Tuesday, June 30, 2020

The Ultimate Guide To Mechanical seal part 1

Mechanical seal

Mechanical seal is a mechanical device which is used to prevent the (leakage) liquid coming from inside casing to outside though between static and rotating parts. Mechanical seals are used in centrifugal pumps. There are many types of mechanical seals used in the many equipment’s. It is classified on the basis of design, working, and arrangement.

The Seal face is the most important part of the seal. Because the face material is the most expensive part of the seal and that creates a seal between static and a rotating part of the equipment. The description of types of the mechanical seal below.

Types of seal

There are two types of seal
  • Static seal
  • Rotating seal or dynamics seal

Static seal

It is used only to prevent leakage between static parts of the equipment and piping flanges. It's not used for  moving or rotating part of equipment. It is  used in flange joints, equipment manway, reactor piping flanges, columns piping flanges, pump casings and others.

Dynamic seal

Dynamic type seal is used to prevent the leakage between static and rotating parts of the equipment. Which rotates to each other. The application of this type of seal is used in pumps, blowers, compressors, turbines, valves, and others.

Types of dynamics seal

  • Gland packing
  • Mechanical seal
  • Labyrinth seal
  • Oil seal
  • Water seal
  • Lip seal
  • Hydrodynamics, etc.

Classification-of-mechanical-seal

Classification of mechanical seal

There are many type of mechanical seals

Classification is based on the arrangement of the seal
  1. Single seal
  2. Dual Mechanical Seal
Single seal

Two types of single seal
  1. Inside mounted single seal
  2. Outside mounted single seal
Inside mounted
The pressure of the liquid acts on the outer diameter of the seal's face.
Outside mounted
Pressure of liquid acts on the inside diameter of the seal part.

Double mechanical seal

If the primary seal fails then the secondary seal is used as a back up seal.
The 0 ring is also used as a secondary seal.

Two types of dual mechanical seal
  • Dual pressurize seal
  • Pressurize seal
  1. Back-to-back arrangements
  2. Face-to-face arrangement
  3. tandem arrangement

Dual pressurized mechanical seal
The dual pressurized seal requires nitrogen or other compatible inert gas and also requires a reservoir pot or nitrogen header line for pressurization. The nitrogen header minimum pressure is required at the level of pressure required to seal it.

Dual non pressurized mechanical seal

In a series arrangement or tandem arrangement. The unpressurized dual seal does not require nitrogen and other inert gas Pressure between the seal face area is higher than the seal chamber pressure is a minimum of 30 PSI.
The dual seal arrangement required an external seal flushing plan. Its pressure approx around the atmospheric pressure of the liquid, the face lubrication is also done by the external sources liquid. Unpressurized seals are used for low pressure, hazardous liquids.

Double mechanical seals are used for many features
  • Inappropriate NPSHA
  • Cavitation by air aspirations
  • On very expensive services
  • For explosive services
  • With toxic and vaporized liquid
  • For volatile liquids that have a tendency to vaporize, convert the gaseous form


Balance and unbalance 


Balance type

If the ratio between closing area to opening area of the seal is less than 1 then it is considered as balance seal. Balance type is less than the closing forces require. Reduces power consumption, It is used for pressure up to 3000 PSI and is mostly used for volatile liquids.

Unbalance

If the ratio between closing area to opening area of seal is greater than 1 then it is considered as an unbalanced seal. In Unbalance seal closing forces require a very high, very low leakage rate and that is used for up to 200 PSI services. but it is not used for volatile liquids.

Cartridge seal and split seal

Cartridge

The cartridge seal is a complete preassemble of seals, flanges and other parts. it is easy to install and does not measure required during the installation. because it is Spring load is fixed during the assembly and already tested by the technician with the help of air and equipment but it is more costly than other types of seal.

