United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-36: Significant Unexpected Erosion of Feedwater Lines

                                                   SSINS No.:  6835
                                                    IN 87-36

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                              WASHINGTON, DC  20555

                                 August 4, 1987


Information Notice No. 87-36:  SIGNIFICANT UNEXPECTED EROSION OF 
                                   FEEDWATER LINES


Addressees: 

All nuclear power reactor facilities holding an operating license or a con-
struction permit. 

Purpose: 

This information notice is provided to alert recipients to a potentially 
generic problem pertaining to significant unexpected erosion which resulted in 
pipe wall thinning in the safety-related portions of feedwater lines and other 
related problems.  It is expected that recipients will review the information 
for applicability to their facilities and consider actions, if appropriate, to 
preclude a similar problem.  However, suggestions contained in this notice do 
not constitute NRC requirements; therefore no specific action or written 
response is required. 

Description of Circumstances:

At the Trojan Nuclear Plant it was discovered that at least two areas of the 
straight sections of the main feedwater piping system 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 ASME Boiler and Pressure Vessel Code (ASME Code) Class 2 piping 
inside containment.  

The pipe wall had thinned in both horizontal and vertical runs that were at 
least seven pipe diameters downstream of elbows or other devices that can 
cause flow turbulence.  Criteria developed by the Electric Power Research 
Institute (EPRI Users Manual NSAC-112, "CHEC [Chexal-Horowitz-Erosion-
Corrosion]," dated June 1987) would not have required that the pipe wall in 
these straight sections be examined.  

Although the straight sections of eroded 14-inch pipe were slightly thicker 
than the minimum required thickness, it was projected that the pipe wall 
thickness would erode below the minimum required thickness before the next 
major outage.  Consequently, the licensee plans to replace this piping before 
restart.  




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.                                                            IN 87-36
                                                            August 4, 1987
                                                            Page 2 of 3


The licensee believes that the high flow velocity of 22.6 ft/sec, in combina-
tion with other operating factors, may be the cause of the thinning. 

This thinning was discovered when the steam piping inspection program at the 
Trojan plant was expanded to include single-phase piping.  Trojan personnel 
inspected essentially all safety-related high energy carbon steel piping 
inside containment.  

In addition, the licensee discovered approximately 30 additional areas of the 
main feedwater piping system where the pipe wall had thinned so the thickness 
of the pipe wall was either less than the minimum thickness required by the 
design code or would have eroded to the minimum required thickness during the 
next operating cycle.  Of these areas, 10 were in the safety-related portions 
of the system, while the rest were in non-safety-related portions.  All of 
these thirty additional areas were in regions that the EPRI criteria would 
have indicated as needing examination.  

Discussion: 

The feedwater system inside containment consists of four lines.  Lines A and B 
are mirror images, as are Lines C and D.  The parameters of the ASME Code 
Class 2 portion of the piping system are as listed below.  

          Design Temperature                           445�F
          Operating Temperature                        445�F
          Design Pressure                              1125 psi
          Operating Pressure                            920 psi
          Piping Material                             A-106 GRB
          Diameter                                      14-in. OD
          Wall Thickness Nominal                      0.593 in  Wall Thickness Minimal (ANSI B31.7)         0.510 in  Oxygen Content                                  4 ppb
          pH                                            9.0
          Flow Velocity                                22.6 ft/sec @ 100% 
                                                         power

The thinning of the straight sections occurred in Lines A and D.  

A number of 45- and 90-degree elbows and two 60-degree elbows were also 
replaced.  The thickness of the remaining pipe wall in these areas ranged from 
0.43 to 0.46 in.  The minimum required thickness is 0.499 in., and nominal 
wall thickness at time of installation was 0.593 in.  

In the non-safety-related portions of the feedwater lines, a total of 20 
pieces of 14-in. pipe were replaced.  This total included elbows as well as 
some straight pieces down stream of the elbows or other discontinuities.  The 
thinning in these segments is very similar to that in the ASME Code Class 2 
portion except that the minimum required thickness was 0.44 in. 

Trojan personnel also replaced a segment of 30-in. header pipe after identify-
ing a localized portion of header pipe that had eroded to 1.018-in. wall 
thickness (a minimum thickness of 1.63 in. was required). 

.                                                            IN 87-36
                                                            August 4, 1987
                                                            Page 3 of 3


The Trojan plant is conducting a failure analysis on the degraded components 
to determine the causes and mechanisms involved in the observed wall thinning 
event.  The NRC is evaluating the data available to determine any generic 
implication of the event. 

Related Generic Communications:

Information Notice No. 82-22, "Failure in Turbine Exhaust Lines," dated July 9, 
1982 provides additional information pertaining to erosion/corrosion in wet 
steam piping.  Other erosion/corrosion events pertaining specifically to the 
feedwater systems (including emergency and auxiliary feedwater) have occurred 
in feedwater pump minimum-flow lines, J-tubes in steam generator feedwater 
rings, and emergency feedwater supply to a helium circulator.  

Information Notice No. 86-106, "Feedwater Line Break," was issued December 16, 
1986.  It described the then-known details of the December 9, 1986 failure of 
the suction line to a main feedwater pump at Surry Power Station Unit 2.  
Supplement 1 to this information notice, which was issued February 13, 1987, 
provided additional detail on the failure mechanism.  Supplement 2, which was 
issued on March 10, 1987, discussed the effects of the system interactions 
that resulted from the line break.  

NRC Bulletin 87-01, "Thinning of Pipe Wall in Nuclear Power Plants," issued on 
July 9, 1987, requested that licensees submit information concerning their 
programs for monitoring the thickness of pipe walls in high-energy 
single-phase and two-phase carbon steel piping systems. 

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional 
Administrator of the appropriate NRC regional office or this office. 



                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation 


Technical Contact:  Paul C. Wu, NRR 
                    (301) 492-8987 


Attachment:  List of Recently Issued NRC Information Notices

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