Contents Issue 4 (2002)

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English Abstracts

Stuart R. Holdsworth

Prediction and Prevention of Stress Corrosion and Corrosion Fatigue Cracking in LP Steam Turbines

The current ability to predict and prevent stress corrosion and corrosion fatigue cracking in LP steam turbines has developed from the knowledge base accumulated during the past 30 years from unilateral and collaborative R&D activities, in particular in Europe, Japan and the US, and from service experience. The two environmental cracking mechanisms are due to the combined influences of (i) material condition, (ii) environment and (iii) applied stress (static or cyclic). The influence of these factors on the material parameters used to predict stress corrosion and corrosion fatigue behavior is reviewed in the paper. The appropriate control of these factors and an understanding of the underlying damage mechanisms provide the basis for preventing stress corrosion and corrosion fatigue cracking in turbine components.
PowerPlant Chemistry 2002, 4 (4)

Thomas McCloskey

Troubleshooting Turbine Steam Path Damage

Steam path damage, particularly of rotating and stationary blading, has long been recognized as a leading cause of steam turbine unavailability for large fossil fuel plants worldwide. Turbine problems cost the utility industry as much as one billion dollars per year. Failures of blades, discs, and rotors in both fossil and nuclear steam turbines represent a serious economic loss of availability and reliability for electric power generation suppliers and other energy supplies worldwide. Turbine problems such as deposition and erosion of blades can result in severe efficiency losses, resulting in significant economic penalties. The primary objective of this paper is to provide a methodology to identify the underlying damage or failure mechanisms, determine the root cause, and choose immediate and long-term actions to lessen or prevent recurrence of the problem.
PowerPlant Chemistry 2002, 4 (4)

Kevin J. Shields and Ewa Labuda

Operational Tube Failures in Heat Recovery Steam Generators: Metallurgical and Water Chemistry Perspectives

Operators of combined cycles with heat recovery steam generators are reporting an increasing extent of boiler tube failures. The most important failure mechanisms include flow-accelerated corrosion in low pressure evaporators and under-deposit corrosion in high pressure evaporators. Careful examination of the failed tubes and the cycle chemistry applied is essential for identifying the actual failure mechanism and for determining or confirming the actual failure root cause.

The failure appearance and other likely microscopic and metallurgic features as well as the failure location help to identify the possible failure mechanisms. Determining the root cause includes, among other things, evaluation of possible environmental factors (e.g., cycle chemistry in the case of water-touched tubes).

This paper describes the troubleshooting procedure and approach applied in two tube failure cases, in the low pressure evaporator of a dual pressure unit and in the high pressure evaporators of two dual pressure units.
PowerPlant Chemistry 2002, 4 (4)

Fred V. Ellis, Sebastian Tordonato, and Michael R. Latour

Root Cause Failure Assessment of Waterwall Tubing

An in-depth study of the waterwall tube failures at Unit 1 of the Newington Station was performed. The service related failure mechanisms were hydrogen damage, oxygen pitting, and corrosion fatigue. The tubing failure history showed a significant increase in the failure rate from approximately four tube failures per year for the years prior to the middle of 1991, to failure rates from approximately seven to twenty failures per year for the years after the third quarter of 1993. The cycle chemistry data analysis showed that the principal reason for the increased failure rate is ingress of contaminants, primarily chlorides (due to condenser leaks) and oxygen. The condenser problems are the direct result of wiring the cathodic protection system in reverse polarity, the significant corrosion activity due to this error, and the failure of remedial measures to stop the leaks. The oxygen ingress was attributed to possible leaks at the deaerator and unit layup procedures. The stress ranking, environment parameter, and equivalent operating hours information were used in determining the probable root cause of failure for the corrosion fatigue failures. For the locations with the higher stress ranks of B and C, the major root cause of failure influence is excessive stresses/strains. Corrective action requires redesign and modifications to alleviate the applied stresses/strains. For the locations with the lowest stress rank of D, the major root cause of failure is the environmental factors of poor water chemistry and boiler layup. Corrective actions are to rehabilitate and/or replace the condenser tubing, utilize the nitrogen blanket system during unit shutdown, and to inspect the deaerator for possible leak paths and repair as required.
PowerPlant Chemistry 2002, 4 (4)

Andrei Yu. Petrov, Abdolreza Zaltash, D. Tom Rizy, and Solomon D. Labinov

Study of Flue Gas Emissions of Gas Microturbine-Based CHP System

The number of distributed energy resources such as gas microturbines and combined cooling, heating and power systems has increased markedly over the last several years. Environmental issues (i.e., emissions, noise) are among the most important aspects of operating these systems. This paper presents the results of an emissions study of the Combined Cooling, Heating and Power Integration Test Facility (microturbine-based with heat recovery) located at the Oak Ridge National Laboratory.
PowerPlant Chemistry 2002, 4 (4)

Karsten Thomsen, Klaus Rauchfuß und Rüdiger Seidel

Kritische Betrachtungen zur Messung der Korngrößenverteilung von Ionenaustauschern

Der Betrieb von technischen Wasseraufbereitungsanlagen stellt an die Ionenaustauscher besondere Anforderungen. Für die Betrachtung der Leistungsfähigkeit sind neben der chemischen Aktivität Informationen über die Korngrößenverteilung der einzusetzenden Ionenaustauscher unerlässlich. Auswirkungen unterschiedlicher Kornverteilungen auf den praktischen Betrieb werden kurz beschrieben.

Im Rahmen der Erstellung einer DIN-Norm wurden verschiedene Bestimmungsmethoden kritisch überprüft. Eine hierzu durchgeführte Ringanalyse beinhaltete die Nasssiebung, optoelektronische Messverfahren sowie die Bildanalyse.
Der Ringversuch zeigt, dass die Summen-Kennziffern der Verteilung – effektive Korngröße, Gleichheitskoeffizient und harmonischer Mittelwert – mit guter Präzision und Vergleichbarkeit mit den verschiedenen Methoden gemessen werden können. Im Gegensatz hierzu sind die Fein- und Grobkornanteile nur mit großer Unsicherheit messbar; diese Unsicherheit muss in die Beurteilung solcher Messungen eingehen.
PowerPlant Chemistry 2002, 4 (4)