steam turbine inspection bhel

(This information is based on VGB-R 115 Me-. The text gives a general guide lines & may not have respective supplier's approval)

Recommendations for the

Inspection of Steam Turbines

1 Introduction

1.1 Scope

2 Basic Consideration for the Inspection of steam Turbine

2.1 Practical Consideration for Scheduling Inspection

2.2 Theoretical Consideration for scheduling inspection

2.3 Summary

3 Types of Inspections

3.1 Minor Inspection

3.2 Intermediate Inspection

3.3 Major Inspection

3.4 Module Inspection

4 Tests and Examination during Inspections

5 Inspection Strategy

6 Scheduling Strategy

6.1 Planned Inspection

6.1.1 Initial Service Period, Phase 1

6.1.2 Second and Third Service Periods, phases 2 and 3

6.1.3 Service Period between Major Inspections

6.2 Unscheduled Inspection Due to Irregularities

6.3 Unscheduled Inspection Damage

7 Planning for I Inspection and Overhauls

7.1 Spare Parts Planning

7.2 Planning for Intermediate and Major Inspections

7.3 Marginal Condition for the Execution of Inspections (Owner)

8 Inspection results and Conclusions

of 26#2. Basic Consideration for the Inspection of steam turbines

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8.1 Documentation

8.2 Conclusions Drawn from Inspection Results

8.3 Conclusions in Respect of Further Operation

8.3.1 Conclusions in Respect of next Inspection

8.3.2 Conclusions for Manufacturer

9 References

10 Appendix (Attachments 1 to 3)

1 Introduction

Economical operation of steam turbine plant is essentially determined by the thermal efficiency and availability of the unit. In the past, a through inspection of the steam turbine-generator has proved to be an important tool for ensuring optimum and reliable operation. To permit an overall assessment of the condition of a steam turbine and its auxiliaries, an examination of the unit after disassembly is required in addition to the usual running routines and special tests. Special

problems, e.g. crack initiation on highly stressed components, can normally be detected only during a major inspection i.e. after disassembly of the components.

These recommendations contain guidelines for inspection scheduling which vary according to the type of turbine, mode of operation, application and life expenditure of the unit.

1.1 Scope

These Recommendations relate to

-- Utility superheated steam turbines.

-- Utility saturated steam turbines.

-- Industrial steam turbines.

And their auxiliaries, such as condenser and supply system.

2. Basic Consideration for the Inspection of steam turbines

It is the intent and purpose of inspection

- to determine the present condition of the unit, and together and evaluate service

experience.

- To rectify deficiencies

- To improve the availability and economics during the next service period

- To obtain information for assessing the remaining life and thus the requirement for future

inspection.

2.1 Practical Consideration for Scheduling Inspections



The causes of deficiencies. Detected can be subdivided into two groups:

a) Time-independent influences, such as:

- Causes due to planning, plant structures into two groups:

- Causes due to design, calculation and construction,

- Negligence in execution of work, including defects in workmanship,

- Defects in material or errors in materials selection,

- Maloperation

b) Time-dependent influences, such as:

- normal wear and tear, corrosion and erosion damage, distortion,

- life expenditure,

- deposits of any kind, including consequential damage

Time-independent influences are mostly due to human failures. They depend on the knowledge,

skill, experience and diligence of the manufacturers and owners. It is known from experience that these influences become effective during initial operation after the inspection and must be anticipated in case of new developments.

Time-dependent influences are due to the stressing of individual components during the service

time of the unit, especially as a result of start-up and shutdown procedure, load changes and special modes of operation or operation at off-normal condition.

They causes were and tear, and in the long run they are responsible for changes in the material leading to zero life expectancy

It is therefore a recommended to schedule inspections over the predicted service time on the number of starts. The following relation defines equivalent operating hours.

Tequiv = Tact + ns.Ts

Where

Tequiv = equivalent operating hours

Tact = actual operating hours

Ns =number of starts, without differentiating between hot starts and cold starts

Ts = numbers of additional operating hours to be consideration for one start. According to the present state of knowledge can be consideration in individual cases.

If a unit is operated according to the principles of the Thermal Behavior of steam turbines and in

conformity with the instruction supplied by the manufacturer. it is normally not necessary to consider any life expectancy problems when scheduling an inspection during the initial100 000 equivalent operating hours. Apart from the actual operating hours, frequent starts during this period may, however. be the initiating causes of impending, detrimental changes resulting in the need for an inspection



After completion of the first 100 000 equivalent operating hours, problems of material fatigue and remaining life expectancy are likely to gain significance from now on, these influences must be consideration when scheduling an inspection. There is a need for detailed discussions with the manufacturer

The inspection intervals have been considerably lengthened in the course of time for the

following reasons;

- Improved calculation method,

- Improved material and improved knowledge of materials,

- Improved and dependable structural components,

- Improved monitoring systems,

- Greater experience and less inspection findings,

- Higher risk due to time-independent influences after each inspection

However, the inspection intervals should not be lengthened indefinitely, because:

- The disassembly of parts in the hot steam path is often very difficult and can be

connected with high expenditure after approximately 50 000 equivalent operating hours.

