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44 st / July 2014 www.sea-technology.com of friction caused by the sharp teeth offsets the 8° taper against the bowl and causes the slip plane to be at the bowl interface rather than at the pipe interface. If a brass slip segment with no teeth is substituted, the coeffcient of friction between the slip segment and the pipe would be the same as the coeffcient of friction between the slip segment and the bowl. With the 8° taper adding a vertical component to the slip seg- ment, the sliding would occur between the slip segment and the pipe. The pipe would then drop. To solve this problem, we did not rely on the single wedging action as- sociated with conventional slips, but rather went with a double-wedging style. The four brass slip segments are not engaged by a conical bowl but rather by two slip carriers approaching from the left and right. The slip carri- ers in turn are engaged by the bowl as they are lowered, but not by a conical surface. There are two 8° fat surfaces that provide the frst wedging. The frst wedging force is amplifed by the sec- ond wedging such that the net normal force against the pipe is greater than the normal force against the bowl so failsafe support is achieved. As these slips were designed and were in the production process, they were used to investigate the synthetic rope testing. For frst capacity, we built a tension test setup and tested a launch and recovery system umbilical with 1.25-inch-outer- diameter brass slips. It has an opposing set of the slips with the double wedg- ing action and was pulled to 13,000 pounds. A slight brass discoloration oc- curred on the umbilical, but it was not mechanically harmed externally. Ad- ditional testing will be required to de- termine what level of compression can be imparted to the umbilical without impacting the conduction. The slip segments were 2.75 inches long and so the 13,000-pound load was about 4,727 pounds per inch, which was not suffcient for carrying the load without degrading the slips. The same test setup was used to determine if the same failsafe capac- ity was available between brass slips and synthetic rope. Again, two iden- tical slip assemblies were attached to the synthetic rope and stretched on the tension frame. The synthetic rope was a 1-inch-diameter Lankhorst (Sneek, Netherlands) LankoForce rope. The testing was successfully con- ducted to 4,200 pounds before the slips ran out of stroke. This is not a characteristic normally associated with supporting pipe because steel pipe is relatively rigid. Due to air spaces in the synthetic rope, it continues to com- press for a considerable distance be- fore it goes completely solid. The slips available did not have adequate stroke to go completely solid. The diffculty in handling synthetic rope lies in its relative "fuffness" in comparison to steel rope or pipe. The synthetic rope needed to be "stuffed" into the slips before the testing could start. The synthetic rope after testing indi- cated a hard core and sides that could not be contained within the present set of slips. It also indicated that the syn- thetic rope has a memory. Compressive stresses are also added to the synthetic rope in a conventional pulley system, but at a lower level. After the testing, the rope was twisted slightly and the memory was gone completely. Conclusions From our testing, we determined that synthetic rope can be supported in failsafe slips. Design work is required to quickly engage the synthetic rope and keep it within the slip area. Work also needs to be done with vendors to determine how to manufacture a syn- thetic rope that is as compact as pos- sible. Analysis needs to be conducted to fgure out if there are detrimental ef- fects when compacting and releasing the synthetic rope. References For a list of references, contact Ben- ton Baugh at bbaugh@baughengrs. com. n (Top) ROV umbilical tested with brass slips showing minimal marking. (Bot- tom) Synthetic rope being tested be- tween a pair of failsafe double wedging slips with brass inserts. Dr. Benton F. Baugh, Ph.D., P.E., is president of Baugh Consulting Engineers, Inc. and has previously worked with Radoil, Beta, Vetco, Cam- eron, Camco and Bowen Tool Co. He is a member of the National Academy of Engineering and a fellow of the National Acad- emy of Inventors, American Society of Mechanical Engineers and Marine Technology Society. He holds more than 100 U.S. patents.