Short-term Overheating Research Articles

Assessing thermal resilience to overheating in a Belgian apartment: impact of building parameters

Globally and in European Union, climate change and heatwaves (HWs) challenges the thermal resilience performance (buildings’ ability to withstand and recover from a shock) of airtight, highly insulated buildings with no cooling strategies. Ensuring thermal resilience in buildings is crucial for maintaining habitability amid climate change uncertainties. This study, under the framework of IEA EBC Annex 80, aims to explore the impact of design parameters (thermal mass, window to wall ratio (WWR), operation of solar shading and natural night ventilation) on the thermal resilience in a Belgian apartment. Although a number of recent studies explored impact of building design on overheating, there is still a lack in the state-of-the-art exploring and varying ranges of the design parameters that impact the thermal resilience performance of apartments during short-term shocks such as heatwaves. In order to reach the aim of this study, building energy simulations were performed. Initially, the default apartment was evaluated during current weather scenario varying the parameters. Results showed overheating risk in default apartment during current weather scenario. Then the worst, improved and, the optimized variation of the building is evaluated against 6 days HW. The apartments’ thermal resilience performance assessment conclude that high window-to-wall ratios (WWR >30%) without solar shading and lighter thermal mass decrease thermal resilience during shocks, highlighting WWR’s significance. For short-term overheating events, heavy thermal mass improves the thermal resilience by pro-longing the absorptivity time (withstanding capability) of the excess heat. However, if excess heat is absorbed by the building (higher WWR resulting in higher solar gains), lighter thermal mass enhances the thermal resilience performance (recovery capability) by flushing out the excess heat. Solar shading and passive cooling strategy like natural night ventilation aids in temperature management, improving the buildings’ thermal resilience performance by prolonging the absorptivity and speeding the recovery from the shock.

High-Temperature Oxidation of Boiler Steels at 650 °C

This study presents a comprehensive investigation of the formation, composition and behaviour of oxide layers during the high-temperature oxidation of four different steel alloys (16Mo3, 13Cr, T24 and P91) at a uniform temperature of 650 °C. The study is aimed at assessing the oxidation damage due to short-term overheating. The research combines CALPHAD (CALculation of PHAse Diagrams) calculations, thermogravimetric analysis (TGA) and advanced microscopy techniques, including scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), to elucidate the complex mechanisms controlling oxidation kinetics and oxide layer development. CALPHAD calculations were used to determine the thermodynamically stable phases for each steel type at 650 °C and different oxygen activities. The results showed different phase compositions, highlighting the importance of the chromium content in steel for the formation of oxide layers. The different oxidation kinetics and oxide layer compositions are presented and associated with the increased risk of material degradation due to overheating. These results have significant implications for industrial applications, mainly the susceptibility to oxidation of low-alloyed steels like 16Mo3 and 13 Cr and contribute to a deeper understanding of oxidation processes in steels.

Failure investigation of a water-wall tube of fossil-fuel fired boiler

Failure investigation of water tube failure in boilers, especially in thermal power stations, is of paramount importance because it plays a crucial role in supplying energy to the dependent processing units in refineries. The failure investigation of the water-wall tube at the roof position in a boiler is presented in this work. In order to identify the root cause of the rupture, various destructive and non-destructive analyses were performed at multiple locations on the failed tubes. Visual inspection revealed a fish mouth-type rupture opening with excessive wall thinning about 60% before its failure and a diametrical growth of up to 150 % from the nominal diameter at the bulge location.From the chemical composition analysis, mechanical testing, and hardness measurements, the material was found to meet the requirement of SA 210 Grade A standards. This is a typical steel grade for high-pressure and temperature systems widely used in boilers. The microscopic examination revealed that the structure of the sound part of the tubes consisted of ferrite and pearlite structures. Whereas the microstructure of the bulged area exhibited a partial decomposition of the pearlite colonies, as well as formations of bainitic structures indicates localized overheating beyond the lower critical temperature (Ac1) of 723 °C for phase transformation. The absence of significant internal deposits and multiple bulges, ductile mode of failure, spheroidization in the ferrite matrix, and violent rupture are indications of short-term overheating. The failure mechanism of localized short-term overheating is identified as a result of the flame impingement due to the burner misalignment. A rupture of a tube in a high-pressure steam boiler can be catastrophic. A proper root cause analysis of the failure provides insight into the operating window for process variables, the interval of tracking feed water quality, and a planned shutdown inspection to avert any unpredictable shutdown in high-temperature applications. Understanding boiler-tube failures may improve stream-generating equipment performance, safety, availability, and reliability.

