bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of tonic GABA inhibitory function, presympathetic neuronal activity and sympathetic outflow from the paraventricular nucleus by astroglial GABA transporters
Authors: Park Jin Bong , Jo Ji Yoon , Zheng Hong , Patel Kaushik P. , Stern Javier E.
Published: August 2009

Neuronal activity in the hypothalamic paraventricular nucleus (PVN), as well as sympathetic outflow from the PVN, is basally restrained by a GABAergic inhibitory tone. We recently showed that two complementary GABAA receptor‐mediated modalities underlie inhibition of PVN neuronal activity: a synaptic, quantal inhibitory modality (IPSCs, Iphasic) and a sustained, non‐inactivating modality (Itonic). Here, we investigated the role of neuronal and/or glial GABA transporters (GATs) in modulating these inhibitory modalities, and assessed their impact on the activity of RVLM‐projecting PVN neurons (PVN‐RVLM neurons), and on PVN influence of renal sympathetic nerve activity (RSNA). Patch‐clamp recordings were obtained from retrogradely labelled PVN‐RVLM neurons in a slice preparation. The non‐selective GAT blocker nipecotic acid (100–300 μm) caused a large increase in GABAAItonic, and reduced IPSC frequency. These effects were replicated by β‐alanine (100 μm), but not by SKF 89976A (30 μm), relatively selective blockers of GAT3 and GAT1 isoforms, respectively. Similar effects were evoked by the gliotoxin l‐α‐aminodipic acid (2 mm). GAT blockade attenuated the firing activity of PVN‐RVLM neurons. Moreover, PVN microinjections of nipecotic acid in the whole animal diminished ongoing RSNA. A robust GAT3 immunoreactivity was observed in the PVN, which partially colocalized with the glial marker GFAP. Altogether, our results indicate that by modulating ambient GABA levels and the efficacy of GABAAItonic, PVN GATs, of a likely glial location, contribute to setting a basal tone of PVN‐RVLM firing activity, and PVN‐driven RSNA.
Recruitment and rate coding organisation for soleus motor units across entire range of voluntary isometric plantar flexions
Authors: Oya Tomomichi , Riek Stephan , Cresswell Andrew G.
Published: August 2009

Unlike upper limb muscles, it remains undocumented as to how motor units in the soleus muscle are organised in terms of recruitment range and discharge rates with respect to their recruitment and de‐recruitment thresholds. The possible influence of neuromodulation, such as persistent inward currents (PICs) on lower limb motor unit recruitment and discharge rates has also yet to be reported. To address these issues, electromyographic (EMG) activities from the soleus muscle were recorded using selective branched‐wire intramuscular electrodes during ramp‐and‐hold contractions with intensities up to maximal voluntary contraction (MVC). The multiple single motor unit activities were then derived using a decomposition technique. The onset–offset hysteresis of motor unit discharge, i.e. a difference between recruitment and de‐recruitment thresholds, as well as PIC magnitude calculated by a paired motor unit analysis were used to examine the neuromodulatory effects on discharge behaviours, such as minimum firing rate, peak firing rate and degree of increase in firing rate. Forty‐two clearly identified motor units from five subjects revealed that soleus motor units are recruited progressively from rest to contraction strengths close to 95% of MVC, with low‐threshold motor units discharging action potentials slower at their recruitment and with a lower peak rate than later recruited high‐threshold units. This observation is in contrast to the ‘onion skin phenomenon’ often reported for the upper limb muscles. Based on positive correlations of the peak discharge rates, initial rates and recruitment order of the units with the magnitude of the onset–offset hysteresis and not PIC contribution, we conclude that discharge behaviours among motor units appear to be related to a variation in an intrinsic property other than PICs.
Multifunctional rapidly adapting mechanosensitive enteric neurons (RAMEN) in the myenteric plexus of the guinea pig ileum
Authors: Mazzuoli Gemma , Schemann Michael
Published: August 2009

An important feature of the enteric nervous system (ENS) is its capability to respond to mechanical stimulation which, as currently suggested for the guinea‐pig ileum, is encoded by specialized intrinsic primary afferent neurons (IPANs). We used von Frey hairs or intraganglionic volume injections to mimic ganglion deformation as observed in freely contracting preparations. Using fast voltage‐sensitive dye imaging we identified rapidly adapting mechanosensitive enteric neurons (RAMEN, 25% of all neurons) in the myenteric plexus of the guinea pig ileum. RAMEN responded with phasic spike discharge to dynamic changes during ganglion deformation. This response was reproducible and increased with increasing forces. Deformation‐evoked spike discharge was not changed by synaptic blockade with hexamethonium, ω‐conotoxin or low Ca2+/high Mg2+, defunctionalization of extrinsic afferents with capsaicin or muscle paralysis with nifedipine, suggesting direct activation of RAMEN. All RAMEN received hexamethonium‐sensitive fast EPSPs, which were blocked by ω‐conotoxin and low Ca2+/high Mg2+. Seventy‐two per cent of RAMEN were cholinergic, 22% nitrergic, and 44% were calbindin and NeuN negative, markers used to identify IPANs. Mechanosensitivity was observed in 31% and 47% of retrogradely traced interneurons and motor neurons, respectively. RAMEN belong to a new population of mechanosensitive neurons which differ from IPANs. We provided evidence for multifunctionality of RAMEN which may fulfil sensory, integrative and motor functions. In light of previously identified mechanosensitive neuron populations, mechanosensitivity appears to be a property of many more enteric neurons than generally assumed. The findings call for a revision of current concepts on sensory transmission within the ENS.
Laminin enhances β2‐adrenergic receptor stimulation of L‐type Ca2+ current via cytosolic phospholipase A2 signalling in cat atrial myocytes
Authors: Pabbidi M. R. , Ji X. , Samarel A. M. , Lipsius S. L.
Published: August 2009

