EPRI-1013249.ppt

computer based training module flow-accelerated corrosion for non-fac personnel march 2006,introduction to navigation,module can be navigated in a linear fashion click page down or enter by following hyperlinks for more information the file must be viewed in “slide show” mode for the hyperlinks to work click on a hyperlink to go directly to related information in the training, clicking page down or enter will take you back to where you left off,introduction to flow-accelerated corrosion,flow-accelerated corrosion (fac) is a corrosion process that degrades carbon steel material fac normally occurs above room temperature under specific chemistry conditions normally found in power plants fac requires that flowing water or water/steam mixtures be in contact with the steel surface fac is normally related to turbulence especially near fittings, e.g., elbows, orifices, valves,description of fac,fac occurs when the normally protective iron-oxides dissolve into the flowing stream this results in a global attack (i.e., widespread thinning) rather than local attack (i.e., pitting or cracking) fac caused failures are often sudden and catastrophic damage rates caused by fac are dependent on the water chemistry indicating that fac is a corrosion process not mechanical in nature (information on erosion) for more details on the fac process,why is fac important?,fac has caused damage and has resulted in failures workmen killed or injured piping and equipment replacements this experience has necessitated expensive plant programs,significant experience surry unit 2,an 18 inch elbow in a condensate line ruptured catastrophically in 1986 four fatalities and several injuries resulted,flow was from left to right,significant experience mihama unit 3,a 22 inch condensate line downstream of an orifice ruptured catastrophically in 2004 five fatalities and several injuries resulted more piping experience slide show,flow from right to left. note orifice flange is at right edge of photo,significant experience point beach 1,fac also occurs in equipment, particularly feedwater heater shells,operating conditions = 347f and about 88% quality,what does fac damage look like?,under single-phase (i.e., water only) conditions, the damaged surface displays a “scalloped” or “orange-peel” surface this type of surface is conclusive evidence that the damage is caused by fac depending on the conditions, magnification may be required to view the scalloping,single-phase fac,note 50m 0.002”,what does damage look like? (continued),under high quality, two-phase conditions, the surface may show a pattern of dark and light areas known as “tiger stripping” tiger-striping is also conclusive evidence of fac more tiger striping slide show,edf tiger striping,susceptibility considerations systems,generally all of the secondary side in pwrs and the equivalent bwr systems are susceptible to damage some bwr auxiliary systems (e.g., rhr) may also be susceptible auxiliary systems such as building steam may also be susceptible,susceptibility considerations piping,piping is susceptible to fac if: the material is carbon steel there is water or wet steam flowing in the pipes the water is deoxygenated (i.e., service water systems do not experience fac) note that both large bore ( 2” npt) and small bore piping systems are susceptible more detail on small bore piping,susceptibility considerations equipment,carbon steel equipment in susceptible systems are normally susceptible, especially: feedwater heaters slide show msr and other tanks slide show steam generator internals in pwrs slide show turbine casings,known problem areas,downstream of control valves downstream of level control valves e.g. millstone 2 & 3 downstream of flowmeters especially orifices e.g. mihama downstream of leaking valves and steam traps crossunder lines,known problem areas (continued),unknown materials of construction (i.e., documentation shows fac-resistant materials but really carbon steel) unknown piping components (i.e., insulation hides pipe spool pieces or other components which may be wearing at different rates than inspected piping) undocumented replacements (i.e., components were replaced and no records kept). this can result in improper wear predictions.,plant programs general,programmatic recommendations for fac programs are found in the current revision of nsac-202l “recommendations for an effective flow-accelerated corrosion program” interaction with other groups is a key part in successful programs details on such interactions,plant programs analysis,a susceptibility analysis is performed to determine the extent of the plant program checworks analysis to predict fac damage rates in susceptible systems, and predict component lifetimes checworks also provides a comparison of predicted and measured wear rates,plant programs inspection,large bore piping is normally inspected using the ultrasonic inspection technique (ut), but occasionally radiographic technique (rt) is used small bore piping is normally inspected using rt or by ut scanning visual inspections (vt) are used under special circumstances checworks is normally used to store and manage the ut inspection data,plant programs other elements,all components are evaluated for acceptance for continued service repair/replacements decisions must be made, often during outages. this process is dependent on the component evaluation process. reinspection intervals for all components must be determined future inspection and replacement scopes must be determined,ultrasonic testing (ut) practices,large bore inspections are performed on a grid templates are sometimes used in place of a drawn grid hand-held instruments are used to take and record data data is usually analyzed using checworks hot ut, measurements during operation, is occasionally used,radiographic testing (rt) practices,many utilities are still using film, but a number of utilities are moving to