Drill String Components-Drill Pipe-Drill Pipe Selection Criteria
Drill Pipe
Let's start with definition of drill pipe.
In Schulumberger Oilfield Glossary drill pipe defined as:
Tubular steel conduit fitted with special threaded ends called tool joints. The drillpipe connects the rig surface equipment with
the bottomhole assembly and the bit, both to pump drilling fluid to the bit and to be able to raise, lower and rotate the bottomhole
assembly and bit.
http://www.glossary.oilfield.slb.com/Terms/d/drillpipe.asp
Drill pipe serve different functions from DC's. Their duty only conduit drilling fluid and rotary to the bit. It is mechanical
linkage from surface to the BHA. So drillpipes not used to weight on bit and they don't have to be heavy and rigid as
DC's
API recommend 3 type of classification for Drill Pipes;
1. Length Classification
Range-1: 18 to 22 ft
Range-2: 27 to 30 ft (Most Common)
Range-3: 38 to 5 ft
2. Grade Classification (Min Yield Strength)
This parameter most important parameter because that is restrict our pull limit
Yield Strength is defined as the stress at which a material begins to plastic deformation. Before the yield point the material will
deform elastically and it will return to its original shape when the stress is released. If the tension applied is over this point the
deformation will be permanent. The chart below you will see different yield strength (psi) via DP different DP class
As you realise the grading number denote 1000's of psi min. yield strength. i.e. D-55= 55000psi
3. Used Drill Pipe Worn Condition Classification
Class-1 (new) represented with 1 white label, this class new never has been used
Premium class represented with 2 white label, Remaining wall not less than 80%
Class-2 represented with 1 yellow label, Remainin wall not less than 70%
Class-3 represented with 1 orange label, remaining wall less than 70%
Class-4 represented with 1 green label
Worn grading is an important parameter because as it should be as while decreasing wall diameter of drill pipe yield
strength also decreases. i.e. Class-2 drill pipe yield strenght approximately less than 30% from new drill pipe.
This figure show us relation between wall thickness and drill pipe worn class.
and about labels different companies could give different labels from other but here is a representation about labeling
which made by StradEnergy company.
http://productadmin.stradenergy.com/Content/img/uploads/productdocument/productdocument_2116.pdf
and more information let's see the API RP 07G table-24
Tool Joints
The enlarged and threaded ends of joints of drillpipe. These components are fabricated separately from the pipe body and welded
onto the pipe at a manufacturing facility. The tool joints provide high-strength, high-pressure threaded connections that are
sufficiently robust to survive the rigors of drilling and numerous cycles of tightening and loosening at threads. Tool joints are
usually made of steel that has been heat treated to a higher strength than the steel of the tube body. The large-diameter section of
the tool joints provides a low stress area where pipe tongs are used to grip the pipe. Hence, relatively small cuts caused by the
pipe
tongs
do
not
significantly
impair
the
strength
or
life
of
the joint of
drillpipe.
( http://www.glossary.oilfield.slb.com/Terms/t/tool_joint.aspx )
addition of above explanation tool joints are basically elements of drill pipe that provides connections of drill string. All API tool
joints have minimum yield strength of 120000 psi regardless of the grade of the drill pipe. API sets tool joint torsional strength
at minimum 80% of the tube torsional strength. Make up torque determining generally 60% of the tool joint torsional strength.
In
this
chart
you
will
see
tool
joint
marking
There are too many thread types and they are interchangeable with others. Thread types are important thing because we have to
use same thread type in our drill string. Some cases drill string components could have different thread types. So we have to use
cross-over subs in able to connect them. In this chart you will see interchangeability of connections.
and most common thread type is in DP is NC. NC = numbered connection. If we measure a pin thread distance from the 5/8" to
shoulder. We will find pitch diameter and for ex. a pitch diameter is 5.0417 inches Multiply pitch diameter with 10 , 50.417
inches.
