Power Research

Arvind Kumar ¹, M. Janardhana ²

Affiliations
1 Engineering Officer, Materials Technology Division, Central Power Research Institute, Bangalore, IN
2 Joint Director & HOD Materials Technology Division, Central Power Research Institute, Bangalore, IN

Abstract

One of power generating utility has reported the failure of boiler water wall tubes after a service life of 10,000 hours against the design life of 30-35 years. The failure of tubes was reported in water wall tubes regions which consist of carbon steel alloy. These boiler tubes were operating under the oxidizing/ reducing atmosphere at high temperature and pressure. This paper represents the investigation the failure of water wall tubes used in a coal fired thermal power plant. The failure investigation covers visual inspection, dimensional measurement, hardness mapping, deposit flux measurement and SEM & EDX analysis of the deposited products. This paper is the case study of failure analysis of water wall tubes due to corrosion and ID deposition on the tube. The analysis reveals that the failures were due to inside corrosion and hydrogen damage attack.

Keywords

Boiler water wall tube, physical observation, grade identification of alloy, dimensional & hardness measurement, corrosion deposit analysis, SEM and EDX analysis, flux deposit, ring test for hydrogen damage

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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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Arvind Kumar ¹, Malabika Roy ², Janardhana M ³, Shekhar Kumar M. ³

Affiliations
1 Engineering Officer, Central Power Research Institute, Bangalore - 560 080, IN
2 JRF, Central Power Research Institute, Bangalore - 560 080, IN
3 Joint Director, Central Power Research Institute, Bangalore - 560 080, IN

Abstract

Boilers being the heart of any steam generating system, failure of its components,will lead to forced outages of the plant, resulting in heavy economic losses in terms of non–availability of plant.Periodic inspection and assessment of boiler tubes has a great impact on the generation of power and economic status. The assessment of boiler tubes minimizes the risk of forced outage of the power plant. This paper presents the assessment of water wall tubes of thermal power plant to avoid any forced outage due to failure of water wall tubes. The assessment includes non-destructive, destructive and failure analysis of failed tubes. The periodic non-destructive evaluation is performed for the boiler tubes for generation of data for assessing and deciding the integrity of the boiler tubes. Destructive and failure analysis of failed tubes gives the information and helps in identifying the ischolar_main cause of failure and to take preventive action for avoiding forced outage.

Keywords

Water Wall Tube, Forced Outage, Corrosion, Erosion, Deposited Product, Scanner, Hydrogen Damage, Microstructure and EDX Analysis

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Arvind Kumar ¹

Affiliations
1 Engineering Officer, Materials Technology Division, Central Power Research Institute, Bengaluru - 560080, IN

Abstract

Several investigations on the failure of boiler tubes of thermal power plant have been carried out. This paper presents the failure analysis of a reheater tube of 210 MW thermal power plant. The reheater tube got damaged after service exposure a life of 1,65,900 hrs. The failed tube has a slit type opening with minor circumferential expansion at the rupture section. Scale was observed on the inside and outside surface of the tube. The scale formed on the outside and in-side surface of the tube was analysed through EDX and XRD to know the constituents of the scale and in evaluating the cause of failure of the tube. The tube was observed through its cross-sectional for the wall thinning. The area around the failed reheater tube sample was prepared and studied for structural degradation; hardness mapping was also carried out on the tube to find the cause of failure.

Keywords

Reheater Boiler tube, Hardness, Oxide scale layer, Wall thinning, Microstructure, EDX & XRD, 1.0

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

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

Abstract

Coal combustion in a thermal power plant generates plenty of ashes, which gets melted at high temperature. These melted ashes, i.e. slag, gets deposited on the external surface of the boiler tube in the furnace and stick to it. This slag greatly affect the heat transfer, which leads to reduction in the efficiency of the boiler. Also, slag deposition slowly corrodes the external surface of the tube. In this paper, a typical slag deposited tube was collected from a coal fired thermal power plant and metallographic analysis was carried out on this tube and the results were compared with an unexposed tube of same material, diameter and thickness. It is concluded from the analysis that there are no significant changes in microstructure, hardness values as well as inslag compositions.

Keywords

Boiler tube, slag, micro-structure, coal fired, slag indices

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