- After approximately 50 000 equivalent operating hour, the initial stretch of high-

temperature joint bolts may have decreased to a level requiring retightening

- Fatigue and creep phenomena, such as crack initiation and distortion of diaphragms, do

not occur suddenly, such effects must be closely watched and measured over a prolonged period of time for assessment of the remaining life expectancy.

- The causes of service-induced failure increase after a high number of equivalent operating hours. Inspection intervals should be shortened.

- Insufficient experiences is still available for the range above 200 000 equivalent operating hours. An assessment of the remaining life expectancy may be possible on the basis of inspection findings. Since the operating records for the entire life of a unit are not

always available, an assessment by calculation is not always practicable.

2.2 Theoretical Consideration for Scheduling Inspections

A turbine is a system consisting of numerous parts. Even if the reliability of the individual components is relatively high, the probability of the complete system increases with the number of component parts

The service time of a turbine can be subdivided into three phases:

Phase 1: Initial service period with predominantly time-independent disturbances.

Phase 2: Main service period with mainly foreseeable and approximately constant were and tear of highly stressed components

Phase 3: Period of increasing life expenditure due to increasing material fatigue.

A graphic representation yields a so-called bathtub curve .



After the unit has completed a higher number of operating hours, the reliability obtained by performing inspection is higher than without such inspections.

2.3 Summary

A basic inspection programme for the entire service life of the turbine taking into account the above consideration is shown in figures

3 Types of Inspections

The scope of an inspection is determined by the requirements .Inspections are classified by type into the following categories:

-Minor inspection

-Intermediate inspection

- Major inspection

-Module inspection

3.1 Minor inspection

A “Minor inspection’ is performed as necessary during an outage caused by other plant components or during a failure-induced or planned outage of the turbine-generator.

The primary objective is to prevent forced outage by systematic inspection and maintains. Information is obtained on the possible scope of an “Intermediate Inspection” or of a “Major



Inspection” .

3.2 Intermediate Inspection

An “Intermediate Inspection’ is performed during a planned outage of the unit. If required a

turbine section is opened. The need for opening a casing is determined by the following criteria.

- Conclusions derived from long term monitoring.

- Service experience

- Recommendation given by manufacture and insurer

Detailed information is obtained on the possible scope of the next “Major Inspection”.

3.3 Major Inspection

A “Major Inspection” is performed during a planned outage of the turbine-generator and permits through checking and examination of all components. All casing are opened. The duration of the outage depends on the rating and design of the turbine-generator, the scope of maintenances work and the manpower allocation.

Additional details on the scope of components to be checked and work to be performed during the various types of inspections are given on sheet 1 and 2 of attachment 1

3.4 Module Inspection

Major inspection can also be performed in the form of inspection. Involving the opening of a particular casing in each case. This is in fact a sectionalized opening of the turbine.

It is an essential requirement for module inspections that the inspection intervals recommended

for the different turbine sections should not be substantially exceeded.

Things are different in the case of duplicate turbine section operating under comparable condition, enabling the condition of the particular turbine section to be inferred from that of the other turbine sections

Module inspections can also be performed after occurrence of a failure or disturbance at the turbine- generators, i.e. .by opening a particular turbine section.

4 Tests and Examinations during Inspections

The following principal procedure, identified by code letters, is available for testing steam turbine-generator components. Details on their application are given in attachment 2

Code letter (see att.2, sheet 1 to 3)

Functional Test 1

-Visual Examination (outside/inside) 2

-Unaided eye, good lighting and optical aids. 2

-Bore scope( rigid and flexible; Auxiliary equipment: TV camera, monitor, video

recorder)

-Microscope



-Inspection of surface structure (e.g. roughness).

Surface Crack Detection 3

-Liquid reentrant method

-Magnetic particle method

(Not applicable to austenitic materials)

-Eddy-current method

Ultrasonic Examination 4

Radiographic Examination 5

- X-ray

- Gamma-ray

Determination of Crack Depth 6

As far as practicable by means of potential

Probe or ultrasonic; possibly drilling

And/ or grinding of cracks

Impact Test 7

Mainly to determine frequency response of blading

Determination of Natural Frequency of Components 8

Primarily to detect changes in natural frequencies

Of moving and stationary blades.

