In the world of horizontal directional drilling (HDD), drill rod is much more than a simple tube that connects things. It’s the most important part of your project that connects the drilling rig’s power to the drill bit and moves through difficult underground terrain.

Picking the wrong drill rod is like wearing the wrong running shoes for a long marathon. At best, it can make you work less efficiently and cost more. At worst, it can cause drill bits to get stuck, drilling failures, and even safety problems.

With so many options for specifications, materials, and grades on the market, how can you make a smart choice that will guarantee the success, safety, and smoothness of your HDD project? This is not a simple choice; it’s a very important one that could make or break your project.

The first step is to understand how hard it is to choose the right drill rod. There is no one-size-fits-all solution. Different types of soil and rock (from soft clay to hard gravel or bedrock), the planned length, depth, bend radius, push and pull forces, and torque of the borehole, as well as the type and pressure of the drilling fluid, all have a big impact on what the drill rod needs to do.

Choosing drill rod based only on experience or price and not taking these factors into account is like sailing into uncharted waters, which is very dangerous.

So, before you start your next HDD project, you need to take the time to learn everything there is to know about how to choose the right drill rod. It’s not enough to just buy a pipe; you need to find the best “power transmission solution” for your specific engineering problem. Next, we’ll talk about the main things that affect the choice of drill rod. We’ll make things clearer and give you practical advice to help you figure out how to choose the right drill rod for your project, which is the key to success.

Let’s talk about the seven main factors that affect how well a drill rod works and whether or not it is right for you. If you understand and carefully think about these seven things, you’ll be able to find the right drill rod for your horizontal directional drilling project. Next, we’ll look at each of these important factors:

Length of the Outside Diameter
Torque for bending radius
Weight of Pressure Resistance
Media that can be used

The size of the outer diameter changes to fit different tools.

The small drill rod has an outer diameter of 50 to 89 mm. A 60mm outer diameter drill rod was used in a municipal pipeline repair project. This type of drill rod is good for small directional drilling rigs. When working under sidewalks, the ground can only be disturbed by 0.5m or less. The outside diameter of a medium drill rod is between 114 and 168 mm. In a project to cross a highway, a 127mm drill rod was used. When used with a 200mm drill bit, it can drill a hole up to 100m in one go. The outer diameter of a large drill rod is 219 to 325 mm. A drill rod that was 273mm long was used to cross an oil pipeline. It can pull a 400mm pipeline back at a rate of 5m/min. The deviation in the outer diameter is less than or equal to ±0.5mm. The drill rod in this batch measured 114.3mm, which made sure it fit snugly with the joints.

Length Requirements Affect the Speed of Building

The standard length of a single rod is between 3 and 6 meters. A 3m drill rod is used to build a residential pipe network. This lets the workers move around easily in tight spaces with a minimum turning radius of 5m. Long drill rods can be anywhere from 9 to 12 meters long. For a long-distance crossing project, a 12m drill rod is used. This cuts down on the number of joints, needing 23 fewer joints per 100m of drill rod than a 3m drill rod. This lowers the risk of leaks. The tolerance for length is ±5mm. A 6m drill rod measured 5,997mm, which was the right amount of joint accuracy. The joint gap was ≤0.2mm.

The bend radius decides how well something can turn.

The minimum radius of bending is linked to the outer diameter. The minimum bending radius for a drill rod with an outer diameter of 114mm is 6m or more. A city project that was being built at a street corner needed a 6m radius turn without permanently bending the drill rod. The minimum bending radius for a large-diameter drill rod (273mm outer diameter) is 15m.

The route for a railway crossing project was planned with an 18m radius, which meant that the stress on the drill rod was evenly spread out, with a bending stress of ≤200MPa per meter. The bending angle for one is less than or equal to 3°. A drill rod used to make a pilot hole bent 30° and still worked normally to transmit torque.

The performance of torque transmission affects how well drilling works.

The outer diameter determines the rated torque. The rated torque for an 89mm drill rod is 2,000 N·m. When drilling through clay, the actual torque was 1,800 N·m and the speed was 2 m/min. The rated torque for a 168mm drill rod is 5,000 N·m. The torque stayed at 4,500 N·m while drilling at a speed of 0.5 m/h in rock that had been weathered a little. The efficiency of torque transmission is at least 95%. One test showed that when the input torque was 1,000 N·m, the output torque was 960 N·m. Losses are mostly caused by friction between the joints.

Pressure Resistance That Works for Mud Circulation

The pressure at which it works is 10 to 30 MPa. A certain horizontal directional drilling (HDD) drill rod is made to work at a pressure of 20 MPa. The internal pressure stays at 15 MPa with no leaks when the mud moves at 500 L/min. The burst pressure is at least three times the working pressure. The burst test pressure for a certain 20 MPa drill rod is 65 MPa, which is much higher than safety standards and means that it won’t break if it gets stuck by accident. The loss of pressure is less than or equal to 0.5 MPa/100 m. A 1000 m long drill rod has a mud inlet pressure of 25 MPa and an outlet pressure of 20 MPa, which is enough to carry slag.

Weight parameters have an effect on the load of equipment.

The weight per unit length changes based on the material and the thickness of the wall. A 114mm drill rod, for instance, weighs 25 kg per meter. The rig can hold 5,000 kg, which is the weight of a drilling rig with 200 m of drill rod. The 273mm drill rod weighs 80 kg for every meter. This drill rod weighs 40,000 kg and can be carried by a big directional drilling rig that is 500 m long. However, the rig needs special permission to work. The weight tolerance is ≤±2%. A batch of 168mm drill rod, which was supposed to weigh 45kg per meter, actually weighed 44.2kg, which was within the standard.

The type of medium used determines how it can be used.

The inside of a water-based mud drill rod is resistant to corrosion. The drill rod carried mud with humus in it across farmland, and after 60 days, the inside wall was rust-free. Oil-based mud drill rods need seals that are resistant to oil. A horizontal well drill rod for shale gas worked in diesel-based mud, and the joint seals didn’t show any signs of wear after three months. Drill rods for special media, like mud with sand in it, need thicker inner walls. A geological exploration drill rod with a 10mm thick inner wall lasts 50% longer than a regular drill rod.

If you carefully think about the seven main factors discussed in this article, you’ll be able to make smart choices. Keep in mind that the right drill rod is like a reliable “blood vessel” that runs through the ground. Picking the right one means picking a sure way to finish the project. Make sure you use this information or talk to an expert before you start your next drill hole to make sure you’ve picked the right “key” for your problem. If you have any questions about drill rod, get in touch with ZHE’s expert staff.