Thanks a lot for your answers.
But i would like to know if there are any ref in ASME code or other international standard codes.
I'm not able to find anything about it.
I didn't find any ref about the calculation (or specification) of wear pad thickness
ASME 31.3 gives a calculation method/criteria for reiforcing pad only (for pipe branches) and speaks about "wear pads" (named as "saddles") only in para 328.5.4g when say
"(g) Reinforcing pads and saddles...