You can transport a 50 beam with little extra effort, check with a trucking company. You can galvanize a 50 foot beam by either finding a company with a large tank or by dipping it twice. Check with a galvanizing company.
I would transport the beam in one piece. I don't really like field welding on galvanized members. The welds are not really protected by the galvanizing, and the cold galvanizing paint they use to touch up the welds is not as good as the original galvanizing.
Your local steel fabricator should be able to advise on shipping. They must do it all the time.
Railroads routinely transport 80' beam sections - so 50' is available - might have to wait awhile as most service centers cut them to 40'. There is a galvanizer either in western Kansas or Nebraska that advertizes a tank longer than 80'. Again it is doable.
Just find a local supplier or Google it and you will find all kinds of sources.
AWS WZC "Welding Zinc-Coated Steel" (formerly AWS D19.0-72), (American Welding Society) covers welding of galvanized steel.
Basic requirements: Remove galvanizing at least one inch from weld location, or specify that this area not be galvanized. When welding is completed, clean and coat with zinc-rich paint.
I'll join the party, this is what my notes say regarding welding galvanized surfaces.
For galvanized coating, repair field damage and site welds with two coats of a two pack epoxy primer polyamide zinc-rich paint coating containing a minimum of 92% zinc dust in the dry film which which will be built up to 75 micrometres minimum.
Not that it matters but if I get it well, your notes refer to the case of repairing the damaged galvanizing part by applying paint (epoxy primer)which means that said part will be coloured and this may not be accepted in some cases.
In Europe we use open trucks for transporting beams, rails etc. longer than 40'- it's not everyday routine but not so rare either.
Standard truck trailers these days are 53' long so a 50' piece is sort of a nobrainer. I used to work for a glulam manufacturer many years ago and we routinely shipped 75'-85' pieces half way across the country (with escorts). A year or so after I left the company they had a local move of some beams that were in the 150' length. That would have been interesting to see.
