国内首批9F燃机P91钢高压主蒸汽管系的安全性检测与寿命评估

通过现场检测和取样试验,对已运行了10a(年)的我国首批9F燃机P91钢高压主蒸汽管系进行了安全性检测和寿命评估。结果表明:高压主蒸汽管系中部分管段存在安装阶段留下的材质缺陷,对其采取了更换措施;9F燃机启停过程中引起的高压主蒸汽管系内外壁温差应力较小,相对于管系的二次应力来说可以忽略不计;硬度合格的焊接接头试样在540℃下具有较高的持久强度,其剩余蠕变寿命大于10~5h。     

管道支吊架管夹变形原因

某电厂主蒸汽管道支吊架D9型管夹发生变形.采用化学成分分析及有限元分析等方法对管夹的变形原因进行了分析.结果表明:该管夹在运行状态下的最大拉应力达到124 MPa,位于管夹折弯角外表面.最大拉应力超过了材料的许用应力值,加速了管夹在高温状态下的蠕变速率,蠕变变形不断累积使得管夹两端变形上翘明显.     

超超临界机组主蒸汽取样管Ⅳ型开裂分析

通过宏观和微观分析、硬度测试和管系应力计算分析了某1000 MW超超临界机组主蒸汽取样管泄漏的原因。结果表明:取样管泄漏性质为焊接热影响区Ⅳ型蠕变开裂。其早期失效的主要原因是管系布置的柔性不足导致二次应力过高。提出对T/P91等马氏体钢管道,需重视支吊架的合理设置和维护检修,以防管道发生早期失效。建议对高合金钢焊接接头进行寿命评估时除考虑等效蠕变应力之外,还需考虑应力三轴因子,以提高焊接接头蠕变寿命评估的精度。     

600MW主蒸汽管道温度套管漏泄的原因分析及处理方法

分析了某电厂主蒸汽管道不锈钢材料的温度测点套管泄漏的原因，阐述了主蒸汽管道温度套管改进的安装及焊接工艺。     

主汽阀旁路接管座热运行焊缝裂漏分析及解决方法

某炼油厂配套动力站热电联产工程的主蒸汽管在设备运行一段时间后,主蒸汽阀的旁路管接管处的焊缝出现裂漏、甚至旁路管断裂现象,严重影响安全运行、经济效益。本文根据主蒸汽阀的旁路管布置、运行条件及长期两管壁温,分析主蒸汽管与旁路管部位应力,并进行应力计算,找到造成焊缝发生裂漏的原因,提出针对性地解决方案,有效地消除了此类缺陷。     

200MW机组高温过热器弯管爆裂原因探讨

对２００ＭＷ机组高温热器弯管爆裂事故作了分析,重点进行了高温过热器管材２Ｃｒ１ＭｏＶ钢的高温短时力学性能试验和高温疲劳性能试验。研究表明,调峰机组高温过热器弯管爆裂的主要原因是长期超温运行及循环蠕变损伤所引起的。     

SA335-P22钢主蒸汽管道非破坏性剩余寿命评估方法

通过宏观检验、多种无损检测方法以及现场硬度测试和金相覆膜方法,对累计运行已超过113 000h的SA335-P22钢主蒸汽管道进行了检测,并结合Larson-Miller公式预测法和蠕变损伤级别分类法共同对该主蒸汽管道进行了非破坏性剩余寿命评估,得出该管道的剩余寿命不超过105 937h。该试验结果可为电厂运行人员提供参考。     

改善蠕变测量技术提高蠕变监督质量

火力发电厂高温蒸汽管道和联箱的蠕变监督测量是电厂运行过程中技术监督的重要内容。根据多年的监督测量经验，指出了以往在长期蠕变监督测量中存在的理论和操作问题。对蠕变测量主客观误差，如蠕变负值、个别测点蠕变值很高、标准杆误差、计算公式引起的误差、线膨胀系数引起的误差、管温引起的测量误差等因素进行了系统分析，提出了提高测量精度的改进方法。     

