Technical Letter Report - Preliminary Assessment of NDE Methods on Inspection of HDPE Butt Fusion Piping Joints for Lack of Fusion
The U.S. Nuclear Regulatory Commission (NRC) has a multi-year program at the Pacific Northwest National Laboratory (PNNL) to provide engineering studies and assessments of issues related to the use of nondestructive evaluation (NDE) methods for the reliable inspection of nuclear power plant components. As part of this program, there is a subtask 2D that was set up to address an assessment of issues related to the NDE of high density polyethylene (HDPE) butt fusion joints. This work is being driven by the nuclear industry wanting to employ HDPE materials in nuclear power plant systems. This being a new material for use in nuclear applications, there are a number of issues related to its use and potential problems that may evolve. The industry is pursuing ASME Code Case N-755 entitled “Use of Polyethylene (PE) Plastic Pipe for Section III, Division 1, Construction and Section XI Repair/Replacement Activities” that contains the requirements for nuclear power plant applications of HDPE. This Code Case requires that inspections be performed after the fusion joint is made by visually examining the bead that is formed and conducting a pressure test of the joint. These tests are only effective in general if gross through-wall flaws exist in the fusion joint. The NRC wants to know whether a volumetric inspection can be conducted on the fusion joint that will reliably detect lack-of-fusion conditions that may be produced during joint fusing. The NRC has requested that the work that PNNL is conducting be provided to assist them in resolving this inspection issue of whether effective volumetric NDE can be conducted to detect lack of fusion (LOF) in the butt HDPE joints. PNNL had 24 HDPE pipe specimens manufactured of 3408 material to contain LOF conditions that could be used to assess the effectiveness of NDE in detecting the LOF. Basic ultrasonic material properties were measured and used to guide the use of phased arrays and time-of-flight diffraction (TOFD) work that was conducted. Millimeter (mm) waves were also used to inspect these assemblies. Fluor and NDE Innovations, Inc. conducted TOFD inspections using their commercially available equipment on all 24 specimens. These NDE inspection results were reviewed and several of the specimens were selected for destructive evaluation using a microtome to slice small blocks of blank and fusion joint material. This interim report provides a status/summary of the work that has been conducted to date. In the areas selected for destructive testing where there were strong acoustic responses, LOF was verified. In areas where there were no NDE responses, no LOF was found. It needs to be noted that only a small amount of material has been destructively characterized at this point and further work is planned to determine if these trends hold up. Some of the material from three of the assemblies was sent off for mechanical testing but the results were not available to be included in this status report. The initial work shows that at least some of the LOF is providing NDE responses that have been verified through destructive testing. Thus, there is promise that a volumetric examination can be conducted on HDPE butt fusion joints. The future work will lead to quantifying what various NDE methods can detect, what they miss, and what they incorrectly characterize as defective.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 934406
- Report Number(s):
- PNNL-17584; 401001060; TRN: US0803795
- Country of Publication:
- United States
- Language:
- English
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Assessment of NDE Methods to Detect Lack of Fusion in HDPE Butt Fusion Joints
PRELIMINARY ASSESSMENT OF NDE METHODS ON INSPECTION OF HDPE BUTT FUSION PIPING JOINTS FOR LACK OF FUSION WITH VALIDATION FROM MECHANICAL TESTING