the newer phosphor plate (digital) imaging technique data interpretation and manipulation are easier with digital images two measurement techniques are used “through wall” usually used to determine the wall thickness of large bore piping “tangential wall” usually used for small bore piping epri research is being directed at increasing the size limits of through wall rt,visual inspection practices,among the specific areas where visual techniques are used: crossunder normally done during crawl through of piping when valves and pumps are opened for maintenance, the opportunity may be used to perform a visual inspection when a piece of equipment (e.g., feedwater heater) is opened for maintenance, the opportunity may be used to perform a visual inspection,vessel inspections feedwater heaters,the most commonly inspected vessels are feedwater heater shells there are several methods used to inspect vessels. these are: ut with grids insulation is removed, vessel is gridded, data is taken ut scans insulation is removed, and scans are made and data recorded,vessel inspections feedwater heaters (continued),pulsed eddy current is used through the insulation pulsed eddy current is used through the insulation. a small portion of the insulation is removed an ut measurements in this area are used to calibrate the pec measurements. automatic techniques using computer controlled carriage to perform ut measurements more information on heater inspections,what to do if there is a leak?,for large bore piping, leak before break does not normally occur sudden, catastrophic failure is possible evacuate personnel and rope-off the area surrounding the leak notify management notify fac program owner,material considerations,alloying elements can reduce the rate of fac over unalloyed carbon steel chromium has been shown to be the most important alloying element with copper and molybdenum also providing resistance some plants use alloy analyzers to account for trace alloy content in their fac programs,materials considerations (continued),resistance to fac has been shown to be well represented by this bar graph,replacement considerations,the cost and availability of the material the resistance to fac (previous slides) thermal expansion of stainless steel versus carbon steel may require a new pipe stress analysis welding issues including pre- and post-weld heat treatment issues with chrome-moly material,repair options piping,on piping and fittings, weld overlay may be used for temporary repairs for crossunder piping, there are several repair options: weld overlay flame/arc spraying slide show,repair options feedwater heater shells,the approach used for repairing shells is called a “window repair” cutting out a section of the shell and replacing with a piece of rolled plate “cap repairs” using engineered caps are sometimes used slide show,water chemistry,water chemistry is a key parameter in controlling the rate of fac oxygen, ph and hydrazine influence the rate of fac the specifics depend on the type of reactor system bwr chemistry pwr chemistry,iron transport,fac is responsible for the generation of most of the iron that is transported to the sg/bwr vessel calculations and experience show that this iron comes primarily from equipment not piping more information about iron transport,where to go for more information,unit program owner _ (filled in by utility) fac book current revision a compendium of information on fac nsac-202l current revision programmatic information,quiz,would you expect fac to occur in the feedwater system of fossil plants? hint the conditions are similar to the conditions in the feedwater system of pwrs. yes no would you expect fac to be worse near an elbow or in an isolated straight pipe? elbow pipe what would be the best strategy for protecting a line replace one or two components with stainless steel or improve the water chemistry? replace water chemistry,quiz,is there an erosive component to fac damage? yes no inspection programs are the main part of a fac program. true false which of the following parameters influence the rate of fac? velocity local geometry wall material water chemistry all of the above,quiz,what are the inspection methods most commonly used to locate fac caused degradation? ut for large bore hot ut for large bore rt for small bore visual for special circumstances all of the above items a, c & d fac damage always appears as tiger striping. true false,quiz,fac affects piping and equipment such as feedwater heaters. true false fac caused damage may result in: piping failures equipment failures high iron transport piping replacements all of the above,training complete,question 1 yes,correct! fac does occur in fossil power plants. the picture is from the pleasant prairie plant in wisconsin. go to question 2,question 1 no,as the conditions are similar to a pwr, fac does occur, sometimes with disastrous consequences please try again,question 2 elbow,correct! fac should be worse downstream of an elbow due to the turbulence created by the flow stream. go to question 3,question 2 pipe,fac in a pipe isolated from upstream flow disturbances should be less than the fac downstream of an elbow please try again,question 3 replace,replacing 2 components will not protect the entire line please try again,question 3 water chemistry,correct! improving the water chemistry will reduce the fac rate for all of the components in the line. go to question 4,question 4 yes,fac is a pure corrosion process, that is there is no erosion wear involved please try again,question 4 no,correct! fac is a corrosion process without a mechanical (i.e., erosive) component go to question 5,question 5 true,inspection programs are only a part of a fac program please try again,question 5 false,correct! inspection programs are only a part of a comprehensive fac program. go to question 6,question 6,fac is governed by a number of factors please try again,question 6 e,correct! fac