Fundamental modeling of environmental cracking for improved design and lifetime evaluation in BWRs

An approach for improved design and lifetime evaluation of environmental cracking is presented based on fundamental modeling of the underlying processes operative in crack advance. In outlining this approach and its application in energy industries, the requirements for a life prediction methodology will be highlighted and the shortcomings of the existing design and lifetime evaluation codes will be discussed. Examples will be given of its use in a variety of cracking systems, such as stainless steels and nickel alloys in hot water, and irradiation assisted stress corrosion cracking.     

Applicability of pipelocks as a remedy for intergranular stress corrosion cracking in BWRs

Design, analyses and first application of the Pipelock as a novel long-term multicycle protection for piping systems in Boiling Water Reactor plants damaged by Intergranular Stress Corrosion Cracking in BWRs is described. Confirmatory tests simulating all design and operating conditions including LOCA are also discussed.

Pipelocks are mechanical devices which prevent pipe break even if it is assumed that intergranular stress corrosion cracking penetrates through-the-wall and around the entire circumference of the pipe weldment. With a fully cracked weldment, the entrapped wedges lock the pipes together, preventing the ends from separating.

In addition to providing defense-in-depth against pipe breaks, pretightening of the Pipelock bolts produces axial and circumferential compressive stresses in the pipe wall at the weldment, thus tending to retard or eliminate crack growth during operation after installing the Pipelock.

Pipelocks are designed to meet regulatory requirements 10CFR50—Appendix B and ASME Code Section III requirements for long-term multicycle operation.

Installed Pipelocks can be disassembled to permit inservice inspection of the weldment. They therefore can be used through several outages subsequent to the installation, thereby eliminating or postponing the need for pipe changeout. The design of the Pipelock also enables their use on weldments which were previously overlaid.     

Retreat from Salix—Swedish experience with energy crops in the 1990s

A wave of Salix (willow) planting rolled over Sweden in the early 1990s, driven by subsidies and optimistic market expectations. The expected economic life span of such investments is 20 years or more. But in fact, many plantations were terminated or reduced much sooner. This article explores the reasons for this retreat. In a survey to Salix farmers, 41 per cent either have retreated or regretted starting at all. The reasons given are mostly agronomic, rather than economic. In particular, many farmers had planted on low-quality lands, ignoring best-practice advice. Policies in support of energy crops have been volatile and badly designed, in the sense of giving incentives to such reckless plantings, rather than promoting good farm management. Prices for wood chips have also been disappointing, but few farmers cite this as a key reason for termination or regrets.     

Environment-assisted cracking in austenitic components

Stress corrosion cracking and corrosion fatigue have been responsible for some costly generic material failures in water cooled power reactors. This paper reviews the main features of two of the most widespread problems, namely intergranular stress corrosion cracking of sensitized stainless steel piping in boiling water reactors (BWR) and of nickel alloy steam generator tubes in pressurized water reactors (PWR). Mechanisms, in so far as they are known, are described together with remedial measures and crack growth models applicable to in-plant components.     

Plastic zone size in fatigue cracking

Fatigue tests were performed on the specimens of Type 304 stainless steel and Inconel 718. To investigate the effects of specimen thickness on crack tip deformation and fatigue crack growth rate (FCGR), specimens of different thickness were used. To validate fatigue crack propagation in terms of plastic zone size, elastic plastic fracture mechanics (EPFM) are studied in this investigation. Results show that FCGR is a function of specimen thickness, which worsens as the specimen thickness increases. It is considered that plastic zone size is an important fatigue crack propagation parameter in conjunction with applied stress level, specimen thickness and crack closure.     

Controlled cracking of tubes

A method is described of inducing an internal, longitudinal fatigue crack in a tube. It is based on a local compression of the tube, using a special loading device, to initiate and propagate a fatigue crack. It is shown that the geometry of this crack can be varied according to loading conditions. Some examples of small as well as of through cracks are given.     

