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OWB - Open Systems Corrosion Problems!
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Ok, here is the skinny on steels........
Carbon steel is iron based..... Plain and simple. Yes, it will rust... The idea is either a closed system, treated open system, or leave it untreated and just rely on the sheer thickness of the still to give it longevity.....
On stainless however, there are two main types.........
3 series (304, 304L, 316, etc) are NOT iron based and WILL NOT rust or corrode except in the presence of certain strong alkaline chemicals...... But, the total lack of iron means that this type of stainless is not very ductile and can be prone to cracking... Plus it's expensive... 304 is considered Food grade, and 316 is considered medical grade.......
4 series (409, 410, 430, 490 etc) are iron based with a lot of nickel to make it shiny..... In some cases, cheap "409" might just be steel with nickel plating to make it shiny.... The iron makes it cheaper, and adds ductility to keep it from cracking.. Unfortunately, most "stainless" OWB's, as well as most car exhaust systems are made of this crap.. In fact, in car exhaust systems, the 4 series stainless will rot out in 4-5 years where aluminized steel (steel that's been plated with aluminum coating) will last a good 10 years and cost much less..... Another tidbit, 4 series stainless is magnetic (due to the iron content) and therefore, at the scrap yard, you wont' get one penny more than for rusty ol' tin.......
Carbon steel is iron based..... Plain and simple. Yes, it will rust... The idea is either a closed system, treated open system, or leave it untreated and just rely on the sheer thickness of the still to give it longevity.....
On stainless however, there are two main types.........
3 series (304, 304L, 316, etc) are NOT iron based and WILL NOT rust or corrode except in the presence of certain strong alkaline chemicals...... But, the total lack of iron means that this type of stainless is not very ductile and can be prone to cracking... Plus it's expensive... 304 is considered Food grade, and 316 is considered medical grade.......
4 series (409, 410, 430, 490 etc) are iron based with a lot of nickel to make it shiny..... In some cases, cheap "409" might just be steel with nickel plating to make it shiny.... The iron makes it cheaper, and adds ductility to keep it from cracking.. Unfortunately, most "stainless" OWB's, as well as most car exhaust systems are made of this crap.. In fact, in car exhaust systems, the 4 series stainless will rot out in 4-5 years where aluminized steel (steel that's been plated with aluminum coating) will last a good 10 years and cost much less..... Another tidbit, 4 series stainless is magnetic (due to the iron content) and therefore, at the scrap yard, you wont' get one penny more than for rusty ol' tin.......
I think you are right about the basic properties, but I have never seen "iron" used as the word to describe the difference in stainless grades. I guess it can be used, but it confuses me because all stainless steels and regular steels are mostly "iron" in the sense that steel is iron (FE). Are we talking more about the amount of carbon it contains?
Here is a basic listing of grades:
http://en.wikipedia.org/wiki/Stainless_steel#Stainless_steel_grades
It's really high tech stuff - a LOT of science in it!
Deere is also right about regular alumized steel....it is what they use for cars, building roofs (metal) and siding and many other such uses and lasts for decades. It is good for fairly high temps, too. I think they use it to make furnaces in some cases.
Either way, the point is the same.
You cannot simply substitute stainless or a better grade of steel for lack of engineering and design. That is why you often hear me ask how many engineers some of these fabricators have on staff.
Here is a basic listing of grades:
http://en.wikipedia.org/wiki/Stainless_steel#Stainless_steel_grades
It's really high tech stuff - a LOT of science in it!
Deere is also right about regular alumized steel....it is what they use for cars, building roofs (metal) and siding and many other such uses and lasts for decades. It is good for fairly high temps, too. I think they use it to make furnaces in some cases.
Either way, the point is the same.
You cannot simply substitute stainless or a better grade of steel for lack of engineering and design. That is why you often hear me ask how many engineers some of these fabricators have on staff.
More info on stainless than you can handle at this link
(broken link removed to http://www.alleghenyludlum.com/pages/products/products.asp)
I commonly encounter the following failures in all types, stainless or not.
Chemically induced corrosion from poor water treatment, cleaning or installation practices. In a lot of cases the chemical shipped by the manufacturer is a very basic nitrite based composition that has some oxygen inhibitors in it. It doesn't address all the things that can be, and often are encountered in various locations. The only sure fire way to make certain you have what is needed is to find a good independent lab and send in a clean sample. The second thing is a failure on the part of the installer to chemically clean the boiler BEFORE adding the treatment shipped with it. In many cases a lot of junk is in the system from fabricating and cutting oils, soldering flux (that's a biggy) and general debris that can interact with the suggested water treatment and render it useless.
