United States Nuclear Regulatory Commission - Protecting People and the Environment

Summary of Responses to NRC Bulletin 87-01, "Thinning of Pipe Walls in Nuclear Power Plants"

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                      OFFICE OF NUCLEAR REACTOR REGULATION
                             WASHINGTON, D.C.  20555

                                 April 22, 1988


Information Notice No. 88-17:  SUMMARY OF RESPONSES TO NRC BULLETIN 87-01,
                                   "THINNING OF PIPE WALLS IN NUCLEAR POWER 
                                   PLANTS"


Addressees: 

All holders of operating licenses or construction permits for nuclear power 
reactors. 

Purpose: 

This information notice is being provided to inform addressees of the results 
of the NRC staff review of responses to NRC Bulletin 87-01, "Thinning of Pipe 
Walls in Nuclear Power Plants."  It is expected that recipients will review 
the information for applicability to their facilities and consider actions, as 
appropriate, to prevent erosion/corrosion-induced piping degradation.  
However, suggestions contained in this notice do not constitute NRC 
requirements; therefore, no specific action or written response is required. 

Background:

On December 9, 1986, Unit 2 at the Surry Power Station experienced a 
catastrophic failure of a main feedwater pipe, which resulted in fatal 
injuries to four workers.  During the 1987 refueling outage at the Trojan 
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 (American National Standards Institute (ANSI) Standard 
B31.7, "Nuclear Power Piping") during the next refueling cycle.  These two 
straight-section areas are in safety-related portions of the Class 2 piping 
inside containment.  In addition, numerous elbows and piping sections in the 
non-safety-related portion of the feedwater lines were replaced because of 
wall-thinning problems.  

Because of the immediate concern about high-energy carbon steel systems in 
operating nuclear power plants, NRC Bulletin 87-01 was issued on July 9, 1987.
The staff requested all licensees to provide the following information within 
60 days of receiving the bulletin:

     -    the code or standard to which the high-energy, carbon steel piping 
          was designed and fabricated





8804180039
.                                                            IN 88-17
                                                            April 22, 1988
                                                            Page 2 of 5


     -    the scope, extent, and sampling criteria of inspection programs to 
          monitor pipe wall thinning of safety-related and non-safety-related 
          high-energy, carbon steel piping systems

     -    the results of all inspections that have been performed to identify 
          pipe wall thinning

     -    plans for revising existing pipe monitoring procedures or developing 
          new or additional inspection programs

Discussion: 

The staff review of licensee responses to the bulletin showed that before the 
rules for piping, pumps, and valves in Section III of the American Society of 
Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) were revised 
in 1971, the secondary coolant systems in nuclear power plants were designed 
and fabricated in accordance with ANSI B31.1.  Fifty-seven percent of the 
licensed units belong to this category.  After 1971, safety-related portions 
of the secondary coolant systems were designed and fabricated in accordance 
with ASME Code Section III, while non-safety-related portions of the secondary 
coolant systems continued to be designed and fabricated in accordance with 
ANSI B31.1.  Forty-three percent of the licensed units belong to this 
category. 

For two-phase, high-energy carbon steel piping systems, the responses to the 
bulletin indicated that programs for inspecting pipe wall thinning exist at 
all plants.  Inspection locations are generally established in accordance with 
the 1985 guidelines in Electric Power Research Institute (EPRI) Document 
NP-3944, "Erosion/Corrosion in Nuclear Plant Steam Piping:  Causes and 
Inspection Program Guidelines."  However, because implementation of these 
guidelines is not required, the scope and the extent of the programs vary 
significantly from plant to plant.  

Responses to the bulletin indicated that limited inspections of the single-
phase feedwater-condensate systems were conducted in most plants after the 
Surry Unit 2 incident.  Most plants developed their single-phase pipe wall 
thinning monitoring programs because of the events at Surry Unit 2 and at 
the Trojan plant.  Some plants developed programs after NRC Bulletin 87-01 
was issued.  The responses to NRC Bulletin 87-01 show that 23 units, of a 
total of 110, still have not established an inspection program for monitoring 
pipe wall thinning in single-phase lines.  Of these 23 units, 17 are operating 
and 6 are under construction.

