Based on the daily maximum surface air temperature records from an updated homogenized temperature dataset for 549 Chinese stations during 1960-2008,we reveal that there is an abrupt increase in the number of days wit...Based on the daily maximum surface air temperature records from an updated homogenized temperature dataset for 549 Chinese stations during 1960-2008,we reveal that there is an abrupt increase in the number of days with high temperature extremes （HTEs,an HTE day is defined when the maximum temperature exceeds the 95th percentile of the daily maximum temperature distributions） across China in the mid-1990s.Before this regime shift,the average number of HTE days is about 2.9 d yr 1 during the period from the 1970s to the early 1990s,while it rocketed to about 7.2 d yr 1 after the mid-1990s.We show that the significant HTE day increase occurs uniformly across the whole of China after the regime shift.The observational evidence raises the possibility that this change in HTE days is associated with global-scale warming as well as circulation adjustment.Possible causes for the abrupt change in the HTE days are discussed,and the circulation adjustment is suggested to play a crucial role in the increase in HTE days in this region.展开更多
The long-term strength retrogression of silica-enriched oil well cement poses a significant threat to wellbore integrity in deep and ultra-deep wells, which is a major obstacle for deep petroleum and geothermal energy...The long-term strength retrogression of silica-enriched oil well cement poses a significant threat to wellbore integrity in deep and ultra-deep wells, which is a major obstacle for deep petroleum and geothermal energy development. Previous attempts to address this problem has been unsatisfactory because they can only reduce the strength decline rate. This study presents a new solution to this problem by incorporating fly ash to the traditional silica-cement systems. The influences of fly ash and silica on the strength retrogression behavior of oil well cement systems directly set and cured under the condition of 200°C and 50 MPa are investigated. Test results indicate that the slurries containing only silica or fly ash experience severe strength retrogression from 2 to 30 d curing, while the slurries containing both fly ash and silica experience strength enhancement from 2 to 90 d. The strength test results are corroborated by further evidences from permeability tests as well as microstructure analysis of set cement. Composition of set cement evaluated by quantitative X-ray diffraction analyses with partial or no known crystal structure(PONKCS) method and thermogravimetry analyses revealed that the conversion of amorphous C-(A)-S-H to crystalline phases is the primary cause of long-term strength retrogression.The addition of fly ash can reduce the initial amount of C-(A)-S-H in the set cement, and its combined use with silica can prevent the crystallization of C-(A)-S-H, which is believed to be the working mechanism of this new admixture in improving long-term strength stability of oil well cement systems.展开更多
For steam tubes used in thermal power plant,the inner and outer walls were operated in high-temperature steam and flue gas environments respectively.In this study,structure,microstructure and chemical composition of o...For steam tubes used in thermal power plant,the inner and outer walls were operated in high-temperature steam and flue gas environments respectively.In this study,structure,microstructure and chemical composition of oxide films on inner and outer walls of exservice low Cr ferritic steel G102 tube and exservice high Cr ferritic steel T91 tube were analyzed.The oxide film was composed of outer oxide layer,inner oxide layer and internal oxidation zone.The outer oxide layer on the original surface of tube had a porous structure containing Fe oxides formed by diffusion and oxidation of Fe.More specially,the outer oxide layer formed in flue gas environment would mix with coal combustion products during the growth process.The inner oxide layer below the original surface of tube was made of Fe–Cr spinel.The internal oxidation zone was believed to be the precursor stage of inner oxide layer.The formation of internal oxidation zone was due to O diffusing along grain boundaries to form oxide.There were Fe–Cr–Si oxides discontinuously distributed along grain boundaries in the internal oxidation zone of G102,while there were Fe–Cr oxides continuously distributed along grain boundaries in that of T91.展开更多
通过室温拉伸、室温冲击、硬度测试、高温拉伸、金相显微镜、扫描电镜和能谱仪等手段研究了超超临界锅炉服役79000 h S30432钢管的组织和性能。结果表明,S30432钢管高温服役79000 h后,室温硬度和抗拉强度升高,塑、韧性均显著降低,断后...通过室温拉伸、室温冲击、硬度测试、高温拉伸、金相显微镜、扫描电镜和能谱仪等手段研究了超超临界锅炉服役79000 h S30432钢管的组织和性能。结果表明,S30432钢管高温服役79000 h后,室温硬度和抗拉强度升高,塑、韧性均显著降低,断后伸长率已低于标准要求;高温下抗拉强度和塑性显著降低,670℃抗拉强度已低于标准外推值;组织严重老化,孪晶消失,除NbC、M_(23)C_(6)等碳化物外,晶内、晶界均不同程度析出了硬脆的σ相,是导致塑、韧性及高温抗拉强度大幅下降的主要原因。展开更多
基金supported by National Key Technology R & D Program 2008BAK50B02National Basic Research Program of China under Grant No. 2009CB421405the National Natural Science Foundation of China under Grant Nos. 40730952 and 40805017
文摘Based on the daily maximum surface air temperature records from an updated homogenized temperature dataset for 549 Chinese stations during 1960-2008,we reveal that there is an abrupt increase in the number of days with high temperature extremes （HTEs,an HTE day is defined when the maximum temperature exceeds the 95th percentile of the daily maximum temperature distributions） across China in the mid-1990s.Before this regime shift,the average number of HTE days is about 2.9 d yr 1 during the period from the 1970s to the early 1990s,while it rocketed to about 7.2 d yr 1 after the mid-1990s.We show that the significant HTE day increase occurs uniformly across the whole of China after the regime shift.The observational evidence raises the possibility that this change in HTE days is associated with global-scale warming as well as circulation adjustment.Possible causes for the abrupt change in the HTE days are discussed,and the circulation adjustment is suggested to play a crucial role in the increase in HTE days in this region.
