MartinLe
Civil/Environmental
- Oct 12, 2012
- 394
The steel type 1.4571 / (X6CrNiMoTi17-12-2, ASTM: more or less 316Ti) is commonly used in wastewater applications due to it's good corrosion resistance. An alternative is 1.4404 / (X2CrNiMo17-12-2, ASTM: 316L), which is often said to be inferior. Several steel plants published information materials to the following effect (don't have an english source, so I summarize the key points):
[ul]
[li]Heat treatment of carbon steels would lead to the formation of Chrome-Carbides, these are attack angles for corrosion. Ni and Ti are added to form 1.4571 because these elements form carbides and so prevent the formation of Chrome-Carbides.[/li]
[li][/li]
[li]Current (since a few decades ...) manufacturing technology allows lower carbon content in steel production, so that addition of Ni & Ti are no longer neccessary to have corrosion resistance as good or better as 1.4571 in many cases.[/li]
[li][/li]
[li]1.4571 is clearly superior in applications with T > 350°C[/li]
[/ul]
All information about the comparative corrosion resistance of these steels I found so far comes from steel plants and traders who have a vested interest in pushing 1.4404: 1.4571 is commonly used in Germany, Austria and some eastern European countries, apparantly the rest of the world moved on to 1.4404 et. al. This means german steel traders need to warehouse two types of steel.
On the other hand, the (German) code DWA-M 275 advises 1.4571 for applications where the Chloride concentration is above 100mg/l. There's a simplified formula for effective resistance, to sujmmarize the effect of different alloying agents on corroson resistance: resistance = % Cr + 3.3 % Mo + 16 % N, 1.4571 would have a value of 25. So far I have not been able to hunt down a proper source for this formula, or even a proper guidance of how to use it (resistance value at least X in conditions Y or so).
To sum it up, I'm not at all sure if the widespread use of 1.4571 in wastewater applications is a historic idiosyncrasy (as the steelmakers say) or if there are sound technical reasons. But every once in a while, the topic pops up - when you specify 1.4571 ("because that's what we always use") and the contractor delivers or offers 1.4404 ("because that's what we always use").
I'm also lousy at metallurgy, maybe someone here can shed some light?
[ul]
[li]Heat treatment of carbon steels would lead to the formation of Chrome-Carbides, these are attack angles for corrosion. Ni and Ti are added to form 1.4571 because these elements form carbides and so prevent the formation of Chrome-Carbides.[/li]
[li][/li]
[li]Current (since a few decades ...) manufacturing technology allows lower carbon content in steel production, so that addition of Ni & Ti are no longer neccessary to have corrosion resistance as good or better as 1.4571 in many cases.[/li]
[li][/li]
[li]1.4571 is clearly superior in applications with T > 350°C[/li]
[/ul]
All information about the comparative corrosion resistance of these steels I found so far comes from steel plants and traders who have a vested interest in pushing 1.4404: 1.4571 is commonly used in Germany, Austria and some eastern European countries, apparantly the rest of the world moved on to 1.4404 et. al. This means german steel traders need to warehouse two types of steel.
On the other hand, the (German) code DWA-M 275 advises 1.4571 for applications where the Chloride concentration is above 100mg/l. There's a simplified formula for effective resistance, to sujmmarize the effect of different alloying agents on corroson resistance: resistance = % Cr + 3.3 % Mo + 16 % N, 1.4571 would have a value of 25. So far I have not been able to hunt down a proper source for this formula, or even a proper guidance of how to use it (resistance value at least X in conditions Y or so).
To sum it up, I'm not at all sure if the widespread use of 1.4571 in wastewater applications is a historic idiosyncrasy (as the steelmakers say) or if there are sound technical reasons. But every once in a while, the topic pops up - when you specify 1.4571 ("because that's what we always use") and the contractor delivers or offers 1.4404 ("because that's what we always use").
I'm also lousy at metallurgy, maybe someone here can shed some light?
