3D analysis of creep voids in hydrogen reformer tubes

Wahab, Azmi Abdul; Kral, Milo V.

doi:10.1016/j.msea.2005.08.223

Cited by 29 publications

(18 citation statements)

References 21 publications

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“…Since dislocation glide takes place on well-defined crystallographic planes, a dependence of void growth rate on the crystallographic orientation of nearby grains is expected and has been already suggested on an empirical basis [32]. Additional experimental evidence was also obtained in this work utilizing submicron tomography [20].…”

Section: Void Growth Due To Viscous Dislocation Motionsupporting

confidence: 66%

Void growth in copper during high-temperature power-law creep

et al. 2011

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Section: Void Growth Due To Viscous Dislocation Motionsupporting

confidence: 66%

Void growth in copper during high-temperature power-law creep

et al. 2011

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“…Although these continuum models of void growth and their modifications are very helpful in understanding various aspects of mechanical behavior, they do not address issues related to the geometry of the material's microstructure. For instance, recent experimental and theoretical investigations have revealed that the growth of nano-size voids in polycrystalline metals depends strongly on the void location relative to grain boundaries and their junctions, and on the interaction of the void with intersecting boundaries and dislocation structure [4][5][6][7]. Another problem with continuum models is the absence of a microstructural length scale in their constitutive equations that may account for the size effects on the void growth in the range of sub-microns and nano-meters.…”

mentioning

confidence: 99%

Molecular dynamics study on the nano-void growth and coalescence at grain boundary

Lin

Niu

Shi

et al. 2011

Sci. China Phys. Mech. Astron.

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Molecular dynamics simulations using embedded atom method (EAM) potential were performed to study nano-void growth and coalescence at grain boundary in face-centered cubic bicrystal copper. Thin-plate specimens subjected to uniaxial tension strain with one-void and two-void at the centered grain boundary were employed to analyze the effect of specimen size, temperature and applied strain rate on the stress-strain response, incipient yield strength and macroscopic effective Young's modulus. The evolutions of dislocations, twin bands and void shapes under different specimen sizes were also presented. The obtained results show that, regardless of the void numbers, the specimen sizes, temperature, the applied strain rate had significant influence on the void shape evolution, stress-strain curve and incipient yield strength, while negligible effects on the macroscopic effective Young's modulus except for the temperature. Moreover, the voids growth rate along the grain boundary was also found to be associated with the specimen sizes.bicrystal, void growth, void coalescence, grain boundary, molecular dynamics simulations, embedded atom method PACS number(s):Void nucleation, growth, and coalescence are known to play major roles in the fracture of ductile metals. In order to predict failure in ductile metals, a lot of works have been done using continuum methods to generate mathematical models capable of describing void growth and coalescence. McClintock [1] first investigated the growth of an isolated cylindrical void and then Rice and Tracey [2] further studied the growth of spherical void in an infinite, rigid-perfectly plastic solid subjected to remote triaxial stress. Gurson [3] originally adopted the unit cell model and derived a constitutive law for a plastic matrix containing spherical voids from an approximate plastic flow potential function, which accounted for the damaging effect of void. Although these continuum models of void growth and their modifications are very helpful in understanding various aspects of mechanical behavior, they do not address issues related to the geometry of the material's microstructure. For instance, recent experimental and theoretical investigations have revealed that the growth of nano-size voids in polycrystalline metals depends strongly on the void location relative to grain boundaries and their junctions, and on the interaction of the void with intersecting boundaries and dislocation structure [4][5][6][7]. Another problem with continuum models is the absence of a microstructural length scale in their constitutive equations that may account for the size effects on the void growth in the range of sub-microns and nano-meters. Phenomenological theories such as strain gradient [8] and nonlocal plasticity [9] have been used to address the size effect on the void growth. However, due to their lack of consideration about the underlying physical mechanism of size effect on void growth, e.g. evolution of dislocation microstructure, the length scale parameter needs to be measured by exper...

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“…In the midsection of the tube (Fig. 2, c), the ageing due to high temperature service induced the formation of many isolated microvoids with a largest peanut shape formed by the coalescence of two or more voids leading to the progress of creep during service [13]. Figure 2, d shows the presence of string of cavities along the grain boundary, which link with increasing strain to form microcracks.…”

Section: Metallographic Observationsmentioning

confidence: 96%

Metallographic and Mechanical Studies of a Cast Heat-Resisting Alloy

Aichaoui¹,

Hadji²

2017

Metallofiz. Noveishie Tekhnol.

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A heat-resistant steel tube from an ammonia plant made of modified HP40 steel that failed after short-term service is studied for damage mechanism. The assessment of material degradation is carried out using optical microscopy, scanning electron microscopy in combination with energy dispersive spectroscopy analysis, x-ray diffraction analysis, and mechanical tests. Results show that precipitation of the chromium-rich carbides induces the coalescence of grain boundaries. Significant growth and poor distribution of secondary carbides are also noticed through the matrix, which lead to a reduction of material ductility even after a short-term service. The main cause of failure appears to be damaged catalyst. Such a problem can cause a rise in temperature leading to localized overheating in the lower part of the tube. Overheating is primarily responsible for significant degradation in microstructure, creep strength, and mechanical properties of the tube.Key words: heat-resistant steel, carbide, damage mechanism, overheating, creep.Для встановлення механізму руйнування було вивчено виготовлену з мо-дифікованої жароміцної сталі НР40 трубу з аміячного заводу, що вийшла з ладу після короткотермінового використання. Вивчення деґрадації ма-теріялу було проведено за допомогою оптичної та сканівної електронної мікроскопій у комбінації з енергодисперсійною спектроскопічною аналі-зою, рентґенодифракційними дослідженнями та механічними випробу-ваннями. Встановлено, що виділення насичених Хромом карбідів викли-кає коалесценцію меж зерен. Також встановлено істотне зростання та ро- Ключові слова: жароміцна сталü, карбід, механізм пошкодження, пере-грів, плазучістü.Для установления механизма разрушения бûла изучена изготовленная из модифицированной жаропрочной стали НР40 труба с аммиачного завода, вûшедшая из строя после кратковременного исполüзования. Èзучение деградации материала бûло проведено с помощüю оптической и сканиру-ющей электронной микроскопий в комбинации с энергодисперсионнûм спектроскопическим анализом, рентгенодифракционнûми исследовани-ями и механическими испûтаниями. Óстановлено, что вûделение насû-щеннûх хромом карбидов вûзûвает коалесценцию границ зёрен. Также установлено существенное увеличение и разрежённое распределение вто-ричнûх карбидов в матрице, что приводит к снижению пластичности ма-териала даже после кратковременного исполüзования. Îсновной причи-ной вûхода труб из строя является повреждённûй катализатор. Эта про-блема может вûзватü повûшение температурû, что приводит к локалüно-му перегреву в нижней части трубû. Èменно перегрев, в первую очередü, ответственен за существеннûе деградацию микроструктурû, ухудшение границû ползучести и механических свойств трубки.Ключевые слова: жаропрочная сталü, карбид, механизм повреждения, перегрев, ползучестü.

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3D analysis of creep voids in hydrogen reformer tubes

Cited by 29 publications

References 21 publications

Void growth in copper during high-temperature power-law creep

Void growth in copper during high-temperature power-law creep

Molecular dynamics study on the nano-void growth and coalescence at grain boundary

Metallographic and Mechanical Studies of a Cast Heat-Resisting Alloy

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