Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9610040032
Anchor/Darling
Valve Company o Williamsport, PA 17701
W. G. KNECHT
Technical Director
September 19, 1996
FAX TO: Dave Skeen
U.S.N.R.C.
301-415-2279
SUBJECT: Part 21 Reported Incident on FP&L, 2" Lift Check Valve
Attached:
--Copy of A/DV letter being sent to customers
who were furnished 2" lift check valves
--Copy of FP&L Final Engineering Disposition
William G. Knecht
Technical Director
Attachments
DATE
TO: Utilities that have been furnished 2" 1878 Piston Check Valves
Gentlemen:
There was a reported failure of a 2" 1878 piston check valve at the
Florida Power and Light, St. Lucie site on July 18, 1996. This valve
failed to close and it was determined that the valve disc was stuck in a
partially open position. It appears that this failure resulted from
fretting wear damage between the piston (disc) and valve body caused by
pressure pulsations of the St. Lucie reciprocating pump.
Anchor/Darling Valve Company has furnished (Utility) with similar
valves of this size on the following order(s):
(Fill in A/DV S.O. and Customer Order #)
We suggest that the valve applications be evaluated for potential
pressure pulsation that could result in fretting of the valve body,
In addition, FP&L and A/DV need assistance to finalize the root cause of
the St. Lucie problem. If an A/DV 2" piston check is in pump service,
we would greatly appreciate receiving the following information:
1. Pump type - centrifugal or reciprocating
2. Forward flow rate(s)
3. Approximate length of service time
4. Description of any found anomalies
Should you have any questions regarding this matter please call Mr.
Floyd Bensinger, our Engineering Manager or Bill Knecht, our Technical
Director.
Sincerely,
Contract Administrator
CR 96-1774
Attach 8 Page 1 of 11
FINAL ENGINEERING DISPOSITION
Scope:
Previous interim dispositions provided an operability assessment for 2"
Anchor Darling check valves installed in Unit 1 (Attachment 1) and Unit 2
(Attachment 7). Attachments 2,3,4 & 6 provided supporting documentation,
Attachment 5 was superseded by Attachment 7.
This attachment provides a final disposition for the CR. Attachments 9-
18 provide supporting documentation. The additional information
developed in this final disposition does not adversely affect the
previous operability reviews.
Corrective actions in this disposition supersede corrective actions
listed In prior attachments.
Background:
CR 96-1738 and In-House Event 96-059 identified loss of Unit 2 charging
flow associated with the potential failure of V2167. V2167, the check
valve for charging pump 2C discharge, was suspected of socking open which
would result In the charging flow recirculating back to the volume
control tank rather than into the RCS. The valve model is a 2" stainless
steel Anchor Darling piston check which was installed In 1994. It is a
piston check valve (straight/T-pattern) located downstream of the
reciprocating pump.
V2167 (serial # E-T401-9-19) was disassembled for inspection and was
found stuck open approximately 1/2". In addition, the body bore
machining in the area where the disc is guided was abnormal (looking from
top with discharge port at 12:00, machining/casting anomalies were
identified from 10:00 to 12:30). The first candidate replacement valve
inspected also exhibited machining anomalies in the same location. A
second spare for V2167 was inspected, found to be acceptable, installed
and successfully tested.
Based on initial review of the valves in stores, a working theory for the
degradation cause was developed and used to disposition the operability
of the Unit 1 valves per Attachment 1. The operability of to Unit 2
valves was subsequently reviewed in Attachment 7 based on a refinement of
the same working theory.
This attachment provides a final CR disposition by documenting tasks
performed to date, developing a root cause evaluation, addressing
regulatory reportability & industry notification and planning follow-up
activities to be pursued under specific PMAI's.
Initial Review of Machining Anomalies and Stuck Open Check Valve By
Manufacturer
The machining anomalies associated with 2" Anchor Darling check valves
and the shack open check valve in the charging system were reviewed with
Anchor Darling. Their initial review is provided in Attachment 2.
Anchor Darling states that the selection of the subject 2" piston check
valve as the charging pump discharge valve is appropriate. They also
state that pressure pulses experienced at the discharge of a
reciprocating pump may tend to force the valve disc toward the downstream
port. They conclude that this system application combined with the
machining anomaly on the body bore could cause the valve to remain open
(i.e., the disc cocked and caught on machining anomaly). They further
stated that other applications may not be as susceptible.
