September-October 2018 NPJ

Robotic Crawler By Chris Allmond, Austin Bauer and Roger Galbraith, Dominion Energy and Jonny Minder and Aaron Huber, Diakont. Chris Allmond Chris Allmond, P.E. is a Nuclear Engineer III at North Anna Power Station. Chris joined Dominion Energy in 2007 in Materials Engineering. He currently works as a Primary Systems Engineer for North Anna. Austin Bauer Austin Bauer is currently a Nuclear Engineer III at North Anna Power Station. Austin joined Dominion Energy in 2015 and is currently the Site Owner for the Coatings, GSI-191, Buried Pipe, System Pressure Tests, Containment ISI, and Boric Acid Corrosion Control programs. Roger Galbraith Roger Galbraith, P.E. is a Supervisor in the Engineering Department of the North Anna Power Station. He has 17 years of experience in the nuclear industry as well as experience as a consulting engineer and Marine Corps officer. The Nuclear Energy Institute’s Top Innovative Practice Awards highlight the nuclear industry’s most innovative techniques and ideas. This innovation won a 2018 Top Innovative Practice Award. The team members who participated included Chris Allmond, Nuclear Engineer III, Dominion Energy; Austin Bauer, Engineer II, Dominion Energy; Roger Galbraith, Supervisor Nuclear Engineering, Dominion Energy, Jonny Minder, Director of Energy Services, Diakont, Aaron Huber, Marketing Supervisor, Diakont. Summary For a small segment, the North Anna auxiliary service water (ASW) lines consist of a pipe within a pipe configuration. As such, determining the external pipe health is difficult, so excavating and completing an external visual inspection would not be possible. To determine the overall volumet- ric health of the ASW piping, Engineer- ing reviewed EPRI Report 3002004395, " Nondestructive Evaluation: Buried Pipe NDE Reference Guide—Revision 3" and EPRI Report 1025228, " Buried Pipe Di- rect Examinations Through Coatings" in search of a non-de- structive examination technique (NDE) to volumetrically exam- ine the ASW lines. Conventional volu- metric examinations on piping consist of gridding a small portion (e.g. 4 feet) with a 2"x 2" grid and completing spot UT measurements. This typically requires a shift to prep, grid, and gather data. While this is an acceptable pro- cess, it is a small sample which may miss an anomaly. Therefore to obtain an overall volumetric exam of the ASW lines, Engi- neering selected Diakont’s EMAT UT tech- nology; the goal of the examination was to obtain an overall wall thickness evaluation while actively looking for degradation. Diakont was selected to perform the EMAT examination of 22"-WS-425- 151-Q3 and 22"-WS-25-151-Q3. The EMAT technique permits full volumetric examination of the pipe material from the inner diameter to the outer diameter while providing information on both inner and outer diameter surface anomalies. Since the EMAT technique does not require couplant or direct contact between the transducer and the substrate (e.g. the pipe), the internal protective coatings did not have to be removed. Design The auxiliary service water system serves as an alternate pathway for service water to travel from Lake Anna into the station to bring both units to a safe shutdown and cooldown. Service Water from LakeAnna would be drawn from the lake via the Auxiliary SW pumps located at the Intake Structure into either the Unit 1 ASW line or the Unit 2 ASW line with an available cross-tie if necessary between the two units. During the late 1980s, the Service Water piping experienced internal wall degradation because of general corrosion and localized corrosion induced by microbiologically influenced corrosion (MIC). Because of these issues, a phased mitigation strategy was implemented in the early 1990s to repair and/or replace service water piping to ensure integrity of the service water system. The Service Water system mitigation strategy was completed in phases, and in one phase, the Auxiliary Service Water (ASW) lines in North Anna’s North yard were replaced utilizing a pipe – thru – sleeve approach. Approximately 139 feet of the ASW lines was replaced with 22" diameter piping which utilized the existing 24" pipes as sleeves. Once the work was completed, some of the supporting structures associated with the replacement of the ASW lines remained, and they were buried with the ASW lines. All of the buried ServiceWater piping is protected with a Cathodic Protection System consisting of four subsections designed to prevent galvanic corrosion of the piping. One CP Subsystem protects two 24-inch auxiliary supply lines from the ASW valve pit north of the station’s protected area fence to the valve pit in the turbine building. The ‘D’Cathodic Protection subsystem was re-energized after the completion of the line replacements. Because of the sleeved configuration, the impressed current CP system only supplied protective current to the buried sleeves and supporting structures; the ASW lines themselves did not receive protective current as designed. Because these lines have not received the impressed current as the design intended, it was unknown whether the outer diameter (OD) of these two sleeved lines had experienced any OD corrosion. The other challenge was these lines are sleeved; therefore, simply excavating them for inspection would not be possible. To address this configuration and determine if these two lines were experiencing wastage due to corrosion, Dominion Energy partnered with Diakont using its EMAT Ultrasonic Testing (UT) method to determine the overall material health of the sleeved portions of the ASW lines. The EMAT (Electromagnetic Acoustic Transmission) Ultrasonic Testing (UT) method utilizes the electromagnetic- Left to right: Chris Allmond, Roger Galbraith, supervisor and Austin Bauer. 48 NuclearPlantJournal.com Nuclear Plant Journal, September-October 2018