8 replies to this topic

[papaya]

There is this question i always have on my mind about which material are generally more superior & how many times are they more expensive & when do you use them.

Generally speaking it's easy to tell that for steel 316 is better but more expensive than 304, i'm looking at this material guide for corrosive service:

http://www.keyindust...l Guide/spi.pdf

It shows under what situation we should use which material, but i really want to have a general which material are the best in terms of corrosive & most expensive.

Common materials i've seen: Carbon Steel, Galvanized Steel, Stainless Steel, Duplex & Super Duplex, Monel, Inconel, Hastelloy B/C, Titanium. I hope you guys who are experienced with material can give ranks based on:

a.Corrosive resistance
b.Strength
c.Heat tolerance
d.Price (SS 316 as base just wanna know how many % more exp or cheaper the rest of the material cost)

I've posted similiar questions long time ago but couldn't get even an answer. Tried googled but hardly find a comparison in terms of the 3 points above.

Edited by papaya, 15 August 2011 - 10:46 PM.

[breizh]

Hi ,
Let you Consider this resource:
http://www.ssina.com...ons/design.html

Breizh

[papaya]

Thanks for the link was very useful, however is there any comparison with trademark materials like monel, inconel, hastelloy & maybe titanium?

Hi ,
Let you Consider this resource:
http://www.ssina.com...ons/design.html

Breizh

[breizh]

Hi ,

Let you try Sandwick web site , you should get more info about alloys otherwise you should to contact a corrosion expert for specific question.

http://www.imoa.info..._2d_Edition.pdf

Breizh

Edited by breizh, 17 August 2011 - 02:39 AM.

[kkala]

Probably a good deal of data you want can be found in Perry's "Chemical Engineers' handbook", 7th edition (McGraw-Hill, 1999), Section 28, Materials of Construction. Previous editions also contain similar data, useful for a general understanding.
However corrosion can be very case specific. In a fertilizer industry NH3 evaporator tubes of 304L were installed above the reaction vessels producing phosphoric fertilizer slurry. They failed in two weeks, while in another factory they had lasted for years. The difference was attributed to the raw material of phosphoric acid production, a mineral (phosphate) containing varying amounts of fluoride. 316L steel should have been used, having superior resistance to fluorides of phosphoric acid.
Another way is to try to get expertise on materials concerning the process you deal with. For instance, "Phosphoric acid" by A. V. Slack, Vol 2, contains an extended section on materials suitable for phosphoric acid production. But even chosing a material from a written reference may not be 100% safe. This may be the disadvantage or challenge of the material science, depending on your perspective.

[Technical Bard]

However corrosion can be very case specific.

But even chosing a material from a written reference may not be 100% safe. This may be the disadvantage or challenge of the material science, depending on your perspective.

I would strongly second this item. There are many examples of more expensive metallurgy lasting less time than cheaper metallurgy, because someone didn't understand the corrosion mechanism. For example, chlorides and oxalates in water are very detrimental to stainless steel, whereas carbon steel is less susceptible to these species. There are similar problems with many alloys, including some very expensive ones (nickel, titanium) when faced with incompatible materials.

[kkala]

Further to remark by Technical Bard, it may be useful to refer to some additional failures from already mentioned (23 Aug 11) fertilizer industry, indicating that material strength should be also taken into account.
1. A 98% H2SO4 line of cast iron was constructed to load rail vessels. This was broken due to water hammer, in a case when the near vessel valve was closed rather suddenly (the vessel would overflow). Cast iron had superior corrosion resistance but less strength compared to carbon steel (and it is more fragile). Carbon steel of generous corrosion allowance (and frequent inspection, e.g. once per year) was then judged as the most suitable material for the specific line, being reconstructed. Corrosion allowance of 3 mm is suitable in this case, as I learnt later.
2. A plastic valve (of fluoride resistant plastic) was placed at the exit of the phosphoric acid tank reactor, operating at atmospheric pressure and temperatures up to 80 oC. Valve supplier reported temperature limit of 80 oC. Cracks on the valve body appeared after ~ 2 weeks of operation. We mechanically supported a similar plastic valve against its weight, making a "column" from ground to it; the valve did not crack. It had indeed superior corrosion resistance, but the lesson was : "avoid material operating at recommended limits".

Edited by kkala, 28 August 2011 - 02:35 AM.

[papaya]

So far thanks for the comparison between SS, steel, but howabout with Inconel, Monel etc? How do they fair in corrosion resistance and strength?

[kkala]

You can have a general idea of the majority of materials in use (including inconel 600, monel 400, etc) in the Perry's Section 28, as mentioned in the post of 23 Aug 2011, with the reservedness expressed there.
I would consider suggestions as possible, but not quite certain for a similar industrial environment. In that fertilizer factory we conducted actual corrosion measurements for a new metal. Also communication between factories of same process and using same raw materials are useful.

Edited by kkala, 10 September 2011 - 11:35 AM.