mode analysis per IEEE 515 standard
for electric traced bundles.
the results of these studies provides what the industry regards as the
best sample transport system available.
OBrienenjoys the industry reputation asthe ultimate solutions provider in analyzer sample transport systems.
transport bundles are in service in thousands of applications around the
world and our experience with sample transport tubing and conditioning
is second to none. The primary considerations of sample transport tubing
would fall under the following:
Know what the composition is for the sample you will extract and transport
to the sample conditioning cabinet. It is not enough to know the theoretical
norm, you must also know what the composition will be under all conditions
that can reasonably be expected. Those include shut-down, start-up and
upset conditions during operation.
composition is not limited to the chemical composition but also the physical
state: pressure, phase (or phases), and temperature.
What is an acceptable delay in the sample cycle time? Often the cycle
time is often narrowly calculated as the time lapse between extraction
and completing the analysis. If the analyzer is part of our process doesn't
it follow that we should also include the time to affect the process fluid
based on the results of the sample analysis in any cycle time calculations?
the selection of where the sample will be taken and the location of the
analyzer shelter there are several variables that affect the total cycle
time or delay. Establish an acceptable delay for the system. Sample size,
process phase, pressure drop and run lengths will become part of
the decision process in specifying the sample transport tubing.
and Freeze Point
You will need to know the minimum temperatures allowable consistent with
maintaining an accurate and representative sample. Determining the lowest
dew point for any component in a gas sample is just as critical as determining
the freeze point of a liquid sample.
both cases (dew point and freeze point) hotter is not always better, nor
does it always lead to an economic or a simpler lower maintenance system.
Generally the hotter the process must be maintained, the more complex
the installation and control scheme becomes.
should set window of allowable operating temperature as wide as possible
determined by the process fluid itself not the accuracy of system components.
Deal with component issues separately otherwise we end up adding safety
factor on top of safety factor and creating a system more complex and
expensive than really necessary to achieve reliable results.
Determine the maximum temperature of the sample during normal and upset
conditions. This will influence the tubing, heater, process connections,
bundle configuration and installation details.
What are the minimum and maximum ambient temperatures. Consider the point
at which the sample is taken not just the climatic average for the region.
The ambient temperature around an ethylene furnace is likely to be 15C
higher than the rest of the plant.
Electric is the most widely used but you must confirm that sufficient
power is available for the installation. Determine what voltage is available
also. Steam may be readily available and if the supply is trouble free
and reliable steam can be a very good choice for heating sample lines.
How long a sample line is required to go from the sample point to the
sample conditioning cabinet? Obviously this affects the cycle/delay time.
The length must include detours for routing along existing pipe racks
and supports. Determine the area classification at each end of the sample
run. It is permissible to route a Division 2 approved assembly through
a Division 1 area as long as there are no tees, splices, or other joints
in the assembly and as long as T-ratings of the heater are appropriate
for the Division 1 area being traversed.
Is this a fast loop? Is the return point near
the extraction location? Is the waste sample going to be routed to a flair?
These determine the number of tubes needed in the sample bundle.