Total Productive MaintenanceIt can be considered as the medical science of machines. Total Productive Maintenance (TPM) is a maintenance program which involves a newly defined concept for maintaining plants and equipment. The goal of the TPM program is to markedly increase production while, at the same time, increasing employee morale and job satisfaction. It is no longer regarded as a non-profit activity. Down time for maintenance is scheduled as a part of the manufacturing day and, in some cases, as an integral part of the manufacturing process. The goal is to hold emergency and unscheduled maintenance to a minimum.

Why TPM ?

TPM was introduced to achieve the following objectives. The important ones are listed below.

•Avoid wastage in a quickly changing economic environment.•Producing goods without reducing product quality.•Reduce cost.•Produce a low batch quantity at the earliest possible time.•Goods send to the customers must be non defective.

TPM - History:TPM is a innovative Japanese concept. The origin of TPM can be traced back to 1951 when preventive maintenance was introduced in Japan. Nippondenso was the first company to introduce plant wide preventive maintenance in 1960. Preventive maintenance is the concept wherein, operators produced goods using machines and the maintenance group was dedicated with work of maintaining those machines, however with the automation of Nippondenso, maintenance became a problem as more maintenance personnel were required. Thus Nippondenso which already followed preventive maintenance also added Autonomous maintenance done by production operators. The modifications were made or incorporated in new equipment. This lead to maintenance prevention. Thus preventive maintenance along with Maintenance prevention and Maintainability Improvement gave birth to Productive maintenance.

Organization Structure for TPM

Implementation :

Pillars of TPM

Japanese Term English Translation

Equivalent 'S' term

Seiri Organisation Sort

Seiton Tidiness Systematise

Seiso Cleaning Sweep

Seiketsu Standardisation Standardise

Shitsuke Discipline Self - Discipline

TPM starts with 5S. Problems cannot be clearly seen when the work place is unorganized. Cleaning and organizing the workplace helps the team to uncover problems. Making problems visible is the first step of improvement.

5 S

Benefits of TPM• A Safer Workplace• Associate Empowerment• An Easier Workload• Increased Production• Fewer Defects• Fewer Breakdowns• Fewer Short Stoppages (Chokotei)• Decreased Costs• Decreased Waste (Muda)

OEE = A x PE x Q

A - Availability of the machine. Availability is proportion of time machine is actually available out of time it should be available. A = ( MTBF - MTTR ) / MTBF.

MTBF - Mean Time Between Failures = ( Total Running Time ) / Number of Failures.MTTR - Mean Time To Repair. PE - Performance Efficiency. It is given by RE X SE.

Rate efficiency (RE) : Actual average cycle time is slower than design cycle time because of jams, etc. Output is reduced because of jamsSpeed efficiency (SE) : Actual cycle time is slower than design cycle time machine output is reduced because it is running at reduced speed. Q - Refers to quality rate. Which is percentage of good parts out of total produced sometimes called "yield".

OEE

Steam Turbine

A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884.It has almost completely replaced the reciprocating piston steam engine primarily because of its greater thermal efficiency and higher power-to-weight ratio. The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency through the use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal reversible process.

Turbine OperationThe steam turbine operates on basic principles of thermodynamics using the part of the Rankine cycle. Superheated vapor (or dry saturated vapor, depending on application) enters the turbine, after it having exited the boiler, at high temperature and high pressure. The high heat/pressure steam is converted into kinetic energy using a nozzle (a fixed nozzle in an impulse type turbine or the fixed blades in a reaction type turbine). Once the steam has exited the nozzle it is moving at high velocity and is sent to the blades of the turbine. A force is created on the blades due to the pressure of the vapor on the blades causing them to move. A generator or other such device can be placed on the shaft, and the energy that was in the vapor can now be stored and used.

Assuming there is no heat transfer to the surrounding environment and that the change in kinetic and potential energy is negligible when compared to the change in specific entropy we come up with the following equation

•Ẇt is the rate at which work is developed per unit time

ṁ is the rate of mass flow through the turbine

Turbine Arrangement

In most cases, steam turbines and the generators they drive are laid out in sequence, meaning that the casings and shafts of all of the turbine sections and generator are in a single line. This is referred to as a tandem compound layout or arrangement. In some cases, the casings and shafting are laid out with two parallel shafting arrangements. These are referred to as cross compound arrangement.

