04 Final RLA Report DNV

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RLA OF STEAM TURBINE & GENERATOR OF GHORASHAL UNIT #4

Condition assessment andrestricted Residual Life

Assessment (RLA)

Power Cell, Power Division Ministry of Power, Energy &Mineral Resources

Report no.: 15-1414, deliverable 6

Date: 2015-06-05



Project name: RLA of Steam Turbine & Generator of Ghorashal

Unit #4

DNV GL - Energy

KEMA Nederland B.V.

P.O. Box 9035

6800 ET ARNHEM

Tel: +31 26 356 9111

Registered Arnhem 09080262

Report title: Condition assessment and restricted Residual Life

Assessment (RLA)

Customer: Power Cell, Power Division Ministry of Power,

Energy & Mineral Resources, Bidyut Bhaban, I

Abdul Gani Road, Dhaka 1000, Bangladesh

Contact person: Mr Mohammad Hossain

Date of issue: 2015-06-05

Project No.: 74107060

Organisation unit: GTC/GTP

Report No.: 15-1414, deliverable 6

Prepared by: Verified by: Approved by:

K. Agema A. Braam R. Meijer

H. Bresser

J. Fricke

☒ Unrestricted distribution (internal and external)

☐ Unrestricted distribution within DNV GL

☐ Limited distribution within DNV GL after 3 years

☐ No distribution (confidential)

☐ Secret

Reference to part of this report which may lead to misinterpretation is not permissible.

Rev. No. Date Reason for Issue Prepared by Verified by Approved by

0 2015-06-05 First issue K. Agema A. Braam R. Meijer

H. Bresser

J. Fricke

© 2015 KEMA Nederland B.V.



DNV GL - Energy – Report No. 15-1414, deliverable 6 – www.dnvgl.com/energy Page i

Table of contents

1 EXECUTIVE SUMMARY ..................................................................................................... 1

2 INTRODUCTION .............................................................................................................. 3

3 CONDITION ASSESSMENT OF THE STEAM TURBINE ............................................................ 3

3.1 Overview of the results of the NDT inspection carried out by Power Machine 3

3.2 Evaluation of the reported results 4

3.3 Missing information 4

3.4 Relevance of NDT results to life extension of steam turbine 4

3.5 Results and conclusions of restricted RLA steam turbine 5

4 CONDITION ASSESSMENT OF THE GENERATOR .................................................................. 6

4.1 Findings and results of visual inspection generator 6

4.2

Review of the replacement works generator 7

4.3 Stator recommendations 7

4.4 Rotor recommendations 8

4.5 Results and conclusions RLA generator 8

5 CONDITION ASSESSMENT OF THE AUXILIARIES ................................................................. 8

5.1 Findings and results of visual inspection auxiliaries 9

5.2 Results and conclusions RLA auxiliaries 9

6 STEAM TURBINE FOUNDATION UNIT #4 .......................................................................... 10

6.1 Investigation of foundation drawings 10

6.2

Adaption of the foundation 10

6.3 Results and conclusions foundation 11

Appendix A Overview results of the NDT inspection carried out by Power Machine



DNV GL - Energy – Report No. 15-1414, deliverable 6 – www.dnvgl.com/energy Page 1

1 EXECUTIVE SUMMARY

Condition Assessment versus ‘restricted RLA’

A condition assessment and restricted Residual Life Assessment (RLA) have been carried out on thesteam turbine, generator, auxiliaries and foundations of Unit #4. This condition assessment is supported

by NDT inspections, carried out by OJSC Power Machine, and witnessed and reviewed by DNV GL.

In this report the term ‘restricted RLA’ or condition assessment will be used because of the following

reasons:

a complete RLA asks for extensive NDT tests and measurements, carried out by our own team. The

NDT inspections, carried out by Power Machine, are geared to operate the steam turbine for 50000

operation hours.

f urther, to determine if the steam turbine of Unit #4 is fit for repowering an ‘estimation of remaining

life’ is required by carrying out finite element calculations on the rotor. These finite element

calculations required for RLA is not a part of the project.

This report gives the results of the condition assessment or restricted RLA of the steam turbine,

generator and auxiliaries of Unit #4.