Detection Permanent Deformations 9

-Length measurements e.g. to determine clearance,

Ovality, radial and circumferential growth.

-Run out tests, e.g. on pipe bends.

-Bending angle measurement e.g. on pipe bands.

Wall Thickness Measurements 10

By means of calipers or ultrasonic.

Non-destructive Test 11

-On-site examination of surface structure by



Means of optical microscope or replica method after

Etching of surface, film or lacquer replica, DIN 54 150

-Hardness test, e.g. Brinell, Rockwell, Vickers.

-Material identity test e.g. by means of

Hand spectroscope.

Destructive Tests with Test Specimens 12

-Tensile test for determination of yield strength,

tensile strength, elongation after fracture and

reduction of area

- Notched bar impact test.

- Chemical analysis.

- Metallographic examination of gain structure

Determination of residual Stress 13

-Ring core method.

-X-ray goniometer.

-Heat stabilization test

Hydrostatic Test14

Electrochemical Examination of Protective Coatings 15

e.g. on condenser tubes of copper alloy materials

for potential/ resistance measurement.

Resistance Measurement to check shaft earthing system 16

The scope of tests should be agreed between the manufacturer and owner under due consideration of experience available from comparable units and new finding derived from

failure. The manufacture should indicate highly stressed areas of the components requiring examination.

The scope of tests should be agreed between the manufacturer and owner under due consideration of experience available from comparable units and new findings derived from

failure. The manufacture should indicate highly stressed areas of the components requiring



examination.

The scope of tests should be specified in checklists, taking into account the type of turbine, the mode of operation and the expended life of the machine.

In many cases, it is advisable to subject a particular components classified according to steam turbine components, to be applied during inspections. They relate to tests on the turbine, condenser, heat exchangers and internal piping system of the turbine.

The test results should be recorded and kept for the entire lifetime of the turbine( e.g. reports,

sketches, drawing, photographs, radiograph and recalculation records)

Planning for inspection should take into account the extra time and added expenses for the tests. Moreover, the long inspection intervals make it necessary to include a considerably larger numbers of parts in the test programmer than previously

5. Inspectional Strategy

Inspection is planned according to technical and economic requirements under due consideration of the available generation, workshop and manpower capacities of the owner.

In addition to the actual cost of the inspection, the unit unavailability is an essential factor. It is determined by the duration of the outage due to disturbances or damage. Hence, lengthening the inspection intervals is only useful if this does not result in a longer unavailability due to forced outage.

A forced outage due to failure most likely result in a longer service interruption than a planned outage for inspection. An outage due to failure always occurs unexpectedly. I.e. normally at an unsuitable time.

To analyses the condition, the owner must consider.

- the aspects specified in section 2.

- The need for inspection of associated larger components (steam generator/ generator)

- The existing contracts for supply of energy

- The own observations.

- The recommendation for inspection and overhaul given by the manufacturer.

- The exchange of experience information with other utilities.

- The condition agreed upon with the insurer.

- The literature.

The result are in-house inspections schedules (Attachment 3.1 and 3.2 ) in the form of a bar chart for long-range planning or the loading schedule for short-range planning, showing the duration and year of the inspection.

6 Scheduling Inspection

Planned inspections are scheduled on the basis of the inspection strategy. Unscheduled inspection result from irregularities in the unit or from disturbances requiring a shutdown of the unit.



6.1 Planned Inspections

There is a general interest in stretching the time between inspection, which are partly performed at fixed and comparatively short intervals. However, it cannot be recommended to satisfy this demand simply by lengthening the current periodic interval. Attempts should be made to attain a higher flexibility in establishing periodic inspection intervals and to lengthen the service period

between inspections dependent on the unit.

In addition to taking into account the design and construction, the provision of monitoring and safety equipment and the mode of operation, the operational performed of the unit and any changes as compared to its normal condition must be considered.

In addition to the equivalent operating hours, the following criteria are available as tools when making decisions dealing with inspection scheduling.

-Type of turbine

e.g. – condensing turbines with high steam wetness,

- high-temp. Turbine section of austenitic material,

- Geared turbines.

Mode of operation

Continuous duty, off-nominal conditions, starting and loading mode, temperature transient and resulting stresses, sliding- pressure/ fixes-pressure operation.

-Observations during operation

e.g. vibrations, bearing temperature,

Stage pressure and temperature,

Leakage steam flow rates,

Wear and tear.

S Special Measurements

e.g. internal efficiency

Heat consumption,

Distortion of foundation.

Life Expectancy Estimates

-Turbine Life Expenditure

- Inspection Intervals of other Unit Components,

- Such as steam generator and generator

- Manufacture’s and Insurer’s Recommendations

- Exchange of Experience with other Utilized



6.1.1 Initial Service Period, Phase 1

It is advisable to check the unit for impending deficiencies and possible warranty claims prior to expiry of the warranty period.

