Edward J. Lemieux

An Evaluation of Carbon Steel Corrosion under Stagnant Seawater Conditions

Corrosion of 1020 carbon steel coupons in natural seawater over a 1-year period was more aggressive under strictly anaerobic stagnant conditions than under aerobic stagnant conditions as measured by weight loss and instantaneous corrosion rate (polarization resistance). Under oxygenated conditions, a two-tiered oxide layer of lepidocrocite/goethite formed. The inner layer was extremely tenacious and resistant to acid cleaning. Under anaerobic conditions, the corrosion product was initially a non-tenacious sulphur-rich corrosion product, mackinawite, with enmeshed bacteria. As more sulphide was produced the mackinawite was transformed to pyrrhotite. In both aerobic and anaerobic exposures, corrosion was more aggressive on horizontally oriented coupons compared to vertically oriented samples.

Carburization-induced passivity of 316 L austenitic stainless steel

A low-temperature (450-500°C) gas-phase process for introducing substantial amounts of carbon, without carbide formation, into 316L austenitic stainless steel has been developed. This process, termed low-temperature colossal supersaturation (LTCSS), provides surface carbon concentration as high as 14 atom % and dramatically improves the localized corrosion resistance of 316L austenitic stainless steel in ambient temperature seawater. In particular, the LTCSS-treated steel increases the seawater breakdown potential by more than 600 mV. This result is remarkable, as traditional carburization methods have historically decreased the corrosion resistance of stainless steels.

Evaluation of Deoxygenation as a Corrosion Control Measure for Ballast Tanks

Abstract Field experiments designed to evaluate deoxygenation of natural seawater as a corrosion control measure for unprotected carbon steel seawater ballast tanks demonstrated decreased corrosion in hypoxic (<0.2 ppm O2) seawater using linear polarization measurements. They also demonstrated the difficulty of maintaining hypoxic seawater. Using a gas mixture it was possible to displace dissolved oxygen. However, aerobic respiration and corrosion reactions consumed oxygen and produced totally anaerobic conditions within the first days of hypoxia. When gaskets and seals failed, oxygen was inadvertently introduced. The impact of oxygen ingress on corrosion depends on the amount of oxygen in the system at the time oxygen is introduced. Carbon steel exposed to cycles of hypoxic seawater and oxygenated atmosphere had higher corrosion rates than coupons exposed to cycles of either consistently aerobic or deoxygenated conditions.

Galvanic Anode Current and Structure Current Demand Determination Methods for Offshore Structures

Abstract The maintenance current density associated with cathodic protection (CP), imaint, which is the current density demand of a structure to affect a given level of cathodic polarization at a p...

Fusion of color, grayscale, and edge-detection algorithms for the accurate assessment of corrosion in shipboard tank and void imagery

Over the last several years, the Naval Research Laboratory has developed video based systems for inspecting tanks (ballast, potable water, fuel, etc.) and other voids on ships. Using these systems, approximately 15 to 30 images of the coated surfaces of the tank or void being inspected are collected. A corrosion detection algorithm analyzes the collected imagery. The corrosion detection algorithm output is the percent coatings damage in the tank being inspected. The corrosion detection algorithm uses four independent algorithms that each separately assesses the coatings damage in each analyzed image. The independent algorithm results from each image are fused with other available information to develop a single coatings damage value for each of the analyzed images. The damage values for all of the images analyzed are next aggregated in order to develop a single coatings damage value for the complete tank or void being inspected. The results from this Corrosion Detection Algorithm have been extensively compared to the results of human performed inspections over the last two years.

Retrofit Cathodic Protection Design for Depolarized and Partially Depolarized Structure

Abstract Experiments were performed whereby steel specimens in natural seawater were successively cathodically polarized, depolarized or partially depolarized, and then repolarized to simulate the life cycle and retrofit of a galvanic cathodic protection (CP) system on space-frame-type offshore structures. Emphasis was placed upon the current density required for repolarization because of the importance of this parameter in the design of CP retrofit systems. Relationships were established between the steady-state current density during the initial and partial depolarization periods and the current density demand for repolarization.

