Norris Drive Rods - Alberta Oil Tool

NORRIS DRIVE RODS®
Over the years, Alberta Oil Tool (AOT) has taken pride in being a world leader in innovation and
manufacturing excellence. Utilizing extensive research and development, AOT has taken the standard,
age-old sucker rod designed for reciprocating application and modified it to be optimized for use with
Progressing Cavity Pump (PCP) systems. AOT has made important improvements to the design to
both the rod and coupling resulting in a rod string that is far superior to any standard sucker rod string in
PCP application.
NORRIS DRIVE RODS®
Conventional sucker rods were originally designed for use with reciprocating beam pumps. They are
very well suited for this type of application and they perform this function effectively. The design of the
sucker rod connection is sound for transmitting high axial, dynamic loads, and has withstood the test of
time by performing well with only minor changes over the past several decades. However, the advent of
the Progressing Cavity Pump (PCP) has caused a shift in the thinking behind rod string connections. In
a PCP application, a connection is subjected to static axial loading as well as high torsional loading. In
this type of loading scenario, the standard API sucker rod connection design is deficient. In response,
AOT developed the Drive Rod® with connections better suited to the type of stresses found in PCP
applications. The Drive Rod® pin has a modified thread profile which is vastly superior with regards to
torsional capacity. The improvement in pin strength also allowed for the Drive Rod® pin to be
downsized. The benefits of downsizing the connection are enormous and include less flow restriction,
decreased tubing wear and longer fatigue life. All of these gains are achieved while still providing a
stronger, more reliable connection between every rod in the string.
Drive Rod®
Sucker Rod
Having smaller connections in a rod string has several key benefits. The first benefit is less restriction
of flow through the tubing. The relatively small cross-sectional area of Drive Rod® connections allows
far more room for fluid to flow through.
Drive Rod® Size
Sucker Rod Connection
Additional Flow Area
Size
when using Drive Rods®
1” w/ 7/8” pin
1” Slim-hole
28%
1” w/ 7/8” pin
1” Regular
51%
1-1/4” w/ 1” pin
1-1/8” Slim-Hole
27%
1-1/4” w/ 1” pin
1-1/8” Regular
50%
Additional Flow Area gained by using Drive Rods® in 3.5” tubing. Drive Rods®
come standard with Slim-Hole couplings and are compared to sucker rod
connections with both Slim-Hole and Regular connections.
This added flow area greatly reduces the pressure on the pump, which results in less stress being
applied to the pump, the drive head and the rod string. The overall effect of lowering the flow restriction
is a longer service life for all components in the pumping system.
A second benefit of having downsized connections is the reduction of tubing wear. In any PCP
application, tubing wear is a concern. Rods rubbing on the tubing is inevitable and can eventually lead
to tubing failure. Since Drive Rod® connections have a downsized outside diameter, there is less of a
difference between the outside diameter of the coupling and that of the rod body. The implication of this
is that more of the rod body contacts the tubing in between the connections. In essence, A Drive Rod®
has its’ rod/tubing contact forces spread over more of the rod body, rather than simply riding on the
connections alone.
Perhaps the most important advantage of using Drive Rods® in a PCP application, is the extended
fatigue life associated with having downsized connections. In a PCP system, by far the most common
cause of failure is fatigue damage caused by well bore deviation. A steel rod which is caused to flex
laterally, even slightly , and then rotated, will experience extreme dynamic loading. Every time the rod
string makes one complete revolution, the bent section will be exposed to one stress cycle. To put this
in perspective, a rod string operating at 200rpm will be exposed to 1,000,000 stress cycles in just three
and a half days. Therefore, it is of utmost importance that the bending loads applied to a rod string be
minimized.
All wells have some degree of well bore deviation. Consequently, a rod string placed in any well must
be able to flex laterally. A key point to consider is that the connections in the string are far stiffer than
the rod bodies. The connections are larger in diameter than the corresponding rod bodies and,
therefore, have a greater resistance to flexing. As a result, when bending loads are applied, the
connection tends to stay more rigid, and the rod body adjacent to the connection is made to flex more.
This means that a great deal of stress is applied to the rod string just below the forged upset, where the
flexible body meets the rigid connection.
The fact that Norris Drive Rod® connections are smaller than those of sucker rods, means that Drive
Rod® connections are far less stiff laterally. More importantly, it means that the stiffness of the Drive
Rod® connection is far closer to that of the Drive Rod® body than is the case with sucker rods. The
difference in the outer dimensions of a Drive Rod® and a sucker rod connection is relatively large, and
being that the relation between diameter and stiffness is exponential, the difference in stiffness between
the two is considerable. For example, a 1” coupling is four times more rigid than a 7/8” coupling. That is
to say that if the same bending load is applied to both a 1” and a 7/8” coupling, the 7/8” coupling will flex
four times as much. The overall effect is that less stress is transferred to the rod body on either side of
the connection, resulting in a dramatic improvement in fatigue life.