We previously reported that attachment of atrial myocytes to the extracellular matrix protein laminin (LMN), decreases adenylate cyclase (AC)/cAMP and increases β2‐adrenergic receptor (AR) stimulation of L‐type Ca2+ current (ICa,L). This study therefore sought to determine whether LMN enhances β2‐AR signalling via a cAMP‐independent mechanism, i.e. cytosolic phospholipase A2 (cPLA2) signalling. Studies were performed on acutely isolated atrial myocytes plated on uncoated coverslips (−LMN) or coverslips coated with LMN (+LMN). As previously reported, 0.1 μm zinterol (zint‐β2‐AR) stimulation of ICa,L was larger in +LMN than −LMN myocytes. In +LMN myocytes, zint‐β2‐AR stimulation of ICa,L was inhibited by inhibition of cPLA2 by arachidonyltrifluoromethyl ketone (AACOCF3; 10 μm), inhibition of Gi by pertussis toxin and chelation of intracellular Ca2+ by 10 μm BAPTA‐AM. In contrast to zinterol, stimulation of ICa,L by fenoterol (fen‐β2‐AR), a β2‐AR agonist that acts exclusively via Gs signalling, was smaller in +LMN than −LMN myocytes. Arachidonic acid (AA; 5 μm) stimulated ICa,L to a similar extent in −LMN and +LMN myocytes. Inhibition of cAMP‐dependent protein kinase A (cAMP/PKA) by either 5 μm H−89 or 1 μm KT5720 in −LMN myocytes mimicked the effects of +LMN myocytes to enhance zint‐β2‐AR stimulation of ICa,L, which was blocked by 10 μm AACOCF3. In contrast, H−89 inhibited fen‐β2‐AR stimulation of ICa,L, which was unchanged by AACOCF3. Inhibition of ERK1/2 by 1 μm U0126 inhibited zint‐β2‐AR stimulation of ICa,L in +LMN myocytes and −LMN myocytes in which cAMP/PKA was inhibited by KT5720. In −LMN myocytes, cytochalasin D prevented inhibition of cAMP/PKA from enhancing zint‐β2‐AR stimulation of ICa,L. We conclude that LMN enhances zint‐β2‐AR stimulation of ICa,L via Gi/ERK1/2/cPLA2/AA signalling which is activated by concomitant inhibition of cAMP/PKA signalling and dependent on the actin cytoskeleton. These findings provide new insight into the cellular mechanisms by which the extracellular matrix can remodel β2‐AR signalling in atrial muscle.
Sub-Surface Cracking in Circumferential Seam Welds: The New Face of an Old Problem? Results of the Metallurgical Analysis of Damaged Welds
Authors: Coleman Kent , Henry Jeff
Published: August 2009

Samples removed from several cracked piping and header circumferential seam welds have been examined destructively as part of an effort to understand why in the last few years there have been an increasing number of such seam weld failures at US power plants. To assist in this effort the information available regarding the design and operating history of a number of those welds has been evaluated where it was available; in addition, a limited review has been made of literature pertaining to cracking at seam welds in elevated temperature piping and headers. Certain features of the failures, such as the fact that the cracks in many cases have initiated sub-surface and that the vast majority of the cracks have been detected in shop-fabricated welds, have raised concerns that these failures represent a new and unique damage mechanism for which no satisfactory technical explanation currently exists. The information obtained to date does not support those concerns. Instead, the results of the destructive analyses of damaged girth welds are consistent with the general understanding of failures at welds in pressure parts operating at elevated temperatures: that is, failure in such welds can occur at times far shorter than the expected rupture time for unaffected base metal for the following reasons: • Welds are heterogeneous structures consisting of multiple discrete regions, the properties of which can differ significantly. In some of these regions the elevated temperature strength and/or ductility of the material can be substantially inferior to the “average” base metal, so that under certain loading conditions the rate at which damage will accumulate in weaker, less ductile regions can be orders of magnitude higher than in the stronger, more ductile regions. • The stress state at circumferential seam welds in elevated temperature piping and headers can be a complex admixture of mechanical and thermally-induced stresses imposed on the metallurgically varied structure. The extensive experience with Type IV or Type IIIa cracking in the CrMoV piping in Europe has demonstrated that under the influence of “normal” operating loads premature failure at weakened regions of the weld are to be expected. That experience also has shown that, in the absence of a very high bending load related to failure of the component support, sub-surface cracking is not unexpected. • The damage in the welds examined as part of this study was in all cases concentrated in portions of the weld that previous research has indicated can be either creep weak and/or creep brittle; other areas of the weld showed no signs of visible damage.
Methodology of Creep Data Analysis for Advanced High Cr Ferritic Steel
Authors: Maruyama Kouichi , Yoshimi Kyosuke
Published: August 2009

