|PART 21 REPORT - RESIDUAL HEAT REMOVAL SYSTEM MOTOR OPERATED GLOBE VALVE EXPERIENCED STEM FAILURES
The following was received via e-mail:
"This notification is being submitted pursuant to the guidelines of 10 CFR Part 21 to report that a 24in Class 150 Globe valve for RHRSW HX [Residual Heat Removal Service Water Heat Exchanger] Isolation MOV [motor operated valves], E1150F068B at Detroit Edison - Fermi 2, experienced two stem failures.
"The site notified WVC USA [Weir Valves and Controls, USA] on November 6 of this issue involving two stems. WVC USA had supplied these stems on orders 20000262-10 and 20012001-10, Detroit Edison PO's [part orders] 4700505700 and 4701149217. A new stem failed after approximately 1 month in service in valve F068B. A replacement stem was installed and failed soon after being placed in service. This second stem failure had previously been in service for approximately three years while installed in sister valve F068A. Both stem breakages occurred at the transition area of the stem backseat and were visually identical. See pictures of failure in Attachment A. In the as found condition, the disc to stem connection appears to have lacked design clearances. The cause of this clearance issue was cleaning of the disc surface where the disc nut is tack welded. The material supplied is A276 410 heat treated and tempered to obtain (269-311 BHN). This material was approved by Powell as an acceptable alternate to the original material A182 F6 (269-311 BHN). During original Part 21 evaluation, testing of the stem material revealed low impact values and reflected effects of temper embrittlement. Other possible contributors to the failure were transition region at stem backseat and the valve service conditions where vibration due to throttling has been experienced. It was determined that although temper embrittlement and other factors may have contributed to the failures, that the lack of design clearance led to the failure of the stems and was not reportable by WVC USA. However, after discussions with Detroit Edison, WVC USA was requested to evaluate the failure considering the effects of temper embrittlement that might lead to future failures.
"WVC USA engineering is unable to determine the effects of temper embrittlement for the A276 410 material. Powell engineering was also consulted and there are no known methods to evaluate the potential for failure on the stem in this condition. As noted in NRC Information Notice No. 85-59, tempering in the 700 degrees F to 1050 degrees F range is not recommended because it results in low and erratic impact properties and poor resistance to corrosion and stress corrosion for 410 stainless steel.
"The stem failures in this case reflected these low and erratic impact properties based on material testing that was performed by DTE [Detroit Edison] Fermi and WVC USA. The A276 410 materials supplied in this event were tempered at 1025 degrees F and 1050 degrees F.
"The best solution is to eliminate the potential for temper embrittlement by using a higher required tempering temperature. The recommendation is to use A276 410 tempered at a minimum of 1100 degrees F. This is also in alignment with Code Case N-62-7. We are in the process of updating our item records to reflect this minimum tempering requirement and expect this action to be completed within one month.
"WVC USA is notifying the following sites of this potential issue so that they can evaluate the impact on the safe operation of the plant.
"74347-10 Entergy PO 10118969 Site Grand Gulf
Item Number P 26126666ASSEMAO_QLA Stem & Disc Assy 14" Qy (1) Shipped 7/28/06
"0020005433-10 Georgia Power Company PO SNG10081312 REV. 2 Site Hatch
Item Number P0000419C Stem/Disc Assy 24-300 Globe Valve Qty (1) Shipped 10/29/15
"0020006979-10 Detroit Edison Company PO 4700846295 Site Fermi 2
Item Number P0000455C Stem Bin Gate Valve Qty (1) Shipped 6/29/15
"0020011676-10 Detroit Edison Company PO 4701123403 Site Fermi 2
Item Number P0000455C Stem Bin Gate Valve Qty (1) Shipped 2/14/18
"0020013251-10 Detroit Edison Company PO 4701230062 Site Fermi 2
Item Number P0000283 Stem Globe 24in 150# Qty (1) Shipped 9/19/18
"0020013586-10 Detroit Edison Company PO 4701259926 C0#6 Site Fermi 2
Item Number P0000283 Stem Globe 24in 150# Qty (1) Shipped 11/13/18
"Stem supplied under order 0020013251-10 is currently installed in F068A and order
0020013586-10 was delivered but not installed. F068B valve has been restored by Detroit
Edison with a stem which has acceptable properties for the service."
The above Part 21 notification affects Grand Gulf, Fermi 2, and Hatch.
Point of Contact: Allen Fisher
Director of Engineering