Information Notice No. 92-78: Piston to Cylinder Liner Tin Smearing on Cooper-Bessemer KSV Diesel Engines

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C.  20555

                               November 30, 1992

                               COOPER-BESSEMER KSV DIESEL ENGINES


All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to problems that could result from specific diesel
engine (piston and cylinder) wear characteristics that may lead to crankcase
explosions.  It is expected that recipients will review the information for
applicability to their facilities and consider actions, as appropriate, to
avoid similar problems.  However, suggestions contained in this information
notice are not NRC requirements; therefore, no specific action or written
response is required.  

Description of Circumstances

In 1989, two emergency diesel generator (EDG) crankcase explosions occurred at
the Susquehanna Steam Electric Station.  Following these events, Pennsylvania
Power and Light (PP&L), the licensee, conducted a root cause evaluation.  PP&L
determined that the root cause of the crankcase explosions was excessive
friction between the piston and the cylinder liner.  PP&L found that the
synergistic effects of rapid loading, piston and cylinder lubrication
conditions, and possibly other factors such as the quality of the lubricating
oil and the temperature of the engine intake air led to an excessive transfer
of tin from the piston to the cylinder liner and a breakdown of the
lubrication film, resulting in overheating of engine parts.  These overheated
components provided an ignition source for the oil vapor in the crankcase,
causing an explosion.  The licensee has taken actions to correct these
problems and has successfully operated the EDGs at Susquehanna since 1990 with
no indications of damage or malfunctions.


PP&L conducted an investigation over a two year period following the crankcase
explosions at Susquehanna in 1989 with assistance from Cooper-Bessemer, the
EDG vendor, and other consultants.  PP&L determined that engine components 


                                                           IN 92-78
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overheated after an excessive amount of the tin from the 0.05 to 
0.075 millimeter [2 to 3 mil] thick tin plating on the piston was transferred
to the pores in the cylinder liner.  The pores in the liner, which has a
porosity of 15 to 25 percent, would normally be filled with oil for
lubrication between the piston and the cylinder liner.  The loss of liner
porosity inhibited the formation of an oil film and caused excessive friction
between the piston and the cylinder liner.  The excessive friction caused
overheating of components inside the engine, most likely bearings associated
with the drive train.  The presence of overheated components in the engine
caused an explosion in the crankcase.  PP&L personnel noted that the tin from
the piston was transferred or smeared predominantly from the non-thrust side
of the piston.

PP&L improved the lubrication of the piston and liner by permanently removing
the wrist pin end caps and the bottom oil scraper ring from the piston.  This
change increases the oil flow to the area where the piston and the liner make
contact.  The EDG vendor, Cooper-Bessemer, considers these modifications to be

The Cooper-Bessemer Owners Group wrote a draft document, "Inspection Manual
for Cooper-Bessemer Model KSV Diesel Engine Cylinder Liners, Pistons, and
Bearings," dated April 8, 1992.  Although the inspection manual was in draft
format and only partially completed, the Niagara Mohawk Power Corporation
followed the guidance in the manual and detected degraded pistons and liners
at its Nine Mile Point Nuclear Station, Unit 1.  Licensee and Cooper-Bessemer
personnel were in the process of completing a 5-year preventive maintenance
inspection on the engines using previously approved inspection procedures and
the inspection personnel had not considered any of the pistons and liners
unacceptable based on those procedures.  However, on the basis of the new
inspection criteria in the draft inspection manual, the licensee rejected and
replaced 15 of 32 pistons and liners on 2 engines because of excessive tin
smear from the pistons to the liners.  

The owners group plans to periodically revise the inspection manual when new
problems or solutions are discovered, including changes to the inspection
procedures and photographic examples of conditions that have been found.

                                                           IN 92-78
                                                           November 30, 1992
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This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.

                                      ORIGINAL SIGNED BY

                                   Brian K. Grimes, Director
                                   Division of Operating Reactor Support
                                   Office of Nuclear Reactor Regulation

Technical contacts:  J. R. Rajan, NRR
                     (301) 504-2788

                     Carl H. Woodard, RI
                     (215) 337-5261

Attachment:  List of Recently Issued NRC Information Notices

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