Plant license renewal and economic issues are highlighting the need for advanced inspection, repair, replacement, and mitigation technologies for buried pipe.

Concerns about the health of buried piping have spurred increased regulatory attention related to license renewal activities, and increased plant attention due to the cost and time required for repairing or replacing pipe with excessive degradation. Unlike above-ground piping systems, buried pipes can corrode and foul from the fluid side and corrode or experience mechanical damage from the soil side. Also, although the corrosion mechanisms are generally slow, they are cumulative, with leak frequency increasing as plants reach 30 years of operation.

EPRI’s Buried Pipe Initiative targets research spanning inspection, repair and replacement options for buried piping. Ongoing activities include:

Buried Pipe Integrity Group – EPRI organized this group to promote buried pipe experience sharing, provide training to plant personnel, compile information from industry experts, and sponsor related research projects. The next meeting will be July 22-23, 2008 in Jacksonville, Fla.

Programmatic Recommendations – EPRI has developed draft “what-to-do” guidance for plant personnel in controlling buried pipe degradation (Technical Report 1016456). A multi-stage review by nuclear industry experts will facilitate final document release by late 2008 or early 2009.

Risk Ranking Software – Because nuclear plants contain 15 to 30 buried piping systems, each potentially encountering tens to hundreds of different conditions (e.g., burial conditions, soil properties, cathodic protection, coatings, linings, materials, joints, applied loads, fluid conditions, etc.), it is not practical or necessary to inspect each system under every condition. EPRI is developing software to apply risk-informed ranking in prioritizing inspection locations. A beta release is scheduled for late summer 2008.

High-Density Polyethylene Piping – High-density polyethylene (HDPE) represents an attractive option for repair and replacement of corroding metal pipe as compared to carbon steel, exhibiting no tendency to corrode, foul, or host tubercles or bi-valves. HDPE can also be installed much faster and less expensively than metal pipe. In January 2007, ASME approved Code Case N-755, which contains rules for the installation of HDPE in Class 3 systems. EPRI is supporting NRC approval of Code Case N-755 for HDPE installation in Class 3 piping systems through materials property development, fusing and repair standards, and nondestructive evaluation methods.