Case Study: Digester

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Mitigating downtime of batch digesters is vital to successful operation of paper mills, because downtime in the digesters can restrict production and cause downstream impacts throughout the mill. Gecko was tasked with partnering with a well-known manufacturer, for the 6th time in one year, at one of their paper mills in the Southeastern US to inspect a batch digester. This included magnetic induction inspection of the Inconel metal-spray coating, along with full ultrasonic thickness on the digester shell, dome, and cone.

Two inspectors on the inspection

Non-Confined
Space Entry

UT Readings

65 Readings
per sqft

Rapid Ultrasonic Gridding

Over 185,000 UT Measurements

Inspection completed with one robot

A Single
8-hour Shift

Inspection completed with one shift

2 Person Crew
(NDT Level II)

The importance of digester inspections cannot be understated due to the extreme heat and pressure present in the digester vessel. In the last few years, there have been disastrous scenarios where digester explosions have caused untold damages to communities and lives around the mill, millions of dollars in plant repair, and millions in unproductive mill downtime. A TAPPI report outlines the value of understanding risk through measuring and alleviating the probability of digester failure. Capturing a thorough inspection of vessel Inconel coating, and comparing that data to the initial lining of the vessel, helps mill personnel understand lining degradation over time and pinpoint areas for repair.

Utilizing the Gecko TOKA robot significantly reduced both the cost and safety risks of the inspection. By eliminating any human entry into the confined space to complete the inspection, there was no need for the cost and coordination of umbrella scaffolding installation for the digester vessel. Completing the on-site inspection required only (1) 8-hour shift of our two-person Level II NDT crew. In that time, over 185,000 thickness measurements were gathered,including over 50,000 on the digester cone, over 50,000 on the digester dome, and over 85,000 on the digester shell.

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