TAPPI TIP 0402-22:2019

TAPPI TIP 0402-22 provides guidelines for inspecting batch digesters in pulp mills. It describes damage mechanisms and addresses inspection frequency, planning, methods, damage or inspection locations, cleaning and preparation, technician qualifications, test equipment and documentation.

The primary focus of this TIP is stationary, vertical, cylindrical, welded, carbon steel digesters that make up the vast majority of the batch digesters in service. Batch digesters may be made from carbon steel or stainless steel. Carbon steel vessels may be wholly or partially internally protected with corrosion-resistant alloy (CRA) weld overlay, clad layer or thermal spray coating. Vertical cylindrical digesters constructed of solid stainless steel are covered in this revision of the TIP.

Digesters of riveted or forge welded construction are not covered in this TIP. Inspection of batch digesters in acidic (sulfite) pulping service, which are stainless steel or have a brick-lining, is not specifically covered by this TIP, although the general guidelines herein apply. This TIP does not provide guidance on interpreting inspection findings, assessing fitness for continued service or designing acceptable repairs. The National Board Inspection Code [1], API 579-1/ASME FFS-1 Post-Construction Code [2], and ASME PCC-2 [3] provide such guidance.

Inspection guidelines in this TIP are to supplement, not supersede, jurisdictional and regulatory requirements.