48 | Mar/Apr 2011 | ME | maintenance & asset management vol 26 no 2

INTRODUCTION: THE STARTING YEARS

Yallourn Power Station was initially

built in the watch of Sir John Monash,

citizen soldier (a First World War

Lieutenant-General) and engineer. It was

the biggest in the state from 1924 up to

1966. Such places tended to have the

best engineers and I was fortunate to

have two excellent bosses there. They had

responded to a request from the manager

of maintenance. He was apparently holding

a sheaf of fault reports, overtime returns

and spare parts usage reports on a turbine

that had just come back into service after

a major strip-down. ‘There has to be a

better way than this’ was his cry. Research

reported in POWER and ASME papers

led to the ‘Valves Wide Open’ test being

applied. My involvement in testing 60MW

and 120MW turbines

there gave me the topic

for my engineering course

dissertation. Performance

tests were also performed

on the boiler feed pumps

and used as a guide to

overhaul.

Measurement and

analysis of the vibration in

a machine, as a guide to

its internal condition was

then very basic. We had a

Philips velocity transducer

and a read-out box that

gave overall vibration in

thousandths of an inch. For

some machines of rotation

speed below 900 rev/

min, a multiplier of 1.5 was

used (nobody explained

why, but later I learned that

it was because velocity

transducers have a natural

frequency below about 900

c/min). We could examine

It had three 200MW units in service, but

would grow by a unit each year to reach

eight, its current size. The boilers were

essentially identical, but there were two

makes of steam turbines and boiler f eed

pumps.

The vibration measurement programme

was as at Yallourn, but more use was made

of the balancing instrument to fi nd relative

phase angles of the 1X vibration to give

a crude operation defl ection shape. For

routine monitoring of the steam turbines,

permanent numbers were painted around

the rotor line at a visible section.

Case study 1A strange vibration was experienced on

the newest machine at the generator

drive-end bearing. When run up following

a shutdown, the machine vibration was

unacceptably high. The operators tripped

it and ran for some hours on turning gear

(low speed rotation at 30 rev/min). Back on

line, the vibration was now acceptable. This

happened repeatedly: sometimes all would

be OK after a shutdown, sometimes not.

Vibration measurements with our crude

instruments on line in both states showed

that the vibration amplitude and phase

angle differed on every run! All I could

say was that ‘these symptoms indicate

that there is something loose inside the

generator rotor around that end’.

Strip-down was arranged and the generator

rotor examined closely. Nothing was found.

Eventually, a message came from the

OEM saying that one of the rotors – that

one – was non-standard. At the end of

manufacture, the rotor centres were bored

out to about 100mm diameter, and the

Lessons Learnt in 45 Years of Condition

Monitoring

Ray Beebe MSc, CEng, MIET

School of Applied Sciences and Engineering

Monash University Gippsland Campus, Australia

the output on a CRO, and tell if most of the

vibration was at rotation frequency and if

there was any ‘high frequency’ present. This

was adequate, as most of the problems

were caused by unbalance due to wear.

Two methods were used, in the fi eld, for

balancing. The timed-oscillation method

required only a stop watch and graph paper

[1]. The other used a manually tunable fi lter

that fi red a stroboscope to detect previously

chalked numbers around the rotor. The

usual vector calculations followed.

Lesson 1 Choose your bosses well...

Lesson 2 and when a plant is new and/

or the major asset makes it

easier to get proposals for

monitoring etc. accepted.

In 1966, after further training attachments, I

was assigned to Hazelwood Power Station.

Figure 1 Cross-section of 200MW generator that proved to have loose bore plugs

maintenance & asset management vol 26 no 2 | ME | Mar/Apr 2011 | 49

hole packed tightly with rubber bungs.

Flaws were found in one of the rotors and

a length was bored to a bigger diameter….

but bungs of the same size were inserted

(see Figure 1). You can guess the effect of

these masses moving around! They were

removed – ‘no longer our practice’ – and

after an expensive 38 weeks off-line, all ran

well.

Lesson 3 Correct and confi dent

diagnosis is often possible

without complex instruments.

Lesson 4 Persist with the ‘5 Whys’ until

every possibility for a cause

has been exhausted - right

back to the intimate detail of a

component’s manufacture.

