STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Hoisting System 575
(text conlznued from page 571)
of the strand, by brazing or electric welding. Joints shall be spaced in accordance
with the equation
J = 24D (4-23)
where J = minimum distance between joints in main wires in any one strand in
in. mm
D = nominal diameter of wire rope in in. mm
Wire rope is most often furnished preformed, but can be furnished nonpreformed,
upon special request by the purchaser. A preformed rope has the
strands shaped to the helical form they assume in the finished rope before the
strands have been fabricated into the rope. The strands of such preformed rope
shall not spring from their normal position when the seizing bands are removed.
Cable tool is one of the few applications for which nonpreformed is still used.
The Lay of Finished Rope. Wire rope shall be furnished right lay or left lay
and regular lay or Lang lay as specified by the purchaser (see Figure 4-64). If
not otherwise specified on the purchase order, right-lay, regular-lay rope shall
be furnished. For 6x7 wire ropes, the lay of the finished rope shall not exceed
eight times the nominal diameter. For 6x19, 6x37, 6x61, 6x91, and 8x19 wire
rope, the lay of the finished rope shall not exceed 7+ times the nominal
diameter. For flattened strand rope designations 6x25 “B,” 6x27 “H,” 6x30 “G,”
and 6x31 “V,” the lay of the finished rope shall not exceed eight times the
nominal diameter.
Diameter of Ropes and Tolerance Limits. The diameter of a wire rope shall
be the diameter of a circumscribing circle and shall be measured at least 5 ft
(1.52 m) from properly seized end with a suitable caliper (see Figure 4-65). The
diameter tolerance* of wire rope shall be
Nominal inch diameter: -0% to +5%
Nominal mm diameter: -1% to +4%
Diameter of Wire and Tolerance Limits. In separating the wire rope for gaging
of wire, care must be taken to separate the various sizes of wire composing the
different layers of bright (uncoated), drawn-galvanized, or galvanized wires in
the strand. In like-positioned wires total variations of wire diameters shall not
exceed the values of Table 4-24.
Fiber Cores. For all wire ropes, all fiber cores shall be hard-twisted, best-quality,
manila, sisal, polypropylene, or equivalent. For wire ropes of uniform diameter,
the cores shall be of uniform diameter and hardness, effectively supporting the
strands. Manila and sisal cores shall be thoroughly impregnated with a suitable
lubricating compound free from acid. Jute cores shall not be used.
*A question may develop as to whether or not the wire rope complies with the oversize tolerance. In
such cases, a tension of not less than 10% nor more than 20% of nominal required breaking strength
is applied to the rope, and the rope is measured while under this tension.