Steam turbineFrom the ‘restricted RLA’ of the steam turbine can be concluded:

the maintenance work on the steam turbine was targeted to ensure that the machine operates

another 50,000 hours smoothly. As per the NDT Inspection by Power Machine, it is confirmed that

this Steam Turbine can operate for 50,000 running hours

after analysing the various tests reports and visual inspections of the inside condition of the machine,it can be deemed that the Steam Turbine has a longer life and is fit for operation in the intended Re-

Powering Project

however, in order to achieve that, periodic maintenance and major Overhauling as per manufacturer

guideline is required after every 50000 operating hours

as the turbine is aging it is strongly recommended to include life remaining related aspects in the

inspections carried out during the coming overhauls, such as replication of the micro structure of HP

and IP casing, steam cross over pipes and NDT inspection of the centre line bore of the HP and IP

rotors

for a decision if the technical condition of the steam cross over pipes and HP/IP turbine rotors allows

a life extension of an extra 100% in a new set-up the current condition of the relevant components,

the total expected life time and the effect of the foreseen life consumption rate in the new set up has

to be estimated for creep and fatigue by finite element modelling and calculations.

GeneratorFrom the ‘restricted RLA’ of the generator can be concluded:

end winding vibrations caused by broken bandaging and loose tangential filling blocks will further

increase and the insulation system will thereby further degrade. The water leakages at the stacks

are directly related to vibrations, it is to be expected that water leaks will remain an issue during

future operation

diagnostic measurements, as Partial Discharge, Capacitance & Tangens Delta were not performed.Due to the absence of this information, input about the condition and ageing of the insulation




materials is missing. As a consequence, it is not possible to determine the remaining life time of the

electrical windings

both visual inspections and assessment of the results of the limited performed High Voltage DC

measurements give a consistent view on the condition of the stator winding of the generator. Thecondition of the windings can be classified as “worse”

the generator can only be used for repowering after a complete overhaul, including the stator and

rotor winding renewal and it is proved by adequate tests that the generator is fit for purpose.

AuxiliariesA visual inspection has been carried out for the following auxiliaries: cooling water filter system; cooling

water pumps; condensate pumps; oil systems and rotor turning gear (RLA was not possible because

manuals, historical data, failure reports and maintenance reports were not present and the installations

were not open):

the cooling water filter system is robust but old. Some wear and tear was detected. This filter system

can be re-used after a refurbishment (a major overhaul with replacement of all wearing parts and

examination of tolerance) or a new filter system may be considered for the intended Re-Powering

Project

the cooling water pumps can be re-used after overhaul and replacement of the wear and tear parts,

if still available. Otherwise it will be necessary to order similar new pumps

depending on the new process situation it can be advisable to install new condensate pumps.

However, according to the process calculations it seems likely that these pumps can be used again

after major overhaul. Frequency control is a good option to install

after extensive cleaning and refurbishment the oil systems (lubrication oil system, seal oil system

and control oil) can be used after repowering. These systems are robust and have proven to bereliable. To install an automatic detection and fire-fighting system is advisable

the condition of the turning gear is acceptable or even good. In case of re-use or refurbishment of

this steam turbine it is recommended that the rotor turning gear will be refurbished as well or a new

turning gear may be considered for the intended Re-Powering Project.

Foundation From the investigation of the foundations can be concluded that re-use of the existing steam turbine

with slightly different load is acceptable. However, steam turbine efficiency will be not optimal

if adaption and optimisation is required for the steam turbine it is most probably possible to keep the

existing outer casings of the steam turbine as it is and the inner casings with vanes, vane carriers,

rotor and blades to be build new. In this case no alterations are necessary for the foundation.

Advantage: efficiency of the steam turbine can be optimized

re-use the foundation in case of a complete new steam turbine is expected to be realistic after

redesign and adaptations of the foundation. These adaptions of the foundation table will probably

result in a forced stop period of the adjacent machineries to prevent trips or damages during

operation. Therefore this option is not preferred.




2 INTRODUCTION

The Government of Bangladesh has applied for financing from the World Bank toward the cost of

Repowering Ghorashal Unit #4, and intends to apply part of the proceeds for the following: Engineering

Procurement and Construction to convert the single cycle Unit #4 (210 MW Steam Turbine Unit) to

combined cycle power plant at Ghorashal Power Station, BPDB, Narsingdi on Turn-Key basis.

This report gives the results of the condition assessment or restricted RLA of the steam turbine,

generator and auxiliaries of Unit #4.

The report is divided in three parts. First part, the condition assessment and restricted RLA of the steam

turbine; containing an overview of the results of the NDT inspection carried out by Power Machine;

relevance of these NDT results to life extension of the steam turbine; and results and conclusions of

restricted RLA of the steam turbine.

The second part contains: the condition assessment and restricted RLA of the generator; findings and

results of the visual inspection of the generator; review of the replacement works of generator parts;

and results and conclusions of restricted RLA of the generator.