Case study 2 The coal mills (64 of them!) were essentially

a large heavy single-stage fan, driven

through a fl uid coupling. The coal fl ow

eroded the blades unevenly, causing

unbalance. Unlike the older much smaller

mills at the older Yallourn power station,

timed-oscillation balancing was not

workable and the phase angle method was

used.

A rough mill would be detected on routine

vibration checks, and arranged to be taken

from service. Next day it was cold, and was

isolated to be safe for phase marks to be

chalked around the drive shaft. De-isolation

was followed by an ‘original run’. Shut down

and isolated, a trial weight was attached

and a calibrating run made. Shut down

and isolated, the balance correction could

be made at the blade chosen. De-isolated,

a fi nal check run was made. Provided

operators were available, this took a day.

I decided to make permanent shaft marks,

and from records of our experience came

the rule: ‘Cut off one pound per thou of

vibration two blades behind the indicated

high spot’. A table giving size of cut and

mass was provided. Balancing now took

an hour or so, as the initial reading was

made on-line when the high vibration was

expenditure on test equipment that the

technical heads in the power stations had

ever seen. He did so on the condition that

each station provided an engineer to work

with me in applying the equipment. This

proved to be very wise, and gained the

‘buy-in’ at each place that a superstar would

not have gained working alone!

Lesson 6 If you fi nd that worthwhile

learning for your organization

can only be obtained outside

it (whether in another country

or not), make the proposal,

but ensure that it is only you

that can be selected to go!

Lesson 7 To get buy-in, involve locals

deeply in any development.

DOCUMENTED TEST PROCEDURES AND PROGRAMME OPERATIONI was assigned to the newest plant –

Yallourn W with two 350MW steam units

(now just called Yallourn) – and set up the

CM programme. Part of this was my belief

that documented test procedures are

essential, not only for our CM people, but to

get operating staff on side. We wrote about

25 of these documents.

[In 1987, I returned as a member of the

management team. The station now had

four units – two 375MW units had been

added. What had happened to the CM

work? I found that more test procedures

had been added – there were now 58!

The CM team was led by a keen technical

offi cer. We produced a regular newsletter

summarising our test work and results

(recommendations for urgent action did

not await its publication!). Never more than

one page long, 70 copies were distributed

throughout the plant. Operators, in

particular, commented favourably, as did

the plant manager, and at privatisation in

1995 the new owners found that the CM

team had better maintenance records than

the offi cial CMMS! Later, they won the CSI

award for best CM programme.]

Lesson 8 For staff training and for

briefi ng of relevant staff,

document the procedures

(include digital pictures) and

make then available to all on

the company intranet.

Lesson 9 To ensure continuity of the

CM program, estimate costs/

benefi ts and maintain a

running score sheet. Even

if only done for a sample

period each year, worthwhile

payback will be shown.

Publicise your activities

modestly, admitting any

shortcomings.

Lesson 10 Initial development of CM

Lessons Learnt in 45 Years of Condition Monitoring

detected. The next day with the mill isolated,

open and cold the correction could be

made and the machine closed up for return

to service.

Case study 3 Routine testing of the boiler feed pumps

was done as at Yallourn, with throttling in on

the outlet valve to get head-fl ow test points

over the widest range allowable. This took

some time and much physical operator

effort. Refl ecting that internal wear has a

consistent effect to the head-fl ow curve, I

realised that throttling was unnecessary,

as one or two points around the normal

operating area were enough. Testing now

takes 15 minutes per pump [2], and later

plants take advantage of their distributed

control system (DCS), see Figure 3.

Figure 2 Large lignite coal mill (eight per boiler)

Figure 3 Boiler feed pump (4500kW): head-fl ow data logged by DCS (truncated diagram)

Lesson 5 Review test procedures

regularly, to fi nd if a test or

procedure is, in fact, still

needed, or can be simplifi ed

or have its interval stretched.

THE UK EXPERIENCEBased on my proposal to learn more about

condition monitoring I was successful in

getting a two-year travelling scholarship

to work in the UK. (500MW boiler

commissioning with Babcock, turbine

design and dynamics with Parsons, and

tests and investigations with the then

CEGB). Unlike my home situation, with the

world’s cheapest fuel, thermal effi ciency

was the priority, but its engineering effort

shares much with condition monitoring.

