Casing Advancement Systems for Down-the-Hole Hammers

Published On: August 18, 2023By Categories: Drilling, Features

Ring bit systems are commonly used for drilling in overburden like boulders or loose formations.

By Mike Price

Williams Well Drilling LLC’s 7-inch pilot bit with (6) ¾-inch gauge buttons and (7) 5/8-inch face buttons, a design that was created by Craig Williams and Mitsubishi Materials USA. Photo courtesy Williams, owner/operator of Williams Well Drilling in Milford, Pennsylvania.

Water well contractors who struggle with drilling in overburden are adding down-the-hole (DTH) casing advancement systems to their toolbox.

Industry manufacturers have created various kinds of ring bit systems and underreamers over the years that continue to be upgraded for the water well market. While many factors should be considered when choosing the appropriate system, the types of formations contractors are drilling in will largely dictate the decision.

“There are a lot of things to consider, and if the wrong type of system is selected, there can be a lot of problems for both the driller and the distributor that sold the system,” says Justin Lewis, product manager of casing advancement and DTH at Mitsubishi Materials USA in Mooresville, North Carolina.

“Choosing which type of device and then using it correctly is much more complicated than standard DTH or air rotary drilling, and in addition to the casing advancement device itself, drillers will also need to either manufacture or purchase additional tools like special lifting slings and diverters to make everything work.”

Lewis, who was interviewed by Water Well Journal about DTH casing advancement systems in the August 2023 issue, has a general checklist (see shaded box) that he covers with contractors who are considering which system fits best for them. Naturally, which system to choose is one of the most asked questions Lewis gets from those who are just starting out.

“I would say it is close to a 50-50 split on the two kinds [contractors choose],” Lewis says between a ring bit system or underreamer. “Each individual driller is also going to have their reason as to why they use this particular method. The most shared reason would be the ability to get casing into the ground in unstable formations that prevent the hole from staying open.”

As Lewis explains, ring bit systems (Figure 1) have two main pieces: a pilot bit that is attached to the hammer and a ring bit assembly that is welded to the bottom of the casing. The pilot bit gets locked into the ring bit assembly to drill the hole and advance casing. The pilot bit breaks the rock, and the ring bit breaks and reams whatever the pilot didn’t get.

In water well drilling, 90% of the time the ring bit assembly stays in the hole. The pilot bit is used on many wells until it is worn out (usually a couple thousand feet), but each ring bit assembly is sacrificial.

Unlike ring bit systems where the drilling gauge is on the ring bit assembly, underreamers (Figure 2) will typically have some type of retractable bit wing or bit head that will extend to start the drilling process. Underreamers are generally used in softer formations containing sands and gravels. They can also be used in harder formations, but the leading edge of the wings/heads will wear out faster and can cause increased rotational torque.

Both the ring bit and underreamers are engaged when turned to the right. To retract the underreamer wings or unlock from the ring bit, turning a half rotation to the left is needed.

Like the dual rotary drilling method, casing advancement systems offer similar advantages while simultaneously drilling and casing holes.

“Even with more and more drillers converting to dual rotary and some even going the route of sonic drilling, there will always be a need for casing advancement systems to drill into the formations that the other rigs can’t,” Lewis shares in the August WWJ Q&A.

Selecting Correct Size Ring Bit System

Figure 1. The main components of a Mitsubishi Materials USA ring bit system.

Part of Lewis’ initial discussion with a contractor in picking out the correct size ring bit system is ensuring that the inside diameter of the ring bit is large enough to get the correct size bit to drill through it so they can install a well screen.

The only thing the ring bit assembly regulates is the outside diameter (OD) of the screen. Since the screen needs to pass through the ring bit, care should be taken in the design process to ensure a large enough bit can pass through the ring bit to set the desired screen size.

The casing string that has the ring bit on it will act as the surface casing. The final well completion, casing, and screen that the pump is set in goes through the surface casing.

