Over 20 years of experience in instrument maintenance safety – sharing it with everyone!

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A friend asked me to write an article on instrument safety; I thought it would be easy to write, so I agreed right away. But when I sat down to start writing, I didn’t know where to begin. I haven’t written articles on this topic for many years; I’m not sure how to structure the paragraphs, so I just write whatever comes to mind, treating it like a chat with a good friend. When it comes to instrument safety, literally, it involves two aspects: instruments and safety. But I think what should be discussed first is: people! Some people say that humans are the most unstable factor in the production process; over 80% of industrial safety accidents are due to human error, that is, they are caused by people. Therefore, from a safety perspective, replacing humans with instruments is an inevitable outcome in the development of industrial production. I believe a large number of people agree with this view, but I think it is somewhat one-sided and does not address the problem at its root. Replacing humans with instruments and automated equipment can greatly improve labor efficiency, enhance processing accuracy and the yield of finished products, reduce the workload on workers, and cut down on various costs related to personnel. However, it should not be forgotten that humans are the decisive factor in the production process! Failing to address the human factor and simply reducing the number of people will not decrease the proportion of human errors in safety accidents. With the increase in automation, liability accidents related to safe production will gradually shift from being individual and small-scale to being systematic and large-scale. There is a very typical example: A chemical manufacturing company frequently experienced various process or safety accidents due to factors such as a lack of responsibility or poor operational skills among its workers, resulting in mistakes in operations, delays in carrying out tasks, unstable performance, and insufficient attention to personal safety. As a result, the company decided to increase the level of automation. Yet, accidents continued to occur regularly. The supervisors found that the operators in the control room often dozed off or were absent from their posts, and the inspection staff would merely walk around without actually conducting proper inspections. Therefore, surveillance cameras were installed on all the key equipment and at important workstations, with centralized monitoring from the control room. But it was discovered that even the supervisors on duty often dozed off or were absent from their posts... So I say that if the human factor isn’t addressed, serious problems will inevitably arise sooner or later. Once, a township enterprise in our county was preparing to start trial production; they approached me through an acquaintance and asked me to help with the inspection as well as to assist in adjusting the instruments. It is a device used for refining petroleum products in order to separate out a certain product. When I went to the site, I was shocked – everywhere I looked, there were potential hazards. Since everything, from raw materials to the final product, is flammable and explosive, I focused on checking whether the explosion-proof measures in place were adequate. It was found that none of the lighting fixtures on the third-floor framework were explosion-proof, nor were the instruments used on site (the DCS system also lacked safety barriers). What was particularly shocking was the presence of a small air compressor on the second-floor framework (of course, its motor wasn’t explosion-proof either). The chimney of a small 10-ton coal-fired boiler was less than 100 meters away from the distillation tower. The workers wore cheap synthetic clothing, there were no professional electricians or instrument technicians, and the construction team was an unqualified local crew. The installation of some instruments was in terrible condition: all double-flange level gauges were installed incorrectly, pressure gauges didn’t have root valves, and the length of the straight sections before and after the flow meters was often inappropriate. In my over 20 years of experience, this was the first time I saw flow meters installed directly alongside valves. Even more absurdly, control valves were also installed together with the valves before and after them... After talking with the company’s owner, I learned that the reason was simple: to save money! I was at a loss for words, so I had to outline the problems and put forward suggestions for improvement, as a way of fulfilling my duty as a friend; after that I never went there again. Later, after the plant had been in operation for three months, an accident occurred during maintenance: no analysis of the components inside the distillation tower was carried out (it is likely that there were no analysts available). Welding work ignited the flammable substances inside the tower, and after using fire extinguishers to put out the fire, no preventive measures were taken before continuing with the welding work. As a result, when a second fire broke out, luck ran out and the entire facility was destroyed by fire. It is evident that if business decision-makers do not prioritize safety, the better the equipment and the higher its cost, the greater the losses in the future will be. Having said all this, the main point is to emphasize the leading role of humans; in terms of instrument safety, everything depends on human intervention: first and foremost, corporate decision-makers must invest adequately, and proper investment must also be made in the installation, calibration, maintenance, and management of instruments, as well as in thorough and proper handling of repairs. Simply put, it means having a sense of responsibility. By putting in effort from top to bottom, instrument safety can be