Tubulars - Drill Pipe Grades

Drill Pipe Grades


There are four common grades of drill pipe which define the yield strength
and tensile strength of the steel being used.


Grade E, composed of a lower grade of steel, is sometimes referred to as
“mild” steel, because it has the lowest yield strength per unit area. As such,
mild steel is generally defined as steel with a yield strength of less than
80,000 psi. As can be seen, Grade E drill pipe has a lower yield strength in
psi than the high strength drill pipe grades, however once the yield strength
is exceeded, it can withstand a greater percentage of stretch or “strain”
prior to parting. Lower grades of steel such as Grade E are also more
resistant to corrosion and cracking. Grade E has been utilized in medium
depth wells (10,000 to 15,000 feet).
In the 1980's, as horizontal drilling, high inclination extended reach wells
and deep hole drilling applications increased, so has the demand for high
strength drill pipe. It is common in deep hole applications for high strength
drill pipe to be utilized in the upper portion of the string to keep the tension
load within the capabilities of the steel. In high dogleg environments, such
as those encountered in medium and short radius horizontal wells, high
strength drill pipe can withstand the associated bending stresses. In high
inclination and horizontal wells, high strength drill pipe is also commonly
run in compression. One drawback of higher grades of steel is that they are
generally less resistant to corrosion, like that caused by hydrogen sulfide
(H2S). Limited availability also contributes to the higher cost.
The yield and tensile strengths are in “pounds per square inch of the cross
sectional area” of the drill pipe. In order to calculate yield strength in
pounds, this cross sectional area must be known. This leads to a discussion
of drill pipe classes.