Optimum Conditions for Blast Cleaning of Steel Plate

Abstract

Technological investigations are further described in which practical blast cleaning of steel plate was simulated in the laboratory.

Removal of rust is fastest when blasting is perpendicular to the surface. The smaller grain size of abrasive leads to higher rates of cleaning. Work-hardening of the surface depends on grain size and extends much deeper than can be deduced from microscope observation of cross-section.

A discussion of the concept ‘properly cleaned surface’ leads to the conclusion that 100% clean is a fallacy and that for the moment the use of a magnifying glass is the only practical method of inspection.

From a few exploratory tests on the cleaning of welds the conclusion is justified that blasting perpendicular to the weld surface leads to the highest cleaning rates. Small grain sizes are to be preferred.

The velocity of abrasive grains in flight was determined by high-speed photograph. Values found were somewhat higher than the ones reported for centrifugal machines. Influence of air pressure and specific gravity of the abrasive could be demonstrated.     

Effects of alkaline cleaners and cleaning methods on phosphate coating weight and surface morphology

Abstract

The effects of some alkaline cleaners and cleaning methods on the phosphate coating weight have been assessed. The morphologies of the phosphate coatings were investigated through scanning electron microscopy (SEM). Single alkaline cleaners are not advantageous to formation of fine phosphate coatings. Additives, such as sodium ethylene diamine tetraacetate, sodium glycerophosphate, sodium tripolyphosphate and trisodium phosphate, in compound alkaline cleaners, can mitigate alkali corrosion of metal, resulting in the surface roughness of metal being decreased. The coating weight of phosphate coating formed on the sample cleaned by compound alkaline cleaners is lighter than by the use of single alkaline cleaners. Compared with the immersion cleaning method, spray cleaning contributes to the formation of the tiny phosphate crystal grains.     

The Use of Stainless Steel and Nickel Alloys To Combat Corrosion In the Brewing,Dairy, Wine and Food Industries

Abstract

Corrosion problems are described as they affect contamination and general hygiene in the brewing, dairy, wine, confectionery and sugar industries, where stainless steel, because of its bacteriological sterility and ease of cleaning, has become the dominant constructional material.

The most suitable grades of stainless steel for specific conditions, preferred surface finishes and methods of cleaning to avoid corrosion are presented.

Some examples are given of pitting corrosion of process equipment in the wine industry. Also exemplified is the action successfully taken to overcome problems of stress-corrosion cracking of stainless steel in the confectionery and sugar industries by upgrading to a nickel alloy.     

Erosive abrasive wear behaviour of stainless steel surface produced by plasma transferred arc hardfacing

Abstract

Erosive abrasive wear is caused by high speed impact of particles entrained in a fluid system on the surfaces of components such as boilers and furnaces. Erosive abrasive wear in boilers results from the impact of hard particles such as ash or clinker entrained in flue gases and can lead to serious damage. The life of boiler and furnace components encountering erosive abrasive wear in service, which are most commonly fabricated from carbon steels, can be improved by hardfacing with a wear resistant material. The effects of wear parameters such as particle size, flux and velocity on the erosive abrasive wear behaviour of a stainless steel surface produced by the plasma transferred arc hardfacing have been investigated using an experimental design approach. The wear resistance of the stainless steel surface was found to be twice that of the carbon steel substrate.     

Tensile test analysis of corroded cleaned aged steel specimens

ABSTRACT

The objective of this work is to analyse the influence of corrosion cleaning employing sandblasting, sand-paper cleaning, high-pressure-fresh-water-cleaning and corrosion cleaning by hammering on the mechanical properties of aged steel specimens. Tensile tests of cleaned corroded specimens are carried out. The specimens were cut from steel box girders, corroded in open sea water. The material properties of five groups of corroded specimens are experimentally estimated including the modulus of elasticity, yield stress, tensile strength and total uniform elongation. The trend of mechanical properties is analysed as a function of the degree of degradation and cleaning procedure, identifying that the cleaning treatment of the corroded surface significantly influences the mechanical properties and stress–strain relationships. A multi-criteria decision technique is employed to identify the most suitable cleaning technique accounting for the efficiency of the cleaning process and reducing the scatter in the mechanical properties of the cleaned corroded specimens.     

