Minxu Lu

Investigation on corrosion of zinc ribbon under alternating current

Abstract Zinc ribbon has been widely used for alternating current (ac) mitigation of pipeline. However, little is known about corrosion of zinc under ac. In this work, the corrosions of zinc under various ac in two scenarios, i.e. with or without direct current (dc) decoupler, were investigated in 4u200agu2009L−u20091 Na2SO4 simulated backfill solution by weight loss tests, low angle X-ray diffraction measurements and electrochemical measurements. It was found that ac accelerated corrosion of zinc dramatically in both scenarios, and it is worth noting that dc density between zinc and pipeline steel increased with ac in the scenario without dc decoupler. Consequently, corrosion rate of zinc was much larger than that in the scenario in which dc decoupler was used. Besides, the charge transfer resistance of zinc decreased considerably due to ac in both scenarios, which would largely increase corrosion rate.

Corrosion Behavior of HAZ Between C4 Nickel-Base Alloy/X60 Steel Dissimilar Metal Weldments

C4 nickel-base alloy and X60 steel were fabricated by Tungsten Inert Gas Welding (TIG) process using a CrNiMo-3 nickel base alloy welding wire filler metal under 100A welding current. The microstructure of welding joint was analyzed by SEM. Corrosion behaviors of heat effect zone (HAZ) and X60 steel matrix were investigated by electrochemical measurement. The obtained results show that weld metal zone consists of fully dendrite structure and the austenite grain of C4 nickel-base alloy coarsening in over-heat HAZ. The HAZ of X60 steel includes coarse (GHAZ) and fine grained zones (FGHAZ). Phase change from bulk ferrite with a small amount of pearlite to granular bainite at CGHAZ. Corrosion current density of matrix of X60 steel is between FGHAZ and CGHAZ.Copyright