Split seal

The split seal is available in two parts,that is mostly axially split, the main advantage is that it is easy to install and does not require more time for installation, also reducing the downtime. but it is also more costly than seals.
What factors consider selection of mechanical seal applications?
Here mention the factors for the selection of mechanical seal considerations below.
  1. Temperature and pressure of the service liquid inside the casing.
  2. RPM for driver, equipment and misalignment
  3. Tolerance runs out of shafts in seal chambers
  4. Clearance of the seal chambers radially and axially
  5. Flushing and cooling plan required
  6. purpose barrier and buffer fluid requirement
  7. Availability of power
What are the factor requirements for smooth operation of the mechanical seal?
Factor requirements for smooth operation of mechanical seal.
  • Service fluid at the pump.
  • Seal leakage rate should be minimum
  • The fluid is in the pump seal area appropriate with seal face materials.
  • Effective force in mechanical seal
  • liquid lubricant for mechanical seal face
  • Mechanical seal face material compatibility with service liquid.
  • Power consumption and power losses
What is the purpose of providing seal plans?
The purpose of seal planes is to provide cooling and flushing to seal face. and remove raised temperatures as well. a variety of mechanical seals are available in the industry, mechanical seals are used in many types of equipment: like pump, compressors, liquid ring compressors, blower fans, agitators, valves, rotators and others.
The API standard used is 682 for the pump, there are many types of seal plans used, and Dry gas seal used in centrifugal compressor There are many components of mechanical seal like springs, O rings, Rotary seal's face, static seal's face, retainer rings, seal's face material, below, spring.
What should be the gap between seal face?
The gap between seal faces is very small. When it is running the hydrodynamic gap is created and that gap is approx around 3 to 5 microns.

There are two types of material used for seal face

for seal face one is a soft material used like carbon and Teflon another
One is a hard material that is tungsten carbide, silicon carbide, PTFE and

Where was the mechanical seal used?


The life of a mechanical seal is very long as compared to gland packing its maintenance time is much less. But it is highly expensive and very sensitive, because of the use of mechanical seals to save the downtime of the equipment.

Mechanical seals are used in many applications like pumps, compressors, blowers, liquid ring compressors, agitators, submersibles, pumps and others.

What is the reason for the mechanical seal being used?
  • To prevent and minimize the leakage of service fluid.
  • Prevent the hazards and toxic fluids and gases that come out of casings of equipment.
  • Reduce the maintenance downtime of equipment and power losses.
seal-selection-on-the-based-of-pressure-of-driver

seal-selection-on-the-based-of-speed-of-driver

What is the advantage of a mechanical seal?
The primary advantage of a mechanical seal use any equipment for a good deal safe operation.
  • Reduction in power losses
  • Save the equipment downtime and
  • Reliability of equipment
  • Safe operations.
Why is the Cartridge seal mostly used?
The advantage of cartridge seals is more than compared to other seals. Advantage.
  • Fewer number of skilled workmen required
  • Increase the reliability of equipment
  • Reduce the time for maintenance
  • Reduce the downtime of equipment
  •  It is easy to fix
Why did the mechanical seal fail?
The key reason for seal failure is
  • Lubrication failure and Dry run
  • Contamination in flushing fluid
  • Foreign materials inside the seal face
  • Rubbing seal faces against each other's system
  • High Temperature
  • Pressure Variations in the Seal Chamber and Misalignment
  • Overloading and not Operating at Designs
  • High vibrations and not installed properly.
What type of force is acting on a mechanical seal face?
  • Radial and axial force
  • Seal faces closing and Opening Force
  • Hydrodynamic and hydrostatic types of force.
Manufacturer names of Mechanical Seals.

Top seal manufacturers are John Crane, Flowserve, Eagle Bergmann, Grundfos and SanMar.
What is the type of mechanical seal face materials?
Seal face materials are

Carbide, carbon, graphite, aluminium oxide, tungsten carbide, silicon carbide, diamond coated, glass coated and others.

Selection-of-seal-face-materials

Wednesday, June 24, 2020

Troubleshooting of centrifugal pump New 1

Troubleshooting of centrifugal pump

There are many types of problems happens with a centrifugal pump that is mentioned below.
  1. Flow not develop or low flow
  2. Low pressure and low head
  3. Power consumption is high
  4. High noise in pump
Troubleshooting-of-centrifugal-pump

Guide to troubleshoot of centrifugal pump mention  below, and we will take a view and try to troubleshoot of centrifugal pump.

Flow not developed or low flow


 Troubleshoot guide for flow not developed or low flow in centrifugal pump is mentioned below.

Problem in Instrument

Instrument like (pressure gauge) not working properly check the instrument if any error, replace or correct it. 

Cavitation in suction line

Check the NPSHa and NPSHr for investigation of NPSH, check the past history of NPSH and check the impeller chocking.

