Creep Deformation Property and Creep Life Evaluation of Super304H

Creep deformation behavior, creep strength property and microstructural evolution during creep exposure were investigated on Super 304H steel for boiler tube. In the high stress and lower temperature regime, creep rupture strength of Super 304H steel is higher than that of SUS304H steel. The slope of stress vs. time to rupture curve of Super 304H steel, however, becomes steeper with increase in creep exposure time and temperature, and the creep rupture strength of Super 304H steel becomes closer to that of SUS304H steel after the tens of thousands of hours at 700°C and above. In the short-term, at 600°C, creep rupture ductility increases with increase in creep rupture life. However, it tends to decrease after showing the maximum value and the creep rupture ductility decreases with increase in temperature. The complex shape of creep rate vs. time curves, with two minima in creep rate, was observed at 600°C. Several type precipitates of niobium carbonitride (Nb(C,N)), Z phase (NbCrN), and copper were observed in Super 304H steel, as well as M23C6 carbide and sigma phase observed in SUS304H steel. The change in slope of stress vs. time to rupture curve is caused by disappearance of precipitation strengthening effect during creep exposure. Accuracy of creep rupture life evaluation was improved by stress range splitting method which takes into accounts of the change in slope of stress vs. time to rupture curves was demonstrated.

Prediction of crack propagation kinetics through multipoint stochastic simulations of microscopic fields

Prediction of crack propagation kinetics in the components of nuclear plant primary circuits undergoing Stress Corrosion Cracking (SCC) can be improved by a refinement of the SCC models. One of the steps in the estimation of the time to rupture is the crack propagation criterion. Current models make use of macroscopic measures (e.g. stress, strain) obtained for instance using the Finite Element Method. To go down to the microscopic scale and use local measures, a two-step approach is proposed. First, synthetic microstructures representing the material under specific loadings are simulated, and their quality is validated using statistical measures. Second, the shortest path to rupture in terms of propagation time is computed, and the distribution of those synthetic times to rupture is compared with the time to rupture estimated only from macroscopic values. The first step is realized with the cross-correlation-based simulation (CCSIM), a multipoint simulation algorithm that produces synthetic stochastic fields from a training field. The Earth Mover’s Distance is the metric which allows to assess the quality of the realizations. The computation of shortest paths is realized using Dijkstra’s algorithm. This approach allows to obtain a refinement in the prediction of the kinetics of crack propagation compared to the macroscopic approach. An influence of the loading conditions on the distribution of the computed synthetic times to rupture was observed, which could be reduced through a more robust use of the CCSIM.

Time Dependances of the Resistance Coefficients of Polymeric Materials

One of the possible approaches to the analysis of a physical mechanism of time dependence for the resistance coefficients of materials is suggested. The material durability at the constant stress is described using the Zhurkov and Gul' equations and the durability at the alternating stress—using the Bailey criterion. The low strains lead to structuring of a material that is reflected in a reduction of the structure-sensitive coefficient in these equations. This affords 20% increase in the durability. The dependence of the resistance coefficient assumes an extremal character; the maximum is observed at the time to rupture lg tr ≈ 2 (s).

Creep Deformation Property and Creep Life Evaluation of Super304H

Creep deformation behavior, creep strength property and microstructural evolution during creep exposure were investigated on Super 304H steel for boiler tube. In the high stress and lower temperature regime, creep rupture strength of Super 304H steel is higher than that of SUS304H steel. The slope of stress vs. time to rupture curve of Super 304H steel, however, becomes steeper with increases in creep exposure time and temperature, and the creep rupture strength of Super 304H steel becomes closer to that of SUS304H steel after the tens of thousands of hours at 700°C (1292°F) and above. In the short-term, at 600°C (1112°F), creep rupture ductility increases with increase in creep rupture life. However, it tends to decrease after showing this maximum value and the creep rupture ductility decreases with increase in temperature. The complex shape of creep rate vs. time curves, with two minima in creep rate, was observed at 600°C (1112°F). Several type precipitates of niobium carbonitride (Nb(C,N)), Z phase (NbCrN), and copper were observed in Super 304H steel, as well as M23C6 carbide and sigma phase observed in SUS304H steel. The change in slope of stress vs. time to rupture curve is caused by disappearance of precipitation strengthening effect during creep exposure. Accuracy of creep rupture life evaluation was improved by stress range splitting method which takes into account the change in slope of stress vs. time to rupture curves was demonstrated.

