The development of model techniques for prediction of creep strains applied to steam turbine casings

Bellamy, R.A. (1973) The development of model techniques for prediction of creep strains applied to steam turbine casings. PhD thesis, University of Nottingham.

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Because of the long service expected from steam power plant it is not practicable to obtain creep data from prototype installations to assist design against excessive creep. Model techniques, however, allow accelerated creep testing in a laboratory environment, which will produce the required creep information in a period of weeks rather than years.

Models are made of a lead alloy and subjected to the scaled mechanical service loads at room temperature. Similarity conditions, based on the usual stress-strain-time relationships, have been developed which allow the measured strain distribution to be used to predict the strains in the engineering component at any time during its useful service life. This prediction requires only the uniaxial creep characteristics of the model and component materials. At present the technique is limited to constant temperature conditions.

A lead-antimony-arsenic alloy has been selected which can be cast in the laboratory, giving good homogeneity, isotropy and fine grain structure; this material shows sufficient creep strain due to conveniently small stresses at room temperature. The steady load stress-strain-time characteristics have been determined from uniaxial tests.

The model technique has been used to study simplified steam turbine casings subjected to internal pressure. The shapes tested consisted of axially split, flanged cylinders with domed end closures containing large bossed central bores to simulate the turbine bearings and glands. The loading of the models was due to the bolting forces and due to internal pressure. Strains on the inner and outer surfaces were measured with electric resistance strain gauges.

Item Type: Thesis (University of Nottingham only) (PhD)
Keywords: Creep testing, Alloys, Stress-strain characteristics
Subjects: T Technology > TJ Mechanical engineering and machinery
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering
Item ID: 29737
Depositing User: Blore, Mrs Kathryn
Date Deposited: 01 Sep 2015 08:57
Last Modified: 13 Oct 2017 04:18

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