BOILER INSPECTION GUIDELINE
Regardless of the original equipment manufacturer, NEE Process Solutions can offer engineering
know how not only to improve unit performance and reliability but also to eliminate operating and
maintenance problems Boilers of the PC or CFB type.
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PURPOSE OF BOILER INSPECTION
The purpose of a Boiler Inspection is to:
Use planned outage time effectively to ensure that unit availability, safe operation and
equipment life is maintained.
Reduce forced outages due to maintenance failures.
Effectively plan outage-required preventative maintenance activities and periodic
replacement of normal wear parts.
A typical boiler inspection will deal with the following component areas:
Waterside
Fireside
Boiler Externals
Fuel Firing Equipment
Air/Flue Gas Systems
Auxiliary Equipment
Controls (if necessary)
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OUTAGE OBJECTIVES
Major scheduled outage should be structured around customer objectives:
Perform known maintenance tasks.
These items are scheduled based on historical data, past outage inspections or items noted during
the pre-outage operational unit walk down.
Inspect equipment to identify areas needing repairs.
Certain equipment can only be inspected during non-operational periods.
Perform preventive maintenance tasks.
Scheduled or routine maintenance includes such items as turbine bearing inspections, hydrostatic
testing of pressure parts, checking and documenting tube minimum wall thickness, packing valves,
etc.
Upgrade equipment and make design changes as part of a plant betterment program.
Implement state-of-the-art improvements to enhance unit operation and eliminate generic design
problems identified by the manufacturer.
Establish a maintenance history for future use.
This objective is perhaps the most important. It helps reach the goal of all the proceeding objectives
and is required if an ongoing comprehensive maintenance program is to be effective. A maintenance
history is developed by thoroughly documenting the outage and inspection findings for every
scheduled outage.
PERFORMING THE INSPECTION
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The boiler inspection identifies and evaluates problem areas (current and potential). This allows the
service engineer to recommend repairs and solutions. The problem areas will have varying levels of
priority.
During an outage, every portion of the unit is thoroughly inspected. The inspection is divided into
three general categories:
The pre-outage walkdown, in which the entire unit and its subsystems are inspected under
operating condition.
The internal inspection of the unit after shutdown and its subsystems
The post-outage start-up inspection in which all the equipment is checked as it is returned to
service.
Inspection activities include visual observations, comparisons, measurements and non-destructive
examination techniques. Accurate record keeping of findings as well as careful labeling of items in
the field will make it easier to communicate punch list items and write the final report. Photographs
are another method to capture and express details.
PRE-OUTAGE WALKDOWN
The pre-outage operational unit walkdown is a significant first-step of the unit inspection. While the
unit is on line, the inspector can assess the operating conditions of the unit and note any
discrepancies that require attention during the outage. Several problem areas are more apparent or
best observed while the unit is still in operation, i.e. safety valve leakage, expansion trams, load-
spring hangers, insulation leakage, etc.
The walkdown should cover the complete unit from top to bottom and all the auxiliary systems.
Auxiliary systems are noted here to demonstrate the scope of a complete unit walkdown.
Structure Components
Boiler Support
Inspect all boiler hanger rods for integrity. Inspect variable load and constant load spring hangers
for loading indications. Note any bottomed-out spring hangers. Also, note any loose hanger rods.
Check all vertical and horizontal buckstays for warpage or misalignment. Inspect all buckstay
stirrups, bolts, nuts, and washers for integrity. Check expansion trams for alignment and note
readings at all reference points with the boiler hot.
Structural Steel
Inspect the structural steel for any interference with the boiler or auxiliary equipment. Inspect the
grating and walkways for missing or loose sections. Check handrails for any missing or broken
sections. Make note of all discrepancies.
Insulation and Lagging
During walkdown, inspect for any areas of missing insulation. Check for discoloration of the
insulation, which would indicate leakage of hot gases or air.
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Check duct insulation in areas of expansion joints for signs of buckling. Ensure the presence of
insulation in areas around inspection ports, sootblowers, and access doors. If possible, check areas
of poured refractory for damage. Note all problem areas observed.
Upper Level Components
Safety Valves
Inspect for leakage around the stem or packing. Note if the valve is leaking across the seat so that
some amount of vapor is discharging from the vent piping. Check for pluggage in the drip pan.
Check for binding or interference between the safety valve and vent piping. Make note of abnormal
conditions.
Sootblowers and Furnace Probe
Check for local and remote operation by cycling each sootblower through its operating sequence.
Check for steam leakage in the sootblower supply lines, valves, and swivel tubes. Check the
sootblower wall box for damage. Check the drive mechanism on all sootblowers. Make sure that
cranks and tools are available to retract a sootblower that has stopped in the "advanced" position.
Observe movement of air heater sootblower swivel mechanism. The furnace temperature probe is
usually made by the same manufacturer as the sootblowers and should also be inspected at this
time.
Fuel Components
Ignitors
Operator to remove operating ignitors from service in order to check the indicator lamps on the local
ignitor control station. Have operator place each ignitor in service to verify operation and to check
the indicator lamps. Inspect electrical cables, oil, gas, and air supply lines.
Tilting Tangential Firing System
During walkdown, check the nozzle tilt indicators for degree of tilt indication of the fuel and air
nozzles. Check all overfire air nozzles for degree of tilt. All corners of tilt indicators should be within
5° of each other.
While in this area, inspect all coal piping entering the windbox for wear, damage, or leakage at
elbows or couplings. Also check all fuel pipe hangers. Note the position of all windbox air dampers
as indicated by the scribe mark on the damper shaft. All dampers on the same elevation should be
at the same position. Inspect the windbox and related duct work for leakage.
Oil Guns
The oil guns are located with the fuel and air nozzles in the corners of the furnace. Check all oil and
steam or air lines for leakage; check all related piping and valves; inspect the oil gun advance and
retract mechanism; and check that spare oil guns are properly cleaned and stored.
Coal Piping
Inspect the coal pipes for indications of wear. Check the coal pipe couplings for signs of leakage. If
so equipped, check the coal pipe constant load spring hangers. Examine for any coal pipe related
expansion problems.
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Coal Feeders
During the inspection of an operating gravimetric feeder, check the position of the tension pulley,
the feeder belt tracking, and the integrity of the feeder housing. Broken observation windows or
improperly closed doors negate this safety feature of the feeder.
On a C-E volumetric feeder, inspect the drive clutch assembly, the movement of the hinged leveling
gate lever, and the feeder housing. Check the drive motor and gear reducer for unusual noises and
verify proper lubrication levels.
Pulverizers
Inspect the mill foundation for cracks. Check the gear case for proper oil level, temperature, and
signs of leakage. Examine the material being rejected from the mill; excessive coal discharge could
indicate worn or improperly adjusted mill internals. Verify the movement of the three journal
assemblies for uniformity. Inspect the separator body for signs of coal leakage. Make a notation of
the classifier settings; they should all be the same. Inspect the mill motor, filters and foundation.
On exhauster type mills, check the exhauster casing, foundation, and bearing assembly. Check for
excessive noise or vibration from the pulverizer gear housing and exhauster bearing housing.
On pressurized pulverizers, check the gear case and journal seal air systems for leakage or crimped
lines.
Fuel Handling Systems
Inspect all coal handling systems. Note any excessive spillage or accumulation, and check all oil and
gas piping for leakage.
CFB Boiler Limestone Feed System
Inspect the limestone feed system for erosion, loose mounting hardware, proper clearances and
binding of rotating equipment. Note any excessive spillage or accumulation, and check all oil and gas
piping for leakage.
Auxiliary System Components
Air Preheaters
Inspect the upper and lower bearing assemblies. Check oil level and for oil leakage. Listen for any
loud noise, which might indicate problems with the air preheater seals. Check the drive motor and
gear reducer for signs of oil leakage, and verify the operation of the air preheater sootblowers.
Fans/Air and Gas Ducts
Check for the following: foundation cracks or loose anchor bolts, vibration meters for excessive fan
or motor vibration, motor amp readings, and bearing temperatures. Inspect fan housings for
damage and check all air and gas ducts for leakage, expansion problems, and missing insulation.
Ash Removal Systems
Inspect all piping for leakage and pluggage.
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Boiler Water Circulating Pumps
Inspect motor and related piping for leakage. Check the pump suction and discharge pressures.
Check and record motor cooling water temperatures. Compare data to normal operating conditions.
Note abnormal conditions.
Pre-boiler Systems
Check all components and piping for leakage. Check all components for any missing insulation.
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INTERNAL INSPECTION – WATER SIDE PRESSURE PARTS
The internal inspection requires unit downtime. Lots of maintenance activity is also scheduled
during the outage. The internal inspection activity is complex and covers a large work area.
This section covers only the water-side pressure parts of an inspection plan.
Steam Drum and Internals
Examine the steam/water separating equipment. Inspect the turbo separators, both the primary
and secondary stages. Look for corrosion, deposits, erosion, missing parts, etc. Examine the
condition of the corrugated plate dryers and the return piping.
During inspection:
Check the condition of the seal around the manway door.
Check the area around the inside of the manway door.
Check the interior of the drum for corrosion and deposits.
Check the condition and mounting of the chemical feed pipe, the blowdown pipe, and the
feedwater distribution header.
Check the downcomer nozzles, screens, and vortex eliminators.
Check all drum internals for wear and fit.
Thoroughly examine the drum liners for cracks. Cracks in the liner will allow boiler water to bypass
the steam separation equipment and allow the carryover of suspended solids into the superheater.
Lower Waterwall Drums
During inspection, crawl through the drum checking for cracks or crack-like indications particularly
around nozzle welds and manway access doors.
Generally, these cracks are shallow, not much deeper than 1/32". Usually found on the wetted
surfaces of the drum is a corrosion indication, which could play a part in promoting a crack
penetration.
If cracks or crack-like indications are found, determine the depth by a number of spot grindings.
Information on the depth together with the specific location of the cracks will permit calculations to
be made to determine whether the remaining material thickness is sufficient to meet the
requirements of the ASME Boiler Code for New Boiler Design and Construction.
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During inspection, check the screens or strainers located in the drum. These screens prevent foreign
material from plugging the orifices. The screens must be intact and firmly secured in place. If any
large holes have developed in the screens, recommend that they be replaced.
Typical Lower Drum Arrangement
Check the locating pin, orifice clamp, and fastener for deterioration, fit, and tightness. Check for
gaps between the orifice adapter and header counter bore. If gaps are found, the adapters may
need to be replaced, repositioned, or repaired.
Check the diameter of the furnace wall supply tube orifices using "Go/No Go" gages. If an orifice is
found to be worn, that is, the opening is enlarged, recommendation should include replacement.
