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Stainless Steel


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#1 chem101

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Posted 17 July 2009 - 03:36 PM

Hi Every One:
why do we use stainless steel in plant? why not carbon steel? how do we conclude that stainless piping should be used where chances of corrosion are very high? I was talking to one of my co-worker. he said that in some of Amine Plants he has been using carbon steel for about five years in same areas, like after the lean rich exchanger, overhead of Amine still., and even the tubes in lean rich exchanger are carbon steel, they are working fine. So why do we use stainless steel. again i know some of you going to say because or corrosion. but here i have a guy who has sold evidence.
thank you very much in advance

#2 SSWBoy

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Posted 17 July 2009 - 06:55 PM

Depending on pressure I believe (off the top of my head) that you can only use CS down to about -20C and LTCS (low temperature) down to -45C beyond this you must use stainless steel.

#3 riven

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Posted 18 July 2009 - 04:32 AM

Check out

http://www.coleparme...fo/chemcomp.asp

Try out some combinations and you will see that different materials are suitable for some materials and not for others. E.g. brass is useless in acetic acid solutions.

#4 Art Montemayor

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Posted 28 July 2009 - 01:50 PM


Chem101:

Let’s keep your argument specifically on the subject of Amine acid gas removal plants and processes. That way we don’t generalize – which is a stupid (in my opinion) way for an engineer to argue or make a case.

In me, you have another “guy” that not only has designed, built, and operated CO2 removal plants using MEA solutions – but I’ve done it with a minimum of stainless steel as material of construction. The only places where I have employed stainless steel is in my steam reboiler tube bundle and in the Rich-Lean MEA heat exchanger tubes. The rest of the plants have been all in carbon steel.

I have worked probably longer than most guys in the business with the Amine acid gas processes – mainly because I’m 72 years old and I started doing that when I was 23 years old – as a young ChE graduate. Therefore, when I take the time out to discuss what I know and what I have done with the amine processes, you should take into consideration that I’m not doing this to impress anybody or go on an ego trip. I simply don’t have time for those types of excursions at my age. I merely wish to share what I know and the knowledge that I’ve picked up along the way.

First of all, be aware of some basic (albeit seldom known) facts:
1. Amines, especially MEA, were first known and used as corrosion inhibitors;
2. Amines, especially MEA, are not corrosive at all. They inhibit corrosion. HOWEVER, the degradation products of amines, especially MEA, are notorious corrosive agents.
3. In my day, we used our common sense in fighting the so-called “corrosiveness” of amines. We removed the corrosive, by-product agents produced by the degeneration of amines. We did this by using Re-distillation Stills. We also employed activated carbon filters to selectively remove corrosive agents in the re-circulated amine solution
4. The weaker the amine solution, the less the degeneration of the amines. Therefore, I always used a 10 – 15% wt. MEA solution in my plants. This immediately curtailed a lot of the corrosiveness in the solution. This allowed me to work with essentially carbon steel construction materials.
5. I always kept reboiler regeneration temperatures as low as I could. This meant operating my reboilers as close to atmospheric pressure as I could. The highest pressure I would tolerate was about 7 to 9 psig in the reboiler vapor space.
6. I always kept my CO2 loading low in my rich solution. This was helped by the low concentration of MEA solution I always used.
7. I always religiously kept a close chemical analysis control on my MEA solution in order to know the moment it reverted to a corrosive state.

With the above criteria, I was always successful in keeping my MEA consumption down to record levels. In fact, one of my plant supervisors (a native Peruvian named German Huanuco) registered the lowest MEA consumption per ton of CO2 removed ever seen or recognized in our company at that time (Liquid Carbonics Corp; 1965). And he only had a grade school education in a remote Andean village! This shows how simple human ingenuity and perseverance can overcome serious and overwhelming problems. You don’t have to be a university-trained chemical engineer to resolve serious problems that simply overcome even experienced and PhD engineers in the field. Common sense dictates that if you apply your basic thinking to the fact that MEA is continually exposed to hot spots and contaminants that continuously degenerate it, then you go to the source of the problem and purify the solution as it is recirculating. The result is an efficient and corrosion-free plant that works around the clock with efficiency. The plant that I designed and built was operated by German for 20 years until he died and it then operated for another 10 years until it was dismantled because it’s production rate (500 kg/hr) was too low for the increasing production demand.

My entire point in all of this discussion is to reinforce your argument that stainless steel is not necessarily an answer to the problem. FIRST, FIND OUT WHAT THE REAL PROBLEM IS. THEN ATTACK THE PROBLEM, NOT THE EFFECT.


#5 Allen

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Posted 29 July 2009 - 03:06 AM

I would open up the debate and turn the problem on its head. In my opinion the choice of material of construction should be based on three main issues, in no particular priority:

1. The ability of the material to resist corrosion for the given duty
2. Costs
3. Design considerations ie heat transfer propoerties, fabrication issues etc.

and not necessarily on what people have used before.

Having spent 11 years in R & D, designing and fabricating pilot and semi pilot plants, I undertook a fair amount of corrosion testing. It was certainly surprising how different grades of stainless steels reacted to particular conditions. For this reason, I'm always careful about generalising when it comes to SS.

#6 vittorio6

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Posted 06 August 2009 - 01:41 AM

<!--quoteo(post=30987:date=Jul 17 2009, 04:36 PM:name=chem101)-->
QUOTE (chem101 @ Jul 17 2009, 04:36 PM) <{POST_SNAPBACK}>
<!--quotec-->Hi Every One:
why do we use stainless steel in plant? why not carbon steel? how do we conclude that stainless piping should be used where chances of corrosion are very high? I was talking to one of my co-worker. he said that in some of Amine Plants he has been using carbon steel for about five years in same areas, like after the lean rich exchanger, overhead of Amine still., and even the tubes in lean rich exchanger are carbon steel, they are working fine. So why do we use stainless steel. again i know some of you going to say because or corrosion. but here i have a guy who has sold evidence.
thank you very much in advance<!--QuoteEnd-->
<!--QuoteEEnd-->


The condition in the different areas of a plant can be quite different leading to different corrosion rates and different materials selection. Usually is not possible to select one single material for all the equipment and piping in a plant.

Causes of Amine Plant Corrosion-Design Considerations


corrosion prevention & control

Vitt

Edited by vittorio6, 08 October 2009 - 11:42 AM.





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