17th World Conference on Nondestructive Testing, 25-28 Oct 2008, Shanghai, China Basic Principles of the Construction of Residual Resource Estimation Systems Abstract Vladimir V. KLYUEV, Mikhail V. FILINOV, Andrey S. FURSOV, Vladimir V. BYKOV JSC SPECTRUM-RII, Moscow, Russia Tel.: +7 (495) 245 5656, Fax: +7 (495) 246 8888 Mail: spektr@co.ru The construction of the Residual Resource Estimation Systems (RRES) is classically based on following principles: Construction of physic-mathematical model of object functioning; Consideration of the initial resource by the condition at the moment of putting an object into operation; Consideration of operation conditions, including load history, and what is even more important, history of overloads; Introduction of the definitive technical parameters set. However data obtained by classic defectoscopy is not enough to form the vector of diagnostic parameters, because defectoscopy deals with defects already developed probably very close to destruction of the material. The application of the inspection methods giving information of the current condition of metal structure and of the dynamics of change of this condition; initiation and propagation of microdefects leading to the development of macrodefects in the process of object operation. Introduction of parameters describing material microstructure increases preciseness of the residual resource prediction. Also, so to obtain real economic effect using RRES, the model is to include parameters which setting in some acceptable range extends the residual resource. Owing to this, in practice more three important parameters are to be considered: Application of non-destructive testing methods, so that inspection procedure itself would not decrease the residual resource of the object under inspection; Introduction of parameters describing the condition of material microstructure; Resource control. Realization of first two principles is reached easily by using on-site metallography. At one hand, the given method is non-destructive, from the other hand, it gives the possibility to get quantitative estimations describing metal structure condition, and to estimate quantitatively the structure changes. It lets to detect presence and to define geometric characteristics of microdefects, and to estimate its propagation dynamics quantitatively. For realization of third principle, the mathematical model of object functioning considering controlling parameters, is introduced in the given paper. keywords: automated systems, important principles, metal microstructure, on-site metallography, the mathematic model Introduction Problems of the residual resource estimation and the extension of the period of safe operation of machines and constructions came highly actual in all industrial countries, especially
in situations of high wear-out of oil, gas, energetic, chemical and other potentially dangerous equipment, combined with inaccurate and incomplete data of load and overload history. The construction of the Residual Resource Estimation Systems (RRES) is classically based on following principles: Introduction of set of definitive technical parameters; Consideration of the initial resource by the condition at the moment of putting an object into operation; Consideration of operation conditions, including load history, and what is even more important, history of overloads; Construction of physic-mathematical model of object functioning. 1. Technical state of the object and residual resource. The concept of technical state of the object for which the residual resource is estimated, is basic in the residual resource estimation system regardless to the stage of object life cycle (design, operation, reconstruction) (Fig.1). Fig.1. Setting of technical parameter set for object state estimation. The technical state of the object in each moment of time and by proper environmental conditions, is described by the set of technical state parameter (TSP) values fixed by technical documentation. Loading parameters and operating conditions, construction parameters and characteristics of the construction material are among TSP. TSP alteration is defined by the construction damageability mechanisms. These mechanisms are defined in each particular case depending to the operation conditions. Depending to damageability mechanisms, TSP that change or may potentially change during the operation process, are defined and included first into the system for monitoring by the operation. TSP alteration describes the alteration of technical state and construction resource. The system of technical state inspection includes testing and inspection methods selected depending to the construction damageability mechanisms. 2. Marginal states of the object. TSP alteration during the operation process can lead the object into the marginal state, by which its further operation or operable state restoration is impossible or is not reasonable. The main task of technical state inspection system is timely detection of the moment when the construction comes to the marginal state. It is the residual resource that define time needed to achieve marginal state in the operation process. In general, the marginal state could be related to: The destruction of certain construction elements or with formation of operational defects, by which further operation is not possible without carrying out resource restoration actions; The change of geometric shape of the construction elements, by which further operation is not possible owing to the danger of destruction or inability to execute its technological functions. Thus, the condition of marginal state is always related with violation of durability or stability by the change of technical state parameters. The marginal states related to the destruction of the construction elements, include: short-time ductile and/or brittle fracture; destruction by the condition of creep; fatigue fracture.