Review of FPL's Surveillance Testing of Installed ADV Valves
Twenty-eight SS & CS Anchor Darling piston check valves (2" and smaller)
are in-service in PSL 1 & 2 for periods ranging from 0 to 36 months
(Attachment 18). A review of the testing records (Attachment 3) shows
approximately 450 valve-months of satisfactory operation (Exceptions are
the Unit 2 V2167 and V2168 failures). The testing population includes 16
of the 17 two-inch piston check valves reviewed in Attachments 1 (Unit 1)
and 7 (Unit 2). Note that V18193 is not included in the tested
population as it is outside the LLRT boundary for its instrument air
containment penetration.
CR 96-1774
Attach 8 Page 2 of 11
Initial Inspections of Valves In Stores:
Inspections were performed on spare Anchor Darting 1" & 2" Carbon Steel
(CS) & Stainless Steel (SS) piston check valves that were in the stores
inventory for use with the small bore valve replacement program. Similar
machining/casting flaws were found in multiple valves as described in
more detail in Attachment 7. Based on these inspections, Attachments 1 &
7 concluded:
1) 2" CS & SS ADV piston check valves in stores are susceptible to
machining anomalies.
2) 1" and under CS & SS ADV piston check valves are not susceptible to
machining anomalies.
3) All sizes of CS ADV piston check valves in stores are susceptible to
internal rusting.
Review of Reportability of Discrepant Material Received from ADV Under
10CFR21
Nuclear Engineering Quality Instruction ENG-QI 2.2 governs evaluations
conducted to determine whether an issue/concern could result in a 10CFR21
Substantial Safety Hazard. This document states: "Note that SSH issues
already reported (by FPL or a vendor to the NRC) do not require SSH
evaluation (although operability evaluation may be warranted)." As
Anchor Darling Valve Co reported the subject situation with their 20
piston check valves to the NRC on 7/25/96 (Attachment 9), an SSH
evaluation by FPL is not required. FPL independently alerted the
industry to the Loss of Charging event caused by the failure-to-close of
the 2C charging pump discharge check valve via tie Nuclear Network
(Attachment 11).
Review of Available NPRDS Information
The Nuclear Plant Reliability Data System was searched for information
concerning Anchor Darling check valves with an 1878 model number. With
the exception of the Shearon Harris event, all other events (see below)
were deemed to involve foreign material within the valve. Information to
support an NPRDS entry for the PSL event was developed and provided to
Joe Cimino (Attachment 10).
NPRDS Search Criteria:
Subject Valve Selected Manufacturer Anchor/ Darling Valve Co
Words equal to or beginning with: check valve, ck vlv, chk vlv Mfr Model
Numbers: 1878
Company, Plant, Service, Noted Problem
Valve, Valve #
CP&L, Shearon Harris 1, CVCS Failure to provide full flow, failure
2 in piston check, 1CS-193 to seat
10CFR21 issued. This event is
discussed separately.
Northeast Utilities, Con Gross Leakage, O-Ring seal came
Yankee 1, CVCS loose from disc, Valve placed back in
1 in piston check, CH-CV-405C service
GPU, Oyster Creek 1, Unusual noises, Disc disengaged due to
Containment Spray missing nut/cotter pin, Valve replaced
2 in swing check, V-3-0133 with swing check
GPU, Oyster Creek 1, Unusual noises (chattering), leaking
Containment Spray past sear Telephoned to clarify
2 in piston check, V-3-0133 NPRDS data: Valve is in seawater
service, no damage to valve, parts
not degraded, normally open -150
gpm, debris behind seat (silt and
shells), have changed valve design
& manufacturers several times.
Info per John Galanto (609-971-4000)
GPU, Oyster Creek 1, Stuck Open, Marine Growth and
Containment Spray Foreign Material, Valve placed
2 in piston check, V-3-1033 back in service Engineering
requested to evaluate possible
valve replacement
GPU, Oyster Creek 1,
Containment Spray Stuck Open, Marine Growth and Foreign
2 in piston check, V-3-131 Material, Valve placed back in
service, Plan to install upgraded
valve
Niagra Mohawk, 9 M Point, FW, Failed LLRT, Dirt and Debris Inside
31-01R 18 in swing check Valves, Valve placed back in service
Niagra Mohawk, 9 M Point, FW, Failed LLRT, Flutter During Flow
31-01R 18 in swing check Condition Inherent to Piping Design,
Valve placed back in service
Niagra Mohawk, 9 M Point, FW, Failed LLRT, Flutter During Flow
31-02R 18 in swing check Condition Inherent to Piping Design,
Valve placed back in service
Portland GE, Trojan 1, SA, Failed LLRT, Foreign Material on
SA-2005 2 in unknown style Seating Surfaces, wire and rubber
gasket foreign material. Valve
placed back in service
NYPA, Fitzpatrick 1, Combustible Failed LLRT, Found no off-normal
Gas Control, 27 CAD -68, 1.5 in conditions, piece of dir believed
unknown style to be responsible returned to service
NYPA, Fitzpatrick 1, Combustible Failed LLRT, Cloth-like debris
Gas Control, 27 CAD -68, 1.5 in prevented closures, valve placed
unknown style back in service
CR 96-1774
Attach 8 Page 3 of 11
Review of Shearon Harris 10CFR21 Report - CSIP Miniflow Check Valve
Deficiency A CP&L 10CFR21 report to the NRC (Reference 7) describes an
event where their 1B Charging Safety Injection Pump (CSIP) was placed in
service when it Was inoperable (due to the inability of its mini-flow
check valve to meet forward flow testing requirements). One CSIP is
normally operating in their system alignment to provide charging flow,
The subject ADV valve failure was detected because it exhibited back
leakage on at least two different occasions. The back leakage was caused
by cocking of the piston toward the valve discharge port and/or damage to
the resilient seat. CP&L attributed the damage to the roar instantaneous
opening of the piston check due to large hydraulic forces caused by pump
startup.
