Cartridge RHB6A 8944183200 NB190027 Isuzu 4BD1-T

So how do I prevent this failure?
A turbo will survive for many tens of thousands of kilometers driving if it is cared for. The simple rule is to ensure that before an engine is shut down that it is left to idle for a short time, particularly if it has been pushed hard or raced. Leaving it to idle will ensure that the heat is dissipated away from the turbo. Water cooled turbos are usually better in this regard, as the water jacket is very effective in soaking up the excess heat. However they are still limited in their operation after engine shut down as the water is no longer circulating around the cooling system.

Do I need to use a turbo timer then?
Not necessarily. Careful maintenance habits such as ensuring the engine is idle before shutdown will be sufficient to ensure that a turbo is not ruined through heat soak. A turbo timer is however a much more convenient way of ensuring that this happens without having to wait around each time you turn your engine off.

Ah, but I’ve got an intercooler, so I don't need to cool my turbo down!
Please go sit at the back of the class. An intercooler does not in any way shape or form assist in cooling the turbo. The function of an intercooler is to lower the temperature of the compressed air coming out of the turbo before the air enters the engine. The typical net effect of an intercooler will be to slightly raise the load on a turbo rather than lowering it.