ML20214H927
| ML20214H927 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 07/20/1986 |
| From: | Marston T, Mcelhaney K, Merrick E ELECTRIC POWER RESEARCH INSTITUTE, TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML20214H850 | List:
|
| References | |
| NUDOCS 8612010094 | |
| Download: ML20214H927 (5) | |
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.E ATTACHMENT B M PC-Vct.Es
- Report No. C010603 -
Improved Technology For Critical Bolting Applications i .
presented at THE 1986 PRESSURE VESSELS AND PIPING CONFERENCE AND EXHIBITION CHICAGO, ILLINOIS ,
JULY 20 - 24,1986 sponsored by THE METAL PROPERTIES COUNCIL INC.
jointly with THE ELECTRIC POWER RESEARCH INSTITUTE THE PVP MATERIALS AND FABRICATION COMMITTEE, ASME editedby E. A. MERRICK TENNESSEE VALLEY AUTHORITY
!.' M.PRAGER THE METAL PROPERTIES COUNCIL, INC.
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THE AMERICAN SOCIETY OF MECH ANICAL ENGINEERS l '
United Engineering Center 345 East 47th Street New Y,ork, N.Y.10017 8612010094 861117 i PDR ADOCK 05000327 P PDR
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OVERVIEW OF ISSUES RELATED TO NUCLEAR BOLTING APf'LICATIONS E. A. h4erriek Tennenee Valley Authority Knouville. Tenneuse T.U.W4ntwo Electric Power Re.sarch Institute Palo AIto.Callfornia K. L. Mstm emey Tennessee Vaftey Authority
, Knouville, Tennessee ,
ABSTRACT The service history of bolting is good; however, e during the past sever,al years, the U.S. Nuclear This paper will furnish information on the failure industry has expertenced an increase in the number of experience, an overview of the AIF program, summarize reported bolt failures. Failure or degradation has some of the results of the work performed, and provide been reported in several generic areas which may impact recommendations on the issues, plant safety or reifability. The generic bolting applications where failures or degradation have been BOLTING EXPERIENCE IN U.S. NUCLEAR PLANTS experienced by the Indust y include pressure boundary manways and flanges, component supports, and There are millions of bolts used in commercial nuclear plants.
embedments, as well as bolting used in component In each unit, two or three thousand of internals. An aggressive program to assure the these are used in the primary reactor coolant pressure continued integrity of bolted joints is nearing boundary components, their internals, and supports completion. While the number of reported bolting fallu,es has increased over recent years, there is some evidence INTRODUCTION which indicates that the increase is a function of th increased number of installed bolts. It appears also This paper updates reference (1), previously that as plant maintenance personnel gain expertence presented at the 8th International Cdnference on during early plant operation, the incidents of leaking Structural Mechanics in Reactor Technology, in joints and reported failures decrease. The success Brussels, Belgium, November, 1985. The Atomic history of fasteners is excellent when compared to the Industrial Forum (AIF), in conjunctior with the number of failures.'
Electric Power Research Institute (EPRI) The Materials Properties Council, Inc. (MPC), the utilities and other The U.S. Nuclear Regulatory Commission (NRC), in industry organizations, responded to the bolting need NUREG-0933, designated the Generic Safety Issue 29 as a by formulating a comprehensive program to address the high priority issue " Bolting Degradation or Fatture in issues. The goals of this program are to provide Nuclear Power Plants" [2), and indicated its concern:
"There are a umerous bolting applications in nuclear definition of the critical issues involved and to power plants ...."
consolidate industry resources in order to supply an appropriate response to the bolt integrity question.
Work includes corrosion and fracture mechanics studies, "The number of bolting-related incidents has non-destructive examination (NDE) development, codes increased ... therefore, there is increased concern and standards activities, and maintenance and training regarding the integrity of the primary pressure tasks. Technology exchange has been effective in boJndary in operating nuclear power plants and the
- asturing increased attentjen to the behavfor of bolting reliability of the component support structures in U.S. nuclear plants. Nothing has been discovered to following a LOCA (loss of coolant accident) or ;f earthquake."
raise concern regarding bolting integrity, primarily due to the redundant nature of bolting in critical closure joints.