Evaluating the Structural Performance of Ship’s Rudder Coatings

Computational simulations are used in many disciplines to determine levels of stress and deformation in a structure for comparison with material allowable limits. In this work, use is made of a detailed 3D model of a typical ship’s rudder to evaluate the stress and deformation characteristics of the rudder structural components including the corrosion control coating applied to the rudder surface. Three commercially available coating materials were evaluated. These coating selections represent a range of material characteristics from high ductility polymer to glassy. Design condition hydrostatic loads were used in all evaluations. Stress and deformation patterns within the rudder structure are discussed. Differences between the structural performance of the coatings are highlighted.

6 – 70/30 copper–nickel seawater piping systems – use of descaling agents and their effects on corrosion properties

Publisher Summary This chapter focuses on the 70/30 copper–nickel seawater piping systems and highlights the use of descaling agents and their effects on corrosion properties. Use of copper–nickel alloys in seawater-cooled heat exchangers is common due to the inherent properties of these alloys—namely, a relatively low corrosion rate, antifouling properties, and erosion–corrosion resistance relative to other alloys. The main causes of failure of copper–nickel alloy components in seawater are usually attributed to either erosion–corrosion at extreme velocities or the pitting phenomena. It is well established that these failures are generally due to detrimental seawater conditions, such as the presence of sulphides or poor designs resulting in extreme flow velocities. Periodic cleaning is necessary on seawater cooling systems due to the gradual formation of scaling and macro-fouling during operation. Several chemicals and procedures can be used to remove these deposits and growths, the most common products being hydrochloric, citric or sulfamic acids. Hydrolancing and mechanical cleaning are in use by the fleet, but these have major drawbacks in terms of costs and labor hours. In addition, most of these methods raise some safety and environmental issues. Three commercial descaling solvents, two hydrochloric acid-based and one phosphoric acid-based, have been identified that claim to be safe, environmentally friendly, and inexpensive and exhibit no detrimental effects on the materials.

Effect of algorithm fusion and aggregation methodologies on the performance of a corrosion detection algorithm

Over the last several years, the Naval Research Laboratory has been developing corrosion detection algorithms for assessing coatings conditions in tank and voids on US Navy Ships. The corrosion detection algorithm is based on four independent algorithms; two edge detection algorithms, a color algorithm and a grayscale algorithm. Of these four algorithms, the color algorithm is the key algorithm and to some extent drives overall algorithm performance. The four independent algorithm results are fused with other features to first generate an image level assessment of coatings damage. The image level results are next aggregated across a tank or void image set to generate a single coatings damage value for the tank or void being inspected. The color algorithm, algorithm fusion methodology and aggregation algorithm components are key to the overall performance of the corrosion detection algorithm. This paper will describe modifications that have been made in these three algorithm components to increase the corrosion detection algorithm’s overall operating range, to improve the algorithm’s ability to assess low coatings damage and to improve the accuracy of coatings damage classification at both the individual image as well as at the whole tank level.

Multiple algorithm fusion in a corrosion detection algorithm used with shipboard tank and void inspection systems

Over the last several years, the Naval Research Laboratory has developed video based systems for inspecting tanks (ballast, potable water, fuel, etc.) and other voids on ships. Over this past year, we have extensively utilized the Insertable Stalk Inspection System (ISIS) to perform inspections of shipboard tanks and voids. This system collects between 15 and 30 images of the tank or void being inspected as well as a video archive of the complete inspection process. A corrosion detection algorithm analyzes the collected imagery. The corrosion detection algorithm output is the percent coatings damage in the tank being inspected. The corrosion detection algorithm consists of four independent algorithms that each separately assesses the coatings damage in each of the images that are analyzed. The algorithm results are fused to attain a single coatings damage value for each of the analyzed images. The damage values for each of the images are next aggregated in order to develop a single coatings damage value for the tank being inspected. This paper concentrates on the methods used to fuse the results from the four independent algorithms that assess corrosion damage at the individual image level as well as the methods used to aggregate the results from multiple images to attain a single coatings damage level. Results from both calibration tests and double blind testing are provided in the paper to demonstrate the advantages of the video inspection systems and the corrosion detection algorithm.