Meters, in Section 2). the effective inner pipc wall roughness can be determined. On the other hand, if the pipe roughness is already known, the existence of a fully-developed axial velocity profile can be established directly by comparing the measured profile with those in the literature.
Measurements of the local fluid velocity can be carried out using standard techniques such as pitot tubes, hot wire or hot film anemometers, laser Doppler velocinieters, etc. (See, for example, ISO 3966, ISO 7194, ASME PTC 11, and similar references.)
A Basic Reference Condition can be established by following the steps outlined below. If necessary, a limited test program is permitted, provided that all of the limitations are documented.
Step 1. Using calibration procedures, establish that the velocity measurement instrumentation
is operating properly and quantify its uncertainty.
Step 2. Install the velocity measurement probe in the pipe with any convenient upstream
straight pipe length, but with at least four pipe diameter lengths of straight pipe down
stream of the probe.
Step 3. If instrumentation allows, measure at a nominal flow rate the radial and azimuthal
velocity components at ten or more locations in the cross-sectional plane. If the
time-averaged values at any given location are not equal to zero within the measure
ment uncertainty, then Basic Reference Conditions do not exist. In this case, pro
ceed to Step 6.
Step 4. If the time—averaged radial and azimuthal velocity components are zero (see 5.1.1).
measure the axial velocity at ten or more appropriately spaced positions along a diameter. Repeat this for several flow rates, preferably ten or more, spaced over the flow rate range of the meter to be tested.
Step 5. Repeat the same procedure as outlined in Step 4 in at least one additional orientation
45 deg or more from the first. Additional profile measurements, each at new angular orientations that are up to 90 deg from a previously used orientation, are desirable.
Step 6. Install the velocity probe with at least five additional pipe diameters of upstream
straight piping and with the same down stream piping.
Step 7. Repeat Steps 3 through 5.
Step 8. Repeat Steps 6 and 7 until an upstream
NOTE: When the available space at a test flow facility or field site is inadequate for the establishment of a standard reference condition. then the facility or site alone cannot be used to determine installation effects (see Section 6.3). However, a meter can be calibrated in-situ for a given installation in that facility, but its calibration curve is valid only for that facility or for a geometrically scaled installation in which pertinent fluid dynamic parameters are the same.
6.1 Nonreference Conditions
Nonreference conditions are those that do not satisfy the definitions for the Basic or Working Reference Conditions given in Section 5. These nonreference conditions may be generated by upstream and/or downstream piping geometry such as single or multiple elbows, by upstream equipment such as a partially opened gate valve, pumps, etc., or by the entrance or exit of a pipe. The flow disturbance must be defined and recorded. This includes the piping upstream of the disturbance, any how conditioner that is used, upstream fittings, and the orientation of system components.
6.2 Method of Establishing the Effects of Nonreference Conditions for a Single Flowmeter in a Given Facility
The effect of these nonreference flow conditions on the performance of flowmeters can be evaluated by first establishing the flowmeter performance under reference conditions, and then teSting the meter in nonrcfcrence conditions and comparing the results. This will identify deviations that occur between reference and nonreference conditions. The calibration tests should be conducted over approximately the same nondimensionalized parameter range (such as Reynolds number range) using the same fluid, instrumentation, and flowmeter as used in the reference condition calibrations. Enough data should he taken to statistically establish the uncertainty and the precision of the tlowmeter. See Section 8 regarding interpolation and extrapolation of results to untested fluids or conditions.
6.3 Method of Establishing the Effects of Nonreference Conditions for a Single.