I am going to be removing quite a few 3/4" button head rivets from some structural steel soon. I don't want to harm the steel as I plan on reusing the members. What procedure is used in boiler repair work to remove rivets without harming the base metal?

Don't know about boiler work, but when I was working for the Chicago Transit Authority in the seventies and eighties, the standard procedure the iron workers used when replacing flanges on the L structure was to "bust" the rivets using a hand held rivet gun. This avoided issues with lead fumes in the smoke that came from the old paint when burning old structural steel, and they also had calculated that the cost of compressed air was less than the gas needed to do the job. Of course, the compressed air was supplied by an electric compressor running on trolley power; I don't know if the cost of the power was factored in.

As I recall, the tool in the hammer was not a chisel, but simply a blunt tool that was applied to the side of the head at as low an angle as possible. The idea was to shear the head off while the shank was held in the holes in the parent material. Typical work sequence was to bust every other rivet, replace them with high strength bolts, then bust the remainder. Of course, this was to allow service to continue on the track above while prep work was in progress; come Saturday OT the nuts were quick to spin off, the web was needle chipped and primed, and the new flanges went on quick. The job was finished with high strength bolts; the CTA had stopped hot riveting sometime in the sixties.

You don't have to worry about maintaining service, of course, but the bolts may be useful to keep a structure together and safe while you deal with the rivets, then dismantle it quickly when the crane is on-site.

If you are good with a torch just burn the heads off.
I have done it many times with little or no damage to the steel.

DBH

Unless a huge number of rivets are involved, you can drill through the head with a bit that is slightly bigger than the rivet's shank. a little experimentation may be needed at first, if the rivets were installed in oversized holes.

This goes quite fast with one person center punching and drilling starter holes and the second following with the bigger bit.

The head will come off when you've drilled far enough- stop immediately! If one side pops up due to the hole being off center, finish removing the head with a cold chisel. The rest of the rivet can usually be driven through fairly easily with a drift punch and puppy pounder or other heavy hammer.

This system works well on structural rivets or those securing sheet metal on car sides, but I would strongly recommend a method that gives more control for rivets on pressure vessels!

Steve Hunter
RMEO

Have a magnetic drill press? Drilling out the head gets a bit easier.
http://www.amazon.com/b?ie=UTF8&node=552788

Burning them out is the fastest and one can do it without any harm to the parent steel. Using a low preheat, "shave" the head of the side you are blowing through from and the exit head. This last point is very important - rust or scale on the "exit" head can turn the oxygen stream back into the parent metal thereby cutting it.

After the heads are shaved back to within an eighth or so of the sheets, keeping a low pre-heat, begin to heat the rivet in the center. When the center approaches oxidation, but with the sides of the rivet still dark, hit your cutting lever. Keep the torch parallel to the axis of the rivet and widen out your cut in a circular motion to within an eighth of the parent steel. When it cools, it will knock right out with a gun or a hand drift.

I've removed thousands of rivets this way without damage to the parent steel.

What Mr. Weaver said!!

A small anecdote from my own experience with rivets that is intended to be humorous at least in retrospect: Many years ago I was burning some rivets off of the frame of an antique car (Model T Ford) that I was restoring. I managed to get one rivet head cut off with the torch and moved around while kneeling to cut another placing the palm of my bare hand down on the concrete to steady myself. I bulls eyed the recently near molten rivet head with the palm of my hand. Left a nice little crater with a black circle. Didn't even hurt for about a half hour, then it hurt like heck!! Moral of the story, wear protective clothing/gloves, and appropriate eye protection etc. and try to be smarter than a rivet.....

Well said, Mr. Bane. I conveniently didn't mention the jet of molten metal that flies back at the operator while coring the rivet ...

Keep your tip cleaner handy...

Steve thanks! That is exactly the info. I was looking for!

You're welcome, sir.