基金National Natural Science Foundation of China(No.51974352 and No.52288101)China University of Petroleum(East China)(No.2018000025 and No.2019000011)。
文摘The long-term strength retrogression of silica-enriched oil well cement poses a significant threat to wellbore integrity in deep and ultra-deep wells, which is a major obstacle for deep petroleum and geothermal energy development. Previous attempts to address this problem has been unsatisfactory because they can only reduce the strength decline rate. This study presents a new solution to this problem by incorporating fly ash to the traditional silica-cement systems. The influences of fly ash and silica on the strength retrogression behavior of oil well cement systems directly set and cured under the condition of 200°C and 50 MPa are investigated. Test results indicate that the slurries containing only silica or fly ash experience severe strength retrogression from 2 to 30 d curing, while the slurries containing both fly ash and silica experience strength enhancement from 2 to 90 d. The strength test results are corroborated by further evidences from permeability tests as well as microstructure analysis of set cement. Composition of set cement evaluated by quantitative X-ray diffraction analyses with partial or no known crystal structure(PONKCS) method and thermogravimetry analyses revealed that the conversion of amorphous C-(A)-S-H to crystalline phases is the primary cause of long-term strength retrogression.The addition of fly ash can reduce the initial amount of C-(A)-S-H in the set cement, and its combined use with silica can prevent the crystallization of C-(A)-S-H, which is believed to be the working mechanism of this new admixture in improving long-term strength stability of oil well cement systems.
基金supported by the National Natural Science Foundation of China (Nos.51901113 and 51775300)the State Key Laboratory of Tribology in Tsinghua University, and the State Key Lab of Advanced Welding and Joining in Harbin Institute of Technology (No.AWJ-21M03)。
文摘For steam tubes used in thermal power plant,the inner and outer walls were operated in high-temperature steam and flue gas environments respectively.In this study,structure,microstructure and chemical composition of oxide films on inner and outer walls of exservice low Cr ferritic steel G102 tube and exservice high Cr ferritic steel T91 tube were analyzed.The oxide film was composed of outer oxide layer,inner oxide layer and internal oxidation zone.The outer oxide layer on the original surface of tube had a porous structure containing Fe oxides formed by diffusion and oxidation of Fe.More specially,the outer oxide layer formed in flue gas environment would mix with coal combustion products during the growth process.The inner oxide layer below the original surface of tube was made of Fe–Cr spinel.The internal oxidation zone was believed to be the precursor stage of inner oxide layer.The formation of internal oxidation zone was due to O diffusing along grain boundaries to form oxide.There were Fe–Cr–Si oxides discontinuously distributed along grain boundaries in the internal oxidation zone of G102,while there were Fe–Cr oxides continuously distributed along grain boundaries in that of T91.
文摘通过室温拉伸、室温冲击、硬度测试、高温拉伸、金相显微镜、扫描电镜和能谱仪等手段研究了超超临界锅炉服役79000 h S30432钢管的组织和性能。结果表明,S30432钢管高温服役79000 h后,室温硬度和抗拉强度升高,塑、韧性均显著降低,断后伸长率已低于标准要求;高温下抗拉强度和塑性显著降低,670℃抗拉强度已低于标准外推值;组织严重老化,孪晶消失,除NbC、M_(23)C_(6)等碳化物外,晶内、晶界均不同程度析出了硬脆的σ相,是导致塑、韧性及高温抗拉强度大幅下降的主要原因。
