The results show that on increasing the pressure the strain increases linearly in all the four cases, however, the maximum strain recorded was less than 0.08% for 1st loading and less than 0.07% for 2nd loading. This indicated that the deformation of the sphere during hydrotesting was well below the elastic limit of the material used for construction of the horton sphere. The amount of AE signals generated during 1st loading cycle was much higher than in the 2nd loading cycle. This was because when a new pressure vessel is hydrotested for the first time, the hydrotest causes relaxation of high residual stresses, induces local yielding in the areas of high secondary stresses and tightens nuts and bolts of the flanges. Moreover, the cluster analysis of the AE source location show that majority of the AE signals have been generated from bottom and top portions of the sphere due to rubbing of the nuts and bolts. These emissions can mask all but the most serious defects. That is why, the reloading cycle was immediately carried following the 1st hydrotest. As the reloading cycle was to 98% of the initial hydrotest load, additional yielding and emissions have been avoided. The amplitude of the AE signals that are generated during the reloading cycle were below the signal amplitudes for crack growth as confirmed by laboratory tests. Moreover, during the load hold at highest pressure of the reloading cycle, no signals were generated. This may be used as an indicator for checking the soundness of the vessels, because any active flaw shall exhibit AE activity during load hold.

From the study the following conclusions may be drawn:

1. For AE testing of a new pressure vessel repressurization should immediately start following the hydrotest, and the data from the 2nd loading cycle should be used to evaluate the conditions of the vessels.

2. Triangular source location method with cluster analysis can be used effectively for a spherical vessel to find out the location of defects.

3. The peak amplitude of AE signals can be used as an acceptance criteria for integrity assessment of containment vessels through AE technique.