Failure of porcelain coated heating elements used in regenerative air preheaters

Wanida Pongsaksawad; Siam Kaewkumsai; Sikharin Sorachot; Ekkarut Viyanit

doi:10.3139/120.110701

Published by De Gruyter April 14, 2015

Failure of porcelain coated heating elements used in regenerative air preheaters

Versagen von Porzellan-beschichteten Wärmeelementen in einem erneuerbaren Luftvorerhitzer

Wanida Pongsaksawad , Siam Kaewkumsai , Sikharin Sorachot and Ekkarut Viyanit

From the journal Materials Testing

https://doi.org/10.3139/120.110701

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Abstract

Sulfuric acid dew point corrosion is still a matter of concern with respect to early failure of heating elements used for air preheating in thermal power plants. Therefore, corrosion protection by means of porcelain enamel coatings is widely used. However, insufficient protective properties of the coating can result in a drastic decrease in service life. In the present study, failure analysis was comparatively performed on damaged heating elements showing different degrees of damage after approximately 1.5 years in service in a thermal power plant. The analytical results indicated that a lower degree of damage was observed for the heating element having higher content of silica. The protective properties of coatings decreased with the increasing pore density formed in the coating layer. The heating element coated with a harder porcelain layer was less severely attacked.

Kurzfassung

Die Schwefelsäure-Taupunktskorrosion ist immer noch bedenklich einzustufen, hinsichtlich des vorzeitigen Versagens von Wärmeelementen, die für Luft-Vorerhitzer in Wärmekraftwerken verwendet werden. Daher wird häufig ein Korrosionsschutz unter Verwendung von Porzellan-Email-Beschichtungen angewendet. Doch unzureichende Schutzeigenschaften der Beschichtungen können sich in Form einer drastischen Reduktion der Lebensdauer auswirken. In der diesem Beitrag zugrunde liegenden Studie, wurde eine vergleichende Schadensanalyse an geschädigten Heizelementen durchgeführt, die verschiedene Schädigungsgrade nach einer Nutzungsdauer von 1,5 Jahren in einem Kraftwerk aufwiesen. Die analytischen Ergebnisse zeigen auf, dass sich ein geringerer Schädigungsgrad bei Elementen mit einem höheren Siliziumanteil einstellt. Die Schutzeigenschaften der Beschichtungen nehmen mit zunehmender Porendichte in der Schicht ab. Das Heizelement, das mit einer härteren Porzellanschicht versehen war, wurde weniger stark angegriffen.

§Correspondence Address, Dr.-Ing. Ekkarut Viyanit, Materials Reliability Research Unit, National Metal and Materials Technology Center (MTEC), National Science and Technology Development Agency (NSTDA), 114 Thailand Science Park, Pathumthani 12120, Thailand, ekkarutv@mtec.or.th

Dr. Wanida Pongsaksawad, born in 1978, is a researcher at the Failure Analysis and Surface Technology Lab, Materials Reliability Research Unit, National Metal and Materials Technology Center (MTEC) in Pathumthani, Thailand. She obtained her PhD degree in Materials Science and Engineering from Massachusetts Institute of Technology (MIT), USA in 2006. Her research areas include cathodic protection, electrochemical process and numerical simulation in corrosion technology.

Siam Kaewkumsai, born in 1975, is Senior Engineer at the Failure Analysis and Surface Technology Lab, Materials Reliability Research Unit, National Metal and Materials Technology Center (MTEC), Pathumthani, Thailand. He received his master degree in Metallurgical Engineering from King Mongkut's University of Technology Thoburi, Thailand in 2007. His areas of expertise are failure analysis and fracture mechanics.

Sikharin Sorachot, born in 1982, is Electrical Engineer at the Failure Analysis and Surface Technology Lab, Materials Reliability Research Unit, National Metal and Materials Technology Center (MTEC), Pathumthani, Thailand. He received his bachelor degree in Electrical Engineering from Mahanakhon University, Thailand in 2004. His areas of expertise are cathodic protection and atmospheric corrosion.

Dr,-Ing. Ekkarut Viyanit, born in 1972, is a researcher and Head of the Failure Analysis and Surface Technology Lab, Materials Reliability Research Unit, National Metal and Materials Technology Center (MTEC), Pathumthani, Thailand. He received his Dr.-Ing. degree in Materials Engineering from Helmut-Schmidt University, Hamburg, Germany in 2005. His areas of expertise include corrosion protection, failure analysis and joining of metals.

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Published Online: 2015-04-14

Published in Print: 2015-03-02

Failure of porcelain coated heating elements used in regenerative air preheaters

Abstract

Kurzfassung

References

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