Edward Valves Quick Closing Equiwedge Isolation Valves Global Qualification V-Rep 85-2

Transcription

1 Edward Valves Quick Closing Equiwedge Isolation Valves Global Qualification V-Rep 85-2

2 By E. A Bake, Research Manager, Pittsburgh, PA, U.S.A. and Didier Thevenet, Technical Manager Rockwell Valves S.A., Unieux, France First Published 1985 ABSTRACT During the 1970 s, Rockwell devoted substantial resources to the development of the Equiwedge gate valve and a very special quick-closing actuator which permitted such valves to be used in critical applications in nuclear power plants. With the decline in construction of nuclear power plants in the United States, many would assume that such development work would have been curtailed. Instead, it has been carried forward to cover an extensive proof test of a size 30 (DN750) valve. Why? Global prospects for nuclear power production remain vital Nations with poor alternative energy resources forecast a continuing need for nuclear power. Technology cannot stand still, so development and qualification of improved valves for critical services had to continue. A major program was necessary to verify performance reliability of new valves built in Rockwell s plant in France for French nuclear power facilities. This program enhances the qualification base of these valves, providing even greater assurance of their reliability for applications in other nations all over the world. Introduction During the exciting decade of the 1970 s, many technical papers and articles were published on a variety of subjects related to the rapid growth of nuclear power production in the United States. Rockwell contributed many articles on the development of special valves for critical services in nuclear power plants. One critical valve application that demanded great attention was the Main Steam Isolation Valve (MSIV). First boiling water reactor (BWR) and then pressurized water reactor (PWR) power plants were required to include large valves that could be closed quickly (typically within 3 to 5 seconds) in main steam lines to isolate the reactor system under conditions that ranged in severity to include an instantaneous main steam line break. The primary function of the MSIV is to prevent or minimize the escape of radioactive material from the reactor or the containment vessel to the steam lines to the turbines, even if a severe accident should occur within the nuclear part of a power plant. Depending on power plant size, MSIV sizes ranged typically from size 16 through size 32 (DN 400 through 800). Until the quick closing isolation requirement emerged, valves in this size range usually had operating speed specifications measured in minutes, not seconds. Previous Rockwell publications (see References at the end of this article) have documented the progressive development of improved valves and actuators dedicated to the assurance of safe and reliable closure of MSIV S. Over about fifteen years, major test and qualification programs were necessary to back up the extensive design and analytical work that had gone into each type of valve/actuator combination. While nuclear power plant construction has declined sharply in the United States over the last five years, nuclear power is still necessary in many other nations with fewer alternative energy resources. In particular, France has maintained an active nuclear plant construction program, with emphasis on PWR plants, but also including work on the new Superphenix liquid metal fast breeder reactor (LMFBR). The Flow Control Division and its Rockwell Valves S.A. (RVSA) plant at Unieux, France, have participated actively in the continuing development of the nuclear power program in France, and, through this work, have maintained an active role in nuclear power activities in a number of other nations. As an illustration of the nature of ongoing work dedicated to global qualification of critical valves for nuclear power plants, this article will describe the extensive test program conducted in France on a size 30 (DN 750) Rockwell Equiwedge MSIV built at RVSA for Framatome-designed Electrocite de France (EDF) 1300 megawatt PWR stations. Background During the late 1960 s and 1970 s, nearly all MSIV development work was associated with specialized balanced disc globe valves. These valves had the advantage that pressure forces acting to assist or resist valve closure could be at least partially balanced. In early applications, this permitted fairly small actuators and control systems to be used to provide rapid but controlled closure of even very large valves. Controlled is a key word, because excessive closure speed of a large valve can be a hazard in itself. Uncontrolled valve closure speed may damage the valve or nearby pipe supports due to dynamic force reactions, and piping and other equipment 2

