9 replies to this topic

[trilok_sontakke]

DEAR FRIENDS

ONE OF OUR REACTOR GOT CORRODED HEAVILY BY ACETIC ACID AT TEMP 100 DEG C. I WONDER THAT SS 316 HAS GOOD CORROSION RESISTANCE FOR ACETIC ACID THEN HOW THIS HAPPENED.

I HAVE SOME QUERRIES REGARDING THIS

1. WHAT IS SS 316 L, IS IT DIFFERENT FROM SS 316 AND IN WHAT RESPECT?
2.WHAT IS CARPENTER STEEL?


THANKS
TRILOK

[siretb]

316L differs from 316 chiefly by its carbon content. 316L has a lower carbon content (say 0.03% or less) whereas 316 may have 0.08%C.
316L is softer than 316.
As for acetic corrosion, both should behave in a similar way.
Carpenter is a trade name

[trilok_sontakke]

thanks for reply

I learnt that our system has 30% acetic anhydried.So i think that corrosion is because of acetic acid+acetic anhydried combined.what will be suitable MOC for this system??.

[joerd]

If you look in Perry's table 23-2, SS316 looks a good choice. So it must be some other component in your mixture that gives the corrosion (chloride, hydrogen, ...)

[trilok_sontakke]

i learnt that we have acetic anhydried present in the system upto 32%.will it accelerate the rate of corrosion??
does anyone have the data regarding corrosion by acetic acid in presence of impurities or other chemicals like acetic anhydried ??

thanks
Trilok

[paulo]

Hi

The company I worked to many years ago had a book named Corrosion Data Survey. It was a fantastic book, with a lot of corrosion tables. I cannot remember the publisher.

Hi

The company I worked to many years ago had a book named Corrosion Data Survey. It was a fantastic book, with a lot of corrosion tables. I cannot remember the publisher.

If you are manufacturing chlorinated acetic acid then both acetic acid and acetic anhydride are mixed together and heated upto 100 deg C. We used to use lead bonded reactors for this. Even the pipes were of lead. You should use Sb free chemically pure lead for this. SS316 will not last long. For cold conc Acetic acid Al is good and can be used for storage. Many industries now a days use glass lined reactors for this reaction and they use PTFE lined pipes. We tried graphite but did not get good result as the bonding resin is attached by the organic acids.

[sgkim]

Sontakke:

316SS or 316L SS can be used for most of acetic acid handling vessels since uniform corrosion rates of these in a wide concentration range of acetic acid solution are usually less than 0.0001 mil/year, which means substantially little corrosion. But the corrosion rate on these may vary quite much with respect to the small amount of chemicals like halogens, aldehydes, other low molecular organic acids, etc. Some of corrosion handbooks summarize a broad spectrum of corrosion rates according to the concentration variation of acetic acid and typical impurities

Along with 316 St-steels even Hastelloy(s) or Zr-705 are used for acetic acid reactors for the chemicals contained in the reaction mixture.

Before you check the durability of 316 St-steels against acetic acid solutions, you first have to investigate the type of corrosion. The possibility of stress corrosion cracking(SCC), intergranular corrosion (IGC), pitting corrosion(PC), uniform corrosion(UC), etc. should be issued to investigate the type of corrosion.

Will you please inform us of (1) the ingredients involved and (2) the type of corrosion to discuss more in detail?

sgkim

A specific answer to one of your question, then a couple of general comment.

316L is a specification for a low carbon version of 316. At this point, I don't remember where it came from, orignally - I think it was something in corrosion that was more specific to the higher carbon content. I am 99% sure that it had nothing to do with acetic acid or anything similar. Asa practical matter within the U.S.A., if one orders 316, one is virtually assured that one will get a material which complies to 316L (it apparently isn't worth making separate grades of 316), but if you order 316L you can get the additional paperwork certifying it to be 316L (one could always do an analysis - which doesn't cost all that much, anyhow), but if you had several miles of pipe, etc. it raises the question of does all of the material comply to 316L.

Acetic acid is the base solvent the conversion of p-xylene to terephthalic acid, one of the starting materials for the polyesters (clothing and 2-liter bottles). (This is a huge worldwide industrial process) Other xylene isomers yield other polyesters. Anyhow, for some portions of the plant, titanium is required; the lifetime of 316 would probably be days to weeks. Oxidation of the other isomers also requires titanium. Temperatures run around 150C. In addition to acetic acid and xylene, water, air, and some inorganic catalysts are also present.

A resource I have used over the years for corrosion of various materials is "Corrosion Resistance Tables" by Philp Schweitzer, P.E. The edition I have (3rd) was published 1991 by Marcel Dekker; I don't know if it there is a more current version. This is a 2-volume set (approximately 2500 pages of tables). Incidentally, in it, 316 mostly looks good to excellent for acetic acid (50%, 80%, and glacial), although unsatisfactory for acetic acid vapors. For acetic acid vapors, alloy 20 (also called 20-cb-3) is rated excellent up to 93C. Alloy 20 has about 30-35% nickel, compared to about 10-14% for 316. Alloy 20 also has somewhat higher chrome than 316

DEAR FRIENDS

ONE OF OUR REACTOR GOT CORRODED HEAVILY BY ACETIC ACID AT TEMP 100 DEG C. I WONDER THAT SS 316 HAS GOOD CORROSION RESISTANCE FOR ACETIC ACID THEN HOW THIS HAPPENED.

I HAVE SOME QUERRIES REGARDING THIS

1. WHAT IS SS 316 L, IS IT DIFFERENT FROM SS 316 AND IN WHAT RESPECT?
2.WHAT IS CARPENTER STEEL?


THANKS
TRILOK

[Samir Gupta]

Trilok
Is the process produces acetic acid? In such cases the culprit w.r.t. corrosion is Formic Acid. Even traces of it may cause considerable damage.
Regards
Samir