Information Notice 1991-18, High-Energy Piping Failures Caused by Wall Thinning
| ML042380261 | |
| Person / Time | |
|---|---|
| Issue date: | 12/18/1991 |
| From: | Rossi C Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| IN-91-018, Suppl 1 | |
| Download: ML042380261 (5) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555 December 18, 1991 NRC INFORMATION NOTICE 91-18, SUPPLEMENT 1: HIGH-ENERGY PIPING FAILURES CAUSED
BY WALL THINNING
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
The U. S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to continuing erosion/corrosion problems affecting
the integrity of high energy piping systems and to alert addressees to
apparently inadequate erosion/corrosion monitoring programs. It is expected
that recipients will review the information for applicability to their facili- ties and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not NRC requirements;
therefore, no specific action or written response is required.
Background
On March 12, 1991, the NRC issued Information Notice (IN)91-18, "High Energy
Piping Failures Caused by Wall Thinning," to describe ruptures and leaks in
secondary systems carrying high energy fluids at the Millstone Nuclear Power
Station, Unit 3, the San Onofre Nuclear Generating Station, Unit 2, and a
foreign plant.
Following the pipe rupture at the Surry Power Station in 1986, the NRC issued
Bulletin 87-01, "Thinning of Pipe Walls in Nuclear Power Plants," July 9, 1987.
In this bulletin, the staff requested licensees and applicants to inform the
NRC about their programs for monitoring the wall thickness of carbon steel
piping in both safety-related and nonsafety-related high energy fluid systems.
IN 91-18 included references related to this bulletin. IN 82-22, "Failures of
Turbine Exhaust Lines," July 9, 1982, also provides relevant information
regarding pipe wall thinning in steam lines.
In 1989, following an audit of the erosion/corrosion programs at ten plants, the NRC issued Generic Letter (GL) 89-08, "Erosion/Corrosion-Induced Pipe Wall
Thinning," May 2, 1989. In this generic letter, the staff requested licensees
and applicants to implement long term erosion/corrosion monitoring programs.
The staff made this request to obtain assurances that procedures or administra- tive controls were in place to maintain the structural integrity of all carbon
steel systems carrying high energy fluids.
9121720218 ATTACHMENT 14
IN 91-18, Supplement 1 December 18, 1991 The Electric Power Research Institute (EPRI) released computer codes CHEC and
CHECMATE in June 1987 and April 1989, respectively, to assist in selecting for
testing those areas of the piping systems with highest probabilities for wall
thinning. The CHEC calculation applies to pipes containing a single liquid
phase and the CHECMATE calculation applies to pipes containing both liquid and
vapor phases.
On June 11, 1987, the Technical Subcommittee Working Group on Piping
Erosion/Corrosion of the Nuclear Management and Resources Council (NUMARC)
issued a summary report describing a method using the CHECMATE computer code for
monitoring carbon steel components exposed to the conditions conducive to
erosion/corrosion.
Description of Circumstances
At Millstone Unit 2, on November 6, 1991, while the licensee, the Northeast
Nuclear Energy Company (NNECO), was operating the plant at 100 percent of full
power, a rupture occurred in train B of the moisture separator reheater (MSR)
system. An 8-inch elbow, located between the first stage MSR drain tank and
the feedwater heater, ruptured at its extrados (Figure 1). The elbow was
located downstream from a 4-inch flow control valve and a 4- to 8-inch
expander. The high energy water in the pipe (approximately 463 F, 470 psig)
flashed to steam, actuating portions of the turbine fire protection deluge
system. The water level in the steam generator decreased slightly. The licen- see had not selected the ruptured elbow for ultrasonic testing (UT) in its
erosion/corrosion monitoring program.
The ruptured elbow was made of carbon steel with nominal wall thickness of
0.322 inch. Wall thickness at the failed area was eroded to 95 percent of the
initial nominal value. Other areas, away from the failed area, showed a loss
of 22 percent of the wall thickness. The identical elbow in the A train had a
maximum wall loss of 34 percent of the initial nominal value.
Discussion
The licensee has had a program for monitoring high energy fluid piping since
1981. The criteria for choosing components to be inspected include component
location and service conditions as determined by the engineering judgement of
the plant personnel. In contrast, more relevant parameters that could indicate
erosion or corrosion wastage include piping material and geometry,'fluid prop- erties (flow, temperature, and acidity), and fluid contents (the acidity- controlling agent and the concentration of dissolved oxygen).