Failure analysis of the water-wall tube in once through Benson boiler

Failure analysis of a water wall tube of a once-through Benson boiler after 100,000 h of use of service is presented. A 15Mo3 material was used in the manufacture of the tube. In order to identify the root cause of the rupture, visual inspection, optical emission spectroscopy, microscopic examinations, mechanical strength measurements, and tube wall thickness measurements at various locations were performed on the failed tubes. Visual inspection revealed a fish mouth puncture opening with thin lips. As a result of optical spectroscopy, mechanical testing, and hardness measurements, the material was found to meet the requirements. Based on microstructure analysis, it appears that the pearlite spheroidized near the rupture site as a result of localized high temperatures. The failure mechanism of the tube was identified as a localized short-term overheating caused by high heat flux based on the results of all the tests and analyses conducted in this study.

A review paper on factors that causes the bulging failure of the metal tube

This paper is a systematic review of the Literature on the general parameters of bulging tube failure. Generally, boiler tubes show bulging tube failure in hot temperature zone in thermal power plants. Unpredictable tube failure affects the utility boiler's effectiveness in power plants due to uncertainty in utility boilers. In this report, the actual circumstances of battling the elevated temperature long-term overheating and short-term overheating and talking over corrosion to the boiler surface. The literature survey and the real-time data obtained from two thermal power stations; highlight that boiler tube failure occurs due to different causes. Overheating and creep deformation are the most prominent causes of bulging tube failure. This article may help understand the leading causes of the bulging tube failure placed in the hot temperature zone and its factors.

Abnormal creep property degradation in a directionally solidified superalloy DZ406 after suffering overheating

Turbine blades may suffer overheating and the resulting severe microstructural degradation or even premature failure during service. At present, the research on the effect of overheating on creep properties of directionally solidified superalloys is still very limited. In this study, directionally solidified superalloy DZ406 was subjected to overheating treatments at 1050 °C, 1150 °C, 1180 °C and 1220 °C for 30 min, and the corresponding stress rupture properties were tested under 980 °C/275 MPa. The results show that overheating resulted in the obvious dissolution of strengthening γ’ precipitates and γ/γ’ eutectic, for example the area fraction of γ’ precipitates decreased to 24.0% after overheating at 1220 °C, and was only about 1/3 of the initial value in the as-received microstructure. However, overheating has negligible influence on microstructural stability of carbides. Moreover, it is abnormal that the creep rupture properties of all samples after various overheating treatments were similar, and the creep voids were all located at the interfaces of MC carbides and γ matrix, and the alloy finally suffered interdendritic fracture. The main reason for this phenomenon is that the seriously degraded γ’ phase will recover before loading during the stress rupture tests, and its area fraction will basically return to the initial value, and thus leads to the recovery of the stress rupture property. Our results indicate that turbine blades will suffer obvious microstructural degradation during sudden short-term overheating, while this degradation may be restored in the subsequent normal service process, overheating does not necessarily lead to the damage of blade performance.

Over-attemperation and Short-term Overheating in Pendant-type Superheaters

ABSTRACT A water-wedge is often suspected to be the root cause for short-term overheating in fossil-fuelled boiler superheaters. However, it can be argued that evaporation of the water-wedge would cool the tube sufficiently and prevent overheating. This study aims to determine if the thermo-physical conditions occurring at low loads support this claim by studying the transient behaviour of a representative superheater segment under postulated conditions. A flow model was constructed to facilitate direct comparison with a boiler pendant superheater of a full-scale fossil-fuelled power plant. Several scenarios of water-wedges sustained by attemperation spraywater were simulated at low load operating conditions. The temperature evolution of the tube wall was tracked and, together with calculated equivalent stresses including thermal stress, was compared to the yield strength of the material. The results show that the stresses exerted over the tube wall and throughout the tube length are not sufficient to overcome the yield strength of the tube material, even for an aged tube under severe process conditions of boiler overfiring. Evaporation of the water-wedge provides sufficient cooling to the superheater tube to prevent failure. It was concluded that water-wedging alone is unlikely to be the root cause of short-term overheating at low boiler loads. Additional keywords: Short-term overheating; water-wedge; boiler superheater tube; attemperation; thermal stress, evaporation.

