7.1.1 General
The theoretical design life of the structural, machinery, and wire-rope components of the crane shall be considered separately. Requirements for the structural components are intended to provide a structure that meets or exceeds the life expectancy of the facility on which the crane is installed. Machinery and wire rope design life should be based on reasonable repair or replacement intervals, consistent with the duty cycle, or specific frequency and magnitude of lifted loads during the expected life of the crane.
The preferred basis of the duty cycle analysis of the crane components is to use purchaser-projected information. In the absence of this information, default duty cycle parameters are provided for typical pedestal-mounted offshore crane classifications. Manufacturers may also provide predetermined life cycle ratings.
The theoretical design life guidelines herein cannot encompass all operational, environmental, and maintenance variables affecting the life of crane components, and cannot be considered as guaranteed. These guidelines are intended to provide a reasonable basis for the design of structural, machinery and wire rope components of the crane which are consistent with the intended usage.
7.1.2 Machinery Duty Cycles
When the purchaser does not provide specific duty cycle data, the expected duty cycle or time between overhaul (TBO) of the primary machinery components is determined from frequency of use in hours during the TBO in years.
The expected magnitude of lifted loads is expressed as a percentage of the maximum load of the individual component that corresponds with the frequency during the TBO. The duty cycle life of the individual components are determined from the maximum allowable load on each crane component based on the component rating without regard to the capacity of the crane as a whole. Operating speeds are based on a percentage of maximum speed, and the machinery is considered to be in use whether the crane is loaded or unloaded, but only if it is in motion.
7.1.2.1 Classification of Typical Offshore Crane Applications
In the absence of information from the purchaser, the operating frequency may be classified by typical offshore crane application as shown in Table 7 for the overall crane, and in Table 8, Table 9, Table 10, Table 11, and Table 12 for the major crane mechanical components.
7.1.2.2 Machinery Duty Cycles by Crane Classification
If typical offshore-crane classifications are used, the theoretical TBO cycle life for the primary machinery
components may be determined from the corresponding magnitude of loading and operating speeds as shown in the Table 8, Table 9, Table 10, Table 11, and Table 12. The commentary discusses the basis of the classifications and TBO information.
7.1.3 Wire Rope Duty Cycles
The duty cycle approach for wire ropes is similar to that of the machinery components, although the time between replacement (TBR) for wire ropes is expected to be less than that of the machinery. The crane designer should consider factors (i.e. the magnitude and frequency of loading, fleet angles, D/d ratios of drums and sheaves commensurate with the duty cycle).
Table 7—Classification of Offshore Crane Applications Crane Duty-Cycle
Classification Annual Operating
(Prime Mover) Typical Applications
Production duty 200 hr Offshore cranes on bottom- supported production platforms Intermediate duty 2000 hr
Offshore cranes on bottom- supported or floating platforms with temporary rigs or intermittent periods of intensive use
Drilling duty 5000 hr Offshore cranes on MODUs or floating production facilities with full- time drilling operations
Construction duty 1000 hr Offshore cranes on construction barges or vessels heavy-lift cranes Table 8—Auxiliary Hoist – 5 Year TBO
Crane Duty Cycle
Classification Theoretical
Design Life % Maximum
Torque % Maximum Speed
Production duty 60 hr 45 % 70 %
Intermediate duty 825 hr 45 % 70 %
Drilling duty 2,100 hr 55 % 70 %
Construction duty 250 hr 45 % 70 %
Table 9—Main Hoist – 5 Year TBO Crane Duty-Cycle
Classification Theoretical
Design Life % Maximum
Torque % Maximum Speed
Production duty 70 hr 45 % 70 %
Intermediate duty 225 hr 45 % 70 %
Drilling duty 500 hr 55 % 70 %
Construction duty 250 hr 45 % 70 %
Table 10—Boom Hoist – 5 Year TBO Crane Duty-Cycle
Classification Theoretical
Design Life % Maximum
Torque % Maximum Speed
Production duty 70 hr 45 % 70 %
Intermediate duty 1250 hr 45 % 70 %
Drilling duty 3750 hr 55 % 70 %
Construction duty 900 hr 45 % 70 %
7.1.3.1 Wire Rope TBR by Typical Offshore Crane Classification
In absence of information from the purchaser, the TBR may be estimated by typical offshore crane application as shown in Table 13.
7.1.3.2 Wire Rope Duty Cycle by Crane Classification
If the wire rope TBR for offshore crane classifications is used, the TBR cycle for the wire may be determined from the corresponding magnitude of loading and number of cycles as shown in Table 14 through Table 16.
Table 11—Slew Mechanism – 5 Year TBO Crane Duty-Cycle
Classification Theoretical
Design Life % Maximum
Torque % Maximum Speed
Production duty 70 hr 45 % 70 %
Intermediate duty 900 hr 45 % 70 %
Drilling duty 2500 hr 55 % 70 %
Construction duty 300 hr 45 % 70 %
Table 12—Prime Mover and Pump Drive – 5 Year TBO Crane Duty Cycle
Classification Theoretical
Design Life % Maximum
Torque % Maximum Speed
Production duty 1000 hr 45 % 70 %
Intermediate duty 10,000 hr 60 % 70 %
Drilling duty 25,000 hr 60 % 70 %
Construction duty 5000 hr 60 % 70 %
NOTE Diesel engine manufacturers typically recommend overhaul at less than drilling duty design life.
Table 13—Wire Rope TBR by Typical Offshore Crane Classification Crane Duty Cycle
Classification TBR
Production duty 3 yr
Intermediate duty 2.5 yr
Drilling duty 2 yr
Construction duty 3 yr
Table 14—Auxiliary Wire Rope Crane Duty Cycle
Classification Lift Cycles to
TBR % Maximum SWLH
Production duty 1,000 45 %
Intermediate duty 12,500 45 %
Drilling duty 28,500 55 %
Construction duty 2,700 45 %