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Saltwater Corrosion Causes Buckets of Rust

The most devastating corrosion and metal wastage on the U.S. Coast Guard’s high tempo, high maintenance (HTHM) cutter fleet was typically found in interior spaces—compartments with topside hatches that permitted the ingress of sea spray during routine operations, as well as inaccessible locations under decking or behind bulkheads full of dead spaces.

Several years ago, around the same time that Lt. Thomas Lowry, HTHM maintenance coordinator, waged his war on corrosion of the HTHM Island-class cutter fleet, an encounter with exfoliation corrosion on top of a fuel oil tank prompted the Coast Guard to launch an aggressive battle to stop corrosion.

During a scheduled dry-dock for maintenance inspection, a layer of exfoliating corrosion around two inches thick in some areas was found over a 40-square-foot area of the starboard fuel oil tank located beneath the galley’s floating deck. Using a shovel, maintenance personnel removed 70 pounds of rust in about 30 minutes. An estimated 35 percent of the original hull plating on the tank top was removed, equivalent to about 200 pounds of metal at original construction, Lowry said.

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U.S. Coast Guard Wages War on Corrosion

Coating Application and Inspection Training Helps Reduce Hull Failures and Keeps High Tempo, High Maintenance Fleet Fully Deployed

Along the southeastern coast of the United States, the U.S. Coast Guard has declared war on an enemy that is particularly treacherous in this region. The Coast Guard has emerged as the victor after carrying out a new strategy for coating application and inspection training to combat corrosion on a fleet of high tempo, high maintenance (HTHM) cutters.

The U.S. Coast Guard’s 110-foot HTHM cutter Kodiak Island is nearing one year out of dry-dock without any lost days or mission degradation due to corrosion-related events.
The U.S. Coast Guard’s 110-foot HTHM cutter Kodiak Island is nearing one year out of dry-dock without any lost days or mission degradation due to corrosion-related events. Photo by Thomas Lowry, U.S. Coast Guard.

The Coast Guard defends this country’s maritime borders and helps sustain the Maritime Transportation System, the marine portion of the national transportation system. It also responds to disasters involving the nation’s waterways and saves those in peril. To carry out this charge, its assets must be service and mission ready.

The HTHM program is designed to fill a gap caused by the loss of some Coast Guard cutters and the reassignment of others to military missions overseas. The eight 110-foot Island-class (WPB) cutters in the HTHM fleet, assigned to the Coast Guard’s District Seven (comprising South Carolina, Georgia, Florida, and Puerto Rico), are equipped with advanced electronics and navigation equipment; attain a top speed of 30-plus knots; and perform search and rescue, maritime fisheries law enforcement, drug interdictions, alien migrant interdiction operations, and national security activities.

Corrosion was found in interior spaces of Kodiak Island, such as the engine room.
Corrosion was found in interior spaces of Kodiak Island, such as the engine room. Photo by Thomas Lowry, U.S. Coast Guard.

Unlike traditional Coast Guard cutters, HTHM patrol boats are operated at twice their operational tempo design, with a 21-day period underway that is interrupted by brief stops for fuel and provisions, and an intensive, seven-day maintenance and repair period that is the maritime equivalent of a pit stop for a race car, said Coast Guard Lt. Thomas Lowry, HTHM maintenance coordinator. In addition to its seven-day maintenance, each cutter is scheduled for dry-dock every 24 months for more extensive maintenance.

These HTHM cutters, commissioned in the late 1980s to early 1990s, are exposed to a continuous sea spray environment. Sea spray forms a salt crust layer on the topside surfaces and within compartments sections ventilated from the outside. Saltwater also enters compartments, gets trapped in inaccessible areas, and forms standing water. Insulated areas wetted by saltwater wick the saltwater up into the insulation layer and form a salt crust in the insulation media.

The High Cost of Corrosion

About three years ago, corrosion had become problematic on the HTHM cutters and was the leading cause of lost days and mission degradation—more than mechanical and electrical faults combined, Lowry stated. Not only was corrosion the leading ship repair expense—accounting for more than 50 percent of a ship’s repair budget and typically consuming 60 to 70 percent of resources during dry-dock—but the unavailability of an asset to do its job because of emergency maintenance created a loss of readiness and a gap in overall mission coverage, he explained.

While topside corrosion was easily accessible for repairs and resulted in little structural damage, the most devastating corrosion and substantial metal wastage was found in interior spaces. The hardest hit were compartments with topside hatches that permitted sea spray to enter during routine operations, and inaccessible locations under decking or behind false bulkheads, for example. The main machinery areas, such as the engine room, aft steering, and auxiliary room, experienced significant corrosion fueled by leaks and fluid losses during maintenance activities.

Corrosion under insulation, caused by wicking, was found near a flat panel, corrugated bulkhead interface.
Corrosion under insulation, caused by wicking, was found near a flat panel, corrugated bulkhead interface. Photo by Thomas Lowry, U.S. Coast Guard.

