United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #:  9503220185

Rosemount Nuclear Instruments      Rosemount Nuclear Instruments, Inc.
                                   12001 Technology Drive
                                   Eden Prairie, MN 55344 USA 
                                   Tel 1 (612) 828-8252
                                   Fax 1 (612) 828-8280

March 21, 1995

Re:  Notification under 10 CFR Part 21 on Certain Nuclear Qualified Model
     1152, 1153 and 1154 Transmitters with Monel Alloy 400 Isolating
     Diaphragms

Pursuant to 10CFR21 Paragraph 21.21 (b), Rosemount Nuclear Instruments,
Inc. (RNII) is writing to inform you that our records indicate that
certain Model 1152, 1153 and 1154 range code 6 through 0 nuclear
qualified pressure and differential pressure transmitters / sensor
modules were supplied with unqualified isolating diaphragm materials.

At this time, RNII has determined two production lots of isolator
assemblies fur sensor modules range code 6 through 0 used in Model 1152,
1153 and 1154 transmitters were manufactured using Monel Alloy 400
isolating diaphragm material.  The correct material for these sensor
modules, according to design specification is 316L Stainless Steel (SST). 
Transmitters and sensor modules from these lots were shipped to customers
beginning about Sept. 1, 1989.

All metallic parts of the Model 1152, 1153 and 1154 transmitters which
come in contact with process fluid are specified to be made with 316 SST. 
Isolating diaphragms are in direct contact with the process fluid and
assist in transmitting the applied pressure to the sensor.  Monel Alloy
400 material has not been qualified for use with Model 1152, 1153 and
1154 transmitters.  However, RNII did qualify to seismic requirements
Monel Alloy 400 for a specific option of Model 1152 transmitters.  These
units are identified under option code "T1815". (Typical model number
1152DP5N22T1815PB).

RNII became aware of the deviation in material during failure analysis of
two customer Model 1153 transmitter sensor modules measuring pressurizer
pressure.  The failure analysis found that the sensor modules failed due
to hydrogen permeation through the sensor isolating diaphragm.  Hydrogen
permeation can severely affect the performance of RNII pressure sensors. 
Material verification of the transmitter isolating diaphragms concluded
the material was Monel Alloy 400 and not 316L SST.

A technical discussion of hydrogen permeation and of RNII transmitters
with 316L SST and Monel Alloy 400 isolating diaphragms is included in the
enclosure entitled Attachment A.

RNII has concluded the use of Monel Alloy 400 is a deviation from design
specifications for standard Model 1152, 1153 and 1154 transmitters. 
Accordingly, we are issuing this notification.

FISHER ROSEMOUNT


10CFR21 Notification
Monel Alloy 400 Isolating Diaphragms
March 21, 1995

1.0  Name and address of the individual providing the information:

     Mr. Mark Van Sloun 
     Vice President & General Manager 
     Rosemount Nuclear Instruments. Inc.  
     12001 Technology Drive
     Eden Prairie, MN 55344

2.0  Identification of Items supplied:

     Certain Model 1152, 1153 and 1154 transmitters / sensor modules
     range 6 through 0.  The specific transmitters and/or sensor module
     spare part kits shipped to your facility are identified in the
     enclosure entitled Attachment B.  If the enclosed Attachment B
     states "No units shipped to your site" none of the affected
     transmitters and/or sensor modules were supplied to your site,

3.0  Identification of firm supplying the item:

     Rosemount Inc. (predecessor to Rosemount Nuclear Instruments, Inc.)
     12001 Technology Drive
     Eden Prairie, MN 55344

4.0  Nature of the failure and potential safety hazard:

     This notification is issued to inform all users of Model 1152, 1153
     and 1154 transmitters / sensor modules which were manufactured with
     Monel Alloy 400 isolating diaphragms instead of the specified 316L
     SST.  Model 1152, 1153 and 1154 transmitters are designed
     specifically for use in nuclear power plant applications.  These
     models are generically designed and qualified per IEEE Std. 323 and
     344 with 316L SST Isolating diaphragm material only.

     The use of affected transmitters can lead to hydrogen permeation
     through the isolating diaphragm under specific operating conditions. 
     These conditions are described in detail in Attachment A.  RNII does
     not have sufficient information to determine the safety impact
     related to plant applications, Licensees must determine the impact
     on plant operations and plant safety and take action as deemed
     necessary.

