Seeking help regarding the relationship between the four-value interlock alarms of storage tanks and the configuration of level gauges
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May I ask how to understand the text marked in red 5.4.5 in the image? (Excerpted from SHT 3007-2014 Code for Design of Tank Areas in Petrochemical Storage and Transportation Systems) To meet this requirement, how should the level gauges of storage tanks be installed/configured? 1. Three level gauges are used: high-high level *1, low-low level *1, and continuous level (including high and low levels) *1 ； 2. Two level gauges are used: high-high level *1, low-low level, and continuous level (including high and low levels) *1 ； 3. Two level gauges are used: low-low level *1, high-high level, and continuous level (including high and low levels) *1 ； What was the original intention and purpose of this provision in the standards, which calls for separate installation of level gauges? How should it be considered? Thank you all first!
It seems better to have someone who specializes in instruments take a look
This question is a bit deep. . . . .
This post was last edited by arpcd on 2017-9-7 17:47. Is not enough liquid in the tank? It’s a very simple instrument design: you just need to select a level gauge (for normal operation), along with two high-high and low-low level switches. Level switches are inexpensive and reliable, and they trigger an alarm automatically when the set values are reached. . . The brothers of the instruments don’t need you to tell them; they know it themselves. . . As for the separate setup, it is there to ensure reliability; there’s nothing complicated about it. The explanatory notes attached to the specifications also explain this clearly. The high-level interlock feeding valve exists to prevent overflow, for safety and reliability reasons. . (The specifications state that you can choose either a level gauge or a level switch; so why do you insist on choosing an expensive level gauge?) ) Of course, unless the owner is a wealthy backer with no financial concerns, you can also choose a level gauge
I checked the price differences roughly: a level switch costs between 15,000 and 20,000 per unit, while a combination of a level gauge and transmitter costs around 45,000 to 60,000 per unit. In other words, the total cost of a level gauge is roughly three times that of a level switch. . . Dry design economic indicators are also very important.
Thank you for your reply! The instrumentation field can indeed provide some suggestions and ideas.
Thank you for your reply! The specification conditions are not detailed or precise enough, leading to various interpretations.
Thank you for your reply! The design process must indeed take into account economy and cost-efficiency while meeting safety, technical, and operational requirements.
Thank you for your reply! Indeed, as you said, for safety and reliability, it is best to use separate level switches or level gauges set at high and low levels specifically for interlock and alarm purposes, along with a three-level gauge that provides continuous measurement of both high and low levels. However, some owners wish to save costs as much as possible and prefer to use one fewer level gauge, such as in options 2 and 3 I mentioned. I’m not sure whether this meets the regulatory requirements
Options 2 and 3 represent typical cases of non-compliance with the regulations, but clause 5.4.3 is not a mandatory requirement; note that it uses the word \"should\" rather than \"must\", which means that this is something that should be done under normal circumstances. If one insists on not complying with the regulations, nothing can be done to force compliance, not even by the court, as it isn’t a mandatory requirement after all. It’s important to pay attention to such subtle details when reviewing the regulations. . As for the owner, it’s easy to explain; the key is whether you’ve truly understood the regulations or not ? The reason why the specifications repeatedly emphasize that a high liquid level must be interlocked is to prevent overfilling; when the liquid level is too high, the material overflows, which poses a danger. On the other hand, if the low liquid level is not monitored, at most the pump will get damaged, as the material won’t be able to escape. Therefore, it’s best to follow the specifications by installing a separate switch for high liquid levels. You can tell the client that even if a switch for low liquid levels isn’t installed, as long as the operators are diligent, it might be fine. But in case the pump gets damaged, its cost could be much higher than that of the switch, which costs over ten thousand ? ? Explain patiently – it’s better to choose 2 rather than 3; ideally, choose 1. Make sure both high and low level switches are available. A sensible homeowner will understand right away. As long as you truly have the homeowner’s best interests at heart, spending an extra ten thousand or so isn’t a big deal. After all, when you’re already involved in the work, why worry about getting your socks wet? Most of the owners I’ve worked with choose either two switches + one level gauge (over 90%), or high/low switches + a level gauge (10%); a reasonable and clear explanation is very necessary. If you only have a superficial understanding of the standards, you’ll expose your ignorance as soon as you speak. .
Schematic diagram of a high-level liquid level switch – it doesn’t require any contact with the material; it’s a non-contact type that is inexpensive, simple, reliable, and easy to use. The cost is around 15,000 per set. I’m the owner and I use it myself to ensure safety. .