Part 21 Report - 1996-732

 
 
ACCESSION #: 9612160224

Anchor/Darling

Valve Company  o    Williamsport, PA 17701

W. G. KNECHT
     Technical Director

November 27, 1996

Mr. Jerry Carter
US NRC
Events Assessment Branch
Washington DC 20555

Subject: A/DV 1878 Class Piston Check Valves

Dear Mr. Carter:

Per our discussion this date the enclosure is the latest copy of our
report to FP&L regarding the piston check valve problem.

Should you have any questions please do not hesitate to call Floyd
Bensinger, our Engineering Manager, or the writer.

Sincerely,

ANCHOR/DARLING VALVE COMPANY

William G. Knecht
Technical Director

WGKjs

cc:  F. A. Bensinger

Enclosure

Anchor/Darling                                         Page 1 of 4
Valve Company

701 FIRST STREET
P.O. BOX 3428
WILLIAMSPORT, PA 17701-0428
(717) 327-4800
FAX: (717) 327-4805

Florida Power and Light Company
St. Lucie Plant
P.O. Box 128
Fort Pierce, FL 24954

November 20, 1996

Attention:          D.J. Denver
                    St. Lucie Engineering Manager

Subject:            A/DV 2"-1878# Piston Check Valves

Reference:          1. FP&L JPN-SPSL-96-0372, August 16, 1996 Letter
                    2. A/DV S.O.'s ET401 and RZ814
                    3. A/DV Test Report No.'s RZ814, Test Report of Flow
                       Test on a 2"-1878# Globe Piston Check Valve,
                       October 2, 1996

Gentlemen:

     A/DV apologizes for the delay in responding to the referenced FP&L
letter.  We had hoped to receive application responses to our
notification letters but as of this writing we have not received any
complete information.

     A/DV has performed a design review of the piston check valve with
the intent to address the functional and re-assembly problems experienced
at St.  Lucie.  The following areas were addressed as noted:

A.   Pressure Seal / Bonnet Area Items

     1.   Bonnet Retainer Capscrews

          FP&L reported having difficulty in sealing the ADVanseal using
          the capscrew without pressure.  The current capscrew is a 5/16"
          diameter capscrew.  A 1/2" diameter capscrew will be used in
          the future.  This will provide approximately three (3) times
          the gasket load.

     2.   Galling of the Bonnet Retainer Threads

          FP&L has experienced galling of the bonnet retainer threads.
          The current retainer is made of 316 stainless steel with chrome
          plated 12 series threads.  A/DV is evaluating replacing this
          design with a 17-4PH bonnet retainer (no chrome plating) with 8
          series threads.  Assuming successful completion of the new
          bonnet retainer evaluation, this design will be put in place.

     A/DV plans to include the philosophy of both enhancement with the
     smaller piston check valves.  These two (2) enhancements will affect
     inventory and part interchangeability.

B.   Cleaning / Drying of Valves Prior to Shipment

     A/DV has evaluated several methods to assure complete drying of the
     piston check valves prior to shipment, i.e. disassembly, baking,
     etc.  We have concluded that the most effective method is to
     disassemble the valves after hydrostatic testing, dry the parts and
     reassemble without the gasket and anti-rotation pin (Part No. 258)
     installed.  The gasket and anti-rotation pin will be packaged with
     the valve and a tag placed on the valve requiring installation of
     these two (2) parts after valve installation.

C.   Valve Performance / Functional Items

     1.   Disc Guide Area of Body Neck Bore

          We evaluated this area to determine if the body guides could be
          improved.  Several methods were evaluated, i.e., sleeving the
          body bore with hardened material, reshaping the exhaust port,
          etc.  All methods are costly.  The conclusion was reached that
          the above changes were cost prohibitive and the better
          resolution is to use a smaller valve for oscillating flow
          application in order to place the disc in a more open position
          where it is better guided by the body.

                                                                        2

C.   Valve Performance / Functional items (Continued)

     2.   Disc - Body Material Couple

          It was stated by FP&L that fretting is more apt to occur where
          a large difference in material hardness exists.  A/DV selected
          the body-disc material couple for wear resistance, galling
          resistance and castability, weldability of the bodies.

          A more important factor to reduce the potential for fretting is
          reduced stress levels.  A/DV does not plan to change the body
          or disc materials.  As discussed in A.1. above and in the later
          root cause analysis, use of a smaller valve would resolve this
          situation.

     3.   Rough Machining left in the Body Neck Bore

          In May, 1993, A/DV had changed its rough machining process to
          setup and rough cut the neck bore and seat pocket using the
          same setup method and single point tooling-boring as the finish
          machining process.  Prior to this time the neck bore was rough
          machined on a radial drill.  This drilling process was not
          always performed on the same centerline as the final machining
          and the drill had a tendency to tail off center.  This area has
          been resolved as described above in May, 1993.

     4.   Ratio Guide Length - Disc Diameter

          A/DV's design criteria limits the potential disc tilt to less
          than 1/2 degree, and requires a ratio of one (1) or greater for
          the disc, guide length to diameter.  The 2"-1878# Piston Check
          disc has a ratio of 1.12:1.  Both A/DV's design criteria and
          the 2"-1878# design are representative of A/DV and competitive
          valve designs which have been proven to be successful in most
          services.

     Root Cause

     A/DV evaluated the as found condition of the piston check valve that
     stuck open.  To assist in our root cause analysis, we performed flow
     tests on two (2) 2"-1878# Piston Check valves (one (1) valve
     returned from FP&L, S/N ET401-9-6).  Reference No.  3 Report,
     enclosed, documents the task and results.  The testing was performed
     to evaluate valve performance at various forward flow rates.  The
     test conclusion was the valve always closed when forward flow ended.

                                                                        3

     Root Cause (Continued)

     As a result of our evaluation of the FP&L failed valve and our
     testing, we have concluded that the root cause is the disc
     oscillation, caused by the reciprocating pump, causing fretting to
     take place in the valve body disc guide area.  The fretting area
     provides a configuration in the body guide that allows the disc to
     stick open without forward flow and with reverse flow.

     A/DV's recommendations to eliminate the valve operational problem
     are (preferred listed first):

     A.   Use of in-line check valves in reciprocating pump applications.
          This valve design provides better wear resistant materials as
          disc guides throughout the entire valve stroke.

     B.   Use of smaller piston check valve (valve size or reduced port)
          in reciprocating pump applications to more fully open the disc
          where better body-disc guiding is available.  Attached are
          graphs of flow rate versus disc position and Cv versus disc
          position to be used to evaluate T-pattern piston check valve
          size selection.  Where a smaller T-pattern piston check valve
          produces too high a pressure drop, use of a Y-pattern piston
          check valve may resolve this concern.

     T-pattern and Y-pattern piston check valves and in-line check valves
     are within A/DV's product lines.  Availability of Y-pattern piston
     check valves is scheduled for the second quarter of 1997.

     If further discussion is required on the above, please feel free to
     contact us.

ANCHOR/DARLING VALVE COMPANY

Floyd A. Bensinger, P.E.
Manager - Engineering

bcc: J. Chappell    G. Parks
     T. Johnson     J. Tarbutton
     W. Knecht      H. Wescott
     G. Kneiser     F. Velez
     R. Maietta

                                                                        4

Chart "2" Smaller T-Piston Check Valves" 3 pages, omitted.

Figure "2"-1878 FULL PORT SOCKET ENDS STAINLESS STEEL PISTON CHECK VALVE
NON-COBALT TRIM" omitted.

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