Please advise of the four options given by my supplier to minimize corrosion, storing boiling sulphuric acid - Graphite impregnated with PTFE resin, 20 Cb-3 stainless steel, Titanium and Hastelloy C.

Dear Gurdeep, It may be a bit late reply to your querry, but I thought the following input may of assistance to you. Out of the materials that you have mentioned, only Hastlloy C and 20 Cb-3 are the most appropriate material to be considered for storing boiling sulphuric acid. One thing that may be added that sullphuric acid occupies two positions regarding oxidizing or reducing acid. At below 85% by weight at room temperature, sulphuric acid is a reducing acid while at higher concentrations, it becomes oxidising acid. Hence, material selection should also take this switching nature of the acid in account. Alloy 20 and Hastelloy C shows similar corrosion resistant in sulphuric acid. However, there are certain advantages in using Alloy 20 over Hastelloy C for storing boiling sulphuric acid. Alloy 20 was originally made for handling sulphuric acid and in my experience, it is quite resistance in boiling 20% to 40% concentrations. If you can provide at what concentration you intend to store the acid, we can provide you a better suggestion. Alloy 20, at higher concentrations at boiling point will have a maximum of 50 mils as corrosion rate while Hastelloy C can have over 200 mils at similar concentrations. Also, Hastelloy C can be pretty vurnerable to stress corrosion cracking if chloride concentration is more that 40 ppm in the acid. Based on the above and within the choice of materials that you have provided, I would recommend Alloy 20 for the intended application. By the way, you may also like to consider Durion which is high silicon cast iron which can be used at temperature as high as 500C. However, there are some limitations in using Durion. One of them is not to use above 100% concentrations in fuming acid. Hope the above is helpful. Please do let me know should you have any further querry. Regards, MetcorrH