Is it possible to check if the weld is full penetration using MT test?
Thanks for answers.

Since MT is a surface examination methode, it will not be possible to verify whether ther is lack of penetration. Sorry

Isn’t there a table in SEC V (table A-110) that has a breakdown of imperfection vs. type of NDT method that is capable of detecting it? I think that incomplete penetration is listed as ….all or most STD techniques are capable of detecting this imperfection under all or most circumstances.that is if you can access that side of the weld

Simple VT would detect lack of penetration if you can access the backside (root) of the weld.