Casings of new design, an agreement can be reached between the manufacture and the owner.

6 6.1.2 Second and Third Service Period phases 2 & 3

If condition monitoring and operational testing detect no irregularities, it is recommended to perform the first major inspection after approximately 50000 equivalent operating hours. This major inspection interval is an empirical value and has been established on the basis of long-term experience in over-hauling steam turbines of different types and operating by different owners, taking into account the service experience gained during the last ten years.

Important reasons for performing an inspection after this period are:

- Easy disassembly of parts in hot steam path.

- Relaxation of bolted joints in hot steam path.

- Blade checked,

- Wear and tear and erosion-corrosion of internal components (e.g. sealing element, keys,

contact faces, casing)

Planning for the next major inspection is dictated by the past inspection findings and the result of tests performed during the first major inspection.

If no serious problems are detected, the next major inspection should be performed after the unit has completed approximately 100 000 equivalent operating hours.

An interval of approximately 50 000 equivalent operating hours between two major inspections can be operating experiences available from comparable turbines indicate the need for short

intervals.

6.1.3 Service Period between Major Inspections

It is recommended to perform a minor or intermediate inspection after mutely 25 000 equivalent operating hours during the service period between two major inspection.

This service is approximately equal to an interval of three and coincides with the inspection interval for the steam generator.

6.2 Unscheduled Inspections Due to Irregularities

The inspection intervals indicated in section 6.1 are applicable on the condition that performed monitoring and other specific measurement (e.g. efficiency, heat consumption or stage pressure

measurements) and the inspection findings reveal no irregularities.

However, if performance monitoring of the turbine-generator reveals irregularities (off-nominal condition) which are substantiated by additional checks ( e.g. measurements), the deficiencies detected may it necessary to advance a planned inspection ( see Attachment 4.1 & 4.2). This inspection is caused by irregularities and can be carried out in the form of a module inspection.

Moreover, information provide by the manufacturer or the insure on indicates experienced on similar units where irregularities have resulted in disturbances can be lead to an unscheduled inspection of a particular plant components. If the inspection findings and test result indicate



the need for a prolonged outage, advancing a planned inspection of the complete unit should be contemplated for economic consideration.

6.3. Unscheduled Inspection due to damage

An unscheduled inspection may become necessary due to actual damage to the turbine-generator or to a non-redundant plant components (steam generator, pressure vessel, unit connected transformer, etc.).

In contact to an unscheduled inspection due to irregularities, which in most cases does not

necessitate an immediate shutdown of the turbine-generator actual damage requires an immediate shutdown. If the time necessary for rectification of the damage results in a prolonged outage of the turbines generator, a planned inspection can be performed sooner than scheduled.

7. Planning for Inspection and Overhauls

It is the goal of inspection and overhaul planning to find a favorable time / cost ratio for a defined scope of inspection work. This includes parts planning, implementation planning and consideration of the necessary marginal conditions.

7.1 Spare Parts Planning

The spare parts considered necessary by agreement between the owner and the manufacturer should be available in the number required for each unit prior to initial start-up.

The decision on the purchase of additional manufacturers-recommended spares essentially depends on the following criteria.

- Significance of the turbine-generator in the utility system.

- Cost of outage due to unexpected failure.

- Probability of failure.

- Delivery time of spare parts.

- Operation of several identical units in the utility’s system.

- Consolidated spare parts inventory shared by several utilities.

In additional to the manufacturer-recommended spares, which should preferably be ordered during the warranty period of the turbine-generator, there are spares which become necessary due to life expenditure and should therefore be purchased in due time.

The spare parts must be stocked in such a way as to be protected against corrosion and damage and to be easily found. Any parts removed from stock should be replaced in due time either by ordering new parts or by reconditioning parts removed from the unit. In the event of the design of the turbine-generator being changed, the spare parts should be examined suitability.

7.2 Planning for Intermediate and Major Inspections.

Approximately one year before the start of the inspection, the owner should inform the manufacture about the scheduled inspection indicating it’s kind and duration. The work required

should be agreed upon during a meeting between the owner and the manufacturer, talking into account the experience available from pervious inspection and from the inspection of similar units.



The scope of inspection activities should be defined in detail on the basis of the owner’s/ operator’s observation and manufacturers schedules and lists of necessary work. In addition, the following points should be clarified.

-Estimated spare parts requirements.

-Spare parts stocked by owner must be checked for completeness and condition. Missing or unserviceable spare part must be ordered immediately.

-Availability of tools and fixtures; items available, items to be made available by the

manufacture.

The following requirements depend on the kind, duration and scope of the inspection;

- Owner and manufacturer should jointly prepare a preliminary manpower and capacity

schedule.

