## Determine free point constant FPC

The free point constant can be determined for any type of steel drill pipe if the outside diameter, in., and inside diameter, in., are known:

where: As = pipe wall cross sectional area, sq in.

Example 1: From the drill pipe stretch table: 4-1/2 in. drill pipe 16.6 lb/ft — ID = 3.826 in.

FPC = (452 — 3.8262 x 0.7854) x 2500 FPC = 4.407 x 2500 FPC = 11,017.5

Example 2: Determine the free point constant and the depth the pipe is stuck using the following data:

2-3/8 in. tubing — 6.5 lb/ft — ID = 2.441 in. 25 in. of stretch with 20,000 lb of pull force a) Determine free point constant (FPC):

FPC = (2.8752 — 2.4412 x 0.7854) x 2500 FPC = 1.820 x 2500 FPC = 4530

b) Determine the depth of stuck pipe:

20 Feet

Feet of free pipe = 5663 ft Method 2

Free pipe, ft = 735,294 x e x Wdp differential pull, lb where e = pipe stretch, in.

Wdp = drill pipe weight, lb/ft (plain end)

Plain end weight, lb/ft, is the weight of drill pipe excluding tool joints:

Weight, lb/ft = 2.67 x pipe OD, in.2 — pipe; ID, in.2

Example: Determine the feet of free pipe using the following data:

5.0 in. drill pipe; ID — 4.276 in.; 19.5 lb/ft Differential stretch of pipe = 24 in. Differential pull to obtain stretch = 30,000 lb

Weight, lb/ft = 2.67 x (5.02 — 4.2762) Weight = 17.93 lb/ft

Free pipe = 10,547 ft

+4 -3

### Responses

• bucca took-brandybuck
What the formula for the free ooint constant?
2 years ago
• crispus
How to calculate drill pipe free point?
10 months ago