The orifice plates assure that each tube circuit gets an adequate flow depending on its location in
the furnace. Orifices are numbered for reference and have indexing holes so they cannot be
incorrectly placed. Orifices could be either fouled or plugged with deposits, or enlarged by wear or
corrosion. If the orifice is fouled, that is, the opening restricted, recommendations include cleaning
during the outage (if possible) or replacing. Check the orifice mounting and locating pins, and the
clamp and fasteners for signs of deterioration and looseness. Inspect the orifice adapter for signs of
bypassing flow. If problems are found, recommendations might include replace, reposition, or repair
the adapter.
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Headers
To perform an internal examination, remove the handhole inspection ports on the header. Examine
the interior for corrosion, deposits, or any other foreign material. Check the area around the
handhole for any signs of cracking. Check the handhole port seal.
During an external examination, visually check the entire header for corrosion, erosion, etc. Visually
check the header nipple welds for signs of cracking. Note cracking and make recommendations for
repair.
Header Inspection
If the header is insulated or covered with refractory, note the condition.
Also inspect all other welds, especially for different material welds (DMW), near the header. If any
cracking is found, determine depth and location, and consult Engineering for recommended repairs.
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Inspect the area around each header for signs of potential problems. Inspect the area where a
header penetrates a wall or floor for cracks or expansion problems.
Check all hanger rods for tightness. Also check condition of hanger rods, clevises, and clevis pins for
bowing, overheating, and damage. Hanger rods are made of a tempered material and should not be
cut and rewelded. If significantly damaged recommendation should include replacement.
The combined circulation units are supplied with orificed waterwall inlet headers that can be
internally inspected if the handhole caps are removed. These headers should be checked for
cracking, deposits (especially on the orifices), loose marmon clamps, and cracking between the
internal partition plates and the ID of the header. Header cleanliness is a must.
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INTERNAL FIRE-SIDE FURNACE INSPECTION
The second part of the internal inspection is the fire-side (gas-side) or furnace inspection. Again, this
is a large area to inspect, with complex components. This section is divided into component
sections.
Bottom Hopper Area – PC Boiler
The coutant sloped bottom tubes and the bottom ash hopper comprise the lower furnace area.
Inspect casing, plates, screens, and the structural condition of expansion and support members.
Remove all debris, bottom ash, and water remaining in the hopper enclosures. Examine the water
seal trough material and structural condition. Inspect trough for corroded and deteriorated lining
and structural support. Look closely at all welds for signs of cracking and indication of expansion
problems.
Examine the seal plate for indications of corrosion, deterioration, and cracks in the surface.
Inspect splash screen for tears and holes in screen material. Examine all support structures for
indication of expansion problems. Inspect for signs of corrosion and deteriorating conditions.
Inspect drip shield for signs of erosion or corrosion.
The attachment welds securing the drip shields to the waterwall tubes should be inspected and dye-
penetrant checked, if cracks are suspected, as some tube leaks have been experienced at these
welds.
Inspect the slope tubes for signs of erosion, corrosion or thermal stress. Problems in this area could
be caused by sliding ash and slag, chemical reaction of the ash and moisture, splashing or surging,
wave propagation, and flooding during filling. Some possible solutions are to maintain ash hopper
normal water level at least 30" below the tubes and have an overflow capable of handling excessive
amounts.
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Lower Combustor – CFB Boiler
Maintenance Issues for the Lower Combustor / Hearth Zone are directly related to Unit Operation.
Improper SA Flow or drop in pressure can result in overheating of the Lower SA Ducts and Start Up Burners.
Improper PA Flow
o Low flow can cause the Fluid Bed to Slump and ash to enter PA Plenum.
o High flow can contribute to accelerated erosion of PA nozzles.
Start Up curve for refractory cure can reduce some refractory spalling repairs.
Cracks in the Plenum Corners above the header and at sidewall gusset supports due to unit expansion.
Inspection Focal Points
PA Nozzles –ash pluggage, broken, and erosion
PA Plenum –ash build up, gusset supports, corners
FBAC ACV Inlets –Grease Air Ports
SA Ducts –Overheat damage
Fuel Chutes –Ceramic Tiles
Start Up Burners –Erosion, overheating
Ash Return Vents –Gaps
SRD Duct Outlets –Refractory and Grease Air
FBHE Return Ducts –Refractory and FA Nozzles
Refractory –Spalling of ledges
Water Walls for erosion and condition of AMSTAR Spray
Lower Dead Air Space
Inspection includes the examination of all skin casing, insulation, refractory, seal boxes, tube
assemblies, and the structural condition of all expansion and support members, supports, braces,
and hanger rods.
Examine all support structures for broken welds, disconnected, broken, or bent rods and missing
nuts and bolts.
Check for bent or twisted supports.
Check all slope tube support buckstays.
Check all framing supports.
Examine condition of bottom slope tubes.
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Dead Air Space Support Steel and Hangers
Hanger Disengaged from Support
Visually inspect the dead air space for ash accumulations due to gaps at the slope tube membranes.
Also check sidewall casing structure for any indication of defects or cracks.
Damaged Waterwall Slope Tube
Large clinker or ash accumulations can build up in the tube assemblies in the top of the furnace and
eventually fall, damaging the lower slope tubes and the structural steel inside the lower dead air
space, especially near the side wall corners.
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Visually inspect the bifurcated tube membranes for cracking near the membrane end at the bottom
of the side wall tubes above the bifurcate. Dye-penetrant checking of this area is also recommended
if there is any history of tube failures. If tube failures have occurred or cracking is evident, treat the
membrane as follows:
Contour the ends of the membrane welds, creating a smooth radius. Cut the middle of the
membrane back from the end a few inches and drill a hole at the end of the cut. Use a pencil grinder
to remove any rough edges from the cut and hole.
Examine sidewall seal boxes for cracks, tears, and signs of expansion problems.
Side Waterwall Seal Box Crack
Furnace pressure or expansion can cause the slope wall scallop bars to tear adjacent to the sidewall
scallop bars. The tear can extend into the side wall tube, causing a failure.
Inspect seal plate condition where waterwall downcomers penetrate lagging. Check expansion
joints (boots) at the lower strut penetrations.
Furnace Waterwalls
Lower Sidewall Tubes
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Inspect the lower sidewalls, looking for signs of erosion caused by sliding ash. Also examine the area
around the lower sootblower openings for erosion.
On many units, the lower sidewall tubes at the center point are tied together by a solid plate.
Failures have occurred in this area, along the tube membrane, due to fatigue resulting from
concentrated areas of thermal stress or corrosion attack, at the high stress concentrations. Inspect
this area, looking for signs of fatigue or corrosion. If damage is found, replace the first two or three
tubes to either side of the centerline and implement the lower sidewall modification.
Furnace Bottom Slope Tubes
Inspect waterwall tubes in the coutant bottom for gouges, dents, bowing, and overall damage due to
slag falls, slag erosion, or a combination of the two.
Erosion (abrasion wear) from tumbling and sliding slag or flyash can wear down the tube surface
exposed to the furnace area. When this happens, the tube can fail from excessive thinning or from a
minor slag fall rupturing a weakened tube wall.
Large sections of slag from the upper furnace can dent the tubes and rupture them at the impact
area or cause an overheating failure elsewhere due to restricted flow.
Failure can occur in the dead air space side of the tubes, at the steel support lugs. The great force of
slag falls can deflect the hopper slope tubes along with the support steel.
Inspect for leaks in the sealed membrane. Leaks can result in overheating of the structural support
steel in the dead air space.
GUIDELINE
When evaluating gouges and dents in slope tubing, indentations that reduce the wall thickness
below the original Minimum Wall Thickness (MWT) should be considered for repair.
Tubing should be considered for replacement when wear or corrosion has reduced wall thickness
below original MWT.
Individual tubes or tubing panels should be considered for repair or replacement when warpage or
bowing has deflected the tube(s) more than 1 tube diameter out of line.
Waterwalls
Thoroughly inspect all waterwalls. Give particular attention to the following
Waterwalls around sootblower openings
Waterwalls around the windbox openings
Waterwall corners
Waterwalls in the high heat absorbing areas
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The extended side walls
Examine waterwalls around sootblower openings for erosion and wear.
Inspect the tubes adjacent to the blowers frequently to determine tube wall thickness. Ultrasonic
testing equipment and actual measurements can be helpful in determining any tube wastage.
If erosion is noted, check the alignment of the blower. The centerline of the swivel tube should be
perpendicular to the face of the boiler tubes. Check the distance of the centerline of the cleaning
nozzle to the face of the boiler tubes.
Inspect the waterwall tube membrane at the sootblower opening. In some instances, this
membrane can be relieved with a saw cut through the center.
Examine the waterwalls in the vicinity of the firing zone for corrosion and wastage. Thoroughly
check the walls around the windbox and corners.
Adjust coal fineness to prevent coarse coal from reaching the furnace.
Maintain equal distribution of coal to all fuel nozzles. Verify by clean airflow distribution testing of
the pulverizers and/or coal line mass flow tests.
Centerwall
On divided furnace units with centerwalls, observe and record the amount and direction of
centerwall tube panel bowing. While some panel bowing is acceptable, bowing in excess of several
feet out-of-plane may be indicative of operational or structural problems and should be investigated
further.
Deflection Arch
Rear waterwall tubes form the deflection arch, projecting forward at the top of the furnace rear wall
and then sloping back underneath the superheater and reheater vertical spaced assemblies.
Examine the upper arch for signs of erosion. Flyash/sootblower erosion can cause considerable
damage to the tubes and peg fins.
Closely inspect arch tubes adjacent to the furnace centerline for evidence of sootblower erosion.
Erosion is more prevalent in this area due to the droop of the lance as it is extended into the
furnace.
Check the entire arch. Depending on unit operation, erosion can occur either on the nose or 3 to 4"
above the bend. Eddying of flyash above the bend can result in even wear, problems may be
difficult to detect by visual observation.
Refractory under the tubes can be eroded away exposing the skin casing, resulting in skin casing
cracking and warping. On newer units the upper arch tubes will be of solid membrane design, which
in most cases has eliminated skin casing problems. Overheating of upper dead air space support
members can also result and can affect the structural integrity of this area.
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Examine the rear waterwall hanger tubes for erosion. The backs of the rear waterwall hanger tubes
are susceptible to flyash erosion where they penetrate the upper slope of the arch. To prevent
damage and subsequent ruptures, these tubes should be shielded at least 4 to 6" up from the arch
tubes and extend shields down to the seal box. In some instances, abnormal flue gas velocities
under the pendants will erode the front side of the tubes. To prevent damage these tubes should be
shielded at least 12" up from the upper arch tubes.
Check all penetrations through the arch for indication of seal damage. Check the steam-cooled
spacer tubes for erosion where they penetrate the upper arch.
Check for extended sidewall movement. Sidewall tubes can move away from the wall by as much as
1 to 1.5" allowing flyash to work its way down and bow the casing.