The third part contains: findings and results of the visual inspection of the auxiliaries; and results and

conclusions of restricted RLA of these auxiliaries.

3 CONDITION ASSESSMENT OF THE STEAM TURBINE

DNV GL was asked to carry out a remaining life assessment on the steam turbine of unit 4. Part of a

remaining life assessment is an assessment of the current condition of the turbine. Early 2015 PowerMachine carried out a standard overhaul of this turbine. During this overhaul DNV GL together with

company DEKRA did a visual inspection of the different turbine components while the turbine was

opened. Visual inspection can only provide a general impression, which in this case appeared to be quite

favourable (refer to report ‘Visual inspection report steam turbine’, 15-0672, date 2015-03-11). More

detailed inspections are required to obtain a reliable impression of the current condition of the capital

turbine components which are relevant for a life assessment.

As part of a standard overhaul Power Machine has carried out many NDT inspections. DNV GL was asked

to evaluate the results of the NDT inspections and the measures taken by Power Machine to correct any

unacceptable defects identified that are linked to the remaining life of the turbine. DNV GL likes to

underline that the overhaul of Power Machine was never intended to be part of a remaining lifeassessment for another 20 years. The acceptance criteria used by Power Machine are intended to

guarantee the equipment for another 50,000 operating hours.

The evaluation is purely based on the English translations provided by Power Machine as part of their

NDT reports.

3.1 Overview of the results of the NDT inspection carried out by

Power Machine

A summary of the results of the inspection reports provided by Power Machine are listed in Appendix I

per component according their position in the steam path.




3.2 Evaluation of the reported results

The reported amount of repairs and rejected components is low for a steam turbine which has not been

overhauled since 20 years. This is in line with the favourable results of the visual inspection. The

cracking noted at the casings of the HP and IP turbine and even the replacement of the first and second

stage rotor blades in the HP turbine can be seen as usual wear and tear for a steam turbine after 25

years. Similarly the erosion damage noted on the last stage rotor blades of the LP turbine is more or less

common to steam turbines.

The reason for the replacements according to contract (rotor blades stage 9-11, 13, 15-18, 27, 31) is

not provided in the NDT reports. According to information obtained from the power plant is the

replacement related to a previous accident of axial shift to the rotor which possible blade damage.

The reports on the hardness measurements on the turbine casing and valve casings show a slightly

lower hardness of the material located at the hot side of component compared to the outer surface. This

would suggest a limited decrease of hardness at the hot surface. How this relates to remaining life is not

specified in the provided NDT reports. Рд10-577-03 “Standard manual control and extend the life of

main elements of boilers, turbines and pipelines of thermal power station” for instance only specifies that

the hardness of P2MA should be more than 180 HB.

3.3 Missing informationSome relevant information which is listed in the work scope of Power Machine is still missing in the NDT

reports:

no information is provided on the results of dye penetrant NDT inspections carried out on the HP

diaphragm segments, the IP diaphragm segments and the LP diaphragm segments in the reports no information is presented on the actions taken on the sets of rotor blades which

were not acceptable for service (stage 1 and 2 in HP turbine, stage 25 and rivets of stage 26 and 30

in LP turbine). Inquiries with plant operator revealed that the rivets of stage 26 and 30 are being

exchanged during the current overhaul.

3.4 Relevance of NDT results to life extension of steam turbine

The results of the inspection carried out during the overhaul revealed no indication which would limit the

turbine life to the current 200,000 hours. Based on the results Power Machine states an allowable

additional operating time of 50,000 hours after which the next overhaul must be performed to inspectthe components and to determine the condition of the turbine at that time.

For a decision if the technical condition of the turbine allows a life extension of 100% in a new set-up (as

part of combined cycle in combination with gas turbine for another 200,000 operating hours) the current

condition of the relevant components, the total expected life time and the effect of the foreseen life

consumption rate in the new set up has to be estimated. The most relevant components in terms of

remaining life assessment of the turbine are the HP and IP casings, the HP and IP rotor and the steam

cross over pipes. During service these components suffer from degradation due to creep and fatigue. The

final stage of creep and fatigue is crack initiation, crack growth and fracture. The fact that during the

recent overhaul inspection no relevant defect was noted in the casings and the rotors does not mean

that no degradation has occurred in the material. Some degradation has surely occurred but it is notvisible. Because both creep and fatigue are well investigated degradation phenomena, the level of creep




and fatigue of used components can be predicted up to reasonable accuracy using general accepted

procedures.

