Corrosion Protection of Steel Highway Bridges: III. Protective primers for the underside of steel bridges

Abstract

The objective of this research contract, for the Department of the Environment, was to assess the behaviour of the various primer types, commonly used on structural steel in the special environment under road bridges. In the first instance unrusted steel was used in order to reduce the number of variables. The work has shown that even in this sheltered situation the protection afforded by primers is dependent on the water resisting qualities of the binder as well as on the inhibitive pigment used.. The results also demonstrated that, by choice of a particularly aggressive site (Norfolk Bridge, Shoreham), assessments of relative performance of different primers could be made almost as rapidly as, and more reliably than, by artificial laboratory tests. Further work is in hand to explore the effects of paint binder more thoroughly and to assess the effects of rust contamination before blast cleaning and priming.     

Anti-Corrosive Treatments for the Protection of Structural Steelwork*

Abstract

Comparative tests of painted metal-sprayed treatments against various paint treatments over grit-blasted conditions steel have been made under various exposure conditions, both laboratory and natural. No one system has proved to give the best performance under all conditions, but with the exception of acid industrial conditions, metal spray plus paint can giveadded long-term protection. Where acid industrial conditions are encountered, lead-based priming paints are the best treatment for grit-blasted steel. Silicate-based zinc-rich paints show promise. Test results on paint systems in natural rural and industrial conditions (after 21/2 years) are not available.     

Experimental investigations of mechanical and tribological behaviours for organic and inorganic coatings deposited on mild steel substrate

ABSTRACT

Surface treatment technologies are constantly evolving. Increasingly, surface functionalisation is of major concern to lighten structures, improve product performance and reduce costs. To fulfil its decorative and protective functions, it is essential that a coating adheres properly to its support. During the last few decades, many new deposition techniques have been developed and more and more tribological and corrosion resistant coatings have been made available. In this context, the present research has focused on two pneumatically sprayed epoxy/polyamide and inorganic silicate coatings which are deposited on the mild steel substrate. First, the main interest in this study is devoted to the analysis of the coating/substrate adhesion strength by using the squaring and pull-off tests. Second, the study has also focused on the analysis of friction and wear behaviours for the two systems of paint coatings under consideration by using a linear reciprocating tribometer under dry sliding condition. Experimental findings have shown that after appropriate surface preparation and degree of cleaning according to the standard ISO 8501-1, selected paint systems composed of organic or inorganic coatings effectively improve the service life of coated steel. Meanwhile, under the same sliding conditions, the wear results have revealed that the organic coatings have a higher anti-wear ability compared to the inorganic coatings. Thus, both organic and inorganic coatings play an important role in protecting the substrate against severe industrial environment. From the squaring and pull-off analyses, it has been deduced that scratch and pull-off behaviours of both coatings have been severely affected by the surface preparation, the number of protective layers and the thickness of coatings. In fact, the best adhesion, friction and wear properties are obtained for the paint system containing organic coatings where the third body is formed on the entire sliding strip in the test.     

面向再制造的油漆清洗技术综述

再制造清洗是再制造中极为重要的环节,清洗的质量会直接影响再制造产品的质量.油漆是再制造清洗中必不可少的一种污垢类型,相比于其他污垢,具有与基体结合时间长,结合情况复杂,清洗难度大的特点.目前,清洗油漆主要采用传统清洗技术,如酸碱溶液清洗、高温热分解、干喷丸清洗等,而对近几年出现的油漆绿色清洗技术的推广应用不够,并且没有一个系统的整理总结用于指导实际应用.针对这一现状,基于国内外学者对油漆绿色清洗技术的研究成果,首先从油漆的性质方面进行整理,如:油漆与基体的结合情况,油漆表面微观形貌以及主要成分等.然后总结了机械领域常用的绿色油漆清洗技术,如熔盐清洗技术、干冰清洗技术、激光清洗技术、高压水射流清洗技术、湿喷丸清洗技术、超声波清洗技术以及超临界CO2清洗技术,重点阐述了各种清洗技术的油漆清洗机理及优缺点,并以清洗效率为衡量标准,对各种清洗技术进行对比分析,为使用者选择清洗技术提供参考.最后根据现有油漆清洗技术存在的局限性,对清洗技术的发展前景进行了展望,提出了绿色化、复合化和智能化的发展理念,为新型油漆清洗技术的提升以及现有油漆清洗技术改进提供思路,促进清洗技术的进一步发展.     

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.     

Failure of aluminium metal spray/organic duplex coating systems on structural steel

Abstract

Individually, aluminium metal spray (AMS) and organic paints are well established as effective protective coatings for steel substrates. These coatings are also frequently used together as duplex systems where their combination should produce a synergistic effect. However in certain, mainly marine, environments premature failure of such coatings, involving early blistering of the paint, has been observed in service after 3–5 years. This work aims to understand the mechanisms associated with the early failure of the AMS+paint duplex system. Various panels were initially prepared for accelerated exposure using combinations of coatings on blast cleaned steel. Visual inspection after salt spray exposure revealed the presence of white corrosion product, which was confirmed afterwards as Al(OH)₃. Observation of the coating microstructures before and after salt spray exposure confirmed significant local corrosion of aluminium underneath the paint layer. It is suggested that failure of the duplex AMS/paint system initiates by corrosion of the porous AMS underneath the organic layer then progresses by the combined effect of volume expansion due to formation of Al(OH)₃ and cathodic blistering of the paint from the AMS surface.     