FISHER-ROSEMOUNT


10CFR21 Notification
Monel Alloy 400 Isolating Diaphragms 
March 21, 1995


5.0  The corrective action which is taken, the name of the individual or
     organization responsible for that action and the length of time
     taken to complete that action:

     RNII has Identified two specific manufacturing lots of isolator
     assemblies for sensor modules in Model 1152, 1153 and 1154 nuclear
     qualified pressure and differential pressure transmitters which were
     supplied with Monel Alloy 400 isolating diaphragm material.  The
     specific units applicable to your plant location are listed on the
     enclosure entitled Attachment B.

     RNII will timely complete internal corrective actions.

     Mr. Van Sloun is responsible for any further action related to this
     issue.

6.0  Any advice related to the potential failure of the item:

     The enclosure entitled Attachment A details the information on the
     expected transmitter performance with Monel Alloy 400 isolating
     diaphragms.  The end-user must determine the full scope of this
     deviation as it relates to plant operations and plant safety and
     take action as deemed necessary.

Rosemount Nuclear Instruments, Inc. has a strong commitment to the
nuclear industry and assures you that we are dedicated to the supply of
high quality products and services to our customers.  We are sorry for
any inconvenience.  If there are any questions, or you require additional
information related to this issue, please contact Tim Layer (612) 828-
8240 or Jane Sandstrom and Ian Baldry (612) 828-8250.

Sincerely,

ROSEMOUNT NUCLEAR INSTRUMENTS, INC.


M. L. Van Sloun
Vice President & General Manager

encl.:    Attachment A 
          Attachment B

MVS:TJL

FISHER-ROSEMOUNT


                              ATTACHMENT A
                10CFR21 Notification Dated March 21, 1995

1.   Background

RNII nuclear qualified pressure transmitters utilize the [symbol
omitted]-Cell capacitance sensing element to provide pressure
measurement.  Process pressure is transmitted from the isolating
diaphragm and silicone fill oil to a sensing diaphragm in the center 
of the [symbol omitted]-Cell.  The displacement of the center diaphragm
results in a sensor capacitance change proportional to the process
pressure applied.  The differential capacitance of the sensor is
converted electronically to a 4-20 mA dc transmitter output signal.

The isolating diaphragm isolates the process fluid from the sensor fill
oil and transmits the process pressure to the sensing diaphragm. 
Rosemount commercial pressure transmitters are offered with a variety of
isolating diaphragm materials, including 316 SST, Hastelloy, Monel Alloy
400, and Tantalum.  316L Stainless Steel Is the standard isolating
diaphragm material offered for RNII nuclear qualified pressure and
differential pressure transmitters.

RNII has identified certain qualified nuclear transmitters and sensor
modules which were manufactured with Monel Alloy 400 isolator diaphragms.

2.  Description of Monel Alloy 400

Monel Alloy 400 is a nickel-copper alloy (66% Ni+Co / 32% Cu) which
provides high strength, durability and corrosion resistance.  Monel is
resistant to most alkalis, salts, waters, food products and organic
substances, both at normal and elevated temperatures.  Monel is offered
as an isolator material on Rosemount commercial pressure transmitters and
option code T1815 for certain Model 1152 nuclear qualified transmitters. 
It is used in a variety of commercial processing applications.  Due to
its high nickel content, Monel is not recommended for applications where
hydrogen is present in the process.

2.1  Hydrogen Permeation

It is widely recognized that nickel and nickel alloys are susceptible to
permeation by hydrogen.  Monel Alloy 400, with a nominal nickel + cobalt
content of 66%, is particularly susceptible, and is not recommended in
applications where hydrogen is present in the process fluid.

Hydrogen permeation can severely affect the performance of sensor
modules.  In simple terms, monatomic hydrogen permeates the isolator
diaphragm and combines to form H sub 2 inside the sensor cell. Gas inside
the sensor will lead to measurement inaccuracies.  RNII discovered the
use of Monel Alloy 400 after two hydrogen permeation failures were found
in a pressurizer measurement application at a customers Pressurized Water
Reactor (PWR).  In this application, a small amount of hydrogen (approx. 
40cc/kg at STP) was added to the reactor coolant process fluid for
corrosion control.  The transmitters functioned normally at a nominal
pressure of 2250 PSI and temperature < 104 degrees F for sixteen months. 
The units were then

FISHER-ROSEMOUNT


Attachment A
Page 2

depressurized during a scheduled outage.  As pressure was reapplied
during plant start up, the transmitters failed (erratic output, off 
scale high).

