United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #:  9503170049


March 10, 1995

U. S. Nuclear Regulatory Commission 
Washington, D. C. 20555

ATTENTION:     Document Control Desk

SUBJECT:       Limitorque Corporation 10 CFR Part 21, Evaluation #52'
               Worm Shaft Clutch Gears Assembly, #0901-161

Date of Discovery -- January 16, 1995

Limitorque Corporation is submitting a report relative to the subject

Duke Power Company, Oconee Nuclear Station returned (2) worm shaft clutch
gear assemblies from (2) Limitorque SB-2 Valve Actuators, serial nos. 
L366900 & L366901.  The clutch sleeves, #60-573-0007-2 which constitute
part of the worm shaft gear assemblies was the failed component.

The two failed clutch sleeves were sent by Limitorque Corporation for an
independent metallurgical and failure analysis.  The results of this
testing indicated that the material and metallurgical quality of the
clutch sleeves were not a factor in contributing to this failure. 
Further the report stated that both failures were the result of a single
overload event.

Limitorque notified Duke Power Company on February 21, 1995 concerning
the above results.  In addition, we requested that Duke provide
additional information, if available, concerning these failures.  Duke
Power Company was not able to provide any additional information.

Limitorque Corporation P. O. Box 11318 5114 Woodall Road Lynchburg, VA
24506-1318 Tel. (804) 528-4400 FAX (804) 845-9736

Page 2
March 10, 1995
Limitorque Corporation 10 CFR Part 21, Evaluation #52
Worm Shaft Clutch Gears Assembly, #0901-161

Refer to the attached correspondence to Duke Power Company dated 2/21/95
and 12/2/83 to support our conclusion.

Limitorque Corporation is closing this evaluation as non-reportable
pursuant to the requirements of 10 CFR Part 21.


Charles L. Hylton
Vice President of Engineering


cc:  Duke Power Company 
     10 CFR 21 - Evaluation #52 File

Limitorque                                        February 21, 1995 

Duke Power Company
Attn: Lew Beck, Nuclear Production Eng., Valve Engineering 
Oconee Nuclear Station
P. O. Box 1439
Seneca, SC 29679-1439

Reference:     Your 1-11-95 letter

Subject:       Failure of Worm Shaft Clutch Gears 
               SB-2/40, S/O #3J3096C, S/N's 366900 & 366901 
               Duke tag no. 3-LP-21 & 3-LP-22

Dear Lew,

The two failed clutch sleeves were sent by Limitorque Corporation for an
independent metallurgical and failure analysis.  Conclusions of this
report indicate that the material and metallurgical quality of the
components were proper.  Further, the report stated that both failures
were the result of a single overload event.

Attached is our Dec.  2, 1983 letter to Duke that outlines previous
history and details the mechanics that could lead to a single overload
failure.  This letter also provides recommendations for a possible gear
ratio change.

Since the trippers have ben removed manual declutching with the motor
energized and subsequent release of the declutch lever or the inadvertent
energization of the motor during manual operation with subsequent release
of the declutch lever provide possibilities for single overload events.

Lew, please investigate the above mentioned occurrences and possibly
proceduralize steps to prevent these occurrences.  Please advise
Limitorque Corporation of your findings since we are evaluating for
potential 10CFR21 applicability and our interim report is due
approximately 2nd week of March.

Also, please provide instructions for the return of the components to
Duke Power Company.

Very truly yours,


P.  G.  McQuillan
Manager Nuclear/Special Projects

Limitorque Corporation P. O. Box 11318 5114 Woodall Road Lynchburg, VA
24506-1318 Tel. (804) 528-4400 FAX (804) 845-9736

                         LIMITORQUE CORPORATION
     5114 Woodall Road o P. O.  Box 11318 Lynchburg, Virginia 24506 
                 Telephone-804-528-4400 o Telex-82-9448

December 2, 1983

Duke Power Company
General Offices
422 South Church Street
Charlotte, NC 28242

Attention:     S. K.  Blackley, Jr., Chief Engineer
               Mechanical and Nuclear Division


Reference:     Your October 17, 1983, Letter to G. Cusack

Subject:       Oconee Nuclear Station, Unit 2 
               Replacement L.C.  Operators
               2LP-21, 2LP-22 MPSCO Order J-27672-73 
               L.C. 3J3096-B SB2-40-3600 RPM 56 Frame Motor 
               File 0S-161

Limitorque Corporation has completed an engineering review of clutch
sleeve failure addressed in your referenced letter.  Investigation
revealed that failure occurred when the worm shaft clutch lugs engaged
the clutch sleeve lugs during transition from manual to electric motor
operation.  (Attached Appendix A describes this operation.)  The results
of our study are as follows:

1.   Dimensional inspection of the failed component indicated that the
     component was manufactured dimensionally correct per engineering

2.   Independent laboratory analysis verified that failed material
     samples were of the correct material and heat treated to engineering

3.   Clutch sleeve failure was the result of high impact forces
     associated with clutch sleeve/clutch lug engagagement.  This impact
     force was generated by coupling a "high acceleration rate" motor to
     a step-up (increaser) gear set which in turn rotates the clutch
     sleeve prior to lug engagement.  Certain terms require definition,

     a.  "High acceleration rate" - The motors accelerate to no load
          speed (3600 R.P.M.) in a short period of time.  The motor
          design in question exhibits acceleration characteristics that
          are greater than twice other motor designs.