Pump casing and section line not vented

Pump casing and section line not venting Check the casing and suction line vent properly.

Suction liquid source (tank's) empty or low level

Suction liquid source (tank's) could be empty or low level Check the level of your tank and maintain the level of the tank.

Not primed properly

Before run the pump should be primed properly if did not do, stop the pump and do the prime properly.

Flange joints in suction line and pump casing loose

Check flange joint in suction line and pump casing if found loose, tighten the all flange because otherwise due to this, air can sucked with suction liquid and cavitation could occur.

Low pressure and Low discharge head


The reason for low pressure and low discharge head in pump mentioned below.

Instrument error

Check the instrument error and correct it.

Cavitation issue

Check the cavitation hammer noise happening, check the net positive suction head available and net positive suction head required and past history of NPSH of the pump.

Suction strainer chocked

Open and check the suction strainer, investigate the suction strainer, clean the strainer and box up the strainer.

Impeller rotate in wrong direction

Check the drivers' direction of rotation and it found wrong then correct it.

Clogged suction line

Check the section line it should be clean from foreign materials like diaries and other, this is also a main reason for low pressure develop.

Warm impeller and wearing

If the impellers or wearing fund worm due to this the clearance between the internal parts has been reduced so flow rate goes down.

Excess the internal parts' clearance

Due to the increased of internal parts clearance the internal circulation of the fluid goes up so the pressure and head of the pump fall down.

Suction valve and discharge valve throttled

Due to the throttle of suction and discharge valve flow stick restrict at the valve body the head goes down.

Minimum circulation line valve in open condition

Due to the open of the minimum circulation line valves the lines fluid circulation increased through the minimum circulation line so this is also a result of pressure or head rate.

Elbow

Reduce the number of elbow used, use short angle elbow.

Instrument equipment’s Problems

Check instrument like pressure gauge temperature gauge and others.

Drivers run at high RPM

check the driver drives of rotations and driver RPM.  Type of pump 

Driver run wrongs direction

Check the drives on direction of rotation of motors if any problems in correct it.

Cavitation in line due to a leaking from flanges

Check the all flags test leak test fund tight. Impeller may be partially plugged

Cavitation
Cavitation is also reasoned for discharge pressure not building then correct it. Sometimes air aspiration type cavitation is also the main reason.

High power consumption


The reasons and troubleshooting for high power consumption of a pump is mentioned below. 

Driver speed is very high

Check the RPM of driver if any found high RPM, correct it.

Liquid viscosity is high

Check the liquid viscosity and install pump as per well-matched with viscosity.

System suction head is lower than as expected

Check the system head npshr of the pumps with the pump designs.

Pump gland seal very tighten

If in the pump gland seals used check the tightness of gland seal and loose the gland and provide proper cooling system.

Access bearing load

Due to the access bearing load also reason for high power consumption, to solve it check the alignment of driver and pump if it is found errors then correct it.

Electrical equipment loose

Check electrical equipment installation in motors and wire connection looseness.

Valve condition in discharge line

Check the valve condition in discharge line if it found throttle, it's must be fully open. Check coupling bolts and bearing housing of pump and driver.

Troubleshooting of pump


High noise in pump casing and line


There are one reason for high noise is cavitation.

Prevent the noise of the pump

To prevent the noise of the pump first troubleshoot the cavitation. There are five type of cavitation. All mentioned in link. Other reason for high noise is rotating part rubbing, if needed overhaul the pump and find the rubbed part and correct it. Some times due to the wrong alignment a reason for create noise in pump.
Thanks for read,

Friday, June 19, 2020

Type of pumps

Type of pumps


Pumps are used for extract the liquid and transfer one source of liquid to another source. Pumps are uses in many industries like refineries, petrochemicals, oil and gas, pharmaceuticals, power plants, hospitality and home application etc. It also is very useful mechanical device. On the basis of working and construction pumps classification into many types. On other site


Classification of pump

  1. Positive displacement pump

  2. Centrifugal pump (Dynamic pump)

Centrifugal pump


Centrifugal pump is a mechanical device, it is work on the principle of centrifugal force. Impeller is rotated by driver, (turbine or motor) in the pump casing. Impeller sucks the liquid through impeller eye from low pressure. After the rotating of the impeller pushes the liquid to outward in casing and where discharge the liquids through nozzle. Centrifugal pump is also called dynamics pump the centrifugal pump converts the kinetic energy of the liquid to pressure energy. There are many types of centrifugal pumps for learn more go to next lecture of centrifugal pump.