To DEKRA’s opinion an estimation of the consumed and remaining creep and fatigue life is required for

the steam cross over pipes and HP/IP rotors, and ideally also for the HP/IP casings. Such estimation

would require finite element modelling and calculation together with information on the standardized

material properties of the rotor material, the relevant dimensions of the rotors and details on the

temperature and load during the total history of the turbine and the expected temperature and load

(cycles) in the new set-up. For a large size turbine casing this procedure is not always carried out due to

the complexity of the design. Common practice is to determine the deformation of the casing (which

over time will become elliptical rather than circular), the level of cracking and the changes to the micro

structure and hardness during subsequent overhauls. For the rotors the estimation of consumed and

remaining life, although complicated, is possible.

Furthermore it is recommended to carry out NDT inspections of the surface of the bore of the HP and IP

rotors during each overhaul to check if any micro defect in the rotor is present and if so, if its size does

extend over time.

The inspections of the steam cross over pipes did not raise immediate concerns. Depending on the

material composition, the temperature and load during service creep is a possible life restricting

degradation mechanism. Regular checks of the hardness, diameter, radius, micro structure, ovality, wall

thickness are required to make sure that they remain healthy. Life consumption estimations of steam

pipes are based on general accepted rules and only if a problem is expected finite element modelling and

calculations are performed.

The rotor blades, diaphragm nozzles and bearings, although their replacement costs might be

considerable, are considered replaceable and remaining life assessments are normally not carried out.Checking the condition during each overhaul is common practice. The results of the recent overhaul do

not raise concern for these components.

3.5 Results and conclusions of restricted RLA steam turbine

The maintenance work on the steam turbine of Unit 4, carried out by Power Machine, was targeted to

ensure that the machine operates another 50,000 hours smoothly. As per the NDT Inspection by Power

Machine, it is confirmed that this Steam Turbine can operate for 50,000 running hours without any

concern. After analysing the various tests reports and visual inspections of the inside condition of the

machine, it can be deemed that this Steam Turbine has a longer life and is fit for operation in theintended Re-Powering Project.

However, in order to achieve that, periodic maintenance and major Overhauling as per manufacturer

guideline is required after every 50000 operating hours. The current unit has run for 25 years without

any maintenance in the last 15 years. Periodic maintenance from now on will improve the operability of

the machine.

Further, as the turbine is aging it is strongly recommended to include life remaining related aspects in

the inspections carried out during the coming overhauls, such as replication of the micro structure of HP

and IP casing, steam cross over pipes and NDT inspection of the centre line bore of the HP and IP rotors.




For a decision if the technical condition of the steam cross over pipes and HP/IP turbine rotors allows a

life extension of an extra 100% in a new set-up the current condition of the relevant components, the

total expected life time and the effect of the foreseen life consumption rate in the new set up has to be

estimated for creep and fatigue by finite element modelling and calculations.

4 CONDITION ASSESSMENT OF THE GENERATOR

Part of the remaining life assessment is an assessment of the current condition of the Generator. Early

2015 BPDB experts carried out a major overhaul of the generator. During this overhaul DNV GL did a

visual inspection of the different generator components while the generator was opened.

As part of a scope of work several electrical measurements were carried out by BPDB experts. DNV GL

was asked to witness and evaluate the electrical measurements taken by BPDB. During the first High

Voltage DC measurement an earth fault was detected at phase A of the stator winding. The subsequent

measurements were cancelled. The results of the electrical measurements, after the repair of the stator

bars have not been made available by BPDB. Therefore, review of the diagnose measurements will be

carried out when they have been submitted to DNV GL.

4.1 Findings and results of visual inspection generator

The generator end windings are contaminated with “brown residue”. This brown residue is a mixture of

dust and oil. The dust is caused by the wear of the end winding insulation, blocking and bandage

material, due to end winding movement; the oil contamination originates from the seal rings that areend cover (shield) mounted. At the bottom inside the stator housing, a pool of oil is visible. At driven end

(DE) 30% of the end winding bandages are damaged or broken and at the non-driven end (NDE) 20% of

the bandages are damaged. 50% of the tangential stator bar filling blocks of the DE end windings are

loose, and 25% of the filling bars at the NDE are loose. No traces of partial discharges between the bars

in the winding overhang region are visible. There are no indications found for local overheating (hot

spots) on the surface of the generator bars.

Access to the stator bars was limited to a boroscopic inspection through the ventilation ducts.

Approximately 30% of the core ventilation ducts have been inspected for dust, contamination and signs

of partial discharges. In some of the core ventilation ducts, black residue was visible. Further a small

amount of oil contamination was found.

