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Improving the Retention Capacity of Clamping Elements

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Document pages: 5 pages

Abstract: An analysis of the discarded drill pipes that had been used in wedge grips has revealed that the main reason for pipe rejection is the reduction of a pipe wall as a result of plastic deformations, due to damaging the pipe surface by the die teeth. The long-term exposure to loads results in the plastic deformations of cylindrical parts, which could lead to unacceptable damage and distortion of the shape. In the oil industry, when drilling and casing pipes are clamped, stresses over some areas in the capture zone exceed the fluidity limit. Multiple clamps of the pipe could reduce the wall of the pipe in the capture area, which leads to premature failure of the pipe. Pipe crumpling occurs not immediately when the load is applied but gradually, by local plastic deformity of the pipe at various points in length and circumference, where the stresses exceed the limit of the fluidity of the pipe material. In order to prevent unacceptable deformations of pipes during hoisting operations, we have considered the possibilities to reduce loads.In this regard, special attention has been paid to the design of clamping jaws that provide the increased retention capacity and the technology of their manufacture. The greatest retention capacity is ensured by jaws with an oblique intersecting notch. In such jaws, the teeth of the notch are arranged chequerwise. This makes it possible to exclude the formation of vertical grooves on the body of the pipe due to slippage induced by the axial load. However, the manufacture of such notches at the inner cylindrical surface of clamping jaws is associated with some difficulties. This relates to that there are no standard tools for making such notched surfaces of complex configuration. The result of our research is the designed and manufactured special tool, as well as the technology for its fabrication. That has made it easier to cut the notches on clamping jaws that ensure the reliable capture of drill pipes.

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