Target Flow Transmitters Failed the Very Midnight

Instrumentation engineering root cause analysis of failed target flow transmitters (TFT) at midnight.

Article Type:Root Cause Analysis (RCA)
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.

Target Flow Transmitters Failed

The Author’s elation of solving a tough problem economically when he left the plant was short-lived; around 2 AM the night superintendent reporting the ammonia flow meters erratic readings gloomed him!

As he believes in checking the problem when it is fresh for accurate diagnosis, he rushed to the plant. It rewarded him!  He found a profusely iced transmitter bottom portion. 

He realized after few minutes of thought that the already low-temperature liquid ammonia throttled from around 6-bars pressures to 3-bars by the header pressure control valve cools to near 0o C, and hence the frozen iced transmitters’ bottom portions at night, stuck transmitter parts, and erratic readings – the root cause.

The bright sun during the day does not let ice form; hence, the turbine flow transmitters (TFTs) read the flow correctly during the day – the problem root cause

RCA Solution

After few minutes of thinking, he thought of adding a 300x300x6 mm thick aluminum sheet with a middle opening to let the head internals pass (previous problem).

Target Flow Transmitter Problem
Note: This is a pneumatic instrument

It serving as a heat sink that would dissipate the cold and hold the head at a near ambient temperature high enough to prevent icing.

The crew did that by the next midday though the TFTs were doing fine. No disturbing calls that night let the author enjoy his sleep!

RCA solution benefits

RCA solution benefits are: 

  1. Practically no cost solution restored the TFT readings reliably and durably and helped the plant realize the TFT’s expected benefits

The solution is least expensive and simple compared to the obvious solution of steam heating, which involves high installation costs, recurring excessive steam consumption, and steam leaks posed housekeeping costs.

Author: S. Raghava Chari

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