Chain conveyor troubleshoot guide

 

Sl No.	Problems	Potential Cause	Solution
1	Chain rises off from sprocket	1. Excess chain slack.	1. Adjust the amount of slack equally at both sides.
		2. Excess wear at the bases of sprocket teeth.	2.Carryout hard facing of the sprockets
		3. Excess chain extension.	3. Replace the elongated chain parts.
		4. Foreign material stuck to the bases of sprocket teeth.	4. Remove the foreign material from the bases of the teeth.
		5.Reverse rotation of conveyor	5.Avoid reverse rotation of the conveyor when chain tightened is uneven
		6.Uneven chain tightening of chain
2	Chain separates poorly from the sprocket.	1. Sprocket misalignment.	1-Adjust alignment.
		2. Excess chain slack.	2-Adjust the amount of slack.
		3. Excess wear at the bases of sprocket teeth.	3-Avoid uneven tightening of the chain
		4.Uneven chain tightening of chain
3	Wear to sides of link plats and sprockets	1-Sprocket misalignment.	1-Adjust alignment.
		2-Trough width is lesser than required	2-Increase trough & runner flat width as per site conditions & links assembled width
		3-Chain runner flats size is less
4	Poor chain flexure	1-Inadequate oiling/lubrication	1-Lubricate properly, use standard lubricant during chain assy.
		2-Foreign materials between pins and bushes.	2-Wash the chain to remove foreign materials, and then oil it.
		3-Corrosion between bushes.	3-Replace with an environment resistant chain series.
5	Abnormal noise	1-Chain is too tight or too loose.	1-Adjust the chain slack.
		2-Inadequate oiling.	2-Lubricate properly.
		3-Excess wear of sprockets and chain.	3-Replace chain and sprockets or get worn-out area filled & hard face it
		4-Sprocket misalignment.	4-Eliminate contact with the case.
		5-Slats touching the trough
6	Chain vibration	1-Excess chain slack.	1-Adjust slack.
		2-Excess load vibration.	2-Reduce load variation
		3-Excess chain speed leading to pulsation.	3-Use guide stoppers to stop chain swaying.
		4-Chain flexes poorly at some points.	4-Replace the more worn-out chain parts during overall maintenance
		Sprocket wear.
		5-Worn out or more clearances in rollers & bushes
7	Damage to pins, bushes, rollers.	1-Inadequate oiling.	1-Lubricate properly.
		2-Jamed foreign bodies.	2-Remove foreign bodies.
	Deformation of link plate holes.	3-Corroded components.	3-Review chain and sprocket selections.
		4-Use with greater than allowable load.	4-Eliminate the abnormal load, and review chain and sprocket selections
		5-Abnormal load action.
8	Chain link cut or pins cut	1-Overload operation	1-Ensure all over load, ZSS protections are working
		2-Low breaking load of chain	2-Select chain with higher breaking load if this problem persists

Points to be kept in mind

1-Never weld the heat treated chains, as heat effect can reduce the strength & cause chain to break

2-Never go for electroplating of heat treated chain links, as it causes the hydrogen embrittlement failure

3-Do not use new chain on worn out sprockets

4-Gradual elongation of chain above 3%  in total chain length, indicates that the chain will soon jump the sprockets

Read SOP Coal handling & DE system

Comparison between Acetylene & LPG fuels for gas cutting operation

 

SL No.	Acetylene	LPG (Propane)
1	Highest flame temperature up to 3100 Deg C	Flame temperature up to 2800 Deg C
2	Flame speed up to 7.5 m/sec	Flame speed up to 3.3 m/sec
3	Most of the heat released is in inner cone	Most of the heat released is in outer cone
4	Higher flame GCV of inner cone (4500 kcal/M3)	Lower flame GCV of inner cone (2500 kcal/M3) as compared to acetylene
5	Stoichiometric air fuel ratio1.2:1 (Requires 2.5 to 3 Oxygen cylinders for burning one Acetylene cylinder)	Stoichiometric  air fuel ratio 4.3:1 (Requires 7 to 8 Oxygen cylinders for burning one LPG cylinder)
6	Can be used in gas welding, as acetylene when burning with air creates reducing zone that cleans the steel surface	Cannot be used in gas welding as it does not create reducing zone
7	Acetylene has Specific gravity 0.9 kg/m3, so if it leaks it will raise in air without harming much	Propane has Specific gravity 1.6 kg/m3, which is heavier than air. So if it leaks it will concentrate in deck level or any other closed/corner area
8	Acetylene requires less air for complete combustion	Propane requires more air for complete combustion, so there may be chances of formation of carbon monoxide (CO) in case of incomplete combustion. This incomplete combustion may result into poisoning of working area, as CO is poisonous gas
9	Can be used for cutting & welding applications in industry	Used only for domestic applications

Why do Bearings fail?

 Following are the 16- top listed reasons for bearing failure or damages

1-Lubrication:

Following are the 7 major reasons for bearing failures related to lubrication

1-Lack of lubrication

2-Less lubrication

3-Over lubrication

4-Contaminants in lubricants

5-Wrong method of lubrication

6-Poor quality of lubricants

7-Selection of wrong lubrication

8-Lubricant failure

2-Bearing clearance:

Bearings may fail if the clearance between rolling elements & race is too less & too more. Lesser bearings clearance than desired creates friction & temperature rise.