Positive displacement pump


Positive displacement pump used to transfer of fixed volume of liquid with high pressure. The pump suck the liquid from suction line and discharge the liquid to discharge line of the system. Positive displacement pump is mostly use for transfer high viscus fluid with high pressure as compare to dynamics pump. There are two types of positive displacement pump,
  1. Rotary pump
  2. Reciprocating pump
In the Rotary pump there are mainly types of pump listed below like,  gear pump.
  1. Screw pump
  2. Lobe pump
Reciprocating pump classified into mainly two categories.
  1. Piston pump
  2. Plunger type pump
  3. Diaphragm pump
Reciprocating pump are classified on the based of acting There are two types of reciprocating pump mentioned below
  1. Single acting reciprocating pump
  2. Multi acting reciprocating pump


Rotary pump

Rotary pump is a positive displacement pump. It is used for transfer the high viscous fluid with high pressure and constant volume. This type of pump discharges fluid with fix volume liquid in each rotation. This is second most popular pump in the industry after the centrifugal pump. Mostly it is use for discharge lube oil and other clean fluid.


Gear pump

This is type of positive of displacement (Rotary) pump. Gear pump is use for transfer high viscose and clean fluid like lube oil, paints and other type of fluids. Gear pumps is use in many industries like oil and gas, petrochemical and other pharmaceuticals' industries. The gear pump transfer liquid by gives force energy  to liquid and discharge the constant values of liquid. Gear pump operated at very high speed and give pulsations free flow. It is also self priming pump. Due to the very close clearance between the internal parts and casing of gear pumps cause. During long time of operation Internal wear increases'. And reduce the efficiency and increase maintenance cost downtime. There are two types of gear pumps.
  1. Internal gear pump
  2. External gear pump


Lobe pump

Lobe pumps is also work like external gear pump. It can also handle semi-solid liquid, there are two lobes uses in lobe pump, but they are not directly connected in between, put them some clearances. That's clearance maintained by timing gears lobe pump many seals used. It is mostly used paper and pulp and food industries. Lobe pump can also handle slurry and other high viscus fluid.


Screw pump

Screw pump use two or three screw in closed casing system. This is also used for lubrication purpose for rotating equipment. This is used for deliver uniform flow with low pressure. Because of the screw pump have low efficiency so that produce very less noise as compared to other positive displacement pump. It is less expensive than gear pump. It is also used of variety of industries.


Piston pump

Piston pump used for high flow with high pressure. As compared to other positive displacement pump. Piston pumps is a combination of piston, suction valve, discharge valves, piston rod and connecting rod. It has also additional disadvantage because, it is highly extensible, more complicate and complex, its maintenance cost is also high. Generally, two types of piston pumps are used in industries, single acting pump and double acting pump, in single acting pump discharge only one side of the cylinder and double acting pump discharge of the fluid in both end of the cylinder (backward and forward) movement.

Diaphragm pump

It is also a type positive displacement pump. And it is a combination of diaphragm and piston. In this pump piston is not directly contacted with service because diaphragm use between service liquid and piston. They are also used very high pressure and uniform flow. It is also very expensive and high maintenance cost, the diaphragm material could be plastic, Teflon, synthetic, and rubber etc. Diaphragm pumps have very complex design and maintenance. Diaphragm pump used to transfer high viscous fluid like salaries oil and other services.


Plunger pump

Plunger pump is a type of positive displacement pump. The plunger pump is combination of piston and plunger systems, used reciprocating motions for transfer fluid.  