Check clearances between the reheater vertical spaced assemblies and the deflection arch
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Superheater Assemblies
The superheater inspection includes the external examination of all tube assemblies. It also includes
the examination of all fluid, steam, and mechanical spacers, tube shields, pad welds, flexible spacers,
and band type spacers.
To inspect the superheater, erect scaffolding or sufficient sky-climbers must be provided to
effectively conduct a thorough examination of all superheater assemblies and support members.
Inspect all vertical superheater assemblies for signs of hard ash deposits. If the deposits are
significant, recommend removal at this time.
Examine each group of assemblies separately, since each group is affected differently by gas flow.
Review previous inspection reports, then determine areas of concern.
Inspect tube assemblies for any sign of failures in the area of dissimilar metal welds. Variables that
can promote this failure are the following:
High temperature
Time in service
Differential expansion
External loading
Cycling of unit
Inspect all tube assemblies for any signs of warping, bulging, and swelling, which might be
indications of overheating.
CRITERIA: If tubes are swelled 2% over specified OD, a sample should be taken for analysis.
When measuring tubes, take measurements at least 18 inches from the shop welds or bends. This
eliminates the effects of manufacturing processes on the tube dimensions.
If problems have occurred in the past, recommend removing a tube sample section and send it to
the laboratory for analysis.
Conduct wastage surveys in selected sections to assess the tube wall thickness. Document the
results to compare to measurements in future outages.
Superheater Division Panels
Steam-cooled spacer tubes help maintain the alignment of the division panels and minimize panel
sway. These spacer tubes bifurcate at the front of the furnace and proceed horizontally across the
left and right sides of the division panels. Because of this, wear between spacer tubes and the
superheater division panels can be a problem and can cause considerable damage if overlooked
during an outage.
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During the inspection, examine all elements and assemblies for any indication of bowing or signs of
misalignment. Examine horizontal tubes for misalignment. Broken slip spacers allow horizontal
tubes of the division panels to distort and collect slag. Once out of alignment, the weight of
additional slag could cause the tubes to sag. Realign any tubes out of alignment and add additional
flexible tube ties. Repair any broken flexible tube ties. Consider recommending replacement of any
misaligned tubes, which are badly bent.
Examine misalignment between flexible tube ties. In these areas, tubes can bow out of alignment
mainly due to the differential expansion between the panels. Check for misalignment between the
top and middle level of slip spacers. Check for misalignment between the roof tube and the first
flexible tie. Realign any bent tubes and add additional tube ties.
Examine girdling tubes for misalignment. Tubes bow out of alignment due to tie lugs breaking away
at the weld. This can be caused by the vertical differential expansion between the girdling tubes on
each side of the panel. Check for broken lugs on each side of the panel. Check for broken
connecting straps. Check for wear between the vertical girdling tube and the horizontal tubes of the
division panel. Install new tie lugs that allow for vertical expansion between the vertical girdling
tubes on each side of the panel.
Examine all elements and assemblies for wear. Tube wear between a steam-cooled spacer and the
division panel tubes can easily be seen when the tubes are separated using a pry bar. Mark each
worn tube so they can easily be identified when repairs are made. Inspect for tube wear between
each support lug and the bottom of the steam-cooled spacer. Inspect the steam-cooled spacer
tubes where they cross over between panels. Check for wear between the wrapper of a division
panel and the spacer tube.
Before any repair work is begun, make note of material changes. This information can be found on a
unit material diagram.
Superheater Division Panel Anchors
The front wall anchors for the spacer tubes on radiant reheat units are subjected to severe wear due
to furnace pulsations (Figure 28). In general, the superheater division panels move from side to side
while the front wall moves from front to rear. The radiant reheat inlet header acts like a buckstay to
reduce front wall movement. There is still some movement however, because the front anchors are
located between the radiant reheat inlet header and the top of the furnace.
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Superheater Division Panel Anchors
Thoroughly inspect the division panel anchors and check the spacer tube roller sleeves. They should
be free to rotate, and centered with respect to the offset tube sleeves. There should be a total of
3/8" clearance between the offset sleeves and spacer tube sleeves. Check to see if the collar is
rubbing against the offset tube instead of the spacer tube sleeve. Check for correct clearances so as
not to cause excessive collar-to-sleeve wear. Check for wear on the spacer tube roller shields.
In making recommendations for repair, make note to rotate roller shields so that the non-worn
surface would be facing the anchor tube shields.
Superheater Platen Assemblies
During inspection, examine the fluid-cooled spacer for tube wear. Inspect for wear between the
fluid-cooled spacer and the superheater pendant platen tubes on both sides .
Check for steam-cooled spacer tube wear. At the front of these assemblies, a steam-cooled spacer
tube passes between the first and second tube assemblies. The newer steam-cooled spacer lug
consists of a scalloped lug, a spacer lug, and a support lug located between two flexible tube ties.
Inspect possible wear areas. Inspect support lugs for thinning due to wear or oxidation. Inspect for
spacer lugs that may have come out of the support lugs.
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Replace spacer and support lugs if required. Type 309 stainless spacer and support lugs should be
used for increased alignment and durability. An arrangement utilizing spacer and support lugs on
both the top and bottom sides of the steam-cooled spacer tube provides the maximum amount of
alignment security.
Examine the assemblies for misalignment due to broken flexible tube ties. Realign any bent tubes by
placing channel pieces with nuts and bolts on both sides of the assembly to draw the tubes back in
place. Replace any broken flexible tube ties and add additional ties as needed. It may be helpful to
add a vertical girdling tube similar to those on the superheater division panels to maintain tube
alignment at the bottom of the assembly.
Examine any misaligned tubes between the flexible tube ties. Misalignment here is most likely due
to the differential expansion between dissimilar materials. Expansion problems in this area should
be discussed with the manufacturer before taking corrective action. Misaligned tubes in this area
are very susceptible to sootblower erosion. Recommend that tubes are realigned and additional
flexible ties added, providing they have not been subjected to erosion to the extent they would
require tube repair or replacement. Inspect for broken slip spacer and saddle lugs on the lower
sections. This would allow tube misalignment and tube-to-tube wear.
The outside wrapper tubes on each assembly should be examined for sootblower erosion. Inspect
for erosion of the outside wrapper tube in the area of tube metal change. Inspect for missing tube
shields or tube shields that have slipped down.
If sootblower erosion is a problem in this area, examine the sootblowing system. Check for
condensate in the steam blowing system. If condensate is present, check the thermal drain system.
Excessive steam pressure can cause rapid erosion. Check that steam pressure and temperature
match setpoints. Check frequency of sootblower operation. High concentrations of flyash can also
increase the erosion process.
Superheater Pendant Spaced Assemblies
The superheater pendant spaced assemblies are located directly above the furnace arch. This area is
susceptible to deposit buildup, wastage due to the combined effect of gas flows and high flyash
concentrations, and tube misalignment.
During the inspection, thoroughly examine this area for deposit buildup, abnormal wear or wastage,
tube misalignment, slip spacer condition, and support lug condition.
Inspect the front and rear steam-cooled spacer tubes at the points where they contact the assembly
tube elements.
Inspect for missing tube shields. Recommend repair or replacement of broken strap welds.
Conduct a wastage survey to assess wall thickness in the leading edges of every 10 assemblies above
the long retractable sootblowers and at the rear of the assemblies.
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Examine all flexible tube ties in this area for indications of cracking and broken welds. Flexible ties
can come out of alignment due to a restriction in movement, which could be caused by ash
accumulation under and between assemblies.
Low Temperature Horizontal Superheater Assemblies
The low temperature superheater assemblies can be either vertically hung pendant assemblies or
banks of horizontal assemblies, depending on boiler design, and are located in the backpass of the
boiler above the economizer. The horizontal assemblies are very susceptible to uneven
temperatures due to the cooler economizer outlet terminal tubes (horizontal superheater support
tubes) passing through the support saddles and causing the adjacent superheater metal surfaces to
be subcooled, relative to the rest of the tube surfaces.
During the inspection of the horizontal superheater, inspect for superheater tube pairs bowing away
from each other due to the uneven temperatures. If the tubes are not breaking away from the
saddle support, leave them alone until the next inspection. Check for flyash erosion on the front
return bends of the horizontal superheater, especially if the front bends extend above the backpass
floor. If this is a problem, recommend installing a method to shield the bends with stainless steel, or
install baffles to redistribute the gas flow adjacent to the tube bends. Whether a refractory or metal
plate baffle is installed, it should be installed so that the baffle is horizontal and does not slope
downwards towards the superheater tubes. This slope will accelerate wear on the tubes as gas and
ash sweep downward off the baffle onto the tubes.
Check for flyash pluggage between the rows of the horizontal superheater tubes. Check for flyash
erosion and pluggage at the rear wall and horizontal superheater assemblies.
Reheater Assemblies
The reheater inspection includes the external inspection of all tube assemblies. It also includes the
examination of all tube shields, pad welds, and mechanical spacers (flexible and band-type).
To inspect the reheater, scaffolding must be erected so that a thorough and safe inspection of all
reheater assemblies and support members may be conducted.
Inspect all vertical spaced reheater assemblies for signs of hard ash deposits. If hard ash deposits
are significant, remove them at this time.
Examine each group of assemblies separately, since each group is affected differently by gas flow.
Review previous inspection reports to determine areas of concern.
Inspect tube assemblies for any signs of failures in the area of dissimilar metal welds. Variables that
can promote this failure are:
High temperature
Time in service
Differential expansion
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External loading
Cycling of unit
Inspect all tube assemblies for any signs of warping, bulging, or swelling, which might be indications
of overheating.
If problems have occurred in the past, remove a tube sample from a section and send it to the
laboratory for analysis.
Conduct wastage surveys in selected sections to assess the tube wall thickness. Document the
results to compare with previous wastage measurements and what will be taken in future outages.
Radiant Reheat Front Wall and Side Walls
The radiant reheat front wall and side wall tubes are located in the upper portion of the furnace
waterwalls in the area surrounding the superheater division panels.
During inspection of this area, check for bowing of the front and sidewall tubes. Realign as
necessary. Check for tube swelling due to overheating. Replace tube sections as needed. Check for
tube erosion, especially at the lower bends where the tubes go through the wall. Pad weld if needed
and install tube shields.
Check for tube metal loss due to tube rubbing. If metal loss is found, recommend installing stainless
steel tube shields at the points of contact. The tube shields should not be seal welded.
Reheater Vertical Spaced Rear Assemblies
The reheater vertical spaced rear assemblies are located after the reheater vertical spaced front
assemblies at the top of the arch.
Install wear strips in crossover tubes where there is contact with the rear waterwall hanger tubes.
Check for broken, burned off, or disengaged slip spacers.
Reheater Vertical Spaced Front Assemblies
The reheater vertical spaced front assemblies are located after the superheater platen assemblies
and are suspended above the arch.
Check broken or missing slip spacers on the front and rear sides of these assemblies, and note
location. Inspect all tube assemblies for signs and magnitude of bowing. Note location and severity.
