Hello
In this video I`ll talk about the drill rods
and tool joint couplings.
Drill rods are used to transfer torque to the drill bit
and deliver drilling fluid downhole.
The drill rod consists of a pipe and tool joints
that connect to the ends of the pipe.
The design is not different in deep oil and gas drilling,
or shallow water well drilling.
But the quality requirements are differed.
Tool joints and the drill rods that are used in deep drilling
must be manufactured strictly in accordance with the standards for this products.
The standards clearly describe the manufacturing technology,
dimensions, characteristics, and quality control methods.
In this industry accidents are very expensive,
so the emphasis is placed on maximum reliability and durability
during the writing of the standard.
To reduce the weight of the drill string, the pipe ends are upset.
This technological operation increases the wall thickness
at the ends of pipe to make a threading.
The upsetting can be internal, external, or combined.
The drill rods, that are used for drilling of shallow wells, must be lightweight,
so that 2 persons can work with them manually.
Also here are used more affordable materials to keep cost down.
Drill rods are manufactured of seamless thick-walled pipe.
Drill pipe couplings are made of 3140H steel,
or 3140 for shallow wells.
To connect the drill pipes is used a special tool joint thread.
This thread is easy to center
and can be completely screwed in a few turns.
It ensures the tightness of the drill string
and withstands big axial and bending loads.
In tool joints, the thread has a tension.
If you screw the coupling, you can see the thread will not fit completely.
To make it fully tightened, you need to make an effort.
The thread tension provides springiness and leakproofness of the connection,
and also prevents untwisting during hammer drilling.
If there is no a thread tension, the drill string bends during operation
and here the gaps appear.
The tightness is broken,
the rods become overgrown with bentonite
and the drill string becomes salted.
This could result the loss of the tool.
Also, if the tightness is broken, the pin thread is washed out by abrasive particles
that are contained in the drilling fluid.
This is especially true in deep drilling.
The rods operate for a long time with a high pressure and alternating loads,
namely:
alternating bending tensions,
torsional impacts,
longitudinal and cross vibrations.
The amount of thread tension is calculated and spelled out in the standards.
It is checked by using a gauge.
There are working and control gauges.
Working gauges are used for thread cutting,
and control gauges are used to check working gauges for wear.
Let's check the thread tension with a gauge.
The first one we take a pin.
We screw the ring gauge on the pin with the effort of one person,
by using 150 mm lever arm.
Next, we measure the distance from the torque shoulder to the reference plane.
The allowed value is specified in the standards.
At the same time, we check the perpendicularity
of the torque shoulder to the thread axis.
We check the distance in several places on a circle.
The allowed deviation is indicated in the standards and is 0.1mm.
Now let's check the box.
We screw it on the gauge and check the size
from the torque shoulder to the reference plane.
According to the standard, it should be 0 plus the allowed deviation.
We measure in several places in a circle
and check the perpendicularity of the torque shoulder to the thread axis.
During drilling, the axial compressive load is transmitted through the torque shoulder.
Thus, under pressure on the drill string, during shocks and vibrations,
the thread will not suffer.
For example, if we use drill pipe couplings without a torque shoulder,
then the compressive axial loads would be distributed over the entire contact area of the threads.
In this case, the thread wears out and the service life of the connections is reduced.
In addition, the thread will tighten so tightly,
that it cannot be unscrewed.
Therefore, the torque shoulder plays very important role.
Before the advent of CNC machines, tool joints were machined on lathes
with an active cross slide
or on usual screw-cutting lathes by using a taper turning attachment.
The design of the threaded part was differed by the presence of
a relief groove for the tool exit.
The relief groove in box coupling is convenient for machining.
However, as a result, we get fewer working threads,
and its use is impractical at high torques.
Therefore, now threading is performed only on machines
with computerized numerical control.
In manufacturing of the drill rod couplings,
it is necessary to control a taper angle.
If it is incorrect, stresses will be concentrated
on the first or last threads.
This will lead to premature wear and leakage,
and make possible loss of the drill string.
The taper angle is checked with smooth gauges before threading.