Long term creep rupture life is usually evaluated from short term data by a time-temperature parameter (TTP) method. The apparent activation energy Q for rupture life of steels sometimes changes from a high value of short term creep to a low value of long term creep. However, the conventional TTP analyses ignore the decrease in Q, resulting in the overestimation of rupture life recognized recently in advanced high Cr ferritic steels. A multi region analysis of creep rupture data is applied to a creep data set of Gr.122 steel; in the analysis a creep rupture data is divided into several data sets so that Q value is unique in each divided data set. The multi region analysis provides the best fit to the data and the lowest value of 105 h creep rupture strength among the three ways of data analysis examined. The conventional single region analysis cannot correctly represent the data points and predicts the highest strength. A half of 0.2% proof stress could not be an appropriate boundary for dividing data to be used in the multi region analysis. In the 2001 Edition of ASME Code an F average concept has been proposed as a substitution for the safety factor of 2/3 for average rupture stress. The allowable stress of Gr.122 steel may decrease significantly when the F average concept and the multi region analysis are adopted.
Development of an Advanced Creep Model for Type 316 Stainless Steel
Authors: Douglas J. , Spindler M. , Dennis R.
Published: August 2009

Methods for predicting stress relaxation behaviour rely on either the integration of a forward creep equation derived from constant load creep data or a stress relaxation equation specifically derived from data measured during dwell periods in either monotonic or cyclic loading. In general, these methods do not explicitly address the effects of prior loading history on the observed relaxation behaviour. In the current work, forward creep data have been acquired to allow identification of a stress-temperature dependent function that represents the observed correlation between measured values of primary creep strain and the initial plastic loading strain. The prediction of stress relaxation from forward creep equations has been extended to investigate the effects of plasticity on creep deformation through the inclusion of a back stress component in the creep deformation equations. The work is based on British Energy’s evolving experimental database for Type 316H stainless steel which includes data from ongoing low stress and stress change creep tests. These tests are currently being conducted to improve the understanding of plasticity-creep interaction effects. Improved methods for predicting stress relaxation in Type 316H stainless steel based on these experimental data are assessed against their ability to adequately describe the influence of prior loading history on primary creep and stress relaxation behaviour.
Design of Cast Heat Resistant Alloys With Improved Creep Strength
Authors: Pankiw R. I. , Voke D. P.
Published: August 2009

Cast heat resistant alloys are used in the petrochemical industry for reformer furnace tubes and ethylene pyrolisis coils. These alloys have traditionally been developed through the casting of trial compositions with differing additions of alloying elements followed by long term (10,000 hour) stress to rupture testing. It is now possible to shorten the development process through the use of computational thermodynamics and a detailed understanding of composition, microstructure and property relationships. This paper will provide examples of how alloys can be developed through a combination of thermodynamic modeling, microstructural characterization, and mechanical property measurements.
Effects of Long-Term Service on the Microstructure and Tensile Properties of Alloy 800H
Authors: Swindeman Robert W. , Zamrik Sam Y. , Maziasz Phillip J.
Published: August 2009

Three sections of piping removed from a styrene furnace were metallugically examined. The piping was fabricated from alloy 800H and was service-exposed at temperatures in the range of 621 to 774°C (1150 to 1425°F) for times in the range of 73,500 to 90,000 hours. These samples were investigated by metallurgical studies and mechanical testing to determine the effect of the prolonged high-temperature service on the integrity of the components. A few specimens from the samples were re-annealed to determine if the properties could be restored to their original values. A few more specimens were re-annealed and aged for 1000 hours to determine if significant changes would occur during short-time exposure to high temperature. With one exception, the service-exposed samples exhibited microstructures and properties that were comparable to mill annealed and short-time exposed material. Modest increases in strength and reduction in ductility accompanied the exposure. The exception was material exposed to the highest temperature for the longest time. Here, a significant decrease in the ultimate strength and ductility was observed in a test at 704°C (1300°F).
Creep Deformation and Failure Assessment of Steel Weldments
Authors: Dogan Bilal
Published: August 2009

The effect of weldments in service performance of high temperature components has been subject to intensive research due to the fact that in the majority of cases where high temperature failure occurs, defects predominate in the vicinity of weldments. Cracking occurs in service due to reduced creep ductility of HAZ and weld metal due to ageing in service, combined with the action of multi-axial stress fields that reduce the creep ductility further. The defects detected or assumed to exist through minimum allowable limits of detectable flaws using non-destructive testing methods is required for structural integrity and residual life assessment of high temperature components. The assessment relies on information obtained from the material’s high temperature tensile, uniaxial creep, crack initiation and growth properties. The concepts used for time dependent fracture analysis of homogeneous bodies are commonly applied for creep crack growth in weldments that show multi-crack initiation and crack branching. This calls for study of deformation behavior and applicability of fracture mechanics parameters for high temperature assessment of weldments. The present paper reports on the material behavior and methodology followed for testing and assessment of the high temperature steel weldments.
Void Growth Simulation of a Steam Turbine Casing Material Under Creep and Creep-Fatigue Loading
Authors: Ogata Takashi
Published: August 2009

