TAPPI TIP 0402-27 ✓ Most Recent

This Technical Information Paper (TIP) provides guidelines for inspecting digester vessels in alkaline pulping service. Digester vessel refers to a continuous digester or an impregnation vessel in one- and two-vessel systems. These guidelines and procedures also apply to level tanks.

This TIP covers inspection of the code-defined pressure-containing “envelope” and of internal parts, including screens and their support structure, the center-pipe and its supports and the bottom outlet device/scraper. The TIP discusses preparing for inspection, inspecting the shell and nozzles for cracking and corrosion, inspecting internal and external components, and how to record the inspection findings and data. The TIP does not cover inspection of M&D, Pandia, Defibrator, other continuous digesters, or batch digester vessels; inspection of the latter is covered in TIP 0402-22 [1].

These guidelines supplement jurisdictional regulations for pressure vessel inspection. This TIP contains no guidance for inspecting associated external piping, auxiliary systems such as liquor heaters, flash tanks, the steaming vessel, the sand separator, or pressure limiting devices. This TIP does not help the reader interpret inspection data or assess the continuing fitness-for-service of a digester vessel, which can be done as described in API 579-1/ASME FFS-1, Fitness-For-Service [2] post-construction code, which is accepted by the National Board Inspection Code (NBIC) [3].