Subsequent to the initial failure, three different disc designs were
installed (resilient seat, hard seat, full body guided) with no
improvement. Originally, the resilient seat was suspected of causing the
valve to stick open because it was found partially off the disc and
degraded. The valve was inspected, measured, and found to be within the
vendor specifications. While no internal machining or casing anomalies
were noted, CP&L was not specifically looking for the problem seen at
PSL. The valves from CP&L are not available for further inspection.
After the problems with the ADV piston check valves (stuck open,
insufficient forward now) were not remedied by subsequent disc
modifications, CP&L ceased efforts to modify the ADV valve and
reinstalled me original Y-pattern piston check valve. No subsequent
problems were identified. CP&L did not develop the root cause
conclusively, CP&L provided the following information regarding the CSIP
recirculation check valves:
1. CP&L changed valve from Rockwell Y-pattern piston check valve to ADV
T-pattern piston check valve in 1994 due to ALARA concerns
(eliminate seal welded bonnet). Experienced problem with ADV valve
(stuck open, insufficient forward flow) that was not remedied by the
disc modifications (see below), ceased efforts, and reinstalled
Rockwell Y-pattern piston check valve.
2. Changed the disc design (resilient seat, hard seat, full body
guided) with no improvement. Originally, the resilient seat was
suspected of causing the valve to stick open because it was found
partially off the disc and degraded. The valve failed-to-open with
the full body guided disc.
3. X-Ray of valve showed disc was cocked with the bottom of the disc
towards the discharge port. CP&L believes disc was always cocked to
discharge port (i.e. the first time the pump was started the disc
would cock). CP&L presented no data to support or refute this
contention.
4. CP&L states the most probable root cause is significant hydraulic
forces acting on the check valve when the pump starts; pump takes
approximately 3 Sec to come up to speed, the valve closes within the
first 1/2 second.
5. The valve was not originally backseat leak tested by the plant.
They noticed the pipe was hot after the ADV valves were installed
and initiated backseat leakage testing.
6. Inspected the body bore of suspect valve with no indication of
roughness or machining marks. Inspected intersection on body bore
and discharge port and found no problems. (Not clear if fretting
damage was identified)
7. Disc Dimensions were within vendor specification: Vendor 1.867, -
0.002, As-found 1.866 Bore Dimensions were within vendor
specification: Vendor 1.875, +0.00.4, As-found 1.875
8. Design Pressure/Temperature: 2735 psig, 200 Degrees F; Operating:
2712 psig, 130 Degrees F: Flow 60 gpm
CP&L has two other ADV 2" piston check valves installed (BA Transfer
Pumps Discharge Check Valves) that have not exhibited the noted problem.
These valves are tested quarterly at 35 gpm (forward flow and backseat
leakage) with no reported failures. The operating conditions of these
valves are different from the CSIP check valves; operating pressure is
lower (120 psig vs 2712 psig) and flow is lower and variable (35 gpm vs
60 gpm), CP&L provided the following information regarding the BAT
recirculation check valves.
1. Anchor Darling T-pattern piston check valve installed in 1994, No
problems reported.
2. Valves tested quarterly for flow and backseat leakage at 35 gpm.
3. Design Pressure/Temperature, 150 psig, 250 Degrees F. Operating,
120 psig, 250 Degrees F, Flow 140 gpm max, varies
The Information obtained from ADV and CP&L is insufficient to
conclusively determine the root cause the Shearon Harris event. There is
insufficient information on which to base any further conclusions. ADV
conducted flow testing but could not replicate the problem. Further
testing is planned for the CP&L scenario, and FPL has supplied a suspect
valve which could also be tested. When further information
CR 96-1774
Attach 8 Page 4 of 11
becomes available, it will be evaluated as appropriate.
