REQUIREMENTS FOR A SNUBBER MANAGEMENT DATABASE
Presented by D. Brown – Lake Engineering Company
Winter 2000 SNUG Meeting

REGULATORY/CODE REQUIREMENTS

•	ASME SECTION XI 
•	PLANT TECHNICAL SPECIFICATIONS
•	ASME OM CODE

SECTION XI vs. TECH SPECS

SECTION XI REQUIREMENTS

•	REQUIRES VISUAL EXAMINATION ONLY
•	PASS/FAIL EXAMINATION CRITERIA ONLY
•	APPLIES TO LESS THAN 5 % OF THE TOTAL SAFETY-RELATED POPULATION FOR ANY GIVEN OUTAGE
•	NO TESTING
•	NO SERVICE LIFE MONITORING

TECH SPEC OUTAGE REQUIREMENTS

•	VISUAL EXAMINATION OF 100% OF THE TOTAL SAFETY-RELATED POPULATION
•	PASS/FAIL AND SERVICE LIFE MONITORING EXAMINATION CRITERIA
•	FUNCTIONAL TESTING OF A SAMPLE OF THE SAFETY RELATED POPULATION WITH ADDITIONAL SAMPLES IF FAILURES ARE FOUND
•	PASS/FAIL AND SERVICE LIFE MONITORING TEST CRITERIA
•	RE-EVALUATION OF SERVICE LIFE PRIOR TO THE NEXT OUTAGE

SECTION XI EXAMINATION FREQUENCY / QUANTITY FOR COMPONENT SUPPORTS

TYPICAL SNUBBER ISI SCHEDULE

TYPICAL ISI UNACCEPTABLE ATTRIBUTES
(LOOKING FOR FAILURES)

•	INADEQUATE RESERVOIR FLUID LEVEL
•	INADEQUATE POSITION SETTING
•	VENTED RESERVOIR ORIENTED SUCH THAT HYDRAULIC FLUID CANNOT  GRAVITATE TO SNUBBER
•	SEVERE CORROSION OR SOLID DEPOSITS THAT COULD RESULT IN UNACCEPTABLE SNUBBER PERFORMANCE
•	WELD ARC STRIKES, PAINT, WELD SLAG, ADHESIVE, OR OTHER DEPOSITS ON PISTON ROD OR SUPPORT CYLINDER THAT COULD RESULT IN UNACCEPTABLE SNUBBER PERFORMANCE

BASIS FOR TECHNICAL SPECIFICATION EXAMINATION REQUIREMENTS

•	CONSTANT LEVEL OF SEISMIC PROTECTION (.065)

•	ASSUMES FREQUENCY OF FAILURES AND FREQUENCY OF FAILURES AND FREQUENCY OF EARTHQUAKES IS CONSTANT

•	EXAMINATION FREQUENCY DEPENDS ON PERFORMANCE LEVEL

TECH SPEC TEST PLANS
(LOOKING FOR FAILURES)

•	10% PLAN 

-	INITIAL SAMPLE: (I) = 10%

-	CONTINUE UNTIL N = I(1 + C/2)

•	37 PLAN

-	INITIAL SAMPLE: 37 SNUBBERS
-	
-	CONTINUE UNTIL N = 37 (1 +C/2)

