12-troubleshooting guide for Boiler Feed Pumps (BFP)

 

                           

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                       12-troubleshooting guide for Boiler Feed Pumps

SL No.	Problem	Root cause	Remedy/Action to be taken
1	High bearing vibrations   What are the reasons for high bearing vibration in Boiler feed pump (BFP)	More clearance in bearing	Maintain bearing clearance within the limit as recommended by OEM
		Contaminants/burs in oil	Replace the oil
		Pump operation in re circulation mode for long time.	Operate the pump at the flow > 30% of rated capacity Pump should not be operated more than 30 min in recirculation mode
		Miss alignment for axial vibrations	Check & correct the alignment
		Looseness in foundation bolt or coupling bolts for vertical vibrations	Tighten the bolts
		Imbalance for horizontal vibrations	Check & conduct balancing test at OEM shop
		Over load operation	Operate the Turbine at or within its maximum capacity
		Looseness in impeller	Inspect the pump thoroughly & rectify the errors in impeller fitment
		Malfunction of the vibration sensor	Get confirm the high bearing vibrations are due to malfunction, if confirmed ensure tightness of all connections.
2	High bearing temperature (Journal)   What are the reasons for high bearing temperature in BFP?	Low lube oil level	Check for any leakages, if there arrest the leakages Top up the oil.
		High lube oil temperature	Check for cooling water flow, remove the blockages if any.
		Over load operation	Operate the pump at or within rated flow
		Less clearance in bearing	Maintain bearing clearance within the limit as recommended by OEM
		Malfunction of the temperature sensor	Get confirm the high bearing vibrations are due to malfunction, if confirmed ensure tightness of all connections.
3	Cavitation/abnormal sound   What are the reasons for cavitation in Pumps?	Low suction pressure	Check the reason for low suction pressure & Normalise
		High feed water temperature at pump’s suction	Reduce the steam flow to deaerator & maintain the suction temperature as pre-design pressure. If pump suction pressure is low, it may reach the vapour temperature leading into steam formation inn pump.
		Low deaerator level	Normalise the deaerator flow by increasing make up water or process return condensate.
		Low deaerator operating pressure	Increase & maintain the Deaerator pressure as per rated pressure
		Low suction water	1.Check for suction valve throttling & increase the suction water flow 2.Check for clogging of pump strainer due to any foreign materials.
		High flow	Reduce the flow & maintain as per OEM design.
4	More Balance leak off pressure   What is the reason for more balance leak off pressure in BFP?	Worn out balance discs	Inspect & replace the discs
		More clearance in balance & counter balance discs	Inspect & adjust the clearance as per OEM manual
		More suction pressure	Maintain the suction pressure as per OEM recommended
		Blocked balance leak off pressure impulse line	Check & clear the line Read>>>Boiler feed pumps SOP
		Higher pump discharge pressure	Maintain the discharge pressure as per OEM recommended
		High discharge flow	Maintain the discharge flow as per OEM recommended
		Faulty pressure gauge	Replace the pressure gauge
5	Low Balance leak off pressure   What is the reason for less balance leak off pressure in BFP?	Less clearance in balance & counter balance discs	Inspect & adjust the clearance as per OEM manual
		Improperly fitted balance discs	Inspect & adjust the clearance as per OEM manual
		Low suction pressure	Check & increase the suction pressure
		Low discharge pressure	Check & ensure the correct discharge pressure
		Leakages in balance leak off line	Arrest the leakages
		Faulty pressure gauge	Replace the pressure gauge
6	Pump overheating   What is the reason for pump over heating?	High feed water temperature	Maintain the feed water temperature as per design
		Operating the pump at higher flow	Optimise the discharge flow
		Operating the pump at flow < 30% of rated	1.Increase the flow beyond 30% 2.Do not operate the pump with discharge valve closed for long time.