2.2  Factors of Hydrogen Permeation

Several factors are known to affect the rate of hydrogen permeation. 
First, the nickel content of the material directly affects the rate of
permeation.  Monel has a high nickel content and is therefore relatively
susceptible to hydrogen permeation.

A second factor is temperature.  The rate of hydrogen permeation is
exponentially related to temperature.  For example, a reduction in
temperature at the isolator of 20 degrees F will decrease the rate of
permeation by approximately a factor of 2.5.

A third factor which affects the rate of hydrogen permeation is process
pressure.  The rate of hydrogen permeation is a function of the square
root of pressure; and, therefore, less critical than temperature.

A fourth factor is the source of the hydrogen.  Hydrogen can be
cathodically generated on the face of the isolating diaphragm.  This can
occur when a galvanic cell is formed due to dissimilar metals in contact
with the process fluid.  For example, in the presence of an electrolyte
such as water, a cadmium plated transmitter flange or zinc galvanized
pipe or fitting near the nickel alloy (Monel) isolating diaphragm will
set up a relatively large galvanic potential.  Under these conditions,
monatomic hydrogen is formed on the cathode, in this care the isolating
diaphragm.  The monatomic hydrogen will permeate the isolating diaphragm
with relative ease and can combine on the other side to form hydrogen gas
(H sub 2), eventually affecting transmitter performance.

A final factor is the relative hydrogen concentration difference between
the process and oil side of the isolating diaphragm.

RNII Model 1152, 1153, and 1154 nuclear qualified transmitters are
generically designed and qualified exclusively with 316L SST isolating
diaphragms.  RNII has supplied some Model 1152 transmitters with Monel
Alloy 400 isolating diaphragms under a specific option code "T1815". 
(Typical transmitter model number 1152DP5N22T1815PB).

For the identified RNII transmitters with Monel isolating diaphragms and
the remaining 316 SST parts that contact the process fluid, a small
galvanic potential will be present due to the dissimilar materials.  (The
ideal situation is where all parts in contact with the process fluid are
of the same material; thus no galvanic potential can exist.) The galvanic
potential between 316 SST and Monel is small, and the two materials are
listed as compatible for industrial use in MIL-STD-889 for Dissimilar
Metals.  Nonetheless, for hydrogen applications where Monel is already
susceptible to permeation, the small galvanic potential present between
the 316 SST parts and the Monel isolating diaphragms is undesirable.

FISHER-ROSEMOUNT


Attachment A
Page 3

In the two confirmed failures of RNII transmitters in a pressurizer
reactor coolant application, the galvanic potential between the Monel
isolating diaphragm and the other 316 SST parts in contact with the
process fluid may have accelerated the hydrogen permeation rate.  The
hydrogen present in this application was dissolved in the water in the
form of molecular hydrogen gas (H sub 2).  The galvanic potential was
likely a catalyst to the formation of monatomic hydrogen, significantly
increasing the rate of permeation.  Monatomic hydrogen will eventually
permeate through the Monel isolating diaphragm even in the absence of a
galvanic catalyst, but at a slower rate.

2.3  Hydrogen Permeation Effect On Rosemount Pressure and Differential
Transmitters

As monatomic hydrogen permeates through the isolating diaphragm, it can
combine to form hydrogen gas within the sensor.  The hydrogen will be
absorbed by the silicone oil.  The volume of the oil and hydrogen will
depend on the process pressure and solubility of hydrogen in silicone
oil.

During operation under pressure, a sensor with hydrogen under the
isolator may not exhibit symptoms or erroneous output, as the hydrogen is
completely dissolved in the silicone oil.  This was the case with the two
confirmed failures in a pressurizer application (See 2.1), The units
reportedly operated normally during the 16 month period prior to the
plant's outage.  The hydrogen permeating the isolating diaphragm during
this time had no apparent affect on the transmitter operation.  However
when pressure is released or significantly reduced, the hydrogen may
outgas from the oil, and if sufficient hydrogen is present, the internal
pressure may distend the isolating diaphragm.  With liberated gas under
the isolating diaphragm, the transmitter output will be erratic.  The
transmitter response would be unstable, and calibration would be
difficult or impossible.