3 may be damaged by pressure surges. In later MSIV applications in PWR plants, quick closure was required with flow from either direction, and a reasonable degree of tightness was expected after closure with pressure at either side. These requirements combined to create a major challenge for non-symmetrical balanced-disc globe valves. The development of the Rockwell Edward Equiwedge gate valve presented an opportunity but also a new set of challenges. The basic Equiwedge valve design was introduced first for normal water and steam isolation services in conventional and nuclear power plants. Quick-closing applications were considered only after successful performance was proven in normal applications. Nevertheless, the symmetrical design of the Equiwedge was an attractive feature for MSIV applications where bidirectional performance was important. It was immediately recognized that better and more powerful stored energy actuators would be required to exploit the advantages of the Equiwedge gate valve, so the development of Rockwell-designed actuators was given high priority. Parallel research work was initiated to provide necessary wear and friction coefficient data on materials used for valve seats and guides, both to assure reliable valve performance and also to assure that actuator output forces could be selected to be certain that the valve would close under the specified conditions. Results of initial work, including testing of a size 16 (DN 400) valve with a prototype actuator were published in Reference 1 (1978). Reference 2 (1980) published results of an actuator qualification program conducted in accordance with IEEE-382 and described the initiation of further fullscale tests of a size 28 (DN 700) MSIV. Reference 3 (1982) detailed an extended program of tests on both size 16 and 28 valves to provide further proof that a fullscale valve would perform its safety-related function under an actual nuclear plant accident condition. While the previously reported test programs were very complete, an even more extensive program was required by Framatome and EDF to verify the performance of size 30 (DN 750) MSIV s furnished for new 1300 mega-watt stations. The size 30 valve to be built in France was to be essentially the same, except for end size to match large pipe, as the size 28 valve built and tested previously in the U.S.A. The valves were to use the same Rockwell A-290 actuator. Still, since there were minor design changes based on lessons learned in earlier work, the valves to be built at RVSA were not identical to the valves previously tested. The French customers were dedicated and conscientious in insisting on additional qualification testing to verify performance of the actual valves that they were purchasing under the specific plant performance conditions that applied to their installations. The first phase of testing to meet French requirements involved an additional test program in the U.S., employing the same size 28 valve and test setup described in Reference 3. EDF and Framatome representatives had witnessed many of the U.S. tests described previously. Like many other U.S. and international customers, they seemed impressed by the test programs that were undertaken independently by Rockwell; still, the French customers wanted more specific qualification relating to their own specific requirements. After receipt of the first production order from France, an additional test program was undertaken on the size 28 valve in the U.S., repeating tests previously performed but simulating pipe loading conditions closer to those specified for French plants. Except for the numerical values of the pipe loads applied during the tests, this test program was similar to that described in Reference 3. These tests were successful, but results will not be detailed here in view of the similarity with the tests described previously. The main program to be described here is that undertaken in France to verify the performance of the first large MSIV s built at RVSA to meet specific Framatome and EDF requirements. This program was designed to fulfill requirements of Framatome specifications, but detailed procedures were developed as a joint effort involving Rockwell engineers in the U.S. and France; procedures were specifically written to accommodate the instrumentation and test capabilities of the finest French test laboratories. Static Load Testing The purpose of this test series was to demonstrate that the Equiwedge gate valve and Type A actuator meet performance requirements while subjected to line rupture and seismic forces. The test program 3

