I am not very familiar with the processes used to make carbon black nor the materials of construction normally used in carbon black plants. From the little bit of reading I have done it seems carbon steel and 316L stainless steel are commonly used for some operations. I believe most corrosion problems seen in these plants are caused by sulfur in the feedstock, chlorides in the quench media, oxygen, and water. The most common types of corrosion seen in these plants are uniform corrosion, stress corrosion cracking (SCC), pitting, and intergranular corrosion. You asked specifically about 304 and 316 stainless steels. Unfortunately, these austenitic stainless steels are known to be susceptible to SCC, pitting, and intergranular attack. The chance of intergranular attack can be minimized by using low carbon versions of these stainless steels such as 304L or 316L. In general, 316L is more corrosion resistant than 304L because it contains molybdenum. I suggest you look for reference materials that specifically discuss materials of construction for carbon black plants for more information.