Intepretation of ISO 5167-2:2003

[steamdude]

Hello Gents (and hopefully lots of ladies)

I am working on some flow meter installations, specifically orifice plates which have to be compliant with the above standard. My predicament is lack of suitable straight lengths of pipework as the pipe diameters are large.

In the standard is a table (Table 3 - required straight lengths between orifice plates and fittings without flow conditioners) which includes distances for s concentric expander 0.5D to D over a length of 2D.

What I would like to know is: do the actual dimensions of the expander have to be 0.5D to D and 2D long or are those max/min dimensions.

I have a 36" to 40" reducer which would have less flow disturbance so surely it must acceptable to use those table figures.

Thanks in advance.

 

[jsummerfield]

Consider another flow element like the McCrometer V-cone. The V-cone requires only three-diameters upstream and one-diameter downstream for suitable measurement.

The straight run requirements are associated with accuracy and repeatability. Consider the API MPMS standard that may have shorter run requirements than ISO 5167-2:2003.


John

 

[cornejoi]

I would take the standard at face value if I were you.

Everyone loves using orifice plates because they are supposedly cheap and nasty and accurate. This statement is not true when you consider installation costs if you require accuracy. Such is your case.

The reason that I would treat the standard at face value is because what they are publishing are the straight run requirements that they've experimented with and can garuntee accuracy (This also includes reducer sets, flow conditioners, ect). If you decide to deviate, you will introduce uncertainties that can only be quantified with a prover.

I'd investigate other technologies to measure flow if I were you, say Ultrasonic, Insertion type turbine, Annubar / Pitot tube.

Orifice plates are good for reapeatable flow. Accuracy is not the Orifice plates forte. AGA report # 3, and the standard that you are using reconfirm this notion since any accuracy that you want out of an orifice plate will come from reproducing lab results which means going to a calibrated meter run (Expensive as you know).

--Igor

 

[NeilatNEL]

We have done a lot of work on orifice plate installation errors at NEL and one of my colleagues chairs the commitee for ISO 5167. (I'm sure he could answer you question in more detail than you would ever want!)

From my experience I would guess that the recommendation in the standard is based on a set of tests with one particular design of expander. I doubt that general data will be available for different designs of expander. If you have a long straight length of pipe (in excess of 100 diameters) upstream of your expander it is probably fair to argue that if you comply with the guidance given in the standard then your installation, with a less severe expansion, will be OK. However I'd guess, given the size of your pipework, that you'll have bends, valves or other fixtures upstream of the expander and relatively close to your flowmeter. If this is the case your flowmeter will not just see the flow disturbance from the expander, it will see the combined effect of the expander and whatever is upstream of it.

How you handle this depends on how important it is to comply with the standard and who you are trying to convince that you have a good flowmeter installation. We have assessed similar installation problems in the past and using comparison with published test data, testing and computer modelling. Another option is to go with a different flowmeter. However, be aware that ALL flowmeters suffer from installation errors and manufacturer's recommendations on upstream straight lengths are often optimistic (for obvious reasons).

If you need any more details of this feel free to ask.

Cheers,

Neil

 

[bk834]

You may consider the use of a "high performance" flow
conditioner upstream of the primary element. These devices,although somewhat expensive in pipe sizes above 24 NPS, have been quite successful in reducing the number of upstream pipe diameters for a well formed flow profile.

Several manufacturers available:

Gallagher Flow Conditioner; Savant Measurement
CPA-50E; Canadian Pipeline Association
Daniel Profiler; Emerson Rosemount

Good Luck

bk