The performance of silicate inhibited cleaning agents in contact with aluminium

Abstract

The present paper is concerned essentially with the inhibiting action of sodium silicate, and particularly sodium metasilicate, on the corrosion and staining of aluminium surfaces· in inorganic alkaline cleaning systems.

In view of the complexity of both the chemical composition of commercial cleaning compounds and the behaviour of the compounds when in contact with aluminium, a simple laboratory test has been used. Aluminium sheet is immersed in cleaner concentrations of O·1 %, 0·25% and 1% for ½h at 70° to simulate relatively mild cleaning conditions and for 4 h at 100° to simulate severe soaking conditions. Action by the cleaner is assessed by loss of weight and changes in appearance.     

Control of weld composition when arc welding high strength aluminium alloys using multiple filler wires

Abstract

An experimental method of controlling weld composition when welding Al2024 has been explored. Utilising the tandem process and a cold wire feed unit, two and three commercially available filler wires were mixed in a single weld pool to control composition. Thermodynamic modelling was used to provide optimum weld compositions for the eradication of solidification cracking. Validation showed that by controlling the principal elements, not only was cracking eliminated, the mechanical properties of the weld could be varied. In particular, a composition was identified, which offered adequate joint strength and ductility. Exceeding this composition resulted in a corresponding increase in weld hardness at the expense of joint ductility.     

Intensity of hydrodynamic movements induced by ultrasounds in ultrasonic cleaning in water solutions

Abstract

The main causative agent of ultrasonic cleaning is cavitation. A helpful factor is liquid movement induced by ultrasound, but in some organic solvents, the intensity of this movement is so high that its significance for the process of cleaning is equal to and sometimes even higher than the significance of cavitation. In the present work, the intensity of hydrodynamic movement induced by ultrasound in water was assessed and compared with those in selected organic solvents used in ultrasonic cleaning.     

The usefulness and application of fuzzy logic and fuzzy AHP in the materials finishing industry

ABSTRACT

It is suggested that fuzzy logic could occupy a more prominent role in the materials finishing industry. While a number of applications have already been made to control finishing processes and help with decision making, there is clearly scope for extending the use of fuzzy logic in the industry. After surveying some of these applications, the background to fuzzy logic is described and its set theory explained. Finally, the steps involved in selecting an environmentally acceptable metal cleaning agent from possible alternatives using a fuzzy analytic hierarchy process (AHP) are described in detail. As illustration, two different sets of selection criteria ranking are considered for choosing (i) the best solvent for cleaning equipment to be used in oxygen service and (ii) for cleaning metal parts prior to further finishing treatment.     

European Solvent Emissions Directive: knowing your surface cleaning options

Abstract

The implications of the new European Solvent Emissions Directive on surface cleaning of components are discussed by Richard Starkey of Safechem Europe GmbH.     

Index of Susceptibility to Stress Corrosion for Austenitic Steels Based on the Electromechanical Model

Abstract

A model for the stress corrosion of austenitic steels is developed based on the assumption that crack growth occurs purely by preferential anodic dissolution at the yielding crack tip. The process is visualised as one proceeding by steps in which a burst of slip precedes or accompanies anodic dissolution, followed by exponential passivation of the exposed surface. It is postulated that during one such cycle of incremental crack growth, an energy balance equation pnalogous to the one developed by Griffith is satisfied. This involves the concept of an electrochemical work term which varies with the effective anodic dissolution voltage and the crack opening displacement at the tip of the crack during the cycle.

Concepts of plasticity are introduced later in the paper which allow the formulation of equations showing the relationship between susceptibility to stress corrosion cracking and lattice stacking fault energy.