The inspection frequency for pipe wall thickness measurements and replacement/
repair decisions is based on a combination of predicted and measured erosion/
corrosion rates.  In general, the pipe wall thickness acceptance criteria use 
measured wall thicknesses and an erosion/corrosion damage rate to predict when 
the pipe wall thickness will approach its Code-allowable minimum wall thick-
ness.  The acceptance criteria provide guidance for determining if a piping 
component needs to be replaced or repaired immediately or for projecting when 
a piping component should be replaced. 

.                                                            IN 88-17
                                                            April 22, 1988
                                                            Page 3 of 5


The primary method of inspection reported was ultrasonic testing, supplemented 
by visual examination and, in a few cases, by radiography.  Measurements of 
pipe wall thickness were either made by or verified by certified level 2 or 
level 3 inspectors.  The NRC staff considers this an adequate inspection 
technique. 

The systems and components reported as experiencing pipe wall thinning in the 
responses to Bulletin 87-01 are listed in Attachment 1.  Pipe wall thinning 
problems in single-phase piping occurred primarily in the feedwater-condensate 
system; the problems in two-phase piping, although varied in extent, have been 
reported in a variety of systems in virtually all operating plants.  Plants 
that were reported to have pipe wall thinning in feedwater-condensate systems 
are listed in Attachment 2.  Although inspection of single-phase lines is not 
scheduled until the next refueling outage for a number of plants, the 
available results from plants already inspected indicate a widespread problem.  

The staff's review also showed that wall thinning in feedwater-condensate 
systems is more prevalent in pressurized-water reactors (PWRs) than 
boiling-water reactors (BWRs).  At the present time, licensees of 27 PWRs and 
6 BWRs have identified various degrees of wall thinning in feedwater piping 
and fittings.  

The staff's review further indicated that of the feedwater-condensate systems, 
the recirculation-to-condenser line (minimum-flow line) has experienced wall 
thinning degradation most frequently.  The line is used to protect the pump 
during low-power operation and is isolated by a minimum-flow valve during 
high-power operation.  Specific information regarding a minimum-flow line 
degradation incident at the LaSalle County Station is provided for recipients 
to review for applicability to their facilities and consider actions, if 
appropriate, to preclude similar problems occurring at their facilities.  

Description of Circumstances of a Recent Event:

On December 10, 1987, at LaSalle County Station Unit 1, when the unit was at 
approximately 100 percent power, an increased floor drain input from the 
heater bay was observed.  This prompted a search of that area by the plant 
Operating Department.  Feedwater leakage was found immediately downstream of 
the 1B turbine-driven reactor feedwater pump (TDRFP) minimum-flow line control 
valve (1FW011B).  This valve discharges immediately into a 45-degree elbow 
that is welded to an 8-inch by 14-inch expander, which is connected to piping 
that feeds directly to the main condenser.  The 45-degree elbow (schedule 160, 
5% chrome, 1/2% molybdenum alloy steel) was found to have through-wall pinhole 
leaks in it.  Further investigation identified the cause of the leakage to be 
internal piping erosion. 

A visual inspection and ultrasonic testing of the other feedwater pump minimum-
flow lines at both Unit 1 and Unit 2 revealed the following: 

(1)  The 2A TDRFP had wall thinning in the 8-inch by 14-inch expander 
     (schedule 80, 5% chrome, 1/2% molybdenum steel), and a 1/4-inch diameter 
     hole in the expander was located 1 inch downstream from the elbow/reducer 
     weld.