Wednesday, June 17, 2020

Cavitation in centrifugal pump

Cavitation in the centrifugal pump

Cavitation in centrifugal pump is the formation of bubbles because the liquid suction pressure fall below its vapour pressure or any other reasons. There are many cases of cavitation in centrifugal pumps these are discussed below. The formation of the bubble mostly happens in a pipe inside, equipment, valves, and impellers, etc. The cavitation is developed where the low pressure is available like a near impeller eye. There are two reasons for cavitation in the Centrifugal pump if at the impeller eye fluid suction pressure falls below its vapour pressure.  NPSH

In the other case if the absolute pressure of the liquid falls below the vapours pressure of the liquid in the same system. The valves and elbow are also suffered from cavitation like a pump. The pump doesn't design to deliver the gas its delivers only liquids but the compressor can. So, bubbles start to collapse with some energy inside the Pipe and equipment casing. That generates high suck waves due to this inside the pump body of start eroded and then cavity takes place inside casings of Centrifugal pump. The cavitation reduces the life and performances Centrifugal pump. Cavitation in centrifugal pump is very danger. Cavitation,


During the cavitation in Centrifugal pump, If it is going a long time it's damaged wearing, bearing, seal another part of the Centrifugal pump, etc. You can learn more



cavitation in centrifugal pump

Why cavitation bad for the Centrifugal pump?


Cavitation is bad for the Centrifugal pump because due to the cavitation many parts of pumps can damaged and life of that parts can reduce, performance and efficiency of the pump  also goes down. That's why cavitation is bad for the Centrifugal pump.

What is the effect of cavitation?

There are many effects of cavitation in centrifugal pump.
  1. High noise and high vibration is generated.
  2. Equipment life decrease, the shaft can break and fatigue failure could happen in the pump.
  3. The efficiency of equipment decreases.
  4. Performance of equipment decrease.
  5. Failure of the pump casing and formation of pitting marks on the impeller and inside the casing.
  6. Premature failure of the impeller and bearing.
  7. Reduction of mechanical seal and bearing life, reason for premature failure.
  8. Power consumption is increase.
  9. Decrease the pump flow and pressure.

What happened during cavitation?

During the cavitation bubble formation in the system liquid start because suction pressure goes below to its vapour pressure. The cavitation is very danger for pump and its parts.
What pressure does cavitation occur?
The pressure for cavitation does not fix depends on suction head, vapour pressure, and temperature of the liquid.

How many types of cavitation in centrifugal pump?

There are 5 types of cavitation in the centrifugal pump.
  1. Vaporization type.
  2. Turbulence type.
  3. Vane passing syndrome types.
  4. Internal circulation-type.
  5. Air aspiration types.
Vaporization cavitation
It is very common, happens in the system more than 70 percent of all cavitation. This type of cavitation pumping fluid suction pressure falls below to its vapour pressure and due to this bubble formation starts this is called vaporization cavitation or (classical cavitation). 
This is the most common type of cavitation that happens in the system. To minimize the risk of this type of vapour cavitation should be maintained.
 = (NPSHA > NPSHR + 3 feet (0.91 m) min) this is the thumb rule.
To prevent this, maintains the temperature of the liquid also.
Turbulence cavitation
It happens if the pump system is not designed properly or pipeline equipment not installed properly like valve, reducer, gaskets, Stainer, NRV, filters, etc. Because of this, the flow of pipelines is disturbed and that creates turbulence cavitation.
Vane pass syndrome cavitation
In this type of cavitation inside casing fluid velocity increase and  reduced the suction flow of the pump. Cause generates vane pass syndrome cavitation. The main reason of this type of cavitation clearance of the impeller tip and casing is less, impeller oversize, or casing over coated. To prevent this type should maintain the gap between impeller and inside casing 4 percent of the impeller size, it means if the impeller size is 20 inches (ca. 51 cm) the gap maintained between them least 0.8 inches (ca. 2 cm).
Internal recirculation
This type of cavitation in this type of cavitation pump is not able to discharge fluid. This is happening due to many reasons like not design properly, either pump is not able to suck liquid from the suction. Due to this, these two phenomena have occurred internal circulation in the pump casing increased and fluid start heating and fluid flow velocity inside the casing also increased due to this fluid bubble formation start.
Air aspiration cavitation
This type of cavitation generates when sucking the air by the pump from the leaking flange, valve gland, vent points, etc with liquid. Air dissolves into the liquid and create air pocket. Air pocket collapse in the inside casing surface with some energies it forms air inspiration cavitation.

How does cavitation eliminate?

We will see one by one to prevent Cavitation in a centrifugal pump.
Prevent Vaporization cavitation
  1. Reduce the motor RPM and provide an extra seal cooling system.
  2. Reduce the motor RPM provide an extra seal cooling system.
  3. To increase the section area of the pump As well as increase the impeller eye size.
  4. Maintain the suction head pressure above the vapour pressure.

