Knowing Your Drill Pipe

The three main drill pipe manufacturing processes, as well as how to get optimum performance from your pipe are presented.

By Mike Burns
 
Quality drill pipe plays a major role in the success of any HDD bore. Drill pipe is the most expensive wear part affiliated with an HDD rig. To make sure you are getting the most out of your investment, you should know the differences in the three main types of drill pipe manufacturing processes, as well as easy day-to-day tips to get the most shots out of your drill string.
 
Integral Forged Drill Pipe
An integral forged or one piece forged drill pipe is made up solely from one piece of material. This pipe has the same chemical makeup for the threaded connections and the mid-body tube with no weld zone between them. The raw material, or green tube, is saw cut to an exact calculated length to ensure proper finished length tolerances. The ends of the green tube are then heated to produce a workable material for the forging or upsetting process. The upsetting process forms the steel to create the desired outside diameter, inside diameter and tong length required for the pin and box connection. The next step is to heat-treat the entire tube to a specified grade or hardness. After the tube has been heat treated and straightened, the upset ends are precision machined and threaded. Final inspection is the last and most important step.

Inertia Welded Drill Pipe
An inertia welded drill pipe is similar to the integral drill pipe in that the green tube is saw cut to length; upsets are forged on each end to form a thicker wall dimension, which creates a larger weld surface. With more cross-sectional area, there is more strength to that weld area. The main difference with the inertia welded drill pipe is that it is made from three separate pieces — the mid-body tube and two threaded connections or tool joints. The tool joints are commonly made up from alloy bar stock. After the bar stock has been saw cut to length, drilled and machined, they are heat treated to a specified hardness. After heat-treat, the tool joints go through a final machining, threading and inspection process. The next step is the inertia welding process. This process is a solid state welding technique that actually forges metal together without causing a melt to occur. Because there is no melt product produced during the inertia weld, there is no recast metal or grain enlargement after the weld is completed.

The mid body tube is held stationary by hydraulic clamps and the threaded tool joint is clamped in a collet chuck on a rotatable spindle. Also attached to the spindle is a flywheel of a pre-calculated weight. The weld cycle consists of the spindle being accelerated to a pre-determined speed, which is controlled electronically to shut off the drive system when the set speed is reached. This allows the mass of the rotating tool joint and spindle to be free and spinning by kinetic energy alone. At the precise time, the machine forces the tool joint and tube together causing friction at the weld interface. The pressure is maintained until all of the energy in the rotating spindle has been consumed in the weld, which in turn stops the rotation. This metal-to-metal fusion creates 100 percent weld penetration. The weld zone is then machined, heat-treated and inspected to ensure proper strength and hardness.

Press Fit & Welded
This process is one of the oldest drill pipe manufacturing processes. The process is quite similar to the inertia welded pipe in that the tool joints are made separately from bar stock and the mid body is forged and machined so the tool joints can be pressed in the forged ends of the tube. After they are precisely pressed, they go through a mig welding process. After they are welded, the weld zone is properly heat-treated to ensure precise strength and hardness.

Any of the above manufacturing processes will produce a quality drill pipe. Just like any other product, if you do it right and refrain from any short cuts you will put out a quality product. After choosing a reputable company to purchase your new drill string from, one must be able to maintain it properly to get the most out of his or hers investment.
 
Increase the Service Life of Your Drill String
One of the most common problems with drill pipe is thread damage, which can be prevented by keeping the threads clean. If pipe is removed from the rack, always use thread protectors. Every connection should be coated with a copper-based thread compound before being made. This compound helps to prevent galling, provides a good seal and controls the friction properties. Make certain the drive chuck or saver sub’s threads are good. These threads are going to be made up with every piece of drill pipe so a quick visual inspection or the use of a thread profile gage will improve the life of the entire string.

Vise alignment is critical so the drill pipe must be centered properly in the vise for make-up with the next connection. When drill pipe connections are not lining up properly, this can lead to stabbing damage to the threads. Most of the time, repositioning of the front or rear of the rig will correct this problem. Also, make sure to periodically change your vise jaw dies.

Know the desired make-up torque of the connection. Every different drill pipe thread has different minimal make-up torque specs. These can be obtained from your drill pipe vendor of choice. If a connection is not made up properly, there is a big risk of an over torque situation down hole. An over torque condition will damage your tool joints and commonly create fatigue cracking, eventually leading to a failure.

Just like any wear part, drill pipe has a lifecycle and will wear out. Choosing the right drill pipe and maintaining that drill string daily will not only increase its service life, but  will also increase the reliability that minimizes any pipe failure-related delays in the field, as well as increase your profitability by getting the most return out of your drill pipe investment.
 
Mike Burns is a partner with Underground Tools Inc., which is based in St. Paul, Minn.