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Raghavendra Naik K ¹, Kumar R K ², Saravanan V ², Shekhar Kumar M ³

Affiliations
1 Senior Research Fellow, Materials Technology Division, Central Power Research Institue, Bangalore-560080, IN
2 Joint Director, Materials Technology Division, Central Power Research Institue,Bangalore-560080, IN
3 Additional Director, Materials Technology Division, Central Power Research Institue,Bangalore-560080, IN

Abstract

High temperature erosion is generally encountered in boiler components in thermal power plants, especially in superheater, reheater, and economisers parts, where in fly ash particles attack the boiler components and cause high temperature erosion phenomena. It is known as fly ash erosion. The erosion behavior at elevated temperature is much different from that of room temperature erosion as there would be a higher erosion loss encountered at higher temperature due to higher plastic deformation as well as weak bonding between grains/particles. It is therefore imperative to study in depth the erosion wear assessment both at room temperature as well as at elevated temperature in the laboratory. This paper investigates thermal sprayed coatings produced by the high velocity oxygen fuel (HVOF) to improve the material performance under such conditions. 35 WC-NiCrBSi HVOF sprayed coatings were tested under high temperature (up to 700℃) erosion by means of an apparatus that simulated real conditions. The results showed that under these tests conditions the 35WC-NiCrBSi coating worn about 1.4 times less than bare SS-310 steel at room temperature and 300℃ Temperature, while at 700℃ C 35WC-NiCrBSi worns about 2 times higher than bare SS-310 steel at 90℃ impact angle. This shows 35WC-NiCrBSi erosion sensitivity at higher temperature.

Keywords

Thermal Spray Coating, HVOF, High Temperature Erosion, Impingement Angles, Surface Analysis.

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Arvind Kumar ¹, Malabika Roy ¹, Janardhana M ¹, Shekhar Kumar M ¹

Affiliations
1 Materials Technology Division, Central Power Research Institute, Bangalore-560 080, IN

Abstract

A power generating utility of 600 MW has reported the failure of boiler tubes after a service life of 265 hours against the design life of 25-30 years. The failure of tubes was reported in Re-heater Inlet Coil tubes which were made up of high strength material alloy of SA 213 T91 grade. These boiler tubes were operating under a high temperature and pressure. The material used for re-heater and super-heater boiler tubes should have enough creep strength to sustain at high temperature and pressure. Even though T91 grade steel has superior quality of metallurgical properties in comparison to low alloy existing material like T11, T12 and T22, T91tube was failed in a short duration. This paper describesthe investigation of the failure of high strength T91 gradereheater tubes in a coal fired thermal power plant. The failure investigation covers visual inspection, dimensional measurement, hardness mapping, oxide scale measurement, microstructural studies, and SEM and EDX analysis of the failed tubes. The analysis reveals that Tube No-3 of re-heater boiler tube failed due to short term overheating and other tubes failed due to secondary damage caused by steam impingement.

Keywords

Re-heater Boiler Tube, Visual Inspection, Grade Identification Of Alloy, Dimensional And Hardness Measurement, Oxide Scale Measurement, Microstructure Analysis

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Vynatheya S ¹, Suryanarayana K ², Shekhar Kumar M ³, Santhosh Kumar B L ⁴, Bheema Raju V ⁵

Affiliations
1 Joint Director, Materials Technology Division, Central Power Research Institue, Bangalore-560080, IN
2 Engineering Officer, Earthquake Engineering & vibration Research Center, Central Power Research Institue, Bangalore-560080, IN
3 Additional Director, Materials Technology Division, Central Power Research Institue, Bangalore-560080, IN
4 Scientist,Laird Technologies, Bangalore-560048, IN
5 Professor, Department of Chemistry, Dayananda Sagar College of Engineering, Bangalore-560 078, IN

Abstract

Although porcelain insulators in power lines have been in use for decades, several undergo catastrophic failures while early in service. A study addressing the materials aspects has been conducted on alumina based porcelain insulators. Apart from their electro mechanical stability characteristics, material aspects like composition, phase and microstructure play a very important role in their performance. The qualitative phase analyses on the insulator samples give an idea about the different major and minor phases present. Attempts have already been made to estimate α alumina and α quartz content in porcelain body. Mullite is another important phase present in the porcelain body, which gets formed during firing of raw materials during insulator manufacture and which has not been estimated quantitatively. An attempt has been made here to assess the mullite content in the alumina based insulator samples by X-Ray diffraction quantitative analysis. Internal standard method of quantification has been adopted successfully for the analysis. This article describes the quantification of mullite phase by the internal standard method based on X-Ray diffraction principle.

Keywords

Porcelain Insulator, Mullite, Internal Standard, Titanium Oxide

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