Careers Extending Continuous Digester Life at Kraft Pulp Mill, Indonesia
At a major Kraft pulp mill in Indonesia, a single vessel hydraulic type continuous digester was experiencing significant corrosion and pitting damage in the extraction and washing zones.Inspection revealed extensive surface degradation, localized gouging, wall thickness loss, and corrosion-related deterioration that threatened equipment reliability and long-term operational performance.
The mill required a solution that could:
- Restore the damage
- Protect against future corrosion and pitting
- Minimize outage duration
- Extend the service life
- Reduce the need for costly component replacement
W11-1094
Solution
IGS implemented a multi-year weld overlay program utilizing Stainless Steel 309LSi corrosion-resistant overlay technology.
The project included:
- Surface preparation through grinding and sandblasting
- Repair of deep gouges and localized damage
- Complete replacement of backing bars and screens in extraction and washing zones
- Automated weld overlay installation using IGS welding systems
- Periodic inspections and targeted maintenance overlays during scheduled outages
The initial 2005 outage addressed the most severely damaged areas, followed by strategic maintenance campaigns in subsequent years.
Scope of work
| Year | Area Repaired | Duration |
|---|---|---|
| 2005 | 3,321 ft2 | 12 days |
| 2006 | 1,016 ft2 | 7 days |
| 2007 | 1,016 ft2 | 7 days |
| 2008 | 1,670 ft2 | 7 days |
| 2009 | No work required | – |
| 2010 | 580 ft2 (planned) | 4 days |
| 2011 | 373.2 ft2 (planned) | 3 days |
Execution
Assessment and Surface Preparation
Initial inspections identified severe pitting corrosion in both extraction and washing zones, along with localized gouging reaching depths of approximately 17 mm into the shell. Damaged areas were repaired and prepared through grinding and sandblasting before overlay installation.
Weld Overlay Installation
Automated weld overlay systems were used to apply Stainless Steel 309LSi cladding across affected areas. The work included transition zones, tie-ins to existing overlays, and installation around extraction equipment and backing bar systems.
Ongoing Maintenance Strategy
Rather than replacing major sections of the vessel, the mill adopted a proactive maintenance approach, performing targeted overlay campaigns during planned outages to address emerging wear areas and maintain corrosion protection
Results
Rapid Turnaround
Large-scale repairs were completed during short outage windows, with up to 3,321 ft² restored in only 12 days and subsequent maintenance projects completed in as little as 7 days.
Long-Term Corrosion Protection
Inspection photographs taken after one, two, and three years of service showed the weld overlay continuing to provide protection in previously damaged areas, demonstrating the durability of the installed cladding system.
Extended Equipment Life
The multi-year program enabled the mill to maintain digester integrity while avoiding extensive vessel replacement, helping extend the digester’s service life.
Reduced Maintenance Risk
The recurring overlay strategy allowed the mill to address deterioration before it became a structural issue, improving reliability and reducing the risk of unscheduled downtime.
Key Benefits
- Restored heavily corroded extraction and washing zones
- Repaired deep shell gouges and localized wall loss
- Completed large-scale repairs during short outage windows
- Demonstrated overlay performance after multiple years of service
- Extended continuous digester operating life while reducing replacement costs
Project Summary
Through a structured weld overlay maintenance program between 2005 and 2011, this Kraft pulp mill successfully restored and protected critical continuous digester areas affected by corrosion and pitting. The combination of automated weld overlay technology, efficient outage execution, and long-term maintenance planning provided a cost-effective solution for extending asset life and improving operational reliability.
Between 2011 and 2025, localized manual welding repairs have been completed outside of the weld overlay zones. These, however caused galvanic corrosion, with IGS invited to repair the areas with automated weld overlay planned for 2027.
WATCH: How a Kraft Pulp Mill in Indonesia Extended the Life of Its Continuous Digester
Free consultation with an IGS Subject Matter Expert
IGS is here to provide information, answer questions and create an effective solution for your needs.