breaking in period (see pg 25-26 for more information). That is the measurement to
be recorded
as
the initial diameter.
The actual rope diameter must be measured. This is defined as the diameter
of
the
circumscribing circle. (ie, its largest cross sectional dimension)
To
insure accuracy
this measurement should be made with a wire rope caliper using the correct method
(b) shown on the facing page. Special techniques and equipment must be employed
for measuring ropes with an odd number
of
outer strands. (eg, circumferential tapes,
calipers with plates
- see illustration on facing page).
Wear occurring at the crowns
of
outer wires is normal. Many standards state a
rope must be removed from service when its actual diameter is reduced to 95%
of
the nominal diameter. The accompanying photos show examples
of
heavy
normal wear on both regular and lang lay wire ropes.
Regular Lay Lang Lay
This picture simulates 6 x
25
fw construction wire ropes with surface wear (only)
of
113
the
outer wire diameter.
Plastic enhanced ropes (impregnated or filled) require careful measurements.
It
is essential to measure the metal, not plastic on the exterior
of
the rope. Exterior
measurement cannot be used to determine diameter reductions
of
the wire rope
in plastic coated (jacketed) ropes.
Rope core deterioration usually results in a reduction
of
the rope's diameter,
making careful measurement important. Although the core provides less than
10%
of
the rope's strength (on standard six
or
eight strand IWRC ropes), that loss
of
strength may not be the primary concern. Deterioration
of
the core Jeads to
increased stress and broken wires in the outer strands
of
the rope. These broken
wires are usually valley breaks which can be more difficult to detect.
BROKEN WIRES
Broken wires are another primary indicator
of
rope degradation, and remaining
useful life. The accompanying table shows allowable wire breaks in typical
installations. These broken wire removal criteria apply to wire rope operating on
steel sheaves and drums. The user shall contact the sheave, drum,
or
equipment
manufacturer
or
a qualified person for broken wire removal criteria for wire
ropes operating on sheaves and drums made
of
material other than steel.
If
no
other information is available, the standard broken wire removal criteria should
be used. However, since the use
of
plastic sheaves may cause internal wire
breakage, the inspector must pay particular attention to evidence
of
valley breaks
or breaks against the core and corrosion in the rope valleys.
Wire Rope Technical Board - Wire Rope Users Manual, Fourth
Edition·
65
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