ML20247P565

Part 21 Rept Re Model SA-A101 MSIV A' Actuator Showing Evidence of Internal Leakage,In Both Directions Past Pneumatic Piston.Situation Being Reviewed to Determine If Failure Could Pose Substantial Safety Hazard

ML20247P565
Person / Time
Site:	Duane Arnold
Issue date:	05/18/1998
From:	Hiller J AFFILIATION NOT ASSIGNED
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
REF-PT21-98 NUDOCS 9805280052
Download: ML20247P565 (3)

Text

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- RNLPH A*. HILLER COMPANY 6005 CNTtnPmst Dnivt Expont.PA 15632

• Tetz: 412 3251200 FAm 412 733-1825 May 18,1998 :

' Document Control Desk United States Nuclear Regulatory Commission -

.. Washington, DC 20555

Reference:

Hiller Document 98-NRC-001

Dear Sir ~,

Per the applicable requirements of Title 10, Chapter 1, Part 21 of the Code of Federal

- Regulations, it is my responsibility as the responsible officer for the Ralph A. Hiller Company to advise the Nuclear Regulatory Commission of the attached "Possible Defect".

As required by 10CFR21, I will be submitting a full, final report, which will indicate if a reportable defect exist or not.

Should you have any questions, you can reach me at (724) 325-1200, or fax me at (724) 733-1825.

Thank you for your attention in this matter.

Yours truly, n' Nl fRandolph Hiller fh Chief Executive Officer :-

' Attachments: (1) " Notice of Possible Defect per 10CFR21" cci file \\

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R LPH A'. HILLER COMPANY coo 5 ENTERPmSE ORIVE EXPORT.PA 15632 T ELE: 412 325-1200 FAz: 412 7331825 Attachment 1 " Notice of Possible Defect per 10CFR21"

Background

The Ralph A. iiiller Company of Export PA is a supp!ier of safety related components to Nuclear Power Plants with a Quality Assurance Program per the requirements of Title 10, Chapter 1, Part 21 of the Code of Federal Regulations. A significant portion of these components has been valve actuators.

Description of Event IES Utilities Inc., Duane Arnold has reported that a Model SA-A101 Main Steam Isolation Valve "A" (MSIV) Actuator showed evidence ofinternal leakage, in both directions past the pneumatic piston. The actuator was returned to the 11 iller Company's production facility for evaluation. Evaluation verified the excessive leakage and discovered a fracture of the pneumatic piston. The crack consisted of a cross sectional (through) crack in the web and reinforcement ribs at the center hub involving a 2180' on the hub area circumference.

Engineering Background The Model SA-A101 MSIV Actuator is a Basic Component, which has been classified as safety related. It consists of a 20" diameter bore pneumatic cylinder in tandem with a 5" diameter bore hydraulic cylinder.

The failure (safety) mode is the rod exterided (valve closed) position. This position is achieved via an external spring pack and is assisted by the pneumatic portion. The hydraulic cylinder is designed for speed control. This family of actuator is used as the MSIV Actuator at many other plants.

The actuators designed by the liiller Company for safety related applications are designed per the guidelines of ANSI B93.10. He piston material is designed to be ASTM A48 cast iron with a tensile yield strength of 35,000 PSI. His material was chosen for its excellent compressive s:rength, good tensile -

strength, good machinability, and excellent resistance to gauling characteristics and is extensively used for pneumatic industry applications. Ilowever, the material does not have good bending strength.

When the Model SA-A101 MSIV Actuator s were purchased in 1989/90 by Duane Amold, the production verification of the pistons for safety related service were programmatically required to be dimensionally checked, assembled, the correct assembly was verified and finally a leak test was required. Our records indicate each of these verifications was successfully performed.

Investigation The failed piston was tested to verify the material and failure mode. The failure was found to be caused by bending stresses due to impact. The material was found to be cast iron with a tensile yield strength of 27,500 PSI. No inclusions were found which would initiate this type of fracture. No other indications of damage were found in the remainder of the actuator that could cause leakage.

Inspection of other MSIV Model SA-A101 MSIV Actuators, which have been in service at Duane Arnold, found another with a similar, less severe crack, actuator "B". This actuator,"B", had been in service on the same Main Steam Line at the plant. He piston web was cracked in the same area, however the crack did not propagate through the part and no leakage was detected. As part ofIES's maintenance plan, both Page1of2 05/18/98 1

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l Actuators "A" & "B" had been refurbished and postproduction tested a second time approximately two I gears ago with no leakage.

Review of the exact nature of these failures indicated that the safety function of the actuator would not have been prevented, even if the fracture had been catastrophic and the piston had become loose from the piston rod. He piston failed safely and would not have prevented the safety mode from occurring, produced by compressed air and springs. Further testing on actuator "B" indicated that normal cycling of the actuator did not continue to propagate the failure.

Discussions with the owner, IES Utilities Inc and the plant designer, General Electric, indicate that

! operationally there is a standard test, which could create a pressure anomaly through the line. Discussions

! with the valve manufacturer, Edwards Valves, concluded this type of event could cause the valve to force l the Actuator's piston rod into the Actuator (retract). The initiating event is still under investigation. He hydraulic control system is not designed to mitigate shock waves that produce excessive internal hydraulic pressures. The excessive energy could cause damage of the pneumatic piston and/or the hydraulic control assembly. The original specification did not require that the Actuator to be designed for this type of event and there has not been a similar reported failure of a piston on any actuator designed by the Hiller Company.

Plan The Ralph A.1-liller Company is currently working to determine the cause and extent of the problem. This work requires a more thorough engineering review of the function of the MSIV Actuator in the plant and the stresses this could create in the piston. Per the applicable portions of the Ralph A. Hiller Company's Quality Assurance Program and 10CFR21 the findings of this investigation along with any recommendations will be reported to the Nuclear Regulatory Commission.

Summary There has been a crack found in two pistons, of two of the MSIV Actuators, in service at a single Nuclear l

Power Plant. A loss of function of the actuator did not occur. These actuators were on the same Main Steam Line and it has been determined that the leaking piston would not have prevented the safe function of the basic component. At this point in time, the situation is being reviewed to determine if this failure could pose a " substantial safety hszard" to the particular, or any other Nuclear Power Plant.

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