prasenjith, it would help a lot if you would state your Code of Construction, if any. Piping? Vessel? US Code? Foreign Code? Custom blind? B16.5 blind?
ASME B16.5 permits blind flanges to have a centrally located tapped hole up to certain sizes, I believe. Otherwise you are likely falling under the Code of construction.
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand