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 16th 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.