.                                                            IN 88-17
                                                            April 22, 1988
                                                            Page 4 of 5


(2)  The 1A and 2B TDRFPs had localized wall thinning in the elbow downstream 
     of the flow control valve similar to that found on the 1B minimum-flow 
     line.  This metal loss did not result in a through-wall leak.

(3)  The 1C and 2C feedwater pumps are motor-driven pumps with smaller minimum-
     flow lines (10 inches rather than 14 inches), and no degradation of the 
     wall thickness downstream of the flow control valves was noted.

The erosion pattern was thought to be caused by the design of the minimum-flow 
control valves and the geometry of the downstream piping.  The valves were 
manufactured by Control Components, Inc., and were pressure breakdown "drag" 
valves.  The valves have a cone-shaped disk and are not designed to be leak 
tight.  Any feedwater leaking past the seat flashes to steam because of a 
vacuum pulling on the water from the condenser.  With a cone-shaped disk, the 
steam is then directed, like a jet, immediately onto the opposing wall of the 
elbow or reducer, causing the erosion (see Attachment 3). 

The feedpump minimum-flow lines are not considered to have a safety-related 
function and, therefore, this failure did not affect the ability to achieve 
a safe shutdown.  However, this could present a plant personnel safety concern 
in the event of a catastrophic failure.  The licensee did a weld overlay 
repair of the wall thinning areas of all four minimum-flow lines.  The lines 
will be replaced during the next refueling outage.  The licensee is evaluating 
a modification to the control valve disk to prevent flow or leakage through 
the line from being focused onto the downstream piping because of the conical 
shape of the disk.  

Past Related Generic Communications: 

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

Information Notice No. 86-106, "Feedwater Line Break," was issued on 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 on 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 Walls 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. 

.                                                            IN 88-17
                                                            April 22, 1988
                                                            Page 5 of 5


NRC Information Notice 87-36, "Significant Unexpected Erosion of Feedwater 
Lines," was issued August 4, 1987.  It described a potentially generic problem 
pertaining to significant unexpected erosion that resulted in pipe wall 
thinning in the safety-related portions of feedwater lines and other related 
problems discovered at the Trojan Plant. 

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical 
contacts listed below or the appropriate NRR project manager.  




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


Technical Contacts:  Paul C. Wu, NRR
                     (301) 492-0826

                     Michael Jordan, RIII
                     (312) 790-5552


Attachments:  
1.  Systems/Components Experiencing Pipe Wall Thinning
2.  Plants Experiencing Pipe Wall Thinning in Feedwater-
      Condensate System
3.  LaSalle Minimum-Flow Control Valve
4.  List of Recently Issued NRC Information Notices
.                                                                 Attachment 1
                                                                 IN 88-17
                                                                 April 22, 1988
                                                                 Page 1 of 1


               SYSTEMS/COMPONENTS EXPERIENCING PIPE WALL THINNING


Single-Phase Line                            Two-Phase Line

�    main feedwater lines,                   �    main steamlines
     straight runs, fittings
                                             �    turbine cross-over piping
�    main feedwater recirculation to 
     condenser, straight runs, fittings      �    turbine cross-under piping

�    feedwater pump suction lines,           �    extraction steamlines
     straight runs, fittings
                                             �    moisture separator reheater
�    feedwater pump discharge lines,
     straight runs, fittings                 �    feedwater heater drain piping

�    condensate booster pump
     recirculation line fittings

�    steam generator letdown lines,
     straight runs, fittings
.                                                                 Attachment 2
                                                                 IN 88-17
                                                                 April 22, 1988
                                                                 Page 1 of 1


      PLANTS EXPERIENCING PIPE WALL THINNING IN FEEDWATER-CONDENSATE SYSTEM


                     Type of  Commercial          Degraded Component
Plant          Unit  Reactor  Operation           Fittings or Straight Runs