More bearing clearance creates vibrations

3-Operating the bearings at higher vibrations for long time:

Bearings can operate satisfactory at the vibrations range up to 5 mm/sec, vibrations more than this reduces the bearing life & eventually failure.

Operation range: 0.5 to 3 mm/sec

Alarm Range: 3 to 5mm/sec

Trip range: > 5mm/sec

High vibrations in machine or bearings are due to;

1-Axial vibrations due to misalignment

2-Horizontal vibrations due to imbalance in machine

3-Vertical vibrations are due to looseness in foundation bolts

4-Shaft run out

4-Operating the bearing at excessive loads:

Excessive load on bearings leads to premature fatigue, over loading creates other side problems like bearing overheating, damage to rolling elements.

Brinelling occurs when loads exceed the elastic limit of the ring material. Brinell marks show as indentations in the raceways which increase bearing vibration (noise]. Severe brinell marks can cause premature fatigue failure.

 

5-Overheating

Overheating & damage of the bearings is due to;

1-Lack of lubrication

2-Over lubrication

3-Improper cooling of bearings

4-Excessive loads

6-Smaller clearance between rolling elements & race

Operating the boilers at higher temperature (>90 deg C for ball bearings & sump cooling) will lead to annealing the races & rolling elements that, eventually fails the bearings.

7-Miss alignment

Running the equipments at misaligned condition creates vibrations & excessive loads on bearings in axial, vertical & horizontal directions that causes bearing failures.

Misalignment also leads into failure of couplings & equipments parts like seals, impellers, pulley etc

8-Frequent start & stops of machine

Leads to jerk load on bearings & leading to reduction of its life

9-Not following of equipment/machine SOP:

If machine SOP (standard operating procedure) is being not followed, then it could cause not only bearing failure but also machine other elements.

For example if pump is not started with discharge valve closed or not stopped without closing discharge valves, it could cause jerk loads on bearings & impellers. After some cycle it will reflect it effect on misalignment, vibrations etc

10-Reverse rotation of machine or reverse loading of bearing element:

Some machines & bearings are not recommended for reverse rotation.

For example: Boiler feed pumps & screw compressors are meant to rotate in only one direction

Also Angular contact ball bearings are meant to take load only in one direction

11-Corrosion in Bearings:

Red brown areas on balls, raceways, cages, or bands of ball bearings are symptoms of corrosion. This condition results from exposing the bearings to corrosive fluids or a corrosive atmosphere. The usual result is increased vibration followed by wear, with subsequent increase in radial clearance or loss of preload. In extreme cases. Corrosion can initiate early fatigue failures.

12-Loose & tight fittings of bearings:

Fitting of bearings loose on shaft or loose in housing leads to rotation of bearings outer race in housing, this causes rubbing & bearing damage.

As like loose fitting, very tight fit can also cause excessive load on rolling elements which eventually creates overheating & vibrations

13-Entry of water in bearings grease

14-Material or manufacturing defects in bearings cause bearing failure as soon as it is been installed.

15-Leakage current in VFD motor bearings lead to bearing failure

16-Carrying out welding near bearings or Plummer blocks without proper earthing can lead to flow of currents through bearings, which ultimately causes bearing failure

CHAIN CONVEYOR MAINTENANCE GUIDE

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Questions & answers on bearings

Why does vacuum in steam condenser reduce or drop??

 

1-High exhaust temperature:

Vacuum drops or maintains at lower side due to high exhaust steam temperature flow into steam condenser. This high exhaust temperature is mainly due to

1-Operation of Turbine at lower loads

2-More clearance in labyrinth seals

3-Not operating exhaust hood sprays

4-More load on condenser

5-Breaking of ejector U loop

2-Low circulating cooling water flow

Vacuum in condenser reduces due to inadequate cooling water flow through steam condenser. This is mainly due to;

1-Problems associated with pumps

2-Air pockets in pipe line

3-Leakages in cooling water line

4-Stuck of discharge valve of pump

3-High cooling water temperature at condenser inlet

Higher cooling water temperature at condenser inlet results into reduction of vacuum due to poor heat transfer from steam to water

4-Poor heat transfer in condenser

Very less or poor heat transfer in steam condenser reduces vacuum to very low level resulting into high exhaust temperature & disturbances in hot well level.

Poor heat transfer is due to;

1-Fouling of condenser tubes due to poor water quality

2-High cooling water temperature

5-Air ingress in condenser & other vacuum pulling system

This is the most top reason for sudden drop of vacuum in steam condenser. Air ingress into the condenser is mainly from flange joints, gaskets, valves etc

Passing of vacuum breaker valve also be the one of the reason for maintaining low vacuum in condenser

6-Low steam temperature & pressure at ejector inlet:

Parameters lesser than rec recommended leads to reduction of vacuum pulling

7-Poor heat transfer in steam jet ejectors

This is mainly due to fouling of ejector tubes

steam condenser vacuum & calculations

8-Damages to air ejector nozzles

Increase in nozzle clearances leads to reduction of vacuum creating efficiency of ejectors

9-Breaking of ejector inter condenser U seal loop.

