Part 21 Report - 1996-160

 
 

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



Page 2



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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