Galvanic corrosion of aluminium alloy members of bridge guiderails under severe atmospheric exposure conditions

ABSTRACT

Aluminium alloys are nowadays preferred as materials for bridge guiderails especially for bridges connecting oceanic islands or spanning inlets due to their inherent corrosion resistance. But because of the limited mechanical strength of aluminium alloy, fasteners of guiderail members are made from steel materials. It has been found that contact between bare steel fasteners and aluminium alloy members can cause galvanic corrosion in the aluminium alloy. Research was carried out to investigate the capability of different surface treatments on fasteners and aluminium alloy members to inhibit galvanic corrosion under atmospheric exposure for periods of one and three years. It was found, among other results, that stainless steel fasteners treated with zinc flake coating were the most effective inhibitors of galvanic corrosion on aluminium alloy members.     

Stainless steel thread forming screws and their susceptibility to stress corrosion cracking

Abstract

Thread forming fasteners incorporate both drilling and hole tapping features and are commonly used in the construction industry to fix together steel sheets of different material types. With this practical application in mind, fasteners manufactured from martensitic and austenitic stainless steels have been subjected to alternating corrosion conditions in accordance with test standards DIN 50021-SS and DIN 50018-K WF 2·0. The torque applied to the screws during these tests was controlled to place the fasteners under equal tensile loads, independent of their tensile strength. Thus, the results provided information on their relative susceptibilities to stress corrosion cracking. At the end of the tests, up to 80% of the martensitic stainless steel drilling and tapping screws had failed due to hydrogen induced stress corrosion cracking. The fasteners manufactured from austenitic materials withstood identical test conditions without any evidence of cracking or crack initiation. It is concluded that fasteners manufactured from modified martensitic stainless steel are more susceptible to stress corrosion cracking under the conditions of test than those made from cold worked austenitic stainless steels. This suggests that in practical applications the potential for catastrophic failure due to stress corrosion cracking could be considerably higher in modified martensitic fasteners in comparison with austenitic stainless steel fasteners, including those with hardened carbon steel drill points.     

Advances in Replacements for Cadmium Plating in Aerospace Applications

This paper examines some of the problems associated with the replacement of cadmium plating for the protection of aircraft components and fasteners manufactured from steel. It reviews the range of coatings which are available commercially and are currently being considered as alternatives to cadmium plating. Results of research being undertaken into the corrosion behaviour and galvanic compatibility of electrodeposited zinc alloy coatings and aluminium-magnesium alloy coatings are presented. Other aspects of coating performance are also considered including frictional properties, effects of coatings on fatigue strength, hydrogen embrittlement of steels and the repair of damaged coatings. It is concluded that although the corrosion performance of cadmium plating may be achieved with several coating systems, no one coating is likely to be acceptable as a replacement for cadmium for all aerospace applications.     

基于海洋环境的紧固件腐蚀防护要求及技术措施

紧固件是实现机械连接大量采用的一种最常见方式,是机械工业中的关键基础零部件。紧固件在各种环境中的腐蚀一直是设计者面临的问题。解决紧固件腐蚀的方法很多,表面处理是其中的重要方法之一。简要分析了紧固件腐蚀防护的基本措施和思路,着重从表面处理技术和结构防腐出发,讨论了紧固件表面涂层在不同工况下的使用要求,提出了表面处理方法和防腐结构设计。     

Electrochemical corrosion characteristics of Ni-Resist type 2 in sea water containing ferrous sulphate

Abstract

The corrosion characteristics of Ni-Resist type 2 alloy in sea water have been determined in relation to dissolved oxygen (DO) content, pH, and concentration offerrous sulphate (injected to inhibit corrosion of copper based alloy condenser tubes). The alloy underwent uniform cathodically controlled corrosion so that relatively high pH and low DO provide an acceptable environment. Compared with similar pH conditions in the absence of added iron, Fe²⁺ dosing of aerated sea water to ≤100 ppm at pH<5 increased the corrosion rate, whereas dosing at 1000-2400 ppm (pH<5) decreased it. Addition of ferrous sulphate to deaerated sea water further suppressed the already low corrosion rates in this medium. Even under aggressive conditions of anodic polarisation, the alloy showed near uniform attack of the major constituent metals, leaving, however, a graphitised surface. The possible stagnation of a concentrated ferrous sulphate solution injected into the condenser circulating cooling water system has been considered. It is also concluded that ferrous sulphate dosing does not alter the stress corrosion cracking susceptibility of the alloy.     

