Information Notice No. NO 86-34: Improper Assembly, Material Selection, and Test of Valves and their Actuators
SSINS No: 6835
IN 86-34
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
May 13, 1986
Information Notice No. NO 86-34: IMPROPER ASSEMBLY, MATERIAL SELECTION,
AND TEST OF VALVES AND THEIR ACTUATORS
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP)
Purpose:
This notice is being issued to advise recipients of potential problems
resulting from improper material selection and improper assembly procedures
for safety-related power actuated valves This information is applicable to
valves at the time of initial installation and during post-maintenance
reassembly or test Although both the cited facilities are BWRs, it appears
that PWRs may be equally vulnerable
It is expected that recipients will review the information for applicability
to their facilities and consider actions, if appropriate, to determine if
similar problems exist at their facilities However, suggestions contained
in this notice do not constitute NRC requirements; therefore, no specific
action or written response is required
Description of Circumstances:
In the recent past, River Bend and Shoreham have reported operational
problems and structural integrity problems with safety-related valves and
their actuators Both BWR facilities are currently in the startup and
initial operational period and have reported significant problems with
severe vibration of components and systems These vibrational problems
appear to exacerbate but not directly cause the identified valve problems
At Shoreham on September 25, 1985, when a valve in the RHR system was being
operated from the control room, a response feedback signal was not received
Local inspection disclosed that the bolts connecting the actuator to the
valve yoke were broken and the actuator was completely detached from the
valve The valve was a relatively small "mini-flow" valve
At River Bend on January 5, 1986, a similar event occurred involving a
20-inch main feedwater system containment isolation valve
8605090010
IN 86-34
May 13, 1986
Page 2 of 3
Discussion:
Licensee evaluation efforts at River Bend disclosed that manufacturer's
instructions on actuator valve assembly were generally vague and sometimes
the information furnished by the actuator manufacturer was contradictory to
that supplied by the valve supplier The 20-inch valve at River Bend has a
Limitorque SMB-4 actuator on a Velan valve The mounting capscrews are 1
1/4-inch diameter, high strength steel, threaded into the 35,000 psi
strength cast iron actuator housing The valve manufacturer specified
assembly torque of 1270 ft-lb The installed bolts did not have the normally
specified 1 1/2 diameters thread engagement, and as part of the failure
analysis, the licensee calculated that the preload stress on the engaged
cast iron threads would approximate the specified ultimate strength of the
cast iron The failure which allowed the actuator to become detached was the
capscrews tearing out of the cast iron Subsequently the licensee, the valve
supplier, and the actuator supplier agreed that a proper installation torque
for the valve-actuator combination would be 700 ft-lb
During reassembly of the 20-inch valve at River Bend, the licensee
discovered that the mating flanges did not come together at the specified
700 ft-lb torque value Review of the actuator vendor installation and
maintenance instructions disclosed a caution that final assembly torque
should be applied with the valve stem at about midstroke If the valve is
closed, the bolt preload may be transferred through the stem to the valve
disc When the valve is next opened, the bolts are relaxed and have low (or
no) preload Such a condition, particularly in the presence of high
vibration, will cause early fatigue failure of the bolts
Examination and testing of other valve assemblies at these sites showed some
with very high torque levels and others where some of the capscrews were
found to be broken The failures appeared to be caused by overload on some
mild steel, low strength bolts or fatigue for higher strength bolts In some
cases it appears that bolting material specifications were missing or not
adhered to Material traceability problems with bolts and other fastenings
are discussed in Information Notice No. 86-25, "Traceability and Material
Control of Material and Equipment, Particularly Fasteners" River Bend and
Shoreham have established specific programs to ensure that in the future
proper bolts are used and are properly torqued
IN 86-34
May 13, 1986
Page 3 of 3
No specific action or written response is required by this information
notice If you have any questions about this matter, please contact the
Regional Administrator of the appropriate regional office or this office
Edward L Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: James B Henderson, IE
(301) 492-9654
Attachment: List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, March 09, 2021