Long-Term Changes in a Heat Exchanger Steel

The steel ASTM A213 P22 is used for superheater outlet header in power plants. During duty cycles lasting over tens of years the temperature is of the order of 545°C and the pressure 125 atm. The microscopic changes in these steels are hard to analyze under working conditions, but they are believed to be responsible for the appearance of creeps in such devices. Investigation of the microscopic modifications will help to predict future failures due to creeps, increasing the reliability and saving a lot of money.We report the investigation of such changes in ASTM A213 P22 steel in use for 30 years as a Superheater header at Haifa power station. The analysis has been carried out using Mössbauer Spectroscopy, X-ray diffraction and optical microscopy. As a result it seems that the morphology and phase change of the carbide phases M₃C/M₇C₃ and M₂₃C₆ are the most prominent changes leading to the material failures.     

Preface

Journal of Thermal Analysis and Calorimetry -     

Positive value of information in games

We exhibit a general class of interactive decision situations in which all the agents benefit from more information. This class includes as a special case the classical comparison of statistical experiments à la Blackwell. AMS 2000 Subject Classification:Primary 91A35.The work of Bruno Bassan and Marco Scarsini was partially supported by MIUR-COFIN. The authors express their thanks to Sylvain Sorin for enlightening comments.     

Carbon dioxide supercritical fluid chromatography-Fourier transform infrared spectrometry

Summary The coupling of carbon dioxide supercritical fluid chromatography with Fourier transform infrared spectrometry (SFC-FTIR) is a powerful tool for the separation and on-line identification of non-volatile compounds. The IR transparency of carbon dioxide in the Fermi resonance bands region versus its density has been studied. Functional groups with stretching vibrations outside the transparent window of carbon dioxide are examined. SFC-FTIR separations allow Gram-Schmidt reconstruction chromatograms or IR window chemigrams with high quality spectra to be obtained. This SFC-FTIR lightpipe (flow cell, beam condensing optics, narrow band detector) has allowed detection limits of 250ng for benzonitrile and 70ng for methyl benzoate to be reached. The feasibility of very rapid SFC-FTIR separations is shown along with the subsequent peak spectra.     

A new algorithm for generation of permutations

A new algorithm for generating permutations is presented, that generates the next permutation by reversing a certain suffix of its predecessor. The average size of this suffix is less thane 2.8. It is shown how to find the position of a given permutation and how to construct the permutation of a given position, where the position refers to the order in which the permutations are generated, and is also new.On leave from the Department of Computer Science, Technion, Haifa, Israel. This work was supported by NSF grant MCS-8302391.     

Comparison of octadecyl-bonded silica and styrene-divinylbenzene copolymer sorbents for trace enrichment purposes fundamental aspects II. Linear chromatographic behaviour of the extracting supports

Summary Two reversed-phase LC systems were investigated by frontal analysis for the determination of linear chromatographic conditions, as defined according to the isotherm concept. The Partisil ODS-3 bonded silica and the PRP-1 polystyrene-divinylbenzene resin were used as stationary phases together withtrans-2-hexen-al as test solute and methanol-water mixtures as mobile phases. Particular attention was paid to the respective influence of the two main parameters which may cause sorbent overloading, that is, the capacity factor (k′) and the solute concentration in the mobile phase (C_m). Provided that k′C_m≤10⁻² M, linear chromatographic behaviour was observed for both sorbents, the maximum capacities of which were found greater than 1mmolg⁻¹.     

Cationic lanthanide complexes of neutral tripodal N,O ligands: enthalpy versus entropy-driven podate formation in water

The cationic lanthanide complexes of two neutral tripodal N,O ligands, tpa (tris[(2-pyridyl)methyl]amine) and tpaam (tris[6-((2-N,N-diethylcarbamoyl)pyridyl)methyl]amine) are studied in water. The analysis of the proton lanthanide induced NMR shifts indicate that there is no abrupt structural change in the middle of the rare-earth series. Unexpectedly, the formation constant values of the lanthanide podates of tpaam and tpa in D2O at 298 K are similar, suggesting that the addition of the three amide groups to the ligand tpa does not lead to any increase in stability of the lanthanide complexes of tpaam in respect to tpa, even though the amide groups are coordinated to the metal in aqueous solution. The measurement of the enthalpy and entropy changes of the complexation reactions shows that the two similar ligands tpa and tpaam have different driving forces for lanthanide complexation. Indeed, the formation of tpa podates benefits from an exothermic enthalpy change associated with a small entropy change, whereas the complexation reaction with tpaam is clearly entropy-driven though opposed by a positive enthalpy change. The hydration states of the europium complexes were measured by luminescence and show the coordination of 4-5 water ligands in [Eu(tpa)]3+ whereas there are only 2 in [Eu(tpaam)]3+. Therefore the heptadentate ligand tpaam releases the translational entropy of more water molecules than does the tetradentate ligand tpa.     

Off-Line and On-Line Preconcentration Techniques for the Determination of Phenylureas in Freshwaters

Abstract

Phenylurea herbicides are analysed by reversed-phase liquid chromatography using UV detection at 244 nm after a concentration step in order to determine ppb or sub-ppb levels in drinking and river waters. With an average UV detection limit of 5 ng, a 500 ml sample volume is necessary to reach the 10 ppt level for spiked LC grade water samples and enables easy determination of concentrations below the ppb level for river water samples. Off-line and on-line methods are compared for the concentration step. Off-line concentration consists in a liquid sorption on n-octadecyl silica (C18) and elution by a suitable organic solvent. Polar phenylureas have low retention volumes on C18 silica and consequently the length of the concentration column has to be 10 cm to concentrate them at the ppb level from 100 ml of water and longer for lower levels of detection. Nevertheless, we show that increasing the size of the concentration column does not improve the limits of detection because of the numerous interferences also concentrated when percolating high volumes of water. On-line technology can be used only with short precolumns and requires a sorbent with a great retention for phenylureas. The copolymer-based PRP-1 is found to be an excellent sorbent and it is then possible to apply on-line precolumn technology with preconcentration through two precolumns (10 × 21 mm ID) in series, the first one being packed with C18 silica and the other with the PRP-1 polymer. Interfering compounds are then trapped onto the first precolumn acting as a filter and common phenylurea-breakthrough volumes on the PRP-1 precolumn are higher than 500 ml. Knowing the amounts preconcentrated on both precolumns and using UV and electrochemical detection help the identification of phenylureas in river water.