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Corrosion of Alternate Marine Hull Valve Materials

Paper Number: 24
Author/s: W. C. Neil, N. Gage, C. Townsend
Organisation: Defence Science and Technology Group, Fishermans Bend 3207, VIC Australia

Abstract

The effects of long term seawater exposure on the corrosion performance of valve materials can be a significant factor in determining the suitability of a material for marine applications. Corrosion assessment by means of a long term exposure in real seawater environments is critical in determining the suitability of these materials.
This work reports on initial assessment of the corrosion of alternative hull valve material after environmental exposure in two Australian locations: Williamstown, Victoria and Innisfail, Queensland. The specimens have been exposed for 6, 12 and 36 months. Materials tested were 2205 stainless steel, Titanium (commercially pure grade 2, CP2), Inconel 625, and Nickle Aluminium Bronze (NAB) in the cast and wrought condition. Test specimens were mounted on PVC frames using nylon nuts and bolts. Corrosion assessment consisted of visual inspection, mass loss, cross sectional microscopy and testing for selective phase corrosion.
Visual inspection of the specimens indicate that the Ti, and Inconel 625 show no signs of corrosion for any length of exposure (either general or pitting) whereas the 2205 stainless steel suffered a small amount crevice corrosion. The NAB specimens show signs of general corrosion and pitting for all exposure periods.

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Corrosion potential study of the Western Australian 1911 Coronation medal

Paper Number: 28
Author/s: Walter R Bloom2 and Ian D MacLeod1
Organisation: 1 Western Australian Maritime Museum, Fremantle, Australia 2 School of Engineering and Information Technology, Murdoch University, Murdoch, Australia

Abstract

The analysis of coins and medallions should only involve methods that do not physically interfere with the actual objects. Much of the collecting and commercial value of numismatic items resides in the quality of their surfaces. Previous studies (MacLeod & Ritchie 1981) had determined that valuable information regarding the nature of the surfaces and underlying alloys of suspected forged coins can be obtained by monitoring the corrosion potential over periods of several days. Since there was uncertainty in numismatic circles regarding the true nature of the Western Australian 1911 Coronation medals, which are variously listed as having been struck in silver or silvered bronze, it was decided to monitor their corrosion potentials (Ecorr) to see if this approach could distinguish between the two materials. The density of the medallions could not be determined as they were intimately bound with silk ribbons and pin bars.

Eleven examples of the King George V medallions were examined and compared with a standard silver-copper alloy from a Western Australian Museum medal. Analysis of the kinetics of the Ecorr plots showed typical sigmoidal curves for silver plated objects. Solid alloys showed Ecorr plots which were linear with the square root of immersion time. The nature of the plated and solid surfaces was compared with results with those obtained using a hand-held (bench-mounted) X-Ray Fluorescence (Bruker Tracer III) instrument for elemental analysis. Data from automatic profilometer studies determined the thickness of the electroplated layers.

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Pitting Corrosion of 5005 Aluminium Alloys in The Temperate Seawater Immersion Environment

Paper Number: 57
Author/s: M. X. Liang1, R. E. Melchers1 & I. A. Chaves1
Organisation: Centre for Infrastructure Performance and Reliability1, The University of Newcastle, NSW2308, Australia

Pitting is the most commonly occurring corrosion form for aluminium alloys. In natural seawater environments, pitting progress can be complex and may be affected by factors that cannot be replicated by accelerated corrosion tests using a simulated seawater as the corrosion media in the laboratory. This paper reports pitting behaviour of 5005 series aluminium alloy sheets exposed to natural temperate seawater at Taylors Beach on east coast of Australia. The corrosion morphologies were observed by Scanning Electron Microscopy and the compositions of different parts of the metal as well as the corrosion products were analysed by Energy Dispersive Spectroscopy. Pitting was observed to initiate at the sites where intermetallic particles are present. Hemispherical pits form as a result of trenching at the periphery of Fe-containing intermetallic particles. After 6 months, characteristic ‘petal’-like morphology was repeatedly observed. Crystallographic pitting was observed on coupons exposed for 12 months and 24 months. These are the dominant pitting morphologies and this possibly indicates a change of mechanism for the pitting process.

