The fast-line velocity can be computed as the product of pipe speed and number of lines strung over the block.

5. The efficiency of the mechanical system for the chains and shafts between the draw works and the engines was calculated in Example 16.2 as 0.834:

861 hp 0.834

= 1,032 hp (engine horsepower)

Wire rope must be monitored for fatigue wear resulting from raising and lowering the drillstring or casing. The usual practice is to evaluate the number of ton-miles of work performed by the wire rope. A ton-mile is defined as the amount of work needed to move a 1-ton load over a distance of 1 mile. After the rope has reached a specified ton-mile limit, it is removed from service. The limits vary for different operations and may range from about 500 for 1.0-in. rope to about 1,800 for 1%-in. rope. Drilling line also is cut (a portion is retired) before any critically strenuous job.

The major factors affecting ton-mile wear on the wire rope are round trips, setting casing, and drilling. Eq. 16.10 computes ton-miles during a round trip:



— ton-miles during a round trip


= hole depth, ft


= length of a drillpipc stand, ft


= effective weight per foot of drillpipe, lb/ft


— total weight of traveling block-elevator assembly


= effective weight of drill-collar assembly minus the effective weight

of the same length of drillpipe, lb/ft

Similar equations are provided in API RP 9B for coring, drilling, and setting casing.

M is the weight of the traveling block assembly. It includes the traveling block, hook, links, and elevators. If the actual weight of the traveling block assembly is unknown, the following approximate values may be used:

Traveling Block Assembly Weight,

Capacity, tons lb

100 6,000

150 9.000

250 350 500 650 750

12,000 19,000 28,000 35,000 48,000

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