How do I know if "stainless steel" is really STAINLESS STEEL

[iamwhatiam52]

Many items sold for our tanks are described as stainless steel (Rio coral cutters, Marlin 24" scissors, various tongs etc) but rust after use.

There are some things that DO NOT RUST, like even the spring on the same Rio clippers.

How can we tell if something is truly rust proof?



I posted this on the DIY forum because the tinkerers and inventors here seem to know the most about materials.

 

[WI reefer55]

interested my self I know alot of stuff just has a coating

 

[reefvilla]

For one, a magnet will not cling to it.

I'm also thinking that the "quality" is not there on some of this chinese or whatever equipment..

 

[stugray]

"For one, a magnet will not cling to it"

That is what I was going to say. However, there are a very few stainless steels that are still magnetic, but it is hard to find.

Stu

 

[Acrylics]

It's been my experience that most, if not all stainless steels will corrode over time. That said, 316 stainless is very good. 18-8 stainless is not as good, but IME most parts made from "stainless steel" will be 18-8 (AKA 304 stainless)

James

 

[cmcgill]

All I know is that SS comes in various grades, similar to gold I guess. The better grade of SS you have the less rust.

 

[EnderG60]

if you paid WAAAAAAAAY to much for it, then its really stainless.

 

[iamwhatiam52]

For one, a magnet will not cling to it.

Yes, in general this is the case, but a powerful magnet will stick weakly to some types. Are these types inferior in resistance to rust?

It's been my experience that most, if not all stainless steels will corrode over time. That said, 316 stainless is very good. 18-8 stainless is not as good, but IME most parts made from "stainless steel" will be 18-8 (AKA 304 stainless)
James

This is the kind of information I was looking for.
I would bet most manufacturers do not supply the grade used in their product information, so we can assume the worst.

if you paid WAAAAAAAAY to much for it, then its really stainless.

I don't mind if the quality is there, but we pay WAAAAAAAAAAY too much for lots of stuff supplied for this hobby that is just crap.

 

[Acrylics]

I would bet most manufacturers do not supply the grade used in their product information, so we can assume the worst.

If you're buying hardware and it's 316, it's usually stamped "316" on it. Every 316 bolt, nut, machine screw, washer, etc., that I keep in stock is stamped as such.
If no mention is made about what grade, yep - you can just about count on it being 18-8/304

James

 

[maynardjames]

304sst is slightly magnetic & will rust over time. 316sst is not magnetic at all, & will not rust. i work at a large machine shop, and we have 316 that has been sitting outside for 8 to 10 years & still has no rust. not sure if it will over longer periods of time or not. not sure what most aquarium tools are made of. but you can find lots of stainless steel that will rust, mainly the 304 grade which lots of products are made from due to cost

 

[schnitm]

One of my other hobbies is sailing. 316's the stuff for saltwater sailboats, although a lot of hardware is still 304. Walk through a marina and you'll see rust stains on the decks around hardware made from 304. You won't see that with 316, but you still can get a bit of spotting on 316.

316's used for surgical tools. Blood is nasty corrosive stuff!

 

[iamwhatiam52]

316 stainless is very good.

316sst is not magnetic at all, & will not rust.

316's the stuff for saltwater sailboats.
316's used for surgical tools. Blood is nasty corrosive stuff!

So 316 is the good stuff!

I will look for it when buying tools and parts.

 

[solitude127]

When I went to buy my Dive knife, the salesman was selling me stainles steel knife. When he was explaining it to me he said that it's not "stainless" it just means that it stains less than regular metal.

 

[Luckless]

Stainless steel does not really do well with salt water, especially if left submerged. The problem is that the 'stainless' property of it comes from a layer of chromium oxide that forms. If removed form an oxygen rich environment, then this thin protective layer can no longer form properly, and you'll get very nasty pinhole corrosion.

The key is to use proper care for your tools. After you are done using them around salt water you rinse in clean water, and dry them.

As far as testing, there are no real reliable ways to do this at home short of direct testing. Your best bet is to only buy from reliable companies that mark their metals with the grade of stainless. Things like if it is magnetic or not are a poor indicator.

 

[mscarpena]

Stainless steel does not really do well with salt water, especially if left submerged. The problem is that the 'stainless' property of it comes from a layer of chromium oxide that forms. If removed form an oxygen rich environment, then this thin protective layer can no longer form properly, and you'll get very nasty pinhole corrosion.

The key is to use proper care for your tools. After you are done using them around salt water you rinse in clean water, and dry them.

As far as testing, there are no real reliable ways to do this at home short of direct testing. Your best bet is to only buy from reliable companies that mark their metals with the grade of stainless. Things like if it is magnetic or not are a poor indicator.