The marginal states related to the change of the construction elements shape, include: accumulation of prohibitive plastic deformation; local and general stability loss. The monitoring of possible achievement of marginal states, related to the accumulation of prohibitive deformations or with the destruction owing to stress concentration near the defect or construction concentrator, does not require material structure inspection. Given kinds of marginal states could be inspected using visual inspection instruments and systems, or material continuity and geometrical parameters inspection methods. However, there are cases in practice when it s not possible to predict the achievement of marginal state timely without the inspection of structural and substructural changes in metal. In the first place this is related to constructions operated under conditions of possible brittle failure. Pipelines and tanks for liquid gas transporting and storage (reservoirs, gasholders, cisterns) could be reckoned into this class. Inspection of metal show, that embrittlement process by low temperatures is associated with forming of micro cracks at the borders of metal grains, i.e. with metal structure alteration. This takes place for significant number of equipment kinds and its operation conditions. 3. Requirements to degradation monitoring technique. By estimation of technical state, the monitoring of mechanical characteristics determining safety factor and fracture toughness limits. Before in most cases such inspection was carried our using sample cutting technique, which has sufficient imperfections. Cutting a sample out of metallic part will lead inevitably to operation shutdown and subsequent repair work. Operation shutdown will lead to economic loss, and since repair work will include welding in the condition of possible steel brittleness, this may lead to cracking in the welding zone. In its turn, this will lead to even more volume of repair work and even longer pause in operation. Finally it will lead to decrease of the residual resource. Therefore, this technique is to be substituted with non-destructive one. The degradation monitoring technique is to comply with following requirements: 1. The inspection is to be carried out without any violation of the material continuity. 2. Representative sampling should be provided, including badly accessible areas. 3. Multiscale examination of metal structure alteration during the development of process mechanical properties degradation of. 4. Optical method in material degradation examination Optical NDT method complies with two last requirements of p.3 completely, however before it was used in combination with destructive sampling. The problem of decrease of the residual resource during material degradation examination associated with destructive sampling as described above, is solved successfully using the mobile complex of onsite metallography. This kind of complex allows to carry out metallographic examination directly on the object surface without any continuity violation, including badly accessed areas. Onsite metallography complex should include portable microscope fixable on surface, digital photo camera of enough resolution, notebook with proper software tool, and portable polishing eqipment. Equipment portability and necessity to perform examination in field conditions require special algorithmic and software solutions so to obtain images of quality allowing to obtain high
measurement preciseness which, in its turn, allows to get acceptable preciseness of residual resource estimation. Portable optical instruments, at one hand, give good accessibility and mobility, but, at the other hand, have high level of contrast and geometry distortions as a feature. There are two approaches to the solution of this problem: Enhancement of the hardware part of optical systems Algorithmic image restoration that compensates distortions brought by optics and electronics. The investigations show that second approach is more admissible to increase the preciseness of measurement on an image in systems with portable optical instruments. This is because enhancement of optical and optical-electronic part will overdesign it inevitably. This will decrease its reliability and increase size of optical part. The mathematical apparatus is developed for compensation of image distortions with a glance of irregularity of distortions in the view field of optical system and metallographic images features. Thus, the software lets to increase measurement preciseness and objectivity of the inspection. It is necessary to notice that it requires following so to increase onsite metallogarphy application effectiveness during residual resource estimation: additional investigations; development of proper physic-mechanical models of durability and residual resource estimation using examination data depending on particular mechanism of degradation of mechanical properties. Thus, another two important principles of RRES construction are to be considered in practice: - non-destructive methods application, so that inspection procedure itself would not decrease the residual resource of the object; - introduction of parameters describing the state of material microstructure. 5. Mathematical model of the residual resource estimation system. The construction of the mathematical model of the industrial object functioning is one of main steps in creation of the RRES. By this, the model should not only define the residual resource of the system in the given time moment, but also it should provide means of residual resource control. This means the model is to include parameters setting of which within some proper range will let to extend residual resource. This lets to obtain real economic effect out of RRES use. Inclusion of the controlling parameters into the mathematical model of the object functioning could be put as one more essential principle of RRES construction. The model that includes controlling parameters could be presented as follows: x = F( x( t ), u[ t,, 0, t] K M y( = G( x( u( ), xˆ( = H ( y( ), Φ( = Ψ( xˆ( u( ), ( 0 [ t0, t ] ), (1) (2) (3) (4) R( = W ( t, xˆ( u( x, Φ( K), (5) where (1) is the equation of state, (2) is the equation of measurements; (3) is the equation of estimations; (4) is the equation of the estimation of actual object state; (5) is the equation of the residual resource estimation (assumes prediction algorithm using equation (1)). In equations (1) - (5): x( is the vector of diagnostic parameters, y( means measurements, direct or indirect, by carrying out inspection (random value), xˆ ( is the
estimation of technical state vector (random value), Φ( is the estimation of actual object state for time moment t, R( is the estimation of the residual resource for the time moment t, x is the vector of marginal values of technical parameters. Following parameters could be used for residual resource: u( are the object operation conditions in the current time moment, u [ t 0, t] are the object operation conditions within time interval [ t 0, t], K is the vector of object operation mode, M [ t 0, t ] is the system restoration function, describing possible repairs. M t = δ χ( t ) N [ 0, t ] i τ i i= 1, where N is the number of components of the system analyzed, δ i is the measure of system breakdown probability by the replacement of i- component, χ( t τ i ) - Heaviside function, and τ i - moment of carrying out repairs.
Fig.1. Setting of technical parameter set for object state estimation.