ISO 15138 standard for flanges

[desheng88]

If i have a circular ducting that is D160mm, I would need to have 4 Dia12 holes.

But, what would the position be? 3, 6, 9, 12 o'clock or 45 degrees angle like 1.30, 4.30, 7.30, 10.30 o'clock position?

Thanks.

 

[europipe]

yes, you should straddle centerlines, so 45deg,135deg, 225deg and 315deg.
In piping we don't use the clockhandsystem.