A Dynamic Modeling Methodology to Estimate the Magnitude of Unwanted Liquid Flows in High Temperature Boiler Components

2020 ◽  
Vol 12 (5) ◽  
Author(s):  
Gary de Klerk ◽  
Pieter Rousseau ◽  
Louis Jestin
Keyword(s):  
High Temperature ◽  
Power Plants ◽  
Fatigue Cracking ◽  
Momentum Equation ◽  
Temperature Gradients ◽  
Root Cause ◽  
Modeling Methodology ◽  
Tracking Model ◽  
Liquid Flows ◽  
Control Volumes

Abstract Due to the penetration of variable renewable energy (VRE) sources into electricity supply grids, conventional coal fired power plants need to operate with greater flexibility while remaining reliable and conserving the lifetime of components. Thick-sectioned components are prone to thermal fatigue cracking as a result of through-wall temperature gradients. These temperature gradients can be significantly amplified during quenching when components at high temperature are unintentionally exposed to colder liquid or steam. Such quench events are known to occur during two-shift operation of a large once-through coal fired tower type boiler. The purpose of this study is to develop and demonstrate a model that can be used to determine the root cause and magnitude of quenching. The model is developed using the least level of detail to make it readily usable by power plant engineers. Two different approaches are used. A liquid tracking model (LTM) was developed from first principles that approximates the liquid level in the superheater as a function of time. The model is presented and verified by comparison with real-plant data. The second approach was to configure a model in flownex, which is a commercially available software package. The LTM model with eight control volumes provided better steam temperature results and was able to simulate the correct superheater pressure behavior without solving the momentum equation. The models proved that a separator overflow was the cause of quenching for this particular case study.

Through Wall Cracking in High Temperature Rotary Cooler

2009 ◽  
Author(s):  
James Frith ◽  
Robert Frith
Keyword(s):  
High Temperature ◽  
Corrosion Fatigue ◽  
Design Principle ◽  
Extreme Temperature ◽  
Fatigue Cracking ◽  
Water Dissociation ◽  
Thermally Induced ◽  
Corrosion Fatigue Crack ◽  
Root Cause ◽  
High Temperature Operation

After operating for a number of years, a high temperature rotary ore cooler suffered cracking. The cracks grew through the shell wall resulting in leakage of water from the water bath into the ore. Under the extreme temperature, the risk of water dissociation into hydrogen and subsequent explosion was of substantial concern and instigated the investigation in to the root cause of the cracking which was deduced to be driven by high thermally induced stresses. The root cause for the thermally induced stressing was found to be related to a design flaw that was not immediately obvious. The investigation outcome was a recommendation to change the design to eliminate the high localized stresses which were believed to be the driving force behind the corrosion fatigue crack propagation. This paper presents the investigation approach which included advanced thermal and stress analysis and reports on the general design principle that should be adopted to avoid thermal stress induced corrosion fatigue cracking under high temperature operation.

Temperature Measurements with Depth and Physical Evidence for the Effect of High Temperature Gradients on Top-Down Fatigue Cracking

2020 ◽  
Vol 2674 (4) ◽  
pp. 384-396
Author(s):  
Adrian Ricardo Archilla
Keyword(s):  
High Temperature ◽  
High Surface ◽  
Fatigue Cracking ◽  
Time Of Day ◽  
Temperature Gradients ◽  
Temperature Measurements ◽  
Measured Temperature ◽  
Horizontal Shear ◽  
Top Down ◽  
Shear Strains

This paper presents the results of pavement temperature measurements with depth over a year obtained with a setup emulating the heat flow on a pavement with 305 mm (12 in.) of hot mix asphalt (HMA) and 152 mm (6 in.) of aggregate base. Several findings related to top-down fatigue cracking (TDFC) in Hawaii were obtained from these measurements. It was observed that pavement temperatures near the surface, which were both the lowest and the highest in the HMA depending on the time of day, were rarely below 20°C, and thus, that most cracking in Hawaii occurs at higher temperatures. It was also observed that passing rains can cause sudden temperature drops of the order of 15°C within short periods (15 min). HMA moduli estimated using measured temperature profiles indicate that high temperature gradients may lead to inverted moduli profiles that when loaded cause the highest tensile and shear strains to occur near the surface, and that these may be a main reason for TDFC in the state. The simulated stresses and strains under high temperature gradients also indicate they may be conducive to delamination problems related to large horizontal shear strains generated near the surface and combined with nearly vertical but small tensile strains at the layer interface. The observation that cracking suddenly and consistently stops under overpass bridges and immediately resumes after them provides strong evidence consistent with the findings of the stress/strain distributions generated from profiles with high surface temperature and high temperature gradients potentially causing TDFC. The paper provides recommendations for further study.

