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Home & Garden Articles
Corrosion Control & Protection
Wed 17 Jun 2009 - 10:15
Corrosion Control & Protection
By [http://ezinearticles.com/?expert=C._C._Ang]C. C. Ang
What is corrosion? Corrosion is a process of rusting through oxidation and weathering of the natural elements of rain and sun on all metal surfaces, if not adequately protected with appropriate coatings. Normally starts with rusting which eventually creeps into the metal causing pitting,then forming scales that chips off weakening the metal.
This happens to all things that is built, constructed of steel structures, metal tanks, pumps, steel piles, pipes and ship hulls, etc. are all subjected to corrosion if they are not protected with the right type of coatings and/or cathodic protection.
Other forms of Corrosion
Apart from the corrosion action of oxygen and water on steel as describe above, there are other causes of corrosion.
1. Corrosion through attack by chemical and chemical fumes.
2. Through use of dissimilar metals. Like joining new steel pipes to old steel pipes. Even old metal plates joined to new metal plates by bolting or welding. New steel is anodic to old steel.
3. Highly stressed surfaces are anodic to unstressed surfaces.
4. Steel are also anodic to mill scale. Mill scale which is formed during the high temperature milling of steel, is a hard brittle coating of distinct layers of iron oxides. It cracks and fissures readily, permitting air and moisture to penetrate and initiate rusting to the underlying steel.
There are many more other forms of corrosion but for our purpose, we will discuss until this section.
Corrosion Prevention
Corrosion prevention is to provide sufficient protection to prevent corrosion taking place for a certain period of time by calculation and inspection, when subsequent maintenance or renewal are needed before the material structures begin to show signs of corrosion.
Surface Preparation
Surface preparation is a very important process before any protective coatings can be applied. New and old metal surfaces should be free from mill scale and rust. They should be cleaned to a certain standard before applying any protective coatings to achieve the best result.
Types of Surface Preparation
1. Solvent Cleaning & Degreasing
a) Removal of oil and grease from all surfaces
b) Solvent or thinner degreasing should be used for small areas only.
c) Water soluble degreasing fluids are most efficient for large areas.
2. High Pressure Fresh Water Washing
a) Removal of soluble salts deposited from seawater, polluted environments or formations from rusted steel.
b) Removal of emulsified degreasing fluid.
c) Removal of loose dust and dirt.
d) Removal of plant and slime fouling
3. Manual Preparation
i) Hard Scrape
ii) Chipping hammers or chisels
iii) Wire brushing
a) Removal of loose superficial rust deposit on small localised areas.
b) Standards of St2 and St3 can be achieved
4. Power Tool Preparation
I.) Rotary Wire Brushing
Care should be taken to ensure the rust is removed and not just
polish.
II.) Rotary Disc-ing
III.) Impact cleaning
Used on relatively small and difficult areas
More efficient then hand tool cleaning
Standards of St2 and St3 can be achieved
5. Dry Abrasive Blasting
The most efficient method of surface preparation
Steel shot and grit, mineral grits, sand and metal slags are used
as abrasives
Does not totally remove soluble salts
Standards of Sa1, Sa2, Sa2.1/2 and Sa3 can be achieved
6. Water Cleaning Processes
Low pressure water washing
High pressure water washing
High pressure Hydro blasting
Ultra high pressure Hydro blasting
Water and abrasive blasting - slurry blasting
Best method for removal of soluble salt
Water alone does not produce a surface profile
The author CC Ang who is the owner of http://engineeringsolutioncentre.com
and has over 60 years of experience in corrosion control & protection, is important for all metal structures. He has given consultations to countless organizations in the industry.
To know more about this industry you can visit his blog http://engineeringsolutioncentre.com
Article Source: http://EzineArticles.com/?expert=C._C._Ang http://EzineArticles.com/?Corrosion-Control-and-Protection&id=2474587
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