It may have been related to the fact that welding/flame cutting galvanized steel apparently releases very toxic gaseous compounds of zinc, so scrappers may have been reluctant to cut it up -- altho one doesn't normally think of scrappers as being a health-conscious environmental lot.... LOL . May have turned into a kind of scrap urban lore, in some locales. Just guessing....
Anyone who has ever experienced zinc-fume fever, even a mild case of it (raises hand) doesn't need health-consciousness to know it's bad news. It's like a short-lived case of flu. In severe cases, it can be really nasty. I got a mild dose from welding or brazing (I forget which) EMT, and I don't want to experience it again.
Today, there are throw-away masks that can protect you from it. 3M makes one, or did. I bought a few around 10 years ago. Ordinary dust masks and solvent-fume filters won't do it.
their description follows; Zinc is used in large quantities in the manufacture of brass, galvanized metals, and various other alloys. Inhalation of zinc oxide fumes can occur when welding or cutting on zinc-coated metals. Exposure to these fumes is known to cause metal fume fever. Symptoms of metal fume fever are very similar to those of common influenza. They include fever (rarely exceeding 102o F), chills, nausea, dryness of the throat, cough, fatigue, and general weakness and aching of the head and body. The victim may sweat profusely for a few hours, after which the body temperature begins to return to normal. The symptoms of metal fume fever have rarely, if ever, lasted beyond 24 hours. The subject can then appear to be more susceptible to the onset of this condition on Mondays or on weekdays following a holiday than they are on other days.
I find it interesting they made comment to it's effects relative to Mondays or holidays. Someone in OSHA has a sense of humor. ignator
I remove the zinc coating from galvanized pipe by allowing the ends to soak in straight muriatic (pool) acid for a few minutes, then neutralize with a water and baking soda solution followed by a water rinse.
The vapor created by the soak is hot, plentiful and Very Nasty smelling, so I only do this outside whilst standing upwind.
The resulting steel welds really well. I've avoided zinc fever so far.
The fumes created by gas cutting powder - coated steel left my nose offline for most of a year, though.
Around 8 or so years ago we discussed the subject here, after I'd complained about the fume fever, and someone -- maybe you -- recommended that treatment.
So I cut off some one-foot test pieces of EMT and stood them up in a plastic peanut butter jar, and poured muriatic acid around them to a depth of xix inches or so. The galvanizing stripped off in minutes.
Someone in the discussion had recommended against the baking soda because he said it could form a salt that would stay in the pores of the steel. So, just for a test, I simply rinsed the EMT off, scrubbing good with a fiber brush, dried them, and stuck them on a shelf in my dampish basement to see what happened. Until I had a really serious flood last fall, there wasn't a speck of rust on them. They were still shiny steel. Now one side of the pieces have a slight blush of rust.
Unfortunately, I haven't welded EMT since that day. d8-(. I had just been using it for practice, anyway.
Yeah, I did it outside. I will not open a container of hydrochloric acid in the same room with my machine tools -- or anything else I don't want to rust.
The caustic soda (NaOH) in drain cleaner also removes zinc, without affecting the steel. The CO2 in the air converts any lye you didn't remove into washing (Na2CO3) or baking (NaHCO3) soda. All are mildly protective of the steel, but not enough for outdoor use. You can see the difference between the silvery zinc and greyish steel to tell when it's done.
Drain cleaner doesn't release any fumes to damage your lungs or machinery. Spilled HCl can be more dangerous than other strong acids because it soaks in rather than reacting immediately with the outer layer of dead skin.
A quick heads up would be to check the ingredients before buying the drain cleaner as my neighbour bought some, I'm in the UK, and found that the main ingredient was sulphuric acid. My neighbour took the drain cleaner back where he bought it for a refund, as it was expensive, and he already had quite a quantity of sulphuric acid that he had bought to make pickling solution for his loco construction. Not all drain cleaners in the UK are sulphuric acid based though, many are caustic soda which is readily available for the purpose.
I don't know about Roebic, but Drano has ingredients in addition to lye. Supposedly they help the drain-clearing process, but are not so good when used for other purposes. E.g., paint stripping. Straight lye is good, Drano not.