The stator bars are directly water-cooled, by an insulated cooling system. The stator bars are connected

to the manifold rings by means of Teflon hoses. In the past water leaks at the water stacks frequently

occurred. These were repaired by BPDB experts by means of blocking the water ducts in the stator bars.

During the inspection all water stacks were covered by a plastic cover and insulation material, therefore

a detailed visual inspection was not possible.

All stator wedges tested by tapping, and visual inspection. Results of the tapping test: 6% are loose, and

25% are starting to loosen; visually no wedges are loose.

None of the six flexible copper connections between the end winding collection rings and the bushings

are visually damaged. A little amount of ambient dust is found in the connection box and the neutral

terminal box.




The retaining rings were mounted on the rotor body, so only a limited access visual inspection with video

boroscope was carried out. The field windings are contaminated by dust and oil. Insulation resistance of

the rotor is 15 MΩ / 500 V, which is as might be expected. The balancing weights are still at original

position, all fan blades were dismounted.

Both slip rings do not show visual damage. The journals do not show signs of sparking or flashover. All

brush holders and brush springs are visually in a good condition. The slip ring housing is contaminated

by carbon brush dust, the interior of the slip ring housing shows no damage.

Both water coolers were dismounted. No indications for leakage are found, the water inlets are slightly

contaminated, and the gas side cooling surface is clean and without indications.

4.2 Review of the replacement works generator

To reuse this generator for the repowering project, a complete overhaul is necessary, including: stator rewind, either with reused stator bars after insulation replacement or new stator bars

rotor rewind, either with reuse of existing copper or using new bars, the complete insulation and

blocking shall be replaced

rotor overhaul; if proved that these are completely fit for purpose (non-destructive testing), the

retaining rings can be reused

up gradation or replace of excitation system, protection system and Hydrogen systems.

4.3 Stator recommendations

Rewind the complete stator, only components and subassemblies (e.g. stator core, stator bars) which

are in an appropriate condition can be reused.

Concise scope of work, please note that this is only an indication and not a complete list:

disconnect all electrical connection at the stator bars

remove all wedges, blocking, binding ropes and filling blocks

remove all the upper and lower stator bars

clean the stator core and ventilation ducts

visual inspection of the stator surface at the slot section and the overhang section

perform a full flux test on the stator core

perform electrical measurements of each individual stator bar

perform visual inspection and NDT of the water stacks and water-cooling system reuse the stator bars when they are in a good condition (i.e. no blocked water ducts, no shorts

between conductors and acceptable results of dielectric measurements)

replace the stator bars which are rejected by new stator bars

rebuild the stator winding with new insulation and support materials

perform visual inspection and NDT of the water stacks and the water-cooling system

renew the Teflon tubes between the manifold rings and the stator bars

perform an adequate set of electrical DC and AC measurements during and after rewinding

perform a full flux test after rewinding

perform a bump test after completely finishing the rewind(incl. curing the insulation in end windings).




4.4 Rotor recommendations

Rewinding of the rotor with new rotor windings or re-insulation of the existing windings is recommended.

Only components and subassemblies which are in an adequate condition shall be reused.

Concise scope of work, please note that this is only an indication and not a complete list:

verify bearing and seal ring journals for run out and hardness

remove the retaining rings

NDT check of the retaining rings and the retaining ring supports on the rotor core

remove the support blocks and retaining ring insulation

remove rotor copper for cleaning and visual inspection

NDT of the rotor wedges

rebuild the rotor winding with new insulation materials and the new filling blocks

reuse the retaining rings in case they are in a good condition

verify slip rings and polish or replace by new slip rings

perform an adequate set of electrical measurements during and after rewinding

high-speed balancing and over speed test, also electrical measurements must be performed during

balancing.

4.5 Results and conclusions RLA generator

The detected brown residue is a mixture of dust of insulation, blocking and bandaging material and oil.

The dust is caused by vibrations of the winding heads. The amount of residue masks any traces of

surface discharges in the end windings.

As a result of the broken bandaging and loose tangential filling blocks, both end winding fixations haveentirely lost their mechanical strength. Thus the end winding vibrations caused by the mechanical and

magnetic forces will further increase. The insulation system will thereby further degrade. Besides the

water leakages at the stacks are directly related to vibrations, therefore it is to be expected that water

leaks will remain an issue during future operation.

Diagnostic measurements, as Partial Discharge, Capacitance & Tangens Delta were not performed during

our visit, and have not been performed in the past. Due to the absence of this information, the input

about the condition and ageing of the insulation materials is missing. As a consequence, it is not possible

to determine the remaining life time of the electrical windings.

