Continuous Digester Process Safety Improvements – Stress Corrosion Cracking and Overpressure Protection Lessons Learned and Opportunities, 2023 PEERS Conference

Georgia-Pacific (GP) has recent experience with Continuous Digester Stress Corrosion Cracking (SCC) repairs where the extent of SCC was more than previous spot inspections had predicted (one digester had anodic protection, one did not). This paper offers an overview of one company reviewed and improved their inspections, used of ‘boat’ samples to quantify the depth of cracking mechanism, and supported repair recommendations for Continuous Digesters based on hardness testing performed on weld repairs. GP also reviewed overpressure protection systems and corrected gaps found in these systems. These included updating to the latest original equipment manufacturer (OEM) designs and formalizing functional testing procedures and practices. This review of digester inspection, testing and repairs since 2020 provides a basis for including a 3rd party corrosion expert to be a part of inspections, removes the use of power-wire brushes, requires 100% phased-array ultrasonic testing and to eliminate SCC, and ensure overpressure protection design and testing is aligned with corporate needs and the site-specific challenges.

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