Beginners Guide to Hammer Drilling

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Those new to DTH drilling should consider these best practices.

By LaTisha Shipman

It seems I have lately had an influx of new hammer drilling customers which excites me. Some are completely new to the drilling business and just getting started, while others are experienced mud or air rotary drillers expanding their existing businesses into the down-the-hole (DTH) method of drilling.

With that, I thought it would be good to review best practices for those new to hammer drilling, those of you who might be considering adding DTH to your existing lineup, and possibly serve as a refresher for those of you who are experienced hammer drillers.

Essential Oil

I know I harp on this in my continuing education courses, but it is essential to properly oil your hammer.

I always mention this because I keep having drillers come up to me after my classes who have been drilling for more than 20 years and never used oil. My rebuttal is that we would not run our trucks without oil, and the piston concept is the same with hammer drilling. We have pistons in our truck engine and pistons in our hammers&#;and both need oil.

Just like in our vehicle, the purpose of the oil is to simultaneously cool and lubricate the steel, thus preserving the integrity of the steel and preventing corrosion and bluing of the steel as it gets hot. Running the proper oil will allow you to get the most life out of your hammer, saving you money in the long run.

Running these hammers consistently beyond what the intended parameters are only results in premature or catastrophic failure.

I recommend the Matex rock drill oil. It is a vegetable-based, environmentally friendly oil and helps to both cool and lubricate your hammer. You should be using 0.2 quarts of RDO per 100 cfm per hour. So, for a typical 6-inch hammer running at 300 cfm, you would need to use 0.6 quarts per hour.

You can monitor the oil usage by using an inline hammer lubricator or you can simply pour the oil down the drill string as you put on a new joint. I have seen some homemade oilers in the field as well. Honestly, it doesn&#;t matter how you deliver the oil to the hammer. Just make sure you are lubricating the hammer.

Protecting the Threads

Thread compound is another lubricant that you need to keep on hand. It&#;s important to apply thread compound to each threaded tool joint so the following connections are protected against seizing, galling, and load bearing stress fractures:

• Between the hammer and the drill pipe
• Between the top sub and the piston case
• Between the driver sub and piston case
• Between each piece of drill pipe
• Between the drill pipe and any sub adapters or shock  subs, stabilizers, and the tophead drive.

There are several different types of thread compound. Matex also makes an environmentally friendly thread compound, but there are also copper-based thread compounds and thread compounds specifically formulated for the water well industry. The thread compound not only protects the threads, but aids in breaking out your tooling.

The Proper Breakout

Speaking of breakouts, it is imperative to use the proper breakout tooling and in the proper locations. You do not want to grab on to the hammer where there are internal threads at the top sub and driver sub ends as that can warp your threads.

There should be a chart in your hammer manual about where to safely grab on to break the tool joints. I would also recommend the petol-type breakout wrenches as opposed to the jawtype breakout wrenches for safety purposes. I&#;ve heard plenty of horror stories about jaws shattering and causing injury.

Know Your RPMs

I&#;ve noticed when air or mud rotary drillers switch to hammer drilling, one of the issues frequently encountered is that of revolutions per minute (RPM). Experienced rotary drillers typically run 60 to 100 RPM for 6-inch range tricone or PDC bits, but the same bit size in DTH only requires about 30 RPM.

RPM is largely dictated by the formation you&#;re drilling in. We cannot expect to attain the same RPM in hard or abrasive formation as we do in soft to medium formations. It&#;s important for a driller transitioning from rotary drilling to DTH drilling to know that they need to slow down the rotation speed on the rig. Faster rotation does not equate to increased penetration rates.

The DTH hammer method is intended to crush new rock with every index of the rotating bit face. When we over-rotate, the bit that was intended to crush is now only scraping and that damages the bit face prematurely, even leading to catastrophic carbide failures. We just recently had a customer who switched from rotary drilling to DTH and ruined a good bit within the first 300 feet due to over-rotation.

Of course, rotating too slow can cause regrinding of cuttings and will also damage the bit. A good rule of thumb to follow is that RPM equals one-half penetration rate per hour in feet. As an example, if the penetration rate is 50 feet per hour, then the RPM should be set at 25.

The Fluids Question

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Key Questions to Ask When Choosing a Heavy Weight Drill Pipe Exporter

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I would like to preface this next topic by first saying there is no such thing as a stupid question. I mention as one I get when a rotary driller is first starting to explore DTH drilling is, &#;Do I run mud/bentonite with hammers?&#;

The answer is no. However, we do run foam with hammers to help with cuttings evacuation. We also run water injection to help with dust suppression and borehole stabilization. So, we run fluids, but it&#;s not the same fluids as with rotary drilling. You can also still run certain clay inhibitors, polymers, etc.

Under Pressure

Another troubleshooting question I regularly get concerns the issue of the hammer not holding pressure.

In fact, I recently had a situation with a new driller who was running a brand new 6-inch hammer. The hammer was holding about 275 to 300 psi, which was optimal as the maximum pressure that this hammer could hold is 350 psi. He was also using a 350 psi/ cfm compressor.

This was a situation where the driller&#;s expectations were not realistic in my opinion. He expected the hammer to hold 400 psi and it just wouldn&#;t hold that. He also thought the minimum pressure this hammer could hold was 350 psi when that was actually the maximum pressure the hammer could hold according to the chart.

Now, I have no doubt the hammer could have held more pressure. But I think that would only be the case if we had a higher rated compressor like a 500 psi compressor for example.

I would like to point out though that even if your hammer can hold more pressure than what is recommended, those recommendations are in place to minimize premature hammer failure. Running these hammers consistently beyond what the intended parameters are only results in premature or catastrophic failure.

There are a few things to consider when you think the hammer is not holding pressure.

One is the age of the hammer. In my recent situation, I didn&#;t feel it was a hammer issue since it was a new hammer, and it wasn&#;t. It basically came down to a misunderstanding of the hammer manual or a miscommunication and expecting the compressor to outperform its operational parameters.

If the hammer is older, we might need to consider that it&#;s time to retire the hammer because it could be nearing the end of its life expectancy. We can check wear limits of the hammer to determine this.

What is the penetration rate? If you are still getting the same penetration rate at a lower pressure, why is there a problem? Most 6-inch hammers operate between 150 to 350 psi, with 150 psi being the bare minimum.

But I do not recommend running at the bare minimum. I would much rather see the hammer operate in the mid to upper range of 250 to 350 psi to help with uphole velocity and cuttings evacuation.

To run your compressor efficiently, it should generally work at 80% of its full capacity. When we are pushing the compressors to their max, and expecting even more than their max, we are not only running our hammers into the ground, but our compressors as well. There has to be a happy medium.

I know we live in a fast-food world, but in terms of DTH drilling, pushing our equipment harder and faster every day is going to get expensive quickly. For optimal results, it&#;s best to stay within the manufacturer&#;s recommended specifications.

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It&#;s always good to review best practices even if you are an old-timer with decades of experience. However, with a lot of new customers coming on board, I thought it good to explain some DTH basics.

Understanding and following these tips will be good for your hammer, the jobs you work on, and finally, your customers.

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LaTisha Shipman is the Texas branch manager for Drilling Equipment Resources. She has more than 20 years of experience in the drilling industry, with most of that time spent working in manufacturing with DTH hammers and bits. She can be reached at .

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