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Pulp & Paper

Recovery boiler and digester outage

2026-07-20 · Black-liquor recovery boilers, continuous & batch digesters (BLRBAC / TAPPI / NBIC)

Measured outcomeCold-outage boiler and digester restart approved on schedule with complete BLRBAC and NBIC NB-23 evidence.

In a kraft pulp and paper mill, the black-liquor recovery boiler and the digester line are the heart of the operation and its highest-consequence pressure equipment. A waterwall tube leak in a recovery boiler risks a smelt-water reaction, making BLRBAC (Black Liquor Recovery Boiler Advisory Committee), TAPPI TIP, and NBIC NB-23 inspections during the annual cold outage non-negotiable.

Current state before intelliSPEC

  • Slow tube and overlay mapping: Ultrasonic thickness grids on thousands of composite waterwall tubes, floor tubes, superheater bends, and digester stainless weld overlays arrived as vendor spreadsheets that took days to reconcile with prior outages.
  • Smelt-spout and airport PT/UT silos: Penetrant and ultrasonic examination records on smelt spouts, primary air ports, and dissolving tanks lived in separate contractor binders from the outage schedule.
  • High-pressure restart reviews: Before lighting the recovery boiler or pressurizing the digester, the mill manager, insurer, and Authorized Inspector had to verify that every flagged tube, weld repair, and hydrotest was signed off.

Configured path

The mill configured intelliVISION, intelliEDGE, intelliINSPECT, intelliNDT, intelliINTEGRITY, and intelliPROJECTS.

  1. Tube-by-tube and cone-to-dome register: Recovery-boiler elevations, ports, smelt spouts, and digester shell zones were mapped in with historical thickness baselines.
  2. Offline scaffold capture: NDE technicians inside the furnace and digester captured UT grid readings and PT photos offline in , syncing at shift change.
  3. Outage wall chart and restart gates: and computed tube thinning rates immediately, routing repair welds into so restart gates could not clear until NBIC R-form and hydrotest evidence was attached.

Measured outcome

  • Zero surprises at hydrotest: Every thin tube and overlay repair was identified, welded, re-examined, and signed on the wall chart before the hydrotest gate opened.
  • Multi-year digester overlay trending: Corrosion and erosion of stainless weld overlay in batch and continuous digesters is tracked by zone across annual outages.
  • Insurer and BLRBAC confidence: Complete audit packages for the property insurer and jurisdictional inspector export in minutes.