144 hour Chinese transit visa.

Your itinerary is fine and you are eligible for 144 hours visa free transit in Beijing area (Tianjin is included). Your itinerary that matters is Abu Dhabi - Beijing - X country. Anyway, now I will point out several conditions that have to be fulfilled. I'm more than confident that your itinerary has met them, but just for a case.

- Your flight from Abu Dhabi to Beijing should not have any additional landing within mainland China.
- Your cruise (you didn't mention your destination), should not have as the first port call, immediately after you leave Tianjin, a place in mainland China, i.e. the first port call has to be in some other country like South Korea, Japan or any other. In case that the first port call is in mainland China, then you wouldn't be eligible for visa free transit.

Now, I suggest you to check your entire itinerary carefully and if you satisfy the above conditions, just proceed with your travel plans. As far as Etihad is concerned, I have heard several complaints regarding of their understanding of Chinese visa free scheme, although I don't expect nothing similar since they have already learnt about this details. In any case, you just have to be firm and decisive and have your documents in hard copy ready to be shown to the authorities.

To clarify one more thing. Your country A is UAE (Abu Dhabi), your country B is China (Beijing) and your country C is your first destination country during your cruise.