Steel fixtures
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The use of Carbon steel (also called black carbon steel) is strongly discouraged in the wooden prefab building sector. Carbon steel has the tendency to quickly corrode (rust) in any environment, in particular when exposed (the bolt parts extending from the wood). For this reason we do NOT use carbon steel fasteners and fixtures   

Galvanization is the process of coating iron, steel or aluminum with a thin zinc layer, by passing the metal through a molten bath of zinc at a temperature of around 860 F (460 C) (called hot-dip galvanizing). When exposed to the atmosphere, the pure zinc reacts with oxygen to form zinc oxide, which further reacts with carbon dioxide to form zinc carbonate, a usually dull grey, fairly strong material that stops further corrosion in many circumstances, protecting the steel below from the elements. The Indonesian quality of galvanized steel is not as good as may be expected, due to less zinc content in the hot bath, a lower dipping temperature and a faster process, which leads to a low zinc coating on bolts. The life time of galvanized bolts (Indonesian made) is as follows:

Submerged in sea water: 2 to 3 years
Unprotected and subject to salt water spray (close to open sea): 5 to 8 years
Same as above but embedded in wood (used as fastener): 10 to 15 years  
Unprotected and not subject to salt water spray (rural areas): 15 to 20 years
Same as above but embedded in wood (used as fastener): 20 to 30 years  

Stainless steel steel does not readily corrode, rust or stain with water as ordinary steel does, but despite the name it is not fully stain-proof, most notably under low oxygen, high salinity, or poor circulation environments. It is also called corrosion-resistant steel when the alloy type and grade are not detailed, particularly in the aviation industry. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and resistance to corrosion are required.
Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steel rusts readily when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide, and due to the greater volume of the iron oxide this tends to flake and fall away. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion and blocks corrosion from spreading into the metal's internal structure, and due to the similar size of the steel and oxide ions they bond very strongly and remain attached to the surface. The stainless steel produced in Indonesia is of quality 304 and can be compared with corrosion resistant steel. The steel will stain somewhat but will not rust. The pitting time (*) of Indonesian made stainless steel is as follows:

(*) pitting time is the period in years to penetrate 1 mm into the steel

Submerged in sea water: 100 years
Unprotected and subject to salt water spray (close to open sea): 150 years
Same as above but embedded in wood (used as fastener): indefinite  
Unprotected and no subject to salt water spray (rural areas): indefinite
Same as above but embedded in wood (used as fastener): indefinite


CONCLUSION: if you will build close to open sea (*) you should opt for stainless steel fasteners. If you wish to build for at least a 20 year life time in any rural area you should consider stainless steel as well. Carbon steel is out of the question in any environment.  

(*) salty sea water aerosol can penetrate up to 20 km inland

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Last modified: August 19, 2013
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