Steam Flow

Orifice plates contain a hole or orifice through which liquid passes. Upstream and downstream piping are required to condition the flow and provide for accurate measurement. Pressure is measured upstream and downstream from the orifice plate with a DP transmitter, which then calculates the flow rate.(a very small hole in the orifice plate different than the main hole must be to the upper side for supper heated steam)

to slecet sutabile transmitter you should know the range of flow (upper value , low value), also take care of how to calibrate transmitter "SMART, HART, Field bus"

now to install the transmitter you must :

1. recognise the high pressure side and low pressure side (flow direction)
2. install lead lines with isolating valves
3. install transmitter >
4. before run the valves you must make zero check and calibraite hi-range lo-range as follow:

• close isolating valves
  
• open bypass valve at minivalve

• close main valves to transmitter
• open vent valves at minivalave
• now make zero to the transmitter "depened on transmitter type"
• set upper and lower range using communicator
• close vent and bypass
• open main valve to transmitter finally open isolating valve
• finally run the steam in the pipe

you will have a transmitter read steam Flow

:)

Hello,

In addition of answer of Ali Zude (good answer), check the range that you´ve calculated before install the transmitter. After calculation of orifice plate you choose a transmitter with the same range.

I am assuming that your installation is completed properly;

1. Orifice plate is installed in proper orientation (stamped information must be facing upstream).
2. Piping trims (i.e. isolation/root valves etc.) are installed facing downward either 45 deg from vertical or vertically downward.
3. Ideally the transmitter should be mounted below the process connections.
4. Impulse lines are installed with appropriate effective slope towards the transmitter.

Personnel from your process engineering department or engineering contractor would have provided the orifice plate manufacturer with the necessary details to size the orifice plate line size and schedule, pressures, temperatures, nominal, max and min flows, fluid parameters such as density etc. The orifice plate manufacturer would have sized the orifice plate and given a nice round figure for the differential pressure at maximum flows lets say 100 in WC (it may be 25 or 50 or 200 inWC etc.), this figure is the differential pressure range of you transmitter.

Now;

1. Configure your transmitter with the appropriate range given on the orifice plate datasheet or stamped on the handle (i.e 0 inWC to ? inWC).
2. Ensure that your flow transmitter is configured for square-root extraction mode (this is because the relationship between differential pressure and flow is Q=√dp. (there is more to it but basically this is it). You will need to set your transmitter configuration to linear output mode instead of square root mode if the square root extraction is done at the automation/monitoring system (DCS or PLC) via calculations (I doubt that this is the case).
3. Configure the appropriate engineering units i.e. flow units and flow range.
4. Verify the calibration of your transmitter note that the measured mA output or output seen on the HHT will not correspond linearly (in terms of % Input vs % Output) to the input applied due to square root extraction.

Placing in Service;

1. Verify impulse tubing connections are correct i.e. upstream tap is connected to Hi or + side and downstream tap is connected to Lo or – side.
2. the integrity of your impulse tubing connections should be checked, it is always a good practice especially with steam applications.
3. Ensure that the isolation valves at the transmitter manifold are closed.
4. Ensure that the equalization valve at the transmitter manifold is opened.
5. Open isolation valves at the process connections (orifice taps) now the process is at the transmitter manifold. Doing it this way allows condensate to accumulate in the impulse lines and therefore prevents the transmitter sensing surfaces from seeing the hot process (although they should be selected to withstand this temperature).
6. Open the high side isolation valve on the transmitter manifold, since the equalizing valve on the manifold is open there will be equal pressure on both the Hi and Lo sides of the dp cell. This prevents over-pressuring one side of the cell and possible deformation which would result in compromised accuracy or irreparable damage to your transmitter.
7. Close the equalizing valve on the transmitter manifold.
8. Open the low side isolation valve on the transmitter manifold. Your transmitter will be measuring differential pressure and outputting and appropriate flow measurement.

Please note that both manifold isolation valves should never be opened if the equalizing valve is open, this will result is steam flowing through the impulse lines from the high side, through the transmitter and to the low side. This means that the transmitter sensing surfaces will be seeing hot process and more critically the impulse lines will get hot, I mean really hot almost instantly, this can result in serious injury to personnel. Please beware of this, safety should always be your #1 priority.

By the way the hole mentioned earlier is a drain hole for steam applications, its purpose is to prevent the build up of condensate behind the orifice plate which will accumulate at the bottom of the pipe, as a result it is located at the bottom of the orifice plate (below the orifice bore or main hole).

DP across an orifice is so "1970"......

Vortex-shedding flowmeters are commonplace on steam these days. E+H versions already have a linearising algorithm built-in for steam (usual disclaimer).

Reply: 3 is covering most of the answer.Please follow the under mentioned procedure to connect up the transmitter to the process.

Before opening the isolation valves, Please open the top of both HP and LP side transmitter condensate pot plugs.Fill both sides with clean water and ensure both HP and LP legs are equal in water column heights.Put the plugs back.

Now ,you open the process isolation valves keeping the equalising valve open.After ensuring the full impulse lines filled with steam ,close the equalising valve.

This will give a proper dp to the cell and the impulse lines and tranmitter chambers wil not be hot .

N.Baskaran.