Answer / miles

The wet leg is there to protect the sensor from high
temperature.

Answer / sam

Unfortunately I don't have a explanation for this one, since
I cannot see the reason for it either.
The standard on steam flow is to use condensation pots as
well, which are to me a bit of a waste of money, time and
effort since these pots have to be certified pressure
vessels, the same as any other pressure vessel on the plant.
I am not sure how many people realize this.

On wet leg levels, and in a case like this, I would rather
use a 1/2" S/S T-piece instead of a condensation pot, it
does the job just as well and it is certified and rated the
same as the S/S impulse lines.

I think the principle behind this whole steam flow
installation was based on what we normally do in the level
application of a pressurized steam drum. Since steam will
condense, we use this fact to our advantage by doing a wet
leg on it. The steam that condenses then make sure the wet
leg stays filled to the same level all the time.

In steam flow it seems like they have tried the same
principle, but according to me it is not necessary, since
the pressure taps will be installed on top of the flanges,
as for normal gas flow application, and not on the sides so
there is NO chance of liquid build up inside the transmitter
or the impulse lines, which are also installed above the
orifice plate. Any condensed liquid will immediately run
back into the line.
Doing the condensation pot installation and installing the
DPT below the line works obviously very well and is a very
good idea, I just cannot see why this is the standard or why
it should be done either.

Anyway it is not up to me or you to chance the international
instrumentation installation standards, so for now we have
to stick to this standard, but it is interesting to question
some of these original standards sometimes.
Good luck

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