The tunnelling phenomenon observed at crack tips in austenitic steels by Nielsen and by Swann and his co-workers is discussed in terms of a possible energy balance on the atomic scale between the stored elastic strain energy per unit length of dislocation and the equivalent ‘overpotential’ required to dissolve an associated volume of unit length and cross section b_oω, where b_o is unit Bergers vector and ωw is the partial dislocation spacing     

Modelling and optimisation of magnetic abrasive finishing process based on a non-orthogonal array with ANN-GA approach

ABSTRACT

Magnetic abrasive finishing (MAF) is an advanced precise finishing method that achieves micro-level to nano-level surface roughness. In industries, MAF is highly recommended where zero or negligible post-process surface defects are an obligatory requirement. In the same context, process optimisation is essential for making it commercially viable. This study presents an artificial neural network and genetic algorithm (ANN-GA), a robust modelling and optimisation tool (applicable to any sort of data set orthogonal array design or non-orthogonal array design) that is applied to scrutinise and improve the performance of the magnetic abrasive finishing of stainless steel SS302. In addition, the results from ANN-GA modelling and optimisation have been compared with conclusions drawn from conventionally used Taguchi-ANOVA analysis. An L₂₇ non-orthogonal array design has been opted for as per machining set-up restriction. Abrasive size, voltage, machining gap, and rotational speed were the design variables considered in the present research work. It was found that the parametric design used in this study provides a straightforward, methodical, and proficient method of modelling and optimisation of change of surface roughness or finishing behaviour during the MAF process. Modelling and optimisation done with ANN-GA show a maximum value of (ΔR _a)_max equal to 0.256?µm, which is 7% better than the result obtained from Taguchi-ANOVA analysis.     

Training for anti-corrosion maintenance of naval aircraft

Abstract

Naval aircraft are exposed to carrosion by sea-water spray in an atmosphere always charged with salt droplets and polluted by fuel-oil combustion products. The elementary knowledge of corrosion that personnel receive in Service engineering training is supplemented by special courses in ‘Aircraft husbandry’ by the regular issue of a Corrosion handbook and by the distribution of portable kits for cleaning and on-the-spot maintenance. Standing Orders contain instructionsto ensure regular periodic inspection and the keeping of records.     

On using mixtures of liquids for ultrasonic cleaning

Abstract

The effects of mixing various liquids on the acoustic properties of the resultant mixtures are discussed. These properties are ultrasonic radiation pressure that induces the agitation of liquids in ultrasonic cleaners and ultrasonic cavitation. Both these physical phenomena are direct causative agents of ultrasonic cleaning.     

Microbiological corrosion of tanks in long-term storage of gas oil

Abstract

Investigations have been carried out to establish the causes of leakages occurring in long-term gas oil storage tanks. Samples of oil, water, etc. taken from the bottom of the emptied tanks and from blisters and pits found in the tank-bottoms have been examined and shown to contain sulphate-reducing bacteria. All of the evidence obtained points towards corrosion being due to the action of these bacteria rather than to any other corrosive effect.

Recommendations for the cleaning and repair of tanks are given.     

Electrochemical study of corrosion-abrasion of stainless steels in phosphoric acids

Abstract

The corrosion-abrasion behaviour of several types of stainless steel in phosphoric acid has been studied using electrochemical techniques. The depassivation action of the abrasive was shown to depend on the nature of the material and on the aggressiveness of the medium. In particular, the existence of a synergy between the abrasive and the impurities (chloride and sulphuric acid) in the phosphoric acids was demonstrated. It was found that abrasion enhances localised corrosion. The effect of molybdenum, tungsten, and copper content on the behaviour of stainless steels under corrosion-abrasion conditions was also examined. It appears that molybdenum additions have the most beneficial effect on the corrosion-abrasion resistance of stainless steels in phosphoric acids.     

Comparison of electrochemical impedance spectroscopy and electrochemical noise measurement of plasma polymerised films as pretreatment for cold rolled steel

Abstract

Plasma polymerised films have shown promise as possible alternatives to phosphating for the corrosion protection of cold rolled steel. After plasma cleaning using either a mixture of argon and hydrogen or a sequential combination of argon and hydrogen followed by oxygen, steel panels were coated with a 250 nm thickness plasma polymerised film of dimethylsilane followed by 30 μm of cathodic electrocoat. Various plasma cleaning conditions were compared, and both electrochemical impedance spectroscopy and electrochemical noise measurement were used to rank the performance of the system. Results from the two types of test correlate reasonably, showing that the system is fairly effective in protecting the substrate from the onset of corrosion. These preliminary results demonstrate that plasma cleaning is a very important step in the process.     

