The corrosion rate of in sulfuric acid is negligible in any concentration from 0 to 99% up to a temperature of at least 150°C. In sulfuric acid at temperatures above 150°C the corrosion rate will have to be considered, but the corrosion rate in high temperature sulfuric acid is magnitudes lower than the corrosion rates of Hastelloy, titanium and zirconium.

Sulfuric Acid Iso Corrosion Curves
This iso corroion curve shows the relative corrosion resistance of several specialty alloys and exotic metals in various concentrations and temperatures of sulfuric (sulphuric) acid (H2SO4).  It can be seen that the corrosive nature of sulfuric acid, as with most acids, is highly dependent on the temperature and concentration of the solution.
 




Corrosion in diluted Sulfuric Acid (0-10%)

In diluted sulfuric acid (less than 10% sulfuric acid) the aggressiveness of the acid is limited, so austenitic and duplex steel and to some extend titanium may be a cost efficient option in the low temperature range. At temperatures above 100C more corrosion resistant materials like Hastelloy grades may be required.

Corrosion in Sulfuric Acid in the Concentration Range 10% to 90%

Sulfuric Acid in concentrations between 10 and 90% is known to be especially corrosive. Common type specialty metals like e.g. titanium and Hastelloy c-276 will show rapid corrosion in sulfuric acid at temperature lower than 100 C. Very few materials including exotic metals like Zirconium and Tantalum materials can be applied above the sulfuric acid boiling point. Tantaline is by far the most economical option. Tantaline will further maintain its corrosion resistance above the boiling point independent on the concentration up to 99%, whereas Zirconium will lose its corrosion resistance in sulfuric acid at concentration above approximately 75%.



Corrosion in Concentrated Sulfuric Acid

Concentrated sulfuric acid (water free) sulfuric acid is less corrosive than water containing sulfuric acid and iron based alloys can shows in general good corrosion resistance in concentrated sulfuric acid. Silicon cast iron show low corrosion rates in 99% sulfuric acid, but will suffer from stress corrosion cracking when in SO3 containing concentrated sulfuric acid (oleum). Depending on temperature austenitic stainless steel can be applied in oleum.

Sulfuric Acid Corrosion Tables

Table: Corrosion Performance and Relative Cost of Materials in Sulfuric Acid at Concentrations from 10 to 90% and Temperatures of 50, 100 and 150C

Performance/ Price Ratio of Materials for Sulfuric Acid service

Offers a chemical performance equal to tantalum at prices similar to nickel alloys having an absolutely unique performance/cost ratio compared to other solutions in titanium, nickel alloys, zirconium and tantalum. As can be seen from the table above Tantaline has superior performance over niobium, zirconium and nickel based alloys at a lower relative price.

Solutions for Sulfuric Acid Service 

A large heater services have been installed in plants for the re-concentration of diluted sulphuric acid arising from metal pickling, oil refinery operations and from petrochemical processes producing alcohols and ketones. 

Limitation of Sulfuric Acid Service

At very high concentrations of sulfuric acid (>98%), the corrosion performance of tantalum will decrease due to existence of "free" SO3. Thus Tantalum metal is in general not suitable for fuming sulfuric acid (oleum).