There are four distinct bolting issues grouped by application and apparent cause as described below:
1
l Grovo 1 - Degradatitn er failure of pressure program and exaaines b2th pressure brundary and boundary bolting ilue to general borated water , structural support bolted connections to assess the
. corrosion (wastage or erosion / corrosion). The degradation of the overall bolted connection. The cause of ,fallure is attributed to high rates'of consequences of joint degradation in terms of leakage corrosion of low alloy steels in the presence of and leak-before-break margin for pressure boundary borated water. This is primarily a maintenance joints, and support stiffness and faulted load problem. . condition margin for structural support joints, is being examined. This approach is an alternative to Grouc 11 - Degradation or failure of pressure individual fastener integrity assessment. Since one of
- boundary bolting due to stress corrosion cracking the principal design features of a bolted connection is
($CC). The cause of these failures can be its stru.ctural redundancy, this alternative seems more attributed to an undesirable combination of realistic, provided that acceptance criteria for both stress, environment, and material condition. safety and reliability can be M t.
Generally, these types of failures are associated with leaking gaskets or the use of certain The ultimate goal is to use the generic analytical lubricants and/or sealants. Failures can be methodologies developed by EPRI for bolted joint eliminated through proper use of tensioning integrity assessment, supplemented by Industry techniques, lubricants and sealants. experience and data - both nuclear and non-nuclear - to demonstrate the safety margins in both pressure Group til - Degradation or failure of internals boundary and structural joints, and to recomend bolting due to fatigue and stress corrosion realistic inspection or maintenance programs for cracking. Fallures are generally related to utilities, materials, heat treatment, forming technique, high steady-state stresses, or cyclic service. CURRENT ACCOMPLISHMENTS Failures can be eliminated by. alternate materials ,
selection and design modifications. The integrated bolting program is scheduled for completion in May 1986. Currently, most of the Grovo IV - Degradation or failure of supports and identified deliverables are available. The most embedmont bolting due to SCC. Failure can be notable are: overall bolting failure and success attributed to a combination of high stress, rates, fracture mechanics (FM) assessment, generalized susceptible material condition, and a wet closure integrity (leak-before-break) model, bolt-up environment. They can be eliminated by attention procedure guidelines, thread lubricants evaluatien, and to pretension and materials.
- mechanical maintenance training tapes.
Failure groups I, II, and IV above have been Overall Bolts Failure probabilities addressed generically under the auspices of a joint AIF/MPC Task Group on Bolting. Pressure boundary An experience base of bolt failures and/or bolting (Groups I and II) has a greater influence on problems has been generated and analyzed. Of the five system integrity and the highest priority in the types of pressure boundary closures studied, Industry program. Internals bolting (Group !!!) is specifically pressurizers, steam generators, reactor being effectively addressed by compenent vendors and coolant pumps, and valves, steam generator m eway owners' groups and is not being considered generically. bolting exhibited the highest total reject rate. The Supports /embedmont bolting (Group IV) presently has a rejectrateGrmanwayboltingattributedtowastage secondary priority in the industry program. The and the rate for cracking was 2.3 x remainder of this paper will focus on the pressure wah2.2x10 10 .
boundary and supports /embedmont generic program. '
Fracture Mechanics Assessment GENERIC INDUSTRY PROGRAM ON PRES 5URE BOUNDARY AND SUPPORTS BOLTING The initial technological thrust regarding bolted joint integrity was directed toward the evaluation of The question of fastener integrity is very complex individual fasteners using probabilistic fracture and involves many disciplines (e.g., metallurgy, mechanics analysis. As with any FM evaluation, loads, fracture mechanics, mechanical and corrosion properties, and crack sizes had to be known. The NDE engineering) and activltles such as bolt tension requirements for the FM based approach exceeded the control, NDE, design, spectftcations and standards, state-of-tha-art capabilities. It soon became evidert manuf acturing, and quality assurance / control.- Research that a more prudent and simpler approach to boited activities have focused on understanding, identifying joint integrity assessment was possible and desirable, and implementing solutions to the issues. The research Nevertheless, the fracture mechanics research has
- work on bolting is in three key areas - structural greatly improved the state of information regsrding integrity analysis (including
- nondestructive bolts and other threaded fasteners. Cipolla (3) has .t examination) corrosion studies, and maintenance studied the application of fracture mechanics to improvements.
fasteners, and has presented a simplified analysis method for apprortsating the stress intensification
, EPRI is completing a " Generic Bolted Joint factor for an elliptical surface crack at the root of a Integrity" project which integrates the industry thread. This approach will be integrated into design, ;
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Leak T1chtness Generailred Jo' int Intearity Model Thetightness.
