The two main reasons for the use of stainless steels and, on occasion, nickel alloys and other metals in the Pulp and Paper Industry is to avoid iron contamination of the product and to resist process corrosion. Although most mills use nominally the same sulphate kraft or sulphite process, there are sufficient mill-to-mill difference that ca affect corrosion behaviour.
304L and 316L are the two most commonly used stainless steel alloys, with the 6%Mo super-austenitics used primarily in the bleach plant, and an increasing use of various duplex stainless steels in kraft liquor applications.
Some of the more common applications for stainless steels include:
- Batch and continuous digesters (sulphate and sulphite)
- Neutral Sulphite Semichemical (NSSC), Thermomechanical pulping (TMP)
- Brown stock washers
- Black liquor equipment and tanks and recovery circuit
- Bleach plant (all types)
- Lime kiln (high temperature properties)
- Tall Oil
- Air and water pollution control equipment
- Waste paper recycling
- Stock preparation equipment
- Paper machine including suction rolls
For a complete discussion of materials selection, see the NI publication 11025 Stainless Steels and Specialty Alloys for Modern Pulp and Paper Mills.