In-Situ Pressure Testing of Steam Generator Tubes

The anatomist John Hunter said, “But why think? Why not try the experiment?” His words are applicable to in-situ pressure testing as a means of performing condition monitoring of steam generator tubes. Other methods of performing condition monitoring include the application of theoretical burst and leakage equations (deterministic methods), probabilistic analyses, and tube pull. The deterministic and probabilistic methods must address uncertainties in the material properties and flow measurements. Destructive examination of a pulled tube provides the verification of the damage mechanism and possible causes of the degradation; however, the axial loads required to pull the tube may affect the degradation. The results of a tube pull are generally not available until after the plant has returned to service. In-situ pressure testing provides structural and leakage integrity of SG tubing conditions. Candidates are selected for in-situ testing based on te EPRI Guidelines and include an evaluation of crak depth, length and/or voltage response from the eddy-current inspection results. Appropriate selection of tubes for in-situ testing provides confidence that the results adequately address the structural and leakage integrity of the SG tube population. In-situ pressure testing, combined with conservative operational assessments for the next cycle, assures that the integrity of the SG tubing is maintained.