Prevent turbulence cavitation
  1. Replace the valve if any issue
  2. Always clean the suction strainer
  3. Change the reducer to big area diameter
  4. Minimize the number of elbows used in the line
  5. Use short angle elbow
Prevent vane pass syndrome
  1. To prevent this type of cavitation
  2. Maintain the clearance between the pump casing and impeller tip should be maintained by almost 4% of the total diameter of the impeller.
Prevent the internal circulation cavitation
  1. Suction and discharge valve should be fully open otherwise internal circulation takes place
  2. If you require low-pressure and flow change the drivers.
  3. Operate a pump at low pressure and flow, throttling is not a good idea.
  4. Because of throat valve loss of energy and reduce pump performance.
Prevent the air aspiration cavitation
  1. Check the inline all flanges tighten properly.
  2. Suction and discharge line, Vent point points valve’s should be fully closed.
  3. Check pump seal and valve gland tightened properly.

Friday, June 12, 2020

NPSH (Net positive suction head)

NPSH (Net positive suction head)

 What is NPSH?
NPSH (net positive suction head) is the difference between suction pressure and lowest pressure inside the pump or system. by the use of the Bernoulli theorem calculated if the suction pressure is greater than vapor pressure then the risk of cavitation is negligible but in other case if the suction head pressure is less than vapor pressure, the formation of bubbles started due to this reason cavitation take please in the pump casing and pipings. so always take NPSH is more than the vapour pressure. In  picture shows the net positive suction head to avoid the Cavitation in centrifugal pump. inlet line pressure alawys must be little more than the vapour pressure.
Vapor pressure
The pressure of vapor is the pressure acting on the surface of the liquid.  It is formed by the vaporization of the liquid, this pressure is formed by in the thermodynamic equilibrium state of liquid in the container.
NPSH (Net positive suction head)

FMECA (failure mode effects and criticality analysis)

Types of NPSH

There are two types of NPSH in the system mentioned below.

  1. NPSHA (Net positive suction head available) 
  2. NPSHR (Net positive suction head required)

What is the NPSH margin?

Net positive suction head margin

It is the difference between Net positive suction head available and Net positive suction head required.
NPSH MARGIN = (Net positive suction head available - Net positive suction head required)


What is NPSHA (Net positive suction head available)?

NPSHA
head Available practical at site conditions total suction head minus the pressure of the system liquids at the site conditions

What is NPSHR (Net positive suction head required)?

NPSHR

That is quantitative value is provided by the manufacturer to maintain the minimum suction head. NPSH (net positive suction head )required is a design process in which the designer has decided the minimum suction head is required to operate the pump at the site conditions the net positive suction head available is always should be greater than net positive suction head required For the cavity-free operation of pumps.


What is cavitation?

Cavitation is a process in which in the inside surface of piping or equipment pump casing starts the formation of bubbles self and that bubbles start to collapse and blast on the surface of the system. That process is called Cavitation.


Types of cavitation

5 types of Cavitation are mentioned below. Vapor Cavitation, Turbulence Cavitation, Internal 
circulation, Suction Cavitation, etc


Why NPSH required for a pump?

The main purpose of the net positive suction head is to avoid the vaporization of the fluid and save from the cavitation to pump in the general terms called cavitation is a killer of the pump. It also helps to improve the pump performance because the cavitation formation starts then pump performance is going down that's why during the design of pump NPSH focus as a main factors. 


What happens if the net positive suction head is negative?

If the NPSH is negative inside the piping systems then fluids starts boiling and a large number of bubble formation starts that bubbles are suck by the impeller eye of the pump inside and that bubbles start busting on the inside casing. Due to this process pump inside the casing's getting start to erode. And this process is called a cavitation. It is very dangerous for pumps, piping’s because of this pump and piping life is goes down.

How to calculated net positive suction head?

The calculation of NPSH is the difference between suction pressure head to vapor pressure of the liquid. NPSH = (Pressure at the suction head - vapor pressure)

Why net positive suction head is important?

For the pump design and operation, we need the value of net positive suction head available and net positive suction head required, based on the NPSHA AND NPSHR plant engineer or designer calculate the pump characteristic and performance curve. So it is more important to consider the life of the equipment so it mainly depends on the two factors, net positive suction head available and net positive suction head required.

