Drill rods, which are commonly known as hydraulic drill rods, are cylindrical tubes that are connected using cylindrical tubes that connect to the drilling bits and the drilling machine and are used to drill holes on solid materials. Drill rods can also be defined as long pieces of steel that can be easily molded and are used to manufacture different tools. Most drill rods are circular in shape but some are also square. Drill rods are commonly used in the machinery and the manufacturing industries. They are used in the manufacturing of cutters, hot-work tools, machine parts, and many others. Drill rods come with many distinct differences in regards to the durability, cost, resistance and their applications.
Drill rods are of great importance in many industries, mainly the construction and manufacturing industries. Although drill rods are used in various ways in industries, they are used according to their grades in different types of work. Thus, not all drill rods for the same purpose.
II. Types of Drill Rods
A. Water well drill rods
Water well drill rods are common in the water drilling industries and firms like the water drilling contractors. The drills are basically used in drilling of water below the earth surface. They are therefore made of durable and hard substances that are resistant to harsh grounds like rocks. To make them hard enough for the task they are made of high-quality steel and other durable materials. They are made of slender tubes and cylindrical metal tubes that are connected to a drill bit that rotates on the surface of the ground and penetrates inside forming a circular shape. The drill bit rotates the drill rod until the water surface is attained.
B. Mining and exploration drill rods
Mining and exploration drills are used by the mining companies for the purpose of drilling and extracting minerals from the earth’s crust. They are made of hard and durable materials that can withstand the harsh conditions on the ground. The difference between mining and exploration drill rods is that mining drills are used to extract minerals from the earth’s crusts and are of bigger diameter than the exploration drills. The exploration drills on the other hand are used for the purpose of determining the existence of minerals in a particular region.
C. Directional drilling rods
Directional drill rods are used to drill holes that do not go straight or vertically down as a result of various aspects on the ground such as rocks or existing pipes. It is mainly used in the drilling of oil and gas. If the drill faces 180 degrees away from the pipe and the casing then directional drilling happens. Technically over the past decades, advancements in technology have made it possible for improvements in angles, turns and underground distances in the directional drilling. The drilling in any particular direction is made possible by the use of BENT sub. This consists of a part of the drill pipe that is usually bent at an angle and therefore can be directed to any position. Directional drilling is important as it brings about precision and has control during the drilling process.
III. Materials Used in Drill Rods
A. Carbon steel drill rods
This is a type of drill rod that consists of carbon as the main alloy though other elements may be present in the manufacture in small amounts. The carbon that is present in the rod enhances the durability and increases the strength of the drill rod. Other elements include steel which is used in some of the manufacturing processes to make the drill rod tough. Oil and tempering agents are also used in the heat treatment process for durability and to increase the strength. Finally, some of the carbon rods may be used to protect the carbon steel rod from wear and corroding.
B. Alloy steel drill rods
The rods are made up of high-quality steel alloys that provide the drill rod with the desired strength, durability and make them resistant to wear. The alloys used may vary depending on various things but the commonly used alloy elements are the molybdenum, vanadium, chromium and nickel.
C. Stainless steel drill rods
In this drill rod, stainless steel is the most used alloy. It also uses iron, chromium and nickel as other additional elements. Carbon steel may be used in some instances because it’s cheap but may not be used in harsh areas, a coat named tungsten carbide is also used to prevent wear and increase the durability. Finally, a diamond coating is used to prevent the drill rod from wearing out.
IV. Manufacturing Processes
A. Cold drawing
It involves the following processes:
Coating: The surface of the raw stock or coil is coated with a drawing oil to aid cold drawing.
Cleaning: Abrasive scale (iron oxide) outer of the hot rolled rough stock is removed.
Pointing: Several inches of the lead ends of the bar or coil are reduced in size by bending or extruding so that it can go through freely to the drawing die. This is done due to the die opening being smaller than the original bar or coil section size.
Drawing: In this process, the material being drawn is at room temperature (i.e., Cold-Drawn). The pointed/reduced end of the bar or coil, which is smaller than the die opening, is passed through the die where it enters a gripping device of the drawing machine. The drawing machine pulls or draws the remaining unreduced section of the bar or coil through the die. The die reduces the cross section of the original bar or coil, shapes the profile of the product and increases the length of the original product.
Finished Product: The drawn product, which is referred to as Cold Drawn or Cold Finished, exhibits a bright and/or polished finish, increased mechanical properties, improved machining characteristics and precise and uniform dimensional tolerances.
B. Heat treatment
In this method the material is subjected to heat and then cooled. Drill rods that are subjected to this process are able to withstand the stresses that they undergo while the process of drilling is taking place. The process also has the following advantages:
- Increases the surface hardness at the ridges
- Increases the life of the thread profile
- Eliminates the appearance of wears
- Gives more rod life hence increasing the drilled meters per rod.
