Shrouds for drill rods

As on our Technical sheet UPHOLE VELOCITY certain drilling conditions require the addition of a shroud to both the drill rods and hammer. This sheet gives a guide as how to manufacture and fit the drill shrouds.

By using the 'up hole velocity formula on the UPHOLE VELOCITY technical sheet, you can determine the correct outer diameter of your shroud. The thickness of your shroud will usually be determined by the availability of tube with the correct outer diameter, but as a rough guide we would recommend a wall thickness of 6 to 10mm dependant upon the diameter of shroud you are going to use. Do not forget that the addition of a shroud on each rod will considerably increase the total weight of the string, and this should be taken into account when both calculating 'weight on bit' and required pull back to lift the equipment from the hole when it is finished.

The shroud length should be 8 to 12mm shorter than the effective length of your drill rod, this guarantees that when the rods are tightened together it is the faces of the drill tubes which lock up, and not the faces of the shroud. This point is very important, as the locking together of the shroud faces will result in failures on the threaded joints of the drill rods.

Once your shroud is machined to the correct length, then you will need to manufacture a pair of flanges. These need to be a minimum of 25mm thick with a bore size 0.25mm larger than the overall diameter of your tool joints of the drill rod, and an outer diameter that is 0.25mm smaller than the bore size of your shroud.

As the addition of a shroud prevents the spanner flats on the original tool joints from being used, you will need to fabricate a minimum of two spanner boxes for each of the flanges. These spanner boxes allow you to split the rods by using 'C' spanners, which are manufactured to suit the diameter of the shroud you are using. Two boxes per end is the minimum, but to speed up the splitting process we recommend you manufacture four spanner boxes for each flange as shown in the diagram. These boxes need to be approximately 75mm wide and 75mm long and a minimum of 50mm deep.

Once the flanges are complete, the next step is to burn a square hole into the shroud. These holes must correspond to the position of the spanner boxes on the flanges, when they are welded in position.

When this is complete one flange should be welded onto one of the tool joints, with the spanner sockets facing towards the centre of the rod. The flange should be positioned 4 to 8mm away from the lockup face of the tool joint. The shroud is then positioned over this first flange, and tacked in position. The second flange is then inserted into the open end of the shroud, and positioned so that its spanner sockets correspond with the holes in the shroud. The whole assembly is then fully welded.

To give extra strength, and prevent debris entering the shroud, the square holes should be fully welded to the sockets below.


Shrouds for drill rods As on our Technical sheet UPHOLE VELOCITY certain drilling conditions require the addition of a shroud to both the drill rods and hammer. This sheet gives a guide as how to manufacture and fit the drill shrouds. By using the 'up hole velocity formula on the UPHOLE VELOCITY technical sheet, you can determine the correct outer diameter of your shroud. The thickness of your shroud will usually be determined by the availability of tube with the correct outer diameter, but as a rough guide we would recommend a wall thickness of 6 to 10mm dependant upon the diameter of shroud you are going to use. Do not forget that the addition of a shroud on each rod will considerably increase the total weight of the string, and this should be taken into account when both calculating 'weight on bit' and required pull back to lift the equipment from the hole when it is finished. The shroud length should be 8 to 12mm shorter than the effective length of your drill rod, this guarantees that when the rods are tightened together it is the faces of the drill tubes which lock up, and not the faces of the shroud. This point is very important, as the locking together of the shroud faces will result in failures on the threaded joints of the drill rods. Once your shroud is machined to the correct length, then you will need to manufacture a pair of flanges. These need to be a minimum of 25mm thick with a bore size 0.25mm larger than the overall diameter of your tool joints of the drill rod, and an outer diameter that is 0.25mm smaller than the bore size of your shroud. As the addition of a shroud prevents the spanner flats on the original tool joints from being used, you will need to fabricate a minimum of two spanner boxes for each of the flanges. These spanner boxes allow you to split the rods by using 'C' spanners, which are manufactured to suit the diameter of the shroud you are using. Two boxes per end is the minimum, but to speed up the splitting process we recommend you manufacture four spanner boxes for each flange as shown in the diagram. These boxes need to be approximately 75mm wide and 75mm long and a minimum of 50mm deep. Once the flanges are complete, the next step is to burn a square hole into the shroud. These holes must correspond to the position of the spanner boxes on the flanges, when they are welded in position. When this is complete one flange should be welded onto one of the tool joints, with the spanner sockets facing towards the centre of the rod. The flange should be positioned 4 to 8mm away from the lockup face of the tool joint. The shroud is then positioned over this first flange, and tacked in position. The second flange is then inserted into the open end of the shroud, and positioned so that its spanner sockets correspond with the holes in the shroud. The whole assembly is then fully welded. To give extra strength, and prevent debris entering the shroud, the square holes should be fully welded to the sockets below.
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