High temperature components in thermal power plants are subjected to creep and creep-fatigue loading where creep voids initiate and grow on grain boundaries. Development of a quantitative evaluation method of the void growth is important for reliable maintenance of these components. In this study, creep and creep-fatigue tests were carried out at 600 °C on a 1Cr-Mo-V casting steel. Creep damaged materials were produced by interrupting the creep tests and microstructure of the damaged materials were observed carefully by a scanning microscope. The creep-fatigue tests were also conducted in a scanning electron microscope, and continuous observation of void growth behavior during the tests was made. From the observations, spherical shape voids initiate and grow up to their length of 2μm on grain boundaries at initial stage of damage, and then these voids change their shape to crack-like to grow until their length reaches around 10μm under both the creep and the creep-fatigue conditions. Under the same stress level, the void growth rate in the creep-fatigue condition was faster than that in the creep condition indicating acceleration of void growth rate by cyclic loading. Previously proposed void growth simulation model, in which the void growth was controlled by diffusion and power law creep, was modified to express acceleration of the void growth by the cyclic loading. Void growth behavior within a certain area under both the creep and the creep-fatigue condition were simulated by the modified program. Predicted void growth behaviors agreed with observed ones. The void growth behavior of an actual turbine casing was also simulated and void growth behavior was discussed based on the result.
Reliability and Limitations of the Non Destructive Replica Technique for the Assessment of Creep Damage in Welded Components
Authors: van Wortel Hans
Published: August 2009

Within a Joint Industrial Programme (JIP) with 12 partners, including inspection companies, engineering companies, end users and a notifying body, the reliability of the replica technique for the assessment of creep damage in welded joints has been assessed. The programme was initiated where significant differences in the interpretation of replicas were addressed and replication was characterised as a not a reliable tool. It is curious that for the preparation and interpretation of replicas persons do not need to be qualified, although a specific expertise is necessary for a proper preparation and interpretation. There are also no international or national certifying bodies. Companies have their own standards. For other N.D.E. methodologies certain levels of competence are always required. Within the JIP the practical work was performed in “Workshop” sessions and 6 inspection companies were involved, covering more than 50% of the replica activities in Western-Europe. For a realistic approach the replication activities were performed on creep damaged welded ferritic, martensitic and austenitic components and not on small creep specimens etc. Starting with the individual company procedures for replica preparation and damage assessment, unreliable results were obtained with an unacceptable scatter. The main source for the scatter was the damage assessor and the method of replica preparation was not. With a new procedure, developed within the programme and accepted by all the companies, the scatter has been dramatically reduced to an acceptable level. Finally the programme resulted in a guideline for the preparation and damage assessment of replicas of ferritic and austenitic welded joints. It also includes flow charts to distinguish creep damage from other types of damage.
Assessment of Creep Rupture Strength for New Martensitic 9% Cr Steels
Authors: Bendick Walter , Gabrel Jean , Vandenberghe Bruno
Published: August 2009

The application of new heat resistant steels in power plants requires reliable long term creep rupture strength values as basis for design. Modern martensitic 9% Cr-steels have complex microstructures that change with service exposure. That is why extrapolations of long term strength properties will be most difficult. Due to new long term test results, re-assessments became necessary for grades 911 and 92. Different methods have been used. Good agreement was obtained between a graphical and the numerical ISO 6303 method. In both cases a two-step assessment procedure was used. First the raw data was prepared in a suitable way, which was followed by mathematical averaging procedures. For comparison a Larson-Miller analysis on the raw data was performed, too. The results turned out to be too optimistic at temperatures higher than 575°C (1050°F). It is shown that a suitable preparation of data can improve the Larson-Miller assessment. As a result of the new assessments the design values had to be reduced for both grades. With respect to previous assessments the new values are up to almost 10% lower. In the case of grade 92 the difference from the former ASME values are even higher. Consequences concerning design and service operation are discussed.
The Performance of Creep-Strengthened Ferritic Steels in Power Generating Plant
Authors: Parker Jonathan , Henry Jeff
Published: August 2009

