Impulse line Blockages


Blockage of an impulse line will cause flowrate information to be lost, with potentially serious consequences in a process control application. The need to avoid blockages is a primary consideration in the specification of impulse-line diameter.

There are  number of problems with installation, and transposition of the problems into the corresponding solutions yields:

1 Provide trace heating (generally by electricity or steam) whenever freezing conditions are possible.

2 Avoid exposure of trace-heating systems to excessive temperatures.

3 Avoid over-tightening or the improper clamping of the tubing bundle (consisting of the impulse lines and heating
line) to its supports, which can cause the insulation to be compressed and prevent proper operation of the traceheating

4 Do not exceed the tubing bend-radius limit.

5 Install effective trace-heating systems and insulation. The simple method of laying on insulating tape, applying an
electric heater cable and then adding more insulation tape and sealing with mastic may not provide adequate

6 Ensure correct slope of impulse lines.

7 Provide high-quality instrument enclosures, which, though expensive, are essential for reliable long-term frost protection.

8 Provide adequate weatherproofing


An open impulse line has high frequency noise due to fluid turbulence. If a line plugs its signal becomes flat. A smart
transducer can “learn” the frequency characteristics of open impulse lines and use them to establish an “OK” condition.
The different frequency characteristics of plugged lines can then be detected and reported using software. It is possible to detect the plugging of one or both lines. This technique requires the use of a very fast pressure sensor.Trace heating must not be so great as to cause liquid to vaporize unintentionally or to prevent steam from condensing.Waxing is another cause of blockage. Lagging or trace heating may be required to prevent this problem.


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