4 was conducted with the intent of subjecting the valve to extremely high loads, simulating the high dynamic forces which a valve could experience due to a line rupture or a seismic event, and demonstrating that the valve would function during or after such loading. While previous tests in the U.S. had demonstrated ability of the size 28 (DN 700) valve to close under simulated line rupture conditions while simultaneously exposed to severe static loading, the U.S. tests could not simulate all possible loading combinations. The tests in France did not include simulated line rupture conditions, but they covered all specified loading combinations. Five combinations of loads were applied to the valve and upperstructure. Resultant bending moments on the body at times exceeded 2,150,000 ft-lb (2920 knm). Loads applied to the valve superstructure simulated static equivalents of dynamic loads as high as 22 g s. The valve used for this and following tests was a size 30 (DN 750) Rockwell Equiwedge gate valve with a Rockwell Model A-290 actuator. Both the valve and the actuator were built at the RVSA plant in Unieux, France. It was a serial production MSIV, except for adaptations for test facilities (e.g. end flanges, instrumentation, etc.). The primary goals of this test program were to demonstrate that: 1. The Valve has sufficient structural strength to withstand the forces and dynamic accelerations which are the immediate result of a line rupture. 2. The valve and actuator are capable of effectively closing during a seismic event after being subjected to the effects of a line rupture. F h1 F h2 SECTION A-A M v F a = AXIAL FORCE M h = HORIZONTAL BENDING MOMENT M v = VERTICAL BENDING MOMENT T = TORSIONAL MOMENT F h1 = F h2 = UPPERSTRUCTURE FORCE PARALLEL TO FLOW UPPERSTRUCTURE FORCE PERPENDICULAR TO FLOW F a A A M h Figure 1: Forces and moments applied in static load tests. 4

5 To accomplish these goals, valve stresses, deflections and significant performance parameters were measured during tests as follow: Baseline Test: The valve was closed with internal pressure but without external loads. Line Rupture Test: The valve was pressurized and subjected to four different load combinations which could exist following a line rupture. Seismic Test: After removal of each line rupture load combination, the valve was subjected to a load combination which could exist during a seismic event. The valve was then closed against internal pressure. TABLE 1 External Load Combinations In Static Load Tests (Refer to Figure 1) Horizontal Vertical Axial Bending Bending Torsional Upperstructure Load Force Moment Moment Moment Force Case F a M h M v T kn (kips) kn kn-m kn-m kn-m (kips) (ft-kips) (ft-kips) (ft-kips) Fh1 Fh (675) (620) (620) (738) (126) (675) (0) (1239) (738) (126) (0) (2065) (620) (738) (0) (0) (2065) (738) (58) (225) (1549) (0) (148) (40) (40) Note: F h1 shown for load case 5 is applied to the valve after application of load case 1, 2 and 3. F h2 shown for load case 5 is applied to the valve after application of load case 4. The external loading applied to the valve was intended to simulate the effects of expected loads from both the attached piping and the valve upper structure. The five types of loading considered were: Axial pipe load Horizontal pipe bending moment Vertical pipe bending moment Torsional pipe moments Valve upperstructure loads The directions of the above loads are shown in Figure 1, and their magnitudes are listed in Table 1. Four different load combinations were applied (Cases 1 through 4); after each combination was applied, loads were adjusted to the values shown for Case 5, and the valve was closed. Case 5 represented the specified seismic loading on the valve. During each test, the valve was internally pressurized with nitrogen over demineralized water at 1220 psi (84 bar). The valve was fastclosed under pressure, and the following valve performance data were continuously recorded: Stem position Actuator gas pressure Actuator hydraulic pressure Closing force Valve body pressure In addition, readings from strain and deflection gages were monitored during these tests to provide a correlation with applied loads. After each valve closure, a 30-minute seat leakage test with water was performed. All of these tests were performed at the RVSA plant at Unieux, France. The valve was mounted in the test fixture, which was designed in the U.S. but built in France. Test instrumentation was provided by a French firm, CETIM; test performance was directed by a combination of U.S. and French Rockwell engineers. Results of these tests agreed very well with predictions based on prior analyses and test data. Recorded valve closing times were very consistent and almost independent of applied pipe and superstructure loadings. Measured valve seat leakages were always well within current requirements for nuclear isolation valves. In all cases, the valve closed without hesitation or binding. There were no significant deviations in performance between baseline tests and the tests with high pipe and superstructure loads. Seismic and Resonant Frequency Search Tests While the A-290 actuator had been qualified independently in a separate dynamic seismic test reported in Reference 2, and other static tests conducted in the U.S. and France left little doubt as to the dynamic integrity of the valve/actuator combination, an additional specific test program was planned and conducted in France to demonstrate the performance of the complete size 30 (DN 750) valve assembly built at RVSA. These tests were performed 5