Creep-strengthened ferritic steels, such as Grade 91, offer the potential for excellent high-temperature performance. To realize the benefits for these alloys requires careful control of original composition and manufacturing processes, such as welding and bending, as well as the associated heat treatments. Laboratory tests indicate that long-term lives may be below the original estimates made based on Larson Miller extrapolation. Furthermore, accelerated rates of damage accumulation in in-service Grade 91 components can occur due to a number of factors including: • Problems associated with design, for example with reinforcement at nozzles and with stress concentrations in piping systems. • Incorrect heat treatment, in addition to proper instrumentation appropriate heat treatment schedules should consider specific compositions. • Bending, problems may be introduced following both hot or cold bending. • High-temperature operation in tubing leading to excessive scale formation and overheating. • Type IV cracking in welds which results from the local reduction in the heat affected zone strength resulting from welding thermal cycles. Review of key information regarding the high-temperature performance of creep strengthened ferritic steels shows that the long-term creep strength may not achieve the levels expected from simple extrapolation of short term data. The problems experienced are highlighted with reference to actual case histories. The additional challenges associated with the development of creep-fatigue damage in high-temperature plant operated in a cyclic mode are also discussed.
Creep-Fatigue Damage and Crack Initiation for a Mod 9Cr-1Mo Structure With Weldments
Authors: Lee Hyeong-Yeon , Lee Se-Hwan , Kim Jong-Bum , Lee Jae-Han
Published: August 2009

A structural test and evaluation on creep-fatigue damage, and creep-fatigue crack initiation have been carried out for a Mod. 9Cr-1Mo steel structural specimen with weldments. The conservatisms of the design codes of ASME Section III subsection and NH and RCC-MR codes were quantified at the welded joints of Mod.9Cr-1Mo steel and 316L stainless steel with the observed images from the structural test. In creep damage evaluation using the RCC-MR code, isochronous curve has been used rather than directly using the creep law as the RCC-MR specifies. A y-shaped steel specimen of a diameter 500mm, height 440mm and thickness 6.35mm is subjected to creep-fatigue loads with two hours of a hold time at 600°C and a primary nominal stress of 30MPa. The defect assessment procedures of RCC-MR A16 guide do not provide a procedure for Mod.9Cr-1Mo steel yet. In this study application of σd method for the assessment of creep-fatigue crack initiation has been examined for a Mod. 9Cr-1Mo steel structure.
Modelling of the Influence of Laves Phase on the Creep Properties in 9% Cr Steels
Authors: Magnusson Hans , Sandstro¨m Rolf
Published: August 2009

Nucleation and growth of Laves phase are calculated for a multi-component system. Coarsening of MX, M23C6 and Laves are also determined. The influence on creep strength is discussed by analysing particle hardening and solid solution strengthening. A model for particle size distribution is presented in order to determine the amount of dislocations that can climb across particles or generate Orowan loops. The model for solid solution hardening is based on a solution of Fick’s second law with a moving frame of reference for the concentration profiles around a climbing dislocation. This is done in order to determine the slowdown in dislocations velocity due to solute drag. The results show a loss in creep strength as the Laves phase grows.
Cold Work Effect on Creep Rupture Strength of Austenitic Boiler Steels
Authors: Masuyama Fujimitsu
Published: August 2009

In order to clarify the effect of cold work, warm work at working temperatures of up to 400°C and chemical compositions on the creep rupture strength of austenitic steels used for boiler tubing and high temperature support structures, long-term creep rupture tests were carried out on typical 18Cr-8Ni system steels consisting of TP304H, TP316H, TP321H and TP347H grade tubes and of TP321 plates. The long-term (100,000 hours) creep rupture strength of these steels was evaluated in terms of working ratio and Ni-equivalent. It was consequently clarified that creep rupture strength was substantially reduced in the cold-worked TP321 and TP321H materials, although warm-work resulted in less work-induced deterioration. It was also found creep rupture strength was enhanced by the higher Ni-eq in 18Cr-8Ni austenitic steels, and that the combined conditions of working ratio and Ni-eq govern the creep rupture strength criteria of weaker or stronger than as-received strength. Additionally the effect of cold work on the creep rupture strength and ductility of recently developed creep-strength enhanced 23Cr austenitic stainless steel (a candidate material for the hot end of superheaters in ultra-high temperature fossil-fired power plants) was considered. The strength of cold worked 23Cr austenitic steel was observed to fall below the as-received strength at stresses within about 120MPa, while re-solution annealing recovered the creep strength level to the as-received strength across the entire stress region.
Creep-Fatigue Properties of Fe-Ni Base 0.08C-23Cr-45Ni-7W Alloy for Piping in 700°C A-USC Power Plants
Authors: Noguchi Yasutaka , Miyahara Mitsuo , Okada Hirokazu , Igarashi Masaaki , Ogawa Kazuhiro
Published: August 2009

Creep-fatigue properties of Fe-Ni base 0.08C-23Cr-45Ni-7W alloy (HR6W) are investigated at 700°C and compared with Ni base superalloy Alloy617 in order to examine applicability of these materials to piping in 700°C A-USC power plants. It is clarified that the fatigue lives of HR6W and Alloy617 are almost the same under PP (fast-fast) type strain waveform, but the life of HR6W is longer than that of Alloy617 under CP (slow-fast) type strain waveform. The crack initiation lives at the ligament parts of superheater outlet headers, which are made of HR6W and Alloy617, are predicted from the results of three-dimensional FE-analyses. The transient heat transfer analysis and the elastic-plastic-creep thermal stress analysis are conducted on several kinds of typical operating conditions to evaluate the inelastic strain caused by the thermal cycles during start-up and shut-down of power plants. The maximum steam temperature and pressure are selected as 700°C and 34.3MPa, respectively, and the maximum cycle time of operation is 1 year. On the basis of the analytical results, creep-fatigue and creep rupture properties of the materials, the crack initiation lives of the headers are predicted with the strain range partitioning method. Inelastic strain in the header of HR6W is larger than that of Alloy617, because HR6W has lower creep deformation resistance and a slightly higher thermal expansion coefficient. However the predicted life of the header of HR6W is longer than that of Alloy617, because HR6W is much superior to Alloy617 in creep ductility and creep-fatigue properties.
Creep Damage Analysis of 9–12% Cr Ferritic Steels by Instrumented Indentation Test
Authors: Komazaki Shin-Ichi , Nakajima Motoki , Honda Tetsuya , Kohno Yutaka
Published: August 2009

