Page 18 - Pipeline Rules of Thumb Handbook

General Information 5

CABLES AND ROPES

Estimating strength of cable

Rule. 1 4
Diameter = =
2 8
1. Change line diameter to eighths
2. Square the numerator 4 2 16
3. Divide by the denominator = = 2
8 8
4. Read the answer in tons
1
1
Example. Estimate the strength of / 2 -inch steel cable: The approximate strength of / 2 -inch steel cable is 2 tons.

Find the working strength of Manila rope

1
The working strength of Manila rope is approximately Example. Find the maximum working pull for a 1 / 2 -inch
2
900 ¥ (diameter) : Manila rope.
W = 900d 2 3 3
,
W = 900 ¥ ¥ = 2 025 pounds.
2 2
where d is expressed in inches.
W is given in pounds. For rope diameters greater than 2 inches, a factor lower
than 900 should be used. In working with heavier rigging it
3
Example. What is the working strength of a / 4 -inch Manila is well to refer to accepted handbooks to find safe working
rope? strengths.
The maximum recommended pull is:

33
¥
W = 900 ¥ = 506 lb
4 ¥ 4

How large should drums and sheaves be for various types of wire rope?

The diameter of sheaves or drums should preferably fall Example. What size should the hoisting drum on a
3
within the table* given below for most efficient utilization of dragline be, if the wire rope is 6 ¥ 19 construction, / 4 inch
the wire rope. in diameter?
From the table, good practice calls for 30 diameters which
1
in this instance would be 22 / 2 inches. Loads, speeds, bends,
and service conditions will also affect the life of wire rope so
Type of Wire it is better to stay somewhere between the “good practice”
and “best wear” factors in the table.
Rope 6 ¥ 19 6 ¥ 37 8 ¥ 19 5 ¥ 28 6 ¥ 25 18 ¥ 7 6 ¥ 7
For best wear . . . . 45 27 31 36 45 51 72
Good practice . . . . 30 18 21 24 30 34 42
Critical . . . . . . . . . . 16 14 14 16 16 18 28 * Construction Methods and Machinery, by F. H. Kellogg, Prentice-Hall,
Inc., 1954.