Sciencemadness Discussion Board - Stainless Steel resistance to acids

Stainless Steel resistance to acids

RogueRose - 12-11-2015 at 21:26

I am wondering if SS can be used as a vessel when doing reactions with say sulfuric, HCL or nitric acid. Could H2SO4 and KNO3 be safely mixed in a vessel like this and used as a distillation vessel?

Hawkguy - 12-11-2015 at 21:27

nope. you need glass, the stuff wont hold acids for too long before it heats up and dissolves.

j_sum1 - 12-11-2015 at 21:33

Chlorides (ie, HCl) lead to pitting of SS. Little holes form followed by catastrophic failure.
Sulfuric, you might get away with if it was dilute. It can be transported in bulk in mild steel rail cars at high concentrations. It won't play nice with the chromium of your SS, but at lower concentrations you might be ok. Just wash between uses.
Nitric -- ask an expert. But I suspect that it will attack your SS. Not in the same manner as HCl but enough to be a problem.

BromicAcid - 13-11-2015 at 04:28

There are multiple grades of stainless steel for a reason, each has their own resistance and niche applications. It's easy enough to search "stainless steel chemical resistance" in Google and find exactly what you are looking for. Even for things that say they are not recommended however sometimes the rate of dissolution is only a few mm per year, low enough to consider it a one use (or infrequent use) vessel. Some charts also give resistance at different temperatures, it might take some digging but it's worth looking up on your own since it really helps to build a knowledge base. However, at the temperatures employed in your distillation I would have to say I am doubtful of sufficient resistance of the stainless steel to attack, and of course the consequence of a catastrophic failure would lead me to dissuade you from just trying it and seeing what happens.

Upsilon - 13-11-2015 at 06:11

SS is very poorly resistant to acids. It is basically carbon steel (which is mostly Fe and is very readily attacked by acids) combined with a small amount of chromium (which is also poorly resistant to acids).

Praxichys - 13-11-2015 at 06:23

A long time ago I made the mistake of cleaning limescale off various ceramic plates with a weak HCl solution in a stainless steel sink. The sink is permanently etched. Luckily it was an already damaged sink that came with the foreclosed house I bought.

AJKOER - 13-11-2015 at 08:22

Yes, I suspect even weak HCl (or other weak acid) would damage "stainless steel" in the presence of ample air/O2 and a good electrolyte (like NaCl, or in this case, FeCl2, formed slowly, in a small amount, by the action of the dilute HCl ) with time.

I suspect the underlying reaction is electrochemical in nature (metal-air batteries, see, for example, discussion and at https://en.m.wikipedia.org/wiki/Metal%E2%80%93air_electroche... ), which can also display a waiting (induction) period.

[Edited on 13-11-2015 by AJKOER]

feacetech - 15-11-2015 at 17:29

Quote: Originally posted by j_sum1

Chlorides (ie, HCl) lead to pitting of SS. Little holes form followed by catastrophic failure.
Sulfuric, you might get away with if it was dilute. It can be transported in bulk in mild steel rail cars at high concentrations. It won't play nice with the chromium of your SS, but at lower concentrations you might be ok. Just wash between uses.
Nitric -- ask an expert. But I suspect that it will attack your SS. Not in the same manner as HCl but enough to be a problem.

H2SO4 is more aggressive when diluted

Mild steel tanks used to hold sulphuric acid usually only get accelerated corrosion at the interface due to atmospheric dilution we have too cycle our acid tank regularly to prevent this from happening.

Battery acid on the skin will burn almost instantly

I have spilt 98% on myself and been able to wash it off without a burn

careysub - 15-11-2015 at 23:35

I researched this topic recently.

First, when discussing "stainless steel" you need to specify type.

The most common types are:
304 (aka 18/8, A2) which contains approx. 18% chromium and 8% nickel.
316 (aka 18/10, A4, marine grade stainless) which contains approx. 18% chromium and 10% nickel, which is more corrosion resistant.

