Vol.7, No3, 2007, pp. 187-194
 UDC 620.179: 621.18

INITIAL STRESS STATE OF BOILER TUBES FOR STRUCTURAL INTEGRITY ASSESSMENT

Jano Kurai 1

Zijah Burzić 2

Nikola Garić 3

Milorad Zrilić 4

Boško Aleksić 5

1 HIP Petrohemija, Pančevo, Serbia

2 Military Technical Institute, Belgrade, Serbia

3 NIS Petrol, Novi Sad, Serbia

4 Faculty of Technology and Metallurgy, University of Belgrade, Serbia

5 CertLab, Pančevo, Serbia

Abstract

Due to detected deficiencies, additional tests were requested for checking the stress-strain state in accepting the new boiler. Residual stresses were measured by hole drilling method in critical zones of boiler drum and damaged tubes. The change of state during and after water pressure proof test was monitored by strain gauges and acoustic emission. In this way, initial (nil) stress state was established before placing the boiler into service.

The initial level of residual stresses (39% to 44% of yield stress) had reduced to 32% after pressure testing, as a consequence of stress redistribution. Stresses calculated based on measured strains are elastic, lower than 99.3 MPa in boiler drum and less than 66 MPa on critical tube 52. This was confirmed by acoustic emission measurements.

Performed tests and analyses showed that boiler can be accepted as fit for service. During exploitation the boiler state can be evaluated comparing to the initial stress state.

Keywords: steam boiler, defects, experiment, stress state, fitness-for-purpose

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