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
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April 22, 1988
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- 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.
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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.
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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.
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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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