aluminium C-profile. Particularly impressive are the lightweight design and the low wear with low coefficient of friction. Furthermore high speeds and accelerations are possible Adjustable tie rods couple the sliding carriages to the central adjustment. They consist of rod end bearings with right-hand or left-hand threads, "EBRM-05" and "EBLM-05". Clevis joints "GERMK-05" are used on both sides as counter bearings. The rod ends and clevis joints are adjusted to run particularly smoothly with very little clearance. This enables all adjustment work on the sensor system to be carried out 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) Tie rod with counter bearing