The graph above is a laboratory simulation of the real plant condition during the whole cycle acid/caustic exposure.
Prior to a plant scheduled acid wash, the Bayer liquor is drained from the circuit then water pumped into the system to remove any caustic left in the pipes. At this stage, diluted acid is pumped into the system to fill up the single pipes and HEX unit vessels, then recirculation starts to actually dissolve the scale formation (DSP) consequently recover the heat transfer coefficient. Immediately after this, the acid is displaced by pumping water through the system until the whole circuit is free of acid. There is a period when the whole system is empty while preparation for service is carried out. To reassume production, hot Bayer liquor is pumped through the system and continues for a few weeks until the next scheduled acid wash.
As we observe, high corrosion peaks are observed during the acid wash and the first 4 hours of Bayer liquor service.
The standard ASTM 179 material, depicted by the "blue line" will always show higher corrosion trends than the Superhex "red lines" and what is more remarkable, the STD ASTM 179 will stay at high corrosion trends and the Superhex will continue reducing as the cycles increase, which is entirely due to its passive film formation.
PLANT DATA WILL BE AVAILABLE EARLY 2021.
The electrochemistry equipment comprises of a high-resolution potentiostat (voltage inputs), 12 channels Multiplexer (switch from sample to sample), and temperature data logger. These three (3) instruments are interconnected and at the same time connected through a single cable to a laptop that drives the corrosion software.
A single electric wire connects the cabinet to the corrosion probe to complete the monitoring system.
The sample holder is the key component of the corrosion probe where the five (5) electrodes are placed. P1, P2 and P4 are positions for specimen under evaluation and P3 and P5 are the Reference and Auxiliary electrodes respectively to complete the corrosion cell.
Two (2) types of flange can be used. One with more penetration than the other. There is another type of flange (LWNF) that also can be considered for maximum penetration.
Position depicted in the picture is between the first two live steam heaters (LSH). This position will provide with the harshest corrosion condition during liquor service.