ABS is less than desirable

Roughly 35 years old. Heat damage for sure. All the cracking is above the boiler piping and in a chase where the heat collects.

I show up and there's a puddle by the boiler and the customer had turned the water off. I turn the water on a touch and the 3/4" copper has a pin hole spraying the ceiling above the boiler. I replace the section and some charkbite couplings from a previous repair and turn the water on. I tell the customer to run the faucets and flush the toilets to check that everything was working and to get the air out.

They flush a toilet and it just starts pouring above the boiler. My first thought was the pipe got stressed when some hack put in the ada tub and clearly did a schit job on the drain. The 3"x1-1/2" wye cracked through the hub, but also after that and after a 3" 45 the pipe cracked all the way around leaving the 45 with some stubs just hanging.

I think the heating and cooling cycles cause the pipe to rip itself apart. My guess is the inner and outer layers of abs expanded at a different rate than the foam core.

There were 3 complete breaks in the basement and the pipe running to the second floor cracked completely through just above the floor and just below the ceiling. Most of the cracks that ran longways were only on the inner layers of the piping but with minimal movement cracked all the way through. The cleanout above the water heater also cracked.

I think the same would happen to foam core PVC.

I have seen schedule 40 pvc in this same situation and it handles it great. But no one uses foam core pvc around here so my guess is that solid core won't rip itself apart from differential expansion.