Effects of Primary and Secondary Creep Formulations on API 579-1 Residual Life Evaluation

A sound material constitutive equation is crucial for the residual life evaluation of pressure components operating in the creep range. In a previous work [1], the authors investigated how a secondary creep formulation encompassing both the dislocational and the diffusional range influences the assessment of damage according to API 579-1 [2] within the whole component stress range. In the present paper the work has been extended in order to include the effects of primary creep in the constitutive equation for the ASTM A335 P22 low-alloy steel used for the manufacturing of the HRSG header whose welded details were previously investigated. The creep damage was first calculated according to API 579-1 Section 10 via inelastic, time-dependent FEA and the Larson-Miller approach (LMP) with code-defined, minimum time-to-rupture data. This led to a first reckoning of the primary creep impact in terms of API 579-1 residual life for the components under evaluation. The API 579-1 time-to-rupture was then assessed with a detailed stress analysis implementing the Omega Method and its creep strain rate formulation. The obtained results were finally compared to those previously determined through the LMP procedure and the different creep correlations (secondary and primary+secondary).

Using MR-FTIR and Texture Profile to Track the Effect of Storage Time and Temperature on Pita Bread Staling

Textural deterioration of pita bread, PB, due to staling is an important quality parameter during storage. Loss of freshness due to PB staling results in significant quality and economic loss. PB staling was studied using both MR-FTIR spectroscopy and textural profile including time to rupture and tensile and compressive forces. The study was conducted at room temperature (23°C) and freezing temperature (−18°C) over 96 h of storage time after baking. Some physical properties of PB such as loaf weight, dimensions, water activity, and density were measured. MR-FTIR measurement spectra in the wavelength 900–1150 cm−1 corresponding to the “saccharides” regions and the range 3000–3600 cm−1 corresponding to O-H bond stretching vibration were able to clearly detect the PB deterioration at different storage times as shown by statistical significance test. Mechanical measurements of tearing force, time to rupture, and 25% compression force were also found to be good indicators of PB quality deterioration. Time to rupture, however, was found to be the best PB deterioration indicator. In addition, PB stored at room temperature showed a significant deterioration (toughening) compared to that stored at freezing temperature which showed little or nonsignificant deterioration during storage. High negative correlation, r = -0.97, was observed between the 25% compression force and the wavenumber 960 cm−1 at room temperature.

Influence of the Upper Die and of the Indenter Material on the Time to Rupture of Small Punch Creep Tests

The Small Punch Creep test has proven to be a suitable technique for assessing the properties of in-service components. It is a reliable, efficient and cost-effective test for predicting the behaviour of the material. The aim of this paper is to analyse the influence of different factors on the Small Punch Creep (SPC) tests. The influence of the specimen clamping has been studied, experimentally and by means of finite element models on different materials. In the analysed conditions, it has been proven that the influence of the upper die on the tests results is generally relatively insignificant, even in the absence of upper die.Furthermore, the use of different materials at the punch has also been analysed. In order to achieve this goal, SPC tests have been carried out on two light alloys (AZ31 and AlSi9Cu3) at 473 and 523 K. Three different balls have been employed: ceramic, tungsten-carbide and steel balls. It has been proven that for the creep ductile alloy (AZ31), there is no apparent effect on the specimen response. On the other hand, for the creep brittle alloy (AlSi9Cu3), a different trend of the material response is shown, dependent on the ball used. As a result, there seems to be a significant influence of the friction between the punch and the specimen on the tests results, related to the material behaviour.

PENENTUAN TEMPERATUR OPERASIONAL “ROD HANGER TUBE HEATER” AGAR MENCAPAI UMUR OPERASI DESAIN

Rod Hanger Tube Heater yang sudah beroperasi sekitar ± 7 bulan akan tetapibelum dilengkapi dengan best practice berapa lama MTBF (Mean Time BetweenFailure) atau Life Time nya. Oleh karena itu dibutuhkan pengujian untukmengetahui berapa sebenarnya Life Time dari Rod Hanger, yang nantinya akanmenjadi acuan MTBF dari Rod Hanger tersebut. Pada tulisan ini akan disajikansuatu hasil pengujian mulur (creep test) dari Rod Hanger, yang kemudiandiekstrapolasi sehingga akan menghasilkan grafik LMP vs tegangan, yangmerupakan kombinasi tiga parameter yaitu waktu (time to rupture), logaritmategangan dan suhu operasi menjadi satu kurva yang disebut Kurva MasterLarson-Miller Parameter (LMP Master Curve). Selanjutnya parameter ini dapatdigunakan untuk menghitung umur pakai Rod Hanger yang dioperasikan padasuhu tinggi, dengan menggunakan persamaan Larson-Miller Parameter (LMP)