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5. Intergranular Corrosion - all austentic stainless steels contain a small amount of carbon. At extremely high temperature, such as welding, the carbon forces local chrome to form chromium carbide around it, thus starving adjacent areas of the chrome it needs for its own corrosion protection. When welding, it is recommended you consider low carbon stainless such as 304L or 316L. 6. Selective Leaching - Fluids will remove metal during a de-ionization or de-mineralization process. This usually happens inside a pipe and is rarely a fastener problem. 7. Erosion Corrosion - This corrosion happens when the velocity of an abrasive fluid removes the passivation from a stainless. Again, this is almost exclusively limited to pipe interiors and rarely a fastener problem. 8. Stress Corrosion - Also called stress corrosion cracking or chloride stress corrosion. Chlorides are probably the single biggest enemy of stainless steel. Next to water, chloride is the most common chemical found in nature. In most environments, the PPM are so small the effects on stainless are minute. But in extreme environments, such as indoor swimming pools, the effects can be extreme and potentially dangerous. If a stainless part is under tensile stress, the pitting mentioned above will deepen, and cracking may take place. If you are using stainless steel bolts under tensile stress, in an environment where chlorine corrosion is likely, you should examine the potential for stress corrosion cracking carefully. According to a NACE International & CC Technologies study, corrosion costs the United States $276,000,000,000 annually. That's $276 billion and 4.2% of the nations GNP. In the power generation and transmission industry alone, it is estimated that nearly 8% of the typical electric bill is attributed to the cost of corrosion. It is unknown how many lives are lost annually due to corrosion but the number could be frighteningly high. Extreme examples thru the years include collapsed bridges and jet airliner crashes. For additional reading on types of stainless, read FAA AC 43.13-1B Section 2 6-11 (document) Methods to combat corrosion in stainless Clean, clean, clean. A simplistic example of the effectiveness of cleaning is right in the house. A stainless kitchen sink can see some of the most hostile chemical attacks in a home. But the stainless stays bright. Why? Because the constant flow of fresh water and wiping down removes the harmful chemicals that if left unattended, could attack the stainless' passive film. The more hostile the environment, the more cleaning required. Cleanliness is essential for maximum resistance to corrosion. Never use abrasive powders or materials on stainless. Always use a soft cloth. Mild detergents and soap can be used but those containing chloride detergents should be avoided. Summary No metal, except for gold and platinum in their natural state, are completely corrosion proof. But stainless steel has proven in thousands of applications, that it is one of the most economical solution's to combat the ever present elements that cause corrosion. Yet as its name implies - it is stain-less, not stain-proof
For additional reading
we recommend the following sites with free pdf downloads Photographs of Corrosion Types Stainless Steel - Corrosion Resistance Types of Stainless Steel Corrosion Excellent article on Galvanic Corrosion with fastener samples NST Center - (follow link) Technical Library - (follow link) A Corrosion Primer Why Stainless Steel Pits - recent discovery from London How to Passivate Stainless Steel Parts
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