Example: A contractor needs to drill a well to a total depth (TD) of 360 feet and set 4½-inch OD polyvinyl chloride (PVC) casing and screen to get a 4-inch pump in. The first 50 feet of that hole is through a formation that contains boulders and gravel and won’t stay open to get the PVC in. At 55 feet the formation changes to solid rock. The contractor could use a ring bit system to drill and set 7-inch OD casing to a depth of 60 feet, sealing off the boulder and gravel formation and accessing the solid rock.

The contractor then trips out the pilot bit and trips in with a 6-inch DTH bit and starts drilling through the middle of the ring bit assembly to a TD of 360 feet into the water-bearing formation. The contractor would then trip in their 4½-inch OD PVC casing and screen to complete the well.

The well would then have 60 feet of 7-inch OD steel casing with 360 feet of PVC inside of it. The well screen is secured depending on the well construction requirements. Figure 3 visualizes this concept.

First-Time Advice Running a Ring Bit System

Craig Williams, owner/operator of Williams Well Drilling LLC in Milford, Pennsylvania, has had just one failure in 20 years of running a ring bit system. The failure came during his first job where he “pushed it too far.” This led to clay swelling around the casing and caused the casing shoe to break off.

Figure 2. The face of a Mitsubishi Materials USA SMB underreamer.

“I tell everybody: Take your time; don’t be in a hurry because when you try to push a casing system, you try to make it hurry, that’s when it’s going to bite you. Just take your time,” says the third-generation contractor who uses a ring bit system for about 30% of his drilling while the majority is conventional air with a DTH hammer.

The top issue that Williams sees is contractors trying to go fast with casing advancement systems. His two recommendations:

  • Don’t run over 150 pounds per square inch (PSI).
  • Don’t run a quality hammer.

“There are so many things that aggression is going to get you into problems,” he shares. “That weld is only going to take so much beating and the older hammers clean the hole better. They clean that stuff away from the bit better because they’re bypassing so much air because they’re wore out. Run a wore out hammer because it’ll bypass more air and then it’ll clean that ring bit out better. It’ll keep everything cleaner, and it won’t bind everything up.

“That shoe is only welded on the pipe. That weld is only going to take so much abuse. The hammer that I run my 7-inch system with is 30 some years old, so I don’t worry about hitting the shoe too hard with it because I’m only drilling dirt.

“It’s not like I’m drilling rock all the time. I don’t run over 150 PSI ever—unless I’m in rock. The most I run it at is 1500 RPM. I don’t even rev it up. I only got 750 air. I just let it do its thing. Put it in and hold back. I don’t force it and have had very good luck that way.”

If running a ring bit system for the first time, Williams naturally advises contractors not to use it on the hardest job. He says instead to run it on a familiar job.

Figure 3. All figures courtesy Mitsubishi Materials USA.

“If you know you can blow it in with a hammer, but it’s just a little bit tough, that would be the job I do first to get used to it,” he says while emphasizing the need to learn the system.

Welding Skills Needed

For a contractor to run a casing advancement system, Williams says they need to possess decent welding skills.

“Run good welding rods and make sure your welds are good because you got to remember you’re pulling that casing down, and one bad weld, it’ll find it,” he says.

Williams welds everything with a 5/32-inch 7018 rod and burns it as hot as possible. He generally welds with only one pass.

“I’ve never had a problem with one pass breaking,” he says. “My theory there on more than one pass is you tend to overheat the joint and the pipe gets too hot, and it gets brittle. That’s my opinion and not sure if it’s right. I’ve had very good luck running one pass with a 5/32 7018 rod and as hot as the steel can stand it.”

