United States Nuclear Regulatory Commission - Protecting People and the Environment

Erosion/Corrosion-Induced Pipe Wall Thinning (Generic Letter 89-08)

 May 2, 1989



TO:  ALL HOLDERS OF OPERATING LICENSES OR CONSTRUCTION PERMITS FOR 
     NUCLEAR POWER PLANTS


SUBJECT:  EROSION/CORROSION-INDUCED PIPE WALL THINNING
          (GENERIC LETTER 89 - 08)


Pursuant to 10 CFR 50.54(f), the U.S. Nuclear Regulatory Commission (NRC) is
requiring information to assess safe operation of reactors when erosion/
corrosion significantly degrades piping and components of high-energy carbon
steel piping systems.  The principal concern is whether the affected plants 
continue to meet their licensing basis when erosion/corrosion degrades the 
pressure boundary to below the applicable code design value.

Main feedwater systems, as well as other power conversion systems, are 
important to safe operation.  Failures in these systems of active components 
such as valves or pumps or of passive components such as piping can result in 
undesir-able challenges to plant safety systems required for safe shutdown and 
accident mitigation.  Failure of high-energy piping, such as feedwater system 
piping, can result in complex challenges to operating staff and the plant 
because of potential system interactions of high-energy steam and water with 
other systems, such as electrical distribution, fire protection, and security.  
All licensees have committed to adhere to criteria, codes and standards for 
high-energy piping systems described in licensing documents.  Such commitments 
are a part of the licensing basis for the facility.  An important part of this 
commitment is that piping will be maintained within allowable thickness 
values. 

Our concerns regarding this issue were prompted by incidents at Surry Unit 2
and the Trojan plant.  The Surry incident occurred on December 6, 1986, and it
was caused by catastrophic failure of feedwater piping.  The Trojan incident 
was discovered in June 1987, which was the first time that pipe wall thinning 
led to piping replacement in the safety-related portion of the feedwater 
lines.  In addition to these two cases, incidents of pipe wall thinning or 
rupture because of erosion or erosion/corrosion have been reported at many 
other nuclear power plants.  In many of these cases, the licensees had 
inspected the two-phase lines for some years, but it was not until the Surry 
incident that they started to examine some single-phase lines.  Many licensees 
discovered pipe wall thinning in the single-phase lines.  Some of the reported 
incidents are listed below: 

1.   A pipe rupture at Haddam Neck occurred in March 1985.  The pipe ruptured
     downstream of a normal level control valve for a feedwater heater.  The
     actual rupture was approximately 1/2 inch by 2 1/4 inches, and the failure
     was caused by flow impingement.  The eroded section of pipe was replaced.
     In addition, corresponding pipes of similar systems were examined.
     
2.   A catastrophic pipe rupture at Surry Unit 2 occurred in December 1986.  
     The break was located in an elbow in the 18-inch line about 1 foot from
     the 24-inch header.  A 2- by 4-foot section of the wall of the suction

8905040276
.Generic Letter 89-08                 -2-                         May 2, 1989


     line to the A main feedwater pump was blown out.  Investigation of the
     accident and examination of data by the licensee, NRC, and others led to
     the conclusion that failure of the piping was caused by erosion/corrosion
     of the carbon steel pipe wall.

3.   During the June 1987 outage at the Trojan Nuclear Plant, it was 
     discovered that at least two areas of the straight sections of the main 
     feedwater piping system had experienced wall thinning to an extent that 
     the pipe wall thickness would have reached the minimum thickness required 
     by the design code (ANSI B31.7, "Nuclear Power Piping") during the next 
     refueling cycle.  These areas are in safety-related portions of the ASME 
     Class 2 piping inside the containment.  In addition, numerous piping 

     components of the nonsafety-related portions of the feedwater lines were 
     also found to have suffered extensive wall thinning. 
     
