Tube plug removal machine

A device for removing plugs from plugged tubes in a steam generator, said device comprising:

• a frame,
• a gear box mounted on said frame,
• a counterbore drill bit extending through said gear box and movable with respect thereto between an operating and a storage position, said counterbore drill bit having a drilling tip sized to a diameter not exceeding the inner diameter of the tube,
• a tap drill bit extending longitudinally through said counterbore drill bit, movable with respect thereto, and having a drilling end comprising a drill point, a tap section and a threaded section, for drilling a hole in the top of the plug, tapping the hole, then threading into the newly tapped hole,
• a threaded splined drill carrier attached to said counterbore drill bit opposite said drilling tip,
• coupling means for coupling said tap drill bit to said counterbore drill bit, said coupling means comprising trip pin means connected to said tap drill bit,
• motor means attached to said gear box for rotating said counterbore drill bit and, when coupled by said coupling means to said counterbore drill bit, said tap drill bit,
• axial indexing means for axially indexing said counterbore drill bit and, when coupled by said coupling means to said counterbore drill bit, said tap drill bit, said axial indexing means comprising a feed gear and a drive gear for engaging said drill bit carrier, said axial indexing means operative for indexing said counterbore drill bit toward or away from said tube, and
• disengaging means for disengaging said coupling means when said tap drill bit has threaded into the hole in the plug thereof, thereby uncoupling said tap drill bit from said counterbore drill bit, said disengaging means comprising trip spline means connected to said counterbore drill bit through said drill carrier and adapted to receive said trip pin means and connecting means operative to axially connect with free rotation said tap drill to said drill carrier after said trip pin means has disengaged from said trip spline means, whereby said tap drill bit drills into and engages the plug and is disengaged from the counterbore drill bit, axial indexing means and motor means, said counterbore drill bit drills out a portion of the tube plug to lessen resistance of the plug to removal, and the plug is removed by axially indexing said tap drill bit away from said tube.

A method for removing a plug from a tube, said method comprising:

• coupling a tap drill bit to a counterbore drill bit, the counterbore drill bit being concentrically disposed about the tap drill bit, for rotation of the tap drill bit by rotating the counterbore drill bit with a motor and for axially indexing the tap drill bit by axially indexing the counterbore drill bit,
• drilling a hole in the plug with the tap drill bit, the tap drill bit having a drill point, a tapping section and a threaded section;
• tapping the hole with the tapping section of the tap drill bit;
• threading the hole with the threaded section of the tap drill bit;
• drilling away a predetermined portion of the plug with the counterbore drill bit mounted concentrically about the tap drill bit for axial movement with respect thereto to release the plug from the tube;
• and
• pulling the tap drill bit out of the tube to remove the remaining portion of the plug from the tube.