QE2 Turbine Failures on Maiden Voyage.
I recently found this article posted on another forum. It may be a little long-winded for some, but for those who persevere, and understand it, it makes interesting reading.
Item 14c below has particular relevance for me - I had a turbocharger overhauled ashore by a well-known world-wide company, and they didn't follow the original pattern of blade groups when installing the new lacing wire. This error promoted resonance in the turbine wheel, which screeched to a halt when the blades broke away in the middle of the night when under full load, and after less than 23 hours in operation. Thankfully, we had two main engines, so eventually made port 4 days later on the other engine.
Skilly.
s.s. "Queen Elizabeth 2"
HC Deb 03 March 1969 vol 779 cc41-5W 42W.
Mr. Edward M. Taylor asked the Minister of Technology what discussions he has had with Upper Clyde shipbuilders regarding the progress made on the "Queen Elizabeth 2"; and if he will make a statement.
Mr. Benn, pursuant to his reply, OFFICIAL REPORT, 26th February, 1969. Vol. 778, c. 305, supplied the following information:
Sir Arnold Lindley has now completed his assessment of the "Queen Elizabeth 2" turbines the full text of which is as follows: In this letter I am reporting to you on the failure of the high pressure turbine rotors of S.S. "Queen Elizabeth 2" together with remedial action which should be taken in accordance with your terms of reference to me dated 10th February, 1969.
1. I have now examined the reports and data concerning the rotor damage submitted by—
(a) John Brown Engineering (Clydebank) Limited
(b) National Engineering Laboratory, East Kilbride
(c) Lloyds Register of Shipping
(d) C. A. Parsons & Co. Limited covering research data concerning blade resonance carried out in their laboratories
(e) Board of Trade
(f) Other interested parties.
2. I have also examined the damaged blading and have inspected the high pressure steam rotors and steam nozzles, and have had the benefit of several discussions with design engineers concerned with the turbine design.
3. I have considered the conditions of operation at sea during the various sea trials to date which may have had a bearing on damage to the turbine rotors.
4. All design information has been made available to me without reservation and I have had the greatest possible assistance from all parties concerned and also from a number of engineers including Dr. Frankel who are experienced in steam turbine manufacture and operation who have given me their opinions freely.
5. Blading damage occurred on both H.P. rotors. The rotors are identical and each rotor provides 12 stages of steam expansion consisting of a first stage in the form of a double Curtis wheel and thereafter 11 single wheels.
6. It is wheel 9 of the Starboard rotor which suffered most damage by losing all its blades. Some blades of wheel 10 became broken and many others were cracked at the junction between the blade section and the root. Wheels 8 and 11 had no cracked or fractured blades.
7. The Port H.P. rotor blades were also severely damaged. Here again, the blades of wheel 9 showed most damage, some being completely detached while others were cracked at the junction with the root. Many blades of wheels 8, 10 and 11 were cracked but none fractured.
8. The fact that both H.P. rotors show similar blade damage at the same wheels, although the damage on the Port rotor is less severe, indicates a common design fault.
9. I wish to report that the cause of blade failure in both rotors is resonant vibration in tangential (clamp pin) mode, caused by excitation from the steam issuing from the preceding steam nozzles. It is a phenomenon well known to steam turbine engineers not only in Britain but also in America and Europe, and in the case of marine turbines which operate under variable speed conditions, this excitation is particularly difficult to avoid.
10. The blades of wheels 8, 9, 10 and 11 of the S.S. "Queen Elizabeth 2" H.P. rotors as designed had resonances which were not only too close to this excitation frequency under normal expected speed and power conditions but were also of a form which included what are known as stress raisers.
11. There is an additional possible source of excitation in the form of torsional vibration of the rotor arising from lack of truth of the main flexible coupling from the turbine to the reduction gears. This may have given rise to a tangential mode of additional vibration but I consider this to be of secondary importance and is in no way connected to the failure of the blades.
12. The details of blade failures and the condition of the rotors are described fully in the John Brown Engineering (Clydebank) Limited Interim Report dated 27th January, 1969. The cause of all blade failures of the H.P. rotors has been the subject of deep study by the engineers of The Cunard Steam-Ship Co. Limited, Upper Clyde Shipbuilders Limited, John Brown Engineering (Clydebank) Limited, Lloyds Register of Shipping, National Engineering Laboratory-East Kilbride, and a number of independent consultants with whom I have had discussions. We are all agreed that blade failures were caused by resonance as described in item No. 9.
13. It should be made clear that there is no reflection whatever on the quality of workmanship or of material used in any part of the construction of the H.P. turbines.