6 through contract with SOPEMEA, a laboratory near Paris. The laboratory was audited by U.S. and French Rockwell engineers and was found to have excellent capabilities. A Rockwell test procedure was developed to utilize the SOPEMEA capabilities to their maximum (the size 30 MSIV was the heaviest piece of equipment ever tested on their dynamic shake tables). Before beginning dynamic seismic testing, a resonant frequency search test was conducted on the valve assembly. Accelerometer data from various locations was used for a model analysis to determine resonant frequencies over a range from 1 to 50 Hz. Low input accelerations were applied and response accelerations and phase relationships were monitored. Tests were performed with the valve both open and closed. A lowest measured natural frequency was determined to be 30.9 Hz, which was below the desired minimum of 33 Hz. However, it was proved that this value was affected by some flexibilities in the test fixture and setup, not by the valve itself. When the effects of test fixture flexibility were removed, it was shown that the lowest natural frequency of the valve assembly was 36 Hz. The most severe test conducted at SOPE- MEA was actually a series of biaxial multifrequency tests conducted on their largest shake table. The valve is cradled in the Rockwell-designed test fixture. This fixture had to be designed carefully to insure sufficient rigidity that test table inputs would not be dynamically amplified excessively by valve/test fixture response. Excessive amplification could damage the shake table or produce spurious inputs to the valve on test. Nevertheless, a degree of flexibility was purposely designed into the test fixture to allow some dynamic amplification in order to give the most severe possible test, considering the mass of the valve and the available input accelerations from the table. These tests included four multifrequency tests, two representing OBE (operating basis earthquake) and two representing SSE (safe shutdown earthquake) conditions. During these tests, the valve was pressurized with nitrogen to 1220 psi (84 bar). Each test duration was 30 seconds, and the valve was energized to perform a fast closure at approximately 15 seconds from the start of the test. During these tests, valve accelerations exceeded 2.0 g s at frequencies up through the zero period acceleration (ZPA) range. This acceleration was determined by table limitations. Prior actuator dynamic tests and valve/actuator static loading tests were actually more severe (in terms of peak loads and stresses imposed on the assembly), but these dynamic tests of the valve/ actuator combination nevertheless gave additional assurance of the reliability of the combination. Dynamic testing proves that local resonances in the structure will not cause a failure of any vital subcomponent. This is something that cannot be verified in static testing, and it is particularly important in the case of a complex assembly. Since the valve closed reliably in each case when it was commanded to do so during the random bidirectional multifrequency tests, these tests demonstrated the successful performance of the entire valve/actuator combination showing that all vital subcompacts functioned properly. Hot Functional Testing Hot functional testing had previously been conducted on a size 16 (DN 400) Equiwedge gate valve, as reported in Reference 1. However, as part of the qualification of the MSIV s for the EDF 1300 megawatt PWR stations, a full scale hot functional test was conducted on a complete size 30 (DN 750) production valve with a Rockwell A-290 actuator. Since the function of the MSIV is to close quickly when required at any time during the life of a nuclear power plant, it was necessary to show that the Rockwell Equiwedge gate valve and Type A actuator can operate reliably and perform their required function under the normal service conditions in a PWR. A procedure was developed, and a test program was conducted at CETIM laboratories in Nantes, France. The valve used for this test was the same as had been used for the other tests described above. The test arrangement capped pipe extension were connected at each end of the valve, and the valve and pipes were partially filled with water. Heated oil in jackets outside the pipes generated saturated steam inside the test assembly. The test procedure required that the valve/actuator combination: Perform at least 400 full-stroke, fast closures using both actuator hydraulic 6