SELECTING REPRESENTATIVE SAMPLES USING THE 10% PLAN
BASIS OF TEST PLANS

•	BASIS: 95% CONFIDENCE OF AT LEAST 90% OPERABILITY

•	NUMBER OF SAMPLES REQUIRED TO BE TESTED MAY VARY FROM OUTAGE TO OUTAGE FOR THE SAME LEVEL OF OPERABILITY

•	IMPOSSIBLE TO IDENTIFY TRENDS BASED ON IST PASS/FAIL RESULTS

•	MANY PLANTS HAVE UNEXPECTEDLY HAD TO TEST AN ENTIRE POPULATION AFTER SEVERAL SUCCESSFUL OUTAGES

TYPICAL SERVICE LIFE MONITORING VISUAL ATTRIBUTES

•	EVIDENCE OF CORROSION

•	EVIDENCE OF SOLID DEPOSITS (E.G., BORIC ACID) FROM LEAKING COMPONENT

•	LOSS OF HYDRAULIC FLUID SINCE PREVIOUS VISUAL EXAMINATION

•	METAL FILINGS ON OR IN THE VICINITY OF THE SNUBBER

•	OBSERVED FLUID LEAKAGE

•	EVIDENCE OF SIGNIFICANT DARK (I.E., BLACK OR DARK BROWN) MATERIAL DEPOSIT ON PISTON ROD

•	ROD WIPER ADHERED TO PISTON ROD

•	ABNORMAL COLOR OF HYDRAULIC FLUID

•	WEAR OR DEFORMATION OF CLEVIS PINS

•	ELONGATION OF ATTACHMENT HOLES

•	EVIDENCE OF WEAR ON SUPPORT CYLINDER

•	CRACKED OR DEFORMED FLUID RESERVOIR

•	EVIDENCE OF FOREIGN MATERIAL (E.G., WATER, SOLID PARTICLES, ETC.) IN HYDRAULIC FLUID

•	DISCOLORATION OF METALLIC PARTS DUE TO HEAT

SERVICE LIFE MONITORING

				LOOKS FOR DEGRADATION AS WELL AS FAILURES

NRC STANDARD TECH SPECS

	The service life of a snubber is evaluated via manufacturer input and information through consideration of the snubber service conditions and associated installation and maintenance records (newly installed snubber, seal replaced, spring replaced, in high radiation area, in high temperature area, etc....).  The requirement to monitor the snubber service life is included to ensure that the snubbers periodically undergo a performance evaluation in view of their age and operating conditions.  These records will provide statistical bases for future consideration of snubber service life.  The requirements for the maintenance of records and the snubber service life review are not intended to affect plant operation.  

SERVICE LIFE MONITORING

•	APPLIES TO MECHANICAL AND HYDRAULIC SNUBBERS
•	A REQUIREMENT IN ALL TECH SPECS
•	A REQUIREMENT IN THE OM CODE
•	REQUIRES THAT AN INITIAL SERVICE LIFE BE ESTABLISHED
•	REQUIRES THAT SERVICE LIFE BE REEVALUATED EVERY OPERATING INTERVAL 
•	REQUIRES THAT SNUBBERS BE REFURBISHED OR REPLACED PRIOR TO EXPIRATION OF THEIR SERVICE LIFE
•	REQUIRES DETERMINATION OF FAILURE CAUSE
•	REQUIRES IDENTIFICATION OF OTHER SNUBBERS SUBJECT TO SIMILAR FAILURE

EVALUATING SERVICE LIFE
•	ESTABLISH AN INITIAL SERVICE LIFE BASED ON MANUFACTURER’S DATA OR INDUSTRY DATA
•	PLANT OPERATING  DATA
•	INSTALLATION CONDITIONS
•	MAINTENANCE RECORDS
•	FUNCTIONAL TEST DATA
•	FAILURE/DEGRADATION EVALUATION DATA
•	TRENDING
•	IDENTIFICATION OF SNUBBERS SUBJECT TO SIMILAR FAILURE

IDENTIFICATION OF SNUBBERS SUBJECT TO SIMILAR FAILURE

REQUIRES LOOKING FOR TRENDS IN:
•	THE SAME SYSTEM
•	THE SAME  OPERATING ENVIRONMENT
•	THE SAME ORIENTATION
•	THE SAME CONFIGURATION
•	THE SAME DESIGN
•	THE SAME SIZE

SNUBBER TRACKING

•	TRACKING vs. TRENDING
•	NEED TO TRACK BY SNUBBER AND LOCATION