ENECON recently completed a project on a Military Sealift Command ship. The ship is a RO/RO (roll on/roll off), 954 feet long and a beam (width) of 106 feet. It is triple screw and has a displacement of 61,680 tons.
Once dry-docked, the rudder was removed along with the associated hardware (pintle/pivot pins). While the ship was pier side, the pintle was clad welded and machined. This had to be completed ‘blind’ as the gudgeon was submerged.
The pintle came back from machining and was fitted with a new key. The riggers doubled up on the capacity of the chain falls for lifting (the pin is 17,000 pounds/8.5 tons) and a 20 ton hoist was used as well as a 10 ton for back up. The scaffolding was in place as well as two man lift bucket trucks and 62kgs of DurAlloy was lifted 30 feet up to the scaffolding.
As the pintle has been exposed to seawater, it may be necessary to quantify the surface salts. A reading of 50 ppm (parts per million) or less is desired. If surface salts exceeds the ppm, it is necessary to wash with hot water and re-blast (sweep blast if the profile is acceptable). This may need to be repeated until the salts are at or below 50 ppm.
The pintle was grit blasted to a near white metal cleanliness, creating a 3-4 mil blast profile. The surface was coated with a release agent to ensure no oil of any kind would be on the surface. The inside of the housing was also blasted a few times and washed out using MEK. A release agent was also applied in the key slot inside the gudgeon. The threads on the top of the pintle were covered in plastic for protection.
A thin film of ENECON DurAlloy was applied to the tapered bore on top of the release agent. At the same time DurAlloy was applied to the pintle. While it was still pliable, the pintle was inserted into the gudgeon to the desired depth and was held there. The pintle was then hoisted into place. As it was going in, there was material exuded out of the bottom. This process took about 30-35 minutes.
The material was let it sit for about 18-19 hours. The riggers set up a hydraulic jack and popped the 8.5 ton pintle out. It was then lowered onto a pallet and the gudgeon was inspected from top and bottom. Everyone was extremely happy with the results and more business will be expected because of this completed project.
The conventional approach for this type of repair would have cost the shipyard well over $150,000. ENECON was able to provide materials and technical support for approx. $19,000. Saving the shipyard over $130,000.