Both visual inspections and assessment of the results of the limited performed High Voltage DC

measurements give a consistent view on the condition of the stator winding of the generator. The

condition of the windings can be classified as “worse”.

The generator can only be used for repowering after a complete overhaul, including the stator and rotor

winding renewal and it is proved by adequate tests that the generator is fit for purpose.

5 CONDITION ASSESSMENT OF THE AUXILIARIES

This chapter shows the findings and results of the condition assessment / restricted RLA of several

auxiliaries of Ghorasal Power Plant Unit #4.




5.1 Findings and results of visual inspection auxiliariesAn inspection has been carried out for the following auxiliaries:

cooling water filter system

cooling water pumps

condensate pumps

oil systems and

rotor turning gear.

These auxiliaries have been visually inspected by a DNV GL mechanical and electrical expert. A

Remaining Lifetime Assessment (RLA) was not possible because manuals, historical data, failure reports

and maintenance reports were not present.

For the inspection of the auxiliaries the following actions were required:

equipment opened, cleaned and all parts directly available around

handbooks and manuals as well as maintenance instructions present

maintenance records, maintenance costs and special events

process information available from at least last (two) years

responsible maintenance staff present, English speaking.

The mentioned equipment was out of operation but not opened. All auxiliaries were still completely

mounted except the turning gear. Handbooks and manuals were not available. No historical maintenance

reports were available. Due to the complete manual operation and control of the installation no data

acquisition system is available and there was only limited process information available. Responsible

maintenance staff was present and interviews were done in good cooperation.

5.2 Results and conclusions RLA auxiliaries

As already explained in the former paragraph a complete RLA was not possible. From the visual

inspection the following can be concluded:

The existing cooling water filter system is robust but old. It is not a very complicated system. Some wear

and tear was detected. DNV GL suggests re-using this filter system when Unit #4 will be repowered. A

refurbishment (a major overhaul with replacement of all wearing parts and examination of tolerance) is

necessary or a new setup may be considered for the intended Re-Powering Project.

The existing cooling water pumps can be re-used when Unit #4 will be repowered then it is

recommended to overhaul the cooling water pumps. If wear parts and other replacements are not

available anymore it is necessary to order similar new pumps.

Depending on the new process situation it can be advisable to install new condensate pumps. However,

according the process calculations made during the feasibility study it seems likely that these pumps can

be used again after major overhaul. One electric motor of the condensate pumps was renewed; one

already overhauled and the third one has to be overhauled. May be frequency control is a good option to

install, depending the progress during process calculations and refurbishment.

After extensive cleaning and refurbishment the existing oil systems (lubrication oil system, seal oil

system and control oil) can be used after repowering. These systems are robust and have proven to be

reliable. To install an automatic detection and fire-fighting system is advisable.

The condition of the turning gear is acceptable or even good. This part of the steam turbine installation

looks not pretty at the outside but that is just the painting layer with dirt. The main components on the




inside looks very solid and in a good condition. In case of re-use or refurbishment of this steam turbine it

is recommended that the rotor turning gear will be refurbished as well or a new setup may be considered

for the intended Re-Powering Project.

6 STEAM TURBINE FOUNDATION UNIT #4

6.1 Investigation of foundation drawings

A search has been carried out to investigate if the current foundation of the steam turbine of unit #4 is

suited for re-use of the existing steam turbine with slightly different loads or suited for a new steam

turbine.

For this investigation DNV GL received 25 drawings of the existing steam turbine foundation of Unit #4.The drawings are made available by jpg-files, number 5214 up to and included 5238 and a hard copy

has been received as well. Many of these drawings contain detail information which may be interesting

for the supplier of a new steam turbine. However, this package of drawings was without any overview

drawings or any description. For this search these detail drawings go far above the purpose as agreed

upon for this investigation.

With the received information it is about possible to build a model to do stationary and dynamic

calculations if necessary. Because it is a must to know the dimensions, weights and operation behaviour

of a possible new steam turbine it is now not recommended to do that kind of calculations.

As far as indicated the existing steam turbine will be re-used again and the foundation is built for this

turbine. It is a stiff foundation; no spring packs are detected to buff vibrations. After an inspection tour

during our visit in February 2015 DNV GL concluded that so far as the foundation could be inspected it

looked well. No (severe) cracks or other ruptures have been found. It must be noted that inspection was

quite difficult due to the major overhaul carried out by Power Machine and the inaccessibility caused by

piping and installed equipment around the foundation. Consultation with operators pointed out that no

trouble regarding the foundation occurred ever, no problems with vibrations et cetera.