Its leak ecst desirable attribute of a bolted joint is Probably the most significant contributton of the A recent NRC survey (5) integrated botting program is the development of the demonstrated that over 90% of all bolted connections in generalized joint integrity model, wherein the closure the primary pressure boundary are leak tight. The key la modeled accurately, incorporating the load shedding elements that contribute to leek tightness are:
and redundancy inherent to bolted connections. With adequate joint design, proper cleanliness, proper the evaluation based upon the overall closure, the gasketing, uniform and sufficient preload. It should details of individual fastener degradation are not be noted that all but the first element are controlled required. As a result, the complexity of the by station maintenance. The integrated bolted joint calculations and data burdens are substantially reduced program addresses two aspects; the uniformity c1 and many of the areas of greatest uncertainty are preload and an evaluation of thread lubrfcants. The avoided. findings indicate that a joint can be prepared with Elther wastage or stress corrosion cracking can be accommodated in the model. Equally important is uniform preload in the bolts even with simple torque the fact that the NDE requirements of the genera 11 red wrenches, if particular attention is paid to bolt-up.
- joint integrity model are well within the Recommendations include stepped torque values with state-of-the-art capabilities. multiple passes and verification of proper preload by ultrasonic or other method. Studs are preferred over The philosophy behind the model is analogous with bolte for many appilcations. Leak tightness can be the leak-before-break philosophy used in FM evaluations assured with proper care.
of other pressure boundary components. The steps required to achieve the desired result, t.e., A second task evaluates thread lubricants. The demonstrate that a degraded joint (due to wastage, work includes laboratory and field tests and indicates cracking, etc.) has ample margin against catastrophic > that the nickel based lubricants can be substituted for failure when the leakage from the joint reaches levels those using molybdenum disulphides (MoS ) without that have a very high probability of detection. modifying the nut factor and, thus, the 2torque values, include: knowledge of the degree of load shedding to A recomendation is made to not use these MoS 2
-based adjacent fasteners due to fastener degradation, lubricants when dissociation is even suspectes, i.e.,
knowledge of the joint opening profile accounting for when the joint will be exposed to water and high gasket spring back and flange distortion, realistic' temperatures. Reviews by Rungta and Majumdar (2) also calculation of leak rates through the degraded joints, included work in this area. The Materials properties margin demonstration in load-carrying capability of
- Council has done extensive studies on various thread degraded joint and margin definition. lubricantsandtheircontributiontoSCC[5).
l This philosophy was initially successfully applied RESOLUTION OF THE GENERIC ISSUES to a steam generator manway cover to show its load carrying capability. Example calculations indicate Industry resolution of the generic issues is that for a typical sixteen bolt joint, about three scheduled for 1986, and is planned to be accomplished bolts must fail before a " detectable" leak (10 gem) is utilizing AIF and EPRI guidelines, and American Society generated. The stresses in the adjacent bolts increase for' Testing and Materials (ASTM) and American Society by less than 30% (well below the yield strength of the of Mechanical Engineers (ASME) standards activtties.
bolts).
On September 20, 1984, the Institute of Nuclear Cipolla and Proctor [4] continued this work and power Operations (INPO) Issued 50ER No. 84-5 entitled.
have proposed a method to establish leak rate margins " Bolting Degradation or Failures in Nuclear power Plants." INPO conducted an independent review of the and nondestructive examination limits for bolting materials comonly used in primary pressure boundary issues and arrived at conclusions which reinforced closures. Analysis methods for determining the previous AIF recomendations. The 50ER serves to structural behavfor and leakage of a balted closure for highlight and provide a " road map through the issues to various amounts of bolt degradation were refined and utilities." The INPO SOER depends heavily on AIF/MPC and EPRI programs, calculations completed for several additional essential components (check valve flanges, reactor coolant pump main flange, and pressurizer manway flange). Initial ASTM comittees, having responsibility over results indicated that leak rates between 1 gpm and 10 bolting material specifications, have reviewed gpm are possible without compromising the closure specifications under their jurisdiction to determine integrity. These analyses'should provide sufficient need for modifications based on comercial nuclear
' basis for recomending rev,isions to present Code NDE industry experience and input from the industry requirements. Use of leak-before-break criterion is program. Several specifications have already been, considered an effective method of assuring closure modified. At the November 1985 meeting of the ASTM
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integrity while reducing demands on NDE. These Subcomittee F16.02 (on structural bolting), it was calculations clearly demonstrate the degradation recomended that a new Subcomittee be formed within g
tolerance of bolted connections. ASTM to rationalize ASTM structural bolting QA requirements. This recomendation is under consideration by Committee F 16.
