Tubulars - Drill Pipe Yield Strength and Tensile Strength

Drill Pipe Yield Strength and Tensile Strength


If drill pipe is stretched, it will initially go through a region of elastic
deformation. In this region, if the stretching force is removed, the drill pipe
will return to its original dimensions. The upper limit of this elastic
deformation is called the Yield Strength, which can be measured in psi.
Beyond this, there exists a region of plastic deformation. In this region, the
drill pipe becomes permanently elongated, even when the stretching force
is removed. The upper limit of plastic deformation is called the Tensile
Strength. If the tensile strength is exceeded, the drill pipe will fail.
Tension failures generally occur while pulling on stuck drill pipe. As the
pull exceeds the yield strength, the metal distorts with a characteristic
thinning in the weakest area of the drill pipe (or the smallest cross sectional
area). If the pull is increased and exceeds the tensile strength, the drillstring
will part. Such failures will normally occur near the top of the drillstring,
because the top of the string is subjected to the upward pulling force as
well as the downward weight of the drillstring.