Measure wastage on the leading elements of the assemblies in the area of the long retractable
sootblowers and record wastage. Sootblowers normally erode only lead tubes in an assembly
(unless out of alignment), but erosion can occur on second, third, or fourth tubes, etc. Appendix D
includes samples tables that are used to collect this data.
Check for flyash erosion resulting from vertical surface pluggage. This erosion can occur as much as
five to six tubes deep in an assembly. One possible cause is high velocity gas erosion, due to the
channeling of gases in a vertical section. This can develop when a reheater vertical section
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experiences severe pluggage, possibly due to a change to high sodium coal or misalignment of
vertical tube assemblies. Sootblowers cut flow path channels through the pluggage, which
eventually grow smaller and deeper into the bank. The resulting orifice creates high velocity uneven
gas flow distribution that is directed at the inner vertical tubes.
Flyash erosion on vertical tubes, resulting from plugged conditions typically exhibit areas of cratered
and protruding surfaces quite different from the classical, generally smooth flyash erosion patterns
found on screen tubes and rear pass horizontal surfaces.
If pluggage occurs during operation, determine the degree of it through the use of observation doors
or by an increase in gas side pressure drops, and in some cases by changes in individual tube
element steam temperatures.
During an inspection, examine closely the vertical sections known to be susceptible to plugging.
Failures due to high velocity gas channeling should be reported as flyash erosion and a description of
the pluggage and the circumstances should be carefully documented.
Check reheater vertical spaced front assemblies and furnace deflection arch for clearances (Figure
30). Inspect condition of tube shields and note locations of missing tube shields. Appendix D
includes samples tables that are used to collect this data.
Check condition of high crown seals where tubes penetrate the roof.
Rear Waterwall Screen Tubes
The rear waterwall screen tubes are located behind the rear waterwall hanger tubes. As their name
implies, they are formed by the rear waterwall tubes forming the arch and bending upward toward
the roof.
On some units, a refractory kicker baffle has been installed at the base of the screen tubes to
redirect the gas flow entering the horizontal SH and economizer sections. Flyash erosion can also
occur on the screen tubes directly above the kicker baffle. If erosion is evident, remove the top 2” of
refractory kicker baffle. Recommend exposing any eroded areas and repairing screen tubes as
required.
Conduct a wastage survey to determine where tube shielding is required. Shield screen tubes with
at least 12” of 309 stainless steel, in such a way that the bottom of each shield rests on the
remaining refractory kicker baffle. Recommend replacing the upper portion of the refractory kicker
baffle so that the bottom of each shield is embedded in the refractory.
Further up on the screen tubes, examine welded-tie vibration restraints for evidence of cracking
(Figure 31). If cracks are found, recommend repairing the affected tubes. If frequent tube failures at
these restraints have been responsible for excessive downtime and/or damage to adjacent tubes, an
additional row of vibration restraints may be required above the welded restraints.
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Rear Waterwall Hanger Tubes
The rear waterwall hanger tubes are located above the deflection arch between front and rear
sections of reheater vertical assemblies. The hanger tubes are furnace rear wall tubes, which pass
straight upward from the furnace rear wall through the deflection arch upward to the roof.
Inspect all existing tube shields and pad welds . Look for cracks in welds, which are an indication of
problems resulting from temperature differentials.
Inspect the hanger tubes for wastage, especially at the top where they intersect with the roof tubes
and at the bottom directly above the slope tubes. If erosion seems uniformly excessive at any point
across the hanger tubes, a wastage survey is recommended.
The backside of the hanger tubes is susceptible to flyash erosion directly above where they
penetrate the arch tubes. The hanger tubes should be shielded anywhere from 4 to 6" from the arch
tubes. The shield should extend down to the seal box. In some instances, flyash laden flue gas will
flow under the pendant assemblies at higher than normal velocity, eroding the front side of the
hanger tubes. The hanger tubes should be shielded up to at least 12" from the arch tubes.
Inspect steam-cooled spacer tubes where they pass between hanger tubes. Inspect for wear at
contact points with the steam-cooled spacer tubes. Pad weld and install wear strips as required.
Examine hanger tubes in proximity of sootblowers. If erosion is evident, shields may be installed,
extending 2 to 3" above and below the centerline of the sootblower locations.
Closely inspect all welded tie vibration restraints for weld cracking which may be caused by vibration
due to combustion gas velocity or stress caused by ash loading.
Upper Dead Air Space
The upper dead air space is located at the top of the furnace between the furnace arch and the
backpass. Inspection includes the examination of all skin casing, insulation, refractory, tubes, and
the structural condition of expansion and support members.
During unit operation, local temperatures inside the upper dead air space are approximately 800F.
If casing leaks develop allowing furnace gases to enter the dead air space, temperatures can
approach 1500F. Overheating of structural steel at these excessive temperatures can lead to
distortion, loss of structural integrity and possible failure.
Visually inspect all supports, braces, and hanger rods for structural integrity. Randomly perform a
"tuning" operation on the hanger rods to check structural soundness by tapping the rod with a metal
instrument.
Examine all support structures for broken welds, bent rods, and missing bolts and nuts. Inspect for
bowing due to extreme temperatures. Examine for cracks, oxidation, and deterioration. Determine
how severe the problem is and explore possible methods for reducing or eliminating excessive
damage.
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Examine all hanger rods and support structures for integrity. Broken, missing or loose clevis pins and
rods must be replaced and properly tensioned. Inspect rods for elongation due to high
temperatures. Examine all turnbuckles for cracked, missing, or weakened assemblies.
Visually inspect all casing structures for any indication of defects.
Check for loose waterwall hangers.
Inspect for loose floor hangers that extend from the backpass extended sidewalls. Inspect for bent
center row hangers. Inspect for loose horizontal buckstay bolts.
Examine seal boxes. Inspect for cracks, tears, and signs of expansion problems. Examine casing for
indication of warping due to overheating.
Inspect all support buckstays for indication of bulging, twisting, and cracks.
Examine the condition of the refractory around the peg finned bifurcated tube assemblies. Missing
and deteriorated refractory and insulation material can cause erosion, overheating problems, and
heavy flyash buildup in this area. Remember that support structures are designed for a predicted
load and stress.
Any amount of skin casing expansion that is greater than the tube expansion must be absorbed by
the expansion joint that runs from left to right. Recommend repairing. Details are in Appendix G
Reduce sootblowing frequency and pressure if frequent tube erosion or refractory and casing
damage is evident. Recommend installing shields on the furnace side between the tubes, on top of
peg fins. On newer units, the rear waterwall upper arch will have a solid membrane between the
tubes instead of peg fins, which in most cases has eliminated the skin casing problems.
Inspect for structural damage at the roof of the dead air space. Reheater front vertical spaced
assemblies are located above the tubes forming the roof of the dead air space. Structural steel
damage occurs when flyash builds up under these assemblies which expand downward. The tube
assemblies push on the ash, which in turn pushes on the roof tubes and structural steel under them.
This flyash restriction can cause roof tube and reheater damage in addition to the structural steel
damage. If necessary, recommend installing sootblowers in this area to minimize ash buildup.
Furnace Roof Tubes
From inside the furnace, conduct a visual inspection of furnace roof tubes. List discrepancies on a
diagram showing plan view of the superheater and reheater assemblies (Figure 33). Inspect
refractory condition, noting any missing refractory. Inspect for sagging roof tubes, paying particular
attention to sidewalls. Check for worn or burned peg fins and missing refractory at the
steam-cooled spacer penetrations.
Continue the inspection inside of the penthouse, especially where sagging roof tubes or missing
refractory are observed. Check for skin casing overheating, deformation, or cracks. Inspect for
cracks in the seals around the superheater and reheater pendant assembly tubes where they pass up
through the roof tubes.
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Economizer
The economizer is located behind the rear low temperature horizontal superheater in the lower
section of the boiler backpass. The economizer is a bare tube, arranged in-line unit.
Inspect each of the banks of the economizer for polishing, tube alignment, and pluggage (Figure 34).
If erosion is a problem, consider recommending the installation of tube shields.
Check front and rear return bends and bare tube surfaces for metal wastage. Ultrasonic testing of
tubes is recommended when heavy polishing or erosion is evident.
Inspect for polishing around sootblower openings.
Check clearance between tube bends and the backpass walls, and between headers and sidewalls.
Examine all economizer support tubes. Check for tube misalignment. Check for tube erosion due to
flyash and gas flow. Inspect material condition of tube shields. Check for wear resulting from
metal-to-metal contact between the vertical support tubes and horizontal economizer tubes.
Inspect all elements for possible pluggage problems and investigate material condition of elements
covered with ash.
Check for flyash/sootblower erosion of tube bundle support hangers.
Inspect for broken support straps. Install additional straps as required. Pull up any elements that
may have sagged due to broken straps. Check for gouging between hanger supports and tubes.
Examine all wire mesh and refractory baffles and the tube surface condition under the baffled area.
Inspect expanded metal screens for tears, holes or missing sections. Inspect refractory baffle
condition noting missing, eroded, or crumbling sections. Inspect for tube wastage where the
refractory ends. In some instances where the tube return bends may be coated with Super 3000,
inspect for deterioration of refractory especially after water washing this section.
Inspect for gaps behind baffles at sidewalls. Increased gas velocities can polish the side wall tubes.
If any gaps are found, recommend installing mesh and filling with Super 3000 refractory.
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Examine condition of refractory at sidewall tubes and recommend repair as necessary.
Examine all header assemblies for metal wastage due to erosion. Outside diameter measurements
will indicate wear patterns. Inspect welds around tube nipples and headers for cracks. Install
erosion shields if necessary.
Examine the economizer ash hopper for structural defects. Inspect support steel and hopper
ductwork for signs of overheating and erosion to the refractory layer. Examine hopper for buckling
and cracks due to expansion problems. High temperatures at the hoppers can usually be traced back
to high temperature gases bypassing the economizer assemblies.
Inspect circumferential welds on the economizer inlet header. Check for stress corrosion fatigue
cracking at inlet tubes.
Penthouse
The penthouse is dead air space located on top of the unit. It houses all of the headers, which are
located in this area, along with the steam drum.
The amount of ash accumulations in the penthouse dictates whether or not removal is necessary
before, during, or after the inspection. If the ash is uniform in depth, it should be removed prior to
inspection. If repairs are required, remove the ash before or during the outage. If small individual
piles of ash are present, inspect the penthouse before ash is removed (individualized piles of ash
indicate areas of possible casing leaks). Exercise care while vacuuming; the ash will retain heat for a
longer period of time than that required for cooling the boiler.
Inspect the penthouse casing structure for any indications of problems. Cracking is the most likely
problem encountered.
Check for cracks in the casing panels that may occur at the transition points, at the junction of tube
assemblies, or at the high crown seals. Recommend repairing large cracks by grinding out the crack
and welding a casing patch in place. Repair small cracks by welding.
