Instrumentation engineering root cause analysis of seal level differential pressure transmitter problems and displacer level transmitters.
| Article Type: | Root Cause Analysis (RCA) |
| Category: | Instrumentation |
| Equipment Type: | Sensors |
| Author: | S. Raghava Chari |
Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of two or three decades ago. These articles will help you to improve your troubleshooting skills and knowledge.
Seal Level Differential Pressure Transmitter Problems
Urea Plant various vessels seal Differential Pressure Transmitters (DPLTs, fig 1) were the worst of all seal instruments. Their far higher costs worsened the situation beyond description.
Problem Solved
Selected Displacer Level Transmitters (DLTs Fig 2) elegantly and inexpensively solved the problems forever.
The author overcame the below-listed constraints made the modifications successful:
- The mechanical crew declined welding taps for jacketed displacer chamber mounting because of the severe welding code requirements
- Fortunately the author thought of vessel mounting the DLT on the vessel top 3” flush flange itself; on his prevailing upon the vendor furnished 3” 300 # and 3” 150 # flanged DLTs – a deviation from his standard
The author feared the severe vessel turbulence would unhook the torque tube suspended displacer and render the instrument inoperable.
He lucked again! He got an idea: suspend the displacer inside stilling well (SW); SW is a 2” Sch-40 one end closed SS-316 pipe with a welded top collar and numerous 3-mm dia fill holes drilled along its length.
SW prevents vessel contents’ turbulences unhooked displacer finding its way into pumps and damaging them, besides no level readings as with the DPLT.
Author Solution
The author after yearlong unsuccessful trials as in the previous problem
Trial Displacer Level Transmitter Installed
Thanks to overcoming the constraints as above, the first trial DPLT was a success.
The abundant caution provided torque tube flushing condensate connection was not necessary; the DLT worked well despite operators forgot flushing.
DLTs replace all DPLTs
Chased by the initially reluctant plant manager, the author provided the remaining 11 Nos. DLTs on war footing
Modification Benefits
High plant safety from reliably restored LI/LC/LA – Hi-Hi and Lo-Lo – enhanced plant safety and boosted operator morale.
The everlasting fit and forget DLTs costed just $700 ea. against $2000 each of a week only lasting DPLTs
- Saves expensive steam jacketed Displacer Chamber (DC) necessary to avoid process liquids freezing purchase costs
- Avoids the dreaded and expensive taking new 2” taps for DCs confirming to strict welding codes
- Chosen mount is lot simpler, less expensive and requires near zero maintenance; on the other hand the second alternative of bolting Displacer Chamber to 2” pipe connecting vessel top and bottom flanges and steam tracing the entire set up.
- Saturated steam the best for heating tasks is not available close by
- Small-bore steam lines leak all over the plant posing wasteful maintenance efforts, housekeeping and high steam costs.
- Fig 2 mount is the simplest, most economical and of near zero maintenance
Author: S. Raghava Chari
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