Creep rupture in HP-Nb refractory steel tubes due to short-term overheating

Creep rupture in HP-Nb refractory steel tubes due to short-term overheating

Assessment of Changes in Microstructure and Hardness of Bearing Steel for Operation at a High Temperature Caused by Short-Term Overheating

Abstract The paper presented research results of the impact of short-term overheating of samples collected from the outer bearing ring suitable for the operation at elevated temperature installed in the turbine engine on the microstructure and hardness of the material. The samples were annealed at the following temperatures: 500, 600, 700, 800, 900 and 1000°C; and then cooled in still air. Microstructure examinations were conducted under metallographic microscope and transmission electron microscope.

Functional properties of hemostasis in piglets after short-term overheating against the background of corrective action

Catosal is considered to be a highly effective bio-stimulator. It showed his properties in animals, realizing the stimulation of their tissues and organs. The purpose of this research is to determine the effect of Catosal on hemostatic parameters in piglets that experienced overheating. 58 piglets at the age of 2.5 months, which belonged to a large white breed, were taken into work. All animals as a result of an accidental emergency shutdown of the air conditioning system in the pigsty suffered overheating for 3 hours. These animals were randomly divided into two comparable groups. One was named experimental; the other was called control 1. Pigs of the experimental group (21 heads) received intramuscular injections of 2.5 ml of Catosal daily for 5 consecutive days, from the next day after an overheating episode. The control group 1 consisted of piglets with a total number of 21. After an overheating episode, they were under the usual conditions of a pigsty and did not receive any effects. In experimental piglets and piglets of the control group 1, all indicators were recorded in the outcome and after 30 days. Control group 2 consisted of 32 completely healthy piglets that were kept under standard conditions of a pigsty for their entire lives. They were examined once. Catosal injections in the observed piglets after overheating led to a decrease in spontaneous and stimulated platelet aggregation to normal levels. Against the background of the use of Catosal in the piglets that made up the experimental group, a weakening of hemocoagulation was found, which improved blood circulation in their tissues. Piglets of control group 1 showed an increase in platelet aggregation and blood coagulation. This had a very negative effect on hemorheology in them and weakened their metabolism. We can assume that in piglets after overheating, in the absence of optimizing effects, hemostasis is activated. This adversely affects the course of microcirculation and inhibits growth. Injections in piglets after overheating of the Catosal lead to a weakening of hemocoagulation and platelet activity to optimum values. This normalizes the course of microcirculation in the internal organs of animals.

Failure evaluation of SA 210C riffle water wall tubes in 70 MW CFBC boiler

Abstract Boiler tubes used as water walls made up of ferritic steels is having some finite life, because of prolonged exposure in the furnace at elevated temperature, stress and aggressive environment, tube failure taking place. Now a day's premature failure of the boiler tube mainly in water walls is one of the very common phenomena in the thermal power plants. The present investigation was done on the as-received ASTM SA 210C failed boiler tube steel used as water walls in the Circulating Fluidized Bed Combustion (CFBC) coal fired thermal power plant. An attempt has been made to understand the cause, because identifying correct failure mechanism often helps to perform meaningful life assessment and also to prevent the future Boiler Tube Failure (BTF). The as-received of failed tube along with the parent (unused) tube from the water wall raiser panel were selected to study for mechanical and metallurgical properties. Tensile test and micro hardness examinations were carried out on both the parent tube and failed tube. Visual examination reveals “fish-mouth” appearance of the as-received failed tube because of short-term overheating. The micro structure of the parent metal has the conventional structure of ferrite (white constituent) and pearlite (dark constituent), whereas for the as- received failed tube reveals Widmanstatten ferrite. A detailed structure - property relationship has been made by using the combined techniques of Optical Microscopy (OM), SEM/EDAX and XRD. Tensile fractography depicts the presence of micro-voids coalescence in the fibrous network shows ductile mode failure in the as-received failed boiler tubes.

