Yards replacing corrosion-prone aluminum plates

The crack in the hull of an aluminum high-speed catamaran last December in Hawaii triggered an investigation by the vessel’s builder, its owner and the U.S. Coast Guard to determine the cause. Similar problems soon became apparent in other vessels recently built on the U.S. West Coast. The unexpected consensus: Some aluminum plates made of 5083-H321 composition used for recent vessel construction were found not to be resistant to corrosion in a saltwater environment.

In the past, builders of aluminum vessels had successfully used both 5083-H321 and 5083-H116. Although the two grades of aluminum differ somewhat in their physical characteristics, both have been generally referred to as marine grade and used in saltwater environments.

After December’s discovery, the shipyards moved quickly to fix all damage, including replacement of undamaged but nevertheless noncorrosion-resistant aluminum as determined by testing.

Nichols Bros. Boat Builders’ initial response was typical. A boat it had built for service in Southern California was found to have cracks in the middle of 3/16-inch-thick aluminum plates mainly in the engine room and water jet pump room.

“We brought the boat back into our yard and ran a double shift,” said Matt Nichols, president of Nichols Bros. “We had to lift the deckhouse off, and replaced with all new material some longitudinal stringers, plates and anything attached.” The work, he said was “taken care of by us at great expense, but the customer is extremely pleased.”

At Kvichak Marine Industries, the response was equally fast to resolve the problems when the first reports came of defoliation and cracking of the aluminum hull on the Hawaii catamaran.

The Coast Guard’s Puget Sound Marine Safety Office identified Nichols Bros., Kvichak Marine and Norsco Marine as the shipyards affected, and Reynolds Metals Company, Alcan Aluminum Corp. and Integris Metals as suppliers of the material.

The extent of the problem is still unknown. In a lawsuit, Nichols Bros. contended “the problem could affect at least 25 vessels built by several shipyards and their total value could exceed $50 million.”

Apparently, the shipyards relied on the commonly used product terminology of “marine-grade aluminum” when purchasing materials for these vessels. But this time, Matt Nichols said, “the 5083-H321 was not corrosion-resistant like it was supposed to be. Once salt water got on the material, it started a process of breaking the material down and defoliation would begin.”

In early February, Integris Metals stated in a letter that the 5083-H321 it supplied was not guaranteed for marine use and could be susceptible to corrosion when exposed to salt water. On March 11, the issue moved to court when Nichols Bros. filed a lawsuit in U.S. District Court against both Reynolds and Alcan to recover damages. The complaint alleged that “Reynolds knew the aluminum Nichols sought was intended for use on a passenger ferry to be used in a marine environment, and that the aluminum would have to be marine grade.” Although the aluminum suppliers had “delivered certificates of conformance … that the aluminum had the characteristics that made it marine grade, the material delivered in fact was not marine-grade.” Further, the complaint contended that because of Reynolds’ “skill and experience” in supplying aluminum, “Nichols left up to Reynolds the choice of aluminum between 5083-H116 and 5083-H321 to supply for use.”

5083-H321 has been successfully used for other vessel construction. One Far Eastern shipyard said that while that material “does not require painting for corrosion protection, it may be advisable to fill and fair hull exteriors and superstructure above the waterline with an epoxy micro-balloon filler.”

In this current problem, Matt Nichols said the low corrosion resistance of the 5083-H321 supplied may be related to a production factor.

“Basically, the Alcan plant in Oswego, N.Y., that was doing the manufacturing changed the procedure from a hot-rolled process to a cold-rolled process,” he said. “In hot rolling, the particles of the components of the material were distributed much better, in a more fluid and more uniform manner. The cold-rolled process just wasn’t as uniform. Once salt water got on the material, corrosion, defoliation and cracking would begin.”

Another factor may be the degree of magnesium particles between grain boundaries in the aluminum microstructure. An independent metallurgist also advised the Coast Guard that factors such as vibration, operational heat from engines, high ambient temperatures and vessel stresses could accelerate the development of cracks.

But in selecting an appropriate aluminum material for corrosive atmospheres, one aluminum supplier that is not involved in the dispute recommends 5083-H116 because “this temper (H116) has characteristics which substantially eliminate the susceptibility of alloy 5083 to exfoliate under certain corrosion conditions.”

Ultimately, defining different tempers of 5083 aluminum and their production methods for use as “marine grade” may have to be clarified. Lt. Cmdr. Tom Miller, chief of inspections with the Coast Guard’s Puget Sound Marine Safety Office, noted that while both 5083-H116 and 5083-H321 currently are used for vessel construction, “It could be argued there is a marine-grade standard, but it is not explicitly defined. That may need to happen.”

Attempts to resolve the issue out of court by negotiations are underway.

A team from Alcoa Inc., Alcan and Integris Metals is “currently gathering information and communicating directly with boat builders and the Coast Guard,” according to the companies.

A meeting at Nichols Bros. with the aluminum suppliers in late March was “very positive, very upbeat,” Nichols said. The Alcan-Reynolds-Integris project team also met with the Coast Guard in early April.

For the shipyards, attempting to recover the costs for the vessel repairs from the aluminum suppliers is one part of their problem. Another is scheduling vessel repairs with suitable aluminum into the sequence of other jobs underway in the yards.

“The shipyards will work through this with their customers,” said one industry source. Matt Nichols was also positive: “Those material problems are just something that will not happen again.”

By Professional Mariner Staff