Materials selection for HBr service

Abstract

This study was undertaken to determine the compatibility of hydrogen bromide (HBr) with common materials of construction used for specialty gas delivery systems. Reactions between reactive gases and materials of construction can result in the formation of particles and volatile metal complexes as well as the creation of corrosion products that can retain water. We found that when moisture is below 1 ppm v (designated as anhydrous), bromine from HBr is not incorporated beyond the native oxide of electropolished 316L stainless steel (EP316L) and no macroscopic degradation of the metal occurs. Also, if adequate purging and evacuation procedures are followed to remove the HBr, this material can be exposed to moist air without diminishing the initial surface quality. However, if adequate precautions are not followed to eliminate water in the presence of HBr, iron-and bromine-rich crystalline deposits form on the surface. Purge and evacuation procedures are inadequate for removal of the reactive species on this surface and corrosion proceeds upon subsequent exposure to air. EP316L exposed to HBr containing 1700 ppm v H 2O appears visually unaltered, but close inspection by SEM reveals the onset of corrosion. Of the materials examined in this study, Nickel-200 and Hastelloy C-22 are more resistant to HBr corrosive environments. In contrast, deleterious reactions occur between anhydrous HBr and elemental iron and the iron-rich surface of oxygen-passivated 316L.