In order to safely extend the interval between outages on a digester it is necessary to address the requirements of the insurance companies and authorized inspection agencies involved. Additionally, the State and Local jurisdictions may have requirements that need to be identified and met. Extending outage intervals also requires knowledge of the original design and installation practices, as well as documentation on maintenance, repairs and alterations that have previously been made to the vessel. The inspections required, and process for making repair decisions need to be agreed upon by all parties involved as part of an overall risk management strategy. While this paper is primarily intended to address issues associated with welded batch type digesters utilized in the kraft (sulfate) pulping process, many of the principals discussed herein are universal to other equipment types.
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