Inspect the floor area for cracked or missing refractory. Recommend repairing missing refractory by
patching.
Inspect all supports, braces, and hanger rods for structural integrity. Check all supports for broken
welds, cracks, bent rods, missing nuts or bolts, and for any bowing or any other signs of
misalignment. Check hanger rods for proper tension. Also check for missing or loose clevis pins and
the condition of the hanger rod turnbuckles.
Inspect all pipe braces, supports, saddles, and hangers.
Visually examine all headers located in the penthouse. Selectively check header tube root nipples. If
any problems are found or suspected, check all nipples on that header. Magnetic particle method
would work very well in finding cracks.
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Check the condition of the insulation material on all high temperature headers in this area. Look for
deteriorated or missing insulation along the walls and roof.
Check the condition of all expansion joints in the penthouse area. Look for signs of expansion
problems.
Thermocouples might be installed on some headers or tubes in the penthouse. Check the condition
of these thermocouples and associated wiring. Exercise caution so as not to damage any of these
thermocouples.
Observation Ports and Access Doors
Inspect observation ports and note condition of spring grips, latch pins, gaskets, liners, and door
opening refractory. Inspect the refractory material around openings in the observation door.
Inspect for slag buildup that can obstruct the view from an observation port. In areas where tube
assemblies are protected by refractory, check for any indications of problems.
Examine refractory material for cracks, erosion, and missing sections. Inspect access doors and note
condition of refractory around opening.
Example of Observation Port Inspection
Desuperheater
The purpose of the desuperheater is to control steam temperature through the use of cool
tempering water. Desuperheaters are installed in both the superheater and reheater circuits.
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The typical in-line desuperheater consists of a shell, liner, and spray nozzle assembly. The shell acts
as housing. The spray nozzle assembly introduces the tempering water. The liner protects the shell
from thermal shock when the relatively cold tempering water is injected into the steam system.
Conduct superheater desuperheater liner inspections every three years. This inspection is
accomplished by inserting a boroscope through one of the penetrating screw holes. Examine the
liner for any gross deformations. Examine the spray nozzles for any enlargement of the nozzle holes.
If extensive wastage is found, replace the spray nozzle. Examine the hole in the liner where the
penetrating positioning screw has been removed and measure the hole for elongation. Without
wear, the hole should be 1.06", +0.016", - 0.00" in diameter. Record any elongation and the
direction with relation to the run of pipe. If the hole has elongated 1/2" longitudinally or is within
1/4" of the edge of the reinforcing ring, recommend replacing the liner.
If inspection shows the liner to be in good condition, replace the penetrating screw through the
liner, and seal weld the screw to the pipe.
The reheater desuperheater liners are not subjected to the temperature differentials seen in the
superheater desuperheater and therefore do not usually require inspections as often.
Steam Cooled Enclosure (Backpass)
The backpass wall and roof sections are formed by the backpass side wall tubes at front, backpass
side wall tubes at rear, backpass front wall tubes, backpass front wall screen tubes, backpass roof
tubes, backpass rear wall tubes and the backpass lower rear wall tubes of the vertical gas pass. The
superheater tubes going to the backpass area from the "back pass at roof inlet header" form the
furnace front roof tubes (above the furnace) and furnace rear roof tubes (above the arch).
The most common problem found is erosion. Both sootblower and flyash erosion are often found
on the backpass wall tubes (Figure 38).
Sootblower erosion is commonly found along the paths of the sootblower lance.
The tubes on the front steam-cooled wall seem to have this problem most often.
Flyash erosion is commonly noted along the sidewalls and at the base of the walls, especially on
tubes that are out of alignment.
The backpass wall tubes should be inspected for overheating. Typical signs include swelling,
discoloration, circumferential or longitudinal cracks, and other problems.
Also, inspect the backpass walls for bowing, conditions of damaged refractory and casing.
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INTERNAL INSPECTION – WINDBOXES
General Description – PC Boiler
The windbox area is not a pressure part, but is a significant part of the furnace inspection. Before
making the initial examination of the windbox assemblies, a review of the windbox arrangement
drawing should be made to determine the windbox concept, fuel and auxiliary air compartment
arrangement, warm-up fuel arrangement, intended method of support of components, furnace and
windbox expansion values, and expansion provisions.
The basic functions of all burners of fossil fuels are to provide the time, temperature and turbulence
to unite the fuel with air and convert the potential chemical energy of the fuel to a more usable
form, heat energy. In order to accomplish the process safely and efficiently, manufacturers have
devised many arrangements of ignition, atomization and fuel-air mixing. In spite of state of the art
improvements to make burners safer and more efficient and extensive standardization, each burner
on a given steam generator seems to perform differently from supposedly identical installations on
other steam generators. We consider fuel burning a combination of science and art.
Tangential firing differs in concept from the wall burners in that the furnace itself is the burner. The
corner mounted nozzles serve only to inject fuel and air into the furnace in layers and at firing angles
that will promote mixing and burning in the furnace.
Oil burning is most efficient with wide open fuel air dampers and a high windbox-to-furnace
differential pressure. This is accomplished by throttling the auxiliary air dampers. Gas and coal are
efficiently burned with throttled or modulated fuel air dampers and lower windbox to-furnace
differential pressures.
Design Features
The following are general design information for tangential firing from furnace corners on field-
erected and modular units:
Fuel suitability - natural gas, waste gases, fuel oils (coal is not covered in this guidebook)
Design turndown ratio - 10 to 1, depending on fuel capability
Oil atomization capabilities - steam or air, wide-range mechanical, straight mechanical
Primary air used for coal transport only
Secondary air (all fuels) splits into fuel air and auxiliary air. Air enters furnace in tangential
layers and can be distributed behind the fuel or parallel to the fuel stream as necessary. The fuel air
dampers are positioned as a function of elevation loading. The auxiliary air dampers control
windbox-to-furnace delta-P.
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Minimum excess air
15 percent on oil*
10 percent on natural gas*
*For improved efficiency and lower emissions, special firing equipment is available, but must be
used in combination with sophisticated controls and careful load regulation.
In recent years environmental regulations have generated a need to burn fuel oils at very low excess
air. In many cases this has required changes to diffusers, air nozzles and oil gun tips. Each case must
be approached separately, but tangential firing has the capability of being operated at less than 3
percent excess air, providing plant instrumentation is suitable to control the process, and operators
and maintenance personnel are trained and motivated to follow more stringent practices than for
higher excess air firing. Low excess air firing requires:
1. Accurate, low maintenance, high reliability excess oxygen monitoring equipment.
2. Controls must be kept tuned and in automatic operation.
3. Secondary air dampers must be carefully set to be at equal positions at the same elevation at all
four corners. Depending on individual firing conditions, the upper or lower auxiliary damper may
have to be pinned or biased open to clear up smoky furnaces.
4. Fuel flows at each corner must be as equal as possible on an elevation basis. With oil firing this
means monitoring burner tip orifices for erosion and separating worn tips within wear groups on the
unit at any one time. The following is suggested standard for tip wear:
Effective Flow
Classification Increase, Percent*
New 0 to 3
A 3 to 5
B 5 to 7
C 7 to 10
*Effective flow increase is approximately equal to the percent increase of the orifice tip diameter
squared.
Discard all tips worn greater than 10 percent flow increase.
Windbox Arrangement – PC Boiler
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There is a vertical windbox assembly in each of the corners of the furnace. A typical windbox
assembly is divided into compartments for the admission of fuel and secondary air into the furnace
Coal compartments contain coal nozzles and also admit "fuel air" into the furnace. The term "fuel
air" is applied to that portion of secondary air that is supplied to a fuel compartment.
Auxiliary air compartments admit "auxiliary air" into the furnace. The term "auxiliary air" is applied
to that portion of secondary air that is supplied to the auxiliary air compartments.
Oil or gas compartments contain oil guns or gas nozzles for warm-up or load carrying duty. When oil
guns or gas nozzles are not in service, these compartments may function as auxiliary air
compartments.
The uppermost air compartments in some installations are termed the "overfire air" compartments.
The term "overfire air" is applied to that portion of secondary air that is supplied above the fire. This
air is used to control the formation of nitrogen oxides (NOx).
Located inside each air, coal, and oil compartment (>18” wide) are turning vanes, which direct the
air around the corner from the windbox damper section into the furnace.
The turning vanes impose a streamlined, even distribution of air to each air, coal, or oil nozzle.
Partition plates form the top and bottom of each compartment.
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Inside each coal compartment is a stationary nozzle and a tilting nozzle, which is also called a nozzle
tip or bucket.
The stationary nozzle is supported at one end by the windbox panels and at the other end by
support plates bolted to the sides of the nozzle.
The tilting coal nozzle tips pivot on pins attached to the stationary nozzle. The tilting coal nozzle tips
can be tilted upward and downward 25 from horizontal.
“Splitter plates” in the nozzle tip direct the flow of primary air and coal into the furnace as the nozzle
tip is tilted from horizontal. A seal plate pivots as required with the nozzle tip to close any gap that
forms between the nozzle tip and the stationary nozzle as the nozzle tip is tilted up or down.
One design of stationary coal nozzle for high-turndown applications is provided with an internal
horizontal splitter plate that separates the primary air/coal stream into a fuel rich and a fuel lean
stream. This ensures that the proper air/coal ratios required for combustion are available over a
greater unit load range. The nozzle tip itself contains diverging corrugated splitter plates and air
deflectors. The irregularly "v" shaped bluff body diffuser induces turbulence to the discharging
air/coal stream. In addition, it creates a low-pressure zone, which causes a high recirculation
pattern to form. These features promote a more stable ignition point over wide load ranges.
Oil Gun Compartment – PC Boiler
The corner windbox may also contain oil gun assemblies.
The oil guns, along with eddy plate side ignitors, may be used for warm-up of the boiler. The oil guns
may also be used for load carrying and to provide the ignition energy needed to light off pulverized
coal at adjacent elevations.
The oil may also be utilized to provide stabilization for the coal fires at low boiler loads.
Each oil gun compartment contains a tilting nozzle mounted on pins inside the windbox frame.
A tilt adjusting mechanism, similar to the design of the air and coal compartments, links the tilting
nozzle tip to the main tilt linkage.
The nozzle is fitted with a vane diffuser for directing the air around the oil gun tip in a circular
motion to create a recirculation zone for proper oil ignition.
Natural Gas Compartment – PC Boiler
Natural gas nozzles may also be provided as a warm-up or alternate main fuel source. They may be
installed in a compartment either alone or with an oil gun.
The natural gas burners consist of rigid piping supplying gas into wide flat nozzle assemblies located
directly behind the tilting windbox nozzle tips.
The gas nozzle tip is secured into brackets or guides on the sides of the windbox compartment.
Flame Scanners – PC Boiler
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Flame scanners are generally located in compartments between the main fuel elevations (coal or oil)
for monitoring fireball stability.