6.2 Adaption of the foundation

From the visual inspection and the drawings it is obvious that the foundation is a very robust and rigid

design. Probably no or only static calculations are made during the design period. There shall be a lot of

reserve regarding the loads, torques and vibrations expected for this steam turbine. Re-use of the

existing steam turbine at this foundation is possible without hesitation. The foundation points do not

change and reinforcement is provided already during the original design. The weight and power in the

new situation shall not differ much so no problems are expected in this area.

Nowadays it is possible to update the inner parts (casings, blades, vanes etc.) of the existing steam

turbine (steam path) completely. The outer casings can be re-used just as the supporting points while

the steam turbine is adapted for the new situation. Recently this is done for a repowering project in the

Netherlands.

If another, new designed steam turbine will be used not only calculations have to be made to be surethat this foundation after adaption is acceptable for that new turbine (i.e. own frequency analysis).

Adaptations are possibly needed which means demolishing of a smaller part of the foundation and/or




filling up with concrete fixed with bars and rods. The steam turbine shall be a bit smaller (less power to

produce) so the weight shall not be the primarily problem. Some supports of the rotor shall have another

position and this has to be built in and anchored in the existing foundation table. How much and to what

extend can only be indicated when the new size and design of the steam turbine is known.

In the most extreme situation the table of the foundation has to be demolished and made according a

new design. Re-use of the supporting legs or piles is recommended.

The present foundation is very rigid and robust design and the piles, if not in the optimal position, can be

connected by the new turbine table. After the design a thorough check has to be done not only for the

static loads but certainly for the dynamic load situation.

All adaption work at the foundation can be carried out by heavy machines (mechanical pickaxes,

jackhammers or machine mounted breakers for instance). Demolishing can sometimes be done partly by

"guided" explosions but it is possible that the concrete is so hard with a lot of reinforcement that this is

not possible without damaging other parts.

It is not known how the situation in the ground is, if piling is used and / or a concrete rigid block but

during demolishing activities it will be very difficult to operate the other units due to vibrations. May be

the works can be done making use of high pressure water (1000-3000 bar). This blow out the concrete

and will leave the steel parts untouched and can be done relative quietly without disturbance of the units

in the neighbourhood.

If adaption needs to be done it is important to realize that in the foundation asbestos piping is

incorporated for several penetrations. If these are part of the changes the removal/adaption work should

be done with care!

6.3 Results and conclusions foundation

Foundation re-use for the existing steam turbine with slightly different (lower) load is acceptable and the

cheapest solution. However, steam turbine efficiency will be not optimal.

If adaption and optimisation is required for the steam turbine it is most probably possible to keep the

existing outer casings of the steam turbine as it is and the inner casings with vanes, vane carriers, rotor

and blades to be build new. In this case no alterations are necessary for the foundation only control

calculations are advisable. Efficiency of the steam turbine can be optimized.

Re-use the foundation in case of a complete new steam turbine is expected to be realistic after redesign

and adaptations of the foundation, but this is the most radical solution. Adaptions of the foundation table

will probably result in a forced stop period of the adjacent machineries to prevent trips or damages

during operation. Therefore this option is not preferred.



DNV GL - Energy – Report No. 15-1414, deliverable 6, – www.dnvgl.com/energy A-1

APPENDIX A

Overview results of the NDT inspection carried out by PowerMachine

Component: Stop valve HP turbine

Item: stop valve casing

result inspection: no indications

type inspection: visual report no. 17


type inspection: dye penetrant report no. 18

Item: material condition stop valve body HPCresult inspection: acceptable

type inspection: hardness measurements report no. 19

Component: Steam cross over pipes HP turbine

Item: steam cross over pipes upper halve






type inspection: ultrasonic report no.70

Item: welding steam pipes upper halve


type inspection: visual report no.72



result inspection: acceptable


Component: Control valve HP turbine

Item: regulating valve casing

result inspection: casting defects box 4 report no. 20

type inspection: visual

action taken: removed by grinding

result after: no indications

result inspection: no indications report no. 21

type inspection: dye penetrant




Item: material condition stop valve body HPC report no. 22

result inspection: acceptable; apparent limited decrease of hardness at inner surface

type inspection: hardness measurements

Item: studs and nuts


type of inspection: visual report no. 35


type of inspection: hardness measurements report no. 36


type of inspection: ultrasonic inspection of studs report no. 37

Component: HP turbine casing

Item: outer surface casing




type inspection: dye penetrant report no.12

Item: nozzle box

result inspection: no indicationstype inspection: visual report no. 76

Item: inner surface casing

result inspection: material missing up to 22 mm depth at 12 locations


action taken: repair by welding without additional heat treatment


result inspection 7 cracks up to 140 mm

type inspection: dye penetrant report no.12

action taken: all crack removed by grinding; 5 welded (if depth>15% wall thickness)

without additional heat treatment


Item: material condition casing

result inspection: acceptable; apparent limited decrease of hardness at inner surface


