Starting from Scratch
As this was to be the first ever use of HDPE in a safety-related water pipe system at a nuclear plant in North America, the team at Callaway had to create a material specification and related procedures from scratch. In the process, they underwent a change in mindset from focusing on what was available to specifying what was really needed. Most importantly, Callaway engineers began to work closely with members of the HDPE pipe value chain. These players included The Dow Chemical Co. (Dow) as the HDPE supplier, WL Plastics Corp. as the pipe manufacturer, and Independent Pipe Products Inc. for the manufacture of special pipe fittings. The consultant, Frank Schaaf, Jr. of Sterling Refrigeration Corp., was also instrumental in the work necessary to gain approvals from the NRC (Figure 3).
3. Plastic replaces steel. HPDE pipe and joint fittings were required to be tested to confirm that they met the quality and safety specifications of ASME Class 3 nuclear service piping systems. AmerenUE submitted a special Relief Request to the NRC in 2008 demonstrating that HPDE pipe could be used instead of carbon steel pipe. Courtesy: Dow Chemical Co.
After an evaluation of available options, and based on the service condition and stringent requirements for HDPE pipe performance, the Callaway team selected CONTINUUM DGDA-2492 Bimodal Polyethylene Resin from Dow as the raw material for its new ESW secondary water pipe system. Given the groundbreaking nature of the application for HDPE pipe, no American Society of Mechanical Engineers (ASME) code and standard is available. Callaway needed to obtain approval from the NRC through a Relief Request. In order to be approved for use by the NRC, water pipes manufactured from HDPE had to demonstrate that they could match the quality and safety specifications of ASME Class 3 nuclear service piping systems. AmerenUE submitted a special Relief Request to the NRC in 2008 with documentary evidence proving that the specified HDPE pipe could be used in lieu of carbon steel Class 3 pipe.
The Relief Request asked for NRC approval for using HDPE pipe based on the specified CONTINUUM DGDA-2492 resin. Callaway engineers knew that the HDPE pipe would need to meet water pressures of 161 psig at 95F and 45 psig at 176F. CONTINUUM DGDA-2492 has a 2.5-year pressure listing by the Plastic Pipe Institute, exceeding the application of a three-month requirement, at 176F.
Initially, the NRC had a concern regarding the effect of increased stress intensity on the slow crack growth (SCG) resistance of the proposed 36-inch pipe. This concern was mitigated because CONTINUUM DGDA-2492 resin has >10,000h PENT, more than 20 times better than the most stringent ASTM SCG requirement for PE4710 (a higher performance standard for HDPE pipe); it meets and exceeds the requirement at the adjusted higher stress intensity. In addition, the NRC requested that Callaway conduct extensive testing on the joint to ensure the integrity of the pipeline. As a result, a total of 168 pieces of fusion joint samples were tested using NRC-recommended test methods. All joints passed the test without a single failure. The request was officially approved by the NRC on October 31, 2008.
Place the Pipe
AmerenUE anticipated such a result, and its engineering firm, Sargent & Lundy LLC, together with its primary construction contractor, Corrigan Mechanical, moved quickly to make the piping replacement at Callaway.
Installation of the HDPE ESW pipe project was completed by December 9, 2008. Approximately 1,800 feet of 36-inch HDPE pipe (with 4-inch wall thickness) was installed underground at the site. A number of special HDPE joint fittings at 45-degree and 22.5-degree angles were also successfully fused to the main pipe components.
The new HDPE ESW system was started up on December 10, 2008, and immediately demonstrated its value. Callaway engineers noted no vibrations in the HDPE sections of the system, though some steel pipe sections in the pump house did vibrate due to a static issue. In addition, due to the lower friction, the new HDPE pipe was found to allow about 150 gallons more water flow-through per minute than the previous steel pipe it replaced, even with a smaller inside diameter.
According to the team at Callaway, this installation is a first important step toward HDPE becoming a preferred material for safety-related water pipe systems at nuclear power stations. AmerenUE is already planning to replace other buried piping with HDPE in other systems in 2009.
— Contributed by Jimmy Zhou (dowpipeline@dow.com), a senior development specialist for the Dow Chemical Co., and Frank Schaaf (treecode@cs.com), an energy industry consultant for the Sterling Refrigeration Corp.
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