EPRI Looks at High-Density Polyethylene for Pipes in Nuclear Plants
Metallic pipes form the backbone of cooling systems in nuclear power plants. Steel is an affordable, strong, readily available, and well-understood material that has been used in pipes in various settings for 150 years. However, it can degrade when exposed to water, presenting potential plant safety and reliability problems.
Since 2005, EPRI has examined high-density polyethylene (HDPE) as an alternative. Made from petroleum, HDPE is a hard, tough, corrosion-resistant plastic, commonly used for natural gas distribution pipes, municipal water transport, and fire protection systems.
“We have a great opportunity to use this advanced material, HDPE, which undergoes none of the corrosion processes that we see in carbon steel piping,” said EPRI Principal Technical Leader Ryan Wolfe. “Before utilities could deploy HDPE pipes in nuclear plants, several technical questions had to be answered. Our research has been aimed at determining whether they are an acceptable alternative to steel pipes.”
When utilities initiate projects to use HDPE pipes in nuclear plants, they do so using an American Society of Mechanical Engineers (ASME) Code Case. This Code Case uses extensive EPRI research performed over the past 12 years as a technical basis.
Scratches, Windows, and Joints
When plastic pipes are moved during construction or installation, their surfaces can get scratched by rocks, soil, and debris. One EPRI test is examining the extent and degree of scratching that HDPE pipes can sustain safely.
“The HDPE piping performed well,” said Wolfe. For two years, pipes with scratches deeper than what is permitted under the ASME Code were subjected to high pressures and temperatures. No failures were observed. These results are being used to propose updates to ASME Code.
If the manufacturer did not thoroughly mix HDPE pipe ingredients, pipes may contain small transparent regions called “windows.” When such pipes are heated and joined, the windows may make the joints more susceptible to cracking. There is neither an established maximum acceptable window size nor a nondestructive technique to detect windows, challenging the use of HDPE in nuclear power plants. EPRI is collaborating with the Plastic Pipes Institute to help address these issues.
Also, the ASME Code Case does not address cold fusion in HDPE joints. Fused joints may appear complete on the surface but may be incomplete and weak within the joint, potentially leading to breakage. EPRI found that three nondestructive evaluation methods—phased array ultrasonics, microwaves, and standing torsional stress waves—are effective in detecting cold fusion in HDPE joints.
EPRI also has examined fatigue, creep, and response to fire and earthquakes.
“So far, every time we answer one of these questions, it’s one less concern about using HDPE pipe in a nuclear plant,” said EPRI Technical Leader Craig Stover.
In 2018, EPRI plans to publish a comprehensive guide for utilities interested in installing HDPE pipes, pending the results of the ASME Code Case.
Key EPRI Technical Experts:
Ryan Wolfe, Craig Stover
- Technical Support for Proposed Polyethylene Pipe Code Case
- Design and Qualification of High-Density Polyethylene for ASME Safety Class 3 Piping Systems
- Nondestructive Evaluation: Seismic Design Criteria for Polyethylene Pipe Replacement Code Case
- Fatigue and Capacity Testing of High Density Polyethylene Pipe Material
- Fatigue and Capacity Testing of High-Density Polyethylene Pipe and Pipe Components Fabricated from PE4710
- Fatigue Testing of High-Density Polyethylene Pipe and Pipe Components Fabricated from PE 4710 – 2008 Update
- Repair of High Density Polyethylene Pipe
- Tensile Testing of Cell Classification 445474C High-Density Polyethylene Pipe Material
- Slow Crack Growth Testing of High Density Polyethylene Pipe–Interim Results
- Capacity Testing of High-Density Polyethylene Bolted Flanged Joints
- Stress Intensification and Flexibility Factors of High Density Polyethylene Pipe Fittings, NQA Report
- Evaluation of Design Methods for Above Ground High Density Polyethylene Pipe
- Fire Testing of High-Density Polyethylene Pipe
- Slow Crack Growth Testing of High-Density Polyethylene Pipe: 2011 Update
- Seismic Properties for High-Density Polyethylene Pipe for Use in Aboveground Applications
- Evaluation of Design Options for Buried Piping Containing Radioactive Materials
- Development of Crack Growth Curves and Correlation to Sustained Pressure Test Results for Cell Classification 445574C High-Density Polyethylene Pipe Material
- Tensile Stress-Strain Properties and Elastic Modulus of PE 4710 Cell Classification 445574C High Density Polyethylene Pipe Material
- Long Term Performance of PE4710 Materials in Disinfectant Treated Nuclear Raw Water Systems
- Feasibility Evaluation of Glass Reinforced Spiral Wound High Density Polyethylene for Circulating Water System Piping
- Applicability of High-Density Polyethylene in Nuclear Piping Systems with Internal Radionuclides
- An Assessment of Industry Data Related to Essential Variables for Fusing High Density Polyethylene Pipe
- Pennsylvania Edge Notched Tensile Resistance of High Density Polyethylene Butt Fusion Joints
- Advanced Nuclear Technology: The Long-Term Oxidative Resistance of Butt Fusion Joints in High-Density Polyethylene Piping
- Advanced Nuclear Technology: Material Properties Affecting the Butt Fusion of HDPE Pipe
- Sustained Pressure Test Results for Surface Scratches in PE4710, Cell Classification 445574C High Density Polyethylene Pipe Material
- Advanced Nuclear Technology: Literature Review of Mechanical Testing Methods to Evaluate the Integrity of HDPE Butt-Fusion Joints