Information Notice No. 87-36: Significant Unexpected Erosion of Feedwater Lines
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555
August 4, 1987
Information Notice No. 87-36: SIGNIFICANT UNEXPECTED EROSION OF
All nuclear power reactor facilities holding an operating license or a con-
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
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
. 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
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.
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
Flow Velocity 22.6 ft/sec @ 100%
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
Attachment: List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Thursday, March 25, 2021