某火电厂主蒸汽管道取样管开裂原因分析

某火电厂主蒸汽管道取样管多次发生开裂。通过管道及支吊架布局分析、管道应力计算分析等方法对取样管开裂原因进行了分析。结果表明:主蒸汽管道取样管和支吊架的布局不能有效承受母管及管道自身的热位移,造成二次应力严重超标,接管座焊缝区应力最高,当局部应力超过断裂强度时,材料将产生裂纹,造成取样管开裂泄漏。     

某电厂后屏过热器管泄漏原因分析

对某电厂材质为12Cr1MoV的后屏过热器泄漏管及附近管段进行了宏观检验、显微组织分析、力学性能试验.试验结果表明:爆口处无明显减薄,爆口附近存在多个轴向裂纹;爆口试样显微组织老化级别为5级,裂纹附近及远离裂纹部位存在大量蠕变空洞,裂纹呈沿晶断裂特征,为典型的蠕变裂纹;爆口管抗拉强度远低于标准要求;泄漏管附近管段组织老化4.5级,抗拉强度略低于标准要求;后屏过热器出口壁温测点监测数据表明机组长期处于超温运行状态.根据以上分析得出后屏过热器泄漏原因为机组长期超温运行导致后屏过热器管组织老化、性能劣化,进而在蒸汽内压作用下发生爆管.     

Influence of initial ovality on creep life of P92 pipe bends subjected to in-plane bending

Initial ovality is an inevitable problem in the process of pipe bends manufacturing which results in the stress redistribution of the pipe bends working at high temperature. In order to study the influence of ovality on creep life of pipe bends, full-size creep experiment of P92 pipe bend subjected to in-plane bending has been conducted. The creep strains and outside diameters of dangerous positions have been measured. The microstructures of three different positions of the pipe bend were compared through SEM and the results showed the number and size of the carbide precipitation were the largest at the flank of the pipe bend, which indicated that the creep damage developed fastest at the flank. The modified Kachanov–Robatnov constitutive equations were used to stimulate the creep of P92 pipe bends with FEA software. The representative stress, damage and multiaxiality distributions of the pipe bends have been discussed. The FEA results were consistent with the experimental results and the influence of initial ovality on creep life of P92 pipe bends were analyzed. The results showed that creep life of pipe bends reduced by the increase of ovality and their relationship coincided with the parabolic law.     

Damage and Residual Life Assessment of Bends for X20CrMoV12.1 Main Steam Pipe after Long-Term Service

The bent sections from a main steam pipe in a thermal power plant in Shanghai were examined after 165,000 h service at 550 °C under 13.73 MPa pressure. The residual life of the bend sections is determined by evaluation of the service stresses and testing to obtain creep rupture data. Metallographic analysis and tensile, impact, and hardness tests are also conducted. These combined tests show that the properties of the steel deteriorated during service, displaying embrittlement tendencies; the corresponding microstructures exhibit grain boundary weakening and creep damage characteristics. However, considering no evidence of localized damage in the form of creep cavitation or surface cracks was observed in the examined parts, considering the residual life of the bends at service condition, they are adequate for an additional 44,000 h of operation. It is recommended that a health assessment should be taken after 25,000 h service exposure for safety reasons.     

A Review of Methods to Estimate Creep Damage in Low-Alloy Steel Power Station Steam Pipes

Abstract:  For large complex structures, such as power stations, refineries and other processing plants, cost-effective operation is essential. With power stations, failures of components without prior warning can have serious consequences for personnel on-site and be extremely expensive in terms of both losses in generation revenue and repair costs. The ability to monitor and assess the evolution of damage is critical to maximise plant availability and to minimise the risk of failures that pose a threat to personnel safety. This paper relates to the methods used to estimate creep damage in service-aged low-alloy steel steam piping. Welds and the extrados of bends in steam pipes are a particular problem with regard to measuring for the onset and progression of creep failure. Existing techniques will be discussed with respect to traditional site-based, sample extraction and assessment. Emerging strain-monitoring techniques will also be described and evaluated that include point-to-point measurement and two-dimensional mapping of creep strain across the weld zone and other creep-susceptible components of power station steam piping.     

