Inspection Alternative/NDT of Mill Storage Tanks - Emphasis on Liquor Cycle Tanks, 2002 Fall Technical Conference

Pulp & paper mill above ground storage tanks (especially liquor cycle, caustic, and acid tanks) requires strategic inspection and testing methodologies to provide accurate condition assessments. This includes compiling static design data, process and inspection history, knowledge of the corrosion / erosion mechanisms, and general degradation characteristics of the tank. Visual inspection (utilizing the guidelines of API 653) is the primary inspection tool worked in conjunction with NDE (Nondestructive Examination) to acquire the necessary data for calculating corrosion rates and remaining service life. Risk Based Inspection (RBI) techniques are also utilized for inspection frequencies. New technologies such as robotic ultrasonic tank crawlers, video probes, FST, ACFM, and flux leakage systems are utilized to gather extensive data, and reduce costs of scaffolding. By focussing inspections to “suspected areas of concern” such as tidal / vapor zones, and impingement areas (agitators, rakes, inlets / outlets) inspection scopes can be reduced by eliminating redundancies.