When many of my readers see the letters “HDD,” they think of the type of rig they might see in a suburb installing utility lines under a road or other small infrastructure. But, as with everything drilling, there’s always a bigger scale. National Driller recently attended the 2017 Underground Construction Technology (UCT) event in Fort Worth, Texas. We sat in on a presentation by James Pfeiffer, North America area sales manager for pipeline equipment for Herrenknecht. His “Latest Generation of HDD Maxi Rigs” talk piqued our interest.

Of course, large-scale HDD rigs aren’t new. But we though readers would like to hear a bit about the differences between the type of rig a small contractor might use and the huge “maxi” rigs that go to work installing our pipeline infrastructure. We sat down at the Herrenknecht booth after Pfeiffer’s talk with him; Michael Lubberger, senior product manager for pipelines for the Utility Tunneling business unit; and Dr. Gerhard Lang, manager for business development, Utility Tunneling business unit.

Our conversation is edited for space and clarity.

Q. How do you define “maxi-rig”?

Pfeiffer: It’s defined anywhere from 100 to 200 tons and up, push-pull. Our product range covers rigs from 80 to 500 tons.

Q. What is the customer base for a rig like that?

Pfeiffer: Usually pipeline contractors. ... That majority is oil and gas pipeline. There’s some sewer, water. But the biggest majority would be to oil and gas.

Q. Beyond pipeline HDD, what other kinds of markets is Herrenknecht in?

Lubberger: Basically, we are in the utility department, everything which comes together with utility. That could be cable, that could be telecommunications, that could be sewage, freshwater, hydropower plants, oil and gas, other products, chemical products — there are pipelines for that. So there are a lot of applications, but the main business is still the pipeline network.

Q. What kind of diameters are we talking about here?

Lubberger: The maximum install with the big maxi rigs is 56 inches. That’s the largest gas and oil pipelines. There are some water pipelines which go beyond, but I would say in the oil and gas 56 is the biggest diameter. On the other end of our product range, we have a crawler rig with 800 kN push/pull force and 4- to 6⅝-inch pipes for installing, for example, cables and HDPE pipes — a rig with a quite small footprint and low transportation requirements.

Q. From an operator standpoint, what are the training considerations for running something like this versus a rig that might install fiber optic under a road?

Lang: Our customers are basically operating larger equipment and they have to excavate longer distances, larger holes. Thereby, depending on the distance, you have to tackle more difficult soil conditions, varying ground formations, and one of the challenges based on the soil conditions is frack out. Conditions like these have to be considered during the design and evaluation process. The soil parameters need to be taken into account to avoid frack out or inadvertent returns. If you go to larger diameters like Michael mentioned with oil and gas dimensions up to 56 inches in diameter, then you are talking about totally different loads and forces, etc. You also have to understand that when you want to install a 56-inch pipeline, you have to over-excavate. You have to create a much bigger hole. So there’s roughly about a 30 percent bigger hole to be drilled before you install your product pipe in this borehole. The 56 inch, you have to stabilize the borehole before you pull in your product pipe. The bigger bores are, the more difficult it is to stabilize. Whereas, in fiber optic cable, it’s much smaller bores so your loads are totally different. In this case, smaller rigs are used. The range of relevant project parameters that are considered for these jobsites varies in some respects.

Q. Is fluid circulation a limiting factor? That’s a huge volume.

Lang: It’s one of the design criteria. To me, it’s a requirement to stabilize the borehole, but also carry the cuttings. So it’s always a compromise: stabilize the borehole, and have enough carrying capacity to bring the soil and chips back up to the surface. ... Small cable installations, small distances are often not as complicated; there the focus is to have as agile equipment as possible, maybe with noise and emission protection, making it ideal for projects in urban areas. When it’s getting bigger, longer distance, it’s getting more complicated where you have to have experienced contractors who have done it and the proper skills to do it and tools to do it. The mud is one aspect, one critical component which needs to be designed properly. To make the process of soil removal more efficient, Herrenknecht introduced new and innovative down-hole tools last year. Our Down Hole Jet Pump cleans the borehole and removes the cuttings directly inside the drill string — a completely new method of soil conveyance in HDD.

Q. Tell me about the whole system for a job of this scale.

Lubberger: It’s the rig itself, and as a secondary part you have the mud handling, which is the mixing of the mud, the separation of the mud, the recycling, the mud pumps. Then you have the tooling, which is down hole, and the tool handling, the handling of the drill pipe. … This all has to be planned in advance.

Q. From a materials standpoint, is the tooling any different other than scale?

Lubberger: It’s more sophisticated because normally the drills we use to make our rig are much longer than the smaller rigs. The project partners are facing much harder conditions because the operations are much deeper than the smaller rigs. They go under rivers and need to have a certain cover. They are most of the time in a depth of 100 to 150 feet, so the deeper you go the harder the formations are.

Q. What kind of lateral runs are you talking about? What kind of distances?

Lang: World records are about 11,000 feet, 12,000 feet. This is made by two rigs, from each side of the crossing and kind of meeting in the middle.

Q. What kinds of data or metrics is a rig like this measuring that can be conveyed to the operator?

Lang: The rig itself comes with a data logging system, which logs all data the rig is producing. The rig is controlled by a PLC system, which means there are more than 400 values. But only the important ones will be shown to the operator, to the driller. That’s most of the time the torque, rpm, push-pull, speed, temperatures, things like that.

Q. When a smaller rig operator is on site, he might be able to make changes based on immediate, tactile feedback from the rig. Based on data fed to the operator of a maxi-rig, how much leeway does he have to adjust on site?

Lang: For the really big drills it is not only the decision of the operator. There are much more expensive things involved and also time involved. I would say the every day rate on such rig jobsites is $30,000-35,000 U.S. dollars. So tripping two days, it’s a big decision. This needs to be discussed and decided together by the project partners involved.