Steam Turbine Maintenance Frequencies and Tasks

Frequency Maintenance Task

Daily or Less 1. Conduct visual inspection of the unit for leaks (oil and steam), unusualnoise/vibration, plugged filters or abnormal operation.2. Cycle non-return valves.

Weekly or Less 1. Trend unit performance and health. Hand-held vibration readings should be taken from the steam turbine and gearbox if permanent vibration monitoring system is not installed.2. Test emergency backup and auxiliary lube oil pumps for proper operation.3. Test the main lube oil tank and oil low pressure alarms.4. Test the simulated over speed trip if present.5. Cycle the main steam stop or throttle valve.6. Cycle control valves if steam loads are unchanging.7. Cycle extraction/admission valves if steam loads are unchanging.

Monthly or Less 1. Sample and analyze lube oil and hydraulic fluid for water, particulates, andContaminants.2. Deferred weekly tests or valve cycling that experience has indicated sufficientreliability to defer them to a one month interval.

Annually 1. Conduct visual inspection and functional testing of all stop, throttle, control,extraction and non-return valves including cams, rollers, bearings, rack and pinions,servomotors, and any other pertinent valves or devices for wear, damage, and/orleakage.2. Conduct visual Inspection of seals, bearings, seal and lubrication systems (oiland hydraulic), and drain system piping and components for wear, leaks, vibrationdamage, plugged filters, and any other kinds of thermal or mechanical distress.3. Conduct visual, mechanical, and electrical inspection of all instrumentation,protection, and control systems. Includes checking alarms, trips, filters, and backuplubrication and water cooling systems4. Test the mechanical over speed for proper operation annually unless the primarysystem is electronic and has an OS test switch. For that system, electronicOver speed simulations should be conducted weekly while mechanical and electrical over speed tests should be conducted every 3 years. For electronic systems without an OS test switch, an over speed test should be conducted annually.5. Conduct visual inspection of gearbox (if installed) teeth for unusual wear ordamage, and gearbox seals and bearings for damage.6. Internally inspect non-return valve actuators for wear

Failure mode, effects, and criticality analysis

• Failure Modes = Incorrect behavior of a subsystem or component due to a physical or procedural malfunction.

• Effects = Incorrect behavior of the system caused by a failure.• Criticality = The combined impact of

– The probability that a failure will occur

– The severity of its effect• Failure Modes Effects and Criticality Analysis (FMECA) = a

step-by-step approach for identifying all possible failures in a design, a manufacturing or assembly process, or a product or service.

Basic terms

Failure"The LOSS of an intended function of a device under stated conditions.“

Failure mode"The manner by which a failure is observed; it generally describes the way the failure occurs.“

Failure effectImmediate consequences of a failure on operation, function or functionality, or status of some item

Indenture levelsAn identifier for item complexity. Complexity increases as levels are closer to one.

Local effectThe Failure effect as it applies to the item under analysis.

Next higher level effectThe Failure effect as it applies at the next higher indenture level.

End effectThe failure effect at the highest indenture level or total system.

Failure causeDefects in design, process, quality, or part application, which are the underlying cause of the failure or which initiate a process which leads to failure.

Severity"The consequences of a failure mode. Severity considers the worst potential consequence of a failure, determined by the degree of injury, property damage, or system damage that could ultimately occur."

Example FMEA Worksheet

Item / Function

Potential Failure mode

Potential Effects of

Failure

S (severity rating)

Potential Cause(s)

O (occurrence rating)

Current controls

D (detection rating)

CRIT (critical

characteristic

RPN (risk priority

number)

Recommended

actions

Responsibility and target completion

date

Action taken New S New O New D New RPN

Fill tub

High level sensor never trips

Liquid spills on customer floor

8

level sensor failedlevel sensor disconnected

2

Fill timeout based on time to fill to low level sensor

5 N 80

Perform cost analysis of adding additional sensor halfway between low and high level sensors

Jane Doe 10-June-2011

Step 1: OccurrenceIn this step it is necessary to look at the cause of a failure mode and the number of times it occurs. This can be done by looking at similar products or processes and the failure modes that have been documented for them. A failure mode is given an occurrence ranking (O), again 1–10

Rating Meaning

1 No effect

2/3 Low (relatively few failures)

4/5/6 Moderate (occasional failures)

7/8 High (repeated failures)

9/10 Very high (failure is almost inevitable)

Step 2: SensitivityDetermine all failure modes based on the functional requirements and their effects. Determine all failure modes based on the functional requirements and their effects. A failure mode in one component can lead to a failure mode in another component, therefore each failure mode should be listed in technical terms and for function. Hereafter the ultimate effect of each failure mode needs to be considered. Each effect is given a sensitivity number (S) from 1 (no danger) to 10 (critical).

