51314-4395-Corrosion Monitoring and Root Cause Identification in High Solids Concentrators

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Product Number: 51314-4395-SG

ISBN: 4395 2014 CP

Author: Pasi Niemelainen

Publication Date: 2014

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CORROSION MONITORING AND ROOT CAUSE IDENTIFICATION IN HIGH SOLIDS CONCENTRATORSHigh solids concentrators have been found to be suffering from aggressive corrosion in many occasions. Especially the 1st and 2nd effect bodies are susceptible to corrosion attacks resulting in tube leaks and wall thinning. This can limit the availability and lifetime of evaporator lines.Corrosion behaviour and utilized construction materials have been studied extensively within the pulp and paper industry in order to understand the corrosion behaviour. However it has been challenging to identify root causes for corrosion and this has limited pro-active measures in minimizing corrosion related damages.In this case corrosion of the 1st phase concentrator was studied by defining the potential regions for; passive area stress corrosion cracking pitting corrosion and general corrosion. This was done by using a technique called Polarization Scan which reveals ranges for the passive area in which the equipment is naturally protected against corrosion.The free corrosion potential of the metal was monitored on-line which enabled defining on-going corrosion risks with 304 SAF2205 and several other materials. In addition the system was also monitoring Linear Polarization Resistance which provided accurate information about the quality of the protective passive layer. An on-line temperature measurement complemented the results adding valuable in-sights to the analysis.A very powerful process diagnostics tool called WedgeTM was used to identify root causes of the corrosion attacks. Many of the root causes were related to process situations that triggered corrosion and once the metal surface was active it was difficult to re-passivate the metal naturally unless a certain potential range was reached.The project enabled the mill to study various process scenarios and find a less corroding formula in which to run the process. Ultimately the mill was able to reduce corrosion risks and thus extend the life time of the vessels.