wide eyed and legless
Well-Known Member
An interesting article from a British site on stainless steel in the food industry, also a quote from assda
Chloride.
The guidelines allow for the presence, but assume that the surface has been passivated. In alkaline environments (pH 7) chloride levels can be tolerated. Higher temperatures over 60 degrees C are not recommended for 304 and 316 as they are at risk of sudden failure from chloride stress corrosion cracking.
So heating up tap water, not good. Lowering the pH of water containing chloride also not good.
[SIZE=large]Chloride Attack on Stainless Steels[/SIZE]
[SIZE=large]Chloride-induced corrosion is not bulk corrosion. We are all familiar with one of the most common forms of bulk corrosion: rust. When iron rusts, the attack is fairly uniform over the surface exposed to the corrosive environment. Chloride attack of stainless steel is exactly the opposite crevices and pits form and grow perpendicularly to the surface being attacked, rather than spreading out evenly as rust does. Some areas may appear essentially untouched by the corrosion, while others will be severely attacked. This means that thicker tubes and pipes will not necessarily last much longer than thin ones before failing due to chloride induced corrosion.[/SIZE]
[SIZE=large]This is an example of pitting:[/SIZE]
[SIZE=large]Stainless steels have excellent corrosion resistance. Water supplies will usually have chlorine or hydrochloric acid added to prevent bacterial growth, it is important to use a material that will resist corrosion by such harsh chemicals. 316 stainless is highly effective in resisting this corrosion.[/SIZE]
[SIZE=large]Stainless steel dissolves very slowly in water, even “RO” (reverse osmosis) water, so only a very small amount of chemical compound elements are added to the water. Using plastic, copper, or iron allows all kinds of unknowns to be added to the water. Plasticiser, from certain plastics, can be leached into the water system, especially when aggressive RO water is used.[/SIZE]
[SIZE=large]Stainless steel is a very clean material and can be sanitised easily. If dead spaces are minimized and surfaces polished to eliminate crevices and pits, bacteria growth is minimized. This is especially true when the piping system is flushed or has continuous water circulation at velocities high enough to cause turbulent flow. Turbulent flow is important because the turbulence creates a scouring of the pipe surface. Low flow or laminar flow leaves a stagnant film of water next to the pipe surface and a biofilm can form.[/SIZE]
Chloride.
The guidelines allow for the presence, but assume that the surface has been passivated. In alkaline environments (pH 7) chloride levels can be tolerated. Higher temperatures over 60 degrees C are not recommended for 304 and 316 as they are at risk of sudden failure from chloride stress corrosion cracking.
So heating up tap water, not good. Lowering the pH of water containing chloride also not good.
[SIZE=large]Chloride Attack on Stainless Steels[/SIZE]
[SIZE=large]Chloride-induced corrosion is not bulk corrosion. We are all familiar with one of the most common forms of bulk corrosion: rust. When iron rusts, the attack is fairly uniform over the surface exposed to the corrosive environment. Chloride attack of stainless steel is exactly the opposite crevices and pits form and grow perpendicularly to the surface being attacked, rather than spreading out evenly as rust does. Some areas may appear essentially untouched by the corrosion, while others will be severely attacked. This means that thicker tubes and pipes will not necessarily last much longer than thin ones before failing due to chloride induced corrosion.[/SIZE]
[SIZE=large]This is an example of pitting:[/SIZE]
[SIZE=large]Stainless steels have excellent corrosion resistance. Water supplies will usually have chlorine or hydrochloric acid added to prevent bacterial growth, it is important to use a material that will resist corrosion by such harsh chemicals. 316 stainless is highly effective in resisting this corrosion.[/SIZE]
[SIZE=large]Stainless steel dissolves very slowly in water, even “RO” (reverse osmosis) water, so only a very small amount of chemical compound elements are added to the water. Using plastic, copper, or iron allows all kinds of unknowns to be added to the water. Plasticiser, from certain plastics, can be leached into the water system, especially when aggressive RO water is used.[/SIZE]
[SIZE=large]Stainless steel is a very clean material and can be sanitised easily. If dead spaces are minimized and surfaces polished to eliminate crevices and pits, bacteria growth is minimized. This is especially true when the piping system is flushed or has continuous water circulation at velocities high enough to cause turbulent flow. Turbulent flow is important because the turbulence creates a scouring of the pipe surface. Low flow or laminar flow leaves a stagnant film of water next to the pipe surface and a biofilm can form.[/SIZE]
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