Central material feeding pipe abrasion

Yes, your aluminium is too soft or your conveyor spped is too fast and it's abrading at the inside corners. Stainless is the "standard" material used.

You will probably soon start to see "streamers" from where the material pellets rub along the inside of the tube and get "smeared" along the rough surface and then comes loose at a later time. (Looks like very thin plastic film with directional grain."

You risk contamination also if you now run another material through the scored pipes since there will be PMMA caught in the rough surface.

Thank you for answering dear collegue;

As can be seen on photos, abrasion occurs on linear pieces in the form of tiny craters (bends are inox or ceramic). We used alluminium pipes in our old system and didn't experience such a problem. Same pipes, same pumps, same machinery different results.

Pipe with abrasion---------------------Virgin pipe

You need to check the velocity of the material being transported and set the vacuum to the lowest functioning level. This will reduce the abrasive effect on the pipe. Another sullution would be to weld a liner on the outter radius on the inside of the curved sections of pipe. To check the velocity you need to drill a hole several feet from the inlet of the pipe and insert a peto tube attached to a gauge. This will be most usefull for keeping the system calibrated once you find the proper rate of flow. When taking these readings due it without product being transported otherwise the peto tube would likely be damaged. J.Conway

Did you check up the hardness/ heat treatment/ process of extrusion of previous aluminium pipe? was there any sort of abrasion resistant coating ?

Check whether it was aluminum alloy (viz Cu-Al) where more abrasion resitance may be achieved.