In my travels, one of the most common questions I’m asked by contractors is: “How long should my tool last?”
Most drillers already know the answer, but are always looking for a way to calculate and justify tooling expenses. I’ve been on jobsites where rock bits have lasted 45 minutes and I also know several contractors who are still using the same bit for the last two years.
There is no question that an HDD tool’s life is finite. Some tools die a violent death buried too deep to save, while others slowly wear out to the point they can no longer go on. The life expectancy of a drilling tool is too complicated to calculate. Factors such as ground condition, operator experience and proper tool selection largely determine the life of any tool, but there are few common causes for tooling failure that can be easily corrected with a few operational changes.
1. High Pressure Fluids: Jetting has always been a popular method for drilling in soft conditions. In harder conditions, however, it becomes less effective and even damaging to the internal fluid passages within the sonde housing and bits. Add to this reclaimed drilling fluids and the combination of excessive pressure and particulates can literally destroy the tools from the inside out. In fairness I should report that I’ve seen high pressure fluid make things happen underground that allowed the bore to continue, but keep in mind the tooling cost associated by doing so.
2. Lack of Fluid or Improper Fluid: Continuing from above it is critical to state that FLOW not PRESSURE is the key to optimal tool performance. Every good driller can espouse the benefits of proper fluid use in successfully creating and maintaining a good borehole. Many boring problems can be associated to poor fluid planning. What is often overlooked is the effect of poor fluid planning on cutting tools. Without proper fluids the cuttings are less likely to be floated out of the bore hole. A high amount of cuttings in the hole increases the wear occurring on the tool. In effect your tools must cut — and recut — the same material that lessens tool life and ultimately costs money.
3. Lost Carbide: Most good tools have a level of carbide or hard surfacing applied to protect the body from premature wear. While it’s hard to tell, this layer of protection can be several times harder than the base metal of the bit or reamer. Once the carbide or hard facing protection is lost, the wear and deterioration of the tools increases exponentially. Simply applying or replacing hard facing will greatly extend the life of your tool. Any delay in replacing the carbide will result in rapid wear of the base metal and diminish the integrity of your tool.
4. High RPMs: Rotation is good. But heavy rotation in hard conditions is rough on tools. Heavy torque loads are directly related to problems such as breaking cutting teeth, thread failures and sonde housing door loss and transmitter damage. Today’s more expensive rock tools are designed with a carbide cutting face that is engineered to perform at a lower RPM. We often suggest starting at 60 to 80 rpm and adjusting as needed. Not only will the tool life be extended, but the performance and productivity of the tool will improve as well.
5. Flush & Clean After Use: All too often tools are sent in for repairs simply from being “Rode hard and put up wet.” Once the bore is complete, the crew is quick to move on to the next task in the project. The tooling is usually disconnected and put aside or stored away. The tool might be hosed off, but a little extra effort will go a long way in extending tool life. All tools should be power washed well enough to remove all mud and cuttings. Once properly washed, the tool’s exterior can be inspected for signs of wear while making notes of areas to repair or apply hard facing. It is very important that ALL tools be flushed with clean water. If bentonite or other mud additives are allowed to dry and harden, the flow of fluid is restricted or can be easily restricted during the next use. Depending on the amount of restriction, damage can result in a number of ways. Fluid restrictions minimize the amount of fluid exiting the tool. Limited fluids cannot adequately remove cuttings from the hole which increases the wear on the tooling. Limited fluids and poor spoils evacuation will generate high amounts of heat down hole that can damage the sensitive tracking electronics, as well as the tool. Furthermore, restrictions can increase the burden on your rigs pump and reclaiming system.
6. Lube: Failing to frequently and properly lubricate contributes to a number of mechanical and tooling problems. HDD crews for the most part are very diligent in keeping their rigs greased and lubricated. It is, however, just as critical to lube your swivels as it is your rig. A good swivel is not cheap. They get even more expensive if the bearings fail during pull back. The swivel should be greased before AND after each use. Greasing each pipe joint prior to connection is a very common practice to extending the life of your drill pipe. Keeping the grease bucket clean and free of debris is also very important. Dirt or other particulates in the grease can be damaging over time so it is a good idea to wipe off old grease and apply new to tooling threads periodically.
With so many variables in play it is very difficult to apply a single cause for tooling failure. There are usually several factors which lead up to the point of failure. After years of designing and repairing HDD tools, it is possible to see trends and common problems which lead to the development of better tools. There are other times it is more obvious that poor drilling practices or tool selection is the probable cause.
Today’s successful HDD contractor is committed to getting the most out of their tooling investment. Tool failures cost time and money thus any problem that can be avoided is valued. Understanding the suggestions above and sharing this information will go a long way in maximizing your tooling investment and reducing costly downtime.
Riff Wright is owner of Radius HDD Tools.