Everything You Need To Know To Find The Best Threaded Water Well Drill Pipe
Drill Pipe Threads 101: The Basics of Good Connections
Recently, buried in thought, I fidgeted with the cap of a bottle of water, twisting the cap on and off. (Yes, even us well owners sometimes drink bottled water.) I noticed how quickly the cap tightened &#; in far less than a single turn. Curious, I looked at the bottle&#;s thread. It was a quad lead! Looking down at the bottle opening, four separate threads started in four equally spaced places. Cool, I thought. Multiple-lead threads are utilitzed on some DTH hammer cases, and they are the norm on raise-bore drill pipe. Remember the double-lead threads on those Portadrill blasthole rigs? Multiple leads speed up pipe and tooling connections.
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In the drilling industry, and in life, we encounter many different threads. Since I am neither a driller nor plumber, my most common thread use is when I connect a garden hose to the outside faucet. Ever wonder about this thread, or is it just me? Is there an organization that regulates it and sets the standards? Or, does every supplier just know to supply this thread?
Well, I have the answer. The standard thread is a GHT (garden hose thread) or, more formally, an NH (national hose). The standard, as with many everyday things, gets defined by American National Standards Institute (ANSI). We are most familiar with a ¾-inch GHT found on ½-inch and &#;-inch garden hoses. This has 11½ threads per inch. You might think garden hose thread is the same as pipe thread, but GHT is straight, not tapered like pipe thread. If you want to connect hose to a pipe thread, you need a crossover adapter. Now you know.
We are all familiar with national pipe thread (NPT). This standard features a slight taper (¾-inch taper per foot, or TPF). When you make the connections, they tighten and seal on the threads. We encounter these when running water lines, with some casing and with indoor plumbing. Typically, they use a coupling.
With drill pipe, we typically rely on the standardization provided by the American Petroleum Institute (API). These are called rotary shouldered connections. These are tapered connections but, unlike NPT, they tighten on the shoulders and not the threads themselves. Thread tapers can run from 4- to 5-inch taper per foot &#; a lot steeper than the national pipe threads.
When connections tighten on the threads, you can help stop leaking by wrapping the threads with plumber&#;s tape. Garden hoses tighten and seal when the tip of the male threads contacts a flat area at the back of the box, an internal shoulder. To seal this, we use a washer. To seal drill pipe connections, we rely on metal-to-metal contact at the shoulders. We ensure this by utilizing the correct make-up torque. This amount of torque also enables the mated connection to act as a unit, so it does not become a weak point.
A ding can prevent a good seal and the connections could leak. It is not always the depth of the ding but the raised portion of it that prevents proper shouldering.
As you periodically inspect your drill pipe &#; like I know all well drillers do &#;pay attention to the thread shoulders. A ding can prevent a good seal and the connections could leak. It is not always the depth of the ding but the raised portion of it that prevents proper shouldering. Other than enabling a leak, improper shouldering is a lead cause of thread failure due to breakage (like snapping off a pin).
Other than working like one of those yard sprinklers we used to run through as kids and getting the operator and helper wet, these can also wash out the tool joint compound and lessen the amount of air entering the drill string. Less air could mean lower uphole velocity, and translate into not-so-good hole cleaning and shorter bit life.
Most drill pipe manufacturers machine an outside bevel on the thread shoulders. Not only does this provide the correct surface area for torqueing purposes, it helps protect the shoulder from dings that may happen while handling the drill pipe.
Another way to safeguard shoulders is to use the thread protectors that came with the drill pipe. Some will save the pin protectors and religiously use them, but using the box protectors can also protect those box shoulders.
Have a leaky top sub? It could be from shoulder damage or it could be due to thread damage. All of your drill pipe connects with your top sub. Thread damage in that top sub can cause thread damage in every drill pipe you use. Do not just ignore it. Inspect, and repair or replace if you find damage.
For repair, you could send your top sub in to have the bottom threads recut. Or, you might find a bad spot that can be addressed with a file or hand grinder. Some rigs do not permit such recutting, since you will lose ¾ inches or more in length (up to 2½ inches with severe damage). You want to make sure it does not become too short to pick your drill pipe out of the table.
Leaky connections lead to leaky wallets. It is worth the time to investigate and make it right.
For more Pipeline columns, visit www.thedriller.com/pipeline.
Important Things to Know About Drill Pipe
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In the past, we have written about tips for selecting proper drill pipe and drill pipe maintenance. What do you need to know when it comes to this important purchase?
