NACE International

Materials for the Handling and Storage of commercial Concentrated (90 to 100%) Sulfuric Acid at Ambient Temperatures - Item No:21050
 N SP0391

Annotation

General

This standard provides information about the design and selection of materials used in the handling and storage of commercial concentrated sulfuric acid at ambient temperatures. The term “ambient” is intended to include temperatures up to 50 °C (120 °F). This is the approximate maximum temperature that arises from solar heating of piping or vessels in a tropical climate.

This standard does not consider sulfuric acid strengths above 100 percent or below 90 percent by mass.

For completeness, this standard includes Appendix A (nonmandatory), which contains a listing of all alloys mentioned in this standard, and Appendix B (nonmandatory), which gives guidance on applicable materials for a sulfuric acid dilution system.

Concentrated sulfuric acid is a colorless, odorless, syrupy liquid whose oily appearance suggested the name oleum (Latin for oil) to early chemists.(1) Today, the term “oleum” is used only for sulfuric acid containing free sulfur trioxide. The term “sulfuric acid” is used to refer to acid that does not contain free sulfur trioxide.

The term concentrated sulfuric acid broadly refers to the concentration range of 90 to 100 percent by mass. Commercial acid is usually stored at 93 percent concentration because its minimum freezing point is –34 °C (–30 °F). Sulfuric acid is commonly transported in the 98 to 99.5 percent concentration range. The latter limit is imposed by the much greater corrosiveness of 100 percent sulfuric acid to carbon steel and by its higher freezing point of about 7 °C (45 °F).

Concentrated sulfuric acid is a corrosive, and because of its affinity for water, it is also a desiccant. The major problems in its handling and storage relate to its hygroscopic nature (absorbing atmospheric humidity), its exothermic reactivity with water on dilution, and velocity effects that tend to accelerate corrosion of iron- and lead-based alloys