Duplex and High Alloy Construction

U-Tube Heat Exchangers For

Duplex and High Alloy Construction
U-Tube Duty

Beyond 316L the choices stop being general purpose and start being specific. Each alloy was developed for a particular problem, and choosing well means naming the problem precisely.

Duplex 2205 and super duplex. A mixed austenitic-ferritic structure giving roughly twice the strength of 316L and far better chloride stress-corrosion cracking resistance. The higher strength allows thinner walls. The caution is that duplex work-hardens noticeably during bending, so minimum bend radius is more generous and forming is less forgiving.

Alloy 20. Developed for sulfuric acid service and still the default there, with good resistance to a range of mixed acids.

Duplex and the U-Bend. Duplex is the alloy where bending most affects the design. It work-hardens significantly, which raises forming loads and springback, and the ferrite-austenite balance in the cold-worked region needs attention.

In practice this means a more generous minimum bend radius, a fabricator experienced with the material, and in some services a post-bend solution anneal. None of it is exotic, and all of it needs to be decided before the tubes are ordered.