The significance of weldment material mis-matching on stress redistribution and creep cracking of high temperature components

A large circumferentially oriented crack was discovered in a weld of a double T-piece in the main steam pipe of a Swedish power plant. The pipe and the weld were manufactured from 0.5Cr0.5Mo0.25V steel. In this paper a nominal creep life assessment and an assessment considering mis-matching are carried out for a defect free component and for a component with a crack. While the nominal prediction of a defect free component indicates a creep life of approximately 2200000 hours, a creep life of 550000 hours is obtained when mis-matching effects and enhanced axial stresses due to system loads are considered. If mis-matching is not taken into account, as opposed to if it is, the estimated incubation plus creep crack growth time is approximately 30–70% longer.     

HIDA activity on P91 steel

The 9%-12% Cr-steels are strategic materials for new power plant and for component substitution for plant life extension. One of these steels, P 91 was included in the project BE-1702 (HIDA) to provide crack initiation and growth data for the improvement and validation of procedures for high-temperature defect assessment. The paper presents an outline of the testing programme and the initial results for P 91. In addition to uniaxial and static/cyclic creep crack growth tests on standard fracture mechanics geometries, feature tests are also included in the experimental programme. These consist of internally pressurised pipe welds, pipe bends and 4-point bend pipes, and C-shaped specimens. The majority of these tests are still ongoing. The static and cyclic loading conditions are being employed to consider the range of creep/fatigue interaction in this alloy. All tests are being conducted at 625°C.     

Creep damage in welded joints of 0.5CrMoV steel

The creep damage in two components along a main steam pipe in a fossil-fired power plant has been investigated using plastic replicas. Extensive damage in the weldedjoints was found in both components including several macrocracks. Out of eight analysedjoints, five showed significant damage. All stages of damage from single cavities to macrocracks were present. At a number of positions around thejoints damage was observed in the weld metal, the heat affected zone and the parent metal. For comparison cavitation was also examined in crossweld specimens from creep tests. Characteristic features of the cavitation in power plant were reproduced. In the heat affected zone adjacent to the parent metal a high density of separate cavities was observed. In the coarse grained part of the heat affected zone rows ofcavities were present in some grain boundaries.     

Some key effects on the failure assessment of weld repairs in CrMoV pipelines using continuum damage modelling

Some typical results obtained from finite element (FE) creep and continuum damage mechanics analyses, for assessing weld repair performance, are presented. The work outlines some developments in failure analyses of repaired welds in pressurised, thick-walled, main steam circumferential pipe weldments made of CrMoV steels. Methods involved in determining the material properties for constitutive equations are briefly described. Results presented cover a range of analyses, taking account of the effects of repair profiles/dimensions, geometry change during creep, end (system) loading, reheating effects in the weld metal of partial repair welds and initial damage level, etc., on the failure life of the repaired welds. The potential uses and limitations of the damage analysis for weld repair performance assessment are discussed.     

Experimental Study of the Creep Lifetime of the 1.25Cr 0.5Mo Steel Pipes

Abstract: In this paper, physical parameters for the creep constitutive equations of the low alloy ferritic steel 1.25Cr0.5Mo have been determined using experimental data. This alloy is used mostly in power generation and petrochemical industries because of its high temperature creep resistance. Test samples have been obtained from a new super‐heater pipe wall of a steam‐generating boiler in Tabriz Petrochemical Plant according to the ASTM standards. By conducting creep rupture tests for 1.25Cr0.5Mo steel, creep behaviour and creep‐rupture properties were examined for this material. Creep rupture tests have been carried out at four temperatures of 700, 725, 750 and 800 °C, under applied uni‐axial stresses of 30, 35, 40 and 50 MPa. The experimental data have been used to obtain the constitutive parameters using numerical optimisation techniques. Also the temperature and stress dependency of the creep lifetime for this alloy has been investigated using Larson–Miller and Monkman–Grant parameters. The results show good agreement with other test data such as ASTM and API. Finally, these constitutive equations have been used to study the creep behaviour of the super‐heater pipe. The results show that the super‐heater tube has been over designed in terms of the creep lifetime and this is in accordance with the in‐plant observations.