Properties of FA-CVD silica coated steel sheet after deformation: coating integrity and corrosion related forming limit curve

Abstract

Thin silica coatings may be used as pretreatments for steel sheet, offering temporary corrosion protection and promoting adhesion of organic coatings. For use as ready to paint product, silica coated steel has to possess also good corrosion properties after deformation and successive paint application. In this paper, we investigate the forming limit curve for flame assisted chemical vapour deposited silica coated steel sheet with respect to corrosion properties after paint application. We find good corrosion properties up to a strain of 10%, indicating a high tolerance towards deformation. Evaluation of the silica coated steel sheet by scanning electron microscopy shows that severe failure takes place at high levels of deformation, but only at a fraction of the surface. Adhesion, cracking as well as deadhesion and flaking of the very thin films (15–50 nm) was furthermore investigated by scratch testing.     

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.     

Optimum Conditions for Blast Cleaning of Steel Plate

Abstract

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

The rate of cleaning is found to increase when more abrasive per unit of time is discharged. This means that high pressure, a large nozzle and a wide valve for metering the abrasive flow are advantageous, but the actual setting of these variables should be mutually adjusted. The optimum blasting angle for removing millscale is about 45°, and the optimum nozzle-to-work distance is 55–75 cm. The smaller the abrasive grains, the quicker is the cleaning process. Under otherwise constant conditions, air consumption decreases as the abrasive transport is increased. High cleaning rates are advantageous because they lead to lower costs per unit area for labour and power, whilst for abrasive increase only slightly.     

Fatigue crack growth of bainitic rail steel welds

Abstract

The objective of the present study is to develop and evaluate novel weld repairs of bainitic rail steel defects, such as detail fracture, induced by in service loading. Slots were machined in the bainitic rail steel to simulate the removal of service defects. Multipass gas metal arc welding was used to fill and repair the slots. Three-point bend tests of the parent and welded steels revealed that the flexural weld efficiency was 75%. Fatigue crack propagation (FCP) tests were performed on specimens from the welded joints and compared with the parent materials to determine the mechanical integrity of the slot repairs. The fatigue lifetime and FCP kinetics were similar for the parent and slot welded bainitic steels, indicating similar resistance to FCP. The fatigue fracture surface morphology of the parent and welded bainitic rail steels both revealed mostly a ductile fracture mechanism in all the three FCP stages.     

轮轨材料/硬度匹配研究进展与展望

车轮与钢轨硬度是影响轮轨磨损的主要因素之一,合理的轮轨材料与硬度匹配对于减轻轮轨磨损、延长服役寿命具有十分关键的作用。当前我国铁路运营过程中存在2种硬度钢轨匹配4种硬度车轮的现象,材料匹配行为复杂。针对铁路轮轨材料和硬度的选用与匹配,至今尚无统一合理的规定与标准。从轮轨材料硬度出发,首先分析了国内外轮轨材料发展与硬度匹配的使用现状,发现不同国家和地区轮轨材料硬度的选用存在较大差异。具体表现为:日本新干线使用的车轮硬度远高于钢轨(H_R/H_W<1),欧洲高速铁路上H_R/H_W值接近1,而中国高速铁路系统中,轮轨种类多,硬度区间大。其次,总结了轮轨硬度匹配研究进展,明确材料硬度和轨轮硬度比(H_R/H_W)对磨损与滚动接触疲劳损伤都具有显著影响,但并没有形成统一的结论,且以往的材料选用经验并不完全适用于当前的铁路系统。然后,针对现阶段轮轨材料与硬度匹配研究,探讨了材料加工硬化、合金钢微观组织、表面热处理工艺、复杂服役环境与车轮运行参数等因素的潜在影响。最后,提出...     

某新型清洗剂在弹药弹筒表面漆膜清洗上的应用

目的用某新型清洗剂代替酒精、汽油应用于弹药弹筒表面漆膜清洗。方法选取先进、可靠、安全环保的某新型清清洗剂,应用于弹药弹筒表面漆膜中间过程中漆膜上的油污、汗渍、红丹、记号笔、药粉等污物的清洗。通过对弹药弹筒表面漆膜的特点、漆膜上各类污渍的组成以及对漆膜中间清洗工艺过程进行分析,同时针对上述特点,拟定清洗剂选用原则,结合清洗剂的组成、特点、除污机理,通过对清洗剂进行应用试验,从清洗剂安全性能、清洗后漆膜附着力性能、清洗后漆膜耐盐雾性能、清洗剂的清洗效果、清洗剂的挥发速度、清洗剂气味等几个方面进行试验。结果某新型清洗剂具备清洗效果好、挥发速度快、清洗效率高等优点,清洗后对弹药弹筒表面漆膜无影响,满足弹劳逸结合漆膜清洗质量要求。结论某新型清洗剂可以代替酒精和汽油在弹药弹筒表面漆膜清洗上进行应用,具有环保、无毒等特点,在弹药弹筒表面漆膜清洗应用领域具有推广意义。     

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.     

