Tianjin & Xian can use Beijing Pass?

You can probably use Beijing Pass in Tianjin and Xian for riding public transportation, because it is a China T-Union card. Chinese news says China T-Union card in all of China T-Union cities, but in reality, it's not the case. Each cities have to update their system, which takes a lot of time. However during COVID era, workers relating to this worked hard to improve the system. I estimate to be average China T-Union card can be used in 90 percent of cases by now.

It is convenient to use China T-Union transportation card. Limitation is that you can only top it up and get a refund at the city the card is issued. Without careful preparation, a person can end up buying multiple China T-Union cards. Or if you top it up too much, remaining balance can be in huge figure.

China T-Union card from major cities doesn't require registration which is good.

Register something in China, then come back later, it may cause headache. Changed passport number, changed SIM card, changed mobile device may cause unexpected malfunction. If they want old numbers, or you have to make phone call in Chinese.

I'm visiting China now, Didi app isn't connecting to my Alipay account unlike my previous visit around New Year of this year. I got my phone repaired from inside, everything got reset.

Alipay say these phone numbers are different
+82-10-1234-5678
+82-010-1234-5678

Didi says they are the same. Actually they are. Payment assistant center in Qingdao Airport was not helping at all. They were speaking only in Chinese.