Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9601160345
DRESSER-RAND Steam Products
SERVICES DIVISION 37 Coats Street
P.O. Box 592, Wellsville NY 14895-0592
(716) 593-1234 FAX: (716) 593-5815
January 15, 1996
ATT: DOCUMENT CONTROL DESK
U.S. NUCLEAR REGULATORY COMMISSION
WASHINGTON, D.C. 20555
Dear Sir/Madam:
On all Terry turbines model ZS and GS, using the 2-1/2" veeport and 3"
venturi governor valves, the original design valve stems are made of
nitrided 410 stainless steel and utilize carbon spacers and flat washers
for packing.
There has been a few nuclear plants who have exhibited corrosion related
valve stem binding. It is agreed that valve stems of this construction
are susceptible to corrosion attack during prolonged exposure to an
environment of stagnant oxygenated water.
The plants that are having this corrosion problem are not adequately
draining the unit and/or have corrosive water chemistry in the steam.
The real solution is to have adequate drainage and eliminate the
corrosive environment. One way to drive the water out of the gland area
is by running the turbine long enough to bring the unit up to normal
operating temperature. Then secure all steam to the turbine. However,
some of these plants have concluded they are unable to assure a dry and
non-corrosive environment. Accordingly, they have identified a need for
a valve stem design with higher corrosion resistance.
Because Dresser-Rand has a high regard for customer satisfaction, there
was a willingness to design and supply valve stems that better suite
those plants that can not assure a dry non-corrosive environment and have
experienced a corrosion related binding problem.
Previously Dresser-Rand had manufactured a valve stem made of 410
stainless steel with chrome plating applied over a layer of electroless
nickel. Now we have developed a valve stem made of 718 inconel with a
chromium carbide coating along the gland area.
For those plant that are not having valve stem binding problems, the
original valve stems or the Chrome/Nickel valve stems are still available
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We have also changed the part numbers for the carbon spacers and flat
washers. These changes were made to limit the sulfur content to less-
than 700ppb in the carbon spacers and the flat washers have a tighter
flatness tolerance and are consistently made of 410 stainless steel. It
is Dresser-Rand's recommendation to order new carbon spacers and flat
washers for the governor valve when ordering a new stem. Also it is our
recommendation to order 25 each of the carbon rings and spacer washers to
sufficiently fill the "L" gland cavity. If there is too much space in
the gland cavity, the washers can tilt and lock/bind the stem in
positions.
If you have any questions regarding the above or wish to purchase any of
the valve stems, please contact us 1-800-828-2818. For technical
questions call myself (ext-3569). To purchase parts call Mike Lauzze
(ext-3436) or Richard Rubadue (ext-3616).
Best Regards
Carlton Slater
Service Engineer
NUCVSTEM
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