Exposure testing of fasteners in preservative treated wood: Gravimetric corrosion rates and corrosion product analyses

Research was conducted to determine the corrosion rates of metals in preservative treated wood and also understand the mechanism of metal corrosion in treated wood. Steel and hot-dip galvanized steel fasteners were embedded in wood treated with one of six preservative treatments and exposed to 27 °C at 100% relative humidity for 1 year. The corrosion rate was determined gravimetrically and the corrosion products were analyzed with scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Although the accepted mechanism of corrosion in treated wood involves the reduction of cupric ions from the wood preservative, no reduced copper was found on the corrosion surfaces. The galvanized corrosion products contained sulfates, whereas the steel corrosion products consisted of iron oxides and hydroxides. The possible implications and limitations of this research on fasteners used in building applications are discussed.     

Corrosion of metals in wood: Comparing the results of a rapid test method with long-term exposure tests across six wood treatments

This paper compares two methods of measuring the corrosion of steel and galvanized steel in wood: a long-term exposure test in solid wood and a rapid test method where fasteners are electrochemically polarized in extracts of wood treated with six different treatments. For traditional wood preservatives, the electrochemical extract method correlates with solid wood exposure which suggests that the reduction of cupric ions is the cathodic reaction in both the solid wood and the extract. For treatments without copper, the extract method predicted a higher corrosion rate than the solid wood exposure. For these treatments, the cathodic reaction appears to be the reduction of acid and dissolved oxygen. The practical implication of this work is that in some cases, the rapid test method could be used to screen new fasteners and wood preservatives. Scientifically, this work increases the understanding of the mechanism of corrosion of fasteners in treated and untreated wood.     

Durability of galvanised fasteners in timber construction

This article describes the possible corrosion conditions for fasteners in timber outdoor constructions. In the case of fasteners (e.g., timber screws), a distinction must be made between corrosion outside the timber and in contact with the timber. In case of contact with timber, the influence of timber constituents (acetic acid and timber protection agents), which are effective when the moisture content of the timber is high, must be taken into account. In the weathered area, the corrosion exposure and the corrosion of zinc coatings in contact with timber can, therefore, be higher than in pure atmospheric corrosion. In nonweathered areas, it may be reversed due to possible concentration of pollutants outside the timber and insufficient timber moisture. Recent research results are explained using timber screws as an example. Furthermore, the requirements for zinc coatings for fasteners in timber construction are presented on the basis of the current standardisation.     

Corrosion and corrosion prevention of magnesium alloys

Introduction of high purity alloys improved the corrosion resistance of magnesium alloys significantly. This has led to an increased use of magnesium for components like valve covers, transmission housing, and gear box housing. Because of the unnoble nature of magnesium, galvanic corrosion is the main challenge when magnesium is used in corrosive environment. By proper material selection, proper design and selective use of coatings and insulation materials, the risk for galvanic corrosion is significantly reduced. Test results show that fasteners made of aluminium of the 6000 series reduce galvanic corrosion of magnesium to very low levels in salt spray tests. Combinations of plated steel fasteners and aluminium washers are very efficient for galvanic corrosion prevention. Furthermore, it seems that sealed zinc plating is the best type of plating for steel fasteners. The plating must, however, be free from defects and the bolt head design is an important factor to get a high quality plating.     

Effect of Thiourea and some of its Derivatives on the Corrosion Behaviour of Cobalt in Concentrated Hydrochloric Acid

Abstract

The corrosion rate of cobalt in 8·4 M hydrochloric acid with and without the presence of thiourea, phenyl thiourea, o-tolyl thiourea or sym di-isopropyl thiourea has been studied by gravimetric and electrochemical methods over the temperature range, 20–80°c.