This creates escape of hot condensate directly into condenser leading to increase in exhaust temperature & reduction in vacuum

10-Low gland steam pressure:

Gland steam pressure lesser than design creates ingress of outside air into condenser through turbine glands.

11-Loading the condenser more than design

If the condenser steam load is more than design, vacuum drops slowly

12-High a temperature & low pressure in the atmosphere reduces vacuum pulling efficiency

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Power plant & claculations

What do you mean by Turbine supervisory system???

Steam Turbine SOPs

Why does load hunting occur in steam Turbines??

 If Turbine does not maintain the load as per set load, then this condition is called load hunting.Following are the some potential reasons for load hunting

1-Problems associated with actuators:

These are related to leakages in actuators, piston stuck up, oil holes elongation etc. Because of these issues there will interruption or fluctuation of secondary oil flow through actuators, this creates the problems of actuator miss-operation & eventually load hunting.

2-Improper calibration of actuators:

This results into mismatch of actuator opening & given set point or valve demand

3-Lower control oil pressure than required:

Actuators are designed for specific pressure of control oil, if the control oil pressure at actuator inlet becomes less, then there will be more chances of mal function of actuator.

4-Fluctuation of control oil pressure/flow:

Fluctuation of control oil pressure or flow due to malfunction of pump or line PRV may lead to actuator misoperation & hence creates load hunting.

5-Control oil line leakage:

Leakages in control oil line welding & flange joints will lead to fluctuation of flow & pressure causing actuator malfunction & load hunting.

6-Contamination in control oil

Foreign particles present in oil lead to improper functioning of actuators, which causes load hunting

7-Burs or scoring marks on actuator spindle & control valves spindles:

Burs or any rough scoring marks on spindles will lead to improper operation of actuator & valves

8-Passing of control valves:

This is the major reason for load fluctuation & Turbine over speed

9-Improperly set control valve cones:

During turbine HP valve assembly after maintenance, HP control valve cones should be set as per factory set readings, if it is disturbed, then there will be issues related to load hunting, low load at more HP demand or over speed.

10-Damage or broken control valves spindle & discs (cones):

Spindle damage or disc damage makes uncontrolled operation, as there will be wrong response from control valves to governor.

11-Wrongly tuned P&IDs in Governor: The disturbed values in P&ID tuning will result into heavy load hunting

12-Malfunction of Governor: This is very rare, but certainly results into load fluctuation of Turbine trip

13-Sudden changes in inlet steam pressure & extraction steam pressure

14-Fluctuation of grid frequency

15-Failure of Turbine inlet & extraction pressure sensor

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Power plant O&M reference books

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Turbine oil flushing procedure

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Why do turbines go into over speed trip???

Why does Boilers main steam temperature increase more than design?

 1-Decrease in Economiser inlet feed water temperature

Upon decrease in economiser inlet feed water temperature, fuel consumption in furnace increases & hence main steam temperature increases more than desired.

2-Load on Boilers is more than design

Main steam temperature increases if the steam generation is more than actual designed

3-Leakage in super heater (SH) coils

If there is any leakages in SH coils, steam flow to SH coil decreases & hence main steam temperature increases.

4-Choking in Super heater coils

Super heater coils Choking due to foreign materials & internal scaling due to poor water chemistry leads to less steam flow through coils resulting into higher main steam temperature due to poor heat transfer.

5-Passing of start-up vent control valve

Passing of start-up control valve loads more on Boiler steam generation, hence main steam temperature increases

6-Passing or pop up of drum safety valves : Lifting of drum safety valves lead to less steam flow to SH coils resulting into higher main steam temperature.

7-High moisture fuel: If the fuel moisture is more than required, then water present in the fuel absorbs heat from furnace & transfer heat convectively to SH coil.

8-Low GCV fuel: Burning of low GCV coal in furnace releases more heat & hence MS temperature increases.

Note: Burning of high GCV fuel with high moisture also leads to temperature shoot-up.

9-Failure of attemperator control system or wrongly tuned attemperator control valves.

10-Operating the Boilers at more negative draught: This causes more convection heat transfer in SH, (& also at economizers & APH) leading into high main steam temperature

11-More excess air also can lead to fast heat transfer, which can result into high main steam temperature

12-Wrongly designed SH coils: If there is provision of more heating surface in SH coils, then eventually steam temperature always maintains on higher side.

13-Very Clean & scale free surface of SH coils: Leads to faster heat transfer in SH zones causing more steam temperature

14-High moisture content combustion air leads to increase in MS temperature

15-Lesser turbulence in furnace leads more convective heat transfer at SH zone & eventually results high main steam temperature.

16-Wrongly designed SH & furnace zone: High velocity of FG in furnace & SH zone leads to fast heat transfer, this causes high main steam temperature.

17-Mixing of fuels in furnace: Causes uncontrolled excess air & draught which causes main temperature to increase.

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