Microstructural changes in weld metal during isothermal process. Study of reheat cracking in flux‐cored arc welding stainless steel weld metal (5th report)

The soiling of the slag, spatter and the fume, etc., which come into contact with the steel sheet surface with welding, is cleaned making use of steel sphere shot material of large particle diameter, high projection pressure with strong peening processing (below, called strong peening cleaning). In this research, the cleaning state of the soiling with welding and improvement of fatigue strength of the hot galvanized welded joint was inspected, when the surface of a SM490A welded joint was cleaned with strong peening cleaning.

The following experimental results were obtained:

1. The fatigue limit of smooth base metal which received strong peening cleaning at about 320 MPa was remarkably high in comparison with smooth base metal at about 245 MPa.

2. The fatigue limit of a welded joint which received strong peening cleaning at about 300 MPa was remarkably high in comparison with a welded joint at about 170 MPa.

3. The strong peening cleaning was highly efficient and the cleaning state was satisfactory.

4. The cause of the remarkable rise of the fatigue limit (300 MPa) of the welded joint which received strong peening cleaning was because the fatigue limit (about 170 MPa, 57%) of the welded joint was improved (about 130 MPa, 43%) with peening cleaning. It was considered that improvement effects were: a rise (about 68 MPa, 23%) of hardness of the weld toe; relief (about 43 MPa, 14%) of stress concentration; increase (about 136 MPa, 45%) of compressive residual stress; and the decrease (about ? 96 MPa, ? 32%) by increase of surface roughness.

5. The fatigue strength of the hot galvanized welded joint decreased remarkably. This was thought to be due to the decrease (about HV40) of hardness of the surface, the decrease (about 188 MPa) of the compressive residual stress and the influence of many factors which accompanied hot galvanizing.

     

Synergistic abrasive—corrosive wear of chromium containing steels

Abstract

Commercial and experimental steels containing various chromium concentrations have been assessedfor their resistance to the combined effects of abrasion and corrosion. The degree of work hardening and macro- and microtoughness of low carbon martensite alloys, dual phase alloys, and metastable austenitic alloys provide good abrasion resistance, while chromium contents > 8% are required. Abrasion and corrosion are synergistic since the kinetics of corrosion are influenced by abrasion. The effects of the frequency of abrasion and corrosion are different for steels of different chromium contents. Low chromium steels perform better under lowfrequency conditions, whereas steels with higher chromium contents resist wear better when there are frequent abrasive periods.     

Microstructure characteristics in non-modified and Sr modified Al–Si–Cu–Mg 319 type alloys

Abstract

This study was carried out on 319 alloys containing low and high levels of Mg, in the non-modified and Sr modified conditions (150 ppm Sr addition). Single step, two step and triple step heat treatments were applied to identify the optimum solution heat treatment to minimise incipient melting of the copper phases Al₂Cu and Al₅Mg₈Cu₂Si₆ in these alloys in relation to the alloy properties. In Mg free alloys, no incipient melting of Al₂ Cu was observed even in samples heat treated at 520°C. Addition of Sr leads to modification of Si particles but also to an increase in area per cent porosity and pore length, especially when the solution temperature reaches 520°C. Addition of Mg results in a decrease in the Si particle aspect ratio but an increase in particle size. Magnesium was also found to increase the possibility of incipient melting resulting from the formation of the insoluble Al₅Mg₈Cu₂Si₆ phase. To some degree, Sr decreases the effect that Mg has in increasing the area per cent porosity and pore length, while Mg impairs the effects that Sr has on modifying Si particles, even though the lowest Al–Si eutectic temperature is obtained for the 319 alloy containing both Mg and Sr.