On the couplings are milled slots for wrench,
or grooves for marking.
It depends on the rig design.
In small-sized drilling rigs to unscrew the thread is used a wrench.
In deep drilling is used a hydraulic gripping,
and the marking grooves are used only to determine
the type of the drill rod coupling.
After machining is carried out volumetric hardening.
Tool joints should have a hardness from 28
to 32 Rockwell units.
If the coupling is soft, then occurs sticking and destruction of the thread,
the connection is difficult to unscrew.
Sometimes the connection cannot unscrew due to high loads.
So, the drill rod connections should be hard,
but not brittle.
If the hardness is too high,
the threads will be chipping off on impact.
Therefore, it is important that the hardness is within the limits
specified by the standard.
There is also a method of hardening the threaded part by induction heating
with high-frequency currents.
But in well drilling, volumetric hardening is more preferable,
and here's why:
Induction method provides a surface hardening.
The depth of heating is regulated by the frequency of the current,
but the hardness in several areas is very different.
The crystal structure is heterogeneous.
Internal stresses appear,
and also a microcracks between the hardened and soft material.
In some cases, the drill rod breaks off
because the threads of the pin were come off
and remained in the box part.
With volumetric hardening
the hardness and structure of the steel is uniform
throughout the full body of the tool joint.
Torque shoulders are not crushed by impact.
The slots and the outer surface of the couplings do not wear out.
To prevent cracking, all corners should be rounded.
For example, a rounding corner must be made
at the base of the pin thread.
Also, the thread profile must have a rounded corner
of the roots and crests of the thread.
All corners are stress concentrators.
In these places, under alternating loads, cracks appear,
which leads to accidents.
Alternating mean loads that often change their direction.
For example,
tensile due to weight of the drill string while lifting
and compression due to pressure on the bit while drilling.
Here is another example:
bending loads due to buckling of the drill string.
During operation, the drill string bends in a sinusoidal shape
and rotates at the same time.
The direction of the bending moment is constantly changing.
Due to such loads, occurs fatigue failure of the metal.
The microcracks appear, which increase over time.
Therefore, in deep drilling, drill rods go through a regular
ultrasonic or magnetic particle inspection to detect cracks.
Tool joint is connected to the pipe by means of a thread or by friction welding.
The threaded connection uses a tapered thread with a triangular profile.
An external thread is cut on the pipe,
and a mating internal thread is cut in the tail of the tool joint.
The thread is screw very tightly.
It is sealed and completely reliable connection.
Requirements for production technology and quality control
are spelled out in the standards.
Friction welding also provides a reliable connection,
but only with strict adherence to technology.
For friction welding are used special machines.
The tool joint is inserted into the spindle gripper,
the pipe is inserted into the support gripper.
The spindle rotates,
the support presses the pipe against the tool joint.
Due to friction, the contact area heats up,
then the spindle stops quickly.
The hydraulic cylinder presses the pipe with increased force
and make forging of the welded joint.
The machine cuts off the flash -
this is the metal squeezed out of the joint.
After welding, the welded joint must be normalized
to relieve stress.
This operation uses an induction heating.
The finished rods are tested for bending and alignment.
The bend test is carried out on a bending press at eight points
around the perimeter in the welded joint zone.
If the welding technology is violated,
or if normalization is not carried out,
cracks may appear in the welded joint.
Therefore, during the acceptance of a batch of drill pipes,
the samples of the pipe body are cut out.
They are being tested on tensile and impact bending.
Destruction of samples along the welded seam is not allowed.
We manufacture drill pipe couplings according to API and GOST specifications.
We also manufacture seamless drill pipes with
a thread connection of the tool joint.
We carry out strict control over the manufacturing technology,
all materials have certificates of conformity.
We have different options of tool joints and drill pipes
for small drilling rigs,
and also for deep drilling rigs.
We ship orders to all countries in the world.
To place an order, follow the link in description
or contact me by phone.
I will calculate the cost of the order and delivery to your country.
Write your questions below in the comments,
I will give a detailed answer.
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Good luck, bye!