Erratic Radar Level Gauges Delays a Refinery Commissioning

Instrumentation engineering root cause analysis of erratic Radar Level Gauges delays a Refinery Commissioning.

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.

Erratic Radar Level Gauges

Problem: Storage tanks’ radar level gauges readings delayed the commissioning progress of a refinery involving several million Rupees losses.

Crews’ Problem-solving attempts: the crew repeatedly checked the radar level gauges’ electronics and found all OK; finally a technician guessed that weld slag protrusions at the still well of 3 to 4 joints could be the Root cause (RC).

Since several tanks posed the problem no other cause was apparent the manager accepted it as a possible RC and checked a few readied still wells at the pipe shop. Indeed, the technician’s guess was true.

How Author Solved the Problem?

Emptying the tanks, cutting the still well to tank roof weld joint, and crane lifting the SW  welding back after repairs were out of the question – a high cost and near-impossible task in the high fire risk tank farm area!

Finally, he solved it ingeniously thus!

1. Remove the Radar Level Gauge from the still well top
2. Insert a meter long ice block with an end shaved to approx. a  480 mm dia for 200 mm into the still well (fig)

The ice melted and the ingot slid like slide fitting piston into the well and cleared out the protruding weld beads.

The resumed level gauge read perfectly! Thus encouraged crew cleaned out all SW bores free of protruding weld beads. The level gauges on all de-beaded SWs worked fine

Operators drained off the ice melt water that reached the tank bottom as they usually drain off the water that comes with hydrocarbons.

Author: S. Raghava Chari

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