Contents Issue 4 (2000)

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Barry Dooley and Peter Chang

The Current State of Boiler Tube Failures in Fossil Plants

This paper is a comprehensive summary of the current state of boiler tube failures in fossil power plants. The leading boiler tube failure mechanisms in order of availability loss (corrosion fatigue, fly ash corrosion, waterwall fireside corrosion, superheater/reheater long term overheating /creep/, and fireside corrosion in coal-fired units) are discussed in detail.

Two of the most misdiagnosed boiler tube failure mechanisms are failures of a tube by (i) long-term overheating, with or without accelerated oxidation, leading to a final failure by creep, and (ii) fireside corrosion by molten alkali sulfates, also resulting in subsequent creep. The distinguishing characteristics of both mechanisms are presented. The preferred method for estimation of the tube remaining life for each root cause is based on the oxide thickness technique.

The importance of cycle chemistry in boiler tube failures prevention as well as the set of goals for boiler tube failures reduction are clarified.

PowerPlant Chemistry 2000, 2(4)

Oleg A. Povarov, Valery N. Semenov, Alexander N. Troitsky, and Barry Dooley

Effect of Chemistries and Steam Purity on Moisture Generation and Formation of Liquid Films in Turbine Stages.

Components of power-generation units operating in phase transition region are subjected to intensive wear. Reduction of reliability and efficiency of turbine stages is largely due to corrosion processes, mainly as corrosion fatigue of rotating blades and corrosion cracking of disks in IP and LP turbines. Steam purity and conditions for generation of highly concentrated solutions on metal surface have a major effect on corrosion processes. Therefore, the study of (a) generation and precipitation of moisture and (b) formation of the early liquid films on the metal surface is very important.

This paper presents experimental results on the effect of different chemistries and steam purity on generation of the early condensate and the liquid films. These results were produced in Moscow Power Institute at different model turbines. The description of test rigs, test procedures, and systems for measurement of droplet size and liquid film thickness is given.

PowerPlant Chemistry 2000, 2(4)

Andrew Howell and Ken Weisser

Loss of Copper Sampled from Main Steam

As part of the investigation into remediation of a high-pres-sure turbine copper deposition problem, loss of main steam copper in sample cooling heat exchangers and in the sub-sequent sampling line was quantified. Loss of copper in main steam coolers and sample lines can cause significant inaccuracies in test results. E.g., for a 12-day test, an average total copper concentration of 0.20 µg/kg was measured at the sampling point, whereas 0.93 µg/kg was lost in the sample coolers and sampling line. In terms of meeting guidelines, the target values in main steam could be very difficult to determine with certainty.

PowerPlant Chemistry 2000, 2(4)

Hans-Hermann Neuburg and Ladislav Bursik

Corrosion and Efficiency Control by Continuous Cleaning of Condenser Tubing

Maintaining the integrity of the con-denser is the most important goal of power plant chemistry. The excellent biofouling resistance and high thermal con-ductivity of copper alloys must be balanced against a meas-urable susceptibility to pitting, crevice corrosion, erosion corrosion, etc.; the brasses, in particular, are quite susceptible to corrosion induced failure. The stainless steels are resistant to most forms of attack, but are susceptible to crevice corrosion and pitting in brack-ish water and seawater; even the newer, high molybdenum grades of stainless steel have suffered some localized cor-rosion under particularly adverse conditions. For this reason and since all de-posits decrease the heat transfer and cause a marked reduction of the cycle efficiency, keeping the inner surfaces of condenser tubing free of mi-cro-fouling and scaling is a very important task.

Operational principles of a continuous condenser tube cleaning system using elastic sponge rubber balls are explained; characteristics of sponge rubber cleaning balls as well as economics and monitoring of mechanical tube cleaning systems are discussed in detail.

PowerPlant Chemistry 2000, 2(4)

Eric V. Maughan, Gerhard Gericke, and Graham Roscoe

The Measurement of TOC in the Cycle Fluid of Modern Power Plants and Correct Selection of Monitoring Equipment

Cycle Chemistry Monitoring in Combined Cycle Units and in Units with Heat Recovery Steam Generators The emphasis in monitoring the cycle fluid in power plant by means of the acid (or cation) conductivity measurement has always been placed on the formation of mineral acids as the result of inorganic contaminants. However, it has been recognised for some time that dissolved carbon dioxide will mask the measured values. In addition low molecular mass organic acids will also contribute to the measurement. The presence of organic matter in the cycle fluid can be a major source of dissolved carbon dioxide and low molecular mass organic acids under steady operating conditions. In order to monitor the organic matter and its ultimate fate in the steam-water circuit, total organic carbon is measured. This paper investigates the measurement of total organic carbon and the analysers currently available to the power plant chemist. Actual examples under plant operating conditions are presented.

PowerPlant Chemistry 2000, 2(4)

Conference: Membranes in Drinking and Industrial Water Production - Advanced Program

The International Water Association (IWA), European De-salination Society (EDS), American Water Works Asso-ciation (AWWA) and Japan Water Works Association (JWWA) organise the Conference "Mem-branes in Drinking and Industrial Water Production" to be held in Paris from October 3 to 6, 2000. The Conference will give an overview of the most recent developments in membrane technology. These four day events bring together research scientists, engineers, managers and operators from water supply companies, industries, government departments, consulting firms, research institutes and universities. The theme of the Conference is membranes in drinking and industrial water production. It includes the treatment of groundwater, river, lake, and sea waters, filter backwash water, industrial and domestic wastewater with membrane processes, i.e., reverse osmosis, nanofiltration, ultrafiltration, microfiltration and electrodialysis.
The advanced conference program with all planned papers and the conference contacts are presented.

PowerPlant Chemistry 2000, 2(4)