is governed by a number of factors including velocity, geometry, pipe material and water chemistry. go to question 7,question 7 a,ut is commonly used for large bore inspections. however, it is not the only commonly used method on the list. please try again,question 7 b,hot ut is sometimes used for large bore inspections, but it is not commonly used please try again,question 7 c,rt is commonly used for small bore inspections. however, it is not the only commonly used method on the list. please try again,question 7 d,visual inspections are commonly used for special circumstances. however, it is not the only commonly used method on the list. please try again,question 7 e,hot ut is sometimes used for large bore inspections, but it is not commonly used. therefore this answer is incorrect. please try again,question 7 f,correct! ut for large bore, rt for small bore, and visual inspections for special circumstances are commonly used for fac inspections. go to question 8,question 8 a,tiger striping is associated with fac occurring in high quality two-phase flows. it is not associated with water-only fac or low-quality steam-water flow. please try again.,question 8 b,correct! tiger striping is associated with fac occurring in high quality two-phase flows. it is not associated with water-only fac or low-quality steam-water flow. go to question 9,question 9 a,correct! fac damages both piping and equipment such as feedwater heaters, sg internals, msr shells, etc. go to question 10,question 9 b,fac damage has been reported in numerous feedwater heaters as well as other equipment please try again,question 10 a,piping failures have been caused by fac, but there are other causes on the list please try again,question 10 b,piping failures have been caused by fac, but there are other causes on the list please try again,question 10 c,high iron transport rates have been caused by fac, but there are other causes on the list please try again,question 10 d,piping replacements have been caused by fac, but there are other causes on the list please try again,question 10 e,correct! fac damage has resulted in piping failures, equipment failures, high iron transport rates, and piping replacements. finish,erosion,damage may be caused by mechanisms other than fac in fac-susceptible systems the most common other forms of degradation are erosive (i.e., mechanical) in nature these include cavitation erosion, flashing erosion, liquid impingement, and solid particle erosion details are found in epri report 1011231 a cbt module for erosion is planned for 2007,fac process,steel surfaces are always covered with a porous oxide layer the composition and the porosity of the oxide layer depend on the operating conditions and the water chemistry ferrous ions (fe+) preferentially dissolve compared to ferric ions (fe+) into the flowing stream surface continues to oxide and material loss continues to occur process shows linear kinetics (i.e., damage is linear with time under constant conditions),edf tiger striping 1,edf tiger striping 2,small bore considerations,there is a very large amount of susceptible small bore piping there has been a history of failures leaks and ruptures in small bore piping including occasional plant shutdowns and power derates small bore problems in socket welded fittings are often attributed to improperly large fit-up gaps,small bore programs,differing plant philosophies are used, including: replace critical piping inspect and replace if necessary run to failure epri with support of the industry is making efforts to provide more guidance in this area,small bore photo 1,background,there was a rash of fac caused damage to feedwater heater shells and internals beginning in 1999 previous problems had occurred but were not widely reported at this time, most us units have inspected their heaters many examples of thinning have been found,pilgrim feedwater heater,2 small holes within circle,susquehanna internals 1,note unsupported tubes,susquehanna internals 2,note unsupported tubes and damaged tube support plate.,susquehanna internals 3,note unsupported tubes and damaged tube support plate.,background,there have been scattered reports of thinning found in shells and tanks problem areas have included: msr shells and internals deaereators pre-separator tanks,edf msr,bruce deaerator,steam generator,as there are wetted, carbon steel components in a steam generator, fac damage may occur susceptible areas have been found to be: thermal sleeves feedrings j-tubes tube support plates separator cans,j-tube/feedring diablo canyon,note damage where flow from the j-tube has impacted the feedring,diablo canyon j-tube section,note damage is the dark areas below #2.,fessenheim tsps,note the loss of ligaments in the two pictures,bruce separator cans,susceptibility analysis,a susceptibility analysis should be a reviewed calculation defining the portions of the plant that are susceptible to damage from fac standard exclusions are defined in nsac-202l these exclusions are for: high chromium content superheated steam high oxygen concentration very low operating time,susceptibility analysis (continued),it is very import that this analysis is complete as any susceptible areas missed may fail it is very important that this analysis be periodically reviewed as changes in plant operation may influence susceptibility in view of the importance of this document, it is recommended that it be independently verified,component evaluation considerations,usual acceptance criterion is that a component must be above tmin-code at the time of the next outage the determination of the code minimum thickness is usually best left to the stress group overly conservative safety factors often lead to unnecessary inspections local thinning criteria may be used if necessary,interactions with other organizations,other groups have input to the fac program operations specifying valve lineups and train operation