I disagree with that statement. I work for a large cheese manufacturing facility and we have stainless steel fully submerged 100% of the time in 92% brine(saltwater) solution. If it is good quality stainless steel it will not rust. The issue is we buy cheap stainless steel coral fragging tools from Pakistan and not quality made American stainless steel. I would think if you go to a medical supply place and buy the tools that doctors use for surgeries you would get quality stainless steel. Rinsing them off will help, but if it's cheap steel it will rust no matter what.

Also stainless steel is a mixture of 2 metals nickel and chromium. They need to be the proper ratio to prevent rusting and 316 is of good quality and should not rust.

 

[jh2pizza]

You can find cheap stainless a magnet will stick too. All of the NFS stuff we use in our restaurants, we cannot get our magnetic training aids to stick too.

 

[BeanAnimal]

I disagree with that statement. I work for a large cheese manufacturing facility and we have stainless steel fully submerged 100% of the time in 92% brine(saltwater) solution.

SS still rusts. There are a lot of factors that determine how quickly a metal oxidizes. We are talking about the salinity, but other factors like pH, ionic charge of the solution, oxygen level and other chemistry also have an effect. While 316 does much better than 304 and some other alloys, it is still not ideal for marine use. There are other 'better' alloys, but they cost more. A google search of the properties of SS alloys and seawater will yield more engineering and scientific data than anybody would likely care to read.

Also stainless steel is a mixture of 2 metals nickel and chromium. They need to be the proper ratio to prevent rusting and 316 is of good quality and should not rust.

316 is a "family" of stainless steel that consists of many distinct alloys.

The main metal is still Iron (about 70%) mixed with 16% Chromium and 10% Nickel, with some Manganese (2%) and trace amounts of Carbon, Silicone and Phosphorus.

316L is less carbon and 316H has More.

 

[Luckless]

I disagree with that statement. I work for a large cheese manufacturing facility and we have stainless steel fully submerged 100% of the time in 92% brine(saltwater) solution. If it is good quality stainless steel it will not rust. The issue is we buy cheap stainless steel coral fragging tools from Pakistan and not quality made American stainless steel. I would think if you go to a medical supply place and buy the tools that doctors use for surgeries you would get quality stainless steel. Rinsing them off will help, but if it's cheap steel it will rust no matter what.

Also stainless steel is a mixture of 2 metals nickel and chromium. They need to be the proper ratio to prevent rusting and 316 is of good quality and should not rust.

And this equipment is never emptied, cleaned, and maintained? (And if not, can you tell me what brands are made there so I can be sure to never buy them?) There are low abrasion coatings that are often applied to food grade containers that greatly reduce the 'rusting' effect, and it is greatly reduced with proper cleaning methods, but it still doesn't go away completely. (I still have a few scars from when I drew short straw and got to squeeze through inspection ports that were apparently designed for small Asian kids.)

The 316 line/formulas are about the slowest to rust of the commonly used, but stainless steel's protective oxide layer (what keeps it from constantly rusting) is easily washed away compared to Aluminum's oxide layer. This means that if a piece, any piece, remains wet and is not allowed to contact air, then it will eventually begin to react to elements in the water. Why food equipment doesn't rust away is they are drained and cleaned, and thereby allowing the thin oxide layer to reform. The piece will remain untouched to the naked eye provided all this is done before the protective oxide layer is completely dissolved away and damage to the material begins.

 

[Tang Salad]

I've used many kinds of surgical forceps/scissors/tweezers over the years, some of them very high quality, straight from the hospital or medical suppliers. Every single one has developed rust, usually within a few months. I personally do not believe there's such a thing as a stainless steel that will not rust when exposed to both saltwater and air.

That said, I treat my tools lazily and often don't rinse them. But that to me is beside the point; if FW rinsing is absolutely necessary, then you can't really say that the item doesn't rust in saltwater.

 

[Engloid]

304sst is slightly magnetic & will rust over time. 316sst is not magnetic at all, & will not rust. i work at a large machine shop, and we have 316 that has been sitting outside for 8 to 10 years & still has no rust. not sure if it will over longer periods of time or not. not sure what most aquarium tools are made of. but you can find lots of stainless steel that will rust, mainly the 304 grade which lots of products are made from due to cost

I've been in the welding and metal fabrication business for over 20 years...and I would have to agree with the above statement. Sure, there's better metals that will resist corrosion better, such as 254SMO (AL6XN), but I doubt you'll find the things you want in that type of metal. For most purposes, items you will buy that just say they are stainless, will be 304. 316 does have a higher corrosion resistance, and is also relatively common, as opposed to things like 254SMO.

An example of real world difference in 304 and 316: I worked at a mayonnaise plant for a while. ALL the piping was made out of 316. They actually banned 304 from the site, because one of the main ingredients in mayo is vinegar, which would eat through 304.

I would be very surprised if you could go into your local hardware store and find bolts in any type of stainless other than 304 or 316.