Residual stress driven cracking in superalloy weldments

Superalloy weldments are normally given post weld heat treatments to homogenize the weld metal microstructure, relieve residual stress, and precipitate strengthening phases. The relationship between microstructure and post weld heat treatment is easily studied; it is less straightforward to study the effects of post weld heat treatment on residual stress relaxation. Using a self-restrained testing procedure, a relatively simple approach was used to investigate the effects of microstructure and post-weld heat treatment on cracking during residual stress relaxation. Candidate superalloys for Advanced Ultra Supercritical steam plants were studied. It was found that cracking due to residual stress relaxation is primarily dependent on grain size, and in cases of intermediate grain size, intragranular precipitation is a controlling factor. These results are in agreement with traditional stress relaxation cracking theories.     

聚氨酯保温管在集中供热管网改扩建工程中的应用

介绍了在黑龙江桦南县集中供热管网改扩建工程中所采用的高密度聚氨酯保温直埋管敷设方式,探讨了该管网在设计、施工中应注意的问题。     

Low energy consumption in Swedish single-family houses

In Sweden, as well as in many other countries, the energy consumption in residential buildings is a burning question.Due to this, the thermal insulation and the tightness of new buildings gradually has been increased.A well defined ventilation is because of this even more important, and the minimum level is given in regulations prescribed by the National Board of Housing, Building and Planning.To fulfil the regulations it is almost necessary to use mechanical ventilation. Since an ordinary ventilation causes a substantial energy loss it is of vital interest to reduce this.The most efficient way of reducing the ventilation loss, is to use an exhaust air heat pump which recovers energy from the exhaust air and supplies it to heating and hot water.In Sweden there have been about 100.000 units installed in single family houses until today.The paper will describe the regulations, the ventilation system, the exhaust air heat pump and the results achieved when installed in single family houses.     

Experimental investigation on the cracking of pre-combustion cracking gas with gliding arc discharge plasma

To improve the quality of pre-combustion cracking gas, the gliding arc discharge plasma is adopted in this paper. The influence of incoming flow rate, electrode gap distance and discharge frequency on cracking effect have been experimentally studied. The results show that through plasma cracking, the concentration of H₂ increases while the concentration of CH₄ and C₂H₄ decrease. With different fuel ratio conditions, the variation trend of C/H ratio as well as the mass flow of carbon and hydrogen atoms in the cracking products vary from each other. The cracking effect becomes weaker with the increase of incoming flow rate, while is better when the fuel ratio is larger. Given the flow rate of 18slpm and 24slpm, the best cracking effect can be acquired with the electrode gap of 1.5 mm. Besides, the effect of gliding arc discharge plasma cracking is weakened as the discharge frequency rises.     

Elimination of circumferential cracking in reactor''s internal jacket

In many petrochemical plants reactors are subjected to cyclic random fluctuation of temperatures over the internal shell surface. The fluctuations cause premature failures of several patterns due to thermal fatigue. In the synfuels production business reactors that are subjected to thermal and mechanical loads are used. These reactors are continuously cooled by means of internal water jackets.

The jackets have been subjected to structural failures in the following order of appearance: Cracking on the manholes necks, patches of cracks resembling “elephant skin” on the parent plates inner surface, circumferential cracks, mainly but not solely along the heat affected zones of the horizontal weld joints, growing permanent bulges. These structural failures have shortened the operating life of the reactors and required periodical replacements. Relatively frequent occurrence of the failures resulted in high costs due to production losses, materials, fabrication and installation costs.

A comprehensive systematic development programme was launched in order to understand the phenomena, direct prioritised solutions evaluate all the possible alternatives. Shortly after start it was realised that the highest cost savings can result from the minimisation of the circumferential cracking and reduction in jacket replacement time. The programme focused on four improvement avenues: Reduction of thermal stresses; elimination of discontinuities; improve material properties; develop alternative structure. This multi-year development program resulted in a new design that incorporated thinning of the jacket, minimising geometrical and material discontinuities combined with simplified installation.

The improved design was installed in all the reactors and after ±6 years of operation it was proved that the installed jackets exceeded the performance of the original ones both in life cycle and reduction in installation. Moreover, no circumferential go through crack occurred for the last 8 years.     

