A vital part of the inspection and maintenance process for mobile cranes often overlooked is the inspection or examination of the boom structure. Being essentially a load bearing component, care of the boom sections is often confined to the paint condition and sign writing.
This neglect can, however, have serious consequence’s as all structures and mechanical components deteriorate over time, with the rate of deterioration depending on factors such as initial design, environment and loading. Without effective inspection and repair of defects mobile crane boom structures and mechanisms may suddenly fail, often with catastrophic results.
Visually inspect all boom sections a minimum of once a week or every fifty (50) hours, whichever occurs first by a competent person. The inspection must be undertaken in a safe cordoned-off area. Set the outriggers to the fully out position then rotate the upper to an area where the boom can be fully lowered and each section extended. Remember to consult the cranes capacity chart first before extending the boom sections.
Once the inspector has access to the entire length of each boom section, a great deal of attention needs to be paid to all the wearing items to ensure that all the original tolerances for pins and bush/bearings are maintained, boom slide pads are within tolerances, boom lock pins (where fitted) are correctly functioning, hydraulic cylinders are not leaking externally or internally, lock valves are functioning correctly, hydraulic hoses for damage or chaffing, sheaves/rollers are serviceable and the correct extension and retraction ropes/chains are installed and serviceable, inspect the hoist cylinder attaching supports, jib or super-lift attachment points are serviceable and all individual boom sections are within manufacturers specified tolerances for straightness and alignment.
Each boom section should also be inspected closely for any structural damage with the boom section fully extended. If an inspection reveals structural damage, nicks, corrosion, gouges, bent components, scrubbing, broken welds, cracks or any type of deformation, missing or illegible indication marking decals on the telescoping sections as well as any unauthorised welding on any of the boom sections this needs to be recorded and where necessary the inspector must remove the crane from service until the cranes boom has been repaired, load tested and certified by a Lifting Machine Inspector. Any deformation in crane boom can lead to a collapse, even without a load on the crane.
When undertaking a performance test of the boom extension/retraction mechanism check for “boom chatter” which is the shaking of the telescoping sections when extending or retracting. This can occur when slide pads are missing or have fallen out, loose bolts, slide pads are worn down with use, slide pads are running dry or the use of the incorrect boom lubricants. This may cause failure of internal boom components, such as extend and retract ropes/chains and their mechanisms. Boom chatter will also have a negative influence on the boom structure and components.
Consideration must to be paid to the manufacturer’s recommendations. For the inspection and replacement intervals of boom mechanical components for example, we know that many manufacturers stipulate a prearranged life on the extension and retraction ropes (or chains) where these are fitted. The records of the crane need to be carefully studied by the inspector to see if any replacement has been carried out in accordance with these recommendations.
Crane manufacturers recommendations must be adhered to regarding the time frame for the replacement of the extension and retraction ropes/chains as well as the slide pads and other internal components as each crane manufacturer differs. Some manufacturers’ state every 8 years and others 10 years for replacement of these parts. However, during the mobile crane’s annual inspection and load test it is at the discretion of the Lifting Machine Inspector to strip the boom for further examination should he/she find any anomalies on or in the boom sections.
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