Sea Technology

MAR 2018

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Page 16 of 45 March 2018 | ST 15 I t is well known that exposure to the changing elements in the marine environment causes many ongoing cor- rosion-related issues to ships and various metallic struc- tures, such as barges, drilling rigs, ballast tanks, bridges, supporting vessels and even concrete structures with rebar reinforcement. Concrete may experience erosion, exposing the supporting rebar structure and causing cor- rosion and rust staining as iron oxide leaches from the affected steel. The splash zone, which generally references areas that are continuously exposed to both water and air in a wet/dry environment, promotes the extreme conditions that initiate the corrosion phenomena. In many cases, crevice corrosion is the general cause for the unsightly rust staining of various surfaces, which can eventually lead to pitting, the failure of the protective coating and the more extreme stages of corrosion. As corrosion pro- gresses, wall loss and possibly hydrogen embrittlement may affect the integrity of these structures, causing great- er, more expensive repairs or even replacement. General rust staining is caused by fluid passing over the rusted or corroded areas where leeching occurs and transporting the iron oxide in liquid form, causing in many cases un- sightly and unwanted staining. Navy, Coast Guard and Merchant Marine vessels are particularly susceptible to this corrosive environment. Historically, the general solutions are limited and include either: painting over the issue to hide the unsightly stain- ing of the specific area, or the refurbishment of the prob- lem area, which includes removal of the existing coating, preparation, material selection and then recoating. A total refurbishment of the stained area is in most cases very expensive and often time consuming. Paint- ing over the rust staining is unnecessary and often caus- es additional problems such as increased weight due to the added coating, thereby increasing flammability con- cerns. Concealing the problematic area is often false econ- omy as the integrity of the actual stained coating is in- tact. Simply covering the is- sue utilizes many man-hours and expensive material costs that hide rather than solve the problem. These combined is- sues have plagued the integ- rity of various structures and surfaces for centuries. Specifically, Navy and Coast Guard vessels that en- counter longer patrolling times in the open seas and oceans and aging steel structures require constant maintenance utilizing human resources Removal of Rust Staining Caused by Crevice Corrosion Enviroklean Reduces Manpower, Materials Cost for Maintenance By Graham George • Sheldon Landsberger (Top right) Scale embedded on steel flange with its before and after weight related to rust treatment. (Photo Credit: Nuclear Engineering Training Laboratory, University of Tex- as) (At right) USS Zumwalt during cleaning. Note the left side of the ship after cleaning with EPDI's Enviroklean.

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