در این بخش از آموزش انجام پایان نامه به زبان انگلیسی نمونه پایان نامه انجام شده به انگلیسی ارائه شده است که دانشجویان می توانند از آن در انجام پایان نامه به زبان انگلیسی با ذکر منبع اقدام نمایند. انجام پایان نامه حاضر در دانشگاه شهید تندگویان آبادان در سال 2010 صورت گرفته است.
In the present work, comprehensive FFS software for evaluating the damage in form of metal loss was developed based on API 579-1/ASME FFS-1 guidelines, and two FFS pilot studies were conducted. Besides, an overview of validation of FFS assessment procedures was carried out. The following list presents the main conclusions from this study:
1. The results of FFS assessments in both case studies reveal that neither the piping section nor the vessel is suitable for continued operation, therefore, it was recommended that the component be repaired, replaced, or rerated.
2. Depending on whether supplemental loads are present or not, the assessment procedure for the circumferential extent of the flaw (longitudinal stress direction) may vary. In Case study 1 the supplemental loads were not present, therefore Tensile Stress Factor criteria were used for evaluating the circumferential extent of the flaw. However, in Case study 2, due to the presence of supplemental loads, a beam bending formulation was used to evaluate the longitudinal stress in cylinders due to supplemental loads. Acceptability of the circumferential extent of the flaw was established by satisfying the von Mises equivalent stress criteria for two critical stress locations on the cylinder cross-section (points A and B).
3. The software results completely by the calculated values and predicted standard results.
4. The results of metal loss assessment may initiate suitable corrective action based on the flaw’s criticality to ensure the safety of plant personnel and the public and to help optimize maintenance and operation of existing facilities to maintain the availability of older plants and enhance long-term economic viability.
5. The methodology suggested in this study is useful for inspection engineers, designers, and plant engineers in the timely detection of metal loss and leaks in the pressure vessels and piping used in the different industry sectors.
6. The detection of corrosion and cracks in pressure vessels used in the petroleum industry sometimes reveals flaws that exceed the American Society of Mechanical Engineers (ASME) code acceptance limits. This does not necessarily indicate that the pressure vessel is unfit for continued operation. This study described how quantitative engineering fitness-for-service analyses can be used to determine whether such vessels can be returned to service without significant risk of failure. These analyses can mean large cost savings as high repair costs can sometimes be avoided, and shutdowns minimized.
RECOMMENDATIONS FOR FURTHER STUDY
1. Developing other FFS software modules–This study uses API 579-1/ASME FFS-1 to evaluate the acceptability of components subject to general metal loss, local metal loss, and pitting corrosion. As cited before, API 579-1/ASME FFS-1 is organized by flaw type and/or damage mechanism. Developing other modules of Fitness-For-Service software for remaining flaw types of damage mechanisms in API 579-1/ASME FFS-1 is highly recommended.
2. Material toughness effects – The material toughness of a shell with an LTA can influence the load-carrying capacity of the component for medium and low toughness steels. An LTA is a natural stress concentration site and may have large triaxial stresses. The stress concentration in combination with the irregular geometry of the LTA may result in a fracture before the plastic collapse. For high toughness steels, this is likely not an issue as most failures due to an LTA-type defect will be mostly a ductile failure. However, for low toughness steels, the stress concentration at the deepest point of an LTA may cause micro-cracks to form and result in brittle fractures contributing to the failure. This type of failure occurs at a lower stress level than a purely ductile failure. A criterion to evaluate the susceptibility of a damaged component to experience a fracture failure should be developed for LTA-type defects. A criterion for crack extension in a cylindrical shell has been developed by Hahn . A similar procedure for LTAs should be developed for inclusion in a later release of API 579. In terms of stress, a modified stress calculation could be developed to include the material fracture toughness and the remaining strength factor to account for the susceptibility of low toughness steels to brittle fracture.
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