Review of Engineering's records indicates JPN was notified of the Shearon
Harris 9/29/95 event by ccMail from FPL Licensing on 10/2/95 due to CPL's
Nuclear Network entry. JPN contacted CPL on 10/7/95 to obtain a copy of
the Part 21 notice and to discuss the event. The cause of the event was
not well understood and no further action was appropriate at that time.
It has been determined that the NRC did not make any formal disclosure of
the Shearon Harris event. Recent conversation with the PSL site resident
indicates that NRC issuance of an information Notice noting both the CPL
and FPL events is likely.
Inspection of V2167 After Sectioning
The initial conclusion that machining anomalies in the 2" ADV piston
check valves were directly responsible for the field failure is not
supported by more recent inspection of V2167 following valve sectioning.
The inspection, as documented in Attachment 14, concludes that local
fretting wear occurred in the body contact area with the disc which
likely led to a local groove, sticking/disc cocking and the valve's
failure-to-close.
As the casting flaw above the discharge port and the machining marks
below the fretting zone did not exhibit any significant wear marks. they
are not believed to have led to the failure of V2167 to close. The
machining marks below the fretting zone, however, could well have
contributed to piston socking for different valve operating conditions.
However, had the machining anomalies been located adjacent to the
observed fretting location (ie., the valve's normal disc location during
flow) they would have affected valve operability/reliability.
Review of the V2167 anomalies indicates the acceptability of
casting/machining anomalies is largely dependent on their location.
While such anomalies are certainly undesirable in a finished product,
their presence can be accepted on a case-by-case basis based on their
extent and location.
Inspection of V02134 After Sectioning
V02134 was removed from service due to galling of the bonnet threads.
The valve was subsequently scrapped and sectioned for internal
inspection. The Inspection of this valve, as documented in Attachment
16, was performed in the presence of ADV. It identified internal
machining anomalies near the discharge port which are not believed to
have affected valve operation. Wear bands in the guide surfaces
(fretting) were identified at the disc land locations. No local grooving
was identified as a result of fretting wear. Local scuffing (abrasive
wear) of the guide area at the edge of the discharge bore was observed.
Review PWO Work History for Trending
Per FRG request, the work order history of V2167 and similar valves was
reviewed to determine whether there was sufficient data to trend a
developing problem with the Anchor Darling valve. Attachment 17
documents this review. An initial report in December of 1994 indicated
V2167 failed to close (flow decreased as recirculation valve opened) but
problem could not be replicated. Further inspections did not identify
valve internal problems and testing was inconclusive, Engineering
concludes there was insufficient data prior to the 7/13/96 event (with
its determination the valve was cocked and stuck open) to identify an
incipient problem.
CR 96-1774
Attach 8 Page 5 of 11
Disposition of ADV Piston Check Valves In Stores
Based on the conclusions drawn from the inspection of V2167, the 20
piston check valves remaining in stores were re-inspected against a
criteria that would allow raw casting surfaces and/or machine marks in
valve guide areas not in contact during valve operation. This review was
based on the criteria depicted in Attachment 13 which provides the basis
for accepting certain valves that would otherwise be returned to ADV as
non-conforming.
Attachment 12 lists all 2" piston check valves received from Anchor
Darling and the remaining 1" and under piston check valves in Stores.
This information for the 2" valves is summarized below:
Table omitted.
As described in Attachment 12, a number of packaging anomalies were
identified from review of tie valves in Stores; these included many
valves that were not yet unpacked from the initial factory shipment.
Anomalies included water droplets inside the majority of the piston check
valves, internal rusting and absence of desiccant. ADV indicates that
disassembly of the valve following hydrotest for dry out and reassembly,
with the valve pressure seal shipped as a loose part, would be an
appropriate corrective action to the first item.
These inspections supported the conclusions from the initial inspections
(see page 2) that:
1) 2" CS & SS ADV piston check valves in stores are generally
susceptible to machining anomalies.
2) 1" and under piston check valves are not susceptible to the
machining anomalies noted in the 2" valves.
3) All sizes of CS ADV piston check valves in stores have various
levels of internal rusting.
The anomalies found in the 1" & under piston check valves (a casting lip)
were different from the generic problems associated with the 2" piston
check valves and were deemed to be an isolated cases. These two valves
will be returned to ADV.