Dresden        2     BWR      January 1970        elbows
Duane Arnold         BWR      March 1974          elbows, reducers, straight runs
Pilgrim        1     BWR      June 1972           elbows
Oyster Creek         BWR      May 1969            elbows
River Bend     1     BWR      October 1985        recirculation line
Perry                BWR      June 1986           straight runs
Arkansas       1     PWR      August 1974         elbows, drain pump discharge 
                                                    piping
Arkansas       2     PWR      December 1978       undefined
Calvert Cliffs 1     PWR      October 1974        elbows, reducers, straight runs
Calvert Cliffs 2     PWR      November 1976       elbows, reducers, straight runs
Callaway             PWR      October 1984        recirculation line elbows
Diablo Canyon  1     PWR      April 1984          elbows, straight runs
Diablo Canyon  2     PWR      August 1985         elbows, and Y
Donald Cook    2     PWR      March 1978          elbows
Ft. Calhoun          PWR      August 1973         elbows, straight run
Haddam Neck          PWR      July 1967           recirculation line
Millstone      2     PWR      October 1975        elbows, heater vent piping
North Anna     1     PWR      April 1978          elbows, straight runs
North Anna     2     PWR      June 1980           elbows, straight runs
H. B. Robinson 2     PWR      September 1970      recirculation lines
San Onofre     1     PWR      June 1967           reducers, heater drain piping
San Onofre     2     PWR      July 1982           heater drain piping
San Onofre     3     PWR      August 1983         heater drain piping
Salem          1     PWR      December 1976       recirculation line
Salem          2     PWR      August 1980         recirculation line
Shearon Harris       PWR      October 1986        recirculation line
Surry          1     PWR      July 1972           fittings
Surry          2     PWR      March 1973          fittings
Sequoyah       1     PWR      July 1980           elbows, straight runs
Sequoyah       2     PWR      November 1981       elbows
Trojan               PWR      December 1975       elbows, reducers, straight runs
Turkey Point   3     PWR      October 1972        feedwater pump suction line 
                                                    fittings
Fort St. Vrain       HGTR*    January 1974        straight run in emergency 
                                                    feedwater line
Rancho Seco          PWR      September 1974      straight runs downstream of
                                                    MFW loop isolation valve
                                                    or MFPs miniflow valves


*  High Temperature Gas Reactor
.                                                            Attachment 4
                                                            IN 88-17
                                                            April 22, 1988
                                                            Page 1 of 1

                              LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES 
_____________________________________________________________________________
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

88-16          Identifying Waste Generators 4/22/88         Radioactive waste
               in Shipments of Low-Level                    collection and
               Waste to Land Disposal                       service company 
               Facilities                                   licensees handling
                                                            prepackaged waste, 
                                                            and licensees 
                                                            operating 
                                                            low-level waste
                                                            disposal 
                                                            facilities. 

88-15          Availability of U.S. Food    4/18/88         Medical, Academic,
               and Drug Administration                      and Commercial
               (FDA)-Approved Potassium                     licensees who 
               Iodide for Use in Emergencies                possess 
               Involving Radioactive Iodine                 radioactive 
                                                            iodine. 

88-14          Potential Problems with      4/18/88         All holders of OLs
               Electrical Relays                            or CPs for nuclear
                                                            power reactors.

88-13          Water Hammer and Possible    4/18/88         All holders of OLs
               Piping Damage Caused by                      or CPs for nuclear
               Misapplication of Kerotest                   power reactors.
               Packless Metal Diaphragm
               Globe Valves

88-12          Overgreasing of Electric     4/12/88         All holders of OLs
               Motor Bearings                               or CPs for nuclear
                                                            power reactors.

88-11          Potential Loss of Motor      4/7/88          All holders of OLs
               Control Center and/or                        or CPs for nuclear
               Switchboard Function Due                     power reactors.
               to Faulty Tie Bolts

88-10          Materials Licensees:  Lack   3/28/88         All NRC licensees
               of Management Controls Over                  authorized to use
               Licensed Programs                            byproduct material.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit 
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