This is the final grouping of steel ingots. Thankfully, they get a bit more clustered at this point.
Go past Wild Bill and up his set of stairs. There's a wooden shack at the top with 3 wildmen inside. Kill them and take their ammo. There are 2 ingots inside their shack along with some other good loot. 2
Turn around and get onto the only catwalk here. Go along the line. Watch out for a trog ambush along the way though. The catwalk isn't exactly an ideal fighting spot. Go further until you get to a spot where there is a large pipe that crosses over the catwalk. Jump onto it and follow it over to the trog at the end. Kill him and grab the 2 ingots he was protecting. Walk back to the catwalk. Continue along it to reach the stairs. There will be a wildman guarding the entrance staircase to the furnace. Kill him and start going up. Don't hug the furnace wall though, since it will give you a nasty dose of radiation. You're looking for the next flat area with some vents. Jump onto it and fight the 4 wildmen on this rooftop. Kill them and start moving through the rooftop. Get to the back area and kill a few trogs who might still be here. There are 4 ingots in a pile of guts in the corner. Pick them up and look over the edge. 6
You need to get to a lower area with four smokestacks and a metal catwalk. It is sealed of ffrom the other area. It's really hard to climb up, so I suggest that you drop down from this rooftop. Look for the one big smokestack right next to the roof's edge. It will be in line with your goal. Save. Then jump out and try to hug the pipe. If you manage to do this, you should slide down the pipe at a slow rate and survive. Drop down further to the metal catwalk and go down the line. Loot the ammo boxes in the area and get to the end. There are 4 ingots in the corner. Picking up the ingots triggers a trog attack, so spin around and take them out. Make your way back to the Wildmen Shack and the staircase. 4
The last grouping is in this high area of the plant. Move up the staircase to the top of the reactor. Be ready for one very serious fight though. 
There are five wildmen and a powerful turret up here. Move along the left side to quickly reach the terminal. Hack it and reset the targeting to hit the Wildmen too. You can stay behind the support beam and just take out the Wildmen as they rush you. Disable the turret once they're dead. Go up the stairs and get to the very top of the structure. Kill any trogs that might be waiting around here. They often jump off the side accidentally, so you might not have to fight any. Once you get to the very top, you'll find 12 ingots on the catwalk. Go back down to the level with the turret. Jump out onto the big steel ramp. Follow it all the way down to the ground level. There are 7 more ingots at the end of the ramp. 19
This should be it, if you have already grabbed the 3 ingots from the abandoned area. If not, grab them on your way out. Report to Everrett for your reward.