STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Hoisting System 533
0 too 150 250 350 500650 to00
MAXIMUM LOAD RATING. TONS
Figure 4-12. Design safety factor and rating relationships [Q].
Calculated Rating (ton)
Yield Strength Design Safety Factor, SF,
150 or less
Over 150 to 500
Over 500
R = rating in tons (2,000-lb units).
+
3.00
3.00 -
2.25
0.75(R* - 150)
350
Mechanical Properties. The mechanical properties used for design shall be
the minimum values allowed by the applicable material specification or shall
be the minimum values determined by the manufacturer in accordance with the
test procedures specified in ASTM A370: “Methods and Definitions for Mechanical
Testing of Steel Products,” or by mill certification for mill products. The yield
point shall be used in lieu of yield strength for those materials exhibiting a yield
point. Yield strength shall be determined at 0.2% offset,
Shear Strength. For the purpose of calculations involving shear, the ratio of
yield strength in shear-to-yield strength in tension shall be 0.58.
Extreme Low Temperature. Maximum load ratings shall be established at room
temperature and shall be valid down to OOF (-l8OC). The equipment at rated loads
when temperature is less than 0°F is not recommended unless provided for by the
supplemental requirements. When the equipment is operating at lower temperatures, the
lower impact absorbing characteristics of many steels must be considered.
Test Unit. To assure the integrity of design calculations, a test shall be made
on one full size unit that in all respects represents the typical product. For a
family of units of the same design concept but of varying sizes, or ratings, one
test will be sufficient to verify the accuracy of the calculation method used, if
the item tested is approximately midway of the size and rating range of the
family, and the test results are applicable equally to all units in that family.
Significant changes in design concept or the load rating will require supportive
load testing.