In all cases these compounds brought about enhancement of corrosion so that, at the higher temperatures, corrosion rates some twenty times those experienced in acid alone were attained. These matched the degree of corrosion stimulation of cobalt developed in the presence of hydrogen sulphide and it is suggested that the thiourea compounds act as depolarisers for the hydrogen evolution reaction, with H₂S being a product of the chemical depolarisation stage. The H₂S is considered to be adsorbed in the molecular state, forming activated sites where anodic dissolution is thereby enhanced.     

Inorganic,physicochemical, and microbial aspects of copper corrosion: literature survey

Abstract

A literature survey on the corrosion of copper in aqueous solutions, with particular relevance to potable water, is presented. Coverage is of inorganic and physicochemical aspects of copper corrosion, namely those dealing with the thermodynamics of copper corrosion reactions, oxygen reduction at copper surfaces, and the photoelectrochemistry of the copper-copper oxide-electrolyte, system. Microbially induced pitting corrosion and transport in associated biomembranes are also considered.     

Electrochemical corrosion testing of fasteners in extracts of treated wood

A recent change in wood preservatives has highlighted the need for a rapid, quantitative test to measure the corrosion rates of metals in contact with treated wood that could be used to evaluate new fasteners or new wood preservatives. A new method was developed where polarisation resistance tests were conducted on fasteners exposed to a water extract of wood treated with alkaline copper quaternary (ACQ). Good correlation was found between the corrosion rates using this new method and previous one year exposure data for carbon steel, hot-dip galvanized and electroplated galvanized fasteners. These data suggest that polarisation tests run in wood extract may be an effective, rapid test method to evaluate new fasteners or wood preservatives.     

镀锌紧固件在储存过程中的锈蚀原因分析

防抱死制动系统(ABS:Anti-lock Braking System)的镀锌紧固件在存储过程中发生锈蚀。分别从大气腐蚀影响因素、腐蚀形貌及能谱分析(EDS)等方面分析了镀锌紧固件的锈蚀原因,并提出合理化建议,避免再次发生类似的锈蚀问题。     

Corrosion Control at Welded Joints in Constructional Steels

Abstract

Corrosion problems at welded joints are considered. Means of corrosion control so that welds in structures have corrosion resistance equal to that of the joined members are discussed. Cheaper and easier expedients, where the technically best method is not practicable, are pointed out.     

South African Corrosion Conference 2—5 November, 1965

Abstract

A laboratory investigation into erosion corrosion in copper water tubing has been carried out. For aerated water at pH 8 and continuous flow, the maximum flow velocity not causing erosion corrosion was 3 m/s at 65°c and 6 m/s at 30°c in small diameter (6/4 mm) tubes; at pH 6·5 the maximum velocity must be reduced. With intermittent flow (<25% of the time), or with water poor in oxygen (as in central heatingsystems) higher flow velocities are acceptable. Small diameter tubes admit higher flow velocity than larger ones.

No differences in erosion corrosion resistance between annealed and hard-drawn copper tubes have been observed. Flared joints are much more liable to cause erosion corrosion at high water flow velocities than are joints withcapillary fittings.

The limits quoted were obtained in well-defined laboratory conditions; in practice a proper safety margin should be allowed.     

Methodology to study cost of corrosion

Abstract

It is essential to have an in-depth understanding of corrosion phenomena, from both a scientific and a technological viewpoint, in order to develop strategies that minimise the costs associated with the corrosion of materials. Looked at in this way, corrosion can be seen to be not merely an economic problem. Studies of the Cost of Corrosion have been undertaken in several countries, including Japan, UK, USA, and have estimated losses to the national economy due to corrosion of up to 5% of Gross Domestic Product (GDP). This high cost stems directly from a general lack of awareness of the economic impact of corrosion, and the poor selection of protection measures. Although a definitive method to determine corrosion costs has not been established, the main methods that have been applied are the Uhlig method, which calculates corrosion related costs based on corrosion prevention methods; the Hoar method, which makes estimates in various industrial sectors, and the Input/Output method, based on an Input/Output matrix. The present study summarises the methods that have been widely used, and the results obtained in each one of the countries in which they have been applied. On this basis, a programme is proposed to estimate the costs of corrosion associated with several important industrial activities.     

