Underwater Coating Application to Seal hull leaks (Ship Husbandry Project – applicable to Ship Husbandry)
On June 24, 1998, divers from Underwater Construction Contractors performed an underwater video and ultrasonic thickness inspection of a water intake barge located on Florida’s Hiwassee River. The ultrasonic inspection of the hull revealed plate thickness ranging between 0.360 and 0.380 of an inch. These measurements were consistent with as-built drawings indicating the hull was constructed from 3/8-inch steel plate. During the inspection, a pattern emerged showing reduced wall thickness (0.005 to 0.010) on the starboard side. Upon inspection of the inner hull, approximately two inches of standing water was found on the starboard side. The port side was found to be dry.
The hull coating was found to be about 90 to 95 percent intact, although rust nodules were found over the entire submerged surface of the hull near the bow. Upon removal of several of the rust nodules, pitting was found. Pit depths ranged between 1/16 to 1/8 of an inch. A majority of the rust nodules appeared to be concentrated along the weld seams. Several inches of water were found in the bilge. It was believed that at least some of the leakage was caused by pinhole perforations of the hull at pitting corrosion sites.
The barge is permanently moored and cannot be dry-docked. It was decided that underwater coating repair of the pitted area would be attempted in hopes that it would not only arrest corrosion but plug any pin hole leaks.
The divers cleaned the surface with a 3,500 psi pressure washer. This was followed by a mechanical surface prep to SP 11 using a 3M Clean N Strip to remove any remaining corrosion and roughen the coating around the pit. Bio-Dur 561 was applied at 40 to 50 mils. Approximately 500 repairs were made, ranging in size from 1/2 inch to three feet in diameter. TFT epoxies are distributed by Progressive Epoxy Polymers, Inc.
The work was performed in a one knot current. Water temperature was 50 degrees F, with visibility at approximately two feet. After the coating was fully cured, the main compartment was sealed and pressure tested to five psi. No pressure loss was detected over 30 minutes. Subsequent inspections indicate there has been no additional leakage.