Callaway Nuclear Plant is the first nuclear plant in the United States to utilize high density polyethylene (HDPE) piping in a nuclear safety-related application. HDPE is being installed in buried sections of the plant’s ASME Section III, Class 3 Essential Service Water (ESW) system. Due to its resistance to erosion, corrosion and microbiologically induced corrosion (MIC), HDPE is well suited to raw water system applications. As with any other first of a kind project, the use of HDPE piping in the Callaway ESW system has presented challenges in all phases of the project. Design, qualification and installation considerations for thermally-fused HDPE in an ASME Class 3 system differ significantly from those for traditional metallic materials. This paper will examine the challenges and lessons learned in the design, qualification testing, installation, examination and pressure testing of the HDPE piping at Callaway Nuclear Plant.

In the design of piping systems, there are many options for transitioning between HDPE and metallic piping. One common option is the use of flanged joints. As a result of the visco-elastic nature of HDPE, the use of HDPE-to-metallic flanged joints requires special design considerations. When HDPE-to-metallic flanged joints are used in ASME Class 3 systems, the design is further complicated by the requirements provided in the ASME B&PV Code, Section III for flanged joint analysis. This paper examines the differences between HDPE piping flanged joints and metallic piping flanged joints, including consideration of industry guidance and available industry testing results. The paper provides a proposed methodology for evaluating ASME Class 3 HDPE-to-metallic flanged joints and HDPE-to-HDPE flanged joints, including the determination of required bolt torque values and the determination of the maximum internal pressure that the joint can resist without experiencing leakage.

The design of buried piping systems requires special considerations. Historically, buried piping was evaluated for thermal expansion and contraction using simple hand calculations considering the piping to be fully-constrained by the surrounding soil. With the development of analytical software, more advanced analysis of buried piping is possible considering detailed piping routing and the stiffness of the surrounding soil and of the piping itself (in cases of more flexible piping materials). Typically, the areas of highest thermal stress occur at changes in direction (i.e. elbows, etc.) due to the applied moments, and the relative stress magnitude is influenced by the stiffness of the surrounding soil. Due to the relatively high coefficient of thermal expansion of polyethylene, stresses in buried piping due to thermal expansion and contraction are of particular note for high density polyethylene (HDPE) piping. This paper examines the relative influence of the analytical representations of a variety of HDPE piping elbow geometries (e.g. mitered elbows, molded elbows, etc.) and corresponding soil restraint. The study demonstrates that total longitudinal stress calculated in a finite element analysis may be reduced using minor to moderate efforts of refinement.

The design of buried piping systems requires special considerations. In the evaluation of seismic loads on buried piping, the associated stresses are typically considered to be secondary stresses as the piping is assumed to move with the soil during a seismic event and inertial seismic loads are considered to be negligible. During a seismic event, buried pipes are subject to relative displacement-induced strains, induced primarily by seismic wave passage. Typically, the areas of highest stress are found at offset locations as a result of applied moments (primarily due to axial loads into an elbow or tee) and/or at transition locations near entry into buildings or subgrade vaults as a result of seismic anchor movements and/or differential settlement. This paper examines the relative influence of the number of diameters of straight piping between offsets and the number of diameters of straight piping in between building/vault entry and the first support on resulting seismic piping loads.

This chapter discusses the current and future nonmetallic construction codes and standards using nonmetallic plastic polymers. It is divided into four parts. Part A provides an overview of the major nonmetallic materials used in structural applications, namely, thermoplastic materials, thermoset plastic materials, and graphite materials. It describes the importance of a design specification as well as its recommended contents and major aspects. Part A also provides information on two extensively utilized thermoplastic jointing techniques: butt fusion and electro-fusion. Part B and C cover NM-1 and NM-2 Standards, which prescribe requirements for the design, materials, fabrication, erection, inspections, examination, and testing of thermoplastic piping systems and glass-fiber-reinforced thermosetting-plastic piping systems, respectively. Included within the scope of the NM-1 Standard is thermoplastic piping which interconnects pieces or stages within a packaged equipment assembly. The contents and coverage of the NM-2 Standard address pipe and piping components that are produced as standard products, as well as custom products that are designed for a specific application. Fiberglass-reinforced plastic pipe and piping components manufactured by contact molding, centrifugal casting, filament winding, and other methods are covered. The organization of the NM-3 Standard, addressed in Part D, is modeled on the ASME Boiler and Pressure Vessel Code, Section II – Materials. ASME NM-3 addresses material specifications and material properties for both thermoplastic and thermoset plastic with glass reinforcing fibers. The NM-1 and NM-2 Standards reference NM-3 Standard for applicable material specifications and material physical and engineering property data. History Some of the material in this chapter had been originally covered in Chapter 3.6 in the Fourth Edition of the Companion Guide but consistent with the current activity of the ASME Code Committees it was considered appropriate by the authors to cover the efforts of the committee in a separate chapter. The current online edition was updated by C. Wesley Rowley and Thomas M. Musto