High Cr ferritic steels have a complex lath martensitic structure consisting of several microstructural units, i.e., fine lath, block, packet and prior austenite grain. Additionally, precipitation, solid-solution and dispersion strengthening mechanisms contribute to their excellent strength. However, it is by no means easy to separate the contributions of such strengthening factors and quantitatively understand them because of the extremely fine and complicated microstructure. In this study, the instrumented indentation test was carried out to clarify the change in contribution of each microstructural factor, particularly, “block” during creep. The material used in this study was turbine rotor steel (Fe-10Cr-1Mo-1W-VNbN). The indentation test was applied to the as-tempered and the creep damaged specimens under a wide variety of maximum loads. The test results revealed that the decrease in contribution of block grain was the predominant factor of the decrease in macroscopic hardness at the early stage of creep life. On the other hand, during the second half of the life, the decrease in macroscopic hardness was mainly caused by the decrease in matrix hardness. The decrease in block’s contribution was attributable to the decrease in the resistance of block boundary to deformation, rather than the coarsening of block grain.
Regulatory Review Results on Allowable Tensile Stress Values of Creep Strength Enhanced Ferritic Steels
Authors: Yoshida Kazuo , Nakai Hirotake , Fukuda Minami
Published: August 2009

In order to evaluate long-term creep strength and to review current allowable tensile stresses of creep strength enhanced ferritic steels, a committee was organized in Japan Power Engineering and Inspection Corporation. In 2004FY and 2005FY, creep test data of Gr. 122, Gr. 91, Gr. 92, Gr. 23 and KA-SUS410J2TB steels were collected and analyzed by means of region splitting procedure in the committee. Based on the analysis, the allowable tensile stresses were reviewed in accordance with METI regulatory base. And the master curves for creep rupture life evaluation of welds were set forth furthermore based on the data analysis.
Creep During Power-Law Breakdown in Phosphorus Alloyed Copper
Authors: Sandstro¨m Rolf , Andersson Henrik C. M.
Published: August 2009

Copper alloyed with 50 ppm phosphorus (Cu-OFP) is selected for canisters for nuclear waste packages to avoid a low creep ductility, which is sometimes present in pure copper. The operating temperatures of these canisters are in the range from 0 to 100°C. Creep readily takes place in copper even at room temperature. At temperatures below 100°C, creep is well inside the power-law breakdown regime. The creep exponent is in the range from 30 to 100. Since creep models for this situation are missing in the literature, a new model for the minimum creep rate based on fundamental principles for climb and glide has been derived. This model gives the correct order of magnitude for the creep rate in the temperature range from 20 to 400°C without the use of fitted parameters. Design against creep can either be based on the total applied stress or the effective stress. In the first case the constitutive equations can be directly obtained from the minimum experimental creep rates. A new approach is proposed to handle the effective stress case, which is based on the initial creep rates. The φ-model is used to relate the initial creep rate to the minimum one. It is shown how the constitutive equations for the creep rate and the back stress can be transferred to multiaxial stress states for use in FE-modelling.
Internet Microstructure Database for Crept Materials
Authors: Murata Masaharu , Tanaka Hideo , Kamihira Kazushige , Yamazaki Masayoshi , Kimura Kazuhiro
Published: August 2009

Materials Database Station of National Institute for Materials Science (NIMS) owns the world’s largest Internet materials database for academic purpose, which is composed of twelve databases: five concerning structural materials, five concerning basic physical properties, one for superconducting materials and one for polymers. All of theses databases are opened to Internet access at the website of http://mits.nims.go.jp/en. Database of Structural materials are NIMS structural materials datasheet online version (creep, fatigue, corrosion and space use materials strength and microstructure database for crept material). The general information, contents and examples of application will be introduced.
Creep Damage Assessment Through EBSD Method and Hardness Measurement for a High Chromium Turbine Rotor Steel Forging
Authors: Fujiyama Kazunari , Saito Takashi , Mori Keita , Hino Takahisa , Ishii Ryuichi
Published: August 2009