Cookware is readily available in 18/8 (304); 18/10 is also available, but I understand that cookware labeling is lax and 8.5% nickel and above can be labeled 18/10.

HCl is incompatible with all steels. Period. All concentrations of hydrochloric acid will attack stainless steels since the acid readily destroys their passivity. In hot moderately strong solutions the alloys are rapidly attacked with evolution of hydrogen. In cold solution the attack is also too rapid to permit use of stainless steels. Mixtures containing small amounts of hydrochloric acid may cause pitting.

H2SO4: Type 316 stainless steel gives useful service at room temp. in sulfuric acid of concentrations lower than 20 per cent and higher than 85 per cent. Between 20 and 80 per cent acid concentration it is subject to rapid attack. At elevated temperatures the corrosion rate increases and even type 316 is not very useful in the acid alone except in very low acid concentrations. However, additions of ferric sulfate, copper sulfate, nitric acid, chromic acid, or oxygen greatly reduce attack by sulfuric acid , thus, nitration reactions involving mixed acid are accomplished in stainless steel equipment. Mixed acid is also stored and shipped in stainless steel containers.

Nitric acid: Both 304 and 316 stainless steels have very good resistance to corrosion by nitric acid in all concentrations and practically all temperatures. This corrosion resistance, which is due to the passivating action of nitric acid.*

Phosphoric acid: Good resistance of stainless steels to practically all concentrations of phosphoric acid at moderate temperatures.

Organic acids: The number of instances where stainless steels are satisfactory for organic acids far outnumber the few cases where they fail. Formic acid is a good reducing agent and is capable of causing severe corrosion of the straight 18-8 stain-
less steels when hot, 316 is resistant.

Weak base attack: Both 304 and 316 stainless steels have excellent resistance to corrosion by weak bases such as ammonium hydroxide and organic compounds like aniline, pyridine, and the aliphatic amines.

Strong base attack: The 18-8 steels usually show very slight attack in solutions up to 50 per cent NaOH concentration at temperatures up to about 220 F. In higher concentrations and temperatures corrosion rates are likely to be appreciable - however even saturate NaOH at boiling only corrodes 304 at 5 microinches per hour, molten NaOH corrodes at about the same rate.

Organic compounds give rise to no corrosion problems with the stainless steels except in a few specific cases involving organic acids and organic halides. The pure
halogenated organic compounds will not attack the stainless steels but upon standing in the presence of water a halide may hydrolyze to yield the corresponding halogen acid which can cause serious pitting.

*A phenomenon that gives rise to the "iron nerve" travelling reaction wave demonstration.

[Edited on 16-11-2015 by careysub]

careysub - 15-11-2015 at 23:43

Quote: Originally posted by Upsilon

SS is very poorly resistant to acids. It is basically carbon steel (which is mostly Fe and is very readily attacked by acids) combined with a small amount of chromium (which is also poorly resistant to acids).

See my long post: halogen acids are right out, and sulfuric acid in the range 20-85% cannot be used (but oddly weaker and stronger are OK) unless a passivating agent is added. Nitric, phosphoric and organic acids are fine.

Calling stainless steel "basically carbon steel" is a confusing use of terminology. "Carbon steel" means "not stainless (or other alloy) steel".

[Edited on 16-11-2015 by careysub]

aga - 16-11-2015 at 00:54

Quote:

Stainless Steel resistance to acids

Even a drunkard can find a reference with just a few seconds googling "stanless steel acid resistance" :-

http://www.engineeringtoolbox.com/metal-corrosion-resistance...

[Edited on 16-11-2015 by aga]

careysub - 16-11-2015 at 07:45

Quote: Originally posted by aga

Quote:

Stainless Steel resistance to acids

Yes, but the data in the table is too "high level" to really be good guidance here. For example according to the table HCl and H2SO4 have equivalent ratings, but actually they are way different in behavior. It simply states that sulfuric acid and SS is "not usable" which is not exactly true, but requires some explanation.

