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The intelligent transmitters of Project 829 exhibited problems such as widespread hydrogen infiltration and oil leakage. This paper provides a detailed analysis of these phenomena and found that bulging of the transmitter diaphragm boxes occurred in high-temperature environments with hydrogen presence; the high-temperature and high-pressure steam conditions led to hydrogen infiltration； Issues such as the diaphragm sticking to the wall and severe silicone oil leakage are likely caused by the diaphragm being scratched by the catalyst during stirring when the catalyst is added, resulting in oil leakage. Based on the above circumstances, we took some corrective actions and drew some lessons learned, which have served as a valuable reference for future selection of intelligent differential pressure transmitters. An intelligent differential pressure transmitter is a type of instrument used to measure parameters such as pressure, level, flow rate, and differential pressure. These transmitters are now quite widespread; they feature high accuracy, a wide adjustable range, easy adjustment, and good stability. The two pressures of the medium under test are applied to the high and low pressure chambers, acting on the diaphragms on either side of the δ element, that is, the sensitive element; these pressures are then transmitted to both sides of the measurement diaphragm through the diaphragms and the filling fluid inside the element. An intelligent differential pressure transmitter consists of a measuring diaphragm and electrodes on the insulating sheets on both sides, each forming a capacitor. When the pressures on both sides are not equal, it causes the measuring diaphragm to move; the amount of displacement is proportional to the pressure difference. As a result, the capacitances on both sides become unequal. Through oscillation and demodulation processes, this is converted into a signal that is proportional to the pressure. Proper selection and maintenance of intelligent differential pressure transmitters can effectively ensure the continuous and stable operation of the systems in which they are used. Project 829 is a neutral demonstration plant with an annual production capacity of 80,000 tons of synthetic oil products. It was built by China Shenhua Coal-to-Oil Chemical Co., Ltd. using its own funds and relying on the patented technologies of Sanchang Synthetic Oil Engineering Co., Ltd., with Shenhua Ordos Coal-to-Oil Branch as the backing. The plant consists of an oil product unit (10805), a decarboxylation unit (10803), a catalytic pretreatment unit (10801) along with their associated tank areas, a Fischer-Tropsch synthesis unit (10802) including its intermediate tank area, a synthetic water unit (10806), and a condensed water treatment unit (10875). Shenhua invested a total of 1.8 billion yuan in this project. This set of facilities is currently the coal indirect liquefaction plant in China that utilizes domestic technology and has the longest process flow. It holds groundbreaking and profound significance for Shenhua in expanding and deepening coal deep-processing technologies. After the successful first operation of the 829 project, Shenhua Ordos Coal-to-Oil Branch modified the experimental unit. However, during inspection, it was found that among the 163 remote transducer diaphragm sensors in Project 829, the diaphragms of 80 of those plug-in diaphragm sensors were manufactured by the German company WIKA, while the rest were imported directly from the Japanese company Yokogawa. For unit 10808, 38 diaphragm sensors were supplied as a complete set by Sanchang, and they are Rosemount products. In 43 of the remote transducer diaphragm boxes manufactured by Yokogawa in Japan, the diaphragms were damaged; in 14 of these transducers, the diaphragms were severely bulged (3 units in reactor 10801, 1 unit in drum 10801-D-104, 8 units in the Fischer-Tropsch synthesis reactor of unit 10802, and 2 units in the thermal cracking reactor of unit 10805). In 38 of the Far East Rosemount transducers and 30 of the other transducers, the diaphragm boxes adhered to the walls, resulting in severe leakage of silicone oil. Phenomena such as extensive hydrogen infiltration and oil leakage in smart transmitters are still quite rare in domestic petrochemical and oil processing plants. We organized relevant experts to conduct a thorough analysis in order to find solutions to the problem. 1 Case Analysis A thorough analysis was conducted on the causes of damage to 43 diaphragm transmitters manufactured by Yokogawa EJA. Based on the results of this inspection, it was found that in all cases where the transmitter diaphragms bulged, high-temperature hydrogen-rich environments were present; thus, it can be concluded with certainty that the diaphragms of all 43 transmitters were damaged due to hydrogen penetration. Hydrogen and steam dissociate into hydrogen atoms or hydrogen ions when they obtain sufficient energy (under high temperature and high pressure conditions) ； Hydrogen atoms or hydrogen ions, due to their very small size, can penetrate or pass through the metal diaphragm of the transmitter. After passing through the diaphragm, they form hydrogen molecule gas, which increases the pressure inside the diaphragm box and causes the diaphragm to bulge or become brittle – this is known as hydrogen permeation. The hydrogen permeation phenomenon is manifested as the diaphragm bulging outward; the surface of the diaphragm takes on a slightly bluish-gray color or appears intact. When tapping the diaphragm with a finger, it is possible to feel the presence of gas inside the capsule. As more hydrogen accumulates within the capsule, the diaphragm will eventually burst. Based on the actual operating conditions, the H2 content in reactor 10801 for the reduction process was as high as 74%, with a temperature of 260°C and a pressure of 3.0 Mpa ； 10802: The FTO reactor has an H2 content as high as 50%, a temperature of 260°C, and a pressure of 3.0 Mpa, meeting the conditions for hydrogen permeation. The other 4 drum level transmitters are all used in high-temperature and high-pressure steam environments, meeting the conditions for hydrogen permeation. Among the 38 Endo-Rosemount transmitters supplied by Sanchang, 30 suffered from the diaphragm box sticking to the wall, resulting in severe leakage of silicone oil. Except for 3 units in which oil leakage was clearly caused by the catalyst scratching the diaphragm during stirring when the catalyst was added – something that could be clearly detected using dye penetrant testing – the other transmitters showed no obvious signs of damage. At present, it is necessary to conduct professional destructive tests by the manufacturer in order to determine the exact cause. The responsible party is not yet clear. 2 Solutions To solve a problem, it is necessary to find the cause of that problem. To ensure the smooth commissioning of Project 829 in September, we adopted a method of identifying problems while supplying the materials. First, Yokogawa Electric Corporation and Endress+Hauser were requested to conduct destructive tests on the smart transmitters where damage was particularly evident, and both companies submitted their test reports to us. So that we can identify the reasons and prevent similar problems from occurring again in the future. Secondly, to ensure that the 829 project can start operating in September, the repair of smart transmitters is carried out in two steps: those that are most damaged are sent back to the factory for repair, while those that are still functional are recalibrated and then put back into use first. Once the issue is clarified, it will be handled uniformly according to the final solution. In future selections of intelligent differential pressure transmitters, the following principles should be followed: when making a choice, consideration must be given to the corrosive effect of the fluid being measured on the metal diaphragm. It is essential to select an appropriate material for the diaphragm; otherwise, the outer membrane will be corroded after a short period of use, which can lead to accidents involving people or equipment. Therefore, the choice of diaphragm material is extremely important. The diaphragm materials for differential pressure transmitters include 316/316L stainless steel, ordinary stainless steel, tantalum, 304 stainless steel, and more. When selecting a model, the temperature of the medium to be measured should also be taken into account. If the temperature is high, for example between 200°C and 400°C, a high-temperature version should be chosen; otherwise, silicone oil will cause vaporization and expansion, leading to inaccurate measurements. When selecting a device, the pressure rating of the unit also needs to be taken into consideration; the pressure rating of the differential pressure transmitter should match the application scenario. From an economic perspective, the material of the insertion part and the outer casing are quite important, and it is necessary to choose them appropriately. However, using flange connections can reduce the requirements regarding materials; options such as chromium-plated steel or carbon steel can be used, which helps to save a significant amount of money. The corrosion issues of the medium under test should also be taken into consideration, but the temperature at which the medium is used need not be considered. This is because in conventional instruments, pressure is introduced inside the gauge, and the operating temperature under long-term use is room temperature; however, the maintenance required for conventional instruments is greater than that for isolated types. First, consider the insulation issue: when the temperature is below zero, the pressure guiding tubes will freeze, which will prevent the transmitter from functioning or even cause it to get damaged. This necessitates the use of insulation enclosures and heating systems. From an economic perspective, when selecting transmitters, ordinary-type transmitters can be used for any medium that does not crystallize easily. For low-pressure media that do crystallize easily, it is also possible to use a purge medium for indirect measurement (as long as the process permits the use of purge gas or liquid). The use of ordinary-type transmitters requires maintenance personnel to conduct regular inspections, including checking for leaks in various pressure conduits, ensuring that the purge medium is functioning properly, and verifying that the insulation is in good condition. With proper maintenance, the upfront cost of using ordinary-type transmitters can be significantly reduced. During maintenance, it is important to combine hardware maintenance with software maintenance. 3 Conclusions Through the analysis of this case, as well as the efforts made by both us and the supplier, we can draw the following lessons: In future projects, we should actively organize in-depth technical exchanges with the suppliers to gain a thorough understanding of the performance of the products they offer ； In-depth discussions should be held with the design institute to clarify the process conditions of the equipment to be installed, and instrument selection should be carried out accordingly ； We will carry out in-depth development of key manufacturers, conduct thorough evaluations, and provide accurate assessments of the products from the manufacturers under our control. Intelligent differential pressure transmitters play a crucial role in ensuring the stable operation of production equipment as well as accurate measurement. Only by understanding the proper selection of such transmitters and knowing how to handle common faults can they be used flexibly in practical applications, thereby enabling them to serve the entire automated system more effectively.