Impact of Metal Pad Etch-Induced Plasma Damage on Dynamic Retention Time Degradation during High Temperature Stress in High Density DRAM Technology

2005 ◽  
Author(s):  
D-J Kim ◽  
I-G Kim ◽  
J-Y Noh ◽  
H-J Lee ◽  
S-H Park ◽  
...  
Keyword(s):  
High Temperature ◽  
Temperature Stress ◽  
Retention Time ◽  
High Temperature Stress ◽  
High Density ◽  
Cell Junction ◽  
Antenna Effect ◽  
Plasma Damage ◽  
Root Cause ◽  
Wafer Processing

Abstract As DRAM technology extends into 12-inch diameter wafer processing, plasma-induced wafer charging is a serious problem in DRAM volume manufacture. There are currently no comprehensive reports on the potential impact of plasma damage on high density DRAM reliability. In this paper, the possible effects of floating potential at the source/drain junction of cell transistor during high-field charge injection are reported, and regarded as high-priority issues to further understand charging damage during the metal pad etching. The degradation of block edge dynamic retention time during high temperature stress, not consistent with typical reliability degradation model, is analyzed. Additionally, in order to meet the satisfactory reliability level in volume manufacture of high density DRAM technology, the paper provides the guidelines with respect to plasma damage. Unlike conventional model as gate antenna effect, the cell junction damage by the exposure of dummy BL pad to plasma, was revealed as root cause.

Comparison of the Limit Loads Between Defected Pressure Pipes With an Internal Pit and an External Pit at High Temperature

2013 ◽  
Author(s):  
Changyu Zhou ◽  
Bo Wang ◽  
Zhigang Sun ◽  
Jilin Xue ◽  
Xiaohua He
Keyword(s):  
High Temperature ◽  
Power Plants ◽  
Structural Integrity ◽  
Load Condition ◽  
Relative Length ◽  
Limit Load ◽  
Relative Depth ◽  
Corrosive Media ◽  
Pressure Pipe ◽  
Pressure Pipes

High temperature pressure pipes are widely used in power stations, nuclear power plants, and petroleum refinery, which always bear combined effects of high temperature, high pressure, and corrosive media, so the local pits are the most common volume defects in pressure pipe. Due to various reasons, the defects usually appear on the internal or external wall of pipe. In this paper, the dimensions of a defect were characterized as three dimensionless factors: relative depth, relative gradient and relative length. The main objects of study were the pipe with an internal pit and pipe with an external pit. Orthogonal array testing of three factors at four different levels was applied to analyze the sequence of the influence of three parameters. In present study, when the maximum principal strain nearby the location of the defects reaches 2%, the corresponding load is defined as the limit load, which is classified as two kinds of load type: limit pressure and limit bending moment. According to this strain criterion and isochronous stress strain data of P91 steel, the limit load of high temperature pipe with a local pit was determined by using ABAQUS. And in the same load condition of the pipe with the same dimensionless factors, the limit load of the internal defected pipe was compared with that of the external defected pipe. The results of this study can provide a reference for safety assessment and structural integrity analysis of high temperature creep pressure pipe with pit defects.

scholarly journals Performance Evaluation of Asphalt Rubber Mixture with Additives

Materials ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1200 ◽  
Author(s):  
Cheng ◽  
Liu ◽  
Ren ◽  
Huang
Keyword(s):  
High Temperature ◽  
Fatigue Cracking ◽  
Crumb Rubber ◽  
Good Choice ◽  
Environmental Benefits ◽  
Fatigue Properties ◽  
Control Group ◽  
Rubber Mixture ◽  
Asphalt Rubber ◽  
Temperature Performance

Crumb rubber, as a recycled material used in asphalt mixture, has gained more attention in recent years due to environmental benefits and the advantages of its pavement, such as excellent resistance to cracking, improved durability, less road maintenance, lower road noise, etc. However, the high-temperature performance of mixture with crumb rubber does not perform well. In order to improve the performance, this paper examined the effect of additives on the laboratory performance of asphalt rubber Stone Matrix Asphalt (AR-SMA) with additives. Three groups of AR-SMA: no additives, Styrene–Butadiene–Styrene (SBS) and Granular Polymer Durable additive (GPDa) were included, with no additives as a control group. Each group was investigated at three asphalt rubber content (ARC): 6.4%, 6.9%, 7.4% with regard to high-temperature and fatigue properties. The results show that with increasing ARC, the high-temperature performance of mixture without additive decreases, and the high-temperature performance increases first and then decreases for SBS and GPDa. Moreover, the rutting resistance of AR-SMA with GPDa at 6.9% ARC performs best. Under the condition of mixtures with appropriate ARC, AR-SMA with GPDa has higher fatigue life and sensitivity to fatigue cracking than the control group. Simultaneously, the fatigue performance of AR-SMA with GPDa is not as significant as that without additive with increasing ARC. In a word, GPDa is a good choice to improve the performance of AR-SMA. However, it should be noted that optimal asphalt content of AR-SMA mixtures with GPDa is higher than that of traditional mixtures.

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