MrHomeScientist - 16-11-2015 at 08:37

Quote: Originally posted by careysub

*A phenomenon that gives rise to the "iron nerve" travelling reaction wave demonstration.

Do you have a reference or link to this demonstration? I tried searching but only turned up a mountain of medical articles. Great information, by the way.

careysub - 16-11-2015 at 12:22

Quote: Originally posted by MrHomeScientist

Quote: Originally posted by careysub

*A phenomenon that gives rise to the "iron nerve" travelling reaction wave demonstration.

Do you have a reference or link to this demonstration? I tried searching but only turned up a mountain of medical articles. Great information, by the way.

Thanks.

Here are my notes on the "iron nerve":

“Iron Nerve” Reaction
"Iron nerve"- the periodic dissolution of an iron wire in nitric acid
W. Ostwald 1910, R. S. Lillie ∼ 1920: iron wire in nitric acid bath; passivation film; local scratch of the film leads to an active wave that propagates over the Fe wire while a repassivation front follows it simultaneously; similar to propagation in nerves.
R. S. Lillie: J. Gen. Physiol., 3, 107–128 (1920), http://www.ncbi.nlm.nih. gov./pmc/articles/PMC2140407/;
J. Gen. Physiol., 3, 129–143 (1920), http://jgp.rupress. org/content/3/2/129.abstract]

feacetech - 16-11-2015 at 12:53

Quote: Originally posted by careysub

However, additions of ferric sulfate, copper sulfate, nitric acid, chromic acid, or oxygen greatly reduce attack by sulfuric acid , thus, nitration reactions involving mixed acid are accomplished in stainless steel equipment. Mixed acid is also stored and shipped in stainless steel containers.
[Edited on 16-11-2015 by careysub]

that is good stuff is mild steel resistant to corrosion from mixed acid the same as it is to conc H2SO4, I would love to put mixed acid through my mild steel tanks and lines but at a guess I would of thought it wouldn't of been a good idea, maybe I was wrong

316 is resistant to 1000ppm Chloride while 304 can only take 100ppm, hence its dislike for HCl, even 316 exposed to see air will start to discolour and pit if its not washed.

[Edited on 16-11-2015 by feacetech]

careysub - 16-11-2015 at 14:07

BTW - I was motivated to research this topic after I recently attempted to concentrate a solution containing HCl in a new enameled steel pot. The enamel is immune to HCl, so what could go wrong?

Well, it seems that even a new apparently defect-free enameled coating is not completely pore free. So after a couple of hours the acid had managed to turn microscopic pores into not-at-all microscopic pits, and thence to an outlet for my boiling acid solution. I was doing this on my patio, so the only damage was to a strip of grass.

zed - 17-11-2015 at 18:08

There are "Stainless Steels" that have pretty good acid resistance. Only problem is, the best of them, they might not technically..... be "Steels"

Oh, they look like Stainless Steels, but they have little or no Iron. Full of other interesting metals. Alloys like Hasteloy C, get pretty good reviews.

If you need to use Heat and Pressure, and you need corrosion resistance, most likely you can find a useful alloy vessel. I've never seen such a vessel, dirt cheap. But, I'm still hoping.

https://www.haynesintl.com/pdf/h2019.pdf

cyanureeves - 17-11-2015 at 18:33

there used to be a video on youtube years back of an arabic guy distilling nitric acid with a stainless steel tank with an inverted cone lid.the tank had sulfuric acid and nitrate salts and ice was placed on the lid to cool down the distillate.the acid would pour down the cone onto a cup with a pipe that led to a spiral track that was welded to the inside of the tank.the track looked like a worm screw and at the lower end of the worm screw track was a hole where nitric acid dripped happily.the video was done like a silent movie type of film with out the captions.i assumed it was stainless steel or aluminum.it was the first chemistry video where i first read the comment"holy terrorist"!