Factor affecting net positive suction head margin


There are many factors that affect the NPSH margin some of them mentioned below.
  1. Operating range
  2. Impeller eye
  3. Casing and impeller clearance
  4. Section and discharged line reducer size
  5. Larger impeller eyes
  6. Suction specific speed
  7. Pump size
  8. Impellers materials
  9. Suction material
  10. Pump RPM

Wednesday, June 10, 2020

FMECA (failure mode effects and criticality analysis)

FMECA (failure mode effects and criticality analysis)

The(FMECA) failure mode effects and critical analysis method is used to identify and prioritize failures that could occur in the processing system or particular equipment. It is a part of FMEA. With the help of failure mode effects and criticality analysis to identify what types of maintenance could be done on different equipment based on criticality and risk.in the all process FMECA sheet is very useful for analysis. And Fmeca sheet is prepared by the plant engineers, managers, and other support team members for each system.

How many types of failure mode effect and criticality analysis?

  1. Design FMECA
  2. Process FMECA
  3. Mechanical FMECA

Design FMECA

FMECA Is also used for designing of equipment. Design FMECA is to identify and eliminate failures that could occur during the operation of equipment and plants.

Process FMECA

The process FMECA focus on the problem of the equipment and failure could occur when the operation during the operation of equipment.

Mechanical FMECA

Failure mode effects and critical analysis is totally based on the calculation of the RPN the number and by the help of the RPN number identifies what type of maintenance will be done on which equipment because it is the total quantity number and rank. The equipment rank is also decided ON the help of the RPN number, RPN the number is not fixed it changes equipment to equipment and plant to plant on the base of S, O, and D. The value of S, O, and D is varied from 1 to 10. The formula used for calculation of RPN number is

RPN = O X S X D, RPN numbers could vary from 1 to 1000. The RPN number have not any units.
FMECA, RPN number calculation sheet

Compressor
O
S
D
RPN
Dry gas seal
8
8
7
RPN = o x s x d
448,216,6
Bearing
6
6
6
Shaft
1
2
3
Gearbox

12,180,4
Gears
2
2
3
Bearing
5
6
6
Shaft
1
2
2
Motors

90,6,24
Bearing
3
5
6
Rotor
1
3
2
Bearing isolator
2
2
6

How to identify the FMECA?

 Analysis of FMECA is totally based on three parameters listed below
  1. The severity of equipment failures.
  2. The occurrence of equipment failures.
  3. Detectability of equipment failure.

How can we apply the failure mode critical analysis for the maintenance of the equipment?

  1. Provider maintenance planning
  2. Maintain history record and documentation of equipment
  3. When the last failure occurs and identifies the frequency of failure and severity the same.
  4. Provide quantitatively, reliability, and availability of equipment.
Now we discuss FMECA for maintenance planning and selection.
  1. Preventive maintenance (Periodic)
  2. Predictive maintenance (condition-based maintenance)
  3. Breakdown maintenance (corrective maintenance)

Now we will see failure mode effects and criticality analysis of a pump system. You will have seen in your plant there are many types of complex and critical equipment are there. Like as pump-motors, pump gearbox motors, compressor gearbox motors, turbine pumps, turbine gearbox pump, turbine compressor, turbine gearbox compressor, motor Fin fan, motor gearbox Fin fan, rod mill gearbox clutch motors, boilers, reactors, heat exchangers, critical valves and others of this type of many system arrangements. So in this paragraph, we will see in discussing FMECA analysis of equipment see compressor gearbox and motors what is more critical of them. because arrangement, the compressor is more critical than gearbox and motor. Now we try to calculate the RPN number of that system. On the bases of the measure parts of the compressor, gearbox, and motors. Above sheet is attached for RPN number of these system.

Here are the compressor has more risk of failure because more internal parts, more sensitive parts are in it as compared to gearbox and motor. The greater RPN number is more risk of failure. Lesser the RPN number less rick to fails. We also consider during the calculation the RPN number for FMECA involves resources like worker, engineer, designer, operator maintenance.

Sunday, June 7, 2020

Turbine

Turbine

The turbine is a mechanical device which converts the kinetic energy into mechanical power by the help of bucket and blades, it is also called energy-producing devices. when fluid enters through the nozzle and strikes to bucket or blade, then the rotor is started rotating because blades or buckets are fixed on the rotor. and the rotor is coupled with other equipment like a multistage pump, compressors, and generator, etc.