Filtered cooling air is delivered to the flame scanners through an air system consisting of the scanner
cooling air fans, filters, and dampers. Cooling air is supplied to each scanner assembly through the
scanner cooling air header located adjacent to the windbox.
Windbox Dampers – PC Boiler
Dampers at the inlet to each windbox compartment proportion the air depending on use, unit load,
and feeder speed.
One damper blade in each compartment is driven.
The damper blades in each compartment are connected by linkage so that they all move together.
Each damper should have a position indicating slot or bar on the end of the damper shaft, which is
visible from the outside of the windbox.
The slot or bar is parallel to the driven damper blade, and shows the exact position of the damper
blades.
Tilting Mechanism – PC Boiler
The fuel and air nozzles are positioned by either electric motor drives or pneumatic tilt drive
cylinders. Although there is one tilt drive for each windbox corner, the tilt drives are controlled so
that the nozzles at all corner windboxes are always at the same tilt angle.
Each corner elevation tilt indicator is equipped with a position indicator, a manual locking pin, a
shear pin, and a spring-loaded locking pin.
The fuel nozzles can typically tilt through a 50 range, 25 up and 25 down.
The oil nozzles can typically tilt through a 60range, 30 upward and 30 downward from the
horizontal.
The auxiliary air nozzles can typically tilt through a 60 range, 30 upward and 30 downward from
horizontal.
Low Nox Concentric Firing Systems (LNCFSTM) – PC Boiler
Tangential firing systems that have been modified for Low NOx operation may include the following
additional features
Modified coal nozzle tips (“Flame Attachment”) - a design to create zones of recirculation for ignition
stability nearer to the nozzle tip.
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Separated Over Fire Air (SOFA) registers - smaller windboxes located above the main windboxes to
provide a significant amount of the secondary air staging.
Fixed Offset “CFS” air nozzle tips - air nozzle tips constructed to direct a portion of the air into the
furnace along a line that is offset from the main fuel. When required, these are utilized only in the
main windboxes.
Horizontally (“Yaw”) adjustable air nozzle tips - air nozzle tips that are adjustable for the amount of
horizontal offset of the air introduction to the furnace. These may be utilized in the main windbox
and in the SOFA registers
These components are arranged in a fashion similar to traditional tangential firing equipment.
However, they incorporate the latest standards for durability.
The Low NOx Concentric Firing System (LNCFSTM) maximizes the NOx reduction capabilities of
existing tangential firing systems while minimizing unit modifications. An LNCFS uses a combination
of techniques to reduce NOx. These are "bulk furnace staging", “local combustion air staging”, and
"early controlled coal devolatilization."
Bulk furnace staging takes a portion of the combustion air, which is introduced at the fuel-burning
zone, and diverts it to retard air and fuel mixing. With conventional tangential firing, the
introduction of excess combustion air during the early stages of coal devolatilization contributes
significantly to the formation of NOx. The LNCFS maximizes the bulk staging concept by using both
separated overfire air and concentric firing.
Local combustion air staging is produced by introducing a portion of the secondary air, called
overfire air, above the primary firing zone. This is accomplished by utilizing a separated overfire air
(SOFA) windbox, which is installed above each corner windbox.
The concentric firing system utilizes a re-direction of the secondary (auxiliary) air, which is admitted
in the main firing zone, diverting it away from the coal stream. In this manner, combustion
stoichiometry is reduced by preventing the fuel stream from entraining with the air stream during
the initial stages of combustion. Fuel nitrogen conversion is reduced, while maintaining appropriate
oxidizing conditions along the furnace walls. The introduction of air in the concentric firing circle is
accomplished with installation of concentric (CFS) air nozzles.
Early controlled coal devolatilization utilizes the technique of early fuel ignition. Initiating the
combustion point at a close distance to the fuel nozzle produces a stable volatile flame that is more
easily controlled under sub-stoichiometric firing conditions. A specially designed coal nozzle is used
to promote a strong primary flame.
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LNCFS Firing System
An unmodified “standard” windbox arrangement is listed in the first column. As the table shows, the
differences in types of Low Nox windboxes are the choices and combinations of close coupled or
separated over fire air compartments. The selection of an LNCFS I, LNCFS II, LNCFS III or TFS 2000
windbox arrangement is based on the required reduction in NOx formation and the furnace
geometry which determines space available for these modifications.
LNCFS common terms and components – PC Boiler
LNCFS
A retrofit package designed to reduce NOx from pulverized coal units without replacing the existing
windbox structures. Generally speaking, LNCFS will utilize new auxiliary air nozzle tips (CFS), new
fuel nozzle tips, and one of three different methods of applying OFA. All the components of the
LNCFS are designed to withhold air temporarily and at different times during the history of coal
particle combustion within the furnace.
TFS 2000
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Coal firing system is designed for minimum total emissions. Techniques employed to reduce NOx
formation, such as sub-stoichiometric primary zone combustion, staging of fuel and air mixing,
reduced excess air, and lower heat release rates, are all aimed at controlling the combustion rate
and reducing peak flame temperatures. Since these conditions may increase the potential for CO,
hydrocarbons, and increased unburned carbon emissions, a balance among these opposing factors is
achieved through an integrated firing system that combines finer coal pulverization with advanced
fuel admission assemblies and in-furnace air staging utilizing multiple air injection levels.
P2 Coal Nozzles
The P2 coal nozzle tip assembly utilizes specific design features to guard against tip deterioration and
nozzle pluggage. The new tip is provided with a rounded corner design to decrease air turbulence in
the tip’s corners and reduce recirculation and deposition of coal and coke. It was developed
specifically for the demands of burner modifications for Phase 2 of the Clean Air Act of 1990.
Aerotip Flame Front Control Coal Nozzle Tips
Aerotip coal nozzle tips are a one-piece fabricated coal nozzle tip. They utilize design features to
guard against tip deterioration and nozzle pluggage. To minimize high temperature oxidation, these
coal nozzle tips utilize an erosion resistant material that offers a superb high temperature oxidation
resistance.
Nozzle tip shroud wall thickness is a minimum of 3/8" to resist warpage as well as erosion from the
coal stream. In addition, the interior walls of the tip as well as all leading edges of the nozzle tip
incorporate a weld overlay hardfacing material for increased erosion resistance.
To help prevent coal nozzle/tip pluggage, the stationary coal nozzle choke area is designed to
maintain proper coal stream discharge velocities based on fuel line velocities. In addition, the coal
nozzle tip utilizes internal splitter plates designed to better control fuel air, especially during tilted
conditions. By more effectively controlling fuel air, a more stable flame front position can be
maintained over the entire tip tilt range.
Crotch Cooling
Crotch cooling consists of an air deflector assembly at the extreme top and bottom of each windbox
to direct airflow adjacent to the refractory lined crotch areas of the bent waterwall tubes. This
improves the cooling of this area as well as controlling the buildup of slag in this area. Both of these
actions serve to increase the reliability and longevity of this refractory material. The windbox is
partitioned through the damper box to ensure continuous airflow through the crotch air deflectors
(no damper control of this airflow).
Air Restriction Blocks
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Air restriction blocks are used above and below coal nozzle tips to accommodate the reduced area
nozzle tips. Tip area sizing has been based the best airflow velocities for stable ignition low NOx
firing conditions.
CFS Tips
In the auxiliary air compartments, some special effects can be generated by the design of the air
nozzle tip. One specialized auxiliary air nozzle tip is called a CFS tip, which directs air away from the
adjacent fuel toward the waterwall. This simultaneously withholds auxiliary air from the adjacent
fuel and provides more O2 in the waterwall area that enhances slagging patterns.
CCOFA
Close-Coupled Overfire Air, is that part of the main windbox where the top air comes out. The
original arrangement had OFA, overfire air. After the top two coal elevations were positioned
(coupled) closer together, the larger top OFA compartment becomes known as the CCOFA.
SOFA
Separated Overfire Air refers to air registers that bias combustion air above and away from the main
burner zone. These air registers are physically separate from and above the main windbox.
External Burner Corner Examination – PC Boiler
The following items are general in scope and should be expanded by referring to contract specific
drawings or prior unit inspections.
Fuel Piping
Check piping at windbox for proper support.
Check oil piping at windbox for proper mounting and installation. Hoses must allow for cubical
expansion of windbox and for travel of retracting mechanism. Hoses must be mounted to operate
free of twist or bind, and shall be erected in accordance with standard hose arrangement drawings.
Check gas piping hoses at windbox. The mounting must allow for cubical expansion of unit, and
hoses must operate free of twist or bind.
Yaw Indicator
Check the actual position of each air nozzle tip and compare to the plant documentation for the
required position.
Check that the locking pin is securely in place.
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Yaw Indicator
Tilt Mechanism (external)
Inspect tilt linkage to insure components are in good condition and there is no interference with
other components, building steel, platforms, piping, etc.
Inspect indicator and pointer for proper relationship with tilting nozzles. Compare the indicator to
both local and remote position indicators of the driving unit or controller.
Inspect constant spring supports, if applicable, to insure proper functioning when tilts are actuated.
Insulation and Casing
Check appearance for any major defects or damage.
Make certain brackets for conduit or instrument tubing do not interfere with expansion movements
of floating casing.
Make certain all removable panels are bolted for tight seal against windbox pressure.
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Clearances
Clearance must be provided for removal of oil guns for cleaning.
Inspect coal piping at windbox to insure adequate clearance for removal of coal nozzles for
maintenance purposes. Where handrails are mandatory, removable sections may be utilized.
Damper bearings
During NOx retrofits new damper bearings may be installed in both the main windbox and SOFA
windboxes. The new style are graphite self aligning bearings. Refer to Figure 46. This damper
bearing shaft design can tolerate both dust and temperature, which in the past has caused
secondary air dampers to stick. Maintenance history has proven that minimal repair is required on
Graphite self-aligning bearings, however it is inevitable that even the Graphite material will
eventually wear out.
If it is found that the damper shaft has lateral movement to the point where the shaft sticks, and the
seal washer is opened and allowing dust to pack in and around the graphite bushing, replace the
bushing, spring seal and gasket. Tighten the four bolts firmly when rebuilding. Tighten the keyless
bushing (transverse torque component) to 125 ft/lbs to lock the lever arm firmly in place. Never pin
or lubricate any part of the keyless bushing. This will result in slipping between the shaft and lever.
Damper Shaft Graphite Bearing
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Internal Burner Corner Examination – PC Boiler
A proportional check should be made of each windbox and nozzle assembly internally.
Set tilts on"0" per indicator on drive mechanism outside the windbox.
All adjustable nozzle tips should be horizontal +0 degrees. If necessary, adjustment may be made at
the bellcrank.
Check clearances between the nozzle tips and the compartment plates. This clearance should be
3/8" minimum.
