Troublesome instrument wells & the tragic history of instrument wells
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This post was last edited by Changfeng Jiwanli on 2009-5-1 at 12:21. The troublesome instrument wells: In petrochemical plants, pipelines for water systems such as fresh water, fire-fighting water, and circulating water usually run underground, with their branching arranged there as well. In this way, common measuring elements such as flow meters, temperature sensors, and pressure sensors are all installed in the instrument well. In areas with low groundwater levels, it’s not a big problem, but in areas with high groundwater levels, it’s an absolute hassle. Here, in summer, water can be found less than a meter underground. Based on past experience, it can be assumed that water generally accumulates in the instrument well. Even with enhanced measures to prevent seepage and leaks, passive protection methods mean that water can enter from all directions; any minor gap will allow water to get in, and it’s almost impossible to avoid such gaps over time. Moreover, it’s not easy to ensure that cement and pipes have the same coefficient of thermal expansion. Therefore, water ingress into the instrument well is almost inevitable; don’t believe in any claims about enhanced waterproofing measures. The fact that the entrance to the instrument well is above ground level and covered with a lid are just lies – they will be of no use when it comes to preventing water from entering. If it is truly necessary to install it in the instrument well, a flow meter with IP68 rating can be chosen. Pressure transmitters are not suitable for use underground; if they are brought to the surface, there is a problem with heat tracing north of the Yangtze River. Thermal resistors are a bit more challenging; ones with slightly longer leads have to be used to prevent them from being submerged in water. Moreover, the lower areas are likely to contain toxic gases or lack oxygen, increasing safety risks. It is better to channel things than to block them; it is better to take initiative than to be reactive. The profound lessons from Yu the Great’s thousands of years of experience in managing floods teach us that we must pay close attention to this. The best approach is to reverse the unfavorable situation of passive protection; therefore, it is recommended that instruments and pressure tapping points be avoided as much as possible in instrument wells. Find a suitable installation location on the ground, or simply bring the pipeline up to the surface to install the meter there. The working method in the design institute is that the plumbing and drainage department creates the necessary conditions for automatic control; after the automatic control team selects the appropriate instruments, it sends them back to the plumbing and drainage department, which then prepares the installation drawings. Therefore, these issues should be noted in the minutes for the plumbing and drainage team when discussing the design plan; specifying them only within the automation team may not be effective. The tragic history of the instrument well: In 2004, we installed a set of instruments related to catalysis and circulating water; the primary components of these instruments were located in the instrument well, with an ultrasonic flow meter being used for measuring flow rates. After we delivered that project, the flow meters didn’t work properly, and the instrument workshop refused to take care of the issue. So I brought in the manufacturer’s technical staff, who worked together with the people from the instrument workshop to get the operators of the circulating water system to assist. We also tried to contact the construction team that had originally carried out this work, but they refused to do the task of pumping water and removing sand from some wells, as those wells contained water or sand. So we had to find another group of laborers to do the job. With such a complex team, we set off in large numbers to the site just for two flow meters, and worked there for several days. In 2005, we built a coking and hydrogen production facility; some of the water pipelines are still underground and are often submerged in water, which makes problems likely to occur. And when problems do arise, it’s troublesome to repair them. In 2006, I helped build a small device, a water meter for measuring water usage. That meter was located in the meter well, and a colleague who was part of the same project stayed there to handle the related data collection. Since they complained a lot about having to open the manhole cover every day to take readings, I felt weak in the face of that MM whenever I met her. In 2007, I was involved in the construction of a chlor-alkali plant; all instrument wells that could be eliminated were removed. However, it was difficult to pull in wires with a diameter of 700, so the instrument wells had to be kept. It was emphasized repeatedly that proper waterproofing measures must be taken. Of course, you know that some promises cannot be trusted. The flow meter and thermal resistors are installed in the water, while the pressure transmitter is led to the surface; there is no heat-supply steam at that location, and only a thin pressure cable can be seen in the spring breeze. I finished the work before summer arrived, and after spending one summer and one winter, the instrument workshop didn’t contact me again. Yet, before my eyes, I could clearly see what would happen with those clocks during the summer and winter months; I could distinctly hear the complaints about me coming from behind them. So, what about 08 and 09? May history not repeat itself! May we make progress step by step!
This post was last edited by Changfeng Jiwanli on 2009-5-1 12:08. Suggestions for instrument wells: 1. Pipes with a maximum diameter of DN500 or less, as well as water pipelines whose installation locations are on the ground, do not require instrument wells. 2. Flow meters, temperature, and pressure instruments for underground pipelines should be installed at suitable locations on the part of the pipeline that is above ground level. 3. If there is no suitable installation location on the ground, find an appropriate place to bring the pipeline out of the ground. 4. In cases where no suitable installation location for the flow meter can be found on the ground, and the pipe diameter is too large to allow it to be extended above the ground, enhanced sealing measures should be taken for the instrument well, with the instrument’s protection rating set at IP68. This is the last resort. To spark some discussion, my question is: How are the instruments used in everyone’s instrument panels? What experience and good tips do you have?
Water doesn’t seep underground in our area, so it’s not like what the original poster said! It’s indeed difficult to deal with water at a depth of less than one meter underground. Here’s another idea: you can weld steel plates around the entire perimeter of the instrument well to create a channel! It is possible to add an additional layer of protection after the civil engineering work completes the instrument well – I wonder if that’s feasible!
Design involves continuous improvement and modification based on the actual conditions on site; there are some issues that are very difficult to handle and tricky to resolve. One can only rely on experience; beginners need to accumulate more project experience in order to create more thorough designs and minimize mistakes. Thank you so much to the original poster for sharing; I learned a lot from it!
Alas! I can only express my sympathy for what the original poster is going through, as we face similar problems as well. The instruments are there to serve the manufacturing process, and everything must be done in accordance with that process. If the process works well, things are fine for us; but if it performs neither well nor poorly, we end up being blamed. What’s most infuriating is that our colleagues often say behind our backs that it’s the \"leaders\" who reap the benefits, while it’s we who do all the hard work. Injustice!
How large should the instrument well be for two pipes with a diameter of 1 meter, OP? Two pipes side by side, both DN1000. One for supply water, one for return water, circulating water. Three gauges on each tube, for temperature. Pressure, flow rate. There are six tables in total.
The instrument pit not only has water seepage issues, but also problems such as rainwater intrusion and leakage from valves – it’s really troublesome. Consider optimizing the measurement method: use an electromagnetic flowmeter for measuring flow, with the electrodes placed underwater and properly sealed to prevent water ingress; the instrument transmitter should be installed on the surface ； The pressure transmitter uses a single flange, with a capillary tube leading it to the surface ； Use an extended protective tube for the thermocouple, or opt for an armored thermocouple, with the wiring box extending above the ground level.
For large pipelines, we do the same thing; it just results in higher costs
Haha, it’s the same here too. Later, the water was drained and the outside of the gauge was completely sealed with silicone; it has been in use for 7 years without any problems.