某电厂后屏再热器爆管原因分析

分析了锅炉后屏再热器发生爆管的原因,管子受到高温烟气腐蚀,同时长时超温加剧腐蚀速率,使管壁减薄,减薄后的管子强度不足,从而引起爆管。     

常熟发电厂1号炉高温再热器管屏变形原因分析

对高温再热器管壁温度、烟气温度的实时监测和分析计算表明，高温再热器的管屏变形不是由管壁或工质温度超限引起，而是由于进／出口温度差，以及同屏各管进／出口温度偏差所产生的胀差引起。同屏管夹破坏是因管子膨胀不畅，管夹焊缝应力超过许用应力，管夹的焊接强度不够而拉裂造成；定位管与各屏外管套的垂直膨胀最不同而产生相对位移，形成定位管脱开后错位。     

屏式再热器爆管原因分析

通过化学,金相和扫描电镜手段,分析了产生爆管的主要原因是由于在相对较高的运行温度下长期过热所造的,提出了预防屏式再热器爆管的有效措施。     

某电厂高温过热器爆管事故分析

本文介绍了锅炉高温过热器爆管的具体情况。通过对该处受热面各项指标详细检查,分析认为爆管的主要原因是长期超温引起的蠕变产生。并根据现场实际情况制定切实可靠的措施。     

某电厂1#炉水冷壁爆管原因分析

对某电厂1#炉水冷壁爆管部位和爆口采用现代分析测试方法,进行化学成分、力学性能、金相组织检验及扫面电镜分析,确定该水冷壁爆管是由于该管在运行过程中处于长时超温状态造成的。     

某电厂低温再热器三叉管表面缺陷原因分析

某电厂低温再热器材质为SA-182M F91的三叉管,运行数月后泄漏导致被迫停炉。通过宏观观察、化学成分分析、力学性能检测和金相组织观察等方法,分析确定三叉管发生泄漏的原因。分析认为,三叉管的化学成分和硬度均符合ASME SA-182M标准对F91材料的要求,三叉管外表面补焊产生的焊缝结构是导致裂纹萌生扩展并最终泄漏的主要原因,裂纹在三叉管最终热处理前已存在。     

锅炉再热器管腐蚀与防止

介绍了某电厂锅炉高温再热器发生失效的基本情况,通过化学元素分析、力学性能试验、宏观检查、金相分析和电子探针微区成分分析等试验表明,管子外表面存在较明显的结垢现象,氧化物下的金属金相组织出现深2～3个的沿晶腐蚀裂纹,沿晶腐蚀产物中存在S元素综合分析认为,其失效类型为高温硫腐蚀,并提出了预防措施。     

某电厂锅炉末级再热器水压泄漏原因分析

本文介绍了某电厂锅炉水压试验时末级再热器管屏泄漏情况及处理措施,分析泄漏发生的原因,并提出预防措施。     

某电厂末级再热器爆管原因分析及处理措施

根据某电厂末级再热器爆管事件,从金相组织、力学性能等多方面分析爆管原因,并提出预防措施及建议.     

某电厂锅炉高温再热器异种钢焊口断裂原因分析

分析了锅炉高温再热器焊口产生断裂的原因,锅炉停炉时产生交变应力,钢管产生裂纹,并发生脆性断裂。     

某电厂锅炉末再管屏间隔系统分析

本文应用管道分析软件对某电站锅炉的末级再热器管屏进行模拟,并根据模拟结果选择适当的活动夹块规格。     

Magnetothermoelastic creep analysis of functionally graded cylinders

This paper describes time-dependent creep stress redistribution analysis of a thick-walled FGM cylinder placed in uniform magnetic and temperature fields and subjected to an internal pressure. The material creep, magnetic and mechanical properties through the radial graded direction are assumed to obey the simple power law variation. Total strains are assumed to be the sum of elastic, thermal and creep strains. Creep strains are time, temperature and stress dependent. Using equations of equilibrium, stress–strain and strain–displacement a differential equation, containing creep strains, for displacement is obtained. Ignoring creep strains in this differential equation a closed form solution for the displacement and initial magnetothermoelastic stresses at zero time is presented. Initial magnetothermoelastic stresses are illustrated for different material properties. Using Prandtl–Reuss relation in conjunction with the above differential equation and the Norton’s law for the material uniaxial creep constitutive model, the radial displacement rate is obtained and then the radial and circumferential creep stress rates are calculated. Creep stress rates are plotted against dimensionless radius for different material properties. Using creep stress rates, stress redistributions are calculated iteratively using magnetothermoelastic stresses as initial values for stress redistributions. It has been found that radial stress redistributions are not significant for different material properties, however major redistributions occur for circumferential and effective stresses.     

Life estimation of pressurised pipe bends using steady-state creep reference rupture stresses

Steady-state reference rupture stresses were obtained for a range of 90° pipe bends, subjected to internal pressure only, using simplified 2D axisymmetric finite element (FE) models. The bends were considered to be circular in shape and not include any ovality. Creep damage FE analyses were performed to obtain realistic failure lives and to determine the skeletal point rupture stresses, using the material properties, obtained at 640 °C, for a service-exposed CrMoV pipe steel. The effects of the normalised pipe bend dimension on the reference rupture stresses are presented. The results obtained confirm the validity of the use of the steady-state reference rupture stress in life estimation for a wide range of pressurised pipe bend geometries. The life predictions were compared with those of the corresponding straight pipes and their relevance considered.     