CR 96-1774
Attach Page 6 of 11
Root Cause Evaluation:
Plant Status When Event Occurred Plant Location Where Event
100% Power Occurred
2C Charging Pump
Activity in which Event Occurred Related Activity In Which
2C Charging Pump Shutdown Event Occurred
2B Charging Pump Startup
after Oil Addition
Type of Inappropriate Action/Job Category Type of Equipment
Not Applicable 2" Anchor Darling Piston
Check Valve
How Human/Admin Error Occurred How Equipment
Not Applicable Degraded/Failed
Failed to Close
Why Event Occurred
Charging application developed fretting wear on disc/body interface
leading to disc sticking open
The failure-to-close event for the 2C Charging Pump discharge check valve
(V2167) initially appeared to be caused by internal casting/machining
anomalies. Physical inspection of a spare 2" valve also indicated
internal machining anomalies which required the consideration of the
continued operability of all installed 2" ADV piston check valves
(Attachments 1 & 7).
Based on a series of verbal discussions with ADV, the cause of the
machining anomalies is believed to be due to the past use of a drilling
process to perform rough machining of the guide area and to develop the
seat pocket recess. This process tends to follow the geometry of the
rough casting. Following brazing of the seat and heat treatment, a
boning process is used for final machining. The centerline differences
between these two processes is believed to account for the observed
anomalies. The quality controls within ADV's manufacturing process
identified the subject anomalies and these were subsequently accepted
following ADV's internal review.
Further review of V2167 internal conditions (Attachment 14) has concluded
that the noted internal casting/machining anomalies are not the primary
cause of the valve's failure-to-close. This conclusion is based on the
location of the casting/machining anomalies in V2167. However, the types
of anomalies noted in other ADV piston check valves (Attachment 12) may
well affect valve operability/reliability.
The present understanding is that the 2C Charging Pump discharge check
valve's (V2167) failure-to-close was due 10 internal fretting damage
within the valve. Fretting damage is believed to be primarily caused by
the valve's material combination and the charging system application
(long service times in a pulsating flow). Increased tolerances due to
casting anomalies may also be a contributing factor. The machining
anomalies in V2167 would not affect valve function.
The charging pumps are triplex positive displacement piston pumps
manufactured by Union Power Pump Company. These pumps have a 2 1/16"
bore & a 5 inch stroke and operate at 213 rpm. The number of pressure
pulsations per minute of run-time is -640 at a nominal discharge pressure
of 2335 psig.
Review of the run time hours for the 2" ADV check valves installed in
charging system service does not indicate that runtime hours, in of
itself, is a good indicator of impending failure.
Charging Pump Discharge Check Valve Check Valve Run Time
1B Charging Pump V02133 1,200 hours
1C Charging Pump V02134 6,500 hours (est)
2A Charging Pump V2169 3,100 hours
2B Charging Pump V2168 9,700 hours (est)
2C Charging Pump V2167 5,700 hours
Unit 2 Common Header V2462 5,850 hours (est)
CR 96-1774
Attach 8 Page 7 of 11
Review of the valve application, knowledge of the disc cocking and
inspections of valves V2167 (Unit 2), V02134 (Unit 1), and valves in
Stores lead to the following failure description. This description has
been updated to reflect additional information; the basic explanation, as
contained in Attachments 1 & 7, remains essentially unchanged. Failure
was due to a combination of causal factors:
1) The constant flow of the charging pump (44 gpm) results in the valve
disc opening to move off its seat approximately 1/2" - 5/8". The
constant flow rate of the positive displacement pump results in a
single disc position leading to the concentration of wear damage at
a single location,
2) As the bottom edge of the disc is not fully supported by the body
bore due to the presence of the discharge port, the disc's bottom
skirt is supported at two relatively wide points on its arc. At 68
gpm, the angle between the arc points (-140 Degrees) is at its
maximum (44 gpm for charging system/-110 Degrees).
3) The pulsating nature of the charging flow (three piston, positive
displacement, reciprocating pump) results in a small continuous
oscillation of the valve disc. The disc movements within the bore
guide surfaces (vertically and side-to-side) result in wear bands
that correspond to the disc land locations.
4) The raw casting of the body bore was apparently oversized/off-center
which led to incomplete machining of the bore and greater clearances
between the disc and bore. Absence of significant wear marks within
these regions indicates the rough guide surfaces did not contribute
to the disc wear. Greater clearances result in larger disc
movements and may lead to higher disc velocities and impact forces.
5) Disc movement led to wear of the disc and the body guide surfaces.
The wear band from the disc's upper end is distributed around the
entire circumference but is more noticeable on the outlet side of
the valve, A lower wear band is also present but more rapid wear
occurs at the two lower land's contact points on the bore/discharge
port intersection.
6) Due to the long in-service time, constant flow, two point support
and softer material of the body, grooving (due to fretting) and
scuffing (due to abrasive wear) occurs at the body bore/discharge
port intersection. Eventually, the fretting wear reaches a point
where the damage results in a cocked disc that is stable under loss
of flow; the spring force is not sufficient to reclose the valve
when the flow stops/reverses.
