IE Circular 76-06, Stress Corrosion Cracks in Stagnant, Low Pressure Stainless Piping Containing Boric Acid Solution at PWR's
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D. C. 20555
NOV 22 1976
J. P. O'Reilly, Director, Region I
N. C. Moseley, Director, Region II
J. G. Keppler, Director, Region III
E. M. Howard, Director, Region IV
R. H. Engelken, Director, Region V
IE CIRCULAR 76-06, STRESS CORROSION CRACKS IN STAGNANT, LOW PRESSURE
STAINLESS PIPING CONTAINING BORIC ACID SOLUTION AT PWR's
The subject document is transmitted for issuance by close of business three
days after date of this letter. The Circular should be issued to all
holders of OL's for PWRs for action. Also enclosed is a draft copy of the
Dudley Thompson, Acting Director
Division of Field Operations
Office of Inspection and Enforcement
1. Circular 76-06
2. Draft transmittal letter
Transmittal letter for Circular 76-06 to each holder of a NRC Operating
License for a PWR.
The enclosed Circular 76-06 is forwarded to you for action. If there
are any questions related to your understanding of the actions required,
please contact this office.
IE Circular 76-06
IE Circular 76-06 Date:
STRESS CORROSION CRACKS IN STAGNANT, LOW PRESSURE STAINLESS PIPING
CONTAINING BORIC ACID SOLUTION AT PWR's
DESCRIPTION OF CIRCUMSTANCES:
During the period November 7, 1974 to November 1, 1975 several incidents of
through-wall cracking have occurred in the 10-inch, schedule 10 type 304
stainless steel piping of the Reactor Building Spray and Borated Water
Make-up Systems at Arkansas Nuclear Plant No. 1.
On October 7, 1976 Virginia Electric and Power also reported through-wall
cracking in the 10-inch schedule 40 type 304 stainless discharge piping of
the "A" recirculation spray heat exchanger at Surry Unit No. 2. A recent
inspection of Unit 1 Containment Recirculation Spray Piping revealed
cracking similar to Unit 2.
On October 8, 1976 another incident of similar cracking in 8-inch schedule
10 type 304 stainless piping of the Safety Injection Pump Suction Line at
the Ginna facility was reported by the licensee.
Information received on the metallurgical analysis conducted to date
indicates that the failures were the result of intergranular stress
corrosion cracking that initiated on the inside of the piping. A commonality
of factors observed associated with the corrosion mechanism were:
1. The cracks were adjacent to and propagated along weld zones of the
thin-walled low pressure piping, not part of the reactor coolant
2. Cracking occurred in piping containing relatively stagnant boric acid
solution not required for normal operating conditions.
3. Analysis of surface products at this time indicate a chloride ion
interaction with oxide formation in the relatively stagnant boric acid
solution as the probable corrodant, with the state of stress probably
due to welding and/or fabrication.
The source of the chloride ion is not definitely known. However, at ANO-1
the chlorides and sulfide level observed in the surface tarnish film near
welds is believed to have been introduced into the piping during testing of
the sodium thiosulfate discharge valves, or valve leakage. Similarly, at
Ginna the chlorides and potential oxygen availability were assumed to have
been present since original construction of the borated water storage tank
which is vented to atmosphere. Corrosion attack at Surry is attributed to
in-leakage of chlorides through recirculation spray heat exchange tubing,
allowing buildup of contaminated water in an otherwise normally dry spray
ACTION TO BE TAKEN BY LICENSEE:
1. Provide a description of your program for assuring continued integrity
of those safety-related piping systems which are not frequently
flushed, or which contain nonflowing liquids. This program should
include consideration of hydrostatic testing in accordance with ASME
Code Section XI rules (1974 Edition) for all active systems required
for safety injection and containment spray, including their
recirculation modes, from source of water supply up to the second
isolation valve. Similar tests should be considered for other
safety-related piping systems.
2. Your program should also consider volumetric examination of a
representative number of circumferential pipe welds by nondestructive
examination techniques. Such examinations should be performed generally
in accordance with Appendix I of Section XI of the ASME Code, except
that the examined area should cover a distance of approximately six (6)
times the pipe wall thickness (but not less than 2 inches and need not
exceed 8 inches) on each side of the weld Supplementary examination
techniques, such as radiography, should be used where necessary for
evaluation or confirmation of ultrasonic indications resulting from
3. A report describing your program and schedule for these inspections
should be submitted within 30 days after receipt of this Circular.
4. The NRC Regional Office should be informed within 24 hours, of any
adverse findings resulting during nondestructive evaluation of the
accessible piping welds identified above.
5. A summary report of the examinations and evaluation of results should
be submitted within 60 days from the date of completion of proposed
testing and examinations.
This summary report should also include a brief description of plant
conditions, operating procedures or other activities which provide
assurance that the effluent chemistry will maintain low levels of
potential corrodants in such relatively stagnant regions within the
Your responses should be submitted to the Director of this office, with a
copy to the NRC Office of Inspection and Enforcement, Division of Reactor
Inspection Programs, Washington, D.C. 20555.
Approval of NRC requirements for reports concerning possible generic
problems has been obtained under 44 U.S.C 3152 from the U.S. General
Accounting Office. (GAO Approval B-180255 (R0062), expires 7/31/77).
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