- A work schedule should be prepared showing the work to be performed at workshops (owner, manufacturer and outside contractors).

- Both the manufacturer and the owner should produce plans ensuring the availability of the necessary workshop and machinery capacity.

- The mode of transport and the provision of transport facilities should be agreed upon between the owner and the manufacturer

Check measurements (e.g. pressure, efficiency, vibrations, foundation displacement, temperature rise of generator) should be performed in due time prior to commencement of the inspection in order to identify the actual condition of the turbine-generator for comparison with the initial condition (reference condition)

Not later than four months before the start of the inspection, a further consult ion should be identify the following additional requirement for completion of planning activities

- The result of the measurements and other operating data recorded should be evaluated to

determine the need for additional inspection and overhaul activities.

- The manpower allocation and work schedules must be updated.

- The required manpower qualification levels as well as the composition of the overhaul.

- Working hours should be agreed upon.

- A time schedule should be prepared for the entire inspection period ( bar chart, critical-

path chart, see Attachment 5.1 & 5.2). Note that dismantling without delay enables the owner and the manufacturer to obtained the inspection finding at an early date and facilities attending to unexpected damage.

- The authority of the turbine chief erector within the framework of the power station organization should be defined before the start of the inspection.

All documents required for the inspection should be on hand before the start of the inspection and overhaul.

If is recommended that owner and manufacturer should meet for an exchange of experience

information as soon as the turbine has been restarted.

7.3 Marginal Condition for execution of Inspection (owner)



Planning should include washrooms and locker rooms for outside contractor’s personnel as well as an adequate number of toilets and spaces.

The availability of accommodation and catering facilities near the power station outside working hours and of rooms for having meals at the power station should be determined.

Good lighting and electric power at the required supply voltages for the connection of the necessary electrical appliances must be available.

The supply of compressed air to the job site must be ensured.

Heating and welding equipment with an adequate supply of oxygen and gas cylinder must be provided.

A cleaning contractor and a thermal insulation contractor should be informed about and

entrusted with the scope of work to be performed.

An allocation plan of the powerhouse indicating the permissible loads should be prepared and handed over to manufacturer field supervisor before the start of the inspection.

It is recommended to set up a tool and material crib in the vicinity of the steam turbine-generator in order to eliminate long distance.

Office and telephone facilities for manufacture’s field supervisor should be provide.

The working time regulation and the rules of conduct at job site must be handed over to all persons concerned before the start of the inspection. The accident prevention rules must be put out.

Lists of all ropes required and of all weights to be lifted should be available. It is advisable to store all ropes in a proper manner in a single location. It is recommended to provide tags with details of safe load capacity, description and length. Spreaders and ropes allowing for adjustment length should be made available. After completion of the inspection, the ropes must be restored to a serviceable from condition.

Racks, cases or containers for small items should be provide on the errection floor for dismantled small items, such as, for instance, spring-loaded shaft glands, labyrinth seals, casing and bearing insert rings, bolts, etc., in order to ensure an orderly lay-down of the parts and to avoid confusion of parts manufacturer from different materials.

In some cases, it is advisable to provide a lockable container for the storage of special parts.

All-important special tools should be available in duplicate to prevent the loss of valuable time for obtaining replacement.

Collecting pans and containers for the oil to be drained should be made available in adequate number.

Materials for the detection of cracks by the liquid penetrate method solvents lubricants in paste form, seal materials and shims of steel or brass should be made available.

An adequate number of planks, support beams and trestles should be made available and checked for their usability before the start of the inspection.

After completion of the inspection all tools and appliances used must be checked for completeness.

It should be ensured that an efficient nearby workshop will be available for use at any time.



The insurer should be informed in due time of the date and scope of the inspection. This will enable the insurers to make recommendations for improvement of the unit components on the basis of their accumulated failure and overhauled experience.

A number of useful tools and auxiliary materials ( see attachment 6) should be available

8. Inspection Result and CONDITIONS

8.1 : Documentation

Detailed documentation of the results is essential when performing an inspection. It is recommended that this documentation be prepared an cooperation between the owner and the manufacturer under due consideration of the actual requirements. The following heading are intended as a recommendation for the preparation and the contents of the documentation. The order selected is not intended to establish any priorities.

Execution of Inspection

Manpower and work schedules. Logging of each day’s activities, their sequence, and the required number of working hours together with a statements of overall condition on the

basis of the operating data recorded.

Inspection Findings

Inspection finding should be described in details and, if possible, be supplemented by photographs, sketches, etc.

Maintenance and Repair Work

Kind and scope of maintains and repair work performed

Replacement Parts

List of replacement parts used. Modification for replacement parts to be specially recorded.

