STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

516 Drilling and Well Completions
Wire line slings or tag lines should have suitable fittings to prevent the rope
from being bent over sharp edges and damaged.
Loads due to impact, acceleration, and deceleration niay be indicated by
fluctuation of the weight indicator readings and the operator should keep the
indicator readings within the required hook load capacity.
In the erecting and lowering operation, the slowest practical line speed should
be used.
Girts, braces, and other members should not, under any circumstances, be
removed from the derrick while it is under load.
The drilling and well servicing structure manufacturer has carefully designed
and selected materials for his or her portable mast. The mast should perform
satisfactorily within the stipulated load capacities and in accordance with the
instructions. Every operator should study the instructions and be prepared for
erecting, lowering, and using the mast.
The substructure should be restrained against uplift, if necessary, by a suitable
dead weight or a hold-down anchor. The weight of the hoist and vehicle, where
applicable, may be considered as part or all of the required anchorage.
Each part of a bolted structure is designed to carry its share of the load;
therefore, parts omitted or improperly placed may contribute to the structure
failure. In the erection of bolted structures, the bolts should be tightened only
slightly tighter than finger-tight. After the erection of the structure is completed,
all bolts should be drawn tight. This procedure permits correct alignment of
the structure and results in proper load distribution.
Sling Line inspection and Replacement
One or more of the three principal factors, including wear due to operation,
corrosion and incidental damage, may limit the life of a sling. The first may be
a function of the times the mast is raised, and the second will be related to
time and atmospheric conditions. The third will bear no relation to either, since
incidental damage may occur at the first location as well as any other.
Charting of sling line replacement shows an erratic pattern. Some require
replacement at a relatively early date and others last several years longer. Early
replacements generally show incidental damage, and it is possible that some of
the longer lived ones are used beyond the time when they should be replaced.
There is no way of judging the remaining strength of a rusty rope; therefore,
rusty sling lines should be replaced. Areas adjacent to end connections should
be examined closely for any evidence of corrosion.
It would no doubt be possible to establish a normal sling line life expectancy in
terms of the number of locations used, as long as a set number of months was not
exceeded. However, this would not preclude the necessity for careful inspection to
guard against incidental damage. A line with any broken wires should be replaced.
A line showing any material reduction of metal area from abrasion should be
replaced. A line showing kinking, crushing, or other damage should be replaced.
Replacement of lines based on normal life expectancy will provide some
degree of safety, but it is important that such provisions do not cause any degree
of laxity in sling line inspection.
Sling lines should be well lubricated. The field lubricant should be compatible
with the original lubricant, and to this end the rope manufacturer should be
consulted. The object of rope lubrication is to reduce internal friction and to
prevent corrosion.
The following routine checks, as applicable, should be made at appropriate
intervals: