Mobile cranes require no modifications from their standard
commercial configuration other than a wire rope design factor of 6.0 or greater.
(This requirement may be satisfied either by de-rating the crane or replacing the
original wire rope with one of higher strength.)
An additional maintenance/condition requirement for mobile cranes
which use hydraulic cylinders for boom elevation, is the limitation of the rate of
leakage of the hydraulic fluid under load. (Such leakage reduces the initial
stability of the crane because the hook load radius increases as the hydraulic
cylinders allow the boom to drift lower.) The specific limits on such boom
cylinder leak-down (usually on the order of 0.5 to 1.0 inch in 10 minutes under
rated load) are established by the local crane engineering organization.
Trolleys and bridge end trucks of OET cranes (and other cranes with
such overrunning components) must be analyzed for the applicable seismic forces
and must be equipped with seismic restraints. Depending on the particular crane
design and seismic zone, the restraints may be required against both lateral
dislodgment and lift-off. The restraints may engage the rail head or the flange
of the structural rail support member.
Portal cranes must be analyzed for the applicable seismic forces.
Portal cranes that rotate on roller path and king pin assemblies, also require the
king pin to be designed for the total shear load due to the horizontal seismic
All external structural welds of indoor cranes must be smooth (so
that they will not tear a cotton cloth when scrubbed on them) to permit complete
removal of any radioactive contamination that may have been accidentally released
and deposited on them.
Cast steel poured sockets, in both outdoor and indoor installations,
require minimum values of fracture toughness. Those cast of carbon steel, must
have a minimum fracture toughness of 15 foot-pounds at 10 degrees Fahrenheit;
those cast of alloy steel, 30 foot-pounds at 10 degrees Fahrenheit. The values of
fracture toughness are to be determined by Charpy V-notch tests on sockets from
the same lot.
Captivation and Containment. Cranes used to lift radioactive materials
or major reactor components directly over open reactor compartments, must include
provision to captivate or contain any fastener, item of hardware, fluid, or other
material in such foreign material exclusion areas. The following design features,
in addition to those listed above, apply:
All load blocks are required to include drip pans fitted around the
shank of the hook and extending outwards to encompass all possible points of
lubrication drips. Individual hoist components, such as gear reducers, are also
required to be equipped with drip pans unless the trolley floor is designed to
contain any lubricant drips from equipment that is mounted on it. Travel drives
require drip pans or other containment provisions at all lubricated components or
assemblies. (Permanently lubricated and sealed bearings are not considered drip-
proof.) On portal, floating, and mobile cranes, only the outer section of the
boom is required to be equipped with drip pans. (Outer section of the boom is
defined as from the tip to 20 feet inward, measured horizontally from the main
hoist sheave nest when the boom is at its maximum operating radius.)