Check clearances between the side of the nozzle tips and the vertical channels or angles. This
clearance should also be 3/8" minimum.
Examine all linkages to insure that they are in good condition and that there is no interference with
other internal components.
Set tilts on +5o and recheck the horizontal clearance and then on -5o and recheck. Horizontal
clearances at this time should be 1/4" minimum.
Set tilts to +30o as indicated on the position indicator. Check actual tilt angle of nozzle tips. Indicated
versus actual should be within +1-1/2 degrees. Repeat at -30o. At extreme tilt positions, nozzle tips
shall not touch each other.
In oil compartments check location of diffuser cone. Refer to unit Instruction Manual for exact
dimensions.
Insert oil gun to firing position and clamp. Distance from face of diffuser cone back to the oil gun cap
should be as per unit Instruction Manual.
Examine ignitor horn and eddy plate assembly.
From inside the secondary air connecting duct, examine and operate dampers in each compartment.
Check for broken welds--blade to shaft. Inspect and correct any linkage that may have been
damaged in shipping and handling. Check installation of turning vanes, welding and completeness of
vanes.
Inspect joint between air connecting duct and windbox damper frame. This joint must be seal
welded inside the duct to preclude air and dust leakage into boiler room.
Make sure each compartment is clean and free of weld rods, scrap metal, tools, etc.
Windbox Nozzle Tip Field Adjustments – PC Boiler
NOTE: Adjustment and verification of the windbox nozzle tip tilt system should be carried out with
the windbox in the vertical position.
Set external direct drive tilt mechanism indicators at 0 degrees. per indicator scale.
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To verify the windbox is vertical and plumb, the reference marks on the windbox frame or the front
flange surface of the throat frame should be confirmed with a level.
Adjustable nozzle tips directly connected to the tilt drive mechanism by the horizontal reach-rod
should be in the horizontal position (relative to the windbox frame) within ± 2 degrees.
Use the measurement reference points clearly marked on both the windbox and the nozzle tip by
the fabricator for a level check.
Any necessary adjustments to the driving nozzle may be made at the threaded end of the reach-rod
(at the bell crank).
Adjustable nozzle tips in the air/oil/gas compartments which are interconnected with the driving
nozzle tip by means of vertical bars can be off from each other by as much as ±2degrees.
All adjustable nozzle tips should be properly centered within each compartment to provide at least
1/2" clearance between the tips and the windbox frame.
All coal nozzle assemblies should be properly centered within each coal compartment to provide
equal clearances between the coal nozzle tip and the adjacent partition plates. The min. clearance
should be 1/2". both of the coal nozzle assembly supports should be firmly resting on the partition
plate. If this condition is not met, excessive external loading by the fuel piping may be distorting the
arrangement of the assembly within the compartment.
Examine all linkages to ensure that they are in good condition and that there is no interference
between other internal components.
Inspect the clearances around the vertical nozzle tip connecting links and the internal connecting
bars, particularly where they pass through the slots in the partition plates. there should be no less
than 1/4" clearance around these items at any point throughout the ± 30 degree tilt range.
Tilts should be moved +5 degrees to -5 degrees and then back to 0 (zero) degrees. The clearance
between the partition plates and the nozzle tips should then be rechecked. the minimum clearance
should be 1/2".
Stroke the tilts between +30 degrees. and -30 degrees through component inspection, look and
listen for anything unusual that may indicate interference. Note that in the extreme positions of the
tilt range the actual tip position may be off from the indicated position by as much as ± 2 degrees.
Lubricating Windbox Internal Components – PC Boiler
Lubricant should be applied during field windbox overhauls. Link pins, stationary pins for bellcranks
(requires removal of bellcranks if it does not contain graphite sleeved bearings) and other accessible
pivots should be lubricated according to the unit instruction manual.
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Fluidized Bed Ash Cooler – CFB Boiler
Check the Function – Combustor bottom ash flows by an ash flow control valve to the FBAC and is
cooled by fluidization of the ash particles that creates a flow of ash between the tubes of each
pressure part assembly.
The bottom ash is cooled from 1700 degrees F to approximately 350 degrees F. The FBAC has two
sectioned compartments that are called the High Pressure and the Low-Pressure Compartments. The
water flow thru the high-pressure tubes is located between the boiler feed pump discharge and the
economizer. The water flow in the Low Pressure is cooling water. A vent or series of vents return
some ash flow back to the combustor transported by fluidization air. The vents allow filling of the
ash cooler with an inventory of ash so the DCS can perform a desired control scheme. FBAC Gravel
Screws remove top size bottom ash particles from the floor of the FBAC.
Instrumentation to the DCS for ash cooler operation includes lower bed ash temperatures, chamber
pressures for inventory indication, main vent temperature, waterside differential temperature and
final outlet ash temperature. Upgraded versions of the FBAC gravel screws include VFD or speed
control of the bottom ash screws from the control room to allow control of the FBAC chamber
pressures. Chamber pressure (ash inventory) to ash temperature relationship. Excessive fluidizing air
to pressure part erosion relationship. Sintering and DE fluidization conditions. Charge FBAC with
bottom ash prior to start up. Ash velocity range during operation is 2 –2.5 fps.
Inspection
Visual/UT inspections of all the HP and LP assemblies
Spread the assemblies apart to allow access for inspection.
UT worn thru Amstar Coating Areas.
Inspect the nozzles for erosion of casting-go no go gauges.
Rotate nozzles depending on erosion location or pattern.
Inspect refractory condition.
Copper Sulfate for Amstar Coated Tube Replacement
Inspect stainless cast handcuffs for cracking/replacement.
Handcuff bolt torque procedure. •Determine worn tubes to be shielded or replaced.
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CFB Cyclones – CFB Boiler
CFB Cyclones - Centrifugal path recycle cyclones are designed to remove about 99% of the solids
entrained by the gas.
Vortex Finder - in the top of the cone has a narrow laminar flow stream that allows only 1% of the
ash out the backend, but 100% of the gases of combustion do exit.
Key Components
Inlet Duct
o Ammonia Injection Grid (AIG)
o Expansion Joint
Outlet Duct
o AIG
o Expansion Joint
Cyclone Body
o Expansion Joints
o Grease Air Nozzles
o Vortex Finder
Inspection Items
AIG –Plugged nozzles, overheated lances
Refractory Walls –Missing sections of refractory
Expansion Joint –Slag buildup
Vortex Finder –Cracked welds/missing, misaligned assembly
Siphon Seal Pots – CFB Boiler
Function – Siphon Seal Pots - Allow the Cyclones to fluctuate in reserve level to store the surplus ash
during transitional periods. Heat transfer has three options for managing thermal inventory.
Return directly to the furnace and enrich the fluidized bed fire. Transits through SRDs(Solids
Return Ducts).
Momentarily fill the lower half of the cyclone as excessive flow is exiting the top of the
furnace.
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Pass through the FBHEs (Fluidized Bed Heat Exchangers) to reduce heat returned to the fire
in the bubbling bed. Flow is controlled by ACVs (Ash Control Valves).
Operating checks
Normal Operating Static Pressure range will increase to ~40” –80” wg. At 100” wg, operator
needs to watch closely for further increases in pressure. At 120” wg, there is possible
pluggage that will require action. Commissioning engineers must field test actual alarm set
points.
Low pressure suggest that fluidizing air flow is being lost.
High pressures (>100” wg.) suggest that the seal is plugging.
Fluidizing Air and Grease Air help to keep the ash flowing through the Siphon Seal Pots,
ACVs, and SRDs.
Key Inspection Points
Siphon Seal Pots
o Refractory
o Fluidized Air Nozzles
o ACV Plug Refractory Seat
o Grease Air Ports
o Seal Pot Support Beams (recently discovered during Spring 2012 Outage)
Ash Control Valves
o Plug condition
o Plug Shaft
o Bonnet
o Anti-Rotation Key
SRDs
o Expansion Joints: packing of ash can lead to fire in joint
o Refractory
o Grease Air Ports
SRD Outlet into Lower Combustor
Refractory Repairs
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Most Major Maintenance Issues for the Siphon Seal Pots/ ACVs/ SRDs are directly related to Unit
Operation.
Improper FA Flow or Grease Air Flow can result in plugging and pressure problems within the Seal
Pots.
Improper Ash Removal from the SRD Expansion Joints can lead to dangerous situations around the
Seal Pots and SRD Expansion Joints.
Start Up curve for refractory cure can reduce some refractory spalling repairs.
Properly trained and disciplined operators can prevent most maintenance issues on CFBs from
becoming major outage projects.
CFB Boiler Fluidized Bed Heat Exchanger
Inspection Focal Points
FA Nozzles
ash pluggage, broken, and erosion
Handcuff Castings -Bumper Pads
Refractory
Spalling around tube penetrations, jacking of inlet wall penetrations, and seams of floor,
sidewalls, roof, and inlet duct
PRE-OUTAGE WALKDOWN CHECKLIST
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This checklist is designed to prompt the inspector to methodically observe all components during an
inspection and to record abnormal data. The data will later be used to evaluate the unit’s condition.
Having a method to the madness of combing a unit from top to bottom adds value to the routine.
Flexibility to roam off course when necessary, knowing the checklist will get you back on track or
remind you which areas were missed.
Note taking is made simple when the item is already listed, all you have to do is circle a “problem
area” in the data-to-collect column and describe what you see.
The checklist coaches the inspector to look at areas that might otherwise be missed.
Sort the list so that the sequence is similar to the actual walkdown. Format the document as a
landscape page and make the “note” column larger. Highlight areas that are known “problem areas”
of the unit being inspected.