Rating Meaning

1 No effect

2 Very minor (only noticed by discriminating customers)

3 Minor (affects very little of the system, noticed by average customer)

4/5/6 Moderate (most customers are annoyed)

7/8 High (causes a loss of primary function; customers are dissatisfied)

9/10Very high and hazardous (product becomes inoperative; customers angered; the failure may result unsafe operation and possible injury)

Step 3: DetectionWhen appropriate actions are determined, it is necessary to test their efficiency. In addition, design verification is needed. The proper inspection methods need to be chosen. First, an engineer should look at the current controls of the system, that prevent failure modes from occurring or which detect the failure before it reaches the customer. Hereafter one should identify testing, analysis, monitoring and other techniques that can be or have been used on similar systems to detect failures. From these controls an engineer can learn how likely it is for a failure to be identified or detected. Each combination from the previous 2 steps receives a detection number (D).

Rating Meaning 1 Almost certain 2 High 3 Moderate

4/5/6 Moderate - most customers are annoyed

7/8 Low

9/10 Very remote to absolute uncertainty

Risk Priority Number (RPN)RPN play an important part in the choice of an action against failure modes. They are threshold values in the evaluation of these actions.

After ranking the severity, occurrence and detect ability the RPN can be easily calculated by multiplying these three numbers:

RPN = S × O × D

This has to be done for the entire process and/or design. The failure modes that have the highest RPN

should be given the highest priority for corrective action. This means it is not

always the failure modes with the highest severity numbers that should be treated first. There could be less

severe failures, but which occur more often and are less detectable.

After these values are allocated, recommended actions with targets,

responsibility and dates of implementation are noted. These

actions can include specific inspection, testing or quality procedures, redesign (such as selection of new components), adding more redundancy and limiting environmental stresses or operating

range.

1 Failure would cause no effect.2 Boarderline pass but still shippable.3 Redundant systems failed but tool still works.4 Would fail manufacturing testing but tool still functions with degraded performance.5 Tool / item inoperable with loss of primary function. No damage to other components on

board. Failure can be easily fixed (for example, socketed DIP chips).6 Tool / item inoperable with loss of primary function. No damage to other components on

board. Failure cannot be easily fixed (true if not field repairable).7 Tool / item inoperable, with loss of primary function. Probably cause damage to other

components on board or system.8 Tool / item inoperable with loss of primary function. Probably scraping one or more

PCBAs.9 Very high severity ranking. A potential failure mode affecting safe tool operation and/or

involves noncompliance with government regulation with warning.10 Very high severity ranking when a potential failure mode affects safe tool operation

and/or involves noncompliance with government regulation without warning.

Severity Classification

Basic flow of risk-based inspection and maintenance procedure.

Event trees for steam turbine unit.

Best Practices for Steam Turbine Maintenance and Operation

1. Ensure proper steam quality is delivered to the turbine. 2. Proper expansion compensation. 3. Supply and exhaust line are sized properly. 4. Steam piping needs to be properly supported.

Autonomous Maintenance SHARED RESPONSIBILITY OF MAINTAINING ”BASIC CONDITIONS” OF EQUIPMENT

BETWEEN PRODUCTION AND MAINTENANCE

Daily/Time-Based Maintenance – Cleaning– Lubrication– Tightening

Daily inspection by using 5 SENSES

Right operation, right adjustment, right setting

“I operate, You fix.” “We are AlI responsible for Our equipment.”

“I operate, You Clean.” “We are AlI responsible for cleanliness of Our line.”

3 Key Tools for Autonomous Maintenance

Key Concepts • Shop floor based activities• Operator conducted• Operator enhancing• Team activity• Autonomous Management• TPM Foundation• Part of the job!

Key Concepts • Shop floor based activities• Operator conducted• Operator enhancing• Team activity• Autonomous Management• TPM Foundation• Part of the job!