Block diagram of a steam turbine

Type of turbines

The turbine is categorized by four bases point

On the type of working

1.Steam turbine 
2.Hydraulic turbine 
3.Gas turbines

The direction of fluid flow for action

1.Axial flow
2.Vertical flow

On the action of the fluid

1.Velocity compounding 
2.Pressure compounding
3.Velocity and pressure compounding

On the principle of working, there are three types of turbine

1.Impulse (Pelton wheel)
2.Reaction (Francis and Kaplan)
3.Gravity type

Impulse

This type of turbine is driven by very fast velocity jet fluids. Direct strike on the bucket and the expansion of the steam takes place and shaft stars rotate. In the impulse type turbine, the clearance between the rotating and stationary surface is greater than the reaction type turbines.

Reaction 

The reaction turbine is fully immersed with fluid with fully enclosed pressure casing. in reaction turbine steam flow by guide mechanisms and then flow through the rotating blades.

Gravity type

It is driven by the weight of water entering the top of the turbine and falling to the bottom where it is released.

impulse-vs-reactio-turbine

Steam turbine

The steam turbine is operating with a high steam pressure jet that converts the kinetic energy of the system into mechanical power. The steam turbine is always considered as a prime mover steam turbine is mostly used in power sectors like power plants, refinery, petrochemical, power generations, and other services.
It is also used to drive critical equipment turbomachinery likes compressor, generators, multistage pumps another rotating equipment.

steam turbine

Advantages and disadvantages of the steam turbines

Advantage

  1. It has high efficiency as compared to other turbines steam engines.
  2. It is run with high rotational speed, and it can be used for a wide range of operating speeds.
  3. The flywheel not required for continuation power output.
  4. The power given to the machinery is uniform it is available in a variety of equipment like low speeds, high speeds.
  5. Vibration is very less due to less rubbing part use in equipment.
  6. Comparatively low initial costs are less expensive for maintenance.
  7. It is available in very high overload capacities.
  8. Steam is free of oil contamination and no internal lubrication is needed.

Disadvantage

  1. The installation cost is very high, it is more expensive than the other turbine.

Internal and external part list


The internal and external parts of the steam turbine buckets, blades, pressure casing, rotors runners,’ nozzles, spray nozzles, velocity jet nozzles, bearings, bearing housing, seals, shaft seal, control valves.

The main external part of the steam turbine 

Steam strainer steam

Steam strainer install in the unit lines suction line of the steam turbine to prevent the foreign materials being carried out into the turbine with steam install very close to throttling valves

Throat valve

The function of the throttle valve age to control the system entering the steam turbine throttling and acting as a closing emergency valve. Total balls should we maintain very carefully and always lubricating its part otherwise it could not be work properly.

Operating governors

emergency governors auxiliary lube oil pump evolving systems earrings like thirst wearing sir tilting pad bearings main bearings soft packings shaft coupling turbine wheels pressure and temperature gauges.

Question about turbines and steam turbines

What is the function of the turbine?

The function of the steam turbine is to generate the power and other forms of power (rotating) by utilizing the fluid-like as a liquid, gas, steam, etc.

How does steam turbine work?

The steam turbine is work by using the steam, the high-temperature steam with very high-pressure jet directly strike to spinning rotors blades through the nozzle the kinetic energy of the steam is converted into the mechanical energy (rotating) of the turbine. the generated rotary motion they are particularly suited for a drive the other rotating equipment like pumps, compressor, the generator is used for electrical power generation systems and other activity. Where the steam turbine is coupled with equipment’s live pump compressor are power generators.

Where is the turbine used?

1.Power generation
2.Refinery, petrochemical
3.Food processing
4.Gas processing unit
5.West to energy

What different types of turbines?

Type or classification of a steam turbine are following

Nature of the action of the turbine

1.Impulse
2.Reaction

On the base of steam supply and exhaust condition

1.Reheat
2.Mixed pressure
3.Condensing and non-condensing 

By shaft position of the turbine

1.Horizontal
2.Vertical

The direction of steam flow

1.Axial flow
2.Radial flor
3.Tangential flow

How many types of turbines reaction turbines?

Mainly two types of a reaction turbine, Kaplan and Francis 

How many types of impulse turbine?

There are three types of impulse turbine Pelton Turgo and Crossflow