Electrodeposition of aluminium from ionic liquids on high strength steel

Electroplated aluminium from ionic liquids is a promising candidate for corrosion protection of steels due to its excellent corrosion resistance. The pretreatment of the substrate is a crucial step for good adhesion of the coating and hence its performance. Conventional aqueous pretreatment of the steel substrate prior to aluminium plating does not lead to satisfactory results. In this paper, the authors systematically investigated anodic polarisation of high strength steel in Lewis acidic 1-ethyl-3-methylimidazolium chloride/AlCl₃ as an electrochemical pretreatment method. The study includes cyclic voltammetry, chronoamperometric and chronopotentiometric methods as well as SEM/EDS analysis, optical microscopy, completed by roughness measurements using laser scanning profilometry and AFM. The removal of oxides and impurities from the steel surface and an increase of the surface roughness leads to excellent adhesion of the deposits. In-situ anodic polarisation and subsequently deposition results in the formation of an aluminium-iron alloy. By separation of pretreatment and deposition baths, high quality pure aluminium deposits can be achieved. It is shown that the developed pretreatment process can be successfully applied for the coating of flat substrates as well as for fasteners; the latter in a barrel plating process. The coating shows good adhesion and is evenly distributed over the substrates. Furthermore, a method for removing ionic impurities (e.g. iron) in the pre-treatment bath is suggested.     

Corrosion of Autoclave Jackets Subjected to a Steam-Water Cycle*

Abstract

The corrosion rate of steel autoclaves which are alternately heated by steam and cooledby water was found, after about 18 months' use, to be greater than was considered acceptable for this type of equipment. The corrosion combined with the stresses caused by differential expansion of the jacket and the autoclave calls also caused crackmg of the welds between the Jacket and the body. The corrosive conditions were simulated in the laboratory and a considerable number of inhibitor systems for the steam and water were investigated. Steel test pieces were exposed alternately to steam for about 2½ hours and water for 1½ hours, provision being made to dose the steam and/or water. In screening tests lasting 20 cycles,addition of a few ppm of octadecylamine,hydrazine or morpholine to the steam (no treatment being given to the water) had practicallyno effect on the corrosion rate of mild steel. Sodium benzoate and mercaptobenzthiazole(NaMBT) additions to the water reduced the corrosion by about 80%; sodium nitrite and sulphite additions were not so beneficial. The most effective inhibitor was 0·1% sodium chromate which reduced corrosion by 90%. Some crevice attack occurred even in this solution, but this could be reduced by a heavy (25ppm) dosage of octadecylamine to the steam. This was confirmed during a test lasting 5 weeks.

Stressed welded specimens were exposed in the laboratory to the water-steam cycle, the water being inhibited with 0·1 % sodium chromate for one year, but although there was some crevice attack, even control specimens in contact with the untreated water did not crack. Over the year, weight-loss measurements showed a corrosion rate of about 0·005 in./yr in the inhibited system, and roughly 10 times this in the control specimens in an untreated system.     

Effect of flow velocity on pipeline steel corrosion behaviour in H2S/CO2 environment with sulphur deposition

The effect of element sulphur on the performance of corrosion inhibitor in H₂S/CO₂ gas field solution was investigated at different velocities. The morphology and composition of corrosion products were characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) methods. The results indicated that L360 QS steel surface suffered from sulphur-induced pitting corrosion at a low velocity due to insufficient sulphur-carrying fluid power. At high flow velocities, the steel surface is likely to be suffered high fluid power which can remove the inhibitor film and corrosion scales by the mechanical erosion effect. The sulphur corrosion mechanism model and the flow-induced corrosion model due to the high wall shear force have been proposed in the study. This work suggested that the gas production rate should be controlled at an acceptable level to guarantee the service safety of pipeline system.     

Corrosion of Mechanical Joints in Aluminium and Aluminium-Steel Structures

Abstract

This paper is primarlly concerned with the problem of poor performanee of mechanical joints, the main reason for which is inadequacy of published informaiion on joint design, construction procedure,, and maintenance. This contention is illustrated by discussion of corrosion problems that arise with mechanical joints, particularly with aluminium-stell joints which are commonly used in shipbuilding.

The need for closer co-operation amongst designers, constructors and corrosion specialists is strongly emphasised. Some methods of making practical corrosion informaiion available to industry are suggested.