Bending Stress In Doglegs

Stresses caused by the bending of tubulars within doglegs is computed with one of either two equations. Lubinski's bending equation resolves the stresses in which the connections contact the wall of the hole but the wall of the tube does not contact the wall of the hole. His equation not only requires a standoff at the wall but that the tube not have bending moments acting on it (positive effective tension or negative buckling tendency).

The second equation is the beam bending equation of mechanics. The equation requires that the wall of the tube fully contacts the wall of a hole which is smooth and circular; for example, slimline tubing in casing. Partial contact near the midpoint of a joint of pipe is possible and in which case a value for the bending stress would lie between the values computed with the two equations.

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