Corrosion of SS316 Material

The most likely cause is a combination of the chemical processes used and the abrasiveness of the particulates in the paper slurry. It is difficult to comment further without some hint as to the chemicals involved and their strengths.

This may help:

http://www.coleparmer.com/techinfo/chemcomp.asp

hello sir thanks for your quick response. I would like to mention you that the equipment we are using is control equipment and not at all in the direct contact with paper slurry. only in case of any leackage some part can be exposed to the slurry. but equipment is corroding at a even rate through out its surface and the same equipment is used in different location using same process and chemicals but experiencing no such problem.

_{["Sir"? How abstruse!]}

Then it is possibly a combination of humidity, temperature and the agressive nature of some substances in the vapour phase. What is being 'given off' by the process? How does it smell? What is the chemistry of the process?

If you're making paper, I'm betting there's sulfuric acid in there somewhere. Sulfuric acid is hard on 316, but if you also have just a few stray chloride ions (impure water or ?) then it just eats away, sometimes very quickly. The other thing you have to watch for is whether the 316 has been welded; if so you have chromium precipitation in the HAZ which really don't like sulfuric acid. You might have to use Inconel or Carpenter metal.

Another thing in today's global market place. it is imperative in situations like this to check Mill Test Reports and possibly do a Positive Material Identification Test to assure both plants are truly using SS316. Many reports of bogus or mislabeled metals are being passed around, especially SS and P series metals.

Have you ruled out the possibility of a galvanic couple on your corroding piece? If the environment is the same, and the process is the same but only one piece is corroding, then there must be something unique about this one piece.

Sir:

Follow that thought with isolation of any possible need to separately ground/isolate, insulate any connected electrical powered equipment, pumps, controls, mounted lighting or like source points of induced or "leakage" current...minor weak short......

I've observed this type corrosion when a down hole motor well pump pipe was use to ground (earth) an isolated/self generated power supply....no commercial power available. 316SS would slowed but not stopped this electrical decomposition

As water "drew down" in well by pump rate...corrosion occurred at changing surface level ground water....ate through galvanized two inch pipe....multiple places.

A minor current will do steady damage.

MR. GUY

I have been informed by many specialist that SS316 will not corrode and suggested use it of it in some places where materials are prone to corrosion.From going through various postings SS316 also can corrode.Can some body which grade of ss resists corrosion?

http://www.coleparmer.com/techinfo/chemcomp.asp

<....SS316 will not corrode....>

Not many things will withstand the 'Green Death' test: a mixture of concentrated nitric and sulphuric acids with ferric sulphate dissolved in it, 90degC........

PW,

Never heard it called "green death" but that's appropriate. I've seen machine shops dissolve broken taps with that stuff.

Hi.

Do you know for sure that we are really talking about SS316? Because SS316 is acid grade stainless steel!

Issa

Hi all,

All engineering alloys can corrode in the appropriate conditions. There are no engineering alloy resistant to all environments.

SS stand corrosion resistant as far as the environment is enough oxidant to form quickly a new oxide protective layer (passivation). In reducing environments all SS can corrode. Sulphuric acid is neither good oxidizer nor great reducer, and in the concentrations expectables in environment must not corrode 316SS by itself.

I'm not familiar with the paper industry, so I'm not able to evaluate completely the problem as I don't know much about the exact chemicals involved. You have to look not only to the climate conditions (even in 200 km the conditions can be very different) but for another industries near the plants which can have emissions with make the environment different.

If the corrosion is rather uniform on all the surface, the reason is obviously due to reducing environment. If the type of corrosion were different to uniform, like crevice corrosion, pitting, etc there could be a lot of different reasons for it.

Anyway, if you want to know more about the behaviour of SS316 you can download many free information from this link: http://www.euro-inox.org

http://www.corrosionist.com/

I use to work in Photofinishing and 316 does not stand up to acids very long. We used titanium which never had a problem with any chemical.

Question for PW Slack, you have mentioned before,GREEN Death regarding a question I had concerning corrosion testing.Where can I find data on this?(i.e. quanity & mixing procedure)

As stated: "a mixture of concentrated nitric and sulphuric acids with ferric sulphate dissolved in it, 90degC".

only the glycerine is missing for a nitroglycerine explosion!

issa

I had always thought 316SS was pretty good around acids till I visited a cogeneration power plant near the seashore. They were burning high sulfur waste oil and 316SS was corroding in the yard OUTSIDE the plant. When I looked into it, I figured the likely trigger was the salt air (-Cl) since NOx emissions were very low. I tried to duplicate the conditions and got the 316 to visibly corrode within hours! This was good quality 316 (pedigree and all that).

In replacing the corroding parts, I eventually found I had to minimize weld heats since I was getting chromium precipitates in the HAZ. After several tries, I gave up, machined a tube stub and used a Carpenter 20 tube fitting (now there's some $!).

Hoke, by the way, used to make one of those little sliding cardboard dohickeys that would tell you about corrosion of various materials under various conditions.

An alloy protects itself by forming a passive oxide film on its surface similar to what happens to steel when it rusts. The oxide (Iron) that forms on steel is not very well attached. Stainless steel on the other hand will form an oxide on its surface, not iron but rather chrome (Cr2O3) and depending on the trace alloying elements (aluminum) the oxide film at the surface will be a hybrid oxide known as a Spinal. Now take into consideration that you need the presence of oxygen in order to form this "oxide" film and if the alloy is exposed to a non-oxidizing (also known as a reducing) environment, the film will not be able to replenish itself. Generally wear and thermal fatigue are the culprits that compromise the film. The answer is an alloy that contains more chrome. The key to this is producing a surface either by spraying or welding whose Chrome content is above 30%. Molly is added to alloys to try to prevent pitting corrosion that begins once the oxide film has been compromised by strengthening the resistance of precipitation at the grain boundaries of the alloy. As you can see this becomes a vicious cycle. The answer lyes not in alloy development but rather in metal composite coatings. Here no grain boundaries exist and the structure of the deposit controls the mechanism of corrosion. Pretty cool stuff. Don't forget that sulphur loves nickel and will readily form nickel sulfides, not good.

Have you checked for chlorine? it is ussed heavily in some paper making processes. it is highly corrosive to stainless steels.

Ah, of course. Bleach. I had forgotten.

Hi, Passivation is normally used to protect 316. Had this been done in both cases?...Clint