Monitoring methodologies of the acid cleaning of steam generators

Some general considerations about the validity and usefulness of corrosion rate monitoring using the polarization resistance method are developed and the theory of Stern and Geary is shortly discussed. The basic aspects of the acid cleaning of steam generators, the role of corrosion inhibitors and the approach of the author with respect to the problem of monitoring this operation are also reviewed. The main aim of this applied research was to verify the reliability of a corrosion meter in predicting the correct order of magnitude of the corrosion rate of a plain carbon steel and two low alloy steels. Measurements under dynamic conditions, with the solution flow rates of 0.5, 1.0 and 1.5 ms^?1, were performed in 5% by weight HCl solutions at 75°C containing a specific commercial inhibitor at two concentrations. Results indicate that the manufacturer calibration of the corrosion meter is not able to provide a realistic evaluation of the corrosion rate of the probe electrodes. Furthermore, it was experimentally demonstrated that probe and tubular specimens of the same material exhibit a different electrochemical behaviour. Therefore, a reliable evaluation of the true corrosion rate of tubular specimens should be made using appropriate calibration charts for the given environment and geometry of the electrochemical probe. At last, some alternating current measurements performed at 10 Hz showed that corrosion rate monitoring based on low-frequency signals could prove very useful for controlling the aggressiveness of the acid-cleaning solution.     

Zu einem Phänomen der Lochkorrosionsbegrenzung bei hochlegierten Sonderedelstählen und NiCrMo-Legierungen in Chloridlösungen

On a phenomenon of the limitation of pitting corrosion at high alloyed special stainless steels and NiCrMo-alloys in chloride solutions Testing the pitting corrosion resistance of high alloyed special stainless steels and NiCrMo-alloys in chloride solutions there was observed a limitation of the pitting corrosion range toward more positive potentials. Above this limitation, the so-called pitting corrosion limitation potential, the pit initiation by all means is prevented, but the growth of pits which had been initiated before in the pitting corrosion range not necessarily comes to a stop. Therefore current density-potential curves which are obtained by downward polarization after an initial potential jump into the transpassive region and chronopotentiostatic tests are more suitable to investigate this phenomenon than cyclic polarization measurements and potentiostatic alteration tests. There is indicated a dependence of this phenomenon on temperature. The phenomenon of a limitation of the pitting corrosion range toward more positive potentials has been found until now at alloy 926, alloy 31, alloy 28, alloy 59 and alloy C-276.     

NMR IMAGING, CALORIMETRIC, and MATHEMATICAL MODELING STUDIES of FOOD FREEZING

Nuclear magnetic resonance imaging (MRI), calorimetry, and temperature measurements were used to monitor cylindrical potato sections frozen at -11C and -42C. MRI showed the advance of the nonsymmetric freezing zone and loss of signal intensity as liquid water turned to ice. Differential calorimetry was used to follow heat removal during transient freezing. Measured times to 95% enthalpy change were 24 min (-42C) and 49 min (-11C), as compared to modeled values of 29 min (-42C) and 100 min (-11C). Times to 95% change in the NMR signal, integrated over the area of the image, were 21 min (-42C) and 56 min (-11C). Changes in NMR signal intensity could be correlated with the amount of unfrozen water remaining after a steady-state had been reached. At -42C, NMR indicated 25% unfrozen water remaining as compared to 26% by calorimetry, and 22% by modeling. At -11C, NMR measured 67% unfrozen water remaining as compared to 48% by calorimetry, and 25% by equilibrium modeling.     

Experimental determination of thermal conductivity of apple and potato at different moisture contents

Thermal conductivity of apple and potato samples was measured by means of a specifically designed apparatus based on Fitch's method. The thermal conductivity was determined at various moisture contents at the sample mean temperature of 30 °C. As expected the conductivity decreases with the decrease in moisture content. Thermal conductivity data were correlated with moisture content using a straight line.     

On the ergodicity of a model of drilling

In this paper a one-dimensional map modeling the process of drilling is studied. The sufficient conditions for the existence of absolutely continuous invariant probability measure and ergodicity are established.     