Electrical or stray voltage corrosion (electrolysis) caused by poor wiring, a bad neutral connection somewhere in the system, improper or no ground. This can take out about any kind of steel you can name, stainless or not.
Under deposit corrosion. This happens when deposits form through use and "seal" an area inside the unit from the water. Corrosion then starts at that point. You will commonly see this occur on the bottom of the boiler where things tend to settle or under an improperly cleaned weld.
Once in a great while I'll see dissimilar metal corrosion but it's pretty rare from what I have seen.. This happens when a steel boiler gets a different metal directly connected to it. Such as a copper fitting screwed directly on the boiler. Personally I'd rather see steel pipe on all boiler at least for a short distance. It acts as a nice sacrificial anode for the whole system. Cheaper to replace a section of pipe than the entire boiler. We do all of our near boiler piping with iron pipe and have never encountered a problem. We also use iron circs on all systems be they open, closed, stainless or mild steel.
So,
Clean your boiler before adding the treatment chemical
Always install a ground rod and bond it directly to the boiler itself
Check the water at LEAST once per season through the services of a good lab. (It's not just about the PH level)
Drain and flush an open system every couple years to limit crud buildup.
Forget using antifreeze in an open system. When it's exposed to air it fails rather quickly and can turn very acidic in some cases.
(broken link removed to http://www.alleghenyludlum.com/pages/products/products.asp)
I commonly encounter the following failures in all types, stainless or not.
Chemically induced corrosion from poor water treatment, cleaning or installation practices. In a lot of cases the chemical shipped by the manufacturer is a very basic nitrite based composition that has some oxygen inhibitors in it. It doesn't address all the things that can be, and often are encountered in various locations. The only sure fire way to make certain you have what is needed is to find a good independent lab and send in a clean sample. The second thing is a failure on the part of the installer to chemically clean the boiler BEFORE adding the treatment shipped with it. In many cases a lot of junk is in the system from fabricating and cutting oils, soldering flux (that's a biggy) and general debris that can interact with the suggested water treatment and render it useless.
Electrical or stray voltage corrosion (electrolysis) caused by poor wiring, a bad neutral connection somewhere in the system, improper or no ground. This can take out about any kind of steel you can name, stainless or not.
Under deposit corrosion. This happens when deposits form through use and "seal" an area inside the unit from the water. Corrosion then starts at that point. You will commonly see this occur on the bottom of the boiler where things tend to settle or under an improperly cleaned weld.
Once in a great while I'll see dissimilar metal corrosion but it's pretty rare from what I have seen.. This happens when a steel boiler gets a different metal directly connected to it. Such as a copper fitting screwed directly on the boiler. Personally I'd rather see steel pipe on all boiler at least for a short distance. It acts as a nice sacrificial anode for the whole system. Cheaper to replace a section of pipe than the entire boiler. We do all of our near boiler piping with iron pipe and have never encountered a problem. We also use iron circs on all systems be they open, closed, stainless or mild steel.
So,
Clean your boiler before adding the treatment chemical
Always install a ground rod and bond it directly to the boiler itself
Check the water at LEAST once per season through the services of a good lab. (It's not just about the PH level)
Drain and flush an open system every couple years to limit crud buildup.
Forget using antifreeze in an open system. When it's exposed to air it fails rather quickly and can turn very acidic in some cases.
Notice on both those links that 400 series is listed as "Ferrous" or "Ferritic"..... i.e of iron (and hence why they are magnetic)
Notice on 300 series there is no mention of iron???
I rest my case......
Notice on 300 series there is no mention of iron???
I rest my case......
Iron can take quite a number of forms with different properties, including magnetism or lack thereof. The terms ferritic, martensitic, austenitic, etc. refer to the primary configuration of the iron atoms in whatever different alloying elements are in the metal at hand. Chrome and nickel mostly in "stainless" steels. A lot of alloy descriptions will list the alloying elements and the rest is given as iron. The notation is added at the end sometimes as " Fe balance".
Even the 300 series is more than 50% iron.
Stainless Steel is a marketing term, not an engineer's term. Each alloy has its place but none of them is completely noncorrosive under every condition.
Correct..... No need to give credit to me.... Just trying to give a simple explanation to the head scratching going on over stainless boilers and such.....
True, all steel contains iron. I guess when I said iron, I meant to say iron in it's typical form....... But, my description does well enough to explain what I was trying to get across....
True, all steel contains iron. I guess when I said iron, I meant to say iron in it's typical form....... But, my description does well enough to explain what I was trying to get across....
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