AREA & INSPECTION CRITERIA DATA TO COLLECT
Boiler Support
Boiler hanger rods Abnormal or loose hanger rods, integrity
Variable load and constant load spring hangers Bottomed-out spring hangers, loading
All vertical and horizontal buckstays Warpage or misalignment
All buckstay stirrups, bolts, nuts, and washers Integrity, abnormal condition
Expansion trams (boiler is hot) Readings at reference points
Safety Valves
Stem or packing Leakage
Drip pan Pluggage
Area between the safety valve and vent piping Binding or interference
Structural Steel
Structural steel for boiler or auxiliary equipment Interference
Grating and walkways Missing or loose sections
Handrails Missing or broken sections
Insulation and Lagging
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Insulated Areas Missing Insulation, discoloration, signs of
leakage
Duct insulation in areas of expansion joints Signs of buckling, leakage
Insulation in areas around inspection ports,
sootblowers, and access doors
Missing or damaged insulation
Poured refractory for damage Abnormal condition
Sootblowers and Furnace Probe
Local and remote operation by cycling each sootblower
through its operating sequence
Failure to operate
Sootblower supply lines, valves, and swivel tubes Steam leakage
Sootblower wall box Damage
Drive mechanism on all sootblowers Damage, interference
Cranks and tools to retract a sootblower which has
stopped in the "advanced" position
Available
Movement of air heater sootblower swivel mechanism Interference
Furnace temperature probe Damage
Ignitors
Operate each ignitor Lamp status, ignitor failure
Electrical cables, oil, gas, and air supply lines Damage, interference
Tilting Tangential Firing System
Fuel and Air Nozzles Degree of tilt
All overfire air nozzles Degree of tilt
All corners within 5° of each other Excess tilt
All coal piping entering the windbox (especially at
elbows or couplings)
Wear, damage, leakage
Fuel pipe hangers Damage, loose
All windbox air dampers Position per scribe mark on damper shaft
Compare All dampers on the same elevation Dampers not in same position
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Windbox and related duct work Leakage
Oil Guns
All oil and steam or air lines Leakage
All related piping and valves Leakage, damage
Oil gun advance and retract mechanism Failure to operate
Spare oil guns Dirty, not stored
Coal Piping
Coal pipes Indication of wear
Coal pipe couplings Sign of leakage
Coal pipe constant load spring hangers Expansion problems, loading
Coal Feeders - Gravimetric
Tension pulley Position
Feeder belt Tracking
Feeder housing (with stands 100 psig spike) Integrity, pressure damage
Observation windows and Doors Broken, will not close
Coal Feeders – C-E Volumetric
Drive clutch assembly Wear or damage
Hinged leveling gate lever Movement
Feeder housing. Integrity
Drive motor and gear reducer Noises, poor lubrication
Pulverizers
Mill foundation Cracks
Gear case oil Level, temperature, leakage
Examine the material being rejected from the mill (sign
of worn or improperly adjusted mill internals).
Excessive coal
Three journal assemblies Movement uniformity
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Separator body Coal Leakage
Classifier Do settings match
Mill motor, filters and foundation Wear, damage
Exhauster type mills: exhauster casing, foundation, and
bearing assembly
Wear, damage
Pulverizer gear housing and exhauster bearing housing Noise or vibration
Pressurized pulverizers: gear case and journal seal air
systems
Leakage or crimped lines
Air Preheaters
Upper/lower bearing assemblies. Wear or Damage
Oil Level, leakage
Air preheater seals Loud noise
Drive motor and gear reducer Signs of oil leakage
Air preheater sootblowers Failure to Operate
Boiler Water Circulating Pumps
Motor and related piping Leakage
Pump suction and discharge Log pressures
Motor cooling water Log temperatures
Compare data to normal operating conditions. Abnormal conditions
Fans/Air and Gas Ducts
Foundation bolts Crack or loose
Motor (use vibration meter) Excess vibration, log amps and bearing
temperature
Fan housings, air and gas ducts Damage, missing insulation, leaks,
expansion problems
Ash Removal Systems
All piping Leakage, pluggage
Fuel Handling Systems
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All coal handling systems Excessive spillage, accumulation
Oil and Gas piping Leakage
Pre-boiler Systems
All components and piping Leakage, missing insulation
BOILER INSPECTION FORM – CHECKLIST
LOWER FURNACE AREA
LOWER DEAD AIR SPACES
Membrane cracks – Especially membrane ends
Hanger rods
Hanger pins
Buckstay alignment
Buckstay connections to front/rear wall and side walls
Buckstay deformation
Seal boxes – leaks/cracks
Drain piping supports/welds
Enclosure support steel (gussets front/rear wall)
LOWER SPHERE/HEADERS/DRUMS
Door hinges
Door alignment
Door sealing surfaces
Orifice mounting hardware
Strainers/screens
Internal surface deposits
Backing rings
Drain piping connection
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BOTTOM ASH HOPPERS
Bottom sluice nozzles
Weir water headers
COUTANT UNDERSIDE OF SLOPE
Scallop bar cracks at seal plate
Drip screens
Drip screen support bar
Membrane cracks
Tube surface cracks
COUTANT TOP SIDE SLOPE
General deformation of tubes
Impact damage to individual tubes
Membrane cracks at junction of front/rear wall and side wall tubes
Membrane cracks top and bottom off set tubes at centerwall
Off set tubes around water cooled doors
Sliding ash erosion of side wall tubes at front/rear wall
Sliding ash erosion at upper bend of Coutant
Corrosion in centerwall seal box area
Wear bar (cracks, weld, wear)
MID FURNACE AREA
LOWER SOOTBLOWER ELEVATION (TYPICAL AT ALL ELEVATION)
Membrane cracks at off set tubes
Seal box refractory
Seal box wall sleeve
Tube erosion
Lance tubes cracks
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Lance tube nozzles
Lance tube alignment and depth and cleaning radius
Corner tube erosion
Lance tube rub damage
BURNER ZONE
Clean upper/lower crotch area
Membrane cracking at upper/lower crotch
Eroded/corroded tubes at upper/lower crotch
Membrane cracks in ignitor off set tubes
Overheating in ignitor off set tubes
Ignitor components
Fly ash erosion of wall tubes in coal nozzle tip area
Burner tip alignment
Burner tip linkage
Burner tip condition – Overheating, erosion, broken welds, warpage, etc.
Coal Nozzle – Erosion of nozzle, burner gate, inlet elbow
Auxiliary air tip alignment
Auxiliary tip linkage
Auxiliary air tip condition
Flame scanner guide tube
SOFA tips
SOFA tilt linkage
SOFA alignment
SOFA support frame work
CENTERWALL
Panel to panel rub
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Fatigue/corrosion in seal box
Hanger springs
Panel alignment/distortion
Sliding ash erosion – penetrate at front/rear wall
Sliding ash erosion at lower bends
Membrane cracks
Rub damage at upper rear wall arch penetration
WATERWALLS
Clean selected areas based on history and characteristics of unit design
Corrosion
Erosion
Discoloration
Swelling/blisters
Deformation
Membrane conditions
Tube surface condition – cracks/pock marks etc
Rear wall outlet header tube nipples (cracks at nipple to header and field welds)
UPPER FURNACE AREA
RADIANT WALLS
Stitch welds
Alignment
Tie welds
Clean tube surface for evaluation
DRUMS
Feed pipe, Continuous blowpipe, & Chemical feed pipe including support brackets and “U” bolts
Downcomer perforated screen box
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Primary separators including secondary separators and attachment bolts
Internal shroud and separator baffles
Corrugated Plate Dryer box and attachment bolts
Drain (drip) pipes
Door hinges and hardware
Door alignment
Door sealing surfaces
Debris
UPPER FURNACE ARCH
Sootblower erosion
Slag erosion
Off set tube membranes at screen/hanger tube openings
Rear wall outlet header tube nipples
Membrane/peg fin cracks
Coatings
Refractory
SCREEN TUBES/HANGER TUBES
Fly ash erosion on leading side at arch
Sootblower erosion
Corrosion in seal box areas
Loose tubes
ROOF TUBES
Sagging roof tubes
Peg fins/ Refractory
Rubs from adjacent assemblies
UPPER DEAD AIR SPACE ENCLOSURE
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Hanger rods
Structural steel
Seal boxes (sidewalls, hanger tubes, headers)
Membrane cracks (below rear outlet header, extended side wall)
Drain line connections
Buckstay connections to rear wall
RETRACT SOOTBLOWER OPENINGS/TEMPERATURE PROBE
Membrane cracks at off set tubes
Seal box wall sleeve
Tube erosion
Lance tube cracks
Lance tube nozzle
Lance tube alignment
Lance tube rub damage
Seal box cracking/leaks/deterioration/seal box refractory
Inserted alignment
CONVECTION PASS AREA
EXTENDED SIDE WALLS AND BACKPASS WALLS
Mechanical rubs from horizontal surface (economizer/SH/RH)
Fly ash erosion (screen tubes and hanger tubes)
Erosion at any gas deflection baffle (sootblower/fly ash)
Membrane conditions – solid or peg fin
Off set tubes at boiler access doors (Fly ash erosion, peg fin cracks, etc.)
Refractory at boiler access door off set tubes
Mill board at access doors
GAS TOUCHED HEADERS
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Erosion (Fly ash/sootblower)
Nipple alignment
Nipple welds
Header Supports
Overheating/Swelling/Blisters Discoloration
OD measurements, shear wave, UT, MT, PT, replication
Internal inspection
Header Distortion
ECONOMIZER
Pluggage
Platenizing
Alignments
Sootblower erosion at hangers
Fly ash erosion (Fin tube, Hangers and alignment straps)
Connection between hanger tube and assembly tube
Hanger tubes/straps
Gas distribution baffle conditions
Erosion throughout the bundles (spread or lift bundle for inspection)
Cracking at fin ends
GAS OUTLET DUCT
Expansion joints
Structural steel trusses/struts
Overheated duct work
Fly ash erosion
Economizer hoppers (Pluggage cracks erosion)
HIGH TEMPERATURE SURFACE AREAS
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PENDANT SUPERHEATER & REHEATER SURFACES
Slag accumulation
Tube deformation within an assembly
Sootblower erosion
Fly ash erosion
Flex tie rubs
Fluid cooled spacer rubs
Mechanical rubs from other tubes or supports
Clean selected area for surface evaluation
Take wall thickness readings at selected sites
Take OD readings at selected locations on tube which operate in the creep range
Inspect tube for swelling, discoloration or blisters
Observe and record general alignment of assemblies
Shields
HORIZONTAL SUPERHEATER & REHEATER SURFACES
Hanger support system
Slag accumulation
Tube deformation within an assembly
Sootblower erosion
Fly ash erosion
Flex tie rubs
Mechanical rubs from other tubes or supports
Clean selected areas for surface evaluation
Take wall thickness readings at selected sites
Take OD readings at selected locations on tube which operate in the creep range
Inspect tube for swelling, discoloration or blisters
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Observe and record general alignment of assemblies
Shields
PENTHOUSE
HIGH TEMPERATURE HEADERS
Discoloration
Scale
NDE evaluation (OD,MT,PT,X-ray, shear wave, bore scope, replications)
Nipples (welds, discoloration, scale, OD, wall thickness, misalignment)
Supports (hanger rods, U-bolts, etc.)
High Crown seal
LOW TEMPERATURE HEADERS
Discoloration
Scale
Nipples (welds, discoloration, scale, OD, wall thickness, misalignment)
Supports (hanger rods, U-bolts, etc.)
High Crown seal
CASING
Cracks
Overheating
HANGER RODS
Looseness
Missing clevis pin lock wires
Broken components
Special case – on divided furnace be sure centerwall rear hanger is not insulated with hot reheat
outlet headers
LINKS
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Discoloration
Scale
Supports (hanger rods, U-bolts, etc.)
Vent piping connections
NDE evaluation (OD, MT, PT, X-ray, shear wave, bore scope, replications)
DESUPERHEATERS
Discoloration
Scale
Supports (hanger rods, U-bolts, etc.)
NDE evaluation of alignment and positioning pins (MT, PT, X-ray, bore scope)
Spray Nozzle
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