Magnetic Hysteresis Loop Technique as a NDE Tool for the Evaluation of Microstructure and Mechanical Properties of 2.25Cr–1Mo Steel

This study intends to understand the effect of short-term overheating on microstructure modifications, and variation in mechanical and magnetic properties of boiler tubes. It is based on the hypothesis that short-term overheating on boiler tubes leads to microstructural changes degrading their mechanical properties, thus resulting in their failure. As part of this study, fresh 2.25Cr–1Mo boiler tube samples were heat treated in the range of 700–950 $$^{\circ }\hbox {C}$$ . Magnetic hysteresis loop (MHL) measurements were carried for the non-destructive evaluation (NDE) of the mechanical properties that get altered due to microstructural modifications. For comparison, MHL was also carried out on a service-exposed boiler tube, which had failed due to short-term overheating. The magnetic parameters were correlated with the change in microstructure and micro-hardness of the samples. A decrease in coercivity, remanence, maximum induction and micro hardness were found at the lower soaking temperatures, due to: easy magnetic domain wall and dislocation motions for the stress relaxation; annihilation and recovery of dislocations; increase in inter carbide distance; and the decrease in the number density of carbides for the coarsening of carbides. A subsequent increase in coercivity, remanence and maximum inductions along with hardness are due to the nucleation and growth of fresh bainitic phase, obstructing the magnetic domain wall and dislocation motion. A drastic decrease in coercivity for the service-exposed tube is due to the transformation of MX type carbides to $$\hbox {M}_{23}\hbox {C}_{6}$$ type and accumulation of such carbides at the grain boundaries along with the decrease in number density of the carbides. The presence of scale has less effect on the coercivity, but its demagnetizing effect largely decreases the remanence and maximum induction. The results of the study show that the MHL can be a suitable NDE technique for the evaluation of change in microstructure and degradation of mechanical properties in power plant steels.

Behaviour of spinel-forming DVM using crucible induction furnaces. A case study on material failure

This article contributes to the understanding of the sintering behaviour of spinel forming dry vibrating mixes (DVM) that are in common use in crucible induction furnaces (CIF) for metallurgic treatment. At present, an unwanted sintering of the DVM as far as to the cold face is reported from the industry. For safety reasons it is indispensable that an unaffected layer is remaining at the cold face of the lining. If not, the material becomes brittle and the risk of crack formation gets unacceptable. The access of liquid melt to the induction coil may cause severe accidents that destroy the furnace which bears the risk of industrial injury.Systematic research on breakout materials by means of SEM-supported microtextural and microanalytical investigations come to the result that a sintering occurs already in areas of the lining where the prevailing temperature could not have exceeded 300°C. Furthermore, it can be carved out that the sintering at the cold face is caused by the formation of spinel. This result is in contradiction to the generally accepted opinion that the spinel formation is kinetically hampered at temperatures lower than 900°C and should not occur. The increased MgO:Al2O3 ratios of the newly formed spinels indicate lower crystallization temperatures. The gradual transformation starts with marginal dissolution of the magnesia grains at the cold face and progrades with the development of skeleton structures of matrix spinels.The spinel formation is favoured of different components as chemical additives, a reduced atmosphere, hydration, and a momentary overheating. However, it is suspected that water and short-term overheating, respectively, play the key role since other known major agents as untypical oxides, and in particular fluorides and chlorides can be excluded by their erratic occurrence. We identified water as a primary unwanted additive which left typical microstructures in magnesia grains of the studied lining breakouts.

Assessing overheating of the UK existing dwellings – A case study of replica Victorian end terrace house

This paper aims to investigate the likely thermal performance of a unique pre-1919 Victorian case study property by using both current and future projected weather data after a deep retrofit. The property is a re-construction within an environmental chamber using reclaimed materials designed to test housing retrofit solutions. Climate projections for Manchester from both UKCIP02 and UKCP09 programmes were used to assess the likely overheating in summer for this ‘Hard to Treat’ property judging by both single and adaptive comfort criteria from CIBSE Guide A and BS EN 15251. In the bedroom, where occupants have less ability to adapt, overheating could occur as early as 2020s; while in the living room, using the annually adaptive approach, overheating may not happen until 2080s. For high expectation occupants, however, short term overheating (weekly or monthly) can occur much earlier. The research highlights the discrepancies in predicting overheating using the two UK climate impact programmes; the inconsistencies of risk evaluation using different comfort criteria; and the differences between risk and severity of potential overheating.

