The standard flat root DI type thread (top) form is fully compatible with Atlas Copco’s radius root DI thread. Both of these thread types share the same thread geometry with the exception of, the root being a full radius with ours. The main benefit of this Atlas Copco thread feature is to reduce material stress levels in critical areas. Reduced material stress levels, lead to an increased resistance to fatigue failures. Making the choice to equip your drillstring with radius root threaded connections, may potentially insure against failures during tough drilling operations.
In addition, the use of shot peening in critical areas will also improve the fatigue life of the pipe and other components. The shot peening process induces residual compressive stress into the peened surface. Micro cracks are less likely to propagate in material that is under compressive stress. This increases the resistance to metal fatigue. The combination of the radius root thread and the shot peening of critical areas is a step above the industry standard.
The next component after the bit in the piloting sequence, the BRS, acts as a cross-over between the DI thread and the API thread of the pilot bit in the drillstring. Its design will resize the wall behind the pilot bit so a corrected diameter is achieved, even when the bit starts to wear. The tight diametrical tolerance between the BRS and the hole wall, controls deviation during pilot drilling operations, keeping the string on target. The BRS features a roller cutter system that can be rebuilt and Atlas Copco offers re-fit kits for the various sizes.
In the piloting sequence the main purpose of using ribbed stabilizers is to control deviation. Minimal clearance between the pilot hole wall and the ribbed stabilizer is required to maintain desired direction control. The hard faced ribs are ground to a dimension just below nominal pilot hole dimension. In most piloting applications the use of 2–4 ribbed stabilizers in a row is enough. In the reaming sequence, at least one ribbed stabilizer should be used adjacent to the stem. It is used to help the stem centralize the reamer in the raise. The first threaded connection from the reamer will also benefit from the reduced bending stress due to the close tolerance between ribbed stabilizer and pilot hole wall.
When raiseboring applications require pushing the reamer, the drillstring has to be stabilized. Since there is no pilot hole that can take up the forces that tend to buckle the drillstring, either a rotating or non-rotating stabilizer will need to be included at intervals into the drillstring. In our product range we supply both stabilizer designs. The typical selection will include the non-rotating type because of its ability to handle higher loading at a lower operating cost. The rotating type has its merits when drilling in broken ground that would tend to “squeeze” the drillstring stabilizers, allowing the operator instant drilling feedback for best operational control.
For machines featuring a swiveling float box it is necessary to use a starter sequence to start off the pilot hole in the correct direction. For the purpose of deviation control it is also recommended to use these components on other types of machines.
The starter pipe and starter bushing are machined to close tolerances in order to give maximum guidance to the pilot bit.
Use anywhere threaded component handling is required! From lifting and moving drill string components – to supporting a reamer assembly – these will get the job done safely and efficiently. Full size range available to suit both API & DI thread applications. Lifting bails are available in two versions: designed to couple with a pin end (external thread) – lifting bell style or to couple with a box end (internal thread) – lifting plug style.