ASME B Division 1 UG 28 to UG 30. Check your design code for more details. ASME B31.3 has info in 304.1.3. Refers to ASME.

If the calc gives no rings you may be better of adding them for manufacturing and erection reasons. 10s large bore (duct size)can be very difficult to handle without rings. If your company is paying for fabrication and erection you can save stack of money by designing rings correctly. If you design them wrong you will not be popular.

How to calculate? Slide rule, pen, paper and a bit of time