The pipe is heated up / the pipe heats up / the pipe gets heated up

Are the following sentences grammatically correct, if not what should I change?

1. The pipe is heated up by the constant flow of steam through it.
2. The pipe heats up due to the constant flow of steam.
3. The steam heats up the pipe due to constantly flowing through it.
4. The pipe gets heated up as the steam is constantly flowing through it.

Cheers.