62
THE HONG KONG AND FAR EAST BUILDER
OF TRADE INTEREST
ITEMS OF
THE PREVENTION OF corrosION
Although rusting is a phenomenon known to everyone and has been the subject of much investigation, its exact mechanism has not yet been definitely established. It has been shown, however, that the presence of both water and oxygen are essential-for example, iron or steel stored under water will not rust provided the dissolved air in the water is kept at a low concentration. Also when iron or steel is partially im- mersed in water, corrosion starts at the air/water interface and is more severe there than on the surfaces below the water level. Corrosion is not limited to ferrous metals but the rusting of iron and steel constitutes, at any rate from the point of view of bulk, the major problem.
From a practical viewpoint rust prevention involves pro- tecting the iron or steel surface from contact with moisture and the following general methods are in use:-
1.
2.
Plating with other less readily corrodible metals, such as chromium, nickel, tin, lead, etc.
Surface treatment, e.g. by oxide or phosphate coatings. 3. Coating the surface with non-metallic materials such as
paints, lacquers or petroleum base products.
Each of these methods has its own particular uses, the petroleum base materials being of particular value where
(a) for functional purposes only an oily type film can be employed-e.g. in the moving parts of machinery, etc. (b) ease of removal is an important factor-e.g. in the case of partially assembled apparatus undergoing tem- porary storage.
(e) the protective material has also to serve as a lubricant. (d) dewatering properties are required.
It
Dewatering will be described later on in these notes. should be appreciated that petroleum base protectives are not intended as substitutes for or improvements on paint.
Rust preventives based on lanolin, petrolatum or mineral oil have been in use, on a rather limited scale, for many years. The 1939/45 war, however, brought a number of urgent cor- rosion problems which were put to the oil companies, and as a result of the work carried out, the science of rust prevention has made very rapid strides in the last four years. Some examples of the type of problem put forward were the develop- ment of a fluid for the dewatering and protection of machinery which had been immersed in sea water, the removal of water from and protection of generators and starting motors of vehicles which had to be driven through the sea during landing operations, the protection of weapons and machinery being sent to and in storage in tropical areas where conditions of high temperature and high humidity prevail.
Although many of these applications are not of practical interest to most readers of this journal, many applications do come to mind immediately. Contractors' plant, whether in use or lying idle, compressors and compressed air tools (cer- tain parts of these are particularly liable to very rapid rust- ing), steel wire rope, small hand tools, particularly those with cutting edges, etc., etc., could all have a far longer life with a much lower maintenance cost were they better protected from corrosion than they normally are.
During the war the Shell companies in Australia, United Kingdom and United States all developed ranges of rust pre- ventives but, owing to the urgency of the problem and the variations in the availability of materials used in blending, different formulae were evolved. These have now been standardised by the Shell companies and can be divided into three main groups, Rust Protective Lubricants, Rust Protec- tive Fluids and Rust Protective Compounds.
The Fluids consist essentially of non-volatile protective material with a volatile solvent. On evaporation of the solvent a uniform thin protective coat is left which prevents the access of moisture to the metal so treated. The higher the concentration of non-volatile matter the thicker will be the protective film and the longer the resulting period of protec tion. Most of the grades in this group are water-displacers, i.e. there is no need to dry the metal parts before application as the fluids will displace all moisture and at the same time coat the dried metal surface with a film of rust preventive. One grade is a dewatering fluid only, having just sufficient protective material to prevent the dried surface from im- mediate rusting. One grade is non-dewatering and is designed
to give long term protection, forming a hard protective film. The Oil Group consists of light mineral oils containing protective additives and are suitable for lubricants for moving parts and for the internal protection of engines, compressors,
etc.
The Compounds Group is used for long term protection. They solidify at normal temperatures and can thus only be applied by hot dipping or hot swabbing.
The water-displacer spreads rapidly over the metal, push- ing the water away and interposing itself between the metal and the water. On evaporation of the solvent the metal is left with a protective coat. The water-displacer also acts as a fingerprint neutralizer in that it partially removes the per- spiration left by a fingerprint and dehydrates the remainder, which is then covered by a film of protective. The fingerprint is thus completely neutralized, so long as it is covered by the film.
The films left may be divided into four classes, oily, soft, medium and hard. The oily and soft films will not stand much handling and can easily be removed by wiping. The medium films can be removed by wiping with a solvent such as kero- sene. The hard films are more difficult to remove and it is preferable not to use them when removal is required at a later date.
The various grades cover an extraordinarily wide range of requirements, giving protection for periods varying from one week to two years under cover and from one week up to twelve months in the open. Protection can be given to spare parts, parts in process of manufacture, fine tools and gauges, electric motors not in use, radiators, I.C. engines, hydraulic rams, strip and sheet steel after rolling, and machinery and plant of all kinds, both in use and in storage, to mention only a few of the more obvious applications.
THE WATERPROOFING AND PROTECTION OF CONCRETE AND STEELWORK.
Crane in a Sulphite Factory in Sweden protected with Inertol.
Concrete has become a standard building material because it is easily adaptable to any desired form, permits rapid con- struction and results in a monolithic structure of uniform strength. Nevertheless concrete represents a vulnerable and complex chemical mixture. At the end of the curing period the new concrete has not the ultimate strength and density it is able to achieve if permitted to mature undis- turbed by outside influences. It is a fact, however, that very few structures are built under ideal conditions and in many cases the concrete is prevented from developing its full strength.
Under certain conditions concrete is liable to deteriorate. although some structures are in more danger than others. In general all concrete buried in wet soil or submerged in water should be protected, particularly bearing in mind the fact that water is very often the carrier of destructive influences of the worst kind.
These conditions apply equally to bricks and to the softer kinds of natural stone which are affected by dampness by virtue of their porous nature.
To summarize the above we may say that the newer the concrete the more vulnerable it is to attack and the sooner it is protected the better will be its ultimate performance.
Steel, if it is to retain its original strength, must also be protected from moisture, salts and acids. A successful pro- Lective coating for concrete or steel must possess sufficient elasticity to follow the expansion and contraction of the con- crete or steel without cracking.
Under the conditions of humid heat and heavy monsoon rainfall which are prevalent in the Far East, such protection is highly important and a great deal of interest is now being shown by architects and others in better waterproofing and dampproofing.
We are, therefore, glad to see that supplies of Inertol, which will be remembered as being in pre-war days one of the best known ranges of protective coatings, are once more avail- able on this market from the factory at Hull, England.
Their rubber base enamels have unusual elasticity and are thus able, besides scaling small cracks in concrete, to follow the expansion and contraction of concrete without themselves cracking. These enamels are also unaffected by acids and alkalis and have the property of preventing the growth of algae, the green slime that appears in water, as the surface of the enamels is such that the algae cannot cling to it; the algae are carried away before they have an opportunity to
grow.
This firm also manufactures a colourless emulsion for application to the outside of brick, stone or concrete walls. The emulsion penetrates deeply into the pores of the walling material without sealing them. There is no interference with aeration and any existing moisture in the walling material can dry out. This water-repelling coating leaves the texture and colour of the wall unchanged and does not give a glossy finish.