Duplex stainless, typically 2205, and super duplex, typically 2507, combine high strength with chloride resistance. They are specified for offshore topsides, seawater systems, desalination, pipelines and chemical service where 316 would pit or crack.
Duplex valves are usually bought with full documentation and are usually in good condition when they become surplus, because they are too expensive to abuse. The documentation is the main value driver after the body material itself.
Review points
What decides the value of duplex stainless valves
Grade
2205 versus 2507 is a significant value difference. Check the marking.
Certification
Material certificates and impact testing are expected.
Service
Offshore, seawater and chloride service. The history tells us what to expect inside.
Selling it
How to present the lot
Count by size and pattern, and note the marking on the body. If you have certificates, include them; if you do not, say so rather than implying they exist.
Do not separate trim from bodies to sell them individually unless the trim is clearly identifiable and valuable on its own. In most cases the assembly is worth more together.
Questions sellers ask
Do you buy super duplex valves?
Yes, and they are among the strongest items in the surplus market.
What about duplex valves with weld repairs?
Weld repairs on duplex need proper procedure and documentation. Tell us what was done.
Are used duplex valves saleable?
Yes, particularly with certificates.