In its response to GL 89-08, NNECo indicated that its Engineering Procedure
EN-21153, "Thickness Testing of Secondary Piping," describes its monitoring
program, established in accordance with EPRI guidelines and using the CHEC pro- gram to select for testing those areas of the pipi ng systems with highest prob- abilities for wall thinning. The licensee also selects areas on the basis of
plant experience. However, although the pipe wall thickness testing program
vlas included in the licensee's procedures, the licensee had not implemented the
methodology using the EPRI computer codes at Unit 2. This omission may account
for the licensee not having tested previously the piping that ruptured on
November 6, 1991.
Li I st
.i~5X*-13, Supp
December 18, 1991 The licensee did use an earlier version of the CHEC computer code in limited
analyses at its other nuclear units. The licensee's program did not reflect
the use of current versions of EPRI codes (either CHEC or CHECMATE). .The
Unit 3 rupture described in the March 12, 1991, issuance of this information
notice prompted NNECo to commit to perform CHEC or CHECMATE analyses at all its
units by December 31, 1991. However, at the time of the second rupture on
November 6, 1991, the licensee was implementing this program at its corporate
engineering office and not at Unit 2. The Unit 2 personnel were consequently
relying on inspection procedures that did not possess the benefit of the EPRI's
methodology for selecting areas of piping for UT inspection. After
November 6, 1991, NNECo performed a CHECMATE analysis that did identify this
portion of the MSR system as highly susceptible to erosion or corrosion and
thus as a candidate for UT inspection.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact one
of .the technical contacts listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
(
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical contacts: K. 1. Parczewski, NRR
(301) 504-2705 Vern Hodge, NRR
(301) 504-1861 Attachments:
1. Figure 1, "Rupture of Elbow in Secondary System at
Millstone Unit 2 on November 6, 1991"
2. List of Recently Issued NRC Information Notices
6"xl2" FISH-ItIOUTH
BREAK AT EXTRADOS
FLOW
4 in. dia. 4 in. dia.
8 in. dia.
Motes:
Vo. 1 B First Stage Moisture Separator
Reheater Drain Tank Drain Line
Pipe: Carbon Steel
No Chromium Content
Fluid: H2O @ 470 psig, 4630F
pH: 8.2-*8.7
02: <2ppb
a' (Dr i.r '
CD
Figure 1. Rupture of Elbow in Secondary System at Millstone Unit 2 on November 6, 199, CD
-
A-ttzac~:.^,
IN 91-18, Supplem~nt 1 December 18, 3991 Page 1 of i
LIST OF RECENTLY ISSUED
NRC INFORMATiON NOTICES
Information Date of
Notice No. Subject Issuance Issued to
91-82 Problems with Diaphragms 12/18/91 All holders of OLs or CPs
in Safety-Related Tanks for nuclear power reactors.
91-81 Switchyard Problems that 12/16/91 All holders of OLs or CPs
Contribute to Loss of for nuclear power reactors.
Offsite Power
91-80 Failure of Anchor 12/11/91 All holders of OLs or CPs
Head Threads on Post- for nuclear power reactors.
Tensioning System During
Surveillance Inspection
91-79 Deficiencies in the 12/06/91 All holders of OLs or CPs
Procedures for Instal- for nuclear power reactors.
ling Thermo-Lag Fire
Barrier Materials
88-92, Potential for Spent 11/29/91 All holders of OLs or CPs
Supp. 1 Fuel Pool Draindown for nuclear power reactors.
91-78 Status Indication of 11/28/91 All holders of OLs or CPs
Control Power for for nuclear power reactors.
Circuit Breakers Used
in Safety-Related Appli- cations
90-57, Substandard, Refur- 11/27/91 All holders of OLs or CPs
Supp. 1 bished Potter & Brum- for nuclear power reactors.
field Relays Repre- sented as New
91-77 Shift Staffing at 11/26/91 All holders of OLs or CPs
Nuclear Power Plants for nuclear power reactors.
91-76 10 CFR Parts 21 and 11/26/91 All holders of OLs or CPs
50.55(e) Final Rules and vendors for nuclear
f1 power reactors.
OL = Operating License
CP = Construction Permit