Session: MF-12-01 Materials and Fabrication: General Topics I

Paper Number: 63062

Start Time: Wednesday, July 14, 2021, 05:00 PM

63062 - Full-Scale Hydrostatic Test of Internal CFRP Repair on a Degraded Pipe With a Postulated Flaw for Short-Term Loading in Safety Related Nuclear Applications 

The use of Carbon Fiber Reinforced Polymer (CFRP) in the nuclear industry is very limited and was not used for any nuclear safety related application until recently.  In 2019, the ASME Boiler and Pressure Vessel (BPV) approved a new Code Case N-871 for Class 2 and 3 safety-related piping using CFRP for Service Levels A, B, C and D and a service life of 50 years.  However, the US Nuclear Regulatory Commission (NRC) is still reviewing and has not approved this Code Case for use in commercial nuclear power plants. 

Code Case N-871 provides very detailed guidance on materials, design, fabrication, and installation of CFRP repair for Class 2 and 3 nuclear safety related piping.  There are two critical design conditions for use of CFRP in nuclear safety related piping application in terms of time duration: short-term loading conditions and long-term service life duration. The final design must satisfy both these conditions in terms of available safety margin for the entire period of service.  This paper focuses on full-scale experimental work to evaluate the safety margin for short term loading conditions.    

The primary goal of this effort was to determine the available safety margin for short-term use by conducting a full-scale hydrostatic test.  This hydrostatic test was conducted on a 40-inch diameter steel pipe which had a machined through wall flaw (“cut-out”) that was repaired internally with CFRP as per the requirements of ASME BPV Code Case N-871.  The internal CFRP repair consisted of three unidirectional CFRP layers and was applied circumferentially over (360°).  Two glass fiber reinforced polymer (GFRP) layers were also applied - one directly against the host metal as a dielectric barrier and the second under the outer-most carbon fiber (between 2and 3) for watertightness.  The design pressure and temperature for this repair was 78 psi and 72 F. 

Details of CFRP repair installation and hydrostatic test are described in the paper. Test results are then analyzed to evaluate the available safety margin for short-term use. Detailed analysis of strain gage data, bulging and video of this test specimen revealed the potential failure mechanism for a typical CFRP repair.  Separately, several smaller-scale watertightness tests as described in ASME BPV CC N871 using specialized fixtures with a similar flaw as full-scale hydrostatic test were also conducted and an effort has been made to correlate these results (failure pressure, failure mode etc.) with those from the full-scale hydrostatic test.

Presenting Author: Mo Uddin Engineering Mechanics Corporation of Columbus

Authors:

Mo Uddin Engineering Mechanics Corporation of Columbus
Fabian Orth Engineering Mechanics Corporation of Columbus
Yunior Hioe Engineering Mechanics Corporation of Columbus
Prabhat Krishnaswamy Engineering Mechanics Corporation of Columbus
Laura Smith Office of Nuclear Reactor Regulation
Chakrapani Basavaraju Office of Nuclear Reactor Regulation