Troubleshooting efforts were devoted to addressing corrosion activity in multiple areas
of an atmospheric tower overhead system. These efforts indicated that three different sections
of the overhead were being simultaneously attacked---each section having its own distinct
corrosion mechanism. The areas affected and their mechanisms were as follows: 1) Corrosion
resulting from ammonium chloride deposits in a "dry" pressure relief valve header; 2) Wet
sulfide corrosion on 70/30 Cu/Ni exchanger tubes; and 3) Velocity accelerated corrosion at the
outlet elbows of these exchangers. The severity of these mechanisms correlated well with
variations in unit operating conditions. Several techniques were used to identify the
mechanisms involved, including electrolyte simulation modeling, metallurgical analysis of
weight loss coupons and ultrasonic thickness (UT) measurements. Recommended mitigation
plans and their effectiveness upon implementation will also be discussed.
Keywords: ammonia, chloride salts, deposition, cupro-nickel corrosion, velocity