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1、Corrosion Fatigue of Water-Touched Pressure Retaining Components in Power Plants TR-106696 Final Report, November 1997 Prepared by Y.S. Garud S.R. Paterson Aptech Engineering Services, Inc. 1282 Reamwood Avenue Sunnyvale, CA 94089 R.B. Dooley R.S. Pathania Electric Power Research Insitute 3412 Hillv
2、iew Avenue Palo Alto, CA 94304 J. Hickling Corrosion and Materials Consultancy Taufkirchen, Germany A. Bursik Stuttgart University Stuttgart, Germany Prepared for Electric Power Research Institute 3412 Hillview Avenue Palo Alto, California 94304 EPRI Project Managers R. B. Dooley R. S. Pathania Stra
3、tegic Research and Development DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES THIS REPORT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE
4、 ORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM: (A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I) WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS REPORT, INCLUDING MERCHANTABILITY AND FITNESS
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7、T PREPARED THIS REPORT Aptech Engineering Services, Inc. Electric Power Research Institute Corrosion and Materials Consultancy ORDERING INFORMATION Requests for copies of this report should be directed to the EPRI Distribution Center, 207 Coggins Drive, P.O. Box 23205, Pleasant Hill, CA 94523, (510)
8、 934-4212. Electric Power Research Institute and EPRI are registered service marks of the Electric Power Research Institute, Inc. EPRI. POWERING PROGRESS is a service mark of the Electric Power Research Institute, Inc. Copyright 1997 Electric Power Research Institute, Inc. All rights reserved. iii R
9、EPORT SUMMARY Corrosion fatigue continues to be the damage mechanism responsible for the largest percentage of availability loss in fossil-fueled power plants. Currently, it is of less significance in nuclear plants, but it is perceived to become more important as plants age. This report contains an
10、 overall review of corrosion fatigue across the broad range of equipment, conditions, cycle chemistries, temperatures, and pressures. Background Since it is the leading single cause of availability loss in fossil-fueled power plants, EPRI has conducted extensive work on corrosion fatigue in waterwal
11、l and economizer tubing (TR-100455-V1-5). However, almost no water-touched component has been unaffected by corrosion fatigue. Corrosion fatigue also has occurred in a number of key nuclear plant components. Thus, corrosion fatigue is clearly a worldwide problem, but to date there has not been a com
12、prehensive study to collate the commonalities in terms of mechanism, materials, morphologies, laboratory testing, and other key variables. Objectives To consolidate useful knowledge on corrosion fatigue in water-touched pressure retaining components from power and other energy producing industries,
13、worldwide; and, to develop an R B, mounted on deaerator; C, Spray type deaerator; D, adjacent deaerator (Bulloch, 1991). 2-2 Figure 2-2 Deaerators are used to strip oxygen from feedwater before entering the boiler. Type shown uses steam to break up water into spray or film, then force out dissolved
14、gases. Interaction in spray area does 95% of the work, last 5% takes place in tray section 2-3 Figure 2-3 Typical design details of a direct contact deaerator. 2-4 Figure 2-4 Location of a direct contact deaerating heater in a once-through supercritical cycle (Bulloch, 1991). 2-5 Figure 2-5 Typical
15、deaerator heating compartment and feed water storage vessel. The head to shell weld is especially susceptible to corrosion fatigue damage (Bulloch, 1991). 2-8 Figure 2-6 Installation of an on-load electrochemical potential monitoring device in a deaerator storage tank (Bulloch, et al., 1995). 2-9 Fi
16、gure 2-7 Effect of load changes on the water chemistry and electrochemical potential of a 20MW peat-fired boiler (Bulloch, et al., 1995) 2-10 Figure 2-8 ECP and oxygen levels of an off-on load transient. Note that the electrochemical potential seems to be most strongly influenced by the oxygen conte
17、nt of the water entering the deaerator (i.e., after the condenser) (Bulloch, et al., 1995). 2-11 Figure 2-9 Effect of dissolved oxygen on ECP (Bulloch, et al., 1995). 2-12 Figure 2-10 Effect of hydrazine transient. During the test run the continuous hydrazine feed was purposely cut-off and switched
18、on again. This resulted in an increase in electrochemical potential by approximately 60 mV SHE and a reduction in conductivity and pH (Bulloch, et al, 1995). 2-13 Figure 2-11 ECP of hot and cold starts. It was found that by keeping the deaerator water hot (during a hot start) that the electrochemica