4.   During the September 1988 outage, the licensee for Surry Unit 2 
     discovered that pipe wall thinning had occurred more rapidly than 
     expected.  On the suction side of one of the main feedwater pumps, an 
     elbow installed during the 1987 refueling outage lost 20 percent of its 
     0.500-inch wall in 1.2 years.  In addition, wall thinning is continuing 
     in safety-related main feedwater piping and in other nonsafety-related 
     condensate piping.  The exact cause of the accelerated wall thinning is 
     still under investigation by both the licensee and the NRC. 
     
In light of the above experiences, the NRC issued six information notices
(86-106 and Supplements 1, 2, and 3; 87-36, and 88-17) and Bulletin 87-01 
addressing this problem.  The staff review of licensees' responses to the 
bulletin indicates that the pipe wall thinning problem is widespread for 
single-phase and two-phase high-energy carbon steel systems.  The systems and 
components reported as having experienced pipe wall thinning are listed in 
Section 6 of the attachment to this letter.  The staff review also showed that 
wall thinning in single phase feedwater-condensate systems is more prevalent 
among pressurized-water reactors (PWRs) but also occurs in boiling-water 
reactors (BWRs). 

The staff audited 10 operating plants (7 PWRs and 3 BWRs) in late 1988 to 
assess implementation of erosion/corrosion monitoring programs by licensees 
and to ensure that adequate guidance was provided for corrective actions and 
other activities regarding repair and replacement of degraded piping and 
components. Detailed audit findings are described in Section 7 of NUREG-1344, 
which is enclosed with this letter.  In general, all licensees have developed 
and put in place an erosion/corrosion monitoring program that meets the intent 
of NUMARC guidelines (Appendix A of NUREG-1344).  In addition, all licensees 
have completed their initial examination as recommended by NUMARC.  However, 
the staff found that none of these licensees has implemented formalized 
procedures or adminis-trative controls to ensure continued long-term 
implementation of its erosion/ corrosion monitoring program for piping and 
components within the licensing basis.  Therefore, you should provide 
assurances that a program, consisting of systematic measures to ensure that 
erosion/corrosion does not lead to degra-dation of single phase and two phase 
high-energy carbon steel systems has been implemented.  The detailed 
information should not be submitted for NRC review. 

.Generic Letter 89-08                 -3-                         May 2, 1989


Additional insight into the phenomena related to erosion/corrosion of carbon
steel components is provided in the enclosure to this letter (NUREG-1344).

You are required to submit your response, signed under oath or affirmation, as
specified in 10 CFR 50.54(f), within 60 days of receipt of this letter.  Your 
response will be used to determine whether your license should be modified, 
suspended, or revoked.  Your response should include information on whether or
not you have implemented or intend to implement a long term erosion/corrosion
monitoring program that provides assurances that procedures or administrative
controls are in place to assure that the NUMARC program or another equally
effective program is implemented and the structural integrity of all high-
energy (two phase as well as single phase) carbon steel systems is maintained.
If this program is not yet implemented you should include the scheduled imple-
mentation date.

This request is covered by the Office of Management and Budget Clearance Number
3150-0011, which expires December 31, 1989.  The estimated average burden is 
200 man-hours per addressee response, including assessing the actions to be 
taken, preparing the necessary plans, and preparing the response.  This 
estimated average burden pertains only to these identified response-related 
matters and does not include the time for actual implementation of the 
recommended actions. 

Send comments regarding this burden estimate or any other aspect of this col-
lection of information, including suggestions for reducing this burden, to
the Records and Reports Management Branch, Division of Information Support 
Services, Office of Information Resources Management, U.S. Nuclear Regulatory 
Commission, Washington, D.C.  20555; and to the Paperwork Reduction Project
(3150-0011), Office of Management and Budget, Washington, D.C.  20503.

                                     Sincerely,



                                     James G. Partlow
                                     Associate Director for Projects
                                     Office of Nuclear Reactor Regulation

Enclosures:
1.  NUREG-1344
2.  Listing of Recently Issued Generic Letters
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