Thesis (Ph. D.)--Washington University, 1920. / Vita. Slightly abridged from Iron and Steel Institute, Carnegie scholarship memoirs, vol. VII (1916) p. 232-298.

A range of HSLA steels reflecting the two major processing routes, quench and tempering and controlled rolling, have been tested in fatigue to assess their potential wider application in the offshore Industry. The six steels chosen have a wide range of yield strenghts (470 to 690Nmm-2), fracture toughness (31 to 260J at -40°C) and carbon equivalent values (0.19 to 0.33). Fatigue testing has in general been carried out at low frequency (0.5Hz) and high load ratio (0.6) however some tests have been conducted at very low frequency (0.1Hz) and low load ratio (0.1). An in-air study was first used to assess the fatigue performance of all six parent plates. Five steels were welded by the Submerged Arc Welding process at high heat input (1.5kJmm -1) to evaluate the Heat Affected Zone (HAZ) fatigue performance. A new test was devised to grow a fatigue crack through a single pass, bead on plate-, HAZ whilst maintaining a constant stress intensity range. The surface crack length was continuously monitored and recorded to an accuracy of 0.01mm. A corrosion fatigue study evaluated the performance of one controlled rolled and one quenched and tempered steel at three levels of impressed current cathodic protection. Extensive metallographic examination was made to study the influence of microstructural features and types on fatigue crack propagation. Techniques used include optical microscopy, scanning electron microscopy, fatigue crack and surface replication and crack profile digitising. These techniques give an assessment of crack path deviation and branching, the influence of precipitates and inclusions, and an indication of the mode of fatigue crack propagation. The wide range of microalloyed HSLA steels tested have shown a significant improvement in fatigue crack propagation resistance over structural steels conforming to BS 4360 grade 50D. Typically an improvement by a factor of two has been observed. Whilst the observed increase in fatigue life was slightly reduced by high heat input welding the slope of the Paris curves remained unaffected thus indicating a similar stress intensity range sensitivity in the HAZ to that shown by the parent plate. The newly developed crack monitoring system coupled to a computer controlled fatigue testing machine has shown a wide variation in fatigue crack propagation rates through a heat affected zone microstructural gradient. Growth rates have increased by a factor of ten in localised coarse grained microstructural regions compared to the adjacent weld metal and outer heat affected zone. The corrosion fatigue study has also indicated that in general HSLA steels retain their superiour fatigue resistance compared to structural steels and in particular respond more favourably to cathodic protection. Both in-air and corrosion fatigue studies have indicated that the controlled rolled steel microstructures developed mainly for line pipe application has the greatest potential for increased use offshore.

Investigations were carried out to assess the role of primer, pretreatments and coating microstructure in preventing cutedge corrosion of chrome free organically coated steels. Zinc runoff was monitored from a range of organically coated steels with a large cutedge length exposed over 18 months at Swansea University roof top site. The zinc in the runoff leaches from the zinc-aluminium alloy coating of the substrate. The paint systems' corrosion performance was assessed by monitoring the levels of zinc in the runoff. Consequently the levels of zinc reflected the effectiveness of the applied paint system against corrosion. Runoff was high in initial months with zinc levels reducing with time due to the build up of corrosion products that hindered the progress of corrosion. An accelerated laboratory test using a distilled water electrolyte was developed that predict long-term external weathering runoff from panels of a range of organically coated steels. The corrosion mechanisms of a variety of organically coated Galvalloy steel have been examined using the scanning vibrating electrode technique (SVET) in 0.1%NaCI. The corrosion behaviour of a coating is related to the zinc-aluminium alloy coating structure and combination of pretreatment and primer. The SVET has been used to assess total zinc loss and the corrosion rate for a comparative measure of organically coating system performance. A correlation has been developed from SVET 24hour experiment data to accelerated weathering data and external weather data that can aid more accurately predicting the in service life of the product. Also considered were the effects of electrolyte conductivity on the morphology of corrosion on pure zinc. A mathematical model has been developed to predict corrosion pit population. Altered microstructure of solidifying zinc aluminium alloy melt via ultrasonication was investigated. Ultrasound irradiation significantly altered the final microstructure. The influence of morphed microstructure upon the corrosion behaviour was explored using the SVET in 0.1%NaCI. The ultrasound manipulated microstructure had generally a positive effect on the corrosion behaviour.

