April - Library

More documents

Recommendations

Info

Lessons Learnt In 45 Years of Condition Monitoring Ray Beebe Monash University Gippsland Campus (Australia) The author was inspired by the concept of condition monitoring to help prevent unnecessary overhauls when he started as a young engineer in power generation in 1964. In parallel with a general engineering and middle management career in several power plants in Australia and the UK, he developed and applied vibration and performance analysis for pumps, steam turbines, boilers and heat exchangers. His experience and passion for sharing knowledge led to presentation of many in-house and public courses and his first book. That in turn led him to Monash University in 1992 and a second award-winning book in 2003. In that role, he reflected on his experiences and has written 70+ papers, many of which have been chosen for conferences and technical journals around the world. The lessons learnt stand forever, but not all are well-known. This paper of brief case studies in narrative style is intended to entertain, inform and even inspire. Introduction: the starting years Yallourn Power Station was initially built in the watch of Sir John Monash, citizen soldier (WW1 Lt-General) and engineer. It was the biggest one 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, spare parts usage reports, on a turbine that had just come back into service after a major stripdown. “There has to be a better way than this” was his cry. Research 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 machine vibration as a guide to its internal condition was very basic. We had a Philips velocity transducer and a readout box that gave overall vibration in thousandths of an inch. For some machines of rotation speed below 900 r/min, a multiplier of 1.5 was used: nobody explained why (later I learnt that it was because velocity transducers have a natural frequency below about 900 c/min). We could examine 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 for balancing in the field. The timed-oscillation method required only a stop watch and graph paper (Beebe, 2001). The other used a manually tunable filter that fired a stroboscope to detect previously chalked numbers around the rotor. The usual vector calculations followed. Lesson #1 Choose your bosses well Lesson #2 When a plant is new and/or the major asset makes it easier to get proposals for monitoring etc. accepted. After further training attachments, I was assigned to Hazelwood Power Station in 1966. 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 feed pumps. The vibration measurement program was as at Yallourn, but more use was made of the balancing instrument to find relative phase angles of the 1X vibration to give a crude operation deflection shape. For routine monitoring of the steam turbines, permanent numbers were painted around the rotor line at a visible section. Case study 1 A strange vibration was experienced on the newest machine at the generator drive end bearing. When runup 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 r/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 “these symptoms indicate that there is something loose inside the generator rotor around that end”. Stripdown was arranged and the generator rotor examined closely. Nothing was found. Eventually, a message came from the OEM saying that one of the rotors – this one - was non-standard. At the end of manufacture, the rotor centres were bored out to about 100mm diameter, and the 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. Vol 24 No 2
AMMJ Lessons Learnt In 45 Years of Condition Monitoring 23 Figure 1 Cross-section of 200MW generator that proved to have loose bore plugs Lesson #3 Correct and confident 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!) are essentially a large heavy single-stage fan, driven through a fluid coupling, The coal flow eroded the blades unevenly, causing unbalance. Unlike the older much smaller mills at the older Yallourn Power Station, timedoscillation balancing was not workable and the phase angle method is used. A rough mill would be detected on routine vibration checks, and arranged to be taken from service. Next day, it was cold and isolated to be safe for phase marks to be chalked around the drive shaft. De-isolation was followed by an “original run”. Shutdown and isolated, a trial weight was attached, and a calibrating run made. Shutdown and isolated, the balance correction could be made at the blade chosen. De-isolated, a final 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 1 pound per thou of vibration 2 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 online when the high vibration was 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. Figure 2 Large lignite coal mill (8 per boiler) Vol 24 No 2
Page 1 and 2: The AMMJ is Sponsored and Supported
Page 3 and 4: info@infratherm.com.au Introducing
Page 5 and 6: 6 10 20 22 30 AMMJ Maintenance Engi
Page 7 and 8: AMMJ Maintenance Enginering and Eng
Page 9 and 10: Locate electrical problems Detect p
Page 11 and 12: technology means that experienced t
Page 13 and 14: 2011 RELIABILITY AND APOLLO ROOT CA
Page 15 and 16: Do our people get smarter when they
Page 17 and 18: existing strategy in place, the tea
Page 19 and 20: To be effective the task of calcula
Page 21: AMMJ Surge Protection Devices 21 to
Page 25 and 26: AMMJ Lessons Learnt In 45 Years of
Page 31 and 32: Vol 24 No 2 AMMJ to preventative ma
Page 33 and 34: Vol 24 No 2 AMMJ - Reduce equipment
Page 35 and 36: Vol 24 No 2 AMMJ • MaintiMizer is
Page 37 and 38: Vol 24 No 2 AMMJ CMMS/EAM DESCRIPTI
Page 39 and 40: AMMJ Fit at 50 39 The enormous cost
Page 41 and 42: AMMJ Fit at 50 41 analog signals. T
Page 43 and 44: AMMJ Fit at 50 43 Figure 10 ABB Tra
Page 45 and 46: AMMJ 0.87ms i.e. 13.051ms divided b
Page 47 and 48: AMMJ Figure 6 Envelope spectrum obt
Page 49 and 50: AMMJ Due to variable compliance eff
Page 51 and 52: Technical Short Feature: Machinery
Page 53 and 54: Maintenance News Penny Melrose, Dat
Page 55 and 56: Maintenance News deviation from the
Page 57 and 58: Seminar 1 Duration - 1 Day The Why,
Page 59 and 60: Len Bradshaw - Seminars 1 & 2 Len B
Page 61: And you thought we just made bearin

April - Library

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?