describes about boiler tube failuresFull description
describes about boiler tube failuresDescription complète
Boiler Tube Failure AnalysisDescrição completa
Descrição completa
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Boiler dapat dibagi menjadi berbagai jenis diantaranya adalah fire tube boiler dan water tube boiler. Berikut ini disajikan perbedaan antara keduanya sesuai dengan spesifikasinya yang dirngk…Full description
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Important information about boilers and pressure vessel for mechanical engineersFull description
Descripción: Important information about boilers and pressure vessel for mechanical engineers
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The root cause of the tragedy in Massachusetts should have been identified as refractory failure rather than tube failure. It was the failed refractory lining that allowed flyash and water t…Description complète
BoilerDescription complète
BOILER PRESSURE PARTS AND TUBE TUBE FAILURES By Sri A.Prabhakar Rao
12.03.2010
Economizer Super Heaters Re-Heaters Water Walls Safety valves De-Super heaters and Boiler Drum
TO PREHEAT FEEDWATER TO RECOVER HEAT FROM FG LEAVING BOILER Finned
– staggered Bare tube – inline
CARBON STEEL
Coal can be saved from 15% to 20%. Increase in 1% Thermal Efficiency for every 6 C change in temperature. Feed water changes to steam quickly. Increases Boiler Life. Decreases thermal stress of Boiler Internal Parts. Decrease in combustion rate.
It increases the temperature of Main steam with the help of temperature of flue gases to get Saturated Steam admitted to the HPT.
PENDANT SPACED SECTION-located behind the screen section – heat transfer by convection . PLATEN SECTION- located above the furnaceheat absorption by radiation.
REAR HORIZONTAL SECTION- located in second
pass- convective counter flow. STEAM COOLED WALL- second pass enclosure. ROOF SECTION- second pass roof
Super heats the steam from Boiler before admitting it to turbine. Removes the moisture contents from the steam to avoid the corrosion and breaking of turbine blade tips.
It heats the temperature of steam outlet from HPT with the help of Flue gas temperature.
Re-heats the steam to increase the thermal efficiency. Increases the energy in the steam to perform additional work before exhausting into condenser from LPT.
Water walls carry feed water from ring headers to Boiler Drum through raiser tubes.
Increase in efficiency. Better heat transfer. Easy and quick erection. Increased availability of Boiler.
These are used to safe guard the equipment in case of emergencies.
It controls the main steam temperatures to safe limit.
It separates the steam from steam-water mixture. It houses all equipments used for purification of steam, after being separated from water.
Stores the DM Water. Limits the Solid contents. Facilitate in adding chemicals to maintain pH value. To facilitate Blow down.
Max. Temp. C (Oxidation Limit)
ASTM SA 210 Gr. A1
Carbon Steel C0.27% Mn 0.93%P.035 S0.10%
425
SA 209
T1
480
SA 213
T11
½ % Mo steel C 0.10to 0.20%Mn 0.30to0.80%P0.025Si0.025 s 1 % Cr. ½ % Mo
550
SA 213
T22
2 ¼ % Cr. 1 % Mo
580
SA 213
TP 304 H
18 % Cr. 8 % Ni (Stainless steel)
700
SA 213
TP 347 H
18 % Cr. 10 % Ni
700
Availability and reliability of boiler decreases with increased tube failures. •
Tube failure results in forced outages and hence direct impact on availability. •
Str ess Ruptu r e Short Term Overheating High Temperature Creep Dissimilar Metal Welds
L ack of Quali ty Contr ol Maintenance cleaning damage Chemical excursion damage Material Defects Welding Defects
- indicates that such problems have not been reported in India
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Mechanism : 1. The formation of carbon depleted zone on the ferritic side of the transition from the ferritic to austenitic structure is the initial step and any treatment which enhances the formation of this zone will enhance the failure probability. 2. The carbon depleted soft feerritic zone is constrained by the sorrounding harder and stronger material and is subjected to strains induced by thermal thermal expansion mismatch, bending, vibration vibration and pressure. pressure. 3. The strain accumulation in the carbon-depleted zone is relieved by creep at elevated temperature. 4. Creep damage in the form of cavitation, grain boundary sliding and tearing results in cracking in the carbon depleted zone along and adjacent to the weld interface
Damage may result from high pH corrosion reaction. NaOH removes protective magnetite iron oxide layer Fe3O4. Iron react with water or NaOH eating away the parent metal. It is also called caustic gouging or ductile gouging.
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Hydrogen damage may occur where corrosion reaction results in the production of atomic hydrogen. Damage may result from Low pH corrosion reaction. NaOH removes protective magnetic iron oxide layer Fe3O4 Iron react with water or NaOH liberating atomic hydrogen Atomic hydrogen diffuses into Iron carbide producing methane gas. Methane or Atomic H2 cannot diffuse, it accumulates resulting in cracks at grain boundaries. Longitudinal burst occur with thick lip
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Pitting corrosion is a localized accelerated attack, resulting in the formation of cavities around which the metal is relatively unattached. Thus, pitting corrosion results in the formation of pinholes, pits and cavities I the metal. Pitting is, usually, the result of the breakdown or cracking of the protective film on a metal at specific points. This gives rise to the formation of small anodic and large cathodic areas
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Information and data concerning the tube failure must be gathered quickly before repair activities can begin. Failure descriptions, operating conditions at the time of failure, historical records, and tube samples must be acquired and transferred to others who will conduct the investigation while repairs are being performed. Immediate corrective actions based on the initial results of the investigation must be approved and implemented before repairs are completed. Follow-up corrective actions based on the complete results of the investigation must be planned and implemented before additional failures are experienced.
Design stage: Selection of material, Compatible for working pressure / temperature
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Steam flow and the velocity / pressure
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Heat transfer characteristics/ surface effectiveness
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Metal temperature/Thermal expansion / constraints
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Radius of bends
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Attachments/ Weldments
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Manufacturing aspects
Transportation / Handling
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Storage
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Erection
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Commissioning
Operation and Maintenance
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FLUE GAS (FLY ASH) EROSION Extensive
inspection of Economiser / LTSH / screen tubes/ re-heater for erosion prone areas,Verifying the condition of existing shields and baffles, LTSH supply tube refractory conditions. Mapping
of thickness and identifying areas / locations for repair / replacement. Baffling
/ shielding at the points of erosion prone areas to the maximum extent possible. Changing
operating conditions like reduced load, low excess
air etc. Flow
model studY
FRETTING / RUBBING.
Determination of the correct failure mechanism is a complex process which can involve many individuals and organizations. Technical specialists in metallurgy, chemistry, combustion, and boiler design are often called in to assist in a failure investigation. The plant’s personnel must provide the initial information on the failure and boiler conditions prior to the failure. The plant’s operating records and failure histories must be in order so that pertinent data may be extracted. The plant’s management and technical staff must follow up on the failure investigation and implement the corrective actions required to correct the problem. By incorporating joint Task force between the plant owner and boiler designer / manufacturer/metallurgists/Experts the tube failures can be prevented/reduced and the availability/reliability can be increased.
