United States Nuclear Regulatory Commission - Protecting People and the Environment


ACCESSION #: 9805280052



RALPH A. HILLER COMPANY

6005 ENTERPRISE DRIVE   EXPORT, PA 15632



TELE:  412 325-1200

FAX:   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,



J. Randolph Hiller

Chief Executive Officer



Attachments: (1) "Notice of Possible Defect per 10CFR21"



cc: file



RALPH A. HILLER COMPANY

6005 ENTERPRISE DRIVE   EXPORT, PA 15632



TELE: 412 325-1200

FAX:  412 733-1825



Attachment 1 "Notice of Possible Defect per 10CFR21"



Background



The Ralph A. Hiller Company of Export PA is a supplier 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 of internal

leakage, in both directions past the pneumatic piston.  The actuator was

returned to the Hiller 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 >/=

180 degrees 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 extended (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 Hiller Company for safety related

applications are designed per the guidelines of ANSI B93.10.  The piston

material is designed to be ASTM A48 cast iron with a tensile yield

strength of 35,000 PSI.  This material was chosen for its excellent

compressive strength, good tensile strength, good machinability, and

excellent resistance to gauling characteristics and is extensively used

for pneumatic industry applications.  However, the material does not have

good bending strength.



When the Model SA-A101 MSIV Actuator s were purchased in 1989/90 by Duane

Arnold, 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.  The piston web was cracked in the same area,

however the crack did not propagate through the part and no leakage was

detected.  As part of IES's maintenance plan, both



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Actuators "A" & "B" had been refurbished and postproduction tested a

second time approximately two years 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.  The 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 the Actuator's piston rod into the

Actuator (retract).  The initiating event is still under investigation.

The 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.  Hiller 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 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 hazard" to the particular, or

any other Nuclear Power Plant.



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