10Cr-1Mo-1W-VNbN steel forging for steam turbine rotors was investigated using TEM (Transmission Electron Microscope), SEM (Scanning Electron Microscope) with EBSD (Electron BackScattering Diffraction pattern) method and nano-indentation tester for the assessment of microstructural change during creep damage process. Long term creep rupture tests and interrupted creep tests were conducted for the subject material and then effective damage parameters were assessed and compared with each other. Dislocation substructure which was observed through TEM thin foil method showed increasing lath/block width according to creep damage accumulation and the same feature was observed through EBSD IPF mapping more clearly and easily. EBSD KAM mapping was also conducted and averaged KAM was shown as an effective index for measuring dislocation microstructural changes during creep. Nano-indentation tests were conducted at the same position of EBSD measurement, which revealed that there was a good correlation between hardness value and the square root of averaged KAM. The differential equation of dislocation density with creep time was arranged to estimate the relationship between averaged KAM and time through the relationship between hardness and dislocation density. The creep damage estimation curves were obtained successfully by the equation expressed with stress and temperature term. The dislocation density based creep damage assessment curves could be effective for creep life assessment of high temperature components.
Long-Term Service Experience With Advanced Austenitic Alloys in Eddystone Power Station
Authors: Okada H. , Igarashi M. , Yamamoto S. , Miyahara O. , Iseda A. , Komai N. , Masuyama F.
Published: August 2009

A service exposure test of advanced austenitic alloys was performed at Eddystone Power Station Unit 1. The alloys tested were TP347HFG, SUPER304H and HR3C as well as 17-14CuMo as a reference material. They were installed in the final super-heater section in 1991 and were removed in 2004. The service exposure duration is 75,075 h with the steam temperature and pressure estimated 615 °C and 35 MPa, respectively. Post exposure examination has proved no marked hot-corrosion and steam oxidation have occurred for the TP347HFG, SUPER304H and HR3C specimens, while severe hot-corrosion and exfoliation of steam-oxide films was pronounced in 17-14CuMo specimens. It is also found that HR3C exhibits the highest tensile strength with a lowest ductility and TP347HFG does vice versa, while the strength of SUPER304H is equivalent to that of 17-14CuMo with much better ductility. Short-term creep rupture strengths of these alloys have been reduced to some extent after the long-term service exposure and a longer-term creep rupture testing has been in progress. Microstructural evolution of the TP347HFG, SUPER304H and HR3C as well as 17-14CuMo during the long-term service exposure have been analyzed using a detailed TEM examination and the chemical analysis of extraction residue of the exposed specimens.
Status of Development of the VM12 Steel for Application at High Temperature in Advanced Power Plants
Authors: Gabrel Jean , Bendick Walter , Lefebvre Bruno , Vandenberghe Bruno
Published: August 2009

Improvement of boiler efficiency is reached by increasing the pressure and temperature of newly designed boilers. Recently developed steel grades such as T/P91 and T/P92 are used in the advanced power plants thanks to their high creep rupture strength resistance which enables maintaining acceptable thickness of the tubes and pipes. Nevertheless their operating temperature range is limited by their oxidation behavior which is lower than classical 12%Cr steels or austenitic steels. For these reasons we have developed a new steel grade which combines good creep resistance and high steam-side oxidation behavior. This new steel, based on chromium content of 12% and with other elements such as cobalt, tungsten and boron, is named VM12. Manufacturing of this grade has been proved by production of several laboratory and industrial heats and rolling of tubes and pipes in several dimensions by different rolling processes. In addition to base metal property investigations — including creep tests and high temperature oxidation behavior — welding, cold bending and hot induction bending qualifications took place. This paper summarizes the results of the investigations and presents the first findings for processing.
Residual Life Assessment of In-Service High Temperature Components by Small Punch Creep Test
Authors: Shan Jianhua , Ling Xiang , Qian Zhenmai
Published: August 2009

The knowledge of mechanical long term behaviour under static loading for high temperature components requires methodologies for residual life assessment in order to employ the full potential of materials, particularly in non-destructive methods. In this paper, in order to apply small punch creep (SPC) test to the residual creep life assessment of in-service high temperature components, a variety of SPC tests for Cr5Mo steel in a protective Argon atmosphere were carried out, which used disc test specimens of 10mm in diameter and 0.5mm in thickness extracted both new material and in-service high temperature components. The relationship of the creep deflection curve, the test load, rupture time and ductility of miniature specimens were investigated. Based on SPC test and finite element numerical analysis methods, a novel residual life assessment method was proposed to substitute conventional uniaxial creep life analysis method by introducing an initial creep damage parameter. Moreover, the fractographic observation and the structural damage detection analysis were examined. Finally, the results using conventional uniaxial creep life analysis method were studied to validate the reliability of SPC life assessment method.
Small Punch Testing for Creep: Progress in Europe
Authors: Hurst Roger , Bicego Valerio , Foulds Jude
Published: August 2009