19、l potential (i.e., the likelihood of localized corrosion or environmental cracking) was significantly reduced when compared with a cold start (Bulloch, et al, 1995). 2-14 Figure 2-12 Typical feedwater heater which includes a large tubesheet to cylinder radius to minimize the differential thermal exp
20、ansion stresses during transients (Yuba.www). 2-15 Figure 2-13 Use of a large tubesheet to cylinder radius minimizes thermal stresses at the tubesheet vessel wall junction (Yuba.www). . 2-16 xii Figure 2-14 HP feedheater tubesheet, maximum stress zones (marked by circle and oval). By slightly modify
21、ing the shape of the perforated zone, it was possible to significantly reduce the stresses and thus extend the service life (Sonnenmoser, et al., 1983). 2-16 Figure 2-15 HP feedheater tubesheet, temperature distribution at t = 35 min after the temperature T of the operating medium has been increased
22、 by 200C in 30 minutes. The isotherms are at 1C intervals. The surface temperature of the metal in the perforated area changes practically with that of the operating fluid due to the high heat transfer coefficient, large heating surface, and low heat capacity. The underlying metal temperature on the
23、 other hand changes only very sluggishly- -leading to large thermal shock stresses (Sonnenmoser, et al., 1983) 2-17 Figure 2-16 Hoop stress in tube inlet rim due to step changes in fluid temperature (Sonnenmoser, et al., 1983). Note: 2-18 Figure 2-17 Corrosion fatigue crack removed from a fossil-fue
24、led power plant feedwater pipe. The extensive corrosion in this funnel shaped crack suggests that on- or off- load corrosion is a significant factor in the damage. (MAG: 25X). 2-20 Figure 2-18 Corrosion fatigue crack removed from a fossil-fueled power plant feedwater pipe (MAG:100X). . 2-21 Figure 2
25、-19 Enlarged view of crack in Figure 2-18 (MAG:200X). 2-22 Figure 2-20 Cross section through economizer inlet header and tubes showing stub tube failure location and longitudinal pattern of cracking (EPRI TR-100455) 2-23 Figure 2-21 Typical thermal fatigue cracking morphology (EPRI TR-100455) 2-24 F
26、igure 2-22 Photomicrograph showing transgranular oxide filled economizer inlet header crack start at pit. x100 (Hunter, et al., 1986). 2-25 Figure 2-23 Temperature, pressure, flow rate excursions for economizer inlet header (Hunter et al., 1986) 2-26 Figure 2-24 Cracks in a tube bend as the result o
27、f thermal alternating straining and corrosion. Operation period: about 100,000 hours. Position of damage: below the upper drum (Spahn, 1972: NACE-2). 2-27 Figure 2-25 Cause and effect diagram for corrosion fatigue of waterwall tubing (adapted from Dooley and McNaughton, 1995). 2-29 Figure 2-26 Major
28、 influence factors for corrosion fatigue of waterwall tubing (Kajigaya, et al., 1995). 2-29 Figure 2-27 Typical locations for tube failures by corrosion fatigue. Locations in tangentially-fired boilers. Numbers refer to additional description given in Table 13-2 of (EPRI TR-100455). . 2-34 Figure 2-
29、28 Typical locations for tube failures by corrosion fatigue. Locations in front/rear-fired radiant boilers. Numbers refer to additional description given in Table 13-2 of (EPRI TR-100455). . 2-35 Figure 2-29 Typical corrosion fatigue cracking pattern in membrane welded waterwall tubing 2-36 Figure 2
30、-30 Typical corrosion fatigue cracking near the tie rods of tangent tube constructed waterwalls 2-36 xiii Figure 2-31 Schematic showing general features of corrosion fatigue cracks (Moles, 1980). 2-37 Figure 2-32 Cross-sections of corrosion fatigue cracks showing typical features: oxide coating of t
31、he fracture surface, corrosion within the crack, wide crack mouths and tips, and a transgranular fracture path (Paterson, et al., 1995). 2-38 Figure 2-33 Strain, temperature and cycle chemistry information collected on the cold start of a 500 MW unit. (CBD) is continuous blowdown. It should be noted
32、 that at the time of peak strain (about 5 hours) the dissolved oxygen level has been reduced to very low ( 10 Bar)Results of Inspections2-46 Table 2-7 Deaerator Storage Vessel Tank Failures as a Function of the Operating Hours 2-47 Table 2-8 Vessel FailuresFine-Grained Structural Steel Vessel 2-48 T
33、able 2-9 Stress-Induced Corrosion Cracking (Example: Boiler Drum) Due to a Local Damage of the Magnetite Layer 2-52 Table 2-10 Characteristics and Fatigue Usage Estimates of Susceptible Nuclear Components, based on the recent evaluation (Ware, et al., 1995). 2-62 Table 2-11 Composition and Mechanica
34、l Properties of Some Nuclear Pressure Vessel Steels at 20C. 2-63 Table 2-12 Water Chemistry Specifications for Normal BWR a number of examples can illustrate the very diverse nature of the problem: Boiler tube failures in fossil plants. Here corrosion fatigue represents the single largest cause of a
