MAINTENANCE & CHECKS FOR POWER PLANT

TOPICS COVERED :

1. RECAP OF BOILER BASIC
2. REQUIREMENT FOR INSPECTION 
3. PART WISE CHECKLIST

RECAP…. Basics

Enclosed Pressure Vessel

The heat generated by the Combustion of Fuel is transferred to water to become steam Process: Evaporation.

Steam volume increases to 1,600 times that of water and produces tremendous force Boilers are hazardous equipment. Care is a must to avoid explosion.

Evaporation VS Boiling

 Normal evaporation is a surface phenomenon – since the vapor pressure is low and the pressure inside the liquid is equal to atmospheric pressure plus the liquid pressure, bubbles of water vapor cannot form. 

 But at the boiling point, the saturated vapor pressure equals atmospheric pressure, bubbles form, and the vaporization becomes a volume phenomenon.

 INSPECTION & MAINTENACE

MOST POWERFUL INSPECTION TOOL

EYES are most valuable; take care of your eyes

THUS VISUAL INSPECTION IS THE MASTER OF ALL TESTING

Before starting any inspection, make sure that you should be equipped with.

• Safety Dress ( Boiler suit, Helmet, Eye Goggle, Safety Shoes, Knee pad, Safety Belt)

• A Power full torch

• A Scale and measuring Tape

• A pen with a small writing pad

• A marker and Chalk

• A Camera with proper holding arrangement

•Availability of drawing/relevant information of parts to be inspected

•Boiler spare Parts & ash in a cooled condition

•Sufficient Illumination and proper scaffolding.

•Electrical connection removed

•Boiler isolated from another system

 •At least one semi-skilled labor for accompanying during the inspection

FURNACE

• Check furnace water wall tube for any abnormal external scale or soot deposit. 
• Try to find out the cause and analyze this deposit wrt fuel feeding, combustion, SA air nozzle location, etc.
• If the deposition appears to be abnormal, it is advisable to have an analysis of this deposit. 
• Analysis of same shall also provide the characteristics of fuel and its combustion-related properties.
• Carry out thorough visual inspection of water wall tubes for swelling or thinning. 
• Try to inspect the tubes viewing from bottom to top with the help of a torch light. This type of nonconventional inspection will highlight the swelling spots.
• For thickness reduction (either through corrosion or erosion mechanism), always inspect the areas near fuel feeding and 

Secondary Air Nozzle insertion location into a furnace.

• Carry out Thickness gauging from a reliable thickness meter at the predetermined spot to have a record of the same and to have a comparison at a later date for monitoring the thickness  

Reduction, if any.

• Check and take corrective action for Fuel Spreader parts projected inside the furnace for wear and tear. Overheating and distortion of such items can be ruled out.
•  Any welding done directly with the tubes for supporting or refractory holding purposes may require Dye Penetrant testing. This testing will be able to detect crack development.
•  Check the tightness of the buck-stay bolt

Operation And Maintenance Of Power Plant

 BOILER BANK

• A boiler bank is an area that can not be inspected as a whole due to constraints in approach. Hence many areas which are prone to damage (erosion) can not be spotted easily. However, it is a must to inspect all the tubes in the areas of flue gas turn. Generally, manholes are provided at these locations.
• Check the thickness of tubes sideways (3 & 6 O ‘clock position) at these locations.
• Check the condition and Integrity of baffles provided for Flue gas turns. Any by-passing of flue gas from the designed flue gas path shall erode the tubes locally at a high rate; hence sufficient care needs to be given while inspecting these areas.
• One may also take the help of modern instrumentation like Fibroscopy, RFET, LFET, or IRIS for inspecting the same.
• Water drum top surface in boiler bank zone shall also be inspected, specifically if ash contains corrosive elements. 
• We also advise checking randomly selected tubes by hands/fingers through steam or water drum at expanded portion for any abnormality.
• Do not forget to inspect tubes in the vicinity of soot blowers.

SUPERHEATERS

• Check tubes visually for a specific soot deposition pattern. 

  Remember, any particular pattern of soot deposition on super 

  hater coils, both vertically as well as horizontally, shall reflect 

  the combustion and flue gas pattern.

• Check superheater tubes for any overheating or thinning symptoms. Although Thickness gauging can reflect the eroded portion, for overheating /swelling damage, it is useful to make a Gauge equivalent to the OD of the tubes and then check. This is a fast and helpful way to detect the 

 Swelling, if any.

• Check the gap between the bottom bend of the superheater coil and the Gooseneck tube. Record it and cross-check it with the specified gap. Any abnormality in this shall reflect the expansion, supporting related problems exclusively for that loop.
• Check specifically the superheater sealing area for any rubbing or gaps at the roof intersection point. The gap observed in this area shall cause flue gas leakage during operation, and rubbing may lead to failure at a later date.
• The pitching of the coil and supporting arrangement need to be seen and recorded for comparison at a later date.
• It is advisable to take a photograph of superheater coils in position prior to boiler light. This will help in comparing the misalignment at a later stage. 

• ECONOMIZERS

• AIR HEATERS

• STEAM DRUM

OTHER INSPECTION AREAS

•  Check the condition of supports (specifically hanger supports).
•    Inspect ID fan impeller, suction cone, and related ducting 

For any abnormal wear and tear.

• Have a look at expansion joints provided in the main flue gas 

     Passage. There is every possibility of leakage/ingress 

     through the gaps.

• Do not forget to attend to the areas of leakages that were 

     identified during the operation of the boiler

• Check the condition of the refiring grit nozzle & its location
• Inspect Stoker from Catenary for any abnormal wear of Grate bar and damage of Supporting beam, chain, and other parts.
• Check condition, Integrity, and ash deposition on guide baffle plate provided in various ducts.
• Check Ducts & Hoppers for any distortion, overheating, or refractory damage ( if provided)
• Check & Mark the leakage area from the furnace and ducts.
• Check the condition of Grit Interceptor pipes for erosion or damage
• Check Deaerator Spray nozzles, condenser & Tray supporting arrangement