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Predicting the Corrosion of Aircraft Using In-field Environmental Sensor Data

Paper Number: 83
Author/s: A Sudholz1, S Jacob2, J Talevski1, C Loader1
Organisation: Defence Science and Technology Group1, Melbourne, Australia, BAE Systems Australia2, Melbourne, Australia

Abstract

The Defence Science and Technology Group (DST) and BAE Systems Australia (BAE) are developing corrosion prediction models to assist maintainers of military aircraft. These models are embodied in an engineering tool known as a Corrosion Prognostic Health Management (CPHM) system. The aim of a CPHM system is to enable condition-based maintenance (CBM) where maintainers can perform targeted inspections, thereby limiting unnecessary and time-consuming maintenance. Key to building maintainer confidence in CPHM systems is the validation of modelling outputs with in-field environmental data.

The current programme has established a series of ground-based stations (GBS) to record local environmental data and monitor corrosion of typical aircraft aluminium alloys. Each GBS comprises environmental sensors and witness plates of a selection of typical aircraft aluminium alloys, and are installed at six sites around Australia representing a broad range of environmental conditions relevant to the Royal Australian Air Force. Corrosion modelling predictions using these environmental inputs can therefore be compared to the corrosion experienced by each aluminium alloy. Such in-field data will assist in validating the predictive capability of current corrosion models and building end-user confidence for use in CBM practices. This paper will detail results from the first 12 months of the GBS programme and discuss the application of in-field data to CPHM systems.

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Case studies from Shipbuilding in Adelaide

Paper Number: 38
Author/s: D. Fosdike, Y. Alba & I. Brundin
Organisation: ASC Shipbuilding1,2, Adelaide, Australia, & ASC Pty. Ltd.3

Abstract

Based in Osborne, South Australia ASC builds and maintains Australia’s frontline naval ships and submarines to world class performance and quality standards. The location of the ASC Shipyard on the Port River presents some challenging conditions for the prevention of corrosion due to the nature of the water.

One of the key areas of focus in shipbuilding and maintenance is the prevention of corrosion in internal seawater pipework. As systems are shut down or in the process of being set to work, they do not see the flow patterns that the pipework would normally see in service and this contributes to the corrosion. In addition to this, ASC, like many other shipyards, is located in an estuarine waterway where the water quality is significantly lower than the water in the open ocean where the ships normally operate.

During the course of the construction and maintenance of various vessels ASC has had to combat a number of different corrosion issues, these include selective phase corrosion in nickel aluminum bronze, welding corrosion in Monel alloys, stray current corrosion and dissimilar metal corrosion. ASC has successfully managed to combat these types of corrosion after their appearance and the incidence of corrosion related failures has significantly reduced under management strategies that have been put in place.

This paper will outline some case studies of corrosion in the shipbuilding industry and the solutions implemented.

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Syntactic Perlite-Aluminium Long-Term loss of Mechanical Properties Immersed in Ocean and Fresh Waters

Paper Number: 2
Author/s: I Chaves, T Fiedler
Organisation: Centre for Infrastructure Performance & Reliability1, The University of Newcastle, Australia, School of Engineering2, The University of Newcastle, Australia

Abstract

Perlite-Metal Syntactic Foam (P-MSF) is a novel lightweight material with good specific strength and excellent energy absorption capabilities. To analyse its suitability in marine applications, P-MSF has been immersed for 2 years in natural flowing seawater as well as freshwater. The change of mass and mechanical properties has been studied as a function of exposure time. Results indicate a slow degradation of mechanical properties that can be attributed to a change of the macroscopic deformation mechanism. Interestingly, no evidence of significant corrosion was observed. Instead, the change in mechanical properties is triggered by the sedimentation of oxides and sulphates within the expanded perlite particles. Implications towards the long-term viability of such P-MSF in marine applications are discussed.