Auxiliary Material and Consumables

List of quantities consumed.

Test Records for Components Parts.

Test records and factory assembly records for replacement parts and components reconditioned at manufacturer’s works, materials test certificate.

Setting Records and Functional Test Records

Setting and testing of control, supervisory, safety and protective equipment, oil throttles, oil pressures, shaft lift oil pressures.

Assembly Records

Records of all measurement taken.

Plant Records

Drawing, piping diagrams, operating instruction, etc. should be checked for facture



validity and revised as necessary.

Operating Records

Operating date should be recorded under comparable steady-state conditions a before

and after inspection. Data to be recorded include live steam condition and valve positions, stage pressures and temperatures, casing temperature , oil pressure and oil temperature, cooling water inlet temperature and temperature rise in oil cooler, terminal temperature difference of oil cooler. Bearing temperature, expansion, vibration, data of gland sealing system and vacuum test, terminal temperature difference oc condenser.

Special Measurements

Efficiency, heat consumption, foundation distortion.

Costs

Determination of total cost of inspection, broken down according to personnel, material and outside-contractor costs.

Desired/ Actual Valve Comparison

Comparison of planning data with actual inspection activities.

8.2 Conclusions Drawn from Inspection Results

8.2.1 Conclusion in respect of further operation

Normally no restrictions need to be observed for further operation if the component

a) have been left in the condition as found due to the absence of deficiencies.

b) Have been replaced by spare parts( e.g. parts subject to wear and tear, such as stems: normally small items which are usually kept on stock)

c) Have been reconditioned at site, at manufacture’s works or at an outside contractor’s facility

In case damaged components( e.g. casing with cracks) had to be left in the condition as found, it

should be decided whether the operating mode must be changed for continued operation of the

unit. This decision may result from;

- non-availability of replacement parts,

- duration of repair,

- envisaged remaining service life of unit.

i.e. condition of the damaged components must be controlled and documented necessary, additional monitoring facilities should be provided. Any required spare parts should be ordered

8.2.2 Conclusions in Respect of Next Inspection

i.e. inspections finding, if possible supplemented by a life expectancy calculation and operating and overhauling experiences available from other units of the amn type. May prompt a change in the current periodic inspection interval establishing for a particular turbine generator.



Shorting the between inspections is always recommended if there are indication of particular components approaching zero remaining life expecincy although a replacement appears not absolute necessary. Even if damage components can initially be left in the condition as found, the previously established inspection intervals may not be retained.

Critical analysis of the procedure details of the replacement parts, dealys in repair of am aged components, difficulties in procurement of material and tools.

The root causes of these problems must be identified and eliminated to prevent their recurrence during the next inspection. Spare parts, consumables and auxiliary materials must be replaced at the earliest possible date. This applies particularly to replacement parts with long delivery times, unless their procurement is not justified for economic consideration and operational rest icons are acceptable.

8.2.3 Conclusions for Manufacturer

Is the task of the manufacturer to evaluate the experience gathered when the inspection is completed by comparing the result with those obtained during inspection of duplicate or similar units in order to established any facts that old true generally.

This approach provide a wide basis for:

a) Sharing preventive maintenance with other owner.

b) Recommendations for optimizing periods.

c) Recommendations for replacement parts to be stocked by owner.

d) Preventive maintenance to be performed in additional to scheduled inspection in order to maintain high availability.

e) Proposals for improvements and modification

f) Hints for new designs.

9.References

1)“VDEW-Empfehlungen for the Revisionintervalle von Generation”( Vdew recommendations for

the inspection intervals of Generators), VGB-RV, 809, 1980 EDITION

2) “Das thernische Verhalten von Dampfturbinen” ( The thermal behavior of steam turbines)

3) “Technische Richtlinie for Uberwachungs-,Sicherhelts-und Schutzeinrichtungen an

Dampfturbinenanlagen”( Technical Guideline for steam turbine Supervisory, safety and protective Equipment) VGB-R 103 M 1977 edition

4) “Empfehlungen fur Schrauben im Be Reich hoper temperature” (Recommendation for high-temperature bolts) VGB-R 505 M 1980 EDITION.

5) “Richtlinien fur interne ROHRLEITUNGEN DES Turbosatzes, soweit site brennbare Medien

further”VGB-R 503 M 1975 EDITION

6) VEB-Empfehlung “Anleitung zum uberwachen von Dampfturbinen durch Messes des inner Wirkungsgrades” Vgb-r 118 m 1982 edition



10.Appendix

Attachment 1/sheet 1

0= As necessary, X =required

Work required during inspection Major inspection

Intermediate Minor inspection

Remove coupling bolts, measure stretch elongation of coupling bolts-check axial & radial ligament, run out clearances.

