M.Wasif,
I am not sure about your project but remember to look at two things when you plan to replace the Romanian tubes with ASTM tubes. One is obviously, the material equivalence, the other is the dimensional standard. While the ASTM material will follow the ASME B36.10, the Romanian tube might follow one of the dimensional standards like STN 42 6710, 42 5716 or 42 5715.
Romanian mills are very versatile. They make pipe & tubes for European, Russian and North American markets
I personally have no experience with Romanian material. This is what I found doing some research.
Ganga D. Deka, P. Eng
Canada