High operating steam pressure and localized overheating of a primary superheater tube

Common boiler sites which likely have tube failures due to short-term overheating are superheaters and reheaters. Severe short-term overheating caused by an unusual operating condition occurs when the tube temperature significantly rises above design limits for a brief period. Therefore, immediate investigation on unusual occurrences preceding failure may be extremely important in identifying the cause of failure. The efforts should be thoroughly addressed to the operating procedures and system design. This paper presents failure evaluation on a primary superheater tube of a power plant. In situ hardness measurements on the selected region of the failed primary superheater tube were carried out. The average hardness was then used for estimating the average operating temperature prior to failure. Creep analysis was conducted to confirm whether or not the creep damage contributed to the failure. Microstructures of the as-received tube were observed through microscopic examinations. Similar incidents occurred at the different units of the power plant in 2007 were reported by Purbolaksono et al. [1] and Rahman et al. [2]. The first failure [1] showed that a primary superheater tube failed with a wide open burst after running at around 28,194 h following the firing of the low quality coal causing heavy clinker formations. At around the same time, another failure [2] occurred due to the similar root cause but it was also in combination with the coal-ash corrosion attack. 2. Operational background On 26 February 2011, one of the units in the power plant was forced to shut down due to a rupture in one of the primary superheater SA213-T12 tubes. It was reported the superheater tube had been in service for around 48,000 h. According to the operational records, the operating steam temperature and pressure for primary superheater are maintained at around 430– 460 _C and 176.5 bar (17.65 MPa), respectively. The superheater tubes have outer diameter of 45 mm, the thickness of 4.6 mm and a standard hardness of 163 HV. Due to limited coal supply in the market during some periods prior to failure, it was reported that several types of coals with different ash fusion temperatures as listed in Table 1 were used in the last 45 days prior to failure. It can be seen from Table 1, there are three types of coal (Types A, D, and G) having lower ash fusion temperatures in comparison to the average furnace flame temperature of 1400 _C. Thus, it would likely trigger the formations of heavy clinker during the firing.

Failure Evaluation on a High-Strength Alloy SA213-T91 Super Heater Tube of a Power Generation

This article presents failure investigation on a high-strength alloy SA213-T91 super-heater tube. This failure is the first occurrence involving the material in Kapar Power Station Malaysia. The investigation includes visual inspections, hardness measurements, and microscopic examinations. The failed super-heater tube shows a wide open rupture with thin and blunt edges. Hardness readings on all the as-received tubes are used for estimating the operating metal temperature of the super-heater tubes. Microstructures of the failed tube show numerous creep cavities consisting of individual pores and chain of pores which form micro- and macro-cracks. The findings confirmed that the super-heater tube is failed by short-term overheating. Higher temperatures of the flue gas due to the inconsistent feeding of pulverized fuels into the burner is identified to cause overheating of the failed tube.

Root cause failure analysis of a division wall superheater tube of a coal-fired power station

Coal-fired boiler tubes are generally exposed to high internal pressure and high temperature of steam and flue gas. The common cause of any metallurgical failure of a superheater tube is due to the tube metal temperature higher than that as originally specified [1]. Tube metal temperature may increase gradually over many years due to the growing oxide scales inside tube or elevate rapidly caused by loss of internal steam or water-coolant flow. Internal pressurized tubes are critical components in water-tube boiler and steam superheater elements. Tubes in such application are vulnerable to high temperature upset condition, undergoing severe creep deformation or even final rupture. Therefore, boiler tubes in power plants have finite life because of prolonged exposure to high temperature, stress, aggressive environment, corrosive degradation, etc. However, uses of suitable boiler tube material in thermal power plants are required to ensure that the materials are safely used under higher temperatures and pressures for a long period of operation [2]. Many works concerning the failure problems in water-tube boiler have been reported. The North American Electric Reliability Council (NERC) reported that the coal-fired boilers are among the highest economic risk components in any other power plant. By far, the greatest number of forced outages in all types of boiler is caused by failures [3]. Elimination of boiler tube failure could save the electric power industry about $5 billion a year [4]. Metallurgists from French, Inc. [1] published data of the top 10 causes of failures where creep (long-term overheating) is 23.4%, followed by fatigue (13.9%) (thermal 8.6%, corrosion 5.3%), ash corrosion (12.0%), hydrogen damage (10.6%), weld failures (9.0%), high temperature (short-term overheating) (8.8%), erosion (6.5%), oxygen pitting (5.6%), caustic attack (3.5%) and stress corrosion cracking (2.6%). In general, 30% of all tube failures in boilers and reformers are caused by creep [5–7].

