4 replies to this topic

[bme]

Hi.
My name is Gen. I currently involve in an aluminum valve that internal medium is corrosive gas & high temperature (Sulfuric acid & Nitric acid).
1. What is the best coating onto aluminum to overcome the corrosion? Does anodizing work?
I like to work around the existing aluminum part since it's more economic, cost effective.

2. If not, please suggest other material that is best for the environment? Stainless steel would improve it, but I am not sure it will overcome the issue.

I look forward for everyone's reply. Thanks,
Gen

[kimo]

Hi.
My name is Gen. I currently involve in an aluminum valve that internal medium is corrosive gas & high temperature (Sulfuric acid & Nitric acid).
1. What is the best coating onto aluminum to overcome the corrosion? Does anodizing work?
I like to work around the existing aluminum part since it's more economic, cost effective.

2. If not, please suggest other material that is best for the environment? Stainless steel would improve it, but I am not sure it will overcome the issue.

I look forward for everyone's reply. Thanks,
Gen

1. are sure that you are having an '' aluminuim valve..etc'' for corrosive gas & ht. media?
2. best material to use is the stainless steel (with the right grade).
3.suggest to check asme code
regards
kimo

[Zauberberg]

Take a look at Dupont webiste, more precisely at: http://www2.dupont.c...ipment_FAQs.pdf

I would also suggest you to contact experienced Materials & Corrosion engineer, and discuss about the use of aluminum in such service. It doesn't appear to be a good idea, although I'm not an expert in this subject.

[Art Montemayor]

Gen:

I have to be cautious responding to your query because I don’t believe you have a background knowledge in Chemistry and much less in Chemical Engineering. Therefore, I don’t want to be misunderstood in what I recommend. Please tell us your back ground and education level.

First of all, you infer that Sulfuric & Nitric acid are corrosive gases. They most certainly are not gases. Additionally, you state that Stainless steel would improve your situation. That also is not necessarily true. It depends on the specific acid, its strength, its temperature, and purity. We can’t recommend a material of construction without having 100% of the details and scope of work.

While I don't consider myself an expert, what I do know of Aluminum and the acids/bases is:

Aluminum dissolves readily in hydrochloric acid, somewhat less readily in sulfuric acid, and is passive or inactive toward nitric acid, which may be shipped in aluminum containers. Aluminum dissolves, also, in concentrated solutions of bases, such as sodium and potassium hydroxide, liberating hydrogen and forming aluminates.

Aluminum and hydrochloric acid react as follows:

2 Al + 6 HCl (aq) ---> 2 Al+3 + 6 Cl- + 3 H2

Note: the AlCl3 is not stable in water; it converts to Al(OH)3 + 3 HCl

Aluminum metal reacts with sulfuric acid according to the equation:

2Al(s) + 3H2SO4(aq) ---> Al2(SO3)3(s) + 3H2(g)

Concentrated nitric acid is a very strong oxidator capable of reacting with the noble metals such as copper or silver (not gold, however). Aluminum and zinc do not react with concentrated nitric acid since a thick, hard to dissolve oxidation layer builds (passive oxidation) that protects the metal against further assaults.

I recommend you consult with an experienced metallurgist or Chemical Engineering consultant before going forward with your ideas.

[Qalander (Chem)]

Dear Art Hello,

Real nice expaining info indeed on complexicities of consequential reaction products and possible corrosion scenarios.

Best Regards
Qalander