Following a shaft crack in a 500MW unit,

vibration monitoring had been further

developed.

I returned full of ideas, and wrote

eleven reports. Only one had a specifi c

recommendation to spend money,

viz. to enhance our vibration analysis

capability by obtaining a real-time analyser,

accelerometers, vector fi lter phase meter,

plotter, tape recorders, etc. The power

generation manager approved the largest

50 | Mar/Apr 2011 | ME | maintenance & asset management vol 26 no 2

applications is well done or

managed by professional

engineers, but ongoing

routine CM is better run by

technical staff whose career

expectations are likely to be

less ambitious. Trades/craft

people can also fi nd this a

fulfi lling career.

IN THE MEANTIMEIt took some months to write specs, call

for bids and then analyse them and place

orders. In my absence the Yallourn (old

station) people had bought a replacement

balancing instrument. It had a signifi cant

advance on the old ones – it had a

frequency scale! Without them realising this

capability, we had a way of fi nding vibration

signatures (spectra). Several intractable

vibration problems were solved [1]. I recall

the stores manager raising his eyebrows

when asked to locate a large mill bearing

and count the number of rollers in it!

Lesson 11 Check your cupboards – you

may have under-utilised

equipment with as yet

unknown capability! See

again Lesson 3.

PUTTING THE ADVANCED VIBRATION ANALYSIS EQUIPMENT TO WORKNo single supplier could provide all the

items we needed (this was in 1975). By

connecting vibration transducer to signal

conditioning to analyser to plotter it was

easy to get a one-off vibration signature. But

as our aim was to start routine signature

analysis, repeatability was essential. After

some experimenting with signal outputs,

gain and attenuation, this was achieved.

The operating instructions were apparently

written by the electronics design engineers

and were diffi cult to understand by us

mechanical types! I wrote a handbook

of simple step-by-step instructions for

applying all the equipment. An example is

shown, in Figure 4, of the RTA front panel,

showing the required buttons and dial

settings.

We designed a special graph paper so that

plots could be compared by holding sheets

up to the light. Our intent was to eventually

have this comparison done by a computer,

but in the pre-PC days….

As the equipment was to be shared around

fi ve power stations, we set up clearly

labelled carry cases to facilitate collection

by any driver. Each case had the required

connecting cables. Unfortunately, after

some time cables got lost. Locating the

cases also took time. In the ensuring years,

more advanced FFT analysers, multi-

channel tape recorders, and later versions

of other instruments were obtained. A major

re-organisation set up a central specialist

group.

Lesson 12 Specialist test

equipment needs

to have a regular

owner and full-

time skilled operator

Hand-portable analyser/collectors and

associated computer packages have now

become commonplace, so our dream has

been realised.

Case study 4 Via the long cable reel, the new graduate

engineer hooked up the accelerometer to

the signal conditioning/readout instrument.

He reported that turbine vibration was

55mm/s rms – over ten times greater than

what might be expected! Before panic

set in, we found that he had used the

cable to connect the accelerometer to the

instrument. It was an ordinary shielded

co-axial type, intended to be used from

the instrument to an analyser. Low noise

cables are required from charge output

accelerometers to avoid tribo-electric

boosting of the output to give a spurious

high vibration reading.

Lesson 13 Check, and re-check, critical

data values if any look to be

unusual.

Case study 5 Using an innovative approach, site trim

balancing was conducted on a 120MW

generator rotor. The coupling between

turbine and generator was unbolted,

and faces held apart. The exciter was

connected to run as a motor, with the

rolling torque provided using the overhead

crane and a rope wrapped around the

rotor. (Appropriate design checks had been

made).

After reassembly, run-up proceeded as

normal until, when nearing normal service

speed, generator bearing vibration suddenly

jumped so much that the fl oor shook and

dust fell from the rafters! The operator

tripped the machine. Subsequent attempts

at run-up were no different. A challenge for

the vibration team! The gear was set up with

the analyser set to PEAK HOLD mode. The

extreme vibration was revealed as at 19 Hz –

the fi rst critical speed of the rotor.

Figure 4 Front panel of the analyser showing how to set it up (from the operating handbook we wrote).

It was noticed that the vibration started

soon after the auxiliary oil pump was

stopped, so it was left running and the

unit was eventually put into service. The

19Hz vibration was still evident, and could

be varied in amplitude by changing the oil

temperature.

