= "effective tension" at one single depth, 'x'
Effective tension is the sum of the moments at a depth in a tube. It is called tension only for convenience. In the below sketch and development, the lever arm, a, is assigned a value of unity for convenience, and because its true value can not be known or computed. Thus, effective tension is the force component of a moment. Treaj is ascertained with a free body and the setting of the sum of forces acting on the free body to equal zero.
Whereas, Te£p is ascertained with a free body and the setting of the sum of the moments acting on the free body equal to zero and then setting the lever arm equal to unity.
With the sketches Trea] is
-Treal + W + P^ - Pb()A0 - WOB = 0 and also with the sketches M is
M = + Wa + [Pbi Ai - Pb0 A0 ] a + [Pt0 Ai - Pti A0] a - WOB a
Considering Af^ to be negligible, setting a = 1.0, and Teff = M, then
which is the effective tension at the top of the section. Note that tensions, pressures, and areas must be computed at one single depth. For example, 8,984 feet could be the chosen depth.
Note that if w^ is the weight of the fluid inside the pipe per unit length, w0 is the weight of the fluid displaced by the pipe, and wg is the weight of the steel per unit length in the wall of the pipe, then the effective weight of the pipe is weff = ws + Wj - w0 = "effective weight" (21a)
All variable in oil field units: lb/ft, lb/gal, inches. This is also called "buoyant weight" or "weight in mud", etc.
The buoyed weight of pipe at a specified depth is the buoyed weight per unit length of the pipe multiplied by the length of pipe below the depth.
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