What precautions should be taken for instrument maintenance during the current cold winter season?
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We are in the south, and generally, not much attention is paid to insulation and heating for instruments during design and installation. It’s extremely cold these days. Today, the operators noticed that the reading displayed by a double-flange level gauge did not match the actual liquid level – the actual level was 42% according to on-site measurements, while the DCS showed 98%. Upon inspection, it was found that the inaccurate readings were caused by expansion due to snow and ice accumulation. It returned to normal after the ice was removed with hot water. Everyone, please share your experiences in maintaining instruments during winter so that we can exchange knowledge.
In winter, the instruments in the north operate intensively to prevent freezing and condensation; in addition to the maintenance tasks required in other seasons, inspections and maintenance of heating systems for insulation are also necessary. Each instrument equipped with heating should have its heating system checked regularly; any issues that arise must be addressed promptly to prevent damage to the instruments, pressure transfer pipelines, and heating pipelines.
I think that double-flange pressure transmitters should not freeze easily if the vacuum level is very low; the freezing point of silicone oil is around minus 45 degrees Celsius. Is it possible to reach such low temperatures where you are? It’s likely that freezing will occur at the flange connections.
I live in the north, where it’s very important to prevent instruments from freezing over in winter. First, we install heat tracing on the parts that are prone to freezing, and conduct regular inspections on a daily basis to ensure the proper operation of the instruments. Secondly, drain the systems at irregular intervals throughout the day, such as for purified air, unpurified air, and the liquid level gauges of the gasoline tank sumps. Another thing is to add antifreeze to the isolation fluid (such as ethylene glycol, etc.). Add insulation boxes to outdoor instruments, etc. In short, there are many ways to prevent freezing in winter; above, I have listed just a few based on our factory’s actual practices, for everyone’s reference.
:In addition to the handshake process, when selecting instruments, the operating temperature requirement is ±40 degrees; for valves, it’s between –40 and 165 degrees. This standard is applied throughout the entire plant to prevent problems before they arise. All instruments are installed with explosion-proof measures to prevent the entry of air and water. The gas supply lines for these instruments are equipped with systems for removing dust and moisture. Instruments installed outdoors require insulation, and those used for measuring liquids are heated using steam or electric heating. Regular inspections are also necessary. This year, the temperature dropped to minus 35 degrees, which was very close to the lower operating temperature limit for these instruments; it’s truly frightening.
This kind of weather is after all rare in the south, so we need to increase inspections!
We use orifice plates for measuring our steam flow; an isolation tank filled with ethylene glycol is placed after the primary valve. After some time, the pressure tap pipes freeze, and during purging and venting, it is found that the isolation fluid has been displaced. What do you use as the isolation fluid?
We’re in the south; we really don’t have any experience with protecting against cold and freezing!