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Aged impellers demand unorthodox procedures

Published on 22 January 2013
Impeller welds are dressed at the Elliott Works in Basingstoke, UK.
Impeller welds are dressed at the Elliott Works in Basingstoke, UK

Specialist advice sought from TWI was used in the refurbishment of six old impellers destined for gas compression work in the Middle East. Handling the work, Elliott Turbo-machinery of Basingstoke, UK, turned to TWI to find out how heat treatment would affect the components during and after refurbishment work.

Unlike many of today's impeller designs the components are riveted and this has added an extra dimension of difficulty to the job, explained shop manager Frank Branagan. 'Our Middle Eastern customer machined down the impellers of this compressor rotor some years ago when working pressure requirements were reduced by the operator', said Branagan. 'He now wants us to re-establish the vane material to the original dimensions. We'll be using the TIG process. It will involve preheating on a semi-automatic basis using a welding manipulator and then laying down the filler material manually.'

It is important that the finished material has a low hardness level. This will mean heat treating to a relatively high temperature and to achieve that temperature could well undermine the strength of the existing rivets. Elliott short-listed two weld repair methods and contacted TWI for support in choosing the better of the two. 'TWI is not just conversant with the welding procedures but also knowledgeable about the material's properties and the effect of heat treatment on the material' commented Branagan. After the welding and stress relief work Elliott performed quality checks including spin testing under vacuum at 15% over speed.

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