NORRIS HIGH STRENGTH COUPLINGS
Manufactured by AOT, Norris High Strength Couplings also differ from standard sucker rod couplings.
Norris High Strength Couplings have unique raw material properties, contact-face dimensions and
manufacturing processes that make them an ideal choice for PCP applications.
Norris High Strength Couplings are made from AISI 4130 heat-treated material and have a higher
mechanical strength than standard Class T couplings. Norris High Strength Couplings have a yield
strength that is 30% greater than standard Class T couplings, making them well-suited for the highstress environment which are typical with PCP applications.
Material
Yield Strength
(PSI)
Hardness
(HRA)
API Class T
AISI 8630
80,000 min
56 - 62
Norris High
Strength
AISI 4130
105,000 min
63 - 65
The Norris High Strength Couplings that are used with Norris drive Rods® also have slightly different
dimensions with regards to the contact face. The contact face of the Norris coupling has been widened
in order to maximize the contact area between the rod shoulder and the coupling. The Norris
connection contact area is more than 37% greater than the standard API connection. The result of this
is increased rod/coupling friction and ultimately, increased connection strength.
Norris couplings are also unique in the way in which they are manufactured. First of all, all Norris
coupling threads are rolled rather than cut into the material. This means that no material is removed
from the inside of the coupling, but instead material is cold-formed to produce threads. This process
resuts in more steel fibers being pressed into the thread roots resulting in a much stronger thread
profile. It is extremely important that all Norris drive Rods® (which also have rolled threads) be fitted
with rolled-thread couplings. Mating a rolled-thread rod with a cut-thread coupling will inevitably lead to
thread galling, an possible connection failure.
In addition, Norris high Strength Coupling threads are subjected to a thread lubrication process known
as “Phosphating”. This process involves chemically adhering a Zinc-Phosphate coating to the interior of
the coupling. The Zinc-Phosphate coating acts as a permanent thread lubricant which significantly
reduces the possibility of thread galling from occurring. After the coating is applied, the contact face of
the coupling is machined so as to remove any trace of the Zinc-Phosphate coating. AOT takes great
care to ensure that the coating is fully removed from the contact face in order to ensure that the friction
lock between the rod shoulder and the coupling is not compromised.
TESTING
All of these unique characteristics of Norris Drive Rods® and High Strength Couplings combine to form a
strong, dependable rod string intended specifically for PCP application. Destructive testing performed
at CFER Technologies has verified the Norris Drive Rod® connection is vastly superior to the standard
sucker rod connection with regards to torsional strength.
The following plots show typical results of the testing performed. The tests were performed using 1”
Pins - both API sucker rod and Norris Drive Rod® - with oversized bodies. This allowed for direct
comparison of the strength of the connections alone. In all tests, the connections were made up using
Norris displacement cards, and then subjected to a 50,000 lb. axial load. While the axial load was held
constant, a torque load was applied. The torque load was slowly increased until ultimate failure
occurred.
The below table clearly shows the Norris Drive Rod® connection using Norris High Strength Couplings
has a torque capacity that is more than double that of the standard APU sucker rod connection. It
should be stressed that these tests involved the connections only and not their associated rod bodies.
Yield Torque (ft.lb.)
Peak Torque (ft.lb.)
API
Norris
API
Norris
Test 1
1900
5100
3400
6599
Test 2
1800
5300
2781
6756
SUMMARY
Norris Drive Rods® have many features which differ from standard sucker rods. All of these differences
were made with the intent of making the best possible rod string specifically for use with PCP systems.
In addition, the quality of these products is highly controlled. Dimensional inspection is performed on
100% of Norris Drive Rods® and Norris High Strength Couplings produced at AOT. Because of this,
the Norris Drive Rod® string is second to none in the industry with regards to strength and durability in
PCP applications.
This being said, the strength of a rod string is only as high as its weakest link. Norris rods should not be
used in conjunction with another manufacturers’ couplings or rods. Norris Couplings are specifically
designed to be used with Norris rods. The type of thread and the dimensional tolerances are very
different from that of other manufacturers. For this reason, rod strings combining Norris Drive Rods®
with another manufacturers’ couplings are at risk of having a very poor run life and torque performance.
norrisrods.com
albertaoiltool.com
Tulsa, Oklahoma
Edmonton, Alberta
P: (800) 767-7637
P: (780) 434-8566
© DAL - Norris/AOT 05/2014