Reinhold, Spiri, and Vreeland published the following equation and table which relates the tube crushing tangential stress derived from slips and axial tensile loads. The steel in the pipe will be crushed when and if S^ is equal to the unit yield strength, YP, of the steel.
S^ = tangential stress in the pipe derived from the crushing action of slips and the effective tension in the pipe; psi
St = axial effective tensile stress in the pipe at the slips;
D = outside diameter of the pipe; inch
L = length of the slips (usually either 12" or 16"); inch
K = lateral load factor of slips
= 4.0 for a coefficient of friction of 0.08 y = taper of slip, usually 9° 27' 45"
z = friction angle = tan"1u u = coefficient of friction between slips and bushing.
= reasonable value for lubricated slips = 0.08
A = cross-sectional area of the wall of the drillpipe;
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