Based on the below review of the failure description, a reciprocating
pump application is expected to be more susceptible to fretting damage
than a typical centrifugal pump application.
Causal Factor Criteria for Selection / Implications
Constant flow rate Results in a single check valve disc position - lift
is a function of flow velocity and density Results in
concentration of wear at one discharge port location
Maximum angle of contact occurs with -68 gpm or 12
ft/sec of water
Pulsating flow of Results in small oscillation of the plug to create
a reciprocating fretting at the points of contact within the guide
pump surface, flow turbulence with a centrifugal pump may
also produce fretting but is expected to result in a
lower wear rate
Mis-cast valve Mis-casting causes greater clearances; more disc
movement may result in more rapid wear depending on
location
Piston & valve Harder disc provides for more rapid wear at points of
body materials contact in bonnet bore/discharge port intersection;
item with greater wear (body) is non-replaceable.
Duration of Wear process is time related; Duration of service at
valve's service flow governs effect of wear mechanism. More frequent
at flow inspections are warranted for valves normally at flow
Absence of one or more factors will increase the time to failure and/or
may prevent the failure mechanism. It is difficult to state whether
fretting will not occur for a centrifugal pump application - given a
sufficient time duration for the damage to be observed. The duration of
time required for failure will also be dependent on the pre-existence of
casting/machining anomalies. Additional field data for centrifugal pump
applications is needed to fully address this potential concern.
CR 96-1174
Attach 8 Page 8 of 11
Fretting is an adhesive wear mechanism between two surfaces having
oscillatory, relative motion of small amplitude. It involves the
repeated formation and fracture of cold welds between two surfaces.
Abrasive wear involves the plowing or cutting of grooves in a soft
material by a harder one. Factors which affect both adhesive and
abrasive wear include relative hardness, surface finish and
microstructure. Generally, harder materials are more wear resistant and
greater hardness differences lead to increased wear. Rough surface
finishes usually cause increased wear, however, very smooth finishes can
increase the tendency for cold welding. Also, similar microstructures
can increase the tendency for cold welding.
The cause of the fretting appears to be small disc oscillations due to
the pulsating flow coupled with a less than optimum material combination
of disc and body materials. Discussion of the material selection with
ADV centered on a rule of thumb of achieving a difference of more than 4
HRC between material couples. This criteria is typically used to prevent
the onset of galling, an adhesive wear mechanism, but does not address
other wear mechanisms. For the material combination of the resilient
seated valves (SA-564 Gr 630-1075 disc and SA 351-CF8M or SA 216-WCB
body) wear data indicates a less than optimum couple. For the material
combination of the hard seated valve (SA-638 Gr. 660 Type 1 disc and SA
351-CF8M or SA 216-WCB body) no wear data was found in the literature.
Based on the hardseated valve disc material hardness (SA-564 Gr 630:43
HRC) compared to resilient valve disc material hardness (SA-564 Gr 630-
1075: 32 HRC), it is reasonable to conclude that wear rates for the
resilient seated valve body will be less than those observed for the,
hardseated valve. Anchor Darling has been requested to review wear
characteristics of their material combinations.
Anchor Darling has stated that piston check valve use in non-pulsating
flow applications, may not be susceptible to the above degradation
mechanism. For a centrifugal pump application (assuming variable flow
through the check valve), the periodic travel of the disc across the
machining anomaly would tend to smooth the damaged area. For larger flow
applications, the greater stroke would result in more available spring
closure force. Anchor Darling suggests that this force may be sufficient
to overcome sicking due to fretting damage and coupled with the disc's
closing momentum may well result in closure of a piston check despite
casting/machining anomalies at tower elevations. ADV suggests a smaller
valve would be beneficial.
Root Cause Summary
The root cause for the V2167's failure-to-close is fretting damage
between the disc and the valve body at two contact points adjacent to the
valve's discharge port. The raw casing surfaces and machining anomalies
noted within the piston guide areas are not presently believed to have
significantly contributed to the failure of V2167 based on their location
and the lack of significant wear marks. However, these type of
manufacturing anomalies may well contribute to failure-to-close/open in
other valves depending on their location, degree and the valve flow rate
application.
The fretting damage was likely caused by the large difference in hardness
between the valve disc (43 HRC) and valve body (78 HRB) and the pressure
pulsations & constant flow application of the charging system. These
conditions would lead to small disc oscillations (due to pressure
pulsations) at a single point (due to constant now) in the valve
discharge port.