35、vailability loss in fossil plants worldwide. It predominantly occurs in the water walls and economizers of sub-critical plant. Boiler tube failures in the steam generating equipment of the oil, petroleum, pulp and on the nuclear side, reviews of environmentally assisted fatigue crack initiation and
36、growth have been carried out Ford, 1992 and Ford, et al., 1993. Similarly in each of the incidences cited above, many studies have been performed. Unfortunately no overall review of corrosion fatigue across the broad range of equipment, conditions, cycle chemistries, temperatures and pressures has b
37、een conducted. This project is intended to fill that gap and to produce a state-of-the-art document which clearly defines the current knowledge and, most importantly, indicates where knowledge is missing and further research is required. It is the intention of the EPRI Project Managers to use the pr
38、oduct from this project in setting up an international collaboration to address these deficiencies. 1.2 Objectives and Approach The primary, longer term goal of this project is the consolidation, development, and application of a useful knowledge-base on the subject of corrosion fatigue, especially
39、in water-touched components, from major industries, internationally. As an initial step, the work documented in this report was carried out to generate a state-of-the-art survey of corrosion fatigue issues in power plants, and to identify knowledge-gaps and needed research. The intent of this projec
40、t is on the industrial application of current technology, supported by common and basic understanding relating the phenomenology of corrosion fatigue as expressed by the leading research groups worldwide. The next step is to formulate an international group, mostly from the individuals and organizat
41、ions contributing to and/or participating in this overall effort, with continued and active interest in the understanding and resolution of corrosion fatigue issues. The objective of this formulation is to pool the technical and financial resources, and to make use of the broader expertise with insi
42、ghts, so as to address and resolve the multi- disciplinary, multi-industry aspects of the corrosion fatigue. The current scope is limited primarily to the pressure retaining components of nominally ductile alloys subject to high purity aqueous (steam or water) environments Introduction 1-3 below abo
43、ut 400C. The industries of main interest are: power generation, petrochemical and processing, and pulp B, mounted on deaerator; C, Spray type deaerator; D, adjacent deaerator (Bulloch, 1991). Corrosion Fatigue Failures in Various Industries 2-3 Figure 2-2 Deaerators are used to strip oxygen from fee
44、dwater before entering the boiler. Type shown uses steam to break up water into spray or film, then force out dissolved gases. Interaction in spray area does 95% of the work, last 5% takes place in tray section Corrosion Fatigue Failures in Various Industries 2-4 Figure 2-3 Typical design details of
45、 a direct contact deaerator. Corrosion Fatigue Failures in Various Industries 2-5 Figure 2-4 Location of a direct contact deaerating heater in a once-through supercritical cycle (Bulloch, 1991). The normal operating temperature range of deaerator vessels is 133C (235F) to 180C (356F) with correspond
46、ing saturation pressures of 0.069 MPa (10 psi) to 0.96 MPa (140 psi). Off-normal temperatures and pressure have often been reported and can result in severe waterhammer events. These are often associated with operational transients in which the inlet and outlet water flows, and deaerator storage tan
47、k water levels and temperature are not within optimal ranges Marshal and Peattie, 1995. Deaerators may be vented to the atmosphere during shutdowns. Under these conditions the oxygen content of water within the deaerator storage vessel can approach air saturation levels (8000 ppb = 8ppm). During ope
48、ration the water entering the deaerator may have an oxygen content of around 20 ppb. This is typically lowered to less than 5 ppb at the deaerator outlet. Deaerators are usually designed in accordance with the ASME Section VIII, Division 1. Recommendations from The Heat Exchanger Institutes (HEI) “S
49、tandards and Specifications For Deaerators and NACE Recommended Practice for Prevention, Corrosion Fatigue Failures in Various Industries 2-6 Detection, and Correction of Deaerator Cracking (NACE RP0590)“ also provide guidance on deaerator design. The deaerator dome and storage tanks are typically fabricated from carbon steel plate. The most prevalent material used in the past was SA285 Grade C, although many were fabricated using either SA212 Grade B, SA285 Grade B, SA515 Grade70, or SA516 Grade 70 steel plate (Table 2-1). The plates are shaped and then joined by weldin