Originally Posted by Diesel911

A couple of things cause the Injector Nozzle to wear out.

The little Pintle is being pushed back down by the Spring that is inside of the Injector and beats on the Metal seat when it stops.

Carbon particles from combustion and particles that make it through that 10 Nominal Micron Secondary Spin-on Filter get between the seating area and when the Pintle is pushed down smashes them into the seating area embedding some of it into the Metal.

Not unlike fast moving pressurized Water erodes through solid Rock the Diesel Fuel erodes the Steel including the seating area.

Combustion erodes the exposed tip of the Injector Nozzle. If the erosion is bad enough it effects the Injector Spray pattern.

And added to the above stuff Heat and temp change stresses.

It is entirely amazing an Injector Nozzle survives as long as they do.