EN Revision Imported Date : 8/14/2019
EN Revision Text: INITIAL PART 21 REPORT - POTENTIAL PREMATURE FAILURE OF AIRMOTOR ACTUATOR DIAPHRAGM
The following is a summary of the information received from ITT Engineered Valves, LLC (ITT) via facsimile:
ITT discovered one batch of ten actuator diaphragms (five at the licensee's facility and five sent to Korea) for a No. 25 Airmotor which have demonstrated a potential to fail prematurely during operation. ITT has no evidence to show that any other batch of diaphragms are at risk. ITT is in the process of determining how to evaluate the effect of the diaphragm anomaly, while determining how to define the scope of the potential defect.
This initial notification will be followed by a written notification by July 14, 2019.
None of the actuator diaphragms were supplied to U.S. facilities.
* * * UPDATE AT 1152 EDT ON 7/12/2019 FROM STEPHEN DONOHUE TO JEFF HERRERA * * *
The following is a synopsis of a report received via email:
"Initial notification of the potential defect was made to the NRC via fax on 6/14/19. The potential defect report was designated Event 54118 shortly thereafter. Per 10 CFR Part 21 requirements, this report is the 30-day written notification to support the initial fax notification.
"This potential defect is limited to the #25 airmotor diaphragm only. This issue is in no way related to any other size of airmotor diaphragm, and does not have any effect on the weir diaphragm within the diaphragm valve itself (the diaphragm identified as ITT's M1 diaphragm).
"Potential impact of nonconformance:
"The #25 airmotor diaphragm is designated as a safety related part when the valve to which it is assembled is identified as an active valve. The normal function of the airmotor diaphragm is to seal the airmotor chamber in order to permit conversion of air pressure to a thrust that can operate (open or close) the valve. The safety function is the same as the normal function. If the diaphragm should fail, the valve would not be capable of actuation, would not be capable of producing a force that would open or close the valve, so the safety function of an active valve would be compromised if the actuator diaphragm were to fail.
"The #25 airmotor diaphragm is not designated as a safety related part when the valve to which it is assembled is identified as a passive valve. A passive valve only needs to fulfill its basic valve function (to open or close at loss of air power) and is not required to operate. That is, a fail-to-close valve will still close (still maintain its primary function) if its airmotor diaphragm has failed, it will just not be able to actuate. Therefore, no safety function is compromised if the actuator diaphragm is part of a passive valve.
"There were two sets of valves that were constructed at the same time (late May of 2018) from the same lot of #25 airmotor diaphragms, and using the same assembly procedures. One set of five valves was never shipped, was disassembled, and found to reveal the potential defect. The other set also consisted of five valves and was shipped to a customer in South Korea. At this time, ITT does not consider any other customers to be potentially affected.
"Preliminary Root Cause:
"At this point in time, it is believed that the cause of the delamination of the diaphragm is excessive assembly torque upon original construction. For the five disassembled valves, during the 110 psig production test the assembler noted that an excessive amount of bolt torque was required to attain a leak-free joint at 110 psig. It was observed that the preload force continued to act upon the already extruded diaphragm edge over time, causing eventual cracking and delamination. While we have not been able to observe for an entire year, we have been able to simulate the same effect in a limited fashion on a brand new diaphragm using the same valve hardware over the last four weeks.
"Future plan of action:
"1. Complete testing on the fifth of five damaged diaphragms.
"2. Continue to evaluate the effects of excessive torque on the #25 airmotor joint. A second valve assembly will be built with a diaphragm from stock with intentionally high assembly torque, while the first unit mentioned above will be disassembled and examined.
"3. The customer noted in [the above] section will be notified and given instructions on how to assess whether the damage observed in Lancaster is also possible on the other five valves that were built in the same time period.
"4. Develop a means to identify problematic diaphragms after assembly, taking advantage of the fact that excessive torque on the joint in question will result in extrusion of the diaphragm beyond the outer diameter of the covers.
"5. Prepare and submit a report or interim report within 60 days of date of discovery, which will be August 13, 2019."
Notified the Part 21 Reactors and Materials group (via email).
* * * UPDATE AT 1725 EDT ON 8/13/2019 FROM STEPHEN DONOHUE TO THOMAS KENDZIA * * *
The following is a synopsis of conclusions from the final report received via email:
Testing confirmed that the cause of the diaphragm failure was due to excessive torque applied to the bolts used on the #25 airmotor joint. The excessive torque was applied due to poor finish (not flat) of the sealing surfaces. Only a batch of five valves shipped to a customer in South Korea is affected. Directions on how to inspect the supplied valves for this defect were provided as follows:
"1. Measure the bolt torque on the joint. If the value for each cap screw is measured to be 72-79 in-lb, the joint was assembled correctly and the diaphragm is likely to be functional.
"2. Observe whether there is significant extrusion of the outer perimeter of the diaphragm. If the diaphragm extends beyond the OD of the covers by 0.12 in. around most of the circumference, the diaphragm is likely to be overtorqued.
"3. Observe the edge of the diaphragm. The edge of the diaphragm should be square and straight. Examine the edge closely, looking for splitting lines within the elastomer or separation of the elastomer from the fabric outboard of each bolt. Any such damage indicates excessive torque."
Valve assembly process will be changed to ensure flat sealing surfaces and to not exceed the specified torque.
The South Korea customer will be notified and provided a copy of the report.
Notified the Part 21 Reactors and Materials group (via email).