Here are some insights to what you need to keep in mind.
The most important thing I can advise about selecting drill pipe for your project is to ask questions. What kind of questions, you ask? Here are a few to keep in mind: Who is the manufacturer of the drill pipe and what is the origin of the tubes and tool Joints. If selecting new drill pipe, ask for the data packet or quality documentation package and go look at the pipe. Ask for a plant tour to see the pipe and the manufacturing process. If selecting or comparing used drill pipe, be sure to see the inspection reports and ask for clarification to make sure you understand the information. Study the O.D. of the pipe in comparison to the O.D. of new pipe and the minimum O.D. allowable for a connection to pass an inspection.
Today, we are going to discuss things you should know about your drill pipe.
Don&#;t Overlook This
Pipe dope application procedures may be the most overlooked and most important thing to know. New threads on new pipe, or freshly recut connections, need special attention to &#;break-in&#; during their initial use. We often say, &#;Only put dope on the threads you want to keep.&#; But all jokes aside, the biggest problem we see when contractors have a problem with new threads is a lack of complete coverage of all threads and seal faces, deep down into the valley of the threads. All thread compounds (pipe dope) are not created equally. Pipe that has been stored for a long period of time should have &#;storage compound&#; such as ZN50. High quality pipe dope such as Kopr Kote can harden if left on threads for a long period of time as a storage compound and create a new set of problems. Avoid putting the pipe into service until storage compound has been removed and fresh new pipe dope has been applied.
Proper cleaning of threads before use is also a key step that is sometimes overlooked. After removing the thread protectors, threads need to be cleaned and checked before use. Mineral spirits are often used, or a high-pressure washer can be sufficient most of the time. The key is getting the threads clean so a visual inspection can verify their condition. Then pipe dope can adhere to the threads and protect them. Again, with complete coverage of all threads and seal faces.
Drill pipe that is stored for a long period of time should be periodically rotated to prevent &#;rack rot.&#; We have seen pipe that is sitting on wood timbers develop rust where the steel contacts the wood and moisture. This can cause pitting that could lead to a failure.
Also Important
Make Up Torque and Initial Break-In of New Connections: The speed of rotation during break-in of new threads is critical and should be slow and steady. Most experts and manufacturers agree that it is best to make-up the connection to 100 percent of recommended make up torque. For example, manufacturers typically complete a three-cycle make and break at the factory when making maxi rig drill pipe. This is done at 100 percent of recommended make up torque on the tool joints before they are welded onto the tubes.
Hard Banding: Hard banding can extend the life of drill pipe when used on rock crossings. Some manufacturers or suppliers install different types of hard banding. Hard banding can be most beneficial in rock formations to help reduce tool joint O.D. wear. Some hard band options are &#;casing friendly,&#; but they do not last as long in abrasive rock formation as other types of hard band. The placement of the hard band for HDD projects can be different than what is found on oil/gas (vertical) well projects. It is beneficial to place hard band on the tapers of the tool joints to prevent wear in a horizontal directional drilling.
Most HDD contractors prefer to use standard, field proven API style connections such as 4-1/2-in. IF, 5-1/2-in. Full Hole or 6-5/8-in. Full Hole. These connections are available in their standard form, or with a &#;double shoulder&#; feature. The double shoulder versions of these connections provide a secondary shoulder at the end of the pin. This adds approximately 30 percent more torsional strength to the connection and helps prevent over-torque to the connection if &#;slip torque&#; is experienced downhole.
Inspection and Stress Cracks: Stress is not measurable until a crack develops. Steel has a &#;memory&#; and is cumulative also referred to as fatigue. There is no way to quantify how much stress is put into a joint of pipe until a crack develops. Regular inspection is the best protection to look for cracks before they propagate all the way through the pipe which is seen as a joint with drilling fluid leaking through it, or a completely broken piece of pipe. Manufacturers have worked with heat treating methods as well as steel components to achieve &#;leak before break&#;. The goal is to have the pipe stay together even if a leak develops to avoid a downhole break. It is best to inspect drill pipe regularly, or after a particularly rough job and especially if the pipe has been used on a tight radius. The most common failures we find from HDD projects are noted as &#;rotational bending fatigue.&#; Meaning that the pipe has been through a tight radius while rotating and drilling.
Again, I stress: Ask questions. Drill pipe suppliers and manufacturers see drill pipe on a regular basis and should be able to provide informative information through resources such as manufacturers, API and T.H. Hill.
Jay Miller is president of J.T. Miller LLC.
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