Accelerated method for testing soldering tendency of core pins

Abstract

An accelerated method for testing die soldering has been proposed and tested. High intensity ultrasonic vibration has been applied through a core pin to molten aluminium in order to simulate service conditions under die casting. Such conditions include high pressure and high impingement speed of molten metal on the pin. Soldering tendency of H-13 steel pins with or without commercial coatings was tested using this accelerated method. The experimental results indicate that soldering occurs within a few minutes of testing using this new method, much faster than that using the conventional methods. The coating failure mechanism identified in this new method is identical to that observed in the conventional methods, suggesting that the new method is suitable for testing soldering tendency of core pins under die casting conditions.     

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.     

Corrosion Protection of Steel Highway Bridges: I Full scale trials of paint systems

Abstract

Full scale trials of ten paint systems, applied on the plate girders of the Loudwater Viaduct, are described. The best performance during four years of exposure was given by a solvent less epoxy system, but its application requirements were stringent and may be difficult to meet in practice. For high corrosivity sites, a chlorinated rubber paint system should give a good performance with easy application, although transportation damage between fabrication shop and site may be a problem. A general conclusion is that aluminium pigment should be excluded from conventional micaceous iron oxide paints. In several instances aluminium has been leached out as aluminium salts leading to deterioration. of the paint system and rusting of the substrate.

The importance of the micro-climate to which sheltered bridge steelwork is exposed is discussed. Steel girders are not washed by rain and the combination of corrosive contaminants and long periods of wetness can be a particularly severe condition for paint coatings under a bridge deck. Further research on the characterisation of bridge sites and evaluation of priming paints has been initiated.     

2024 aluminium alloy wettability and superficial cleaning improvement by air cold plasma treatment

2024 aluminium alloy is used for parts and structures which demand high-strength/weight ratio. In particular, Al2024 is, for its high specific strength and good chemical stability, a suitable material for aerospace application. Aluminium alloys are involved in corrosive phenomena when they are used in critical applications, such as the aeronautic ones. The solution commonly adopted to solve corrosive problems is to paint aluminium alloy surface including 2024 aluminium alloy which is the subject of this study. The applied paint film protects the aluminium alloy from corrosion. In order to improve the adhesion of the paint film it is necessary to pre-treat the manufactured surface. The objective of the pre-treatment is to develop a cleaned, uniform, wettable surface. Cold plasma is an efficient, economic and environmentally attractive alternative to the use of the traditional pre-treatment. This work aims to study the relationship between cold plasma and 2024 aluminium alloy wettability and cleaning. Surface samples have been analysed by: (i) standard procedure to measure the quantitative wettability; (ii) Energy Dispersive X-ray Spectroscopy or EDS to determine a quantitative measure of organic contaminant.This work demonstrates that air cold plasma treatment improves significantly wettability and cleaning of 2024 aluminium alloy surfaces both associated with pre-cleaning by MEK^® and without pre-cleaning by MEK^®: the wettability reducing has been greater than 70% and the contaminants reducing greater than 65%.     

Experimental studies of salts removal from metal surfaces by wind and rain

Abstract

This paper outlines an experimental programme aimed at determining the mechanisms of salt removal from metallic surfaces by wind and rain. The paper provides data and process understanding that will be integrated into a holistic model of atmospheric corrosion. Experiments are reported in which fine salt crystals were deposited either wet (as fine droplets of seawater) or dry onto a surface. The surfaces were then placed in a wind tunnel and salt loss was determined as a function of wind speed. In another experiment, the motion of simulated raindrops falling onto metal plates was determined. Finally, in a third series of experiments, video footage of simulated rain on metal surfaces was studied in order to determine both the subsequent motion of rain and its cleaning efficiency. The efficiency of surface cleaning by wind and rain, as determined by these experiments, was then related to Australian climatic conditions. A future paper will present mathematical models of the processes defined in this paper.     

Tests on painting metal-sprayed structural steel

Abstract

Over 400 channel sections and over 100 flat specimens have been metal-sprayed, painted and exposed to variousus environments in order to confirm that good protection, without unduly short paint life can readily be achieved by the use of composite coatings of sprayed aluminium or zinc and a wide variety of paint schemes. After 2 years, most of the test material was still in good condition, but there were some failures. The probable causes of occasional failures found in practice are highlighted and are attributed to incorrect schedules of operations or injudicious selection of paints. In particular, weatheringprior to completion of the full paint scheme should be avoided whenever possible. Recommendations are made as to how to ensure good paint life over sprayed metal coatings.