Disassemble bearing, check bearing metal, measure clearances, check bearing seat in bearing housing.

Examine, overhaul and, if required, replace bearing of bearing housings.

Inspect bearing housing and casing guides for

contamination (oil choking). If binding is detected, remove clean overhauls keys.

Examine sliding performance, remove and overhaul lubrite plates inserted below bearing housings.

Lift off bearing housing as far as practicable for overhaul of sliding surfaces and guides.

Check spacer bolts at bearing housing and casing brackets and, if required, correct clearances.

Check emergency stop, control and bypass valves, if required, replace wearing parts of

hydraulic and steam element.

Remove steam strainers; check for foreign

matter and damage and, if required, recondition strainers.

0

0

0

0

0

-

x

0

-

X

X

X

X

X

0

x

x

x

X

X

X

X

X

X

X

X

X




Examine check valves of automatic and no automatic extractions. Renew gaskets if, required replace parts subject to wear and tear.

Inspection drains for foreign matter, open and clean silt traps.

Inspect admission chest for oxide deposits and unobstructed movement.

Measure casing distortion, checks joints for erosion, perform cracks testing.

Alignment checks of turbine casing and bearing

housing.

Check inner casing guides for unobstructed

movement and wear. Overhauling work.

Measure permanent elongation of high-temp.joint bolts. Inspect bolts for embitterment. Inspect bolts for cracks.

x

o

-

-

-

-

-

x

x

0

0

0

0

0

X

X

X

X

X

X

x

Work required during inspectionMajor inspection

IntermediateMinor inspection

Check shaft glands and labyrinth seals for were and oxide deposit. Examine springs of resilient segment.

- 0 X

Check rotors for cracks. Perform run out checks

Remove scores on shaft journals. Check

coupling

0 X

Clean complete balding and inspect blades for damage. Check seal strips for oxide deposits. Perform cracks and vibration test of freestanding LP BLADES.

- 0 X



Visual examination of last stage of condensing turbines( crack testing as necessary)

x x X

Examine ear thing brush and contact face on shaft.

x x

X

Open main oil pump, check baring, seal rings, haft, impeller, etc. Open auxiliary oil pumps only if necessary.

0 0

X

Examine control and protective equipment,

giving particular attention to parts subject to wear and tear and to parts susceptible to contamination. Replace parts as necessary.

x x X

Perform functional testing of supervisory equipment for proper mechanical, electrical and hydraulic condition. Overhaul and recalibrate equipment as necessary.

x x X

Inspect condenser interior, tubes and water boxes for damage perform leakage tests on cooling water and steam sides. x x X

Drain oil tank, separate oil, if required. Checks oil tank clean strainers.

- 0 X

Check oil filters for leaks. Remove and clean filter element and examine for damage.

x x X

Remove tube bundles of oil coolers; examine tubes for mechanical damage and corrosion.

Clean sump.etc. - o X

Inspect oil pipes for damage. Remove oil leaks.

x x X

Inspect steam pipes in turbine interior for



0= as necessary x= required

Attachment 2/Sheet 1

Test procedure to be applied to steam turbine components inspection

cracks, distortion and expansion. - 0 X

Check dimensions of pipes supports and correct

as necessary.- 0 x

Component Inspection findings Test procedure Remark

Rotors Radial/ axial rubbing deformation of blade

grooves surface cracks

Mechanical damage

Erosion, corrosion

Internal defects

Perament deformation

Damage to shaft journals

2,3,(4),(11),(13)

2,3,9

2,3,(4),6

2.3.(9)

2,(3)

4.5

9,11

2,3,9

Including central and radial boars as

well as welds

Coupling Looseness of coupling

halve Eccentricity

Permanent deformation

Cracks

2 (4) 7

9

9.11

1.3

Also check for

possible damages to bolt holes

Non-contacting seal element

Mechanical damage

Fracture

Erosion, corrosion


2.3.(9)

2

2

2.11

Discs Radial/ axial rubbing

Deformation of blade grooves

Loose shrink fit of discs

2.11

2,3,9

2,(4),7,9,13

2,3,(4),6

Primarily disc bore



*) Code numbers according to section 4.

Test procedure in parentheses should only be applied if preceding tests have revealed a deficiency or if recommended by the manufacture.

