Duplex and Stainless Steel Pipes for the Pulp and Paper Industry
Recommended Pipe & Tube Materials
Pulp and paper mills run some of the most chemically varied processes in heavy industry: hot alkaline cooking liquors, chlorine-based or oxygen-based bleaching chemicals, sulfur compounds and acidic condensates. This article explains where duplex 2205, 317L, 904L, 6Mo and nickel alloy pipes are used in a modern mill and why.
Corrosion Environments in a Pulp Mill
- Kraft digesters and cooking liquor: hot, alkaline, sulfide-containing liquors, with erosion from fibre and chips
- Bleach plants: chlorine dioxide, hypochlorite, peroxide and acid stages, with chlorides and low pH
- Recovery boiler and evaporators: hot, concentrated liquors and sulfur compounds
- Stock preparation and paper machine: chloride-containing process water, often warm and recirculated, which promotes pitting and crevice corrosion
Materials by Process Area
Digesters and Liquor Handling
Duplex 2205 is widely used for digester shells, liquor lines and heat exchangers. Its high strength allows thinner sections, and it resists both stress corrosion cracking and erosion-corrosion better than 304/316. Lean duplex grades may be used in less aggressive liquor service.
Bleach Plants
The bleach section is the most demanding area:
- 317L and 904L for moderate chloride and acid conditions
- 6Mo (254 SMO) and super duplex 2507 for chlorine dioxide stages and more aggressive filtrates
- Alloy 625 or C276 for the harshest, hot and highly oxidizing conditions
Evaporators and Recovery Area
Duplex stainless steel tubes and pipes are used in liquor evaporators and heat exchangers for their combination of corrosion resistance and strength. Stainless clad or solid duplex is often chosen instead of carbon steel to extend life.
Paper Machine and Water Systems
316L and 2205 for white water, stock lines and closed-loop circuits where chloride levels build up.
Why Duplex Is Popular in Pulp and Paper
| Advantage | Benefit to the mill |
|---|---|
| Higher yield strength than 316L | Thinner walls, lower weight and cost |
| Good resistance to chloride SCC | Longer life in hot, chloride-bearing liquors |
| Good erosion and abrasion resistance | Less wear in fibre and slurry lines |
| Better cost stability than high-nickel alloys | Lower lifecycle cost in many services |
Recommended Standards
- ASTM A790 / A928 (duplex pipe) and ASTM A789 (duplex tube)
- ASTM A312 (317L, 316L), ASTM B677 (904L)
- ASTM B444 (Alloy 625) and ASTM B622 (Alloy C276)
Selection and Fabrication Tips
- Identify the liquor, pH, temperature and chloride level for each pipeline instead of using one grade for the whole mill
- Follow duplex welding procedures (controlled heat input and interpass temperature) to keep the phase balance
- Pickle and passivate welds to restore corrosion resistance
- Consider erosion allowance in lines with solids or high velocity
- Email: info@duplex-stainless-steel.com
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Frequently Asked Questions
Q1: Why use duplex 2205 instead of 316L in pulp mills?
Duplex 2205 has roughly twice the strength and better resistance to chloride stress corrosion cracking and pitting, which extends service life and can reduce material weight and installed cost.
Q2: Which stainless steel is best for bleach plant piping?
It depends on the stage. 317L and 904L work in milder stages; 6Mo, super duplex or nickel alloys are chosen for chlorine dioxide and high-chloride, acidic stages.
Q3: Can duplex stainless steel pipe handle white and green liquor?
Yes, duplex grades are commonly used for white liquor and other alkaline liquor systems, subject to temperature and composition.
Q4: Do you supply pipe in large diameters for pulp mill projects?
Please tell us the required diameter range, wall thickness and quantity; we can quote both seamless and welded pipe.
Request a Quote for Pulp and Paper Pipes
Send us your process area, grade, standard, OD × wall thickness × length and quantity, and we will reply with a recommendation and pricing within 24 hours.