Feasibility of Monitoring Flaws in Nuclear Reactor Primary Loop Piping Systems Using Surface Strain Measurements—Phase 2: Pressurized Welded Pipe Mock Ups

Abstract The material presented in this article summarizes the results from phase 2 of a larger Electric Power Research Institute (EPRI) study to determine if permanently mounted strain sensors can be used to monitor and quantify the presence and growth characteristics of flaw indications in primary loop piping in light water nuclear power reactors (LWRs). The samples utilized in this phase 2 work consisted of butt welded sections of austenitic 304 stainless steel pipe segments. Axial and circumferential notches, intended to simulate service flaws of varying depths and lengths, were generated into the inner diameter (ID) of the samples. Resistive strain gauges were applied in longitudinal (axial) and transverse (hoop) orientations, on the outer diameter (OD) in the vicinity of the notch locations. The axial notches perpendicularly intersected the weld while circumferential notches were generated along the weld fusion planes on one side (15 deg from the radial direction). The notch morphologies, strain gauge placement details, and a summary of the strains measured during pressurization tests are presented in this article. Based on the strain data obtained, transverse strain measurements may be sufficient to allow online monitoring (OLM) of axial and circumferential flaws in the vicinity of welds in the LWR pressurized primary coolant loop austenitic stainless steel piping and components.