3.   Monel Alloy 400 Effect on Transmitter Normal Operating Functional
and Performance Specifications

The affected transmitters, assembled with Monel Alloy 400 isolating
diaphragms, are limited to range code 5 through 0.  From the sensor
assembly level, through module and transmitter assembly, the Monel
assemblies were fully tested in accordance with our standard in-process
and acceptance test procedures and found to perform within standard
specifications. A partial list of these tests include: helium leak checks
at the isolating diaphragm assembly and sensor assembly levels (weld
integrity verification); high pressure aging of the sensors (glass to
metal seal and weld integrity verification): temperature performance
testing of the sensor module; overpressure and static pressure effects
testing of the sensor module; hydrostatic pressure of the pressure
retaining boundary (150%max. rated pressure); and standard transmitter
calibration (linearity/hysterisis/accuracy verification).

FISHER-ROSEMOUNT


Attachment A
Page 4

The key difference is the physical difference in isolator material. 
Monel Alloy 400 is generally superior to 316 SST relative to corrosion
resistance.  However, the customer must evaluate the acceptability of
Monel Alloy 400 as the process fluid interface in each application. 
Particular attention must be given to applications where hydrogen is
present in the process fluid.

3.1  Monel Alloy 400 Effect on Transmitter Nuclear Qualification and
Accident Specifications

RNII has not performed an IEEE 323 qualification on pressure transmitters
with Monel Alloy 400 isolators. Therefore, no physical test evidence is
available to document performance under accident conditions.

Monel Alloy 400 contains similar constituents as 316 SST, only in
different relative composition percentages.  RNII is not aware of any
inherent limitations based on the composition of Monel Alloy 400 relative
to performance under accident conditions.  However, since no
qualification testing has been performed on Monel sensors, RNII cannot
verify the expected performance under accident conditions.

4.0  Summary

RNII has identified certain nuclear qualified transmitters and sensor
modules which were manufactured with Monel Alloy 400 isolating
diaphragms.  Monel Alloy 400 sensor modules are not generically qualified
per IEEE 323 or 344 for use with Model 1152, 1153, or 1154 pressure and
differential pressure transmitters.  RNII has supplied specific Model 
1152 transmitters with Monel Alloy 400 isolating diaphragm material under
option code "T1815".  (Typical model number 1152DP5N22T1815PB).

Monel Alloy 400 is a nickel alloy which provides high strength,
durability and corrosion resistance.  However, due to its high nickel
content, Monel is not recommended for applications where hydrogen is
present in the process fluid.

There have been two confirmed failures due to hydrogen permeation of RNII
Model 1153 transmitters with Monel Alloy 400 isolating diaphragms. 
Nickel content of the material, temperature, pressure, galvanic potential
in the presence of an electrolyte and the relative concentration of
hydrogen between the process fluid and the fill oil are key factors
relative to hydrogen permeation.

FISHER-ROSEMOUNT



Attachment A
Page 5

During operation at pressure, a transmitter having hydrogen permeation
may exhibit no symptoms or erroneous output, since the hydrogen is likely
dissolved in the silicone fill oil.  If pressure is relaxed, the hydrogen
may outgas and distend the isolating diaphragm. Transmitter response to
pressure and its output will then become erratic and detectable.  The
unit will be difficult or impossible to calibrate.

The affected transmitters / sensor modules with Monel Alloy 400 isolating
diaphragms successfully passed all RNII manufacturing testing which
indicates the units should operate within specifications under normal
operating conditions where hydrogen is not present.

FISHER-ROSEMOUNT


                                   Rosemount Nuclear Instruments, Inc.
                                   12001 Technology Drive
FISHER-ROSEMOUNT                   Eden Prairie, MN 55344-3695
                                   USA

DATE:     March 21, 1995                PAGE(S) INCLUDING LEAD SHEET: 10

                    TO                                 FROM

COMPANY:       NUCLEAR REGULATORY       FAX NUMBER: (612) 828-8280
               COMMISSION

ATTENTION:     MR. GREG CWALINA         SENDER:   JERRY VALLEY

FAX NUMBER:    301-415-2968             PHONE NUMBER: (612) 828-8242

SUBJECT:       PRELIMINARY MONEL SENSOR LIST

CC:

GREG,

PER YOUR REQUEST TO KEN EWALD, HERE IS THE LATEST LIST OF
TRANSMITTERS
AND/OR MODULES AFFECTED BY THE MONEL DIAPRAGM ISSUE.  YOU WILL
NOTE THAT
THERE ARE SEVEN MODULES STILL NOT ACCOUNTED FOR.  WE ARE CONTINUING
TO
PURSUE THESE.

REGARDS,

JERRY VALLEY


Table "SENSORS THAT CONTAIN ISOLATOR MATERIAL FROM LOT 020 OF
01153-0252-
0042, dated 03/21/95", 7 pages, omitted.


*** END OF DOCUMENT ***

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