The small punch or disk bend test has particular value in life prediction of operating equipment since the test requires very small amounts of material (a common test specimen disk is 0.5 mm thick with a diameter of 6 to 10 mm), and usually the required volume of material can be acquired from operating equipment in a virtually nondestructive manner. The application of the small punch (SP) test for creep has gained significant interest in the last decade, primarily as a result of research in Europe. The CEN (one of three European standardization organizations recognized by the EC) has been working to develop a Code of Practice for the small punch test. The Code documents, very recently completed, focus on use of the test for creep rupture and tensile and toughness properties. This paper summarizes the European round-robin work leading to the Code of Practice and key aspects of the Code. Included is a description of the currently recommended semi-empirical interpretation of data from the multiaxially-loaded small punch test specimens, less straightforward than that from conventional uniaxial specimens. As the SP test sees more field use and as the specimen and test configurations achieve better uniformity, we can expect that its application to creep life prediction will increase.
A Long-Term Local Deformation Measurement System for Notched Specimen at High Temperature
Authors: Zheng Yangyan , Ling Xiang , Chen Jianjun
Published: August 2009

This paper describes the design and evaluation of a novel optical instrumentation system that has been developed for measuring high temperature creep deformation under long-term loads. The system includes short optical fibers, a super long working distance microscope, a CCD camera, and digital image processing software. Short optical fibers are pasted on the small region on one side of the specimen surface as markings. The two optical fibers are illuminated by a light and are focused onto the CCD camera by the super long working distance microscope. The images tracked at intervals are processed by digital image processing software. The distance between the fibers at each picture can be measured. The local creep deformations versus time are obtained by measuring the variation of relative distance between the fibers. Experiments on Cr5Mo notched specimens were carried out. The results demonstrate that the system is capable of measuring creep deformation at elevated temperature.
Creep Damage Evaluation of Fine-Grained HAZ in Mod. 9Cr Ferritic Heat-Resistant Steel Weldments
Authors: Yoneyama N. , Kubushiro K. , Yoshizawa H.
Published: August 2009

9Cr steel weldments are concerned with evaluation of creep life time and creep rupture mechanism. In fine grain HAZ (FG-HAZ) of weldments, TYPE IV cracking and creep voids occurred at lower stress than rupture stress level of base metal. In the crept specimen, FG-HAZ sometime has large coarsening grains near creep voids. These recovery phenomena are localized in FG-HAZ, and recovered microstructures are dependent on heat input of welding. In this study, creep tests are examined in two types of weldments, and relations between creep life time and coarsened sub-grains or grains have been studied by microstructural changing with EBSP analysis. In crept specimens, boundaries are moved and boundary density is decreasing in the fine-grained HAZ. Maximum grain size and creep life time have linear function, and EBSP can evaluate creep life time of 9Cr weldments. These microstructural changing are considered by morphology of precipitates in the several crept specimens.
Field Test Results of Newly Developed Austenitic Steels in the Eddystone Unit No.1 Boiler
Authors: Komai Nobuyoshi , Igarashi Masaaki , Minami Yusuke , Mimura Hiroyuki , Masuyama Fujitmitsu , Prager Martin , Boyles Peter R.
Published: August 2009

Six new grade austenitic stainless steel tubes including SUPER304H® (C.C. 2328), TP347HFG, NF709®, TEMPALOY A-3®, HR3C® (TP310HCbN) and TEMPALOY CR30A® were selected and installed in the superheater of the Eddystone No.1 boiler for the purpose of extending tube service life by reducing fire-side and steam-side corrosion. No significant corrosion was observed on the outer surfaces at 75,075h of exposure. Precipitates due to exposure were identified by TEM-EDS analysis. The thickness of steam oxidation scale was less in high-Cr materials, and high Cr content was thus demonstrated to have effectively improved steam oxidation resistance. HR3C showed comparatively poor impact properties, while the other materials exhibited acceptable impact values of over 30J/cm2 at 20°C. All materials showed reduced creep strength compared with unexposed materials after service exposure under high stress test conditions. However the differences became smaller at lower stresses.
Practical Methods for Creep Assessments: Data Extrapolation and Crack Propagation
Authors: Penny R. K. , Kohlho¨fer W.
Published: August 2009

In seeking robust methods for creep assessments of quality, two key topics need urgent attention. These are creep data extrapolation techniques derived from relatively short-term tests and creep cracking prior to rupture. This paper provides proposals to these ends, which are practical in use and offer some insights for more economic data collection.
Developing New Cast Austenitic Stainless Steels With Improved High-Temperature Creep Resistance
Authors: Maziasz Philip J. , Shingledecker John P. , Evans Neal D. , Pollard Michael J.
Published: August 2009

Oak Ridge National Laboratory (ORNL) and Caterpillar have recently developed a new cast austenitic stainless steel, CF8C-Plus, for a wide range of high-temperature applications, including diesel exhaust components and turbine casings. The creep-rupture life of the new CF8C-Plus is over ten times greater than that of the standard cast CF8C stainless steel, and the creep-strength is about double. Another variant, CF8C-Plus Cu/W has been developed with even more creep strength at 750–850°C. The creep-strength of these new cast austenitic stainless steels is close to that of Ni-based superalloys like 617. CF8C-Plus steel was developed in about 1.5 years using an “engineered microstructure” alloy development approach, which produces creep resistance based on formation of stable nano-carbides (NbC) and prevention of deleterious intermetallics (sigma, Laves). CF8C-Plus steel won a 2003 R&D 100 Award, and to date, over 32,000 lb have been produced in various commercial component trials. The current commercialization status of the alloy is summarized.