The Role of Moisture in the Corrosion of HBr Gas Distribution Systems

Controlled studies of the effect of moisture content on the corrosivity of HBr toward common materials of construction were performed. Coupons of EP316L stainless teels, two types of stainless teel welds, and Hastelloy C-22 were exposed to HBr containing 0.5, 10, 100, and 1000 ppm moisture. The coupons were exposed to HBr for 10 days, then the HBr was thoroughly purged from the reactor. The samples were then transferred under nitogen into a scanning electron microscope and analyzed by scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). The corrosion products were then removed by washing and the coupons analyzed by atomic force microscopy (AFM) and ion chromatog-raphy. The SEM and EDS data showed little reaction between EF316L stainless teels and HBr with 0.5 ppm moisture. The two welded samples howed minor bromide incorporation i to the weld bead at this moisture level. Exposure to HBr with 10 ppm moisture caused a thin deposit o form on the surface of the stainless teels and both welded samples. The EDS spectra at this moisture level showed 1 atom percent (a/o) bromide incorporation over a sampling depth of about 1 t~m, indicating the onset of corrosion. HBr with 100 ppm moisture formed corrosion pits on EP316L. HBr with 1000 ppm moisture caused a ense bromide scale to form on all the stainless teel samples, and the samples showed 11 atom percent bromide incorporation (EDS) over a sampling depth of about 1 ~m. From the SEM images, it appeared that the Hastelloy C-22 was unaffected at all moisture levels, but the Hastelloy showed bromide incorporation by EDS after exposure to HB