Attachment 2/ sheet 2

Test procedure to be applied to steam turbine components inspection

Surface cracks

Mechanical damage

Erosion, corrosion

Internal defects

2.3.(9)

2,(3)

4,5

Nozzles stationary blades, diaphragms

Radial/ axial rubbing

Mechanical damage

Deposits

Erosion, corrosion

Surface cracks

Change in blade attachment


2,3,7,(11)

2,3,9

2,11,12

2,3,(8)

2,3,4

2,(4),7,8,(9)

2,9,(11)

Moving blades Radial/ axial rubbing

Mechanical damage

Deposits

Erosion, corrosion

Surface cracks

Change in blade attachment


2,3,7,(11)

2.3.(9)

2,11,12

2,3,(8)

2,3,4

2,(4),7,8,(9)

2,9

Blade root, air foil, damping element,

lacking wires, should tension pins of pinned fork blades


Outer casing , Mechanical damage 2,3,9(11) Sealing fitting



inner casing,

admission chest,

valve casing

(ESV/ Control valves),

bearing housings

Distortion

Surface cracks

(inner, outer surface)

Erosion corrosion

2,9

2,3,(6)

2,(3)

and sliding

faces

Flange and joints bolts Permanent deformation

Mechanical damage

Surface cracks

Erosion corrosion

2,3,9(11)

2,9

2,3,4,(12)

2,(3)

VGB-R 505 M(4)

Valve seats

Valve stems.

Valve cones

Mechanical damage

Surface cracks


Erosion corrosion

Deposits

2,3

2,3,6

2,9

2,3

2,12

Supervisory

Limiting and protective equipment control system

Component

Impaired performance

Mechanical damage

Corrosion

Deposits

1

2,3

2,3

2,12

Including clearance changes

Bearings Mechanical damage

Surface cracks

Corrosion

Cavitation

Damaging currents

Deposits

Loose white metal

Seat contact

Change in support

2,3

2,3,

2,3

2,3

2,3,16

2,12

2,4,7,(14)

2,(9)

2,9

External steam pipes (hp and IP)

Surface cracks


2,3,10,11,(12)

2,9,11,(12)

Primarily at welds and bends, if




Test procedure in parentheses should only be applied if preceding tests have revealed a

deficiency or if recommended by the manufacture.


Change in support 2,9 necessary,

dimensional control of pipes


Internal, steam pipes, conn.

Element,

Expansion joints;

Drain pipes

Impaired performance

Surface cracks

Abrasion


Erosion corrosion

Changes in cold pull

1,2

2,3

2,3,10,(11)

2,9,10,

2,9,10

2,9,

Primarily at

welds

Steam strainers, incl.housing Surface cracks

Mechanical damage


2,(3),11

2,3

2,9

Including material embitterment and solid-particle erosion

Control & bearing oil piping Leakage

Abrasion

Surface cracks

Deposits

Corrosion

“Primarily at welds

2,14

2,3,10,11

2,3

2,12

2.12

VGB-R 503 M (5)

Condenser heat exchangers Disturbed flow path

Surface condition

Mechanical damage

Cracks

Erosion corrosion

Leaks

1,2

2,(3),(10),(15)

2,(3),(12)

2,(3),(12)

2,10

2,14

For instant protective coating,

Deposits

Gear Tooth contact pattern 2,3,11




Test procedure in parentheses should only be applied if preceding tests have revealed a deficiency or if recommended by the manufacture.

Attachment 3

List of tools and Auxiliary Materials

Heaters for loosening and shrink-fitting of joints bolts

Special fixtures(e.g. for removing valve seats and grinding)

Surface grinder for machining all keys and shims to required size.

Lathe with magnetic faceplate and adequate length between centers for run out check of pump shaft

Machinist’s tools( pneumatic screwdriver for bolt loosening)

Corundum blocks with handles for work to casing joints

Work benches in sufficient number in turbine area

Electric scrapers, hand scrapers of different design

Measuring taps

Special dial gauges with supports for gear and alignment checks

Measuring tools for shaft gland

Alignment shaft with inductive pickup

Fixture for spring-loaded inter stage and cylinder glands

Cleaning brushes

Blast cleaning equipment ( water, glass beads, dust)

Grinding pastes

Chemical de-rusting and rescaling agents

Oil-resistant blue,blueing plate

Temperature- indicating crayons

Surface cracks

Mechanical damage

Deposits

Damaging currents

Change in clearances

2,3

2,3

2,12

2,16

2,9



Means for detecting and revealing cracks

Spreaders and suitable attachment devices

Portable hydraulic jacks

Lifting tackle in sufficient number

Skids for rotors and facilities for on-site handling of heavy plant components

Oil purification plants( centrifuges, filter presses)

Oil heating devices or equipment

Lint-free absorbent cloth, oil binding agent

Special lubricant( aerosol sprays, assembly compounds)

Anti-corrosion agreement ( paints and protective compounds)

Sealing material in board or sheet form of sufficient size

Shims ( brass and steel)

Lead wire of different diameter.

Suitable planks for covering joints of lower half turbine casing after opening wood blocks and planks for setting down heavy machinery parts

Tables for drawing and files

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