ensured. Now, let’s talk about the instruments. When discussing instrument safety, the first thing to consider is that the instrument itself must be safe; this leads to the issue of instrument selection. Different selection tables should be developed for various instruments, with information including: measurement content, measurement range, composition of the medium being measured, pressure range of the medium, temperature range of the medium, and the installation method of the instrument (flange installation: DN: ； PN: ； Flange material: . Threaded installation: M * ； Material: . Immersion type: m. Top-mounted: Opening size: . External measurement type: Installation location: . etc.), as well as the on-site environment (high temperature, high pressure, low temperature, low pressure, humidity, dust, vibration, corrosive gases, flammable and explosive gases, direct sunlight, lightning strikes, water splashing, flooding, oil immersion, frost, high altitudes, etc.). By filling out the form, we can consider the selection of instruments more comprehensively, avoiding potential safety hazards resulting from improper selection and ensuring the proper operation and service life of the instruments. For example, most smart meters require an operating temperature range of -20°C to 60°C; under normal conditions, the temperatures in North China do not exceed this range, so no special protection is needed for sensors installed outdoors. However, in summer, direct sunlight can cause the surface temperature of the instruments to exceed the allowable level, leading to incorrect readings on the instruments and resulting in accidents. Therefore, sun protection needs to be considered for some important instruments. Another example is that some instruments, when measuring corrosive substances, consider only the corrosion resistance of their measuring elements and fail to take environmental factors into account; as a result, the aluminum alloy casing of the instrument becomes too corroded to be opened, forcing it to be discarded. Furthermore, in chlor-alkali plants, the corrosion resistance of titanium in wet chlorine and dry chlorine is quite different. One company, due to an improper choice, used titanium sleeves for the thermoresistors used to measure the temperature of dry chlorine; as a result, titanium reacted with the chlorine and caught fire. Fortunately, it was detected in time, preventing any serious accidents. Some companies install measuring instruments at high heights due to the characteristics of their equipment (such as tower-type equipment), but fail to provide ladders or maintenance platforms; as a result, any issues with the instruments cannot be addressed in a timely manner, leading to shutdowns. In one manufacturing facility of a certain company, many flow meters were inaccurate to the point that production could not proceed. Upon inspection, it was found that the flow meters with problems were mostly vortex flow meters and electromagnetic flow meters. The installation locations of these flow meters experienced severe vibration; since this vibration could not be eliminated, metal rotor flow meters were used instead, which basically solved the problem. An organic chemical manufacturing company experienced an accident due to malfunctioning control valves; this was caused by the cables connected to those valves not being protected, their insulation aging, which led to cable short circuits. In a paper manufacturing plant, the electric control valve used to regulate steam flow was exposed to a humid environment for an extended period, which caused a short circuit in its motor circuit and led to damage, resulting in the inability to start the paper machine. A small chemical manufacturing company encountered severe delay in the response of its control valves during production in winter, a situation that could potentially lead to safety accidents; as a result, it was forced to shut down operations. At first, I thought there was an issue with the parameter settings; after checking, they seemed to be normal. Trying to adjust some PID parameters based on experience also did not solve the problem. Upon going to the site, it was found that the air supply for the control valve contained moisture, and ice formation in the air circuit of the valve actuator caused delays in regulation. The situation returned to normal after using steam to clear the moisture. The reason for this phenomenon is quite simple: to save money, oil filters and water filters were not installed in the instrument air system. Previously, when discussing instruments, the focus was on hardware, whereas when talking about security, the focus is on software. It includes various laws and regulations, rules and regulations, operating procedures, implementation standards, instrument records, etc., which are essential for the safe operation of instruments and safe production. They specify the measurement and control ranges of the instruments, as well as their alarm and interlock values. They outline the procedures for the installation, operation, maintenance, calibration, and repair of these instruments. They define the responsibilities of the personnel involved in using, maintaining, and managing the instruments. Additionally, they specify the processes that must be followed throughout the life cycle of an instrument, from procurement and storage to issuance, installation, use, calibration, repair, and disposal. Instrument safety, as well as the overall safe production of an enterprise, begins with strict compliance with these laws, regulations, rules, norms, and standards. It is only through such strict compliance that safety can be ensured to the greatest extent possible. In summary, instrument safety is a very complex issue that is difficult to explain clearly in just a few words. Due to my limited knowledge and shallow understanding, the views presented in this article are merely preliminary suggestions; I hope that my colleagues will offer their corrections.