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The tee pipe is generally considered as one of the vulnerable fittings in the entire piping owing to the sudden change of the flow direction. Hence, it is necessary to carry out failure analysis and reliability evaluation on the tee pipe for safe operation of the industrial piping. In this study, unexpected perforation as well as corrosion of tee pipe in the steam system of a large specialty chemical plant was addressed. Based on the systematic and comprehensive investigation including materials inspection, morphologies observation, scales detection, water quality inspection and finite element analysis, it was determined that the failure was primarily ascribed to the synergism between the localized corrosion and the flow erosion. Particularly, the vortex effect in the corrosion pit further aggravated the extent. The detailed mechanisms were discussed and the pertinent countermeasures were proposed. Achievement of this paper will help to better understand the synergistic effect of erosion and corrosion on the tee pipe under similar service conditions.

Extraction columns are one of the important liquid–liquid mass transfer equipment with wide applications in industries like petrochemical, chemical, food, pharmaceutical and so on. Therefore, reliability evaluation and failure analysis plays an important role in safe and normal operation of them. In this study, root causes analysis of localized abnormal wear on the inner wall of one extraction column for manufacturing methyl methacrylate (MMA) was addressed. Based on field investigation, wear surfaces analysis, scales inspection, precision testing and finite element analysis, the results showed that out-of-roundness of the sieve plates and deflection of the main shaft were the root causes. The detailed mechanisms were then discussed, and the pertinent countermeasures were proposed to prevent the recurrence of similar cases.

Due to the flammable and explosive characteristics of hydrogen gas, the safe operation of the equipment is particularly important. Any minor negligence may lead to serious accidents in the process of hydrogen production so great attention should be paid to the safety of each equipment in the production line. In this paper, the abnormal leakage failure of the TP321 stainless steel pipe that conveyed medium temperature shifting gas in a petrochemical factory was systematically studied. In order to find out the causes of the failure, the operating conditions, the material qualities of the failed pipe, the macroscopic and microscopic morphologies of the fracture, and the gas flow velocities were comprehensively analyzed. The results showed that the root causes of the failure were processing stripes and incomplete passivation film on the inner surface of the pipe due to inappropriate surface processing, which then initiated pitting corrosion and intergranular corrosion. Besides, the additional assembly stress between the pipe and fitting also produced larger longitudinal tensile stress, facilitating the initiation of stress corrosion cracking. Under the interaction of pitting corrosion, intergranular corrosion and stress corrosion cracking, the pipe leakage finally happened during its service. Based on these failure causes, some feasible countermeasures were then put forward for leakage prevention of similar structures or equipment in hydrogen production industry.

Buried high-density polyethylene (HDPE) pipes are widely utilized to transport gas and water due to its great shape flexibility, light weight and cost effectiveness. Because of the concentration of population and wealth, leakage accidents of buried HDPE pipelines would lead to catastrophic loss of life and property. Therefore, the comprehensive investigation and understanding of the mechanisms behind the unexpected failure of buried HDPE pipes is of great significance. In this paper, abnormal leakage occurred on the buried HDPE pipes in China. Multiple of holes and cracks were observed on the buried HDPE pipes during visual examination. Considering that no obvious third-party interference existed during the service period, systematic analyses on both mechanical properties and chemical structure were conducted to figure out the root cause of the failure. The results indicated that the abnormal leakage of the buried HDPE pipes resulted from the biological degradation by termites. Some countermeasures were also proposed to avoid the similar failure occurred again.

Electro-hydraulic servo-valves, which are considered as the crucial core element of digital electric hydraulic control system, are widely applied in thermal power plants. In this paper, motivated by the long stable operation of thermal power plant, an abnormal blockage failure of the electro-hydraulic servo valve in digital electric hydraulic control system of 125 MW thermal power plant was investigated systematically. Three body abrasive wear was identified as the main failure mechanism. Comprehensive analysis results finally revealed that the unqualified material of the valve spool with abnormal coarse carbides caused by improper preparation process was ascribed to be the root cause of the failure. During the operation, the abnormal coarse carbides acted as stress concentration source and were peeled off from the valve spool under the effect of the friction between the feedback wire and the valve spool. After that, the exfoliated carbides served as third bodies, resulting in three body abrasive wear. In this process, some of the carbides with size exceeding 5 μm driven by fire-resistant oil entered the clearance between the valve spool and the valve sleeve, leading to the abnormal blockage failure since the maximum allowable clearance was 5 μm. Countermeasures were then proposed to address corresponding problems. Considering that practical failure of the electro-hydraulic servo-valves is seldom reported before, the finding of the paper could be helpful for better understanding the failure mechanisms of the electro-hydraulic servo-valves under actual service conditions.

Heat exchanger tubes are regarded as a vulnerable component of reboilers due to different working conditions between tube side medium and shell side medium. In this paper, an unexpected perforation failure of heat exchanger tube that occurred in methacrylic acid reboiler of a German world's leading specialty chemical plant was investigated in depth. Macro observation showed that the perforation presented concave appearance both on the inner and outer walls of the failed tube. This was fairly different from the appearance of perforations reported in the past literatures. Comprehensive analysis finally reveled that this unique failure was caused by unreasonable flushing operation of steel water gun with the initial water pressure of 2300 kgf/cm2. It produced several irregular shallow indentations on the inner wall of a tube at first. Erosion then happened with a shallow impact angle in the indentations where pits were gradually formed. After a period of operation, the selective local erosion was accelerated by the occurrence of vortex erosion on the pits, resulting in perforation failure. Countermeasures were thus put forward to avoid the recurrence of similar failure. Considering that this kind of perforation failure in heat exchanger tubes caused by improper flushing operation is seldom reported in the world, the achievement given by this paper would be very conducive to enhance the safety maintenance management of similar equipment.