Difference between Ti Gr 2 and Ti Gr 12 of Titanium

[mthakur]

We have an exchanger in Nitric acid plant, the channel of this exvhanger is parially made in Ti Gr 2 while rest of it is made with Ti Gr 12. We have been experience corrosion in the HAZ of G 12 Titanium and would like to understand the difference between these grades in terms of corrosion resistance.

 

[EdStainless]

Have you gone to the Timet web site and downloaded the Ti corrosion handbook? Start there.
Here is a quick list

http://www.alleghenytechnologies.com/ludlum/Documents/tibluesheet.pdf

The two grades have similar strength, but 12 has small Ni and Mo additions. This is to improve corrosion resistance (enhance repassivation kinetics) at lower cost than adding Pd or Ru.
My hunch is that the gr12 in in the hotter section or the more dilute section of the exchanger. It is probably failing because it is not good enough. You may need to build this exchanger with three different grades, 2, 12, and 16 in the harshest areas.

Get a professional failure analysis done. If you make any mistakes it will be very expensive.


= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[MikeMet]

Grade 12 with its Mo and Ni additions was developed to increase the crevice corrosion resistance and higher temperature that can be a problem with the CP grade. But even Gr. 12 does have some limits based on pH and temperature above about 200F. Even though Ti is used extensively in nitric acid, one needs to be careful when using Ti in nitric acid streams. Depending on ion contamination or purity of the nitric, you can get very agressive corrosion. I lost an entire Ti-Gr 2 bundle due in a narrow zone where concentrated, pure, nitric acid at high temps was forming. Same acid at same temp with oxidizing ions, Ti-Gr2 worked well.

I agree with Ed, get help from a metallurgical consultant who is experienced in corrosion and do a careful evaluation of your process stream.