Reliability-based assessment of polyethylene pipe creep lifetime

Lifetime management of underground pipelines is mandatory for safe hydrocarbon transmission and distribution systems. The use of high-density polyethylene tubes subjected to internal pressure, external loading and environmental variations requires a reliability study in order to define the service limits and the optimal operating conditions. In service, the time-dependent phenomena, especially creep, take place during the pipe lifetime, leading to significant strength reduction. In this work, the reliability-based assessment of pipe lifetime models is carried out, in order to propose a probabilistic methodology for lifetime model selection and to determine the pipe safety levels as well as the most important parameters for pipeline reliability. This study is enhanced by parametric analysis on pipe configuration, gas pressure and operating temperature.     

On the development of creep damage constitutive equations: a modified hyperbolic sine law for minimum creep strain rate and stress and creep fracture criteria based on cavity area fraction along grain boundaries

This paper reports (1) the latest development and application of a modified hyperbolic sine law for minimum creep strain rate and stress for both low Cr and high Cr steels, and (2) the development of a creep fracture criterion based on cavity area fraction along grain boundaries for high Cr steel. This work is part of the fundamental development of creep damage constitutive equations which were identified through a critical literature review. In the former the application of the new law results in an improved fitting; in the latter, a new creep fracture criterion based on cavity area fraction along grain boundaries was derived and quantitatively calibrated using the latest detailed cavity nucleation and growth kinetics models for high Cr steel. Furthermore, this paper revealed the trend of nucleation rate coefficient with stress, and the trend of creep life time coefficient with stress, which provide reliable and universal prediction capabilities. This paper contributes to the specific knowledge on the minimum creep strain rate and stress function, the development of a scientifically sound and novel creep rupture criterion based on the cavity area fraction along grain boundaries for high Cr steel, and the provision of creep damage/life prediction tools.     

Parametric peak stress functions of 90° pipe bends with ovality under steady-state creep conditions

Stress-based life prediction techniques are commonly used to estimate the failure life of pressurised pipe-related components, such as welds and bends, under creep conditions. Previous research has shown that reasonable life predictions can be obtained, based on the steady-state peak stresses, compared with the life predictions obtained from creep damage modelling. In this work, a series of parametric steady-state peak rupture stress functions of right-angled pipe bends with ovality are presented, which are based on the results obtained from finite element (FE) analyses, covering a number of material property and geometry parameters in practical ranges. Methods used to determine the stress functions are described. The FE analyses have been performed using axisymmetric models, subjected to internal pressure only, with a Norton creep law. Typical examples of parametric peak stress curve fitting are shown. In particular, the accuracy of the interpolation and extrapolation abilities of the stress functions is assessed. The results show that in most cases the interpolated and extrapolated peak stresses are accurate to within ±3% and ±5%, respectively.     

滨海发电厂防腐蚀接地方法探讨

保证接地网的可靠性对于保证电厂安全运行是十分重要的,滨海电厂厂址地下水受海水入渗影响含盐量较大、对钢材腐蚀较大,为了防止和减缓厂址地中接地网的腐蚀,应采取必要的防腐蚀措施,以已建成投运的福建省莆田燃气电厂为工程实例,通过技术经济比较,探讨在福建省滨海电厂建设中应采用何种措施才能既经济、环保又安全、可靠地防止接地网的腐蚀。     

Evaluation of conversion relationships for impression creep test at elevated temperatures

This paper contains some results related to the evaluation of the conversion relationships between impression creep test data and conventional uniaxial creep test date, for determining the secondary creep properties at elevated temperature. Some important aspects, including conversion factors, specimen dimensions, typical test results and validity of the test technique etc are briefly reviewed. The method used to determine the conversion factors is based on a reference stress approach using the results of finite element (FE) analyses; this is described in the paper. The conversion factors (reference parameters) obtained from 2-dimensional (2D) and 3-dimensional (3D) FE analyses are compared and the effects of specimen geometry, on the conversion relationships, are assessed. The recommendations on the use of these conversion factors, in practical impression creep testing, are given. Proposals for future exploitation of the technique are addressed.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Creep damage in small punch creep specimens of Type 304 stainless steel

Small punch creep tests on Type 304 stainless steel have been performed at 650 °C. Based on these tests, a finite element model, with modified Kachanov–Rabotnov creep damage constitutive equations, was established. The variation of central deflection and creep strain with time and the evolution of creep damage under constant loads were analysed by using the finite element model. The central creep deflection curves in the specimens were obtained at different loads in both tests and simulations and have three different stages, similar to conventional creep tests. There is good agreement between experimental results and simulation data. The creep damage at the central part is high, and localization of damage is obvious. Initial failure occurs at the bottom surface, about 0.8 mm away from the centre which agrees well with the finite element mode observation.