            Automated Valve Actuators and Jacks for Industry

                                                                   Page 2

     b.   "Step-up gear set" - A gear combination that increases input
          speed.  A 0.8/1 gear set will produce an output speed 1.25
          greater than input speed.  The actuators in this application
          were fabricated with a 0.78/1 gear set.

     c.   "Impact force" - This is a function of the relative rotational
          velocity of the clutching lugs.

4.   Testing determined the unacceptable range of gear ratios to be
     0.78/1 through 1.12/1 when coupled with the 40 foot pound-3600-56
     frame motor.

5.   Additional testing verified the problem does not exist with other
     motor sizes regardless of the gear ratio utilized.

Resolution of this phenomena can be accomplished in either of two
methods, i.e.:

1.   Removal of the clutch trippers as was field accomplished on 1LP-21
     and 1LP-22, Limitorque 3J3096-A.

2.   Usage of an acceptable motor/gear ratio combination.  (Previous
     discussions indicated that the valve closure time is critical and
     cannot be increased.)  Valve closure time does not increase if the
     overall gear ratio in the actuator does not increase.  Units are
     fabricated.  with an overall gear ratio of 26.24/1 (33/1 worm gear
     set and 0.78/1 motor gear set).  Gearing could be modified to
     produce an overall gear ratio of 25.55/1 (13 1/3/1 worm gear set and
     1.92/1 motor gear set).  It should be noted that this method results
     in a worm/worm gear set which may allow the torque switch electrical
     contacts to remake after their initial opening control function. 
     The plant control scheme must not utilize a maintained contact to
     energize the motor starter or repeated motor energization will occur
     as the torque switch contacts cycle from open to close electrically.

Please advise the writer of your preference for resolution.  This also
affects 3LP-2 and 3LP-22, Limitorque 3J3096-C, which are tentatively
scheduled for late January, 1984, delivery.

As a further note, Limitorque Corporation has reviewed our records and
determined that this unique combination of unit/motor and motor gear
ratios has not been previously supplied to Duke Power Company or any
other customer of Limitorque Corporation's.

                                                                   Page 3

Should you have any other questions, please do not hesitate to contact
the writer.

Very truly yours,


P.  G.  McQuillan
Q.  A.  Administrator


cc:  J.  Knost/Duke Power
     G.  Cusack/Charlotte

cc:  T.  S.  Mignogna
     E.  K.  Denham
     W.  J.  Denkowski
     R.  J.  Kornsey
     I.  E.  Wilkinson
     D.  S.  Warsing
     C.  Hylton
     W.  Miluszusky

                                                               APPENDIX A

                        SB-2 CLUTCHING MECHANISM

The SB-2 actuator is equipped with a clutching mechanism which allows the
actuator to be shifted from motor to manual or manual to motor operation. 
In motor operation (see Figure 1) the lugs of the clutch and clutch
sleeve are engaged.  Torque is transmitted from the motor pinion (via the
motor clutch gear, clutch sleeve and clutch lugs) to the worm shaft. 
Input torque from the handwheel shaft is uncoupled from the worm shaft. 
When the declutch fork is rotated through actuation of the external
manual declutch lever, the clutch is moved along the worm shaft until the
clutch/handwheel pinion clutch lugs are engaged.  The declutch fork is
held in the manual position by a latching interface between the declutch
fork and clutch tripper.  Torque can be transmitted from the handwheel
gear (via the handwheel clutch pinion/clutch lugs) to the worm shaft.  In
this position, the motor pinion torque interface is decoupled from the
worm shaft.  When the motor pinion is energized with the declutch fork in
the manual position, rotation of the clutch sleeve causes the clutch
sleeve pin to strike the clutch trippers which release-the declutch fork
from its manual position.  When the clutch trippers release the declutch
fork, the clutch compression spring pushes the clutch along the worm
shaft until the clutch/clutch sleeve lugs engage allowing for
transmission of motor torque.


                                                       APPENDIX A

Figure 1 "SB-2 CLUTCHING MECHANISM" omitted.


Page Last Reviewed/Updated Monday, January 27, 2020