Part 21 Report - 1998-440
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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