Tube failures due to cooling process problem and foreign materials in power plants

Abstract Cooling process which uses water for heat transfer is an essential factor in coal-fired and nuclear plants. Loss of cooling upset can force the plants to shut down. In particular, this paper reports visual inspections and metallurgical examinations on the failed SA210-A1 right-hand side (RHS) water wall tube of a coal-fired plant. The water wall tube showed the abnormal outer surface colour and has failed with wide-open ductile rupture and thin edges indicating typical signs of short-term overheating. Metallurgical examinations confirmed the failed tube experiencing higher temperature operation. Water flow starvation due to restriction inside the upstream tube is identified as the main root cause of failure. The findings are important to take failure mitigation actions in the future operation. Discussion on the typical problems related to the cooling process in nuclear power plants is also presented.

Survival types of high mountain plants under extreme temperatures

Extreme temperatures are a main factor limiting plant growth in high mountain habitats. During winter, the risk of frost damage is highest at windblown and often snow-free sites. During summer, actively growing plants are particularly endangered by episodic cold spells, but also by short-term overheating. The current review gives an overview of extreme temperatures in the European Alps and observations of temperature damage on plants in their natural habitats. Furthermore, seasonal time courses of frost and heat resistance derived from laboratory tests on different plant growth forms are presented. Study species were the cushion plants Silene acaulis, Minuartia sedoides, Saxifraga oppositifolia and Carex firma collected on wind-exposed ridges; the rosette plant Soldanella alpina collected on snow-protected sites, and three Sempervivum species collected in xerothermic habitats. The temperature resistance of leaves, stems, rhizomes and roots were tested in two annual time courses. Frost treatments were conducted in controlled freezers by rapid cooling (10 K h −1, for current resistance) as well as by stepwise cooling (1–3 K h −1, for hardening capacity). Heat treatments followed a standardised procedure by exposing samples to heat for 30 min in hot water baths. The damage was visually estimated using the topographic tetrazolium test. During winter, cushion plants from exposed sites were fully hardened (LT 50 below −70 °C). Rosette plants, which are protected by a constant snow cover, survived temperatures of down to −25 °C. During the growing period, foliage and shoot tips of the investigated species were damaged at −5 to −8 °C (LT 50). Stems and rhizomes were only partially damaged by temperatures of −10 to −15 °C. Heat resistance in cushion plants generally reached 56–58 °C (LT 50), shoots and rhizomes of C. firma could reach 60 °C. Succulent plants like Sempervivum arachnoideum and S. tectorum from hot and dry microsites were the most heat resistant among the tested species (62–64 °C). The investigated mountain plant species showed highly varying resistance patterns, with variation in maximum hardening capability and seasonal time courses of resistance. Plants were capable of rapid adjustments to extreme temperatures, which is crucial for survival in a high mountain climate.

Failure analysis on a primary superheater tube of a power plant

In this paper failure analysis on the SA213-T12 superheater tube by visual inspection, in situ measurements of hardness and finite element analyses is presented. A primary superheater tube has failed with a wide open burst after running at around 28,194 h. Heavy clinkers were found to almost entirely cover the primary superheater region. In situ hardness measurements were carried out on the selected primary superheater first row tubes at the middle region between furnace rear screen tube and primary superheater blower flow path. Hardness measurements are also taken on the as-received failed tube. Finite element analyses on possible features prior to failure are also conducted in order to illustrate and deduce the failure mechanism and failure root cause. Localized short-term overheating of the tube due to localized and concentrated flue gas flow resulted in a failure of the primary superheater tube.