First
There
Drill
2
digit
are
indicate
17
NC
NC
connection
is
in
Pipe
use
so
this
from
thread
NC-10
is
to
NC50
NC-77
Upsets
The upset refers to the wall of the tool joint at the threaded connection. Drill pipe is offered with an internal upset (IU), an external
upset
(EU),
or
an
internal-external
upset
(IEU).
Increased thickness provide stronger connection decreases pipe failure risks. While remaining ID remain same size
it
enables
to
good
flow
characteristic.
Internal
Extarnal
Upset:
Upset:
OD
ID
remain
remain
same.
same.
Here is the some chart about recommended make-up torque and tensile load ( API 7 RPG ) after skim through this
chart
we
will
do
an
example
about
how
to
find
tensile
load.
Make-Up
Torque
Part
of
the
strength
of
the
drillstring
and
the
seal
for
the
fluid
conduit
are
both
contained
in
the
tool
joints.
It
is
very
important
therefore,
that
the
correct
make-up
torque
is
applied
to
the
tool
joints.
If
a
tool
joint
is
not
torqued
enough,
bending
between
the
box
and
pin
could
cause
premature
failure.
Also,
the
shoulder
seal
may
not
be
properly
seated,
resulting
in
mud
leaking
through
the
tool
joint,
causing
a
washout.
Exceeding
the
torsional
yield
strength
of
the
connection
by
applying
too
much
torque
to
the
tool
joint
could
cause
the
shoulders
to
bevel
outward
or
the
pin
to
break
off
the
box.
Recommended
make
up
torques
for
drill
pipe
and
tool
joints
are listed in the API RP 7G.
Calculate
Tensile
As we
If we
5"
Tensile
the
capacity
new
is
maximum
5"
allowable
S-135
pulling
grade
force
before
tensile
reach
capacity
elastic
limit.
mentioned before 135 in drill pipe grading code represent 1000* min yield strength in psi.
multiply yield strength (psi) with cross sectional are ( sq-in) we will find tensile capacity.
DP
ID:4,276"
so
cross
sectional
are
is=
5,275
sq-in
Capacity = 135000 x 5,275= 712070 lb. (please check with API chart you will see same result)
So
if
we
do
this
calculation
for
premium
DP,
only
cross
sectional
are
changed.
We mentioned before in premium DP wall thickness is the 80% of the new drill pipe.
New
DP
wall
thickness
is
=
5"-4,276"=
0,362"
Premium
DP
wall
thickness
is=
0,362"*0,8=0,290
So
inner
diameter
is
not
change
wearing
only
occur
in
outer
diameter
so
premium
DP
outer
diameter
is
=
4,276+2*0,290=
4,856"
new
cross
sectional
area
is
= π(
4,856^2-4,276^2)/4=
4,154
sq-in
Tensile
Capacity
is
4,154
sq-in
x
135000
psi=
560764
lb.
Drill
In
Pipe
drill
pipe
selection
Drill
Drill
Selection
2
major
Pipe
parameters
Criteria
take
consideration.
Size
Pipe
They
and
are
Weight
Strength
Largest ID is suitable for drilling applications, largest ID provide less pressure loss and it allows to work in large gap
interval.
Drill
Drill
Drill
pipe
have to support all
pipe
have
pipe
have
to
weight
below
to
resist
it
including
sustain
burst
BHA
and other
over-pull
collapse
and
drill
pipes.
load.
forces.
Tension
Design
Greatest tension occur at top joint on the drill string. So total weight carried by the top joint calculated as with this
simple
equation:
Total Weight: [(Ldp X Wdp)+(Ldc X Wdc)] x BF
Ldp = length of Drill Pipe
Wdp = weight of Drill Pipe per unit length
Ldc = weight of Drill Collars
W dc = weight of Drill Collars per unit length
Margin
Of
Overpull
In some case like stuck pipe we need to apply over pull our drill string. As you know min. yield strength restrict our
over pull capacity in order to prevent permanent deformation. You could find maximum tensile load in API charts
above.
First
we
have
to
find
maximum
allowable
tensile
load
from
API
charts.