During an emergency dry-docking of one cutter in 2009 to repair a hull breach and flooding in the engine room, Lowry spotted an alarming trend. Almost a year earlier, he had started collecting structural failure data for the four HTHM patrol boats assigned to the Coast Guard Sector Key West, Florida. When he analyzed the data, he found that the total number of hull and structural failures was increasing over time, and had reached the point where one hull failed per week.

“It was at that moment that the insidiousness of corrosion was clear, and I saw the need for action,” Lowry said. The approach to coatings maintenance up to that point had been aesthetically oriented rather than focused on coating performance and substrate protection, he said. While doing research to find a solution, he happened upon the root of the problem. “It wasn’t a lack of high-performance super-coatings aboard our cutters that was the problem, it was a training issue,” he said.

Lowry discovered that 70 percent of coating failures in the industry are due to inadequate surface preparation, and this inadequacy applied to the HTHM fleet. Using funds provided by the DoD Corrosion Policy and Oversight Office, Lowry and 75 active-duty maintenance personnel received training and certification through the NACE Coating Inspector (CIP) Level 1 program. Thirteen out of this group advanced to the CIP Level 2—Marine Certification. In addition to certifying personnel, preservation work items and standards that govern ship repair contracts were updated to mirror industry preservation standards and also target factors that contributed to the corrosion on the cutters.

The corrosion on this interior bulkhead was caused by sea spray entering through a topside vent.
The corrosion on this interior bulkhead was caused by sea spray entering through a topside vent. Photo by Thomas Lowry, U.S. Coast Guard.

Before attending the training, Lowry said, the maintenance team had been burnishing surfaces with wire wheels, painting over surfaces containing soluble chlorides that were more than 10 times the allowable limit, using unauthorized solvents, and engaging in “field chemistry” of liquid coatings. Inspection tools had not been available in the HTHM maintenance inventories, nor had they been part of the normal preparation, priming, and painting efforts.

During the ship repairs that followed the training and new adherence to standards, Lowry mentored the maintenance work force in properly evaluating contractor performance and understanding and enforcing coating standards. Among the host of improvements in maintenance and inspection, personnel are now given the tools needed to apply coatings to meet the standards; coating systems are properly inspected during application and repair; standards for ship repair contractors are fully enforced; and substrate preparation is done according to the standards.

Additionally, the HTHM long-range maintenance plan was expanded to include side scan ultrasonic thickness measurements of the hull plating, and thorough compartment inspections that will be repeated every six years. “We turn the ship inside-out like a sock,” Lowry explained, adding that since it is much less expensive to paint rather than replace steel, compartment inspections are very aggressive and comprehensive.

Lowry stressed that the philosophy now is to get intrusive, get in the tight spaces, and find and eliminate the rust. “If something is close to failure, then it is driven to failure so it can be repaired while in dry-dock,” he said.

The increased level of knowledge and understanding of the industry standards for surface preparation, as well as the improvement in coating systems application and inspection techniques has helped the Key West HTHM fleet to move away from a failure rate of one hull per week and operate more than one year—and still counting—without a corrosion-related hull or structure failure, lost cutter day, or mission degradation event.

Overall, the HTHM fleet is at a steady state and fully deployed. The cutters are no longer undergoing emergency dry-docking for corrosion, or being taken out of service to weld temporary corrosion-related repairs, Lowry said. The ships are launched on time and recovered on time. The routine "chasing rust" during normal seven-day maintenance periods has been replaced with routine washing and repair of any scratch or scrape in the coatings, which is effectively a maintenance-free posture, he added.

A “before” (left) and “after” (right) view shows the battery cableways and wiring in an engine room after the preservation coating was applied using updated standards and trained personnel. A “before” (left) and “after” (right) view shows the battery cableways and wiring in an engine room after the preservation coating was applied using updated standards and trained personnel.
A “before” (left) and “after” (right) view shows the battery cableways and wiring in an engine room after the preservation coating was applied using updated standards and trained personnel. Photo by Thomas Lowry, U.S. Coast Guard.

Now the Coast Guard highly recommends that port engineers who administer and oversee ship repair contracts be certified as professional coating inspectors. In addition, coating inspector training has been added as a training module to the course that is recommended for all Coast Guard personnel who transfer to a port engineer position.

Based on the success of the HTHM corrosion prevention program, the Coast Guard is working to implement an organization-wide policy that requires a coating inspector to be certified by an accredited institution. It also mandates a comprehensive coating inspector training course for port engineers in order to broaden the education base of its front line naval engineers.

“The HTHM program is the epicenter of the war on corrosion, and this paradigm shift is spreading across the U.S. Coast Guard, but we are not at a fully deployed status across all platforms,” Lowry concluded. “We are making huge progress toward getting the Coast Guard up to the same steady state as the HTHM fleet, but it will take time to train the rest of our personnel, get the tooling fully deployed, and for the new personnel to become proficient.”

Editor’s Note: A version of this article originally appeared in the October 2011 issue of Materials Performance magazine.

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