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Galvanised steel

Zinc coatings on steel (galvanised) are attacked in the same way Jis iron, but usually more slowly. Very alkaline waters are usually aggressive to zinc and will often remove galvanised coatings the corrosion products consist of basic zinc carbonate or other basic compounds and may take the form of a thick creamy deposit or hard abrjisive particles. [Pg.358]

Figure 9.17 The protective coating formed by zinc on steel galvanisation, (a) Before and (b) after formation of the protective corrosion product... Figure 9.17 The protective coating formed by zinc on steel galvanisation, (a) Before and (b) after formation of the protective corrosion product...
High strength steel galvanised prestressing strand... [Pg.651]

Typical Use Copper, iron, steel, galvanised pipes and fittings. Typical Use Oily metals. Oil-impregnated sintered bushes. ... [Pg.103]

Aluminium is much less sensitive to the attack by sulphur dioxide (SO2) than steel, galvanised steel and zinc. It has been shown that during exposure to industrial atmosphere, aluminium absorbs 1 mg-dm of SO2, while steel absorbs between 22 and 55 mg dm of SO2 under the same conditions [11]. [Pg.250]

Fig. 2. Friction factors for cylindrical pipe where line A represents drawn tubing line B, commercial steel C, galvanised iron and lines D, E, and F,... Fig. 2. Friction factors for cylindrical pipe where line A represents drawn tubing line B, commercial steel C, galvanised iron and lines D, E, and F,...
How does galvanising work As Fig. 24.4 shows, the galvanising process leaves a thin layer of zinc on the surface of the steel. This acts as a barrier between the steel and the atmosphere and although the driving voltage for the corrosion of zinc is greater than that for steel (see Fig. 23.3) in fact zinc corrodes quite slowly in a normal urban atmosphere because of the barrier effect of its oxide film. The loss in thickness is typically 0.1 mm in 20 years. [Pg.234]

Fig. 24.4. Galvanised steel is protected by a sacrificial layer of zinc. Fig. 24.4. Galvanised steel is protected by a sacrificial layer of zinc.
At first sight, the answer would seem to be to increase the thickness of the zinc layer. This is not easily done, however, because the hot dipping process used for galvanising is not sufficiently adjustable and electroplating the zinc onto the steel sheet increases the production cost considerably. Painting the sheet (for example, with a bituminous paint) helps to reduce the loss of zinc considerably, but at the same time should vastly decrease the area available for the cathodic protection of the steel and if a scratch penetrates both the paint and the zinc, the exposed steel may corrode through much more quickly than before. [Pg.235]

A note of caution about roof fasteners. A common mistake is to fix a galvanised or aluminium roof in place with nails or screws of a different metal copper or brass, for instance. The copper acts as cathode, and the zinc or aluminium corrodes away rapidly near to the fastening. A similar sort of goof has been known to occur when copper roofing sheet has been secured with steel nails. As Fig. 24.6 shows, this sort of situation leads to catastrophically rapid corrosion not only because the iron is anodic, but because it is so easy for the electrons generated by the anodic corrosion to get away to the large copper cathode. [Pg.236]

Under aggressive corrosion conditions it is estimated that the maximum corrosion current density in a galvanised steel sheet will be 6 X 10 A m . Estimate the thickness of the galvanised layer needed to give a rust-free life of at least 5 years. The density of zinc is 7.13 Mg m , and its atomic weight is 65.4. Assume that the zinc corrodes to give Zn " ions. [Pg.289]

Artefacts Galvanised steel sheet, new and old anodised Al polymeric roofing material corroded exhaust system. [Pg.295]

A whole science, called metallography, is devoted to this. The oldest method is to cut the alloy in half, polish the cut faces, etch them in acid to colour the phases differently, and look at them in the light microscope. But you don t even need a microscope to see some grains. Look at any galvanised steel fire-escape or cast brass door knob and you will see the grains, etched by acid rain or the salts from people s hands. [Pg.27]

The metals most commonly used for water systems are iron and steel. These metals often have some sort of applied protective coating galvanised steel, for example, relies on a thin layer of zinc, which is anodic to the steel except at high temperatures. Many systems, however, contain a wide variety of other metals and the effect of various water constituents on these must be considered. The more usual are copper, brasses, bronzes, lead, aluminium, stainless steel and solder. [Pg.347]

An important aspect of design is to predict the lines of run-off of surface water. This is because the water will contain minute particles of brown rust, especially in the pre-stabilisation period, that will stain some surfaces. Matt, porous surfaces stain particularly easily and run-off should not be over concrete, stucco, galvanised steel, unglazed brick or stone. [Pg.517]

