Inspection may vary from hook manufacturer to manufacturer as well as the different standards that the crane load hooks can be classified into, size and type of load hook. It is therefore of the utmost importance that the inspector has the knowledge and experience on the inspection procedure on the type of hook being examined.
This inspection does not cover split-nut assembly hooks as this is a different inspection procedure regarding the shank interface area. However, all other inspection criteria to the load hook will remain the same.
Hooks are a critical part of the crane’s frequent inspection process on mobile cranes. Unexpected hook failures which will be sudden and may have devastating consequences cannot be predicted under routine maintenance. They can be caused by several things such as hidden parts in the hook assembly.
It is essential that the crane operator as far as possible should examine all visible parts of the load hook assembly every day or on the commencement of each shift as part of his/her check list and should be inspected quarterly by a qualified person or Lifting Machine Inspector having knowledge and experience on such load hooks.
The frequency and documentation requirements of the periodic inspection shall be dependent on duty cycles and/or environmental conditions in which the hooks are used in. The inspection requirements also depend on the standard you are working to or local government regulations.
If the manufacturer, relevant standard or legislation does not specify the inspection frequency, in the interest of safety it is advisable to disassemble the load hook and inspect the components annually.
During the inspection, some of the conditions that should be looked for include but not limited to.
What are the critical inspection points of the crane load hook?
- The Inspection requires the load hook to be removed from the block assembly and that the threads on the hook shaft and retainer nut are cleaned for inspection.
- Examine the threads for any cracks using the dye penetrant test method. Normally the first three threads from the bottom and thread relief area are the most critical areas to inspect. If any cracks are suspected remove the hook from service and have it examined by a certified NDT technician.
- Examine the threads for wear and corrosion. The thread area may appear tapered from top to bottom if corrosion has rounded the thread profile over time. Remove from service if more than 20% of the thread length is deformed or corroded.
- Check that the nut retaining pin, set screw or key which prevents relative movement between the hook and the nut. Examine the hook pivot and the axial bearing, cross pin, and the block bearing plate for cracks, wear and any other damage affecting the safe use of the hook assembly.
- Examine the load hook and where necessary use the dye penetrant test method.
- If the load hook has any of the following signs of cracks or excessive wear, remove the hook from service:
- The throat opening measured at the narrowest point has increased by more than 15% of the original opening.
- The hook has twisted more than 10 degrees from the original plane of the hook.
- Wear in excess of 5% in the neck of the hook and 10% in other areas including the bow of the hook.
- The hook has nicks, wear, gouges, deformation damage or cracks to the hook and exceeds any criteria specified by the manufacturer’s standard or local legislation. This includes non-OEM gouges placed on hooks to measure throat openings. Exposure to excessive temperatures will damage the heat treatment and material strength, severe weld splatter and arc strikes to the load hook can create stress concentration.
- Additionally, on Block or Ball Hooks. Elongated ball pin holes hook latch pin holes and swivel eyes exceeding 5% of the original diameter.
- Swivel end play gap exceeding 2mm. Excessive endplay may indicate damaged to internal set screw
- Check the hook latches work correctly, ensure that the latch bridges the throat of the hook when in the automatic closed position and that it activates correctly.
If the crane load hook is being used for the purpose of lifting personnel in a man basket the hook shall have a positive locking latch device fitted.
All hook blocks shall have identification plates with the following information. Manufacturers name, serial number, hook lifting capacity and weight of the hook assembly.
Before reassembling of the load hook, make sure the bearing is greased as required and the hook/ nut threads are coated with a commercial sealant to provide a corrosion resistant surface.
During reassembly check that the length of the threads engaged between the hook and nut is at least equal to the hook thread diameter.
Also check that the nut retaining pin, set screw, or key which prevents the nut from backing off the hook is in place and secured.
Finally, the load hook and assembly block shall be tested annually by a Certified Lifting Machine Inspector.
Remember that failure to comply with your required responsibilities may result in serious injuries or fatalities.