Then multiply
Tmax=
with
max allowable
0,9
MOP=
load
(SF)
with
safety
Tmax
MOP=
[0,9
(SF)
If
Ldp
tensile
x
[(Tyield
When
X
stuck
Tyield.]-
[
[(Ldp
X
will
find
Tmax.
Tyield.
0,9-MOP)
/
(Wdp
situation
Tsurf
Wdp)+(Ldc
isolate
pipe
we
-
we
=
factor
x
X
Wdc)]
x
Ldp
X
occur
BF)]
-
BF
BF]
alone
[(Wdc/Wdp)
should
X
be
Ldc]
neglected
Exercise
What
is
DC
MOP=100K
DP
BF=
the
maximum
hole
length:
600'
OD:5",
19,5
that
can
be
drilled
DCweight=
with
this
150
lb/ft,
DP?
lb/ft
lbs
NC-50
0,85
G-105
Solution:
We
So
assume
our
Tmax=
drill
pipe
is
0,9
premium
class
x
so
it's
yield
436150=
strength
is
392535
436150
lb
lb
Tsurface
=
[(Ldp
X
21,92)+(600
X
150)]
x
0,85
21,92 lb/ft (from API RP7G tale-9) is the approximate weight (weight with tool joints) of the DP
We
put
Tmax
in
order
to
Tsurface
to
find
max.
drill
depth.
Ldp
=
Ldp=
[(392535
As
Ldp=
you
[(Tyield
realize
[(392535
X
0,9-MOP)
lb
-
we
done
lb
-
0)
/
(21,92
this
100000
/
with
lb
)
(Wdp
X
0,85)]
neglect
/
X
-
MOP.
(21,92
X
BF)]
-
[(150/21,92)
So
1)]
Solve
-
[(Wdc/Wdp)
X
again
600]
with
[(150/21,92)
X
X
=
Ldc]
16962
considering
600]
=
ft
MOP
9840
ft
We take BF=1 while solving this problem with MOP because we need MOP in stuck situation and while stuck pipe
situation
occur
BF
should
be
neglected.
Collapse
Load
The highest external pressure tending to collapse the string will occur at the bottom when the
string is run empty into the hole. (This only occurs when running a Drill-Stem Test - DST tool).
If a non-return valve is run (preventing upward flow of fluid into the drill-pipe) it is normally
standard practice to fill up the pipe at regular intervals
when running in. The
highest
anticipated
Pcollapse=0,052x
external
pressure
MW
on
the
(ppg)
pipe
x
is
given
TVD
by
(ft)
This assumes that there is no fluid inside the pipe to resist the external pressure. The collapse
resistance of new and used drill-pipe are given in table below
The collapse resistance of the drill-pipe is generally de-rated by a design factor (i.e. divide the collapse rating by
1.125). A suitable grade and weight of drill-pipe must be selected whose de-rated collapse resistance is greater than
Pc.
Bending
Strength
Ratio
BSR is the ratio of the relative bending stiffness of the box to the pin for a BHA connection. It is used as an approximate
indicator

of
the
suitability
of
a
connection
A connection is be supposed to be balanced if the BSR is 2,5
When BSR is higher pin failure tend to be occurred
When BSR is lower box failure tend to be occurred.
between
two
BHA
components.
and here is the some API charts about BSR
Stiffness
Stiffness
Ratio
ratio measures
the
SR
should
SR should be 3,5 for rough drilling.
stiffness
be
of
a
connection
5,5
in
a
for
transition
between
routine
2
type
of
pipe.
drilling
Slip
Crushing
Slip crushing force is an additional force that should be consider that avoiding crushing in drill pipe slip are.
Burst and Collapse
Force
Heavy
Weight
Drill
Pipe
HWDP's are used in transition zones between DC and DP to prevent DP buckling.
HWDP' are the same OD as a standard drill pipe but with much reduced inside diameter (usually 3” for 5” DP) and has an integral
wear pad upset in the middle.
It is used between standard Drill Pipe and Drill Collars to provide a smooth transition between the different sections
of the drillstring components.