Catawba Nuclear Station Use of High Density Polyethylene ... · PDF fileCatawba Nuclear Station Use of High Density Polyethylene Piping Installation of ASME Class 3 HDPE Pipe to Main

Catawba Nuclear Station

Use of High Density Polyethylene Piping for ASME Section III Class 3 Service

International Atomic Energy Agency

Technical Meeting on Ageing Management of Buried and Underground Piping and Tanks at Nuclear Power Plants

October 13, 2014

Philip H. Kohn, P. E.

Duke Energy

Catawba Nuclear Station

Use of High Density Polyethylene Piping for ASME Section III Class 3 Service

Catawba Nuclear Station Use of High Density Polyethylene Piping

Installation of ASME Class 3 HDPE Pipe to Main Emergency Diesels is now complete with the systems in service!

This presentation provides an overview of the Catawba project that installed ASME Class 3 HDPE piping.


Corrosion and fouling problems in original carbon steel piping along with successful Catawba experience with HDPE used in the non safety related cooling water system led Catawba to submit a relief request to use HDPE piping in the nuclear safety related cooling water system.


Before replacement with HDPE in the non nuclear safety related service water system, flow control valves were fully open to the containment ventilation chillers with chiller condenser pressures near 150 psig trip set point. After replacement with HDPE and two operating cycles, flow control valves were 50% open with chiller condenser pressure around 125 psig.


Summary of Catawba Relief Request

•4000 feet of 12 inch HDPE pipe,SDR 11 (1.159 in. wall thickness)

•HDPE 4710 Material (ASTM D3350 cell classification 445574C)

• Replaced 10 inch sch 40 carbon steel piping abandoned in place

•Transitions from HDPE to steel were made in underground vaults


Summary of Catawba Relief Request

•Limited to replacement of buried ASME Section III Class 3 service water piping for the four emergency diesel generators for Units 1 and 2

• HDPE design and installation requirements based on draft of Code Case N-755 Rev. 0

•Limited to HDPE Pipe, Mitered Elbows and Flange Adapters

•Limited to Butt fused joints and flanged joints


Timeline – Catawba HDPE Use • 1995 – HDPE use in non safety service water system •June, 2005 - Meeting with NRC to discuss plans for use of HDPE pipe for ASME Class 3 buried piping •October, 2006 - Relief request submitted to the NRC for use of ASME Class 3 HDPE for service water piping for emergency diesel generators

•March, 2007 - ASME Code Case N-755 issued for HDPE piping in buried Class 3 service

• May, 2009 - NRC issued Catawba safety evaluation

•June, 2009 – Began installation of ASME Class 3 HDPE piping to the emergency diesel generators

•October, 2010 – Unit 2 ASME Class 3 HDPE, buried service water piping to the emergency diesel generators completed and in service

•June, 2011 – Unit 1 ASME Class 3 HDPE, buried service water piping to the emergency diesel generators completed and in service


ASME Class 3 HDPE


ASME Class 3 HDPE


ASME Class 3 HDPE


ASME Class 3 HDPE


ASME Class 3 HDPE


Safety Evaluation for Catawba

•Supplemental Requirements to Code Case N-755 imposed by the NRC safety evaluation issued for the Catawba relief request.

•HDPE flaw depth allowance of 0.041 inches

•Reporting of ongoing industry HDPE test program results

•Periodic tensile impact testing of field joints

•Provision for access to inside of pipe

•Remote visual inspection of fused joints from inside pipe


Catawba NRC Safety Evaluation Requirements Flaw Depth Allowance

• Flaw depth allowance of 0.041 inches based on testing for 4 inch, SDR pipe (PE 3408) that qualified piping for resistance to slow crack growth with a gouge of 10% of the wall thickness.

•For 12 inch SDR 11 pipe, 0.041 inches allowance corresponds to 3.5% of the wall thickness.

•Pipe with indications > 3.5% was either cut out and replaced or indications were removed by blending and remaining wall thickness verified to be greater than the design wall thickness.

•Sample gouges in HDPE pipe in Catawba storage yard inspected


Typical scratches in HDPE Sample NPS DR Depth %

1 24 9 0.022 in 0.8

2 24 9 0.140 in 6.3

3 8 17 0.029 in 5.5

4 8 11 0.029 in 3.7

5 30 21 0.049 in 2.7

6 30 21 0.032 in 2.3

7 12 11 0.039 in 3.3

8 12 11 0.071 in 6.1

9 10 11 0.047 in 4.9

10 20 11 0.002 in 0.001

Sample 5


Catawba NRC Safety Evaluation Requirements Ongoing Industry Test Plan

•Licensee will submit information obtained from industry HDPE testing program (such as tensile and fatigue tests, slow crack growth resistance tests on parent material and butt fusion joints, and SIF of various components) •If information supports operation of HDPE piping for the remainder of plant life, then this information will be submitted to the NRC staff for information only •If results from testing program do not support use of HDPE piping for the remainder of plant life, information will be submitted to the NRC staff as part of a subsequent relief request for the next 10 year ISI Interval.


Catawba NRC Safety Evaluation Requirements

Ongoing Industry Test Plan, EPRI Reports

•EPRI Report 1020438, Capacity Testing of High-Density Polyethylene Bolted Flanged Joints published March 23, 2010

•EPRI Report 1020439, Stress Intensification and Flexibility factors of High Density Polyethylene Pipe Fittings, NQA Report published October 18, 2010.

•EPRI Report Number 1022565, Slow Crack Growth Testing of High Density Polyethylene Pipe – March 2011 (Draft Report)


Catawba NRC Safety Evaluation Requirements Periodic Tensile Impact Testing

•Impact tensile testing performed on daily and random samples of fused joints. •Impact tensile test first fusion joint of each work shift for each fusing machine. (daily joint) •Impact tensile test one random fusion joint chosen during a four work shift period. •At least 10 percent of field joints from each machine required to be tested during a production shift. •Fused joints involving fittings were excluded from random testing.



Periodic Tensile Impact Testing

U N I T

Joints Daily Joints

Random Joints

Joints Total

% of Joints Tested

1 107 66 16 189 43%

2 63 40 8 111 43%

1&2 170 106 24 300 43%



Periodic Tensile Impact Testing

•No failures of tensile impact tests

•A minimum of 20% of the joints were tested each work shift compared to the minimum of 10% required by the safety evaluation

•Random testing performed on 13% of the Unit 1 joints

•Random testing performed on 11% of the Unit 2 joints



Access to Inside of Pipe

• A steel tee with a blind flange on the outlet of the tee was installed for each line adjacent to the HDPE / steel flanged joint.

•Tee with blind flange is located in a buried vault.

•No requirement for examination of pipe imposed by safety evaluation.



Remote Inspection Inside of Pipe

• Inside surface examples of visually acceptable and unacceptable joints used for comparison standards

•Remote internal visual inspection was performed for each field fused joint


ASME Class 3 HDPE

•Unit 1 realized a 20-25% flow margin improvement due to HDPE.

•

•Unit 2 has data indicates that improvement will be on the order of 15%. The Unit 2 improvement is probably less than Unit 1 improvement because of the smaller amount of buried piping on Unit 2.


Summary

•HDPE used at Catawba has provided an effective and cost efficient way to address problems of corrosion and fouling in service water piping.

•Catawba HDPE piping requirements provided by ASME Sections III/XI Code Case N-755

•Supplemental requirements imposed by NRC safety evaluation

Questions?

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Catawba Nuclear Station Use of High Density Polyethylene ... · PDF fileCatawba Nuclear Station Use of High Density Polyethylene Piping Installation of ASME Class 3 HDPE Pipe to Main