WorldWide Drilling Resource

55 WorldWide Drilling Resource ® JUNE 2013 Drilling Steel Dilemma by JD Sullivan Brunner & Lay, Inc. When it comes to underground drill- ing in mines, it seems nothing is ever as easy as it seems. This is especially true when it comes to bolting optimiza- tion or efficiency. Let’s face it, bolting steel and bits are expensive. Having to replace them frequently means drill rig downtime, productivity losses, and just plain hassles. Most bolting string life spans get shortened significantly because dirt and rock are tough on threads. Getting just a little on the joint threads while drilling will cause havoc with threaded connec- tions. As the threads are abraded and prematurely wear, they cause the drill steel to be subjected to deflection stress. This stress is oftentimes where we see most failures occur. The threads get worn down, start to bend, and finally break. You can see this illustrated in the figure below - regular bolting steel under extreme stress and the resulting failure (yellow region) created by drilling oper- ation. Cures can be as easy as ensuring the joints, connections, and bits are tight before commencing drilling. This pre- vents cuttings or threads from damaging drill steel thread. Watch bits for uneven wear as this can cause the drill steel to deviate and open threads to cuttings or debris. Bits that are wearing unevenly can be a sign the rotation or down hole pressures are too much. Some drilling contractors want to “ram and jam” and cause great stress on the drill string. Drill strings under this kind of stress very often fail long before their normal life or nominal footage rate is reached. I have fielded numerous complaints that this steel didn’t last as long as pre- vious steel or brand X. Upon a more detailed investigation, I see threads bro- ken by alignment issues due to the bit following the path of least resistance. There can also be issues with the bit snagging on the mat. I oftentimes find the drill rig was adjusted incorrectly for drilling conditions or the particular bit they were using. Optimizing efficiency is not a static operation, but rather requires dynamic intervention. Conditions change, drilling professionals differ, drill rigs are different, and lithology changes. Drill string manufacturers are con- stantly upgrading their products and looking for technological improvements. One such is the recent introduction of dual drive bolter steel. The design isolates the threads from bending forces created by bit deflection. This greatly reduces thread stress and premature failure. The design also minimizes the introduction of dirt and cuttings to threaded joint, and allows the bit to slide past the mat without snagging or hanging up. Pre- liminary tests indicate 20-50% longer drill steel life. Let’s hope the design improvement finds its way into many underground mines and leads to improved efficiency, safety, and significant cost savings. JD JD Sullivan may be contacted via e-mail at admin@ worldwidedrillingresource.com Whether you are ready to buy or sell drilling equipment or supplies, you can save money using the WorldWide SUPER MART™ ! 850-547-0102 or e-mail classified@ worldwidedrillingresource.com