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
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,