Bearing dimensions and clearances

were found, and the bearing wedge

pressures (giving shaft loading) and oil

temperatures noted in order to calculate

the Load Parameter. As shown in Figure

5, the resulting plot on a bearing stability

assessment chart showed that the

operating range was well outside the

‘recommended’ area [3].

The only variable that could be changed

permanently was the ength of the

bearings (to increase the specifi c loading).

Surprisingly, the spares in the store were

found to be shorter, as were those on

maintenance & asset management vol 26 no 2 | ME | Mar/Apr 2011 | 51

the adjacent ‘identical’ machine! Bearing

changeover was the cure. This was a

strange case, as this machine had operated

for seventeen years without this problem.

The vibration team gained superhero status

for this success [4].

CM BY PERFORMANCE ANALYSIS – THE BIG BUCKS

Case study 6 I had developed performance tests, with

useful outcomes, for both types of 200MW

machine at Hazelwood, and continued this

at Yallourn W, the methods followed having

subsequently been published [5]. On one

unit our tests were run before the offi cial

acceptance tests.

Routine tests on a 350MW unit showed a

small but signifi cant decline in performance.

Prior to a planned outage, a steam forced

cool was conducted. This procedure is

used to bring the machine to standstill more

quickly by cooling the turbine metal, rather

than allowing slow natural cooling. The inlet

steam temperatures were slowly decreased

over some hours during offl oading. Testing

after return to service showed that the

performance had returned to its initial level.

Close examination of the data led to the

conclusion that there was some restriction

in the intermediate pressure section,

deduced to be from blade deposits [6].

Soon afterwards, the OEM site manager

met with the plant manager to tell him that

as the fi rst unit had reached two years

of service, it was time to arrange a major

outage and strip-down. When asked the

reason for the recommendation he was

told that an inspection after two years was

standard practice in the OEM’s country. The

manager had been my boss and mentor

in my initial job, so was well versed in CM!

He did not support an overhaul given

our vibration and performance condition

assessment, and the machine continued to

operate for seventeen years before its high

pressure section was opened.

Lesson 14 Take OEM recommendations

into careful consideration, but

do not follow them blindly.

Case study 7 In 1995 tests run on a 500MW turbine

at the latest plant (Loy Yang B) led to an

overhaul to remove metal debris carried

from the boiler. Long experience elsewhere

had shown that accurate special tests

were needed to obtain CM data, as plant

instruments were neither suffi ciently

accurate nor repeatable.

As this plant had a DCS opportunity had

been taken at each accurate (and high

cost) ‘Valves Wide Open (VWO)’ test to

extract data from the plant historian and

compute the same condition parameters.

Although the same values were not

obtained, a directly comparable trend was

clear, as shown in Figure 6 which shows

the VWO trend over its life from its initial

acceptance test.

Lesson 15 Assess whether the plant

instruments can be used to

give a usable trend for CM. If

a DCS exists, then try data

extraction and utilisation.

Case study 8 The superheater tubes in a series of large

coal boilers of the same natural circulation

drum type design leave the furnace through

spaces between roof tubes, and connect to

later sections, often via headers. There are

several superheater sections in series. The

platen superheater at the top of the furnace

has thirty sections, each with sixteen tubes

in a U-shaped pendant loop, hanging

through the roof tubes of the furnace. Unlike

other designs, where the leading tube down

has a kink so that it becomes an inner tube

in the up direction, these pendants are laid

out such that the assembly would be fl at,

i.e. the inner tubes are progressively shorter

than the outer tube. The platen is heated

mainly by radiation, so the longest tubes

on the outside of the array take up more

heat than those on the inner side. These

tubes are then led out of the furnace space

through gaps in the roof tubes into the

dead space, where they connect to primary

superheater inlet tubes. There are eighty of

these superheater sections across the gas

path, so each has six tubes.

Excessive metal temperatures lead to

considerable reduction in creep rupture

life. At these temperatures an increase of

Figure 6 Comparison of accurate tests (upper plots) with results calculated using DCS data (lower more numerous points)

Lessons Learnt in 45 Years of Condition Monitoring

Insert Figure 5 Bearing stability chart showing eff ect of oil viscosity and bearing length

52 | Mar/Apr 2011 | ME | maintenance & asset management vol 26 no 2

the furnace wall rather than specifi c tube

numbers. The lesson here is to check such

points in detail if two ‘identical’ plant items

show quite different behaviours [8].

