I'll add a bit more claification.
You do not want to hard roll the tubes prior to welding.
- It can lead to blow holes from traped gas/moisture in the joint
- It is very difficult to leak test the weld, and only the weld
You must hard roll the joints after welding.
- You need to be careful to stay away from both faces of the tubesheet, rolling the welds can cause cracks, rolling to the back of the tubesheet can cause tube problems
- You need the tubes well supported. If they are 'loose' in the holes and only welded at the front you can get vibration and the tubes rattling in the holes. They fatigue quickly this way.
You must have mock ups that are destructivly tested. And no re-welding unless a joint fails leak test. You don't care if they look good, you want them to work.
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Rust never sleeps
Neither should your protection