BISRA tests on galvanised steel pipe buried for five years at five different sites are described by Hudson and Acock The galvanised pipes resisted corrosion rather better than steel at all sites. Galvanised pipes of small diameter are frequently used to provide underground water services in farms and similar establishments, and little trouble is experienced. [Pg.820]

Because of the financial importance of this process to steel producers (about one-third of all the steel produced in the world is subsequently galvanised) a great deal of research has been carried out throughout the world to establish the true equilibrium phase boundaries in the Fe,, -Zn( system and the critical temperature of stability of the f phase. Since the AG -7 diagrams or the phase stability diagrams could not account for these discrepancies in this system, AG ,-concentration curves were used for... [Pg.1136]

The corrosion of painted mild-steel window frames is often troublesome, especially on horizontal members where moisture tends to collect. This effect can be reduced by bevelling the edges with putty before painting, to help drainage. It is preferable, however, to use more resistant materials such as galvanised steel, stainless steel or aluminium for window frames. [Pg.45]

Probably the most familiar coated steel sheets are the ubiquitous galvanised corrugated roofing and cladding sheets which have been used for many years, particularly for farm buildings, either painted or unpainted. In addition to zinc other metallic coatings are available, e.g. hot dip aluminium and hot dip aluminium-zinc alloys. [Pg.47]

Nowadays, however, zinc-coated steel sheets, either continuously galvanised or electroplated, are often used as a basis material for overcoating with plastic materials or paints. The coatings are usually applied continuously and have a range of uses both externally and internally. Many surface finishes are obtainable, e.g. plain or embossed, and in an extensive range of colours, to suit almost any requirement . [Pg.47]

Vast amounts of continuously galvanised steel sheets are produced, and unless they are painted or otherwise coated, their life depends on the thickness of the galvanising and the service environment in which they are used. Similarly in the case of steel sheets coated with aluminium or aluminium-zinc alloys, their performance is dictated by their coating thickness (see Section 13.4). A problem often associated with such material is corrosion at the cut edges. From work carried out by BISRA and others it has been shown that providing the bare steel edge is less than 3 mm in width, the amount of corrosion is minimal and the life of the sheet is not adversely... [Pg.47]

Zinc in contact with wood Zinc is not generally affected by contact with seasoned wood, but oak and, more particularly, western red cedar can prove corrosive, and waters from these timbers should not drain onto zinc surfaces. Exudations from knots in unseasoned soft woods can also affect zinc while the timber is drying out. Care should be exercised when using zinc or galvanised steel in contact with preservative or fire-retardant-treated timber. Solvent-based preservatives are normally not corrosive to zinc but water-based preservatives, such as salt formulated copper-chrome-arsenic (CCA), can accelerate the rate of corrosion of zinc under moist conditions. Such preservatives are formulated from copper sulphate and sodium dichromate and when the copper chromium and arsenic are absorbed into the timber sodium sulphate remains free and under moist conditions provides an electrolyte for corrosion of the zinc. Flame retardants are frequently based on halogens which are hygroscopic and can be aggressive to zinc (see also Section 18.10). [Pg.52]

Galvanised steel provides increased corrosion resistance in carbonated concrete. In concrete with more than 0.4% chloride ion with respect to the cement content, there is an increased risk of corrosion and at high chloride contents the rate of corrosion approaches that of plain carbon steel. In test conditions the rate of corrosion is greater in the presence of sodium chloride than calcium chloride. Fusion-bonded epoxy-coated steel performs well in chloride-contaminated concrete up to about 3.9% chloride ion in content. [Pg.55]

For prestressed concrete, either high-tensile steel wires or occasionally bars of steel alloy containing manganese and silicon, can be used. Galvanised wires may also be used for prestressed concrete, but it is recommended that they be chromated before use. [Pg.55]


See other pages where Galvanised steel is mentioned: [Pg.785]    [Pg.115]    [Pg.649]    [Pg.818]    [Pg.187]    [Pg.115]    [Pg.785]    [Pg.115]    [Pg.649]    [Pg.818]    [Pg.187]    [Pg.115]    [Pg.130]    [Pg.130]    [Pg.552]    [Pg.555]    [Pg.375]    [Pg.521]    [Pg.234]    [Pg.236]    [Pg.4]    [Pg.220]    [Pg.221]    [Pg.232]    [Pg.347]    [Pg.516]    [Pg.699]    [Pg.823]    [Pg.1136]    [Pg.1289]    [Pg.1323]    [Pg.52]   
See also in sourсe #XX -- [ Pg.9 , Pg.53 ]

See also in sourсe #XX -- [ Pg.9 , Pg.53 ]




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