Orifice Flange Tap Location For Steam Measurement 2

[JORMAC]

Hello,

I have typically seen installations for orifice plates with the flange taps located on the side of the orifice flanges (in a horizontally run line). Is it acceptable to have the taps located on the top on the flanges? If so, would condensate pots need to be added to the impulse lines? Is there a standard (API, ISA, etc.) which illustrates this type of installation?

The DP transmitter would be located at grade (below the taps).

Best,

KC

 

[m777182]

Actually I do not see a prefered position for the flange taps even if the both impulse lines are full of condensate. In such a case it is important that both lines are full to the same level. This additional delta h will not contribute to the pressure difference through the orifice.Think of it as a measurement of delta P with an U-tube manometer filled with water, oil or some coloured liquor.
A thermal insulation of the orifice and the inflow and outflow length of it is advised.
M777182

 

[shobi]

Steam DP transmitter tubing should slope downwards toward the DP cell and include a "dead leg" or pigtail.If either the condensate levels or both legs of DP cell can not be kept at the same height, the difference in elevation (levels or diaphragms) will cause a DP offset that must be compensated for by offsetting the transmitter calibration. So to answer your question, there is no preffered position of the taps but the key is that at no flow condition the condensate in both legs should be at same level or the calibration is compensated for it.

 

[MarkTX]

My first introduction to steam flow measurement was in 1975, at this time all the meters I came accross had the orifice taps located on the side. The root valves were installed horizontally and the transmitter tubing sloped down to the transmitter. Installations in some older units used condensate pots, but I was told that this was an unecessary extra. I have not seen these in years.

Due to maintenance of pneumatic instruments most transmitters were mounted at ground level. With the introduction of electronic d/p cells the maintenance has been reduced so access is not needed as often. Some of the maintenance was caused by the long tubing lengths. The trend I see and follow now is to reduce the length of tubing, mounting the transmitter closer to the orifice taps.

I do want to mention that the past few years I have been running into installations where the taps are off the top of the orifice flange. The tubing goes up then a 90 degree bend into the transmitter. I am guessing at this bend is where the condensate forms to protect the transmitter from getting hot. I figured this was a local engineer doing this and not an industry trend.

I continue to mount the steam flow transmitters below and the taps off the side. The majority of my experience has been in Texas and Lousiana.
Mark

 

[ICman]

You could also used a sealed system (with diaphragms) to insure that both lines are equal.

I've seen pigtails used to keep condensate out of the impulse lines, as well.

I believe you should install a bleed/drain valve at a low point to drain any collected condensate once in a while.

 

[sabap]

Why do we want to drain the condensate? In steam application, we do not want steam to come in contact with cell directly. Condensate is at low temperature. Longer the lines, lower the temperature.

 

[shobi]

When dealing with steam application it is important to protect the transmitter from possible over temperature conditions. The best way to do this is to take the impulse piping out the side of the process piping into the outlet of a Tee. Another steam transmitter installation I did in the past was very simple. The transmitter was mounted below the connection on the run of the tee. The impulse line was filled with water and the other tee opening was plugged. This ensured that hot steam is kept out of the transmitter.

 

[lcms]

Dear Sirs,

I have a similar problem in my factory. The orifice plate where the flange taps are connected is 3 m above the differential pressure installed on the ground level. The orifice plate is installed in a steam superheated line and is used for measure our steam consumption for charges purposes, so I depend on it to save money, I mean: - if my readings are greater than actual consumption, I would pay more than I should. I am not sure, but it seems that the readings are greater than we expect, and I am concerned about the level of condensate of impulse lines. I think they are not at the same level. Do you guys have any proposal to check it? Is there any recommendation on ISO-5167 that could help me to solve this problem? How could I cross check my readings (pitot, ultrassonic, whatelse). I would appretiate a lot ome suggestions from your previous experiences.

Thanks.

LCMS.

 

[quark]

You can fill the impulse tubings with water as suggested by shobi. However, you need not worry if the height of condensate leg downstream the meter is more(PS: Don't practise it). Do you have both temperature and pressure compensation with your meter? Corriolis mass flow meter is the best to calibrate with.

Regards,