I have no method. But usually RO are thin. Its a question of mechanical resistance. Often 3 to 5 mm will do.
Keep in mind that is the orifice is not thin (e/d >> 0.2) then the characteristics of the RO will change.
Can you expand it abit more? I didn't quite understand it! "Keep in mind that is the orifice is not thin (e/d >> 0.2) then the characteristics of the RO will change."
Morten A,
Appreciate your try. What is determined by a piping engineer is the thickness of permanent blind not RO.
May I ask what country you are working in?
If you review the thickness of orifice plates for flow measurement you will find the basis to be structural design for a maximum of 1000 inches of water pressure differential. This is likely based upon the differential at the flange taps. My restriction orifice sizing uses pipe tap calculations for permanent loss. The flange tap differential would be higher. The 1000 inch maximum likely pertains to distortion of the plate - detrimental to the accuracy of the flow measurement but not likely a threat to mechanical failure. Perhaps API or ISO have other guidelines.
If you are taking a large drop near the top of ASME Class 600 toward ambient such as a blowdown application I would use a choke.
Plates are suitable for permanent drop but not using the standard flow element thickness. If your restriction orifice exceeds 1000 inches of water but not as significant as 1000 psi differential, my "throw-down" recommendation would be to double the thickness required by API/ISO/ASME etc. for the flow element. I would use double the standard orifice thickness as the basis for anything in flange Class 300. I would not use this basis if the plate is large and in Class 600 or higher.
API MPMS 14.3.2 includes an Appendix 2-F on plate deflection. This refers to constants found in Mark’s Standard Handbook for Mechanical Engineers. Some work appears necessary to calculate the plate deflection based upon a design pressure differential at an operating temperature.
By that rule, if I have a 3/4" bore, then my plate is 3/4" thick also? Seems a bit thick.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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Im working in Denmark - but not as a piping engineer. My guess was just that the easiest way to make an RO would be to take a blind flange and drill a hole... Since its not for emasurement then accuracy could be less important than durability - and if the blind flange can withstand the pressure then surely the RO allso could?
But at least the poor soul got some (more) qualified bids
Actually in a number of cases space is limited like the case I have run into. Ro can be made from Blind Flange but sometimes they are much more thicker. Material is SS.
Now im a little curious - why would they be thicker than a blind flange? I would assume that stress on the flange/RO would be from the diffefrence in pressure across the flange/RO and dP cannot be greater than for a blind flange?
Orifice flanges and a plate make more sense to me than drilling a blind flange in the lower pressure classes. What do you plumb to the drilled side of the blind flange?
For higher pressure classes the "bean" style fixed chokes are a good fit. Chokes associated with the old "oil patch" technologies are a commodity. Several patterns exist from about 1935 that are cloned by many manufacturers. The choke "beans" can be found at many supply houses throughout the world. The bean is an a venturi path within an angle body designed to accommodate any errosive wear etc. This makes for easy replacement if required.
Another method for small low pressure applications has been a union fitting with a washer plate. I do not recommend these as my industry minimizes the use of threaded fittings.
I would just like to contribute 2 hints to this discussion:
The first one comes from DIN-1952 paragraph 18 (“Regeln für die Duchflußmessung …”)
Thickness of an Orifice should not exceed 0.1 D; thickness of cylindrical bore should be less than 0.02 D. If overall thickness is less than 0.02 D, no bevel is required.
And the second hint comes from a TÜV approved list for minimum thickness of line blinds for pressure testing of steel pipes. Just take the first line (test pressure 7 bar(g))
API MPMS 14.3.2 and ISO 5167 also include a minimum for flow elements. ISO states that "The thickness e of the orifice shall be between 0,005D and 0,02D." This requirement is not applicable as the purpose of a restriction orifice is to drop pressure instead of measure flow. My suggestion is to double the thickness required for the flow element plates because their published structural limit is 1000 inch water pressure differential.
Thanks for your replies. In my case, I have a condensate re-run pump which sends the unstabilised condensate (class 300#) to the condensate tanks (Class 150#).