Williams also suggests:

  • Ensure the weld is clean. Williams typically rinses it off with a pressure nozzle on the rig before he welds.
  • Ensure the casing is straight and the joint is tight together. Williams uses a casing alignment clamp to achieve this. His drilling assistant clamps the casing and looks around it for any gaps. If there is a gap, Williams moves the jacks on the drilling rig to close the
  • If the system has them, when filling in the plug welds, start welding in the bottom and work your way in a circle. The plug welds spread the shock out on the casing so it’s not all concentrated to one spot.
Checklist of General Questions to Consider When Deciding Which System to Run
Below are some of the general questions Lewis asks drillers when deciding which type of system to run. Based on the answers to these questions, either Lewis or the driller may have more questions until everyone agrees as to which type would be best.

  1. Have you used a casing system before?
    a. If so, which type and what did you like or dislike about it?
  2. Which types of formations are you encountering when yfou need a casing system: sands and gravels, boulder fields, rock shelves, etc.?
  3. How deep are you planning to drill with the system?
  4. Will the casing be removed after the system is used?
  5. Do you need to drill through the bottom of the casing?
    a. What size hole do you need to drill through the bottom?
  6. Which type of wells are you using the system on: water well, environmental, geotech, construction, etc.?
  7. Which type of rig do you have?
  8. What air package do you have?
  9. What is the casing OD and wall thickness you will use the system on?
  10. Which hammer shank are you running?

Benefits of a Ring Bit System

Craig Williams

Williams often contends with wet overburden with flowing sands and clay formations where he’s located in the northeast corner of Pennsylvania. The casing advancement system has been a game-changer for him.

“Jobs when I first started business it’d be two or three days just trying to get pipe in. Now I go put pipe in two or three hours with a casing system,” states Williams who opened his business in 2000, “and it’s done and just makes my life that much easier.

“It’s more setup and getting going; it takes about an hour to set up and get going, but once we’re going, we’re putting 20 feet an hour in. And the thing is, once you drill those 20 feet with a casing system, that’s 20 feet that’s done. You don’t have to mess with that again.”

Like with the dual rotary drilling method, Williams benefits from seeing instant samples of what he’s drilling in. There are no mixed samples.

“I know exactly what I’m in immediately,” he shares. “That’s really nice. Color changes and whatever.”

Knowing his formations before drilling is essential, and if Williams knows it’ll be 400 feet of casing, he won’t use his casing advancement system. He’ll use the mud rotary drilling method. But if he knows it’s 160 feet to rock but challenging drilling, he’ll use the casing advancement system.

“Ninety percent of my drilling is less than 200 feet of pipe,” he says, “so I get a lot of jobs where I only put in 80 feet of pipe, but it’s nothing but sand and gravel all the way down. Our issue here in this area is we have a very hard top layer on the rock, and you drill 5 feet into it and the rock is loaded with water. The quality of that water is garbage, so you want to seal that water off and get 15 or 20 feet into the rock and seal that top water off.”

Williams, whose wells are 95% open hole in bedrock, also loves the versatility of a casing advancement system in an area that has numerous gravel wells. He can run the system down and stop the bottom of his casing wherever he wants.

“If you’re drilling and driving in gravelly or sandy formations, you drive the pipe down, then you’d have to cut it, trip in the hole, clean it out, blow on it, see if it’ll clear. If it won’t clear, weld on another piece of pipe on,” he explains.

“For a casing system, I can drill it down to a gravel layer and unhook from the drive shoe and pull up inside the pipe and blow on it for a while [develop the well], and if I see it’s making sand, I can go in there and just tap on that pipe down [by down-feeding to ring bit] just 6 inches and then blow on it some more. If I’m still making sand, tap it down another 6 inches, blow on it some more. If it’s not making sand, make it a well right there. Cut the casing off and pull your rods out and you’re done.”

New Pilot Bit and Ring Bit Designs

Upon meeting at a customer appreciation day at East West Machinery & Drilling Inc. in February 2022 in Mifflinburg, Pennsylvania, Williams shared with Lewis his discontent with the current ring bit systems that he was using. The two came up with a plan that day with Lewis taking Williams’ initial requests to begin working with Mitsubishi’s engineers in Japan.