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

A thesis submitted to the Faculty of Engineering and Built Environment, University of the Witwatersrand, in fulfilment of the requirements for the degree Doctor of Philosophy (Materials and Metallurgy) Johannesburg, February 2019 / The first corrosion map of South Africa (SA) was published in 1991. Since then only minor variations have been made to this map. However, due to the lack of differentiation of inland locations, overstatement of the corrosivity of environments, changes in international standards regarding the measurement of corrosive atmospheres, increased industrialisation of SA’s large metropolitan areas, global climate change effects and improved mapping techniques, this chart has become outdated. The present study focused on the development of a new corrosion map for SA, with the emphasis placed on the provision of more detail concerning the atmospheric corrosivity of the Greater Johannesburg Metropolitan Area (GJMA) – SA’s economic heartland. In the study, historical published and unpublished corrosion data for South Africa were assimilated and analysed. The atmospheric corrosivity of the GJMA was also measured using ASTM G116 wire-on-bolt and ISO 9226:1992 open aluminium, zinc and copper wire helix devices, including ISO 9226:2012 flat mild steel and hot-dip galvanised steel coupons. Coated mild steel specimens were also exposed to determine the corrosive effects of the GJMA’s atmosphere on organic materials. The morphologies and chemical compositions of the mild steel corrosion products, using SEM-EDS, FTIR and Raman spectroscopy, as well as pH and water-soluble salt measurement techniques were furthermore investigated, along with correlations between the measured corrosion data, and general meteorological and pollution parameters for the GJMA area. The study showed that the corrosivity of SA’s coastal environments decreases rapidly within the first 150 m from the ocean and that for most inland locations, very low (C1) to potentially high (C4) corrosive conditions may be expected, as per the ISO 9223 rating scheme. High correlations were also found between the first-year corrosion rates of mild steel, hot-dip galvanised steel, zinc, aluminium and copper. Moreover, it was confirmed that the corrosivity of the GJMA is influenced by precipitation, humidity, PM10 and PM2.5 particulate matter, as well as SO2, NO2, NO, CO and O3 levels in the atmosphere, including wind direction and daily temperatures (maximum and minimum). Other factors found to affect the corrosivity of the GJMA’s atmosphere are: elevations above sea and ground level; the presence of vegetation and large water bodies; topography; shielding and shading effects; the occurrence of an El Niño or La Nina event; and acid rain. Moreover, it was established that the GJMA is most corrosive during spring and summer and that at least 90% of the area can be rated Upper-C2 (low to medium) corrosive. The results furthermore revealed high correlations between the ISO 9223 (1992 and 2012) corrosion monitoring devices and that wire-on-bolt (CLIMAT) units are better indicators of the impact of atmospheric pollutants on the 12- month corrosion rate of hot-dip galvanised steel than uncoated steel. A strong linear correlation was also found regarding the average corrosion rate of mild steel with every 20 mg/m2 rise in the concentration of water-soluble salts in the corrosion product. The East Rand of the GJMA rated most corrosive, with corrosion trouble spots identified at Aeroport, Bonaero Park, Brakpan, Chloorkop, Dalpark, Dunnottar, and Nigel. The Kagiso-Randfontein area was the only other area, outside the East Rand, that rated more corrosive. Extrapolations of the long-term corrosion rates of mild steel and hot-dip galvanised steel in the GJMA were additionally made based on logarithmic regressions of the 6-, 12-, 18- and 24-month corrosion data. Finally, geoprocessed (metal specific) corrosion maps were developed for the GJMA, subsequently incorporated into several corrosion maps for SA (also metal specific), to provide better clarity regarding SA’s inland areas. Keywords: Corrosion, atmosphere, South Africa, Greater Johannesburg, inland Metropolitan, wire-on-bolt, CLIMAT, ISO 9223, mapping, pollution, mild steel, hot-dip galvanised steel, aluminium, zinc, copper, coatings / E.K. 2020

Call number: LD2668 .T4 1965 K21 / Master of Science

Analysis of corrosion in marine and acid environments is a complicated task, involving the interaction of thermodynamic, kinetic and geometrical factors. Two mathematical models which predict corrosion behaviour have been implemented for personal computers. The first program uses an assumption of unidirectional current flow to simplify the prediction of potential distributions for systems of essentially cylindrical geometry containing natural seawater-based electrolytes of differing strength. Using experimentally determined electrochemical and flow rig data, experimental and theoretical results were compared. The correlation between the two was shown to be poor, and this is attributed to the unrepresentative nature of the electrochemical data input to the model. The second model involves the synthesis of polarization curves. Several algorithms to model passivating behaviour have been studied, and one was selected and incorporated into the calculation routine. A number of kinetic and thermodynamic parameters are used in algorithms describing such behaviour, along with activation, concentration and solution polarization effects, for a number of redox reactions, which are then combined to produce an overall potential-log current density curve. Experimentally determined data for pure iron and different stainless steels in marine and acid environments of differing dissolved oxygen content and temperature were obtained. Theoretical models were constructed for each system, and compared to experimental data. Excellent correlation between experimental and theoretical data was obtained for potential ranges in excess of 2 V. Trends in parameter values were discussed, and compared to published data. The transition between stable and unstable passivity of stainless steels was shown to be dependent on the oxygen reduction diffusion limited current density and the iron dissolution reaction free corrosion current density, which in turn was linked to the dissolved oxygen content and temperature of the electrolyte. A new model for the behaviour of stainless steels in the transpassive region was proposed.

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

D. Tech. Chemical, Metallurgical and Materials Engineering / Corrosion is the chemical or electrochemical interaction between a material, especially metals, and their environment resulting in mild to severe deterioration of the material and its properties. The economic impact and problems resulting from corrosion has drawn strong attention from scientists and engineers worldwide. Stainless steel is the most important engineering metal worldwide, and industrially stainless steel is used extensively due to its resistance to corrosion e.g. in acid pickling, industrial acid cleaning, acid descaling, oil well acidizing and the petroleum industry. The corrosion resistance of stainless steels is due to the formation of a protective film which covers the steel surface instantaneously when exposed to mild operational conditions in the presence of oxygen; however, the oxide is most often porous and insufficient to protect the steel from further oxidation and corrosion attack in harsh environments. It is hypothesized that: In-depth understanding of the electrochemical behaviour of ferrous alloys in interaction with selected organic compounds in acidic environments will enhance inhibitor application for corrosion control; Failure and poor performance of most inhibitor admixtures can be eliminated with comprehensive knowledge of electrochemical interaction at the metal-inhibitor interface, passive film formation, duration and breakdown, adsorption characteristics, bond formation and molecular structure effect; Optimization of the current electroanalytical method will enhance effective pitting corrosion detection, analysis and control with the use of organic inhibiting compounds. The primary aim of this research is to develop the science required for the effective assessment, development and confident use of organic compounds (heterocyclic compound, organosulphur compound, simple alcohol, aromatic amine compound, aromatic amine derivative and aminoalcohol) and tested alloys (austenitic stainless steel type 304 and mild steel) for applications in astringent environments through conventional and optimized corrosion monitoring techniques.