Vacuum brazing super duplex stainless steel is difficult because the slow heating and cooling cycles can form deleterious secondary phases such as sigma. Working with Krohne and TWI on the Innovate UK Adv-Flow project, we helped develop a furnace process that brazes super duplex without harming its mechanical properties or corrosion resistance.
The project
Langley Alloys worked with Krohne and TWI on the Innovate UK project Adv-Flow. The aim was to develop a process for producing advanced Coriolis mass flow meters in super duplex stainless steel, opening up applications in more challenging environments such as oil and gas.
The brazing challenge
Vacuum brazing assembles Coriolis flow meters with a high degree of accuracy and repeatability, but both the heating and cooling rates are relatively slow. For standard meters in Alloy 316L this is not an issue. In Alloy 2205 duplex stainless steel it becomes harder, because slow cooling in a vacuum can form deleterious secondary phases. Super duplex stainless steels are even more sensitive to phases such as sigma, which was the central challenge for the team.
Developing the process
TWI, a leading authority on joining and fabrication, replicated candidate process settings in its vacuum furnaces. Krohne then reproduced and validated those settings in its large-scale production facility. Furnace parameters were optimised so that super duplex could be processed without affecting its mechanical properties or corrosion resistance. With the parameters fixed, the team shortlisted suitable braze alloys on wettability and joint strength at the given temperatures, and successfully produced super duplex Coriolis flow meters for more challenging applications.
Super duplex stock
We carry an extensive stock of super duplex stainless steel as bars, plates and pipes:
- Ferralium® 255 (S32550, 1.4507, F61)
- Alloy 32760 (S32760, 1.4501, F55, Zeron 100®)
- Alloy 32750 (S32750, 1.4410, F53, SAF2507)