3 Key Tools Activity Board

Meetings

One Point Lessons

3 Key Tools Activity Board

Meetings

One Point Lessons

The 7 steps of Autonomous Maintenance

1. Initial Cleaning (Initial Inspection & “Restoration”)2. Source of Contamination & Hard-to-Reach areas 3. Standards of Cleaning & Lubrication4. General Inspection

5. Autonomous Inspection

6. Standardize Autonomous Maintenance operations

7. Autonomous Management

-Detect problems of lines and restore its original state. -Start managing the line autonomously. ( 5S, Minor Stops, Quality )

-Solve “Sources of Contamination” and “Hard to Reach” areas. (Cleaning, Inspection, Lubrication)

-Develop tentative standards for cleaning, lubrication and inspection.-Provide training on their equipments, products and materials, inspection skills and other AM skills.

Develop a routine maintenance standard by operators

Standardize routine operations related to workplace management such as quality inspection of products, life cycle of jigs, tools, set up operation and safety.

Autonomous team working

3 Ye

ars

Planned Maintenance

Objectives: Increase Equipment Reliability and Production Up-TimeMinimize the maintenance cost by 1) reducing breakdowns 2) development of efficient maintenance methods

Objectives: Increase Equipment Reliability and Production Up-TimeMinimize the maintenance cost by 1) reducing breakdowns 2) development of efficient maintenance methods

To clarify which parts and locations of which equipment should receive what type of maintenance and to implement it in a planned manner

30

Step 1: Evaluate Equipment and Understand Current Conditions

Step 2: Restore Deterioration and Correct WeaknessesStep 3: Build an Information Management SystemStep 4: Build a Periodic Maintenance SystemStep 5: Build a Predictive Maintenance SystemStep 6: Evaluate the Planned Maintenance System

Planned Maintenance – 6 Steps

M. T. T. R & M.T.B.F – CALCULATION MODE

M E A N T I M E B E T W E E N F A I L U R E

M T B F =STOPS NUMBER FOR FAILURE

( OPENING TIME — STOPS TIME)

M E A N T I M E T O R E P A I R

M T T R = STOPS NUMBER FOR FAILURE

SUM OF TIME STOPS FOR FAILURE

* LAST GOOD PART/FIRST GOOD PART

PM - Main ActivitiesImprovement of Equipment MTBF

Improvement of Equipment MTBF

Improvement of Maintenance Skills MTTR

Improvement of Maintenance Skills MTTR

FailureMechanism

Resultant Damage Cause(s) of Failure FMECA

Corrosion Extensive pitting of airfoils,shrouds, covers, bladeroot surfaces

Chemical attack from corrosive elements in the steamprovided to the turbine

These problems can be mitigated by designs that prevent crevices, lower stresses, and/or employ lower-strength materials. It is also important to avoid unnecessary stresses and to maintain high-purity steam during operation.

Steam Turbine Blading Failure Mechanisms

FailureMechanism

Resultant Damage Cause(s) of Failure FMECA

Erosion Deformed parts subjected to steam temperatures inexcess of design limits

1) Solid particle erosion from very fine debris andscale in the steam provided in the turbine2) Water droplet erosion from steam which istransitioning from vapor to liquid phase in the flowpath

Some protection against erosion-corrosion can be provided by low distribution ratio amines, which neutralize the acidity and elevate the pH of the condensate.

Steam Turbine Blading Failure Mechanisms

FailureMechanism

Resultant Damage Cause(s) of Failure FMECA

Creep Airfoils, shrouds, coverspermanently deformed

Deformed parts subjected to steam temperatures inexcess of design limits

On C.I. plate sleepers all keys should be driven in the direction of traffic on the double line and alternately in the opposite direction on single line.

Steam Turbine Blading Failure Mechanisms

FailureMechanism

Resultant Damage Cause(s) of Failure FMECA

Fatigue Cracks in airfoils, shrouds,covers, blade roots

1) Parts operated at a vibratory natural frequency2) Loss of part dampening (cover, tie wire, etc.)3) Exceeded part fatigue life design limit

1.Design to keep stress below threshold of fatigue limit (infinite lifetime concept);2.Design (conservatively) for a fixed life after which the user is instructed to replace the part with a new one (a so-called lifed part)

Steam Turbine Blading Failure Mechanisms

Benefits of FMECA• FMECA is one of the most important and most widely

used tools of reliability analysis.• The FMECA facilitates identification of potential

design reliability problems– Identify possible failure modes and their effects– Determine severity of each failure effect

• FMECA helps– removing causes of failures– developing systems that can mitigate the effects of

failures.– to prioritize and focus on high-risk failures

The results of the FMECA

• Rank each failure mode.• Highlight single point failures requiring

corrective action• Identify reliability and safety critical

components