Page 93 - Air and gas Drilling Field Guide 3rd Edition

84 CHAPTER 4 Downhole Equipment

the API material grade designations and respective standards for minimum yield,
maximum yield, and minimum tensile strengths of the steel grade. For an AISI
grade of steel to be used to fabricate the drill pipe of a particular API grade, the
AISI grade must satisfy the minimum and maximum specifications given in
Tables 4-2a and 4-2b.
Tables 4-2a and 4-2b show that for API E75 grade the minimum yield is 75,000
psi (517 MPa), the maximum yield is 105,000 psi (724 MPa), and the minimum
tensile (ultimate) strength is 100,000 psi (690 MPa). Similar data are shown for
API X95, API G105, and API S135 steel grades.

4.4.2 Heavyweight Drill Pipe
Heavyweight drill pipe is an intermediate weight per unit length drill string
element. This type of drill pipe has a heavy wall pipe body with attached extra
length tool joints (see Figure 4-21). Heavyweight drill pipe has the approximate
outside dimensions of standard drill pipe to allow easy handling on the drill rig [7].
The unique characteristic of this type of drill pipe is that it can be run in
compression in the same manner as drill collars. Most heavyweight drill pipe is
fabricated in Range 2 and 3 API lengths. It is also available in custom lengths
1
shorter than Range 2. Heavyweight drill pipe is available in 3 2 = -in (89 mm),
5
1
1
4-in (102 mm), 4 2 = -in (114 mm), 5-in (127 mm), 5 2 = -in (140 mm), and 6 8 = -in
(168 mm) nominal outside diameters. Figure 4-21 shows two typical heavyweight
drill pipe elements standing in a regular drill pipe rack in a drill rig. One unique
feature of heavyweight drill pipe is the wear pad in the center of the element. The
wear pad acts as a stabilizer and improves the stiffness of the heavyweight stand
in the drill string and thus reduces the deviation of boreholes.
Tables 4-3a and 4-3b give the dimensional and mechanical properties for Range
2 heavyweight drill pipe (tube body and tool joints). For heavyweight drill pipe sizes
1
from 3 2 = in (89 mm) and greater, the pipe tube body is fabricated of steel alloys
with a minimum yield stress of 55,000 psi (797 MPa). The tool joints for these sizes
are fabricated of steel alloys with a minimum yield stress of 120,000 psi (828 MPa).
7
The 2 8 = -in drill pipe is fabricated entirely of 110,000 psi (759 MPa) steel alloy.
Figure 4-22 shows a “tapered” drill string with a drill bit at the bottom, drill
collars above the drill bit, heavyweight drill pipe above the drill collars, and stan-
dard drill pipe above the heavyweight drill pipe.
Heavyweight drill pipe elements are used in a number of applications in rotary
drilling. Because this drill pipe can be used in compression, this drill pipe can be
used in place of drill collars in shallow wells with small single or double rotary
drilling rigs. This drill pipe is also used in conventional drill string for vertical dril-
ling operations as transitional stiffness elements between the stiff drill collars
and the very limber drill pipe. Their use as transitional stiffness elements
reduces the mechanical failures in the bottom drill pipe elements of the drill
string. The practice is to run from 6 to 30 heavyweight drill pipe on top of a
conventional BHA.