Referring to the previous post, it is difficult to find drill pipe stretch table or there is no data available for you when you are really need it. This post will show you how to calculate free point constant (FPC) based on cross section of drill pipe, tubing or any cylindrical objects.
The free point constant (FPC) formula for any type of steel drill pipe is listed below:
FPC = As x 2500
where: As = pipe wall cross sectional area, sq in.
As = (OD2-ID2) x 0.7854
This method requires outside diameter and inside diameter data.
Example#1: Determine free point constant (FPC) of 4 in. drill pipe 14.0 lb/ft, inside diameter of drill pipe = 3.34 inch.
FPC = (42 – 3.342) x 0.7854 x 2500
FPC = 9512