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EPRIisdevelodingtworeferencemanualsto industries expected to benefit from BTC technology address how to identify safety-related joints, includes the fastener, chemical, petroleum, aerospace, selection of appropriate procedures, insembly and nuclear power, automotive and manufacturing industries.
dissembly procedures using various methods, inspection and verification of previous procedures to solve problems which have occurred in the past. These CONCLUSION manuals will serve as a repository of useful Information learned from EPRI analytical and The purpose of the AIF/MPC Task Group was to experimental programs and, when published, they will develop and execute the AIF program for resolution of give the utility industry guidelines for bolted joints. generic bolting issues. Since this has been
- Several utt11tles are already using drafts of these accompitshed and all work is nearing completion, the guidelines in their efforts to enhance their bolting Task Group was disbanded in November 1985. The AIF program, it is believed that the bolting reference Subcommittee on Materials Requirements will be manuals will satisfy the industry's need for guidance available to handle any residual problems, in this area.
Plans are to develop two comprehensive documents EPRI is developing an Interpretive p' aper on pressure boundary bolts and structural bolts for use cxplaining the current ASME Boller and Pressure vessel by utilities. These would be considered the final Code Rules for Bolting. ANSI /ASME Section !!!, Nuclear products from the program. They will be approved by Power Plant Components, has been reviewed and the AIF Subcommittee on Materials Requirements and recosenendations have been developed for clarification distributed to utilities and the NRC for their use and cnd ampilfication of existing requirements. ANSI /ASME information in resolution of the issues.
Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, is considering recommendations The bolting issue is an example of a cooperative to rationalize bolting inspection requirements to focus effort between the utt11tles, the vendors, and the NRC cn "at-risk" applications in service sensitive lines. fo resolve a problem with potential safety Results from the EPRI generic joint integrity program signift:ance. Shortcomings in design, material will be used as input to develop empirical rules for specification, procurement, and maintenance were inspection frequency and acceptance requirements. NDE identified. Fixes to alleviate concerns regarding rules will be modified to accomodate recent pressure boundary bolt integrity were formulated and developments in NDE technology. are being implemented. The implementation of the recommendations will result in improved plant An EPR1/MEAC workshop was held in November 1985 availability and reliability, with reduced maintenance, in Charlotte, NC to enhance technology transfer. This man-rem exposure, and inspection costs.
workshop was aimed primarily at informing maintenance &
personnel of the issues and alerting them to the REFERENCES practical tools being developed in this program to aid I 1
them in achieving leak free joints. The workshop was a 1. Merrick, E. A. and Marston, T. U., " Industry tremendous success with participants agreeing that additional workshops would be useful.
Response to the Issue of Bolting Degradation or Failure," Paper No. 06/1, Presented at SMIRT/8, j
P E;
Brussels, Belgium, August 1985.
The Bolting Technology Council was formed to provide opportunttles for threaded fastener and tool 2. NUREG-0933, "A Prioritization of Generic Safety users to engage in ecoperative activities. As stated Issues," Safety Program Evaluation Branch, in their Bylaws, the purpose of the Counct) is "to Olvision of Safety Technology, U.S. NRC, December sponsor research; to recomend practices; to act as a 1983, New Generic Issue 29, "8olting Degradation clearinghouse for information; and to provide education or Failure in Nuclear power Plants."
concerning the art and science of the installation and behavior of mechanical fasteners and their interaction 3. Cipolla' R. C., " Stress Intensity Factor with the joints they are used in." Approximations for Semi-Elliptical Cracks at the Thread Root of Fasteners, Improved Technology for Although a large number of engineering and Critical Boltina Applications, ASME Ptessure industrial societies have been organized to deal with Vessel and Piping Conference, Chicago, July 198f.,
various aspects of fasteners and joints, very little attention is paid to the important job of installing 4. Cipolla, k. C. and Proctor, R. R., " Application of fasteners correctly. It is therefore the intent of the Leak-Before-Break Acalysis Methods to Primary Council to complement rather than duplicate the work of System Bolted Closures," Improved Technoloav for_
cthers. Critical Boltino Applications, ASME Pressure Vessel and Piping Conference, Chicago, July 1986.
lhe Bolting Technology Counell is affiliated with The Materials Properties Council, Inc. (MPC), formerly 5. U,$. Nuclear Regulatory Comission NUREG 1095, The Metal Properties Council. Specific areas of " Evaluation of Response to IE Bulletin 82-02,
, interest include achieving, maintaining and post- Published May 1985, assembly changes in preload, behavior of the joint-
- 6. The Metal Properties Council, Inc., " Progress under load, and joint failure modes. A partial list of Reports and Background Technical Information on MPC Bolting Task Group Study of Lubricants and
- 4 Sealants,", December, 1985. .
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