I just looked up the US DTA and it appears under Article 20 that Social Security payments are taxable only in the US, so any SS money you transfer to Thailand will not be taxed in Thailand.
I'm Australian. "Pensions" paid in Australia are not taxable in Thailand. I don't know about Social Security. You will need to read and absorb your country's DTA
If you're talking about taxes in Thailand, read and absorb the DTA relevant to your country. Chances are if you are importing pension money you will pay zero