Electrochemical noise analysis of polyurethane coated steel subjected to erosion-corrosion

This paper presents the degradation mechanisms of porous and non-porous PU coatings on steel subjected to slurry erosion–corrosion using a purpose-built apparatus. The samples were subjected to a slurry jet made of 3.5% wt. NaCl solution, containing 0–3% wt. sand particles (90° impact angle, jet velocity 4 m/s). Prior to testing the corrosion reactions present on the steel substrate were examined by Electrochemical Impedance Spectroscopy (EIS) and during the test by Electrochemical Noise Analysis (ENA) on the corrosion current. The non-porous coatings remained fully protective at least 10 months when exposed to a purely corrosive solution, and until total stripping by the sand particles when exposed to a corrosive slurry. In contrast, for the porous coatings, corrosion reactions were rapidly initiated on the substrate after solution transport, via defects in the coating, to the coating/metal interface. However, no synergism was detected between the erosion and the corrosion under these test conditions. Analysis of corrosion current fluctuations provided information on the coating degradation mechanisms. The mean and standard deviation were found to act as effective qualitative indicators of the extent of coating damage. The skewness, kurtosis and PSD slope indicated the initiation of the corrosion reactions on the substrate, i.e. the beginning of coating breakdown

Development of a knowledge-based system for materials management

In the past, many mistakes have been made in selecting the best materials for a given task. Thus, tools for humans to optimise the selection of materials will be valuable assets, particularly when the field of application is broad, the problem complex, the operating envelope variable, or the environment is aggressive. In this paper, a methodology for construction of a generic computer materials selector is described. A knowledge structure is presented in which materials selection and failure analysis are at opposite ends of a spectrum of materials performance. An example of the selection of a coating for marine use is given. Besides being of great value to designers, the tool is of considerable potential use for general materials information systems and computer-based learning module

The performance of marine coatings and pipe materials under fluid-borne sand erosion

A program of tests is described in which pipe materials and steel substrates with various coatings were subjected to fluid-borne sand particle erosion conditions. Sand-water slurry jets were used at velocities between 2–30 m/s and at a jet impingement angle of 90° to create a range of erosive conditions to evaluate the performance of the pipe materials carbon steel AISI 1020, stainless steel AISI 316. Cupro-Nickel 90/10, medium density polyethylene and glass reinforced plastic test coupons. Further tests at an impingement angle of 30° and at 10 and 20 m/s velocity compared the performance of the carbon and stainless steels with various polymeric, metallic and ceramic coatings. Flexible polyurethane seems to have promise for future use in fluid-borne sand particle erosion environments. The erosion mechanisms of flexible polyurethane have been identified as micro-cutting at low angle impingement and fatigue/crack propagation at normal impact