热管式余热锅炉热管爆管原因分析

主要介绍了在冶炼余热制酸系统中热管余热锅炉出现的爆管现象,针对热管爆管的原因进行了分析,并提出了解决方案。     

凝汽器冷却用管——铜管和不锈钢管的性能比较与探讨

旨在对各类凝汽器冷却用管性能进行深入比较与探讨,提出并推荐可以替代传统冷却用管———铜管的替代产品不锈钢波螺管。通过分析表明,在汽轮发电机组凝汽器冷却管中用不锈钢波螺管替代铜管是可行的选择。     

The Swedish wood fuel market

In Sweden, wood fuels are traditionally used in the Swedish forest products industry and for heating of single-family houses. More recently they are also become established as an energy source for district heating and electricity production. Energy policy, especially the energy taxation system, has favoured wood fuels and other biofuels, mainly for environmental reasons. There is now an established commercial market for wood fuels in the district heating sector, which amounts to 45 PJ and is growing 20 per cent annually. Price levels have been stable in current prices for a decade, mainly because of good access to wood fuels. Price levels are dominated by production costs on a market that is largely governed by the buyer.It is expected that the use of wood fuels will increase in Sweden in the future, which will push a further development of this sector on the market and bring about technological changes in the area.     

瑞典能源模式解析

近20年来,瑞典实现了国民生产总值增长44％,但是温室气体排放量却降低近9％。分析发现,瑞典政府通过征收C02税,采用绿色电力认证系统,对环保型汽车提供补贴与优惠税收等方式鼓励使用可再生能源。因地制宜使用本国特色的能源,大力发展生物质能源、水力发电及核电,并开始关注风力发电。重视提高能源效率和节能,为耗能企业引入能源管理体系,并进行大量研发投入。瑞典的企业、公民和政府都在能源体系中做出了各自的贡献。     

Implementation of energy-efficient windows in Swedish single-family houses

A questionnaire survey of 1010 homeowners in Jämtland and Västernorrland, which are two counties in central Sweden, was conducted to understand the factors influencing their decision to install energy-efficient windows. We complemented this survey with an interview of 12 window sellers/installers in the county Jämtland. The annual energy cost reduction, age, and condition of the windows were the most important reasons for the window replacement decision. Approximately 80% of the respondents replaced their windows with energy-efficient windows with U-value of 1.2 W/m² K. Condensation problems, perceived higher prices, and lack of awareness about windows with lower U-values were important reasons for non-adoption of more energy-efficient windows. Window sellers/installers have a strong influence on homeowners’ window selection that was indicated by the 97% of homeowners who bought the windows that were recommended to them. Sellers/installers revealed that they did not recommend windows with U-value of less than 1.2 W/m² K because they thought that investing in such windows was not economical and because windows with U-value less than 1.2 W/m² K could cause water condensation on the external surface of window pane.     

工业锅炉小孔式给水管和加药管流动特性的研究

本文构建了等节距分布的小孔式给水管和加药管的流动模型，经理论推导获得了流动特性的分析解和流量偏差公式，藉此可使小孔式给水管和加药管的设计计算或校核计算更为准确、合理。     

热再热管道钢管中频弯制后开裂情况及原因分析

某300 MW热电机组热再热管道4支钢管在中频弯制中出现横向开裂,通过对成分、组织性能和在现场进行宏观检验,基本判定开裂原因是由于热轧参数不正确或坯料加热不良等原因在热轧中产生折叠,而所产生折叠在后续的外表机加工工序中未被充分去除所致.     

Impedance Pipe Heating

Impedance heating, to maintain fluid temperature in transfer piping or to increase temperature in process-heating applications, is advantageous because the pipe itself is used as the heating element. In contrast to simple resistance heating, heat attributable to the I²R effect from impedance heating is further increased by heat from the proximity effect, eddy currents, and hysteresis. Heating from these effects is induced in pipes connected to the terminal of a step-down transformer. The electrical circuit is completed by a return conductor that closely parallels the pipe. Principles, advantages, and applications of impedance heating are discussed.