C. Thread rolling
This is the process in which the physical, hardening and strengthening ability of a material is changed. It has low cost and increases the production. In general, it involves the formation of threads on the drill rod by the use of a thread rolling machine. It involves the following steps:
- Preparing the drill by ensuring that it is clean and straight
- Inserting the rod in the machine which consists of sets of dies. The dies are pressed on the rod which leads to deformation of the rod and formation of threads
- Inspection of the rod is the third step where the rod is inspected to make sure that the required conditions are met.
- Finally, any excess materials are cut off and protective coats are applied on the surface to prevent corrosion.
D. Surface treatments
This is a very important aspect in the manufacture of drill rods, where the surfaces of drill rods are treated against corrosion and wear by coating, plating and heat treatment. Coating is the process in which the surfaces are equipped with a protective layer while heat treatment involves the use of heat to make the surfaces hard. By increasing the hardness of the rod, they are more resistant to tear and wear during the drilling process. Plating involves the deposition of a thin layer of metal on the surface of the drill.
V. Thread Types
A. API threads
The threads are generally used in the drilling of applications that are above 153 mm in diameter and up to 12 meters. All the drills come in with strong joints and contain nitride to enable them to have the limited wear resistance. The API threads allow for the manipulation of some threads that are essential for the activeness of the thread. There are 4 different types of API threads namely;
- Line pipe thread
- Round thread
- Buttress thread
- Direct connection type of a thread
B. DTH threads
Down-The-Hole drilling threads are used where blasting force is required such as breaking large rocks. DTH drilling involves using a hammer string at the end of the drill bit. The hammer strikes the rock repeatedly as the drill string rotates forcing the rock to break. This drill method relies on three main elements to drill holes. These are weight, rotation and air. It is commonly used in construction sites, drilling boreholes and in the mining industry to blast rocks.
C. Other proprietary thread designs
Drill rods have a variety of customized thread patterns, each with special qualities and benefits. Here are a few illustrations:
- DCDMA threads: The Diamond Core Drilling Manufacturers Association (DCDMA) developed these exclusive thread types for use in diamond core drilling.
- Mayhew Junior threads: These threads, created by the Mayhew Steel Products firm, are frequently used in drilling operations for geotechnical and environmental purposes.
VI. Drill Rod Selection Criteria
A. Drilling application
1. Geology and formation
This is more applicable in the oil drilling industry where the geology and formation affect the penetrating rate. The drilling bit that is selected is highly dependent on the different types of drilling bits, size of hole, the rotation speed and efficiency of personnel and the equipment’s. Geological factors affect the rate of penetration. The formation also affects the resistance to penetration. The geological and formation factors affect the drilling process as they determine the type of bit to use, the weight of bit, the rotation speed, hydraulic action among many other factors.
2. Drilling depth
For most underground drilling, the holes are not deep, for example 200 meters instead of 1,000 meters. This may cause the engineers to choose more conventional drilling methods rather than using wireline drilling methods. The thinner kerfs found in core bits used in conventional drilling can lead to a better rate of penetration in any type of ground.
B. Drilling equipment compatibility
Drilling and excavation require a wide variety of tools and it depends on the type of the project. When choosing the tools needed one should consider the location which means that the type of soil and the substrate of the moisture content will have to be considered. Inspections should be regularly carried out and all the data including the soil sampling results should be available. All this should be available before the billing stage in order to determine on the compatibility and the right tools to use for the job.
C. Budget and cost considerations
Cost is a big consideration when choosing the drill rod to use. To maximize the budget of drilling one should use the right drill for the appropriate task and therefore saving on the cost of drilling. The cost of drill rods varies due to the depth of drilling, the geological conditions of the area among many other factors. Though it is important to economize on the budget it is important to choose the best drill rods that will produce maximum output and attain the required results.
VII. Drill Rod Maintenance and Handling
A. Proper storage and transportation
The store in which the drills are kept should be kept dry, ventilated and the moisture-proof kept in good condition. Drill rods with damaged packaging or damp, bent, bruised, or blocked water holes should be inspected and repaired one by one, and then repackaged and stored separately.
B. Regular inspection
Drilling rods should be checked at regular intervals to ensure that they are not faulty. They should be checked at least once per month though it is appropriate to check them every day after work to make sure that they are in the right working conditions.
C. Thread lubrication and protection
Threads should be greased using a special greasing agent to provide proper protection against corrosion and metal to metal in diamond tip drill rods that is employed in rock drilling when high temperatures are applied.
D. Avoiding common drilling issues
Common mistakes such as mixing rods from different manufacturers and choosing the wrong drill rod should be put into consideration in order to reduce the cost of maintaining the tools. Fixing common problems with the drill rods such as replacing worn out rods and regular lubrication should be put into consideration to avoid bigger problems.
Choosing the right drill is important as it makes the drilling process easier and saves on the time required to carry out a particular project. Drill rods come in various sizes and diameters and therefore it is crucial to choose the right drill with the appropriate diameter for the specific activity thus reducing on wastage of materials during the process. Tools and equipment that have undergone proper maintenance offer maximum performance and quality work and therefore drill rods should be maintained regularly to prevent them from breaking down during the drilling process and to offer a longer production life.