The traveling block, crown block, and wire line are the three components whose function is to connect the supporting derrick or mast with the load of pipe to be lowered into or withdrawn from the hole. During drilling operations, load usually consists of the drill pipe and drill collars, with the bit attached to the bottom of the drill collars. However, a string of special pipe called casing, which is often a heavier load than the drill pipe and collars, has to be lowered into the hole and cemented. The wire line is reeved around sheaves in the crown block of the top on the derrick or mast.
As is true of almost every part of many rotary rigs, the blocks and wire-line assembly must have great strength to be able to bear heavy loads .Friction must also be eliminated in the blocks insofar as possible while still maintaining the desired strength. Thus, well made bearings and proper lubrication of these bearings by the crew are very important.
As wire-rope manufacturers like to emphasize, a wire ripe, or wire line, is in itself a machine in the sense that it requires lubrication. This is because of the constant movement of strands within the wire line rubbing against one another as the rope flexes over sheaves in the block assembly. Because wire line is an expendable item, it can be an appreciable expense on any drilling rig; this is particularly true unless a planned program of purchase and use of the wire line is in effect from the beginning.
To achieve the greatest economy from the use of wire line on a drilling rig, the line selected should be of the proper length and its diameter should be in accord with both the load requirements and the design of the sheaves in the traveling block and crown block through which the line must travel. The line should be frequently inspected to ensure that it is in good condition. The drilling line should be moved periodically-slipped is the field term-so that it wears evenly as it is used. Cutoff procedures should take into account the amount of usage-that is, the ton-miles of service. (If a wire line has moved a 1-ton load a distance of 1 mile, then the lie has received 1 ton-mile of usage.) |