Life expectancy of plastic pipe

[worms]

I noticed tonight that the plastic waste pipe from my dishwasher has perished. This was never an elegant piece of plumbing, as instead of joining everything into the main waste pipe from the sink, some plumber has taken it out through the wall and (by a series of 90 degree bends) down into the sink waste drain outside. I don't know what sort of plastic this was, it is some sort of 1.5 inch or 40 mm push-fit, with rubber O-rings in the joints and has to be about 25 years old. The pipe was coated in numerous layers of exterior paint and several more of limewash and there was probably more strength remaining from the paint coatings than there was from the plastic - it crumbles like an egg-shell when you push your thumb into it.

Questions: Is this just the life expectancy of plastic pipe? Or is it a reaction to the caustic effects of dishwasher powder? If either of these, then I would be better to replace the whole run, inside and outside. Or could this be a reaction of the plastic to the caustic effects of limewash? - in which case there is no need to replace the inside run (which looks fine at present) but may require thought about what else the limewash is eating away at!

As ever, the collective PPUK wisdom would be welcome!

 

[CliffordPope]

I've never noticed this specific trouble, but I have observed that water-based emulsion paint has a peculiar effect on certain plastics, most notably electric cable sheathing.

 

[Keith Bowman]

It happens to our external sink drain pipes and we have no dishwasher so you can rule that out!

 

[skier-hughes]

Internal pipe has shorter life expectancy outside due to the sun, you need to use external pipework outside.

 

[worms]

Thanks, guys!

Pipe exits on a north-facing wall behind a plant trough, so it doesn't get a lot of UV exposure, however the inside surface of the pipe still looks ok, as if it is rotting preferentially from the outside. There is a similar external arrangement for the bedroom sink waste, but I am not brave enough to press that one with my thumb at the moment, just in case!

I think I might be able to reconfigure it so that the dishwasher waste joins the sink and washing machine waste pipes inside.

As is often the case, this is a job that I thought was way down the line, when I replace the sink...which I would do when I replace the kitchen work surface...which I would do after I replace the kitchen window...which I would do when the Premium Bond comes up!