When a tensile load is applied into a drillstring, it results in elongation of the drillstring.

The formula to determine pipe elongation is listed below;

**Oilfield unit**

**e = (L x T) ÷ (735,000 x W)**

Where;

e = elongation, inch

L = length of drill string, ft

T = tensile load, lb

W = drill string weight, lb/ft

**Metric (SI) unit**

**e = (L x T) ÷ (26.7 x W)**

Where;

e = elongation, mm

L = length of drill string, metres

T = tensile load, kN

W = drill string weight, kg/m

**Note:** The equations are taken from API RP 7G 16^{th} Edition, August 1998.

**Determine the pipe elongation from the following data (this example will use “oilfield unit” for calculation.**

5” DP, S-135, 4-1/2” IF Connection. The pipe specification is listed below.

W = 23.52 ppf

Length = 8,500 ft

Pick up weight = 300 Klb

Block weight without drill string = 70 Klb

Tensile load applied into the drill string is equal to pick up weight minus block weight.

T = 300 – 70 = 230 Klb

e = (8,500 x 230,00) ÷ (735,000 x 23.52)

e = 113.1 inch

**Ref books: Drilling engineering books**

Good stuff for oil field duds.

Very usefull

How did you derive the formula to determine the drill pipe elongation due to tension?

This is derived from Young’s Modulus relationship.