Joint stick-slip friction compensation of robot manipulators by using smooth robust controllers

In this article, two new smooth robust nonlinear compensators have been developed, respectively, for positional regulation and trajectory tracking of rigid robot manipulators with internal joint stick-slip friction. The proposed controllers can improve not only the positioning accuracy but also the smoothness of motion. No exact knowledge of the friction models is required for the design of the controllers. Furthermore, the tracking controller is also robust with respect to the uncertain link parameters. Using Lyapunov's direct method, we can show that the time-invariant positional regulation controller guarantees the global boundedness stability of the closed-loop system, while the time-varying positional tracking controller guarantees the global asymptotic stability of the closed-loop system. The numerical simulations of the controllers on a two-link robot are presented as illustrations. © 1994 John Wiley & Sons, Inc.     

ADS expert

ADS Expert is an integrated system that (a) provides suggestions about suitable optimization algorithms for a particular structural optimization problem, (b) it offers explanations and guide lines, in the form of hypertext, that refer to the optimization strategy, optimizer and one dimensional search method, (c) it produces the required gradients for the objective function and the constraints using symbolic differentiation, (d) establishes a direct linking with ADS routines and (e) it monitors the evolution of the optimization process. The system can be used as an educational tool for structural optimization and as an efficient integrated system for small to medium size optimization problems for which the objective function and the constraints are given in the form of explicit functions of the design variables. The system is a Windows application and runs quite satisfactorily on PCs.     

METHODS FOR BRAZING CERAMIC AND METAL-CERAMIC JOINTS

Owing to improved manufacturing processes technical ceramics on the basis of oxide as well as nonoxide ceramics have gained an increasing technical potential. Among other joining techniques brazing has proved to be the most flexible joining process that can easily be adapted to various ceramic-metal-combinations. In order to induce a wetting reaction there are two different approaches. The more complicated process encircles a pre-metallization process and a subsequent brazing process. The less sophisticated process is the 'active brazing process' where special brazing alloys are employed that are able to wet ceramic base materials. Although both joining processes are very flexible there are restrictions regarding the filler metals to be used, the premetallization process and the actual (active-) brazing process.     

Anabolic steroids and blood cell production

In the past anabolic steroids were the first-choice treatment for pancytopenic disorders that were often poorly classified. They are now superseded by other more recently developed methods of treatment--for example bone marrow transplantation and immunosuppression. This contrasts to the authors' experience, and to that of many other haematologists, who have noted anabolic steroid-induced responses in patients who were unsuitable for or unresponsive to the new treatments. Anabolic steroids did not, however, demonstrate an obvious effect in recent controlled trials involving patients with aplastic anaemia. Their use with immunosuppressive treatment is currently under investigation. Although anabolic steroids rarely reverse the course of anaemia in a myelodysplastic syndrome, even a slight haemopoietic improvement is desirable. Children with Fanconi's anaemia may benefit from a reduced transfusion requirement. Uraemic patients may experience significant side effects on standard erythropoietin (epo) treatment. There have been no controlled trials comparing epo versus anabolic steroids or epo versus epo in conjunction with anabolic steroids. Data from uncontrolled studies indicate a better response to anabolic steroids in children and females than in men. In spite of the fact that anabolic steroids have been used for almost 30 years, they should be carefully re-evaluated in scientifically controlled trials to test their efficacy and to compare them with the new treatments. Such trials, however, are impeded by the limited knowledge available with regard to pharmacological parameters and optimal treatment schedules.     

Inhaled induction and emergence from desflurane anesthesia in the ambulatory surgical patient: the effect of premedication

We studied the effect of premedication (1 microgram/kg fentanyl and 0.04 mg/kg midazolam 5 min before induction of anesthesia) on airway reactivity and hemodynamic stability during inhaled induction using desflurane in 10 ambulatory surgical patients. Eight patients who were anesthetized without premedication served as the controls. Induction and emergence were rapid and unaffected by premedication. End-tidal and inspired concentrations of desflurane at loss of consciousness were significantly reduced by premedication (10.1% end-tidal/14.1% inspired, no premedication, vs. 5.3% end-tidal/8.9% inspired, premedication). Airway irritability was markedly attenuated by premedication (100% no premedication versus 30% premedicated), as was apnea (37.5% no premedication versus 0% premedicated). We observed an increase in mean arterial blood pressure and heart rate after loss of consciousness (mean arterial pressure 103 vs 121 mm Hg, heart rate 73 vs 100 bpm) in the unpremedicated patients, whereas both groups demonstrated a decrease in mean arterial blood pressure with no change in heart rate when baseline values were compared to those at incision (103 vs 74 mm Hg, no premedication, 99 vs 81 mm Hg premedicated). Patient acceptability was satisfactory and unchanged by premedication. We recommend the use of such premedication when desflurane is used during the induction of anesthesia.