UNS S32550 / F61

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Alloy 32550 (super duplex 255) is a super duplex stainless steel supplied in the hot worked and annealed condition. It achieves higher strengths than most stainless steels and alternative corrosion resistant alloys, offering the potential to reduce section size and therefore weight and cost.
As a 25% Cr alloy, with significant additions of copper, Alloy 32550 offers excellent corrosion resistance in a wide variety of corrosive chemicals including sulphuric, nitric and phosphoric acid. In seawater and other chloride containing environments it also provides outstanding resistance to pitting and crevice corrosion, with Critical Pitting Temperature exceeding 50°C. Excellent ductility and impact strength at both ambient and sub-zero temperatures combine with a high resistance to abrasion, erosion and cavitation erosion.
Listed in NACE MR 01 75 for sour service and having gained ASME Approval for Pressure Vessel applications, Alloy 32550 is tested to the highest degree using tests designed to guarantee that the trade-marked product possesses high integrity, a correct phase balance and the absence of sigma and other deleterious phases.

Chemical Composition

Mechanical Properties

Physical Properties


  • Ferralium® 255 – SD50 (Super Duplex 255)
  • 1.4507
  • ASTM A276/A479
  • UNS S32550
  • ASME A182 F61

Product Features: Key Features:

  • Originally developed in 1960’s, Alloy 32550 pioneered the addition of nitrogen, to create the first super duplex stainless steel
  • Originally developed in 1960’s, Alloy 32550 pioneered the addition of nitrogen, to create the first super duplex stainless steel
  • First super duplex stainless steel to achieve 586N/mm2 as a minimum 0.2% Proof Stress, up to 12” (300mm) section sizes
  • Pitting Resistance Equivalent (PREN) >40, indicating outstanding resistance to pitting and crevice corrosion
  • Very low levels of sulphur minimise the likelihood of inclusions as sites for potential pitting corrosion
  • Higher copper content provides self-healing effect at sites of pitting to inhibit further growth
  • Available as bars, plate, pipe and fittings with complementary weld wire
  • Particularly suitable for larger components as the formation of sigma phase is much less likely than it is for other Super Duplex grades


  • Oil & Gas industry pumps, valves, wellhead and subsea equipment
  • Pollution control scrubbers, precipitators, fans and pumps
  • Marine propellers, shafts, rudders, seals, pumps, valves
  • Bolts and fasteners
  • Process industry equipment in sulphuric acid, nitric acid, phosphoric acid, PP / PVC/TiOx production, agrochemicals
  • Grain and vegetable processing plant, sugar cane centrifuges
  • Pulp and paper digester blow vales, feed valves, washers, black liquor heater tubes, bleaching components
  • Copper smelting fans, tuyere bars, wet scrubbers, leaching area precipitators
  • Sewage treatment, seawater cooling, desalination plants

Our Products

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