Supercritical Boilers-Challenges Ahead Dr. S.K.Nath Engineering - - PowerPoint PPT Presentation

Condition Assessment of Supercritical Boilers-Challenges Ahead

Central Power Research Institute Thermal Research Centre Koradi Nagpur-441111

• Dr. S.K.Nath

Engineering Officer

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
• f 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.

Rankine Cycle

Supercritical Rankine Cycle

3740 C; 225 Kg/cm2

Enhanced steam parameters require superior materials

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

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

Comparison of allowable stresses between conventional and advanced materials

Supercritical Boiler

Item Section Material Specification (ASME)

Water Wall Tubing

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

Various damage mechanisms in supercritical boilers

• Short term damage mechanisms:

Erosion, Fireside corrosion, short- term overheating

• Long term damage mechanism:

Creep, Thermal Fatigue

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)

Manifestation

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

Manifestation (contd.)

• Metallurgical
• Creep life
• Structural integrity
• Steam Starvation
• Sudden Rupture

Various damage mechanisms and suitable NDE methods

Damage Mechanism NDE Methods for detection Erosion Visual Examination (VE), Ultrasonic Thickness Survey Blockade in water circuit Fibroscopy Welding defects Ultrasonic Test (UT), Magnetic Particle Test (MPT), Dye Penetrant Test (DPT), Radiographic Test (RT) Creep In-situ Metallography, Hardness Measurement Oxide Scale growth Ultrasonic Test (UT) Thermal fatigue crack detection and sizing Ultrasonic Time of Flight Diffraction (TOFD) inspection, potential drop technique Short Term overheating In-situ Metallography, Hardness Measurement Swelling Dimensional Measurement (OD)

What is Creep?

• The time dependent, thermally assisted

deformation of components under load (stress) is known as creep.

Structural Classificati

• n

Microstructure features Action needed Expended life fraction Undamaged Ferrite & pearlite None 0.12 A Isolated cavities None until next major scheduled maintenance

• utage

0.46 B Oriented cavities Replica test at specified interval preferably within 1.5 to 3 years 0.50 C Linked cavities (micro cracks) Limited service until repair and better to inspect within 6 months 0.84 D Macro cracks Immediate repair 1.00

In-situ metallography (Replication)

Major Findings

Bulging

Damaged microstructure (creep cavities)

Fatigue

Start-ups, load changes

• Crack initiation – Stress Analysis, Nf
• Crack propagation

CRACK PROPAGATION

• Initial Crack length – Assessed by a

suitable NDE technique (e.g. Ultrasonic)

• Critical Crack length – Assessed based
• n the prevailing stress field and

geometry of the job.

Crack propagation Paris Law:- da/dN = ckn c, n = material constants For k = M(a) ai

ac a-n/2da = cnMn/2dN;

M = parameter related flaw shape

Ultrasonic Time of Flight Diffraction (TOFD) Inspection

TOFD - How it works

COMPLEX WELD WITH DISSIMILAR THICKNESS

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

C Z a x S tLW     2

   

C B a x H T T S tBW

2 2 2 2

2       

   

C B a x H d d S t

2 2 2 2 1

2       

     

C B a x H h d h d S t

2 2 2 2 2

2         

Indian Boiler Regulation (IBR)

Statutory Perspective

Objectives:

• 1. Safe Operation
• 2. Update Boiler memo

 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.)

• 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.)

Component Visua l Ultrasonic testing Magnetic Particle Inspection Liquid/ Dye Penetrant Inspection Replication Sampling Deposit Analysis Outside Diameter And Thickness Fibroscopic Inspection Hardness Other (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) Drum(Steam) Yes Yes No Yes Yes No Yes Yes No Yes Water Drum Yes Yes No Yes Yes No Yes Yes No Yes Low Temp. Headers Yes No No Yes No No No Yes Yes Yes Attemperator Header Yes Yes No Yes Yes No No Yes Yes Yes Swell measur ement High Temp. Economiser tubes Yes No No No No Yes No Yes No No Low Temp. Economiser tubes Yes No No No No Yes No Yes No No Convection Superheater coils Yes No No No No Yes Yes Yes No Yes Primary Super heater coils Yes No No No No Yes No Yes No Yes Pre final Super heater coils Yes No No No No Yes No Yes No Yes

TABLE -1

Component Visua l Ultrasonic testing Magnetic Particle Inspection Liquid/ Dye Penetrant Inspection Replication

Samplin g

Deposit Analysis Outside Diameter And Thickness Fibroscopic Inspection Hardness Others Final Super heater coils Yes No No No No Yes No Yes No Yes Reheater coils Yes No No No No Yes No Yes No Yes High Temp. headers Yes Yes No Yes Yes No No Yes Yes Yes Final Super heater header Yes Yes No Yes Yes No No Yes Yes Yes

Swell measur ement

Reheater header Yes Yes No Yes Yes No No Yes Yes Yes

Swell measur ement

Main steam Piping Yes No No No Yes No No Yes No Yes Platen super Heater header Yes Yes No Yes Yes No No Yes Yes Yes Primary super heater header Yes Yes No Yes Yes No No Yes Yes Yes

TABLE -1 (Contd.)

Component Visual Ultrasonic testing Magnetic Particle Inspection Liquid/ Dye Penetrant Inspection Replication

Sampl ing

Depo sit Anal ysis Outside Diamet er And Thickn ess Fibrosc

• pic

Inspecti

• n

Hardness

• thers

Economiser Header Yes No No Yes No No No Yes No No Auxiliaries Yes No No No No No No Yes No No Boiler Bank Tube Yes No No No No No No Yes No No Water Wall Yes No No No No Yes No Yes No No Furnace Water Wall Yes No No No No Yes No Yes No No

TABLE -1 (Contd.)

Table – 2.

Component Visual Ultrasonic testing Magnetic Particle Inspection Liquid/ Dye Penetrant Inspection Replicatio n

Samplin g

Deposit Analysis Outside Diameter And Thickness Fibroscopic Inspection Hardness Other Drum(Steam) Yes No No Yes No No No Yes No No Water Drum Yes No No Yes No No No Yes No No Economiser Tubes Yes No No No No Yes No Yes No No Convection Super Heater coils Yes No No No No Yes No Yes No No Primary Super Heater coils Yes No No No No Yes No Yes No No

Non destru ctive

• xide

thickn ess inspe ction

Final Super Heater coils Yes No No No No Yes No Yes No No High Temp. Headers Yes No No Yes Yes No No Yes Yes No

Final Super Heater Header Yes No No Yes Yes No No Yes Yes No

Swell meas ureme nt

Economiser Header Yes No No No No No No Yes No No Auxiliaries Yes No No No No No No No Yes No Boiler Bank Tube Yes No No No No No No Yes No No Water Wall Yes No No No No Yes No Yes No No Main steam Piping Yes No No No No Yes No Yes No No

TABLE -2 ( Contd.)

Statutory Perspective (Contd.)

OUTCOME

• Scientifically assured safe operation

for a specified period.

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.

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

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

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 4-5th 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