Main Hook Block Repairs

This diving support vessel is equipped with an NOV 250 ton Active Heave Compensated Offshore Crane which required main hook block repairs.

The OC4475KSCE-(50-250) crane was undergoing maintenance in a Singapore shipyard and our Alatas Singapore Specialised Workshop was entrusted with the overhaul, rebuild, overload testing and recertification of the main hook block.

The way the hook block is used is very irregular as it is mostly used for overload tests and then stored again. Due to upcoming crane overload test, the hook block had to be inspected, overhauled and recertified.

Inspection Before Main Hook Block Repairs

• Dismantled the complete hook block and cleaned all items for inspection
• Inspected hook including the thread on hook shank as well as hook lock nut in very good condition
• Inspected hook trunnion and found without wear. Removal of trunnion had to be done with 150ton hydraulic jack as it was stuck in the side shield due to corrosion
• Thrust bearing, shaft bearing and rope sheave bushing (composite material) in good condition
• O-rings will need to be replaced
• All lock nuts for the studs that were removed (nine in total). These needed to be replaced as they cannot be reused once removed
• Carried out NDT testing on the trunnion, hook, lock nut, rope sheave and side shields at the load-bearing areas. No cracks were found.

For more information, please reference NDT Test Report no. 161542-1A when you speak to us.

Job Scope for Repairs

1. Removed and replaced nine lock nuts
2. Replaced O-rings
3. Assembly of hook, trunnion and lock nut with cleaned bearings. Secure lock nut on hook shank with bolted key plate (Loctite 243 on screws)
4. Reassemble complete hook block unit and send it out for testing & witnessed by Owner & DNV Surveyor
5. After load testing, carried out post-NDT on the hook and repaint those unpainted and touch up locations

The work and reporting were carried out to the highest standard Alatas customers have come to expect.

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