Am looking for some advice on Gas Orifice plate resizing due to change in min/max flows. If anyone could point me in the direction of any good websites etc?

 

Is the meter for custody transfer or just in plant metering for control?

Contact your transmitter supplier. The calculations are easy enough, but knowing how to use them, well that is a learning experience!

 

For a basic sizing calculator, that is free, you can use this website: http://www.pipeflowcalculations.com/orifice.

However, all vendors will perform the same thing, generally free of charge, if you ask them. They will also push you for pertinent information that you may not include yourself, including required accuracy and turndown.