14. The remedial measures necessary to restore the rotors to full operational condition, and also to remove the possibility of further blade trouble, will require blades of modified form not only for wheels 8–11 but also for wheels 7 and 12. These measures are listed below.
(a) The blade form should be changed to "rhubarb" section which provides considerable improvement in strength at the junction between blade and blade root.
(b) To reduce blade stresses it is necessary to increase the section of blade material at the root junction which is known as root re-inforcement. This should be carried along the blade to a point 1.1 inches along the blade length where it would resume the original blade section.
(c) Lacing or binding wires must be provided at the mid-point of the blade length. The lacing wire should correspond in length to the present group arrangement of blades. The introduction of the wire inhibits the mode of vibration described in item no. 9 and changes the response to a frequency outside the operating range.
(d) All blading on wheels 2–6 need to be replaced with blades of the original design but with the fillets at the junction of the blade with its root removed to eliminate the stress concentration.
15. The remedial measures referred to in item no. 14 are substantially those contained in section 3 of the John Brown Engineering (Clydebank) Limited Interim Report dated 27th January, 1969. I fully endorse these proposals and they are also agreed by all those who have taken part in this investigation either directly or with whom I have had consultation including Dr. Frankel.
16. In accordance with item (f) of my terms of reference, I would like it to be considered whether there is any advantage to be gained in widening the gap between the new blade resonant frequency and the excitation frequency from the steam nozzles of stages 7, 8 and 9 by reducing the number of nozzle openings. There may be disadvantages in other directions involved in this modification. Time is required for investigation and should it be finally agreed that this modification is worthwhile, it could be carried out at a future date. Perhaps during the first overhaul.
17. Item (e) of my terms of reference enquires whether further sea trials should now take place. In my view the remedial measures are adequate and when complete, trials can be resumed with every confidence. Repairs to the turbines are well advanced and a tentative programme has been drawn up by The Cunard Steam-Ship Co. Limited, Upper Clyde Shipbuilders Limited, John Brown Engineering (Clydebank) Limited, Lloyds Register of Shipping and the Board of Trade for re-commissioning R.M.S. "Queen Elizabeth 2".
Briefly, this programme is as follows— It is expected that:
Re-assembly of turbines in ship will be completed by 21st March.
Over-speed tests, Basin trials and Inspection by end March.
Departure for proving voyage by early April.
Subject to the foregoing the ship's trials will be completed and the ship ready for handing over during the second half of April. 18. This programme must be considered in the light of the ship having already undergone many trial runs, including satisfactory operation at maximum power. There are other functional trials yet to be carried out in which the turbines may not be directly involved. It is expected that anything which might arise can be taken care of during normal operation without affecting commercial commitments.
19. It was thought during the preliminary trials that expansion of the various steam pipes might have created unacceptable thrust on the turbine casings. Modifications have been made concerning this and it is intended to check this point to ensure that the high pressure turbines are not adversely affected.
20. In putting this report together I have been assisted by a number of supplementary reports produced by various parties which are enumerated as follows:
John Brown Engineering (Clydebank) Limited Interim Report dated 27th January, 1969.
National Engineering Laboratory Memo X/Supt/I dated January, 1969.
National Engineering Laboratory Report Z2/14/6024/29 dated February, 1969.
Lloyds Register of Shipping R. & T.A. 8255 dated 5th February, 1969.
Lloyds Register of Shipping R. & T.A. 2716 dated 14th February, 1969.
Lloyds Register of Shipping R. & T.A. 2745 dated 21st February, 1969.
C. A. Parsons & Co. Limited Report dated 18th February, 1969.
Miscellaneous memoranda, letters, etc., from various parties.
21. I have not referred to the double stage Curtis wheel at the steam inlet end of the HP turbines. The design at this stage is such that there may be advantage in changing the nozzle control. This has been discussed and is a subject for further investigation.
22. The HP turbines with modifications as recommended should put them into the condition of giving service as would be normally expected for this class of machinery. They have the advantage of having already had trial runs which have brought out points that needed modification. To this extent there should be every confidence in their performance within the guarantees normally given by manufacturers. Although there is a wealth of experience in the manufacture and use of steam turbines, they are not built in mass production, as for instance in the case of aircraft engines. Steam turbines are built to a specification often on a once-off basis or in pairs. It is for this reason that trouble arises from time to time as there has been little opportunity for development. I must say with emphasis that in high power marine steam turbine drives, more work should be done in turbine development and instrumentation under running conditions so that reliable running without risk of breakdown can be achieved. This, of course, is a matter of cost of development.
23. I hold myself at your disposal for any further information you may require.
Yours sincerely,
ARNOLD LINDLEY.
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