corrosion protection against H2SO4 3

[csaba]

Hello there!

I have a client who wants me to protect a stainless steel (DIN: 1.4301 i.e. X5 CrNi 18.9) storage/dosing tank against H2SO4 of a concentration of 93%. Companies I knew of offered protection by rubber lining up to 70% of concentration only. Someone offered a lining with epoxy resin but I did not hear of so good references of this method. There is a temperature fluctuation between 10 to 30 °C. The tank is located indoors.

A company offered a corrosion protection by ceramic bricks but it would have radically changed the design of the tank.

Does anyone have a good ide of what to do?

Thanks a lot!

Csaba (ProMinent Hungary Co. Ltd. -

http://www.prominent.hu)

 

[cub3bead]

Have you considered replacing the tank with one of HDPE construction?

 

[csaba]

hello,

yes, i have considered it. it would have been the easiest but the customer does not want to get rid of the idea of using stainless steel tank even if technically inappropriate.

csaba

 

[ApC2Kp]

To csaba,
The choice of stainless steel for 93% sulfuric acid tank in the indoors location is a very good technical choice. If the tank is already fabricated, then I won't go into the other metal alloys to further upgrade from stainless steel.
A stainless steel tank for 93% sulfuric acid should give many years of service with proper care. Most 93% acid storage tanks are fabricated of carbon steel with an extra 3mm-6mm corrosion allowance. The most important item of operation would be to avoid low concentration acid events. Corrosion greatly increases with sulfuric acid concentrations between 90%-30%. Atmosheric humidity can be pulled into the tank during normal use and draining. Weak acid will form on the liquid surface and attack the tank walls near the normal liquid level. The importance of a good dry inert gas venting system must be emphasized. See thread 124-93379 about the 96% acid storage tank venting discussion.
Many acid towers and tanks are brick-lined steel, and work well for the hot concentrated acid services. The weak acid (20% and lower) services are better handled by the rubber, plastic, and fiberglass+resin materials. If your client absolutely requires a liner in the stainless steel tank, then I would suggest the approach used in railroad tank cars. The railroad tank cars are carbon steel with a phenolic coating. The phenolic coating takes on a charred appearance from oxidation by acid, but remains in place for protecting the steel. The trend is to use stainless steel for truck trailer tanks. Other coatings of bonded teflon, FEP, eTFE, kynar have limits for applying the coating depending on the vessel size, along with the coating costs. Look on the nace.org website for articles on sulfuric acid equipment and piping, especially the paper by C.M. Schillmoller, "Selection and performance of stainless steel and other nickel-bearing alloys in sulphuric acid." Other sources of information are the sites for acid plant production personnel,
h2so4dtoday.com
members.rogers.com/h2so4 (sulfuric acid on the web)
enviro-chem.com

 

[csaba]

Thank you very much for you all! This has been my first attempt to get answers on this forum and you helped a lot.

Csaba

 

[NickelDave]

As stated previously, 1.4301 (304) stainless steel is acceptable for 93% Sulphuric Acid. Anodic protection could be considered, especially if general corrosion rates, as indicated by widespread thinning, show unacceptable tank life.
As sulphuric acid readily absorbs water from the atmosphere, liquid line corrosion is a potential cause of failure. This can be minmised by mixing the tank contents by recycling some of the pump discharge back into the tank feed line. For 304 SS, 93% strength is the minimum recommended.
Higher strength acid (up to about 99% maximum)also lowers the corrosion rate, so obtaining 98% acid, if available would be beneficial. This may be difficult in a cold climate, due to freezing point limitations.
The Nickel Institute provides some general publications, free of charge. NACE has a number of standards that can be purchased.