Implications of Root Cause Determination
Based on the above description of the failure causes, it would follow,
but is not certain, that fretting damage would be significantly less
pronounced for a centrifugal pump application, This presumption is based
on pressure pulsations from a centrifugal pump being less than for a
reciprocating pump and the variation in pump flow distributing any
postulated fretting wear across a wider surface area. The first
presumption, though reasonable, may delay rather than prevent the onset
of significant fretting damage. The presumed beneficial effect of flow
variation is reasonable for a centrifugal pump discharge check valve
application where system flow rate varies with time. For a mini-
recirculation line check valve serving a Centrifugal pump that is
normally operated in a near dead-headed application, the flow variation
through the recirculation line would be negligible. This latter
application is descriptive of the Shearon Harris CSIP application.
CR 96-1774
Attach 8 Page 9 of 11
Based on the above, the Shearon Harris event may bear more similarity to
the St. Lucie event than first realized. Based on discussions with ADV
and Shearon Harris, fretting damage was not identified within the valve
discharge bore. At this point in time, Shearon Harris and ADV continue
to believe the cause was related to the initial insurge of the flow from
the CSIP pump. Until further data is obtained, it would be prudent to
inspect 2" ADV piston check valve internals on a more frequent basis for
applications where valves see long periods of service at flow.
Based on the current level of understanding, 2" ADV piston check valves
are suitable for intermittent service or service in varying flow regimes
without restriction. Further use of ADV piston check valves in near
continuous use, constant flow service must consider the potential for the
valve to fail-to-close after long periods of service (2500-3500 hrs at
constant flow).
An in-depth design review and in-service applications of the 2" piston
check valve is warranted and has been requested by letter to Anchor
Darling (Reference 8).
Specific long term corrective actions will be required for the installed
valves in constant flow service. These corrective actions are under
review and will be determined based on the work to be performed by Anchor
Darling. The changes will likely include a reduction in valve size of
specific ADV piston check valves.
In the interim, the following specific countermeasures are recommended:
1. Perform yearly internal inspections of the ADV piston check valves
in charging pump discharge check valve service until further notice.
These inspections will develop trending information and should be
sufficient given the rotation of the pumps.
2. Perform an inspection each refueling outage of other ADV piston
check valves in charging service until further notice.
These inspections should be based on GMP-01 and specifically target
fretting damage in the discharge bore. Inspection by SCE personnel is
recommended.
General anions have been specified below to prevent recurrence. These
include a QA audit of ADV discrepancy identification, evaluation
practices, & packaging practices to prevent recurrence at the
manufacturing facility. Training of FPL welders is also planned so that
similar potential valve problems would be identified prior to
implementation.
Corrective Actions:
Corrective actions In this disposition supersede corrective actions
listed in prior attachments.
1. Inspect and, replace if necessary, ADV 2" piston check valves
installed in Unit 1 & 2 per the schedule requirements of Attachment
15. All Work Orders for these inspections have been written by SCE.
No further action is required at this time for this item.
2. Following completion of the initial valve inspections under
Attachment 15, perform periodic inspections of ADV valves in
charging service until further notice:
a) Perform yearly internal inspections of the valves in charging
pump discharge check valve service. Recommend pump discharge
valve inspection be bed to charging pump maintenance with
instructions to disassemble valve and inspect if not already
performed in last 6 months.
b) Perform an inspection each refueling outage of other ADV piston
check valves in charging service.
Inspections should be based on GMP-01 and specifically target
fretting damage in the discharge bore Localized fretting of the type
seen in V2167 (a groove on each side of the discharge port) is cause
for replacement. Inspection by SCE valve component specialist is
recommended.
Issue a PMAI to ENG-Systems Engineering to institute GMP-01 testing
on ADV piston check valves in charging service on a more frequent
basis. Recommend pump discharge check valve inspection be tied to
charging pump seal maintenance with instructions to disassemble ADV
discharge check valve and inspect if not performed in last 6 months.
Recommend other downstream Charging System ADV piston check valves
be inspected during each refueling outage until further notice. Due
Date 10/18/96.
CR 96-1774
Attach 8 Page 10 of 11
3. Safety Evaluation JPN-PSL-SEMS-96-052 allows temporary manual
isolation of the Unit 2 recirculation valves while the associated
charging pumps are operating. Implementation of the safety
evaluation shall be implemented and Controlled by approved changes
to plant procedures in accordance with section 9.0 of the safety
evaluation.
The recirculation valves for all 3 Unit 2 charging pumps shall be
closed until V2462 is inspected and/or replaced as appropriate.
This action provides an additional compensatory measure to prevent
backflow (intersystem LOCA), in the event V2462 fails to close.
Closure of the manual stop valve on the discharge of a charging pump
(V2336, V2464, V2339) to allow pump maintenance is an equally
acceptable compensatory measure for that specific pump. With the
manual stop valve closed, the respective charging pump and its
recirculation valve may be disassembled or tested as required. The
recirculation valve shall be closed prior to reopening the manual
discharge stop valve.
