Duplex 2205 Stainless Steel Welded Pipe: What the Grade Really Is
Duplex 2205 stainless steel welded pipe is formed from UNS S31803 or S32205 strip, a balanced ferritic-austenitic structure with about 22% chromium, 3% molybdenum and 5% nickel. That chemistry lifts the pitting resistance equivalent number (PREN) to roughly 34, against about 24 for 316L, and it is the reason duplex 2205 stainless steel welded pipe holds up where chlorides attack austenitic grades.
Buyers comparing duplex 2205 stainless steel welded pipe with the 316L line already on their P&ID are rarely arguing about corrosion alone. The decision turns on wall thickness, weight, support spacing and how many shutdowns the line will need over a twenty-year design life.
Chloride SCC resistance | Limited above about 60 C | Service proven above 100 C
Relative material cost per kg | 1.0 | 1.3 to 1.5
Why the Wall Gets Thinner
With 450 MPa minimum yield against 170 MPa, a duplex 2205 stainless steel welded pipe can often run at 60% to 70% of the 316L wall thickness at the same design pressure, once corrosion allowance and mill tolerances are applied honestly. On a 1,200 mm OD line that is several tonnes of steel per hundred metres, and it also cuts welding time, freight cost and structural support load.
The catch is that duplex grades are less forgiving in the weld zone. Heat input has to be controlled, root shielding with nitrogen-rich gas is normal practice, and the finished component needs solution annealing at 1,020 to 1,100 C followed by rapid cooling to restore the ferrite.austenite balance and keep sigma phase out.
Where Duplex 2205 Pays Off
Seawater cooling circuits, desalination trains, chloride-bearing chemical streams, pulp bleach plants, flue gas desulphurisation scrubbers and brine tank farms are the classic territory for duplex 2205 stainless steel welded pipe. In each case the alternative is either a short-life 316L line or an expensive super duplex upgrade.
Welding and Testing Large Diameter Duplex Pipe
At SHIWANG PIPE, duplex 2205 stainless steel welded pipe is formed on 8,000 tonne, 15 metre presses and welded with controlled heat input, then solution annealed and pickled. Testing follows the purchase specification: 100% radiographic testing or ultrasonic testing on request, dye penetrant on welds, hydrostatic test, ferrite content check and a full EN 10204 3.1 material test certificate with heat number traceability.
How to Specify Your Order
Give the outside diameter, wall thickness, length, grade and standard (ASTM A358, A312 or A240, EN 10217-7), the test regime, the certificate type, marking and packing. Ambiguity in any of these is where delivery delays start.
Related reading on this site: large diameter thick wall stainless steel welded pipe, stainless steel welded pipe for chemical engineering and welded pipe for water treatment.
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