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A failure incident of heat-exchange tubes in ammonia evaporators, which suffered from unexpected wall thinning after only one-year service with respect to their original design lifetime of fifteen years, was reported and carefully analyzed. After overall inspection, many tube walls in the evaporators were found to experience severe degradations at both sides with distinct corroded defects and general cracking of corrosion layers. Thus, comprehensive investigations including external appearance, microscopic morphology and chemical composition were carried out by using a series of characterization methods. The analysis results demonstrated that the unexpected wall thinning of tubes was primarily ascribed to multiple corrosion factors including uniform corrosion, pitting and interaction behavior between them. Relative failure mechanisms were discussed in detail and prevention measures were also proposed for ammonia evaporators under similar operating condition. [ABSTRACT FROM AUTHOR]

• Failure of electro-hydraulic servo valve in 125 MW thermal power plant was studied. • Unqualified material of valve spool with abnormal coarse carbides was failure cause. • Abnormal coarse carbides were peeled off from valve spool under effect of friction. • Some carbides with size exceeding 5 μm entered the clearance, resulting in failure. 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. [ABSTRACT FROM AUTHOR]

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. • An unexpected perforation of tee pipe in the steam system of specialty chemical plant was investigated. • The synergism between the localized corrosion and flow erosion in the tee pipe was addressed in detailed in this study. • The vortex flows would aggravate the flow erosion extent, and eventually led to the large corrosion pit in this paper. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • A localized abnormal wear failure case of MAA extraction column inner wall was investigated. • The wear traces were discovered in different heights and directions, eliminating the possibility of incline of the column. • Pertinent countermeasures were proposed to prevent the recurrence of similar incidents, and were proved effective on site. [ABSTRACT FROM AUTHOR]

Double-pipe heat exchangers are widely used in the high-pressure and high-temperature applications for their simple and tight tube-in-tube configuration, but therefore normal and stable operation of such pressure-bearing equipment turns to be of greater significance because potential safety risks and economic losses will be aroused if failures occur on them. To deal with this issue, abundant researches have been conducted so far, however most of them focused on the flow and fluid characteristics by numerical simulation and experimental verification, while little attention was paid to the actual cases from the engineering practice. In this paper, such an actual failure case study concerning leakage on the jacket pipe of one double-pipe heat exchanger in a high-pressure polyethylene facility is addressed. In order to find out the causes of this failure, investigation including materials inspection, chemical phase analysis, microscopic morphologies observation, micro-area chemical compositions detection and finite element analysis etc. was carried out. The results indicated that the leakage was firstly induced by the uniform corrosion and the under-deposit corrosion successively, and then stimulated by the effect of erosion from the complicated fluid characteristics around the tee structure. Finally, the related mechanisms of this synergistic effect between corrosion and erosion were discussed, and the pertinent countermeasures from both design and maintenance point of view were proposed, including descaling of the fouled inner pipe, improvement of the circulation cooling water quality, and upgrading of the pipe materials etc. Achievement of this paper will supplement the failure cases database of double-pipe heat exchangers, based on which design optimization and failure prevention will be possible. Double-pipe heat exchangers are widely used in the high-pressure and high-temperature applications for their simple and tight tube-in-tube configuration, but therefore normal and stable operation of such pressure-bearing equipment turns to be of greater significance because potential safety risks and economic losses will be aroused if failures occur on them. To deal with this issue, abundant researches have been conducted so far, however most of them focused on the flow and fluid characteristics by numerical simulation and experimental verification, while little attention was paid to the actual cases from the engineering practice. In this paper, such an actual failure case study concerning leakage on the jacket pipe of one double-pipe heat exchanger in a high-pressure polyethylene facility is addressed, seen in Fig.1. In order to find out the causes of this failure, investigation including materials inspection, chemical phase analysis, microscopic morphologies observation, micro-area chemical compositions detection and finite element analysis etc. was carried out. The results indicated that the leakage was firstly induced by the uniform corrosion and the under-deposit corrosion successively, and then stimulated by the effect of erosion from the complicated fluid characteristics around the tee structure, seen in Fig.2 and 3. Finally, the related mechanisms of this synergistic effect between corrosion and erosion were discussed and illustrated in Fig.4, and the pertinent countermeasures from both design and maintenance point of view were proposed, including descaling of the fouled inner pipe, improvement of the circulation cooling water quality, and upgrading of the pipe materials etc. Achievement of this paper will supplement the failure cases database of double-pipe heat exchangers, based on which design optimization and failure prevention will be possible. Image 1 • Present a premature failure case of leaked jacket pipe on double-pipe heat exchanger. • This heat exchanger is used in a high-pressure polyethylene facility in China. • Countermeasures were proposed from both design and maintenance point of view. • The synergism from both corrosion and erosion was addressed in detail in this paper. • Failure analysis case database of double-pipe heat exchangers will be enriched. [ABSTRACT FROM AUTHOR]

• Perforation failure of heat exchanger tube with unique failed appearance is studied. • Improper flushing of steel water gun is found to be the root cause of the failure. • Mechanical indentations with the effect of cutting erosion are developed into pits. • Selective local erosion accelerated by vortex erosion leads to perforation failure. 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. [ABSTRACT FROM AUTHOR]

• Abnormal leakage failure of TP321 stainless steel pipe in hydrogen production system was systematically studied. • The processing stripes on the inner surface of the pipe were the root cause of the failure. • Incomplete passivation film on the pipe surface was another root cause. • The additional stress caused by pipeline installation process was also an important cause. 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. [ABSTRACT FROM AUTHOR]