In addition to the above requirement:
a) The recirculation valve for pump 2A (V2555) shall be kept
closed until valve V2169 has been inspected or replaced with a
suitable spare. Closure of V2336 is an equally acceptable
compensatory measure.
b) The recirculation valve for pump 2B (V2554) shall be kept
closed until valve V2168 has been inspected or replaced with a
suitable spare. Closure of V2464 is an equally acceptable
compensatory measure.
The above requirements have been accommodated by a permanent change
to OP 0210020 which provides for a normal charging system alignment
with the three recirculation valves in the closed positions. This
system alignment change is acceptable for one fuel cycle per safety
evaluation JPN-PSL-SEMS-96-052.
Issue a PMAI to operations to revise OP 0210020 to return to the
design basis use of the charging pump recirculation valves after the
inspection and replacement, as appropriate, of Anchor Darling check
valves V2462, V2167, V2168, and V2169. This PMAI is to include a
Mode 4 hold for the power ascension following the 1997 refueling
outage (Cycle 15). Due Date 5/15/97.
4. Issue a PMAI to Nuclear Materials Management to return rejected ADV
piston check valves to the vendor as identified in CR 96-1774
Attachment 12. Valve Serial, # E-T401-9-25 is to be released to
ENG. Valve Serial # E-T401-9-30 is to be tagged "Restricted Use -
requires Engineering Approval (Reference CR 96-1774) Gordon McKenzie
ext 7276". Valves designated as "Rework" are to be segregated for
rework by MM prior to field use. Due Date 8/30/96.
5. Issue a PMAI to Mechanical Maintenance to perform rework of selected
ADV valves as identified in CR 96-1774 Attachment 12. Engineering
will provide support as required. Due Date 10/25/96.
6. Issue a PMAI to Mechanical Maintenance to perform training for
welders to ensure they would identify and report casting and
machining problems of the type noted within the 2" ADV piston check
valves. Engineering will provide support as required. Due Date
9/27/96.
7. Issue a PMAI to QA to perform an audit of ADV manufacturing and
packaging process controls. Manufacturing controls should have
prevented shipment of valves with casting/machining anomalies. A
potential solution would be written guidelines governing evaluation
of discrepant bore surfaces. Packaging controls should have
prevented the water observed within shipped valves. Disassembly of
the valve following hydrotest for dry out and reassembly with the
valve pressure seal shipped as a loose part is a potential solution
Due Date 10/18/96.
8. Issue a PMAI to Engineering to provide appropriate long term
corrective actions (valve replacements and/or procedure/inspection
program changes) based on the root cause determination within CR 96-
1774 and ADV's subsequent input requested by Reference 8. Review
plant documents (eg., SOER 86-03 inspection Database, GMP-01) for
Potential revision to address the root cause determination Due Date
11/15/06.
Attach 8 Page 11 of 11
Attachments:
1. Engineering Disposition related to Unit 1 Operability Review
2. Anchor Darling Letter dated July 19, 1996
3. Inter-Office Correspondence, "Testing of Anchor Darling Check
Valves", July 20, 1996
4. Anchor Darling Piston Check Valves Summary of Inspection Findings,
July 20, 1996
5. Engineering Disposition related to Unit 2 Operability Review
(Superseded)
6. Anchor Darling Letter dated July 23, 1996
7. Engineering Disposition related to Unit 2 Operability Review
(Revision 1)
8. Final Engineering Disposition
9. ADV 10CFR21 Letter to NRC dated July 25, 1996
10. NPRDS System Notification
11. Nuclear Network Notification
12. Disposition of ADV Piston Check Valves in Stores
13. Acceptance Criteria for Raw Casting/Machining Anomaly Locations
14. FPL Met Lab Report 96-170, dated August 5, 1996
15. Inspection Results for Installed Valves (8/16/96)
16. FPL Met Lab Report 96-180, dated August 15, 1996
17. Review of PWO History for Trending
18. Installed Anchor-Darling Check Valves, August 16, 1996
References:
1. Unit 1 FSAR, Amendment 14
2. Unit 1 Technical Specifications, Amendment 142
3. Anchor Darling Drawing W9323936, Rev A
4. Unit 2 FSAR, Amendment 9
5. Unit 2 Technical Specifications, Amendment 82
6. Design Basis Document DBD-CVCS-2, Rev 0
7. CP&L Letter to NRC dated Sept 29, 1995
8. FPL Letter to ADV dated August 16, 1996
9. Union Pump Technical Manual 2998-3414, Rev 15
10. Crane Technical Paper 410, 1991 Printing
Prepared by
Verified by
Approved by Date
*** END OF DOCUMENT ***
