If all else fails and assuming the end of the drill is soft.

Cut the drill off close to the chuck jaws and drill or bore out to 18mm or so. The remaining 'tube' will probably collapse enough to enable the chuck to be loosened.

Martin

Might be worth trying freezer spray on different parts, or putting it in the freezer then dipping the outer shell in warm water?

Sorry to bring a non engineering solution into play but when I have had a key less chuck lock up I found two large Stilsons in opposite directions have always worked sometimes with the the help of a BGH.

Although I've done the Stilsons trick in retrospect there is considerable risk of distorting the hood, which is quite thin in places, thereby preventing the chuck from working properly ever again. I know plenty of folk have successfully used this technique but after jamming up a chuck I'm pretty sure that I'm not feeling lucky today so further exciting the workshop gremlin colony seems less than prudent! That said when I did the stilson trick the push needed to release was pretty modest. Getting somewhere near the monster heave needed to shift rusted iron pipe fittings would be a whole 'nother story.

Best option is probably to remove the hood in the manner prescribed when stripping the chuck for servicing. As soon as the hood starts to unscrew pressure will be released. Having started you might as well take the thing completely apart for a proper birthday. This **LINK** shows what is involved along with simple, safe to use tooling for taking it apart. I believe all engineering keyless chucks are essentially similar to the Albrecht layout. Searching Goodgle for rebuilding an Albrecht chuck comes up with plenty of nice pictures so you can see what you are going to have to deal with, before you drop all those balls too. Drill slipping back and associated jamming are generally considered strong indicators that servicing is needed anyway. Its important that the inside of the hood isn't completely smooth. It needs to be lightly scuffed, 320 grit abrasive is said to leave the right finish, so that the jaws can get a grip on it even when oily. This grip is important if the self tightening is to work efficiently.

Clive.