		Low suction flow	Check the strainer & clean Check the suction valve & ensure it’s open 100%
		Cavitation	Ensure suction pressure & temperature are as per design
		Bearing failure	Replace the bearing or maintain the clearance
		Continuous operation of the pump	Follow pump change over schedule.  Boiler feed pumps SOP
		Internal rubbing due to improper thermal expansion	1.Ensure uniform expansion of pump.   2.Do not start pump as soon as hot water induced into it. Allow it for some times for uniform thermal expansion.
7	Journal bearing failure   What is the reason for BFP pump bearing failure??	No lubrication	1.Ensure proper oil level. 2.Follow lubrication & lubricant replacement schedule.
		Insufficient cooling & operation of the pump at higher bearing temperatures	1.Ensure bearing temperature is in the range of 50 to 70 deg C. 2.Ensure proper cooling water is flowing in & out of the bearing cooling jacket.
		Operating the pump at lower speed for long time	Ensure the pump will be operated at speed >80% to ensure proper splitting of lubricant oil to bearing liners
		Starting of the pump at lower speed	Always start the pump at speed reference > 50% Ensure pump will attain its 50% speed (1500 rpm) in initial 10-12 seconds, this will protect the bearing from lack of lubrication at initial lower speed.
		Frequent start & stop of the pump	Ensure pump will not be started or stopped frequently
		Starting of the pump with discharge valve opened	Never start the pump with discharge valve open to avoid sudden jerk load to the pump, which not only damages the bearing even harms pumps internals, coupling & motor
		Stopping of the pump with discharge valve opened	Never stop the pump with discharge valve open to avoid sudden jerk load to the pump, which not only damages the bearing even harms pumps internals, coupling & motor Boiler feed pump SOP
8	Insufficient discharge flow or pressure   What is the reason for low discharge or low discharge pressure from Boiler feed pump?	Pump is running on partial load or lesser speed	Increase the speed
		Discharge valve throttled	Ensure 100% opening of the discharge valve
		Suction valve throttled	Ensure 100% opening of the suction valve
		Air lock	Ensure proper priming of the pump. Keep open drain/vent provided at suction strainer for 3 sec.
		ARC (Automatic recirculation) valve stuck or passing	Servicing of the ARC valve
9	Frequent tripping of pump during start up   Why does the pump trip during start up?	Discharge valve Open	Close the discharge valve & start the pump
		Pump jam	1.Ensure proper lubrication 2.Ensure uniform thermal expansion
		Electrical related problems	Check at Motor & Panel side and rectify the identified problems
10	Excessive Noise & Vibration   What are the reasons for excessive noise & vibrations in pumps?	Cavitation in pump	Ensure suction pressure & temperatures are normal
		Pump air lock	Ensure proper priming of the pump
		Bearing damage/worn out	Inspect and replace if needed
		Internal rubbing	Inspect & replace damaged internals
		Pipe lines vibrations	Inspect supports & rectify if required
11	Mechanical seal leakage/Gland leakage   What are the reasons for Mechanical seal failure in pumps?	Improper installation	Check & reinstall the seals
		Seals parts damaged	Check the root cause & replace the damaged parts
		Frequent start & stop of the pump	Ensure pump will not be started or stopped frequently
		Worn out shaft sleeve	Replace the sleeve
		Jerk loads on seals	Ensure discharge valve is closed before starting or stopping of the pump
12	Pump consuming more power   What are the reasons for more power consumption by Boiler feed pumps?	Automatic Recirculation Valve (ARC) passing	Get done the overhauling of valve
		Bearing friction	Maintain required clearance in bearing
		Internal rubbing	Replace the worn-out parts
		Lesser efficiency of coupling & motor	Replace the worn-out couplings Verify motor load & efficiency
		Higher flow	Ensure pump is delivering flow as per design
		Lower pump efficiency	1-Check pump hydraulic power 2-Check fluid temperature & suction pressure and ensure both are as per design. 3-Ensure pump’s discharge pressure is as per design

