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Condition Assessment of Supercritical Boilers-Challenges Ahead

Condition Assessment of Supercritical Boilers-Challenges Ahead. Dr. S.K.Nath Engineering Officer. Central Power Research Institute Thermal Research Centre Koradi Nagpur-441111. Supercritical Technology in India. Availability of coal both in quality and quantity

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Condition Assessment of Supercritical Boilers-Challenges Ahead

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  1. Condition Assessment of Supercritical Boilers-Challenges Ahead Dr. S.K.Nath Engineering Officer Central Power Research Institute Thermal Research Centre Koradi Nagpur-441111

  2. Supercritical Technology in India • Availability of coal both in quality and quantity • Reduction in emission-environmental obligation • Low Average efficiency of power plants in India in the range of 27% - 34%. • Achieving the required economic growth • Major Power Producer NTPC Ltd. has gone for first Supercritical Units in India followed by others. • Estimated 25 Nos. of SC projects are under different phase of development while more than 35 projects are under proposal stage.

  3. Rankine Cycle

  4. Supercritical Rankine Cycle 3740 C; 225 Kg/cm2

  5. Enhanced steam parameters require superior materials

  6. Requirements of materials for high-temperature application Adequate strength to resist deformation-high temp. and pr. Adequate fatigue strength against vibratory stress Sufficient ductility to accommodate cumulative plastic strain and notch strength against stress concentrations Good resistance to service environment to withstand oxidation, corrosion and erosion Structural ability to resist damaging metallurgical changes at operating conditions

  7. Requirements of materials for high-temperature application (contd.) 6. Ease in fabrication (machining, forging, casting and welding) 7. Low coefficient of thermal expansion to resist thermal stresses 8. Good thermal conductivity to minimise thermal gradient 9. Low density to provide high strength-to-weight ratio – for last staging blading of large steam turbine 10. Availability of long-term test data to validate the design 11. Availability in the desired size and shape

  8. Comparison of allowable stresses between conventional and advanced materials

  9. Supercritical Boiler

  10. Various damage mechanisms in supercritical boilers • Short term damage mechanisms: • Erosion, Fireside corrosion, short- • term overheating • Long term damage mechanism: • Creep, Thermal Fatigue

  11. Operational effects on supercritical boiler components • High temperature effect (ageing) • High temperature corrosion (ash attack) • High velocity flue gas with particulate burden (erosion) • Thermal cycling • Steam side oxide scale growth • Maintenance repair (weld, foreign material entrapment)

  12. Manifestation • Mechanical • Material loss • Wall thinning • Weld defect • Crack • Swelling • Slagging, fouling • Loss of material strength

  13. Manifestation (contd.) • Metallurgical • Creep life • Structural integrity • Steam Starvation • Sudden Rupture

  14. Various damage mechanisms and suitable NDE methods

  15. What is Creep?-The time dependent, thermally assisted deformation of components under load (stress) is known as creep.

  16. In-situ metallography (Replication)

  17. Major Findings Bulging

  18. Damaged microstructure (creep cavities)

  19. Fatigue • Start-ups, load changes • Crack initiation – Stress Analysis, Nf • Crack propagation

  20. CRACK PROPAGATION Initial Crack length – Assessed by a suitable NDE technique (e.g. Ultrasonic) Critical Crack length – Assessed based on the prevailing stress field and geometry of the job.

  21. Crack propagationParis Law:-da/dN = cknc, n = material constantsFor k = M(a) aiac a-n/2da = cnMn/2dN; M = parameter related flaw shape

  22. Ultrasonic Time of Flight Diffraction (TOFD) Inspection

  23. TOFD - How it works

  24. COMPLEX WELD WITH DISSIMILAR THICKNESS

  25. Specimen simulating complex geometry weld namely terminal weld between pipe and valve containing various defects

  26. Indian Boiler Regulation (IBR)

  27. Statutory Perspective Objectives: 1. Safe Operation 2. Update Boiler memo

  28. Statutory Perspective (Contd.) • Boiler Act • IBR- Rules & Regulations • Prescriptions • Authority – Inspectorate of Boilers • Jurisdiction – Within the State Territory • Boilers > = 22.75 Litres • > = 1,00,000 Hours • > = 25 years old

  29. Statutory Perspective (Contd.) • Agency: Approved as per Act • Methodology: • Table 1 and Table 2 • NDT inspection of Drum, Headers, Pipes • &Tubes by Visual, UT,DPT, Replication, OD • & Thickness, Fiber optic inspection, • Hardness, Oxide scale thickness measurement.

  30. TABLE -1

  31. TABLE -1 (Contd.)

  32. TABLE -1 (Contd.)

  33. Table – 2.

  34. TABLE -2 ( Contd.)

  35. Statutory Perspective (Contd.) • OUTCOME • Scientifically assured safe operation • for a specified period.

  36. Role of Indian Boiler Regulation (IBR) With age of currently available supercritical boilers in their infancy, the deployment of NDE will be limited to failure analysis and condition assessment of the component for quality control of repair programmes during any forced outage event and IBR relevance may be seen here.

  37. Issues of Supercritical Technology in India • Critical issues to be resolved for faster development : Technological issues :- a) Water wall cracking b) Negative flow characteristic c) Slagging. d) Designing as per Indian condition e) Welding technology for new material

  38. Issues of Supercritical Technology in India(contd.) Operation & Maintenance Issues: • Availability of sufficient field data w.r.t. material behavior, boiler tube leakage (BTL) • Availability of critical spares for supercritical plants. • Availability of skilled manpower • Large number of foreign suppliers of SC Power Plants , but have comparatively long delivery period . • Availability of contractors for O&M activities

  39. Reference:1. R.Viswanathan, “Damage Mechanisms and Life Assessment of High Temperature Components”, ASM International, Metals Park, Chio 44073.2. ArindamSinha and Akhilesh Kumar Singh (2011), New Era in Indian Thermal Power Sector-Evolvement of Supercritical Technology, Workshop on Remnant Life Assessment (RLA) Study of Boilers organized by Central Power Research Institute on 4-5th March, 2011 at Raipur (CG) 3. Modern Power station practice, Boilers and Ancillary plant, BEI Volume – B.4. Indian Boiler Regulation, Act 1923 & Regulations 1950, Akalank Publications, Delhi-110 006, 9th ed., July 2007.5. S.K.Nath et al (2011), Non-Destructive Evaluation in Remnant Life Assessment (RLA) study of Boilers Workshop on Remnant Life Assessment (RLA) Study of Boilers organized by Central Power Research Institute on 4-5th March, 2011 at Raipur (CG)6. B.J.Robbins, D.M.Farrell, J. Stallings and S. Cardoso, The Monitoring of Circumferential Fatigue Cracking of Furnace Tubes in Supercritical Boilers, Rowan Technologies Ltd., Manchester, UK and Electric Power Research Institute, Palo Alto, CA, USA.7. Kulvir Singh (2006), Advances in Materials for Advanced Steam Cycle Power Plants, BHEL Journal

  40. Thank You

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