Stainless Steel Nozzle on Carbon Steel Tank

[SEJohn]

I am specifying a tank for 93% sulfuric acid following NACE SP0294-2006. The document recommends using carbon steel for the tank but appears to be recommending stainless steel for the nozzles. Is this normal? It seems like there would be a corrosion problem at interface of the stainless and carbon. Also, are there any special requirements on welding the dissimilar metals?
Thank you in advance.

 

[fegenbush]

Requirements for welding dissimilar metals are covered in Annex SC of API 650. SC.3.4.2 allows nozzles to be of different material than that of the shell to which they are attached at the request of the Purchaser.

It is common for the nozzles in acid tanks to be of different material than that of the shell. I have encountered it both in API 650 tanks and in ASME pressure vessels. The galvanic effects are small in comparison to the effect of removing the passive layer formed in unlined carbon steel tanks in 93% H2SO4 tanks.