7 manifolds while the valve assembly is internally pressurized to 1040 psi (72 bar) with steam at 547 degrees F (286 degrees C). Be subjected to four thermal transients, one after each 100 full fast closures discussed above. Each transient was to consist of (1) closing the valve at full pressure and temperature, (2) allowing the assembly to cool to below 122 degrees F (50 degrees C), (3) performing a leakage test, (4) reopening the valve, and (5) reheating to restore full pressure and temperature, Perform at least 400 exercise cycles, consisting of closing the valve 10% from its full-open position using both actuator manifolds, again under full pressure and temperature conditions. During these tests, instrumentation recorded the actuator gas pressure, actuator hydraulic pressure and temperature, steam pressure and temperature, external valve body temperature, and valve closing times. Generally, the valve performed very well throughout this testing. During the first 200 of the full fast closure cycles, an anomaly was observed; this required extensive analyses of test data (by engineers in France and the U.S.A.) before the problem could be understood and corrected. After 65 full fast closures without any performance flaws, the valve sporadically performed closures that exceeded the 5-second maximum time limit. It was ultimately determined that the problem was created by excessively high actuator solenoid valve temperatures, which in turn were caused by excessive hydraulic fluid temperatures. The heat buildup in the hydraulic fluid was traced to the energy input from the pump in the hydraulic system. Since the pump had to function continuously during valve openings between each of the fast closure cycles, and since the valve and actuator did not have to be designed for continuous, repeated cycling, the high hydraulic fluid temperature condition which produced the anomaly was not representative of a condition that would exist in an actual valve actuator in a nuclear power plant. Once the cause of the anomaly was found, after 200 cycles of which 40 exceeded the time limit, the valve and actuator cycle rate was controlled to limit the increase in hydraulic fluid temperature to 72 degrees C (163 degrees F); this is still greater than the fluid temperature expected under any realistic condition when the valve would be required to close. After the cycle rate was controlled, there was no recurrence of the slow closure anomaly. However, because of the incidents during the first 200 cycles in the test, they were not counted; the fast closure cycle test program was increased to 600 cycles, and there were no further flaws in valve or actuator performance. The thermal transient and exercise cycling tests likewise produced no problems. There was no measurable seat leakage after each thermal cycle, and there was no observed stem packing leakage while the valve was hot or cold (no packing gland adjustments were made throughout the tests). After each cooldown, the valve opened without any binding or excessive force requirement. In summary, the valve operability was demonstrated under functional conditions as severe or more (in terms of frequent cycling) than those which will be encountered in an actual PWR nuclear power plant. While there was a performance anomaly, it was traced to a test condition that was not representative of actual service conditions; after correction of the test procedure, the valve and actuator performance was flawless. Post-Test Inspection Following completion of all of the tests described above, the test valve was returned to the RVSA plant at Unieux for final tests and inspection. Seat leakage tests were conducted, and no significant leakage was noted. The valve and actuator were then disassembled for a detailed inspection with Framatome and EDF witnesses present. All wearing surfaces were checked carefully, and visual inspection revealed no damage. Dimensional inspection showed no unusual wear on either valve or actuator parts. Liquid penetrant inspections were performed on all guiding and seating surfaces, and these examinations revealed no indications at all. In general, the valve condition was excellent, showing little evidence of degradation attributable to the severe tests that had been conducted. With the agreement of EDF and Framatome, the test valve was refurbished for shipment to one of the French 1300 Mw nuclear plants. 7

8 Conclusion The MSIV test program described in this article represents probably the most extensive qualification program ever undertaken on a valve of such a large size, at any time, at any place in the world. The fact that this program was conducted in France is an indication of the global nature of the nuclear power business today. Rockwell was able to participate only because of its manufacturing and engineering base established at RVSA in Unieux, France. While this test program was specifically designed to meet the requirement of Framatome and Electricite de France for qualification of MSIV s for new 1300 mw power plants, it has global significance because of the continuing development of nuclear power installations in many other nations. While this program