Component: HP rotor




Item: outer surface rotor

result inspection: no relevant defects


inspected parts: seals, fillet, combs, blade discs discharge openings, holes for stud

bolts coupling

result inspection: no defects


inspected parts: fillet discs, blade discs discharge openings, holes for stud bolts

coupling


type inspection: ultrasonic report no. 45

inspected parts: rim, combs, discharge openings, fillets, holes for stud bolts, T-slots

result inspection: acceptedtype inspection: hardness measurements report no. 46

inspected parts: ends of rotor, disc stage no. 1 both sides

Component: HP nozzle segments

result inspection: accepted after removing limited impact damage

type inspection: visual inspection report no. 63

Component: HP rotor blades

result inspection: stage 1&2 replace; stage 3-8 accepted; stage 9-11 replace according

to contract; stage 12 accepted


result inspection: stage 3-8 and 12 accepted


Component: nuts and studs HP turbine

Item: outer surface and thread

result inspection: tears in thread for 5 studs; 4 nuts replaced

type inspection: visual report no 29

action taken: tears removed by mechanical means


type inspection: ultrasonic inspection report no. 31

Item: material condition nuts and studs



Component: Stop valve IP turbine




Item: stop valve casing





Item: material condition stop valve casing



Item: studs and nuts




type of inspection: ultrasonic of studs report no. 40



Component: Steam cross over pipes IP turbine

Item: steam cross over pipes upper halve

result inspection: no indications type inspection: visual report no. 71





Item: welding steam pipes upper halve


type inspection: visual report no.73





Component: Control valve IP turbine

Item: regulating valve casings


type inspection: visual report no. 26 action taken: removed by grinding





result inspection: 5 cracks up to 55 mm outer surface casing #1


action taken: removed by grinding, welded without additional heat treatment


Item: material condition stop valve casing report no. 28


type inspection: hardness measurements

Item: studs and nuts of valve 1 & 21




type of inspection: ultrasonic of studs report no. 40



Component: IP turbine

Item: outer surface casing





Item: inner surface casing

result inspection: material missing up to 10 mm depth at 8 locations


action taken: repair by welding without additional heat treatment


result inspection 4 cracks up to 170 mm


action taken: all cracks removed by grinding; 3 welded (if depth>15% wall

thickness) without additional heat treatment


Item: material condition casing


type inspection: hardness measurements report no.16

1studs and nuts of IP regulator valve 3 and 4 apparently not accessible during the overhaul.




Component: IP rotor


result inspection: no relevant defects


inspected parts: fillet, blade discs discharge openings, holes for stud bolts couplings,

rivet area



inspected parts: fillet discs, blade discs discharge openings, holes for stud bolts

couplings, rivet area



inspected parts: rim, combs, discharge openings, fillets, holes for stud bolts, T-slots,

rivet holes



inspected parts: ends of rotor, disc stage no. 13 both sides

Component: IP nozzle segments

result inspection: accepted


Component: IP rotor blades

result inspection: stage 13 & 15-18 replace according to contract; stage 14 &19-23

accepted



type inspection: dye penetrant report no. 55 3

Component: LP rotor




inspected parts: fillet, rim, combs, holes for stud bolts coupling, rivet area



inspected parts: fillet discs, holes for stud bolts couplings, rivet area


2 minor mistakes in calculation of average values were noted

3 another report no. 55 was delivered as results of visual inspection of IPR with similar results as report no. 54





inspected parts: rim, combs, fillets, holes for stud bolts, rivet holes

Component: LP nozzle segments



Component: LP rotor blades

result inspection: stage 27&31 replace according to contract; stage 24, 25, 26 & 28, 29,

30 accepted, rivets stage 26&30 not acceptable, stage 25 rejected due

to missing tips two opposite blades (cut off)


result inspection: stage 24, 26, 28-30 accepted


Components: Bearings

result inspection: scratches, worn out in single position


result inspection: detachments noted

type inspection: dye penetrant report no. 25 result inspection: detachments noted


action suggested: maintenance required for 5 out of 7 bearings



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04 Final RLA Report DNV

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