INTRODUCTION

Sulfuric Acid is undoubtedly the most important raw material in the chemical and pharmaceutical industry today. This fact is not unique to the United States, but is true on a worldwide basis. One can often look to the production and/or use of sulfuric acid as an indication of the industrial activity of a nation. Few chemicals are manufactured without sulfuric acid being involved. It is a strong dibasic acid and can be a reducing acid, an oxidizing acid, and/or a dehydrating agent.

In the chemical industry, sulfuric acid has many diverse applications. The largest quantities are used in the manufacture of phosphate and nitrogen based fertilizers. The petrochemical sector utilizes sulfuric acid in alkylation and paraffin refining. The inorganic branch of the chemical industry uses sulfuric acid in the production of chromic and hydrofluoric acids, aluminum sulfate and sodium sulfate. The organic arm employs sulfuric acid in the manufacture of explosives, soaps, detergents, dyes, isocyanates, plastics, pharmaceuticals, etc. Everywhere one turns in today's world we encounter products which use sulfuric acid in their manufacturing process.

Many chemical plants use sulfuric acid in one or more process steps and this generally results in severe corrosion problems. Each process has unique minor constituents that can change the way metals corrode. Zirconium has been used very successfully in many sulfuric acid applications. The advantage of zirconium is that corrosion rate will be very small if properly applied and equipment life of over 20 years is expected. Since there is no corrosion maintenance repair, downtime and replacement costs do not exist and will quickly pay back for the slightly higher initial cost.

Zirconium is one of the most suitable metals for the containment of sulfuric acid. It is cost-effective, reliable and non-contaminating to the environment. The information that follows gives the reader sulfuric acid corrosion information in a nutshell.

CORROSION DATA

Corrosion of metals by sulfuric acid is very complex, as there are oxidizing and reducing conditions depending on concentration. The graph in Figure 1 gives approximate conditions where different metals can be used successfully. Warning: this chart is not intended to be used for metal selection especially at the boundaries of the ranges marked. There are several alternatives if the temperature is low, from ambient to 150° F. Once the process temperature requires operation at boiling point or above, very few construction materials are available. At high concentrations, above 95%, the environment is oxidizing, while at low concentrations the conditions are reducing. This requires different metals to be used depending on the conditions.

One of Six 1 2 3 4 5 6