SA-179 constant corrosion

[Mous1747]

tube bundle for ammonia vaporizer heat exchanger made out of SA-179 normalized and annealed (HRB 66)
we have been having corrosion problems alot due to the low PH of the water due to nitric acid carryover

is carburizing case hardening would help? or nitro-carburizing?

 

[EdStainless]

Raise the pH, surface treatments on the steel will not help

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P.E. Metallurgy, Plymouth Tube

 

[Mous1747]

why SA-179 is the preferred material in this heat exchanger? is there any coating that would provide higher corrosive resistance to this low PH water?

 

[Mous1747]

beside raising the pH, is there anything from the metallurgy stand point that i can do to make my tube bundle more corrosive resistant ?

 

[TugboatEng]

Maybe an electroless nickel coating like Nye-Kote or Kanigen.

 

[EdStainless]

How much acid are you talking about?
You need to look at the complexity/cost of either reducing the carryover, or neutralizing it, or going to stainless steel tubing.
Coatings are a bad idea, where ever there is a microscopic breach in the coating you will get attack of the underlying metal.

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P.E. Metallurgy, Plymouth Tube

 

The mention of case hardening suggests you are out of your depth. I suggest you retain a heat exchanger design specialist. If that resource is not available in-house, there should be a boutique company in your neighbourhood. The lethal nature of the chemicals involved underscores the necessity for reaching out to an expert.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[cap1a79]

If there is any possibility for nitric acid carry over, the application of carbon steel (SA 179) might not be a suitable option.
Referring to CORROSION RESISTANCE TABLE (Philip A. Schweitzer PE, Consultant, York, Pennsylvania, USA, Marcel Decker, INC), the penetration rate is as below.


1) 5% Nitric Acid / 10 % Nitric acid
- CS --> Unsatisfactory for all range of temperature
- SS 316 / 316L / 304 / 347 --> Excellent up to 93 C. (Below 2 mils)

2) 20% Nitric Acid
- CS --> Unsatisfactory for all range of temperature
- SS 304 / 347 --> Excellent up to 82 C.(Below 2 mils)
- SS 316 / 316L --> Excellent up to 38 C.(Below 2 mils)

3) 30% Nitric Acid
- CS --> Unsatisfactory for all range of temperature
- SS 304 / 347 --> Excellent up to 93 C.(Below 2 mils)
- SS 316 / 316L --> Excellent up to 38 C.(Below 2 mils)

4) 40% Nitric Acid
- CS --> Unsatisfactory for all range of temperature
- SS 304 / 347 --> Excellent up to 93 C.(Below 2 mils)
- SS 316 / 316L --> Excellent up to 26 C.(Below 2 mils)

4) 50% Nitric Acid / 70% Nitric Acid
- CS --> Unsatisfactory for all range of temperature
- SS 304 / 347 --> Excellent up to 26 C.(Below 2 mils)
- SS 316 / 316L --> Excellent up to 26 C.(Below 2 mils)

Reference from Corrosion Resistance Table, Metals Nonmetals, Coatings, Mortars, Plastics, Elastomers and Linings and Fabrics, Fifth Edition, Revised and expanded, Part C, ISO-POT, Philip A. Schweitzer, PE


Lee SiHyoung,
Material & Corrosion,
WorleyParsons Oman Engineering,
cap1a79@gmail.com