Galvanized and Stainless Steel Bolts Interaction 9

[EngineeringEric]

I am working on two projects that I am debating the use of Galvanized steel plates and Stainless Steel Bolts.... Both cases will be considered marine and will be in cyclic conditions of wet/dry.

1) Wet, exposed, bridge. I want to use 1/4" plate connections with stainless through bolts to timber members. I have experienced overly rusted bolts and compromised timber in the past but the plates hold up quite well...

2) similar to first only more complex structure and now we introduce the presence of chlorine (like heavily chlorinated pool water)

... So any issues with material interactions that I am not aware of, or something i can specify to eliminate said interactions? and does the presence of chlorine effect the annodic-cathodic relation ship?

Both of these are large projects and the use of epoxy coatings will destroy the budget and the owner would rather just invest in a more routine maintenance program... but we all know how those maint. programs go.

Thank you for any advice/knowledge

 

[EdStainless]

I would stick with HDG for all of it.
Rain is good, it washes away crap that settles, especially near salt water.
You might want to look and make sure that you don't have places that can trap water though.
How the joints are made up can matter, often it is scuffing from tools or nuts (or bolt heads) turning against plates that scrape the Zn and create places that start to rust first.

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Plymouth Tube

 

[TVP]

I would be inclined to go with HDG too, based on your budget concerns. I have concerns about Type 304 stainless in this situation, and even 316 is marginal for crevice corrosion. The links I provided on swimming pools shows austenitic alloys that are considerably more expensive than even 316.

 

[EdStainless]

The trend for infrastructure work is to use duplex stainless grades.
They are about the same price as 316, but much stronger.
While they have similar crevice corrosion resistance to 316 they do have significantly better SCC resistance.
Grades like 2101, 2003, 2102 are becoming more popular for rebar, but they haven't worked into hardware like you are using yet.
The traditional duplex, 2205 is more expensive but it has higher corrosion resistance.

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Plymouth Tube

 

[TVP]

FWIW, Bumax Stainless in Sweden manufactures fasteners using duplex grade 2101. They aren't off-the-shelf items, but it is possible to obtain them:

http://www.fera.org.uk/pdf/Fera seminar 2 Feb 06 - Soren Andersson - Bulten.pdf

http://www.bumax.se/wp-content/uploads/2013/06/BUMAX-portfolio-pdf.pdf