Testing of Differential Pressure Cone Type Flow- Meters to Various International Standards

Philip A Lawrence - Chairman ISO TC193 Sc#3(Upstream Natural Gas Standards)

8th

Technology is advancing at an ever increasing rate, as a consequence,engineering methodology and applications in flow measurement are forcing a change for the better.

These newer technologies can often bring advances to the operational processes within many industries.

The advances can also improve the overall production of a facility by a better performance, better reliability, and lower costs.

In the past however, the introduction and use of these newer technologies had been an issue due to the standardization process needed for acceptance.

Abstract

Measurement Standards from organizations such as the InternationalOrganization for Standardization, the American Petroleum Institute and the American Gas Association have experienced from time to time some examples of delayed publication.

Whilst these paper standards serve to protect and guide companies in their use of technology, they have often prevented the introduction of new and often better technology by virtue of the long process time in production, agreement, and administration of the said standard.

Thankfully today newer and vibrant standards writing committees with younger members are helping to get a document through a committee and to the draft stage in much shorter times than in the past.

Abstract

The standardization bodies are gradually moving to produce standardization protocols that are being used to help newer devices in their quest for acceptance.

These protocols such as MPMS API 22.2 differential pressure test protocol or the OIML R137 are a new family of documents that can be used not only to demonstrate a meters fidelity but also to show a “real world” installation philosophy by virtue of the standards installation and perturbation testing parameters.

Abstract

This paper details the recent testing of various cone type differential pressure meters at various laboratories including the CEESI air test facility in Nunn Colorado.

An explanation and overview of the technology will also be discussed in the paper together with a view of some new ideas in this technology genre.

Abstract

Cone Type Meters

Cone Type D.P flow meters are becoming increasingly popular world wide in the oil and gas industry and are showing increasing promise as an alternative to conventional orifice plates and other such D.P. meter types.

The cone D.P meter is a member of the Generic Differential Pressure (DP) Meter family and operates according to the same physical principles as other DP meter types, the hydraulic flow equation is exactly the same for the family of cone meters as is the Venturi and Orifice plate

Cone Type Meters

Where as the orifice and Venturi meters constrict the flow-stream across a beta edge boundary contraction the cone meter differential element causes the fluid flow to be pushed towards the pipe wall away from the centerline of the meter and through an annulus whilst having a consistent “ meter tube diameter ”!

Over a predetermined cone length the centrally mounted cone element also produces a linearization effect in the throat of the meter.

The first meter using this Philosophy was invented by Burton Dunglinson of the Electroflo-Meter Company Ltd in 1935 from the UK. (Figure 1.0 next)

Cone Type Meters

Burton Dunglinson – 1935 Patent

Cone Type Meters - Primary Device Calibration

API 22.2 and OIMLR137 are not meter design standards but in fact test protocols can, be concerned with artifact compliance calibration techniques during the field application of the device proof or type tested within these protocols.

If the relationship between geometric similitude (mechanical and dynamic) of the various sized metering devices and corresponding data sets are not drawn together properly there may be performance issues !

The need for each installed meter to be calibrated in a traceable laboratory over the Reynolds number (ReD) flow range that corresponds to the in field condition or application may be needed in certain cases.

Cone Type Meters - Primary Device Calibration

Calibration of the standardized orifice meter using the artifact compliance technique requires conformity and accuracy during manufacture of the plate and plate holder.

Correct installation, seal ring integrity, correct DP tap communication, plate concentricity in manufacture and installation plus a meter tube manufacturing accuracy and surface roughness compliance as stated in the relevant standards (usually API MPMS Chapter 14.3 or ISO 5167- Part1 ).

Cone Type Meters - Primary Device Calibration

ISO 5167 Part 1, - Performance of the standardized orifice plate, nozzle, Venturi nozzle and Venturi d.P. Meters across proven geometric designs and over particular ranges of flow conditions or Reynolds number.(ReD).

The ISO 5167 and API standards cover these meter types due to a long research history where large test data sets are usually publicly available for peer review and confirmation.

This is why we do not need to test each orifice plate each time under kinematical flow conditions to obtain its (C.d.) coefficient of discharge, but just to make sure the artifact geometry (dimensions) are correct and the installation and operation flow region is correct.

Cone Type Meters

Standardization of Generic Cone Type Meters

Currently ISO 5167,or API design standards do not cover cone type DP meters since the patent protection has only recently lapsed and no large independent research or JIP’s have yet shown that a cone type meters design geometries have repeatable and reproducible performances over given flow condition ranges.

This is due to many factors but one main factor is the differing dimensional differences between the various manufacturers designs, tap geometries, cone angles together with slight differences in the methods to support the differential producer cone element on a stem cantilever system.

Cone Type Meters

The cantilever support of the cone and its stability is critical if the fidelity of a cone meter device and long-term performance is to be maintained.

Some meters in particular with larger diameters >6 inch have cones that are fabricated from steel sheets which can have an effect on the repeatability between successive meters due to heat stress and torsion by the welding process thus causing slight changes in the cone dimensional position for each meter manufactured.

Cone Type Meters

Manufacturing Control

Control of the surface roughness of the cone element and meter tube for each meter manufactured may also help to narrow some of the C.d. point spread that has been seen over recent years.

Provided that these larger diameter welded meter types are manufactured in a similar way by using repeatable manufacturing processes & jigs that offer repeatable construction between devices, then differences between each manufactured device can be reconciled by using a calibration performed over the intended in field ReD range.

Cone Type Meters

P

P1 P2

Beta Change

22.5deg65deg

Support CantileverSystem

Flow

0.45 0.65

L

Beta Change

22.5deg65deg

Support CantileverSystem

Flow

0.45 0.65

L

Figure 2 - Typical Cone Meter Layout (Standard Design)

Cone Type Meters - Hydraulic Equations

P

P1 P2

Beta Change

22.5deg65deg

Support CantileverSystem

Flow

0.45 0.65

L

Beta Change

22.5deg65deg

Support CantileverSystem

Flow

0.45 0.65

L

When metering a mass flow rate (m) or volume flow rate ( Q ) with a cone type DP meter , the high pressure is read from the inlet pressure port (P1) and the differential pressure (or “P”) is read as the difference between the inlet pressure and the low pressure (P2) at the centre of the rear of the cone. P = P1-P2 , the low pressure point (P2) is the pressure in the cones “wake” at the centre of the pipe. (Figure 3 next ).

Cone Type Meters - Hydraulic Equations

The generic cone hydraulic .P. equations showing both mass and volume flow rate equations are shown next as equations 1 & 2 respectively.

-------- (1) --------------(2)

Note that “ ”represents the fluid density. “E” is the “velocity of approach” and “At” is the “throat area”.

These are both constants for a specific d.P. meter design geometry.

The velocity of approach is solely a function of the beta ratio shown in equation 3. Beta Ratio in (4)

“At” = Throat Area

-------- (3) -------- (4)

--------------(5)

Cone Type Meters - Cone Wake and CFD

Higher Pressure. CFD

Lower Pressure. CFD

Wake Vortex Motion

Stream Lines

Higher Pressure. CFD

Lower Pressure. CFD

Conduit

Flow L.P.Tap

Static P L.P