Hi Nalla,

U need to requalify PQR. U existing PQR  can cover only 16 mm and above ( if CVN is required) whichever -20 degree C or – 40 degree C.
    Table 4.6 # 2  Minimum thickness qualify is T or 5/8 in( 16 mm) whichever is less, except if T less than ¼ in( 6mm)then the minimum thickness qualify is 1/8 in( 3 mm).

Meaning that if PQR qualify 25.4 mm then the minimum thickness qualify is 16 mm. Let said if u PQR qualify 6 mm then minimum thickness still same 6 mm. Unless u PQR qualify less than 6 mm then u can use minimum thickness qualify is 1/8 in( 3mm). Please take note that if qualify less than 1 in(25 mm) the maximum qualify rang is only (thickness x2).

I guess that – 20 degree C  u mention is a  design temperature for structure. Not CVN requirement.

If im missing something. Hope senior members here in AWS welding forum. please help to clarify.

Thank,

S. Winai