Vol.6, No3, 2006, pp. 111-120
 UDC 621.791:621.643

FITNESS-FOR-PURPOSE ASSESSMENT OF REPAIRED FEEDWATER HEATER

Taško Maneski, Aleksandar Sedmak 1

Ljubica Milović 2

Antun Fertilio, Stojan Sedmak 3

1 Faculty of Mechanical Engineering, University of Belgrade

2 Faculty of Technology and Metallurgy, University of Belgrade

3 Society for Structural Integrity and Life, Belgrade

Abstract

The leakage of tube-tubesheet joint of feedwater heater on the inlet required redesign and repair by additional tube welding. The original design took into account only the sealing, and subsequently after some period leakage occurred due to tube displacement in tubesheet, caused by thermal and mechanical overload. Repair procedure included cutting out the heater header along the welded joint, preparing and welding the tubes to the tubesheet, and repeated welding of the header. The header and tubesheet are made of carbon steel. Welding procedure anticipated an austenitic soft interlayer and local heat treatment for residual stress relaxation before final joining. Fitness-for-purpose assessment has been issued and models were developed by finite element analysis according to the design solution and condition after repair. The results of mechanical and thermal responses of model confirmed that repaired feedwater heater is fit for purpose.

Keywords: water heater, fitness-for-purpose, repair by welding, modelling, stress analysis

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