How to Select the Right Crane Duty Class
Learn how load spectrum, operating cycles, average travel, starts per hour, environment, and production consequences influence overhead and gantry crane duty classification.
HAOKCRANES Application Engineering Group
Crane selection engineeringLoad spectrum, operating cycles, mechanism duty, environment, and project data definition
HAOKCRANES Crane Design Review Group
Technical review | 2026-06-08Structural and mechanism classification inputs, standard alignment, and inquiry data completeness
Start With the Load Spectrum
Estimate the percentage of lifts near rated load, medium load, light load, and empty-hook travel. A crane lifting its rated load once per week has a different fatigue demand from a crane repeatedly handling 70 percent of capacity every hour.
- List typical and maximum load weights.
- Estimate lifts per hour, shifts per day, and operating days per year.
- Separate normal production from shutdown, maintenance, or exceptional lifts.
- Identify tandem lifts, below-the-hook devices, magnets, grabs, and other permanent loads.
Describe the Motion and Process
Mechanisms may require a different classification from the crane structure. Hoisting, trolley travel, and bridge travel should be reviewed using their own cycle frequency and operating time.
- Record average lifting height and average bridge or trolley travel distance.
- Count starts, reversals, inching movements, and positioning cycles per hour.
- Note whether the crane follows a repetitive automatic sequence.
- Define required speeds, acceleration, positioning accuracy, and anti-sway needs.
Add Environment and Consequence
Heat, dust, corrosion, outdoor wind, explosive atmospheres, molten metal, cleanrooms, and high-altitude sites can change motors, brakes, enclosures, materials, controls, and maintenance intervals even when the nominal duty class stays the same.
- State minimum and maximum ambient temperature.
- Identify dust, humidity, salt, chemicals, heat radiation, or hazardous zones.
- Define whether crane failure stops a critical production line.
- Confirm access restrictions and the site's maintenance capability.
Information to Send With an Inquiry
A useful inquiry includes capacity, span, lifting height, travel length, power supply, load spectrum, estimated cycles, operating environment, control method, drawings, and the required classification standard.
- Do not convert FEM, ISO, CMAA, or national classes by name alone.
- Ask the supplier to state the selected structural and mechanism classes.
- Confirm assumptions in the technical offer before comparing prices.
- Treat an underspecified low price as a technical risk, not only a commercial advantage.
Frequently Asked Questions
Is a higher duty class always better?
Not automatically. A higher class can increase size, weight, energy use, and cost. The goal is a classification that safely matches the verified operating profile with appropriate design margin.
Can two cranes with the same capacity have different duty classes?
Yes. Capacity is only one input. Cycle frequency, load spectrum, starts per hour, travel, environment, and process consequence can produce very different classifications.
Can FEM and CMAA classes be directly converted?
Direct one-line conversion can be misleading because the systems use different assumptions and classification methods. The project should identify the governing standard and compare the underlying duty data.
Use This Guide On Your Project
Download the printable worksheet for engineering discussions, inspections, and documented follow-up.
