Duplex or Nickel Alloy Tube How to Decide
The cost difference between duplex and a nickel alloy is large enough that the decision deserves stream data rather than a rule of thumb.
What duplex actually buys you
Duplex stainless is roughly half austenite and half ferrite, which gives about twice the yield strength of 316L and much better resistance to chloride stress corrosion cracking.
The range runs from lean grades S32101 and S32304 through S31803 and S32205 to super duplex S32750 and S32760, and hyper duplex S32707.
Tubing is produced to ASTM/ASME A/SA789 and pipe to A/SA790, in tube sizes from 12 mm to 76.2 mm and pipe to 273.05 mm.
Where duplex runs out
Reducing acids. Hydrochloric and sulphuric service is where Hastelloy B2, B3 and C276 are specified instead.
High temperature. Duplex loses its phase balance and its toughness in the temperature range where Incoloy 800H and Inconel 617 and 625 are used.
Hydrofluoric acid and high velocity seawater, where Monel 400 remains the reference material.
The nickel alloy families
Nickel and nickel-copper: Nickel 200, Monel 400, K500.
Nickel-chromium: Inconel 600, 601, 602, 617, 625, 690 and X750 for oxidising and high temperature duty.
Iron-nickel-chromium: Incoloy 800, 800H and 825 for furnace and sulphuric service.
Nickel-molybdenum and nickel-chromium-molybdenum: Hastelloy B2, B3, C276, C22 for reducing media and mixed acid streams.
A practical sequence
Identify the mechanism, not the general corrosivity: pitting, chloride cracking, reducing acid attack, creep or erosion.
If chloride cracking and strength are the drivers, duplex is usually the economic answer.
If the stream is reducing, very hot, or hydrofluoric, price the nickel alloy - a duplex tube in that service is a replacement job waiting to happen.
Name the specification with the grade. B163, B622 and API 5CRA carry different testing requirements for the same alloy.
Tube Referenced Above
Duplex Stainless Steel Tube
Duplex and super duplex seamless tube and pipe to ASTM A789 and A790
Tube outside diameter: 1/2" - 3" (12 mm - 76.2 mm) · Tube wall thickness: 0.02" - 0.5" (0.5 mm - 12.0 mm)
Nickel / Nickel Alloy Tube
Monel, Inconel, Incoloy and Hastelloy grade seamless tube for the hardest corrosion duty
Tube outside diameter: 1/2" - 3" (12 mm - 76.2 mm) · Tube wall thickness: 0.02" - 0.5" (0.5 mm - 12.0 mm)
Stainless Steel Tube
Austenitic and super austenitic seamless tube and pipe to ASTM A213, A269 and A312
Tube outside diameter: 1/2" - 3" (12 mm - 76.2 mm) · Tube wall thickness: 0.02" - 0.5" (0.5 mm - 12.0 mm)More guides
Reader Questions
Is super duplex enough for seawater cooling?
It depends on chloride level, temperature and velocity. Super duplex S32750 and S32760 are widely used; at high velocity or elevated temperature the selection moves to a nickel alloy.
Which specification should I quote for nickel alloy heat exchanger tube?
ASTM/ASME B/SB163 covers seamless nickel and nickel alloy condenser and heat exchanger tubes. Other grades fall under B165, B167, B407, B423, B444, B622 or B690.
Apply This to Your Bundle
Send the duty, the stream data and the envelope. We will tell you which geometry and grade the guide points to in your case.
[email protected] · Tel 0086 512 58392615 · Monday to Saturday, 08:30 - 17:30 China Standard Time (GMT+8)