Gripping Without Slipping — The Safe Handling and Running of Chrome Pipe with Hard Surfaces

Abstract

Abstract In a corrosive downhole environment, the service life of a completion can be severely reduced if suitable precautions are not taken. Pipe made of corrosion resistant alloys (C.R.A.) is used to minimize corrosion. Recently, steel manufactures have developed modified corrosion resistant alloys (C.R.A.), specifically derivatives of Cr13, that are characterized by a black smooth scale surface on the outside of the pipe. When these so called "Super" or "Hyper" alloys were first used, occasional slipping was reported by field personnel. Fortunately no string was lost and no injuries occurred, however, precious rig time was lost in resuming safe operations. These slippages occurred with various inserts and with all types of slip-type elevators or spiders. An investigation carried out by the University of Hannover revealed that the surface scale on the pipe had a hardness of over 60 Rc. Even inserts specifically designed for C.R.A. pipe that use special gripping elements, such as the Micro-Grip™ system have a hardness that is only slightly higher than this surface scale. Using conventional wedge type spider and elevator systems can lead to slippage under certain load conditions, if no special precautions are taken. Based on these results and on the operating principles of wedge type spiders and elevators, a new Compact Spider/Elevator was designed. This device can be either air or hydraulically operated and puts an additional downward force onto the slip, as much as 40 tons for the hydraulic version, so that a firm grip is assured. In addition to conventional steel inserts, the device can be equipped with so called MicroGrip ™ inserts, a gripping system that distributes the required load equally onto a large number of small peaks. This minimizes the indentation of each single peak and thus, as previous research and field experience has shown, preserves the surface integrity of the pipe with regard to corrosion [2, 3, 4]. The device can be run flush-mounted, further enhancing safety on the rig-floor.