 

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What is the significance of post weld and Pre-weld heat treatments (PWHTs)?

 

Post weld Heat Treatment (PWHT):

Post Heating in welding is a process where heat is applied to a welded joint after welding to control the cooling rate and reduce the risk of cracking.

When to carry out post weld heat treatment?

It is commonly used in materials that are prone to hydrogen-induced cracking, such as high-carbon steels, alloy steels, and cast iron.

What is the significance of post weld heat treatment?

Importance of post weld heat treatment

Prevent Hydrogen Cracking: Slows down cooling to allow hydrogen to diffuse out, preventing cracks.

Improve Mechanical Properties: Enhances toughness and ductility.

Reduce Residual Stresses: Helps relieve stresses induced by rapid cooling.

Improve Metallurgical Structure: Minimizes hardness variations and prevents brittle micro structures.

What actually is being done in post weld heating process?

In post weld heat treatment, the welded component is heated to a specified temperature say 450 deg C to 700 deg C. This temperature is maintained for a certain duration up to 6 to 8 hours based on material composition and its thickness, later slow cooling is ensured, often using insulation or controlled cooling methods.

What are the different methods of post weld heat treatment (PWHT)?

Torch/Gas cutter Heating: Using an oxy-fuel or propane torch for localized heating.

Furnace Heating: Placing the component in an oven or furnace for uniform heating.

Electric Resistance Heating: Using heating pads or ceramic heaters.

Induction Heating: Applying electromagnetic induction for controlled heating

What is the criteria for post weld heating or heat treatment (PWHT) or heat treatment of carbon and alloy steels as per IBR regulations?

Actually, arc welded butt joints should be post weld heat treated effectively except in the following cases;

For high pressure alloy steel post weld heat treatment (PWHT ) is not done

1-If 0.5% Molybdenum steel having thickness & Tube OD are < 13 mm and < 127 mm respectively

2- If 1 Cr & 0.5 % Molybdenum steel having thickness & Tube OD are < 13 mm and < 127 mm respectively and it is been pre-heated to 125 deg C

3-In case of 2.25 Cr & 1 Molybdenum steel, PWHT is not necessary in following conditions;

a-Maximum Chromium content is 0.3%

b-Maximum Nominal out side diameter is 102 m

c-Maximum thickness of the alloy steel is 8 mm

d-Maximum specified carbon content 0.15%

e-Minimum pre-heated temperature is 150 deg C

For Carbon steel post weld heat treatment (PWHT ) is not done if;

1-Maximum Carbon percentage is 0.30%

2-Maximum thickness is 9 mm

Pre- weld heat treatment

What is the significance of Pre- weld heat treatment?

Pre-weld heat treatment, often referred to as preheating, is a critical process applied to the base material before welding.

Its main goal is to prepare the metal for welding by ensuring that temperature gradients are minimized, thereby reducing the likelihood of thermal stresses, cracking, and other welding defects.

Importance of Pre-weld heat treatment

To reduce or remove moisture content in the materials: Preheating helps evaporate moisture from the base metal, which is particularly important for materials prone to hydrogen embrittlement.

Reduce Thermal Stress: Preheating helps in minimizing the rapid temperature changes that occur during welding. This gradual change reduces residual stresses in the weld and surrounding base metal.

Prevent Cracking: By slowing down the cooling rate, preheat treatment decreases the risk of hydrogen-induced or cold cracking, especially in materials with high carbon content or high strength.

To get quality weld: A controlled preheat ensures that the weld area is at a uniform temperature, improving the fusion between the base material and the weld metal, leading to a more sound joint.

Read more>>>>20- metallurgical differences among Carbon steel, Alloy steel and Austenitic (Stain less) steel tubes in Boilers.

When to use Pre-weld heat treatment process?

Generally applied for Alloy steels, high carbon steels & Cast irons where there is a possibility of cracking due to rapid cooling.

Pre-heating is also done during rainy seasons or cold climate conditions to remove moisture from the steel.

What is the temperature for Pre-heating?

The required preheat temperature varies with the material type and its carbon or alloy content. For example, mild steels might require preheat temperatures of around 100–150°C, while high-carbon or high-strength steels might need 200–300°C or higher.

 

What are the different methods of Pre heat weld heat treatment ?

Torch/Gas cutter Heating: Using an oxy-fuel or propane torch for localized heating.

Electric Resistance Heating: Using heating pads or ceramic heaters.

Furnace Heating: Placing the component in an oven or furnace for uniform heating.

Induction Heating: Applying electromagnetic induction for controlled heating

In most of the applications gas heating is done.

Tips for best Pre-weld heat treatments:

1-Uniform heating: Select the weld area to be pre-heated, apply the heat uniformly thought the selected area to avoid the development of localized temperature gradients.

2-Proper controlling of Temperature: Ensure pre-heating temperature is within limit. Make use of calibrated temperature sensors.

3-After completing the welding: Allow the metal to cool slowly. Faster cooling again induces stresses and even form cracks.

For conducting pre & post weld heat treatments skill of welder & welding team is also plays a vital role.

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