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Overhaul of 250T main Hook Block of NOV Offshore Crane

The diving support vessel is equipped with a 250 ton main crane, i.e. an Active Heave Compensated Offshore Crane, male National Oilwell Varco, type OC4475KSCE-(50-250) AHC

The Crane was undergoing maintenance in a Singapore Ship Yard, and our ALATAS Singapore specialized Workshop was entrusted with the overhaul, re-build, overload testing and re-certification of the main hook block.

Repair Report 250 Ton Hook Block

Reason for Repair
• The hook block is used very irregular, - mostly for overload test and then stored again. Due to upcoming crane overload test the hook block has to be inspected, overhauled and re-certified.

Inspection Findings
Dismantled the complete Hook Block and cleaned all items for inspection:
• Inspected hook including 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 150to hydraulic jack as it was stuck in the side shield due to corrosion.
• Thrust Bearing, Shaft Bearing & Rope Sheave Bushing (composite material) in good condition
• O-rings will need to be replaced.
• All Lock nuts for the studs that were removed (9Pcs) need to be replaced as they cannot be re-used once removed.
• Carried out NDT testing on trunnion, hook, lock nut, rope sheave and side shields at the load bearing areas. No cracks were found. Please refer to enclosed NDT Test Report, no. 161542-1A

Scope Of Repair
• Replaced 9Pcs of Lock nuts that were removed.
• Replaced O -rings.
• Assemble hook / trunnion / lock nut with cleaned bearings. Secure Lock Nut on Hook Shank with bolted key plate (Loctite 243 on screws)
• Re-assemble complete hook block unit and send it out for testing & witnessed by Owner & DNV Surveyor.
• After load testing, carry out post NDT on the hook and repaint those unpainted and touch up locations

The work and reporting was carried out to the highest standards expected by our customer.


Hook loaded for transporting to workshop
Re-assembling of Hook Block.
Hook Block dismantled and paint removed for NDT inspection
Rope Sheave
All parts dismantled awaiting to
be cleaned and prepared for
NDT Testing.
Lock Nut installed (thrust
bearing sufficiently greased)
Hook assembled into trunnion.
Hook Block dismantled and paint removed for NDT inspection
New Lock Nuts supplied and
Hook block was completely
cleaned and touch up painting
Unit being installed back into the
parking frame.
Unit inside parking frame.


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