What is "Steelduct"

I am making a composter, and I have a piece of "steelduct" that would be perfect, but it will be used outside and I am concerned about rust.
I don't know what steelduct is and a search didn't turn anything up. It "looks" like galvenized steel conduit; but I am hoping someone actually knows. If it is galvanized, is it galvanized on the inside also, or just the outside? Thanks.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

We used to get "steel duct" for culverts in the Midwest. Galvanized inside and out.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Then I got lucky! Thanks
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.