was indeed very complete, it does not stand alone. Prior Rockwell qualification programs in the U.S. provided many important underlying foundation stones. Earlier Rockwell tests on a valve just larger than half the scale permitted some tests that were more severe (only because the valve size was more manageable). An IEEE 382 qualification test on a Type A actuator also provided certain testing that was more severe than could be performed on a complete valve/actuator combination of the size in question (considering the state of the art and available test facilities). Finally, the flow interruption testing previously conducted in the U.S. provided a demonstration of the capability of half and full-scale MSIV s to close under simulated line rupture conditions, even with the valve subjected to loading conditions similar to those that might exist in an actual nuclear power plant. The test program conducted in France enhanced the qualification base of the Rockwell Equiwedge MSIV and Type A actuator through the performance of additional full-scale tests, eliminating the requirement for large extrapolations between test results on smaller valves and the full-scale valves actually used in critical services in nuclear power plants. Many valves have been accepted for use in plants around the world based on such extrapolations; at least in the case of the Equiwedge MSIV and Type A actuator, we are pleased that the more recent full scale tests have produced no data that would compromise confidence in valves previously furnished based on extrapolations. Nevertheless, the full scale tests serve to enhance the confidence that can be placed in all valves furnished in the future. Acknowledgements The authors wish to acknowledge the many contributions made by others to the planning and performance of the tests described in this article. In particular, recognition is due to J. B. Gallagher (Pittsburgh), Y. Portefaix (Unieux), and G. Rouchouze (Unieux) who devoted many long days, nights, and even weekends auditing, observing, and writing reports on the tests conducted at Unieux, Paris, and Nantes. In addition, we wish to acknowledge the contributions and suggestions of many people (too numerous to list here) from CETIM, SOPEMEA, Framatome, and EDF who were consulted during the planning of the tests and the evaluation of data. References 1. E. A. Bake and R. L. Clapper, QUICK- CLOSING ISOLATION VALVES THE EQUIWEDGE ALTERNATIVE, Rockwell Technical Article V-Rep E. A. Bake, THE ROCKWELL TYPE A STORED ENERGY ACTUATOR- DEVELOPMENT AND QUALIFICATION, Rockwell Technical Article V-Rep E. A. Bake and J. B. Gallagher, QUICK-CLOSING EQUIWEDGE- ISO- LATION VALVES ONGOING QUALIFI- CATION, Rockwell Technical Article V- Rep

9 Flow Control Division Edward Valves Flowserve Corporation has established industry leadership in the design and manufacture of its products. When properly selected, this Flowserve product is designed to perform its intended function safely during its useful life. However, the purchaser or user of Flowserve products should be aware that Flowserve products might be used in numerous applications under a wide variety of industrial service conditions. Although Flowserve can (and often does) provide general guidelines, it cannot provide specific data and warnings for all possible applications. The purchaser/user must therefore assume the ultimate responsibility for the proper sizing and selection, installation, operation, and maintenance of Flowserve products. The purchaser/user should read and understand the Installation Operation Maintenance (IOM) instructions included with the product, and train its employees and contractors in the safe use of Flowserve products in connection with the specific application. While the information and specifications contained in this literature are believed to be accurate, they are supplied for informative purposes only and should not be considered certified or as a guarantee of satisfactory results by reliance thereon. Nothing contained herein is to be construed as a warranty or guarantee, express or implied, regarding any matter with respect to this product. Because Flowserve is continually improving and upgrading its product design, the specifications, dimensions and information contained herein are subject to change without notice. Should any question arise concerning these provisions, the purchaser/user should contact Flowserve Corporation at any one of its worldwide operations or offices. For more information about Flowserve Corporation, contact or call USA FLOWSERVE CORPORATION FLOW CONTROL DIVISION Edward Valves 1900 South Saunders Street Raleigh, NC USA Toll- Free Telephone Service (U. S. and Canada) Day: After Hours Customer Service US Sales Offices Phone: Facsimile: Facsimile: Visit Our Website Flowserve Corporation, Irving, Texas, USA. Flowserve and Edward Valves are registered trademarks of Flowserve Corporation. V-Rep /03 Printed in USA