For Williams’ 7-inch device that he uses on 7-inch OD × 0.250-inch wall casing (called 154.5 mm system), he wanted larger buttons on the pilot bit, a drill through diameter large enough for a 6-inch bit to pass through, and wanted to be able to check the face design and tolerances of everything to be assured the tools were what he wanted.

“We narrowed the device down to our Ultra MaxBit Big Bore model with our Venturi design to help him through his flowing sands and clay formations,” Lewis shares from his notes. “This device normally comes with [9] 14 mm gauge row carbides and [12] 12 mm face carbides.

“Craig wanted bigger carbides for his large boulders, and we started with designing the pilot bit with all ¾-inch carbides, but after we did a 3D drawing, we didn’t like the lack of buttons on the face of the pilot bit, so we did another design with [6] ¾-inch gauge buttons and [7] ⅝-inch face buttons.

“This new design allowed for larger than original carbides as well as sufficient face coverage. We also had to make sure that he could drill through the ID of the ring bit assembly with a 6-inch-diameter bit. With changing the size of carbides, we also had to change the face design in order to achieve the Venturi effect we were after.”

In late July, after running the 7-inch system, Williams was planning to weld up grooves on it so it won’t vacuum as much.

For Williams’ 10-inch device that he uses on 10¾-inch OD × 0.250-inch wall casing (called 240 mm system), the two again went with the Ultra MaxBit Big Bore device but with the standard face design, not Venturi.

“The areas Craig drills contain very large boulders that are both extremely abrasive and hard,” Lewis says, “so he wanted to change carbide size and placement. The original pilot bit comes with [20] ⅝-inch face buttons and [12] 11/16-inch gauge buttons.

“The original design ring bit has [20] ½-inch buttons. We again redesigned the face so we could fit all ¾-inch carbides on the pilot bit, 20 on the face, and 12 on the gauge. We also redesigned the ring bit on this one to have all ⅝-inch carbides. We did not have to make any changes to the inside diameter of this ring bit since it was already large enough for the bits he was passing through it.”

Williams shared in late July that the 10-inch system ran to his liking.

“I’m just looking to make a better product,” Williams explains. “I think the whole thing is I’m saying something that everyone wants to say.

“The No. 1 thing is button size for me. That’s our biggest problem. I’d blow the buttons out of the drivers [pilots]. What good is a driver [pilot] bit if you keep having to replace buttons in it, and broken buttons don’t do me any good, so that was pretty much the main thing that I was looking for. Same thing on the ring bits—a little bit bigger buttons in them.”

Mitsubishi now produces and stocks pilot bits and ring bits in its North Carolina warehouse specifically for Williams Well Drilling.

“I have always been of the opinion that quality innovation comes not only from the engineering side, but also the end users’ input on the design before being manufactured,” Lewis concludes. “If a driller has an idea for a new tool—or a way to make our tools better—we will always do what we can to make it happen.”

Groundwater Week 2023 Workshop on Casing Advancement 101
Lewis will present the workshop “Casing Advancement 101” at Groundwater Week 2023, December 5-7 in Las Vegas, Nevada.

Justin Lewis

Attendees will learn about modern DTH casing advancement systems and their history. Lewis will discuss standard operating procedures including air requirements, rotation speeds, and weight on bit. Best practices for welding drive shoes and ring bit assemblies to the casing, maintaining the tools as well as the complete system setup from device to the swivel will be covered. Click here to learn more.

Learn More
Click here to read the August WWJ Q&A with Lewis. Lewis talks about the most common systems used in the water well industry and how their use has grown in popularity in recent years.

Mike Price is the senior editor of Water Well Journal. In addition to his WWJ responsibilities, Price contributes to the Association’s scientific publications. He can be reached at, or at (800) 551-7379, ext. 1541.

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