Abstract
An analytical approach that can discriminate between various forms of microscopic corrosion initiation has been successfully employed in natural gas gathering and storage facilities. Subjected to a combination of analytical techniques, steel test coupons for electron microscopy, "EM coupons", provided information about the surface microbiology and internal corrosion of the systems monitored. Optical microscopy, scanning electron microscopy (SEM), Nomarski Differential Interference Contrast (DIC), phase-contrast and epifluorescence microscopy were employed in the coupon analysis protocol. Special preparation techniques were also utilized to maximize the data obtained from the coupons. Relationships between physical/microbiological surface conditions and corrosion initiation events have been observed over a twelve year period using these combined methodologies in laboratory and field tests. Information provided by the analysis of EM coupons has led toward the better understanding and improved diagnosis of the initial stages of internal corrosion in natural gas gathering and storage facilities.
