Method for the protection against corrosion of a steel part made of austentic or semi-austentic steel during the production of sulfuric acid

Abstract

This invention relates to a method for the protection against corrosion of steel parts made of austenitic or semi-austenitic steel during the production of sulfuric acid. To improve the corrosion resistance of the steel parts which are in contact with the sulfuric acid, it is proposed to use austenitic or semi-austenitic steel which has a Cr content of 15 wt-% to 36 wt-% and an Ni content of 9 wt-% to 60 wt-% and in which the ratio of the chemical elements (Cr+Si)/(Ni+Mo) lies in the range from 0.9 to 1.9 or in which the ratio of the chemical elements Cr/(Ni+Mo) lies in the range from 0.8 to 1.5, and to additionally provide this steel part with an anodic corrosion protection.

1 . A method for the protection against corrosion of at least one steel part of a device which is used in a plant for producing sulfuric acid, and in which the steel part contacts concentrated sulfuric acid, comprising at a sulfuric acid concentration of 93 wt-% up to 100 wt-% and a temperature of 140° C. up to the boiling point of the sulfuric acid, using as the steel part is one made of austenitic or semi-austenitic steel which has a Cr content of 15 wt-to 31 wt-% and an Ni content of 9 wt-% to 60 wt-%, and in which the ratio of the chemical elements (Cr+Si)/(Ni+Mo) lies in the range from 0.9 to 1.25, and in which the steel part has an anodic corrosion protection, connecting an anode, a cathode and a reference electrode with a potentiostat which supplies an adjustable direct electric current, and placing the cathode and the reference electrode in contact with the sulfuric acid and the anode in contact with the steel part:  
     
     
         2 . The method as claimed in  claim 1 , wherein the ratio of the chemical elements (Cr+Si)/(Ni+Mo) lies in the range from 1.01 to 1.25.  
     
     
         3 . The method as claimed in  claim 1 , wherein the ratio of the chemical elements Cr/(Ni+Mo) lies in the range from 0.8 to 1.5.  
     
     
         4 . The method as claimed in  claim 3 , wherein the ratio of the chemical elements Cr/(Ni+Mo) lies in the range from 0.8 to 1.1.  
     
     
         5 . The method as claimed in  claim 1 , wherein the steel part is made of austenitic or semi-austenitic steel which has a molybdenum content of 0 wt-% to 2.5 wt-%.  
     
     
         6 . The method as claimed in  claim 1 , wherein the steel part is made of austenitic or semi-austenitic steel which has a molybdenum content of 2 wt-% to 2.5 wt-%.  
     
     
         7 . The method as claimed in  claim 1 , wherein the concentration of the sulfuric acid lies in the range from 97 wt-% to 99 wt-%.  
     
     
         8 . The method as  claim 1;  wherein the temperature of the sulfuric acid is about 160° C. to 230° C.  
     
     
         9 . The method as claimed in  claim 1 , wherein the steel part is used in a heat exchanger.  
     
     
         10 . The method as claimed in  claim 1 , wherein the steel part is used in an acid-conducting pipe.