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.
Urea Plant’s various vessels seal Differential Pressure Transmitters (DPLTs, fig 1) were the worst of all seal instruments, because these, costing several times more than the seal pressure transmitters too failed as frequently.
The author after yearlong unsuccessful previously described efforts to make the DPLTs work, gave up and selected Displacer Level Transmitters (DLTs Fig 1).
The below given formidable constraints almost aborted the first displacer level transmitter (DLT) trial; the author thought out, shown under each constraint effective, economical, and easily implementable solutions – shown in italics – won the first DLT trial approval:
The author proposed bolting the DLTs to the existing 3” vessel top flange itself involving no welding on the vessel
Vessel top flange bolted DLTs require no heating steam
The author’s solution: suspend the displacer inside stilling well (SW); SW is a 2” Sch-40 top collar, bottom cover welded and numerous 3‑mm dia fill holes drilled along the SS-316 pipe length. SW prevents not only the vessel turbulent contents unhooking the displacer, but also the consequent lost level readings and the unhooked displacer entering the pump and wrecking it.
Thanks to the author pointing out the possibilities of 10 Nos. of DLTs order the vendor relented and accepted supplying 3” 300#/150# flanged DLTs – a deviation from his standard. This overcame the mounting problem
Thanks to the above solutions overcoming all the constraints, the plant approved the first displacer level transmitter (DLT) trial (figure 3). The trial succeeded beyond expectations.
The displacer level transmitter (DLT) worked well even with experimentally closed torque tube condensate flushing – an abundant caution measure – pipe tap valve.
The initially reluctant, but now highly delighted urea superintendent and general manager chased the author to provide the remaining 9 Nos.
Displacer level transmitter (DLT) benefits are:
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
Author: S. Raghava Chari
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