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

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 374 0 C; 225 Kg/cm 2

5. Enhanced steam parameters require superior materials

6. Requirements of materials for high-temperature application 1. Adequate strength to resist deformation-high temp. and pr. 2. Adequate fatigue strength against vibratory stress 3. Sufficient ductility to accommodate cumulative plastic strain and notch strength against stress concentrations 4. Good resistance to service environment to withstand oxidation, corrosion and erosion 5. 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 Supercritical Boiler ItemSection Material Specification (ASME) Water WallTubing SA213-T22 Superheater Header & Piping SA335 - P12 SA335 - P91 Tubing SA213-T12 SA213-T23 SA213-T91 SUPER 304H Reheater Header & Piping SA106-C SA335 - P12 SA335 - P91 Tubing SA210Gr.C SA213-T12 SA213-T23 SA213-T91 SUPER 304H Economiser Header & Piping SA106-C Tubing SA210-C Seperator Storage Tank SA302-C

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 Damage MechanismNDE Methods for detection ErosionVisual Examination (VE), Ultrasonic Thickness Survey Blockade in water circuitFibroscopy Welding defectsUltrasonic Test (UT), Magnetic Particle Test (MPT), Dye Penetrant Test (DPT), Radiographic Test (RT) CreepIn-situ Metallography, Hardness Measurement Oxide Scale growthUltrasonic Test (UT) Thermal fatigue crack detection and sizing Ultrasonic Time of Flight Diffraction (TOFD) inspection, potential drop technique Short Term overheatingIn-situ Metallography, Hardness Measurement SwellingDimensional Measurement (OD)

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

18. Structural Classificati on Microstructure features Action neededExpended life fraction UndamagedFerrite & pearlite None0.12 AIsolated cavities None until next major scheduled maintenance outage 0.46 BOriented cavities Replica test at specified interval preferably within 1.5 to 3 years 0.50 CLinked cavities (micro cracks) Limited service until repair and better to inspect within 6 months 0.84 DMacro cracksImmediate repair1.00

19. In-situ metallography (Replication)

20. Major Findings Bulging

22. Damaged microstructure (creep cavities)

23. Fatigue  Start-ups, load changes  Crack initiation – Stress Analysis, N f  Crack propagation

24. 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.

25. Crack propagation Paris Law:- da/dN = c  k n c, n = material constants For k = M  (  a)  ai ac a -n/2 da = c  n M n/2 dN; M = parameter related flaw shape

26. Ultrasonic Time of Flight Diffraction (TOFD) Inspection

28. TOFD - How it works

29. COMPLEX WELD WITH DISSIMILAR THICKNESS

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

31. Indian Boiler Regulation (IBR)

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

33.  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 Statutory Perspective (Contd.)

34. 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. Statutory Perspective (Contd.)

35. ComponentVisua l Ultrasonic testing Magnetic Particle Inspection Liquid/ Dye Penetrant Inspection ReplicationSamplingDeposit Analysis Outside Diameter And Thickness Fibroscopic Inspection HardnessOther (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) Drum(Steam)Yes NoYes NoYes NoYes Water DrumYes NoYes NoYes NoYes Low Temp. Headers YesNo YesNo Yes Attemperator Header Yes NoYes No Yes Swell measur ement High Temp. Economiser tubes YesNo YesNoYesNo Low Temp. Economiser tubes YesNo YesNoYesNo Convection Superheater coils YesNo Yes NoYes Primary Super heater coils YesNo YesNoYesNoYes Pre final Super heater coils YesNo YesNoYesNoYes TABLE -1

36. ComponentVisua l Ultrasonic testing Magnetic Particle Inspection Liquid/ Dye Penetrant Inspection Replication Samplin g Deposit Analysis Outside Diameter And Thickness Fibroscopic Inspection HardnessOthers Final Super heater coils YesNo YesNoYesNoYes Reheater coilsYesNo YesNoYesNoYes High Temp. headers Yes NoYes No Yes Final Super heater header Yes NoYes No Yes Swell measur ement Reheater header Yes NoYes No Yes Swell measur ement Main steam Piping YesNo YesNo YesNoYes Platen super Heater header Yes NoYes No Yes Primary super heater header Yes NoYes No Yes TABLE -1 (Contd.)

37. ComponentVisualUltrasonic testing Magnetic Particle Inspection Liquid/ Dye Penetrant Inspection Replication Sampl ing Depo sit Anal ysis Outside Diamet er And Thickn ess Fibrosc opic Inspecti on Hardness others Economiser Header YesNo YesNo YesNo AuxiliariesYesNo YesNo Boiler Bank Tube YesNo YesNo Water WallYesNo YesNoYesNo Furnace Water Wall YesNo YesNoYesNo TABLE -1 (Contd.)

38. Table – 2. ComponentVisualUltrasonic testing Magnetic Particle Inspection Liquid/ Dye Penetrant Inspection Replicatio n Samplin g Deposit Analysis Outside Diameter And Thickness Fibroscopic Inspection HardnessOther Drum(Steam)YesNo YesNo YesNo Water DrumYesNo YesNo YesNo Economiser Tubes YesNo YesNoYesNo Convection Super Heater coils YesNo YesNoYesNo Primary Super Heater coils YesNo YesNoYesNo Non destru ctive oxide thickn ess inspe ction Final Super Heater coils YesNo YesNoYesNo High Temp. Headers YesNo Yes No Yes No

39. Final Super Heater Header YesNo Yes No Yes No Swell meas ureme nt Economiser Header YesNo YesNo AuxiliariesYesNo YesNo Boiler Bank Tube YesNo YesNo Water WallYesNo YesNoYesNo Main steam Piping YesNo YesNoYesNo TABLE -2 ( Contd.)

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

41. 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.

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

43. Issues of Supercritical Technology in India (contd.) Operation & Maintenance Issues: 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

44. Reference: 1. Reference: 1. R.Viswanathan, “Damage Mechanisms and Life Assessment of High Temperature Components”, ASM International, Metals Park, Chio 44073. 2. Arindam Sinha 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 4-5 th 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, 9 th 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 4-5 th 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