corrossion resistant buried fasteners

[cr1973]

I'm looking at options for fasteners used for mechanical joint connections in water main construction projects. The typical "cor-blue" bolts are hardly corrosion resistant, aside from the manufacturer's claims. We are looking at 304 or 316 stainless steel, but I'm wondering if there are any better options? The nuts and bolts are buried with the fittings in either sand or crushed stone, with the surrounding earth in some areas being moderately or severely corrosive in some cases. Perhaps an additional requirement to spray mastic before burying?

 

[TugboatEng]

Stainless steel must not be used in buried applications. Bronze would be a better option. However, Normal practice is to use carbon steel fasteners and apply a coating over the flanges after they are assembled. There are various paint/trowel on rubber coatings and tapes that are available for this.

 

[MJCronin]

https://www.whitfordww.com/wp-conte...or-Renewable-Energy-in-Harsh-Environments.pdf

https://www.eng-tips.com/viewthread.cfm?qid=424698

https://www.appliedbolting.com/pdf/anti-corrosion_coatings.pdf

MJCronin
Sr. Process Engineer

 

[EdStainless]

I have seen where some systems are using duplex 2205 SS fasteners as they are more corrosion resistant then 326 and muchmore cracking resistant.
Coated steel is the common choice.
Brass or Bronze will have issues long term, but a NiAlBronze should be very durable.
What about non-metallic, fiberglass bolts are available.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[alchemon]

Would it be feasible to add a field coating to the standard bolts/fittings? For example, on gas pipelines, we often specify a wax primer/tape type system. However, we also have cathodic protection on the pipe. I wonder if coating the bolts is asking for trouble?

 

[MJCronin]

Please see the PTFE coatings system offered by Whitford .... I posted a link

MJCronin
Sr. Process Engineer