Lesson 16 In critical cases, do not

believe everything you read

in the control room without

verifi cation of labels and

actuality at and inside the

plant.

CONCLUSIONS AND FINAL LESSONSCondition monitoring can be a key

contributor to higher reliability and availability

when set up properly and run by trained

and dedicated people. Some investment is

needed in equipment but much useful work

can be achieved with simple instruments.

Lesson 17 Training is essential before

starting CM work, followed

by regular reinforcement

via courses, conferences.

Consider getting certifi cation

to verify capability.

Lesson 18 Share your learning via on-line

forums, conferences, articles

in engineering magazines.

Lesson 19 Make recommendations clear

and concise: put the technical

complexity in appendices.

only 11°C can halve the life, so operational

monitoring is important. Manufacturers

use thermocouples installed in tube walls,

sometimes in special sections, to try and

measure the maximum metal temperature

[7]. Such sophistication was not available

when these boilers were built so, at several

sections, fi ve thermocouples were fi xed

across the gas path to primary superheater

outlet tubes in the dead space, and the

limits for operation derived by calculation.

Two boilers built almost at the same time

exhibited quite different temperature

behaviour at otherwise similar operating

conditions. One was often close to alarm

limits, and operation was adjusted to keep

within them. The other showed no such

high temperatures. After some years of

service the ‘good’ boiler suffered a spate of

superheater tube failures due to overheating

and creep rupture, and the complete

superheater had to be replaced. Why

should two identical boilers be so different?

Close investigation and painstaking

tracing of tube path layouts showed that

the hottest tubes from the outside of the

platen array led mostly to leading tubes,

but sometimes to the tube behind it in the

primary superheater, as the number of

platen tube banks is less than the number

in the primary superheater. The monitoring

thermocouples were installed on leading

tubes. Unfortunately, in the ‘good’ boiler, the

thermocouples were installed on leading

tubes that did not come from the hottest

tubes out of the platen. Presumably, the

installer was given set distances in from

Lesson 20 THE MAJOR ONE. Condition

monitoring is not an end in

itself, and should be applied

along with other maintenance

strategies as decided by an

RCM or similar analysis.

REFERENCES

1. Beebe R, Machine condition monitoring, MCM Consultants, Hazelwood, 2001

2. Beebe R, Predictive maintenance of pumps using condition monitoring, Elsevier, London, 2003

3. ESDU 66023, Calculation methods for steadily loaded pressure fed hydrodynamic journal bearings, Engineering Sciences Data Unit, IMechE London, 1966

4. Beebe R, Diagnosis and solution of resonant whirl on a steam turbine generator, Proceedings ICOMS2002, Brisbane, 2002

5. ASME, Simplifi ed procedures for routine performance tests of steam turbines, ASME PTC 6S Report, 1970. (Re-affi rmed and revised 2003)

6. Beebe R, Recent experience with condition monitoring of steam turbines by performance analysis, IEAust Mechanical Engineering Transactions, pp 42 – 49, 1978

7. BEI (British Electricity International), Modern power station practice: incorporating modern power system practice (3rd Ed), Oxford Pergamon Press, 1990-1992

8. Beebe R, Is your control room data telling you what you think it is? Maintenance and Asset Management, Vol 22, No 3, 2007 (and other journals)

ABOUT THE AUTHORRay Beebe has a passion for condition

monitoring acquired from 28 years in

power generation, followed by 18 years

at Monash University where he led the

postgraduate (off-campus learning)

programmes in maintenance and reliability

engineering. Since retiring from tenured

service he continues teaching and

speaking involvements and is working on

a third book. He was awarded Engineers

Australia’s 2004 George Julius Medal for

his second book Predictive Maintenance

of Pumps using Condition Monitoring. He

has spoken at conferences world-wide,

and his many papers have appeared in

technical journals. He can be contacted at:

Ray.Beebe@monash.edu

His papers are available on request. A

complete list can be found on –

http://www.gippsland.monash.edu.au/

science/aboutus/people/academics

raybeebe.shtml

Figure 7 Boiler cross-section above furnace.