FIGURE 23 - uploaded by Angela Wensley
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Argon back purging for field welding of a duplex stainless steel batch digester using the GTAW process.
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Duplex stainless steel has become the preferred material of construction for new kraft digesters, both for reasons of excellent corrosion resistance and cost effectiveness compared with other materials of construction. Most duplex stainless steel digesters have been constructed using UNS S32205 (type 2205) stainless steel due to the greater availab...
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Duplex stainless steel has become the preferred material of construction for new kraft digesters, both for reasons of excellent corrosion resistance and cost effectiveness compared with other materials of construction. Most duplex stainless steel digesters have been constructed using UNS S32205 (type 2205) stainless steel due to the greater availab...
Citations
... The current state-of-the-art material for continuous digesters is type 2205 duplex stainless steel. Except for the highly-stressed bottom scraper, there have been no significant corrosion or cracking problems with type 2205 duplex stainless steel in continuous digesters [5]. ...
... Audouard [9,10], Kivisäkk [12], Troselius [13], Leinonen [14,15], and Singh [17] have demonstrated that 2205, 2304, and 2507 duplex stainless steels (typically containing 40% to 50% ferrite in the microstructure) are much more resistant to SCC in alkaline liquors than are 304L and 316L austenitic stainless steels (100% austenite in the microstructure). The current material of choice for new digesters is 2205 duplex stainless steel [5]. The central pipe in the Line 1 digester was replaced using type 2205 duplex stainless steel. ...
Progress in controlling corrosion is discontinuous. Eight breakthroughs in corrosion control or materials engineering in the pulp and paper industry during the last 80 years have been examined to discover keys to success in research and implementation. Successful cooperative research programs have focused goals, well-planned research and organization structures that involve both funding managers and the engineers who will implement the results. Entrepreneurial breakthroughs by supplier companies confirm that catastrophes are not a prerequisite for success. However, for novel technologies to be implemented, their operation and benefits must be well understood by the engineers who will implement them. Recognizing hidden problems and applying developments from other industries can have breakthrough benefits but requires a type of thinking not normally sought in mill engineers. Because of reduced research funding by pulp and paper companies, future breakthroughs in corrosion control and materials engineering will depend on research and development largely funded by governments, equipment suppliers or other industries. Technology roadmaps may be the best tool for prioritizing precompetitive research that has broad industry support.
Duplex stainless steels are particularly well suited for the kraft chemical pulping process and they have become the de facto standard materials of construction for digesters, steaming vessels, level tanks, sand separators, flash tanks, liquor tanks, and concentrators. The tendency to push these materials beyond their limits has resulted in corrosion, cracking, and erosion. Duplex stainless steels have not fared well in corrosive bleach plant applications. Examples are given of good and bad applications, with the resulting ugly consequences that can occur if duplex is pushed too far.
