Fitness for Service Approach (FFS) in Fatigue Life Prediction for a Spherical Pressure Vessel Containing Cracks
Subject Areas : Mechanical EngineeringJ Jamali 1 , E Mohamadi 2 , T Naraghi 3
1 - Islamic Azad University, Shoushtar Branch, Shoushtar, Iran
2 - Islamic Azad University, Shoushtar Branch, Shoushtar, Iran
3 - Amirkabir University of Technology, Tehran, Iran
Keywords: Pressure vessel, Fitness for service, Fatigue life assessment,
Abstract :
During the pressure vessels' operating life several flaws are likely to grow in long term operations under cyclic loading. It is therefore essential to take practical and predictive measures to prevent catastrophic events to take place. Fitness for service (FFS) is one safety procedure that is used to deal with maintenance of components in the petroleum industry. In this method, proposed in Codes of practices such as API 579 and BSI 7910, in certain cases, an overly conservative safety prediction is obtained when applied to the operation of pressure vessel containing surface fatigue crack growth. By using improved analytical techniques as well as nonlinear finite element methods critical cracks lengths may be derived more accurately thus reducing conservatism. In this paper, a specific pressure vessel analyzed for fitness for service which sees fatigue crack growth rate is assessed using analytical and numerical stress intensity factors. The estimated fatigue life is compared with both methods. It is found that both approaches give similar predictions within a range of scatter assuming that the fatigue properties used are the same in both cases. However, it can be said that the numerical approach gave the more conservative predictions suggesting a detailed analysis is always preferable in FFS examinations.
[1] Hearn E.J., 1997, Mechanics of Materials, Butterworth-Heinemann.
[2] Ibrahim A., Ryu Y., Saidpour M., 2015, Stress analysis of thin-walled pressure vessels, Modern Mechanical Engineering 5: 1-9.
[3] Matthews C., 2004, Handbook of Mechanical In-Service Inspection: Pressure Systems and Mechanical Plant, John Wiley & Sons.
[4] Folias E.S., 1970, On the theory of fracture of curved sheets, Engineering Fracture Mechanics 21: 51-65.
[5] Folias E.S., 1973, A finite line crack in a pressurized spherical shell, International Journal of Fracture Mechanics 1: 23-32.
[6] Erdogan F., Kibler J.J., 1969, Cylindrical and spherical shell with cracks, International Journal of Fracture Mechanics 5: 229-241.
[7] Wang B., Hu N., 2000, Study of spherical shell with a surface crack by line spring model, Engineering Structures 22: 100-123.
[8] Sun X., Ning J., 1987, Fracture mechanics analysis of spherical shell with surface crack, Theoretical and Applied Fracture Mechanics 7: 189-204.
[9] Choa Y., Chen H., 1989, Stress intensity factors for complete internal and external cracks in spherical shells, Internatinal Journal of Pressure Vessel and Piping 40: 315-330.
[10] Brighenti R., 2000, Surface cracks in shells under different hoop stress distribution, Internatinal Journal of Pressure Vessel and Piping 77: 503-514.
[11] Green D., Knowles J., 1994, The treatment of residual stress in fracture assessment of vessels, Journal of Pressure Vessels and Technology 116: 345-357.
[12] France C., Chivers T., 1994, New stress intensity factors and crack opening area solutions for through-wall cracks in pipes and cylinders, ASME PVP Conference Fatigue and Fracture.
[13] Zang W., 1997, Stress intensity factor solutions for axial and circumferential through-wall cracks in cylinders, SAQ. Report SINTAP/SAQ/02.
[14] Anderson T.L., 2003, Stress intensity and crack growth opening area solutions for through-wall cracks in cylinders and spheres, WRC Bulletin.
[15] Fitness-for-Service, API 579-1/ASME FFS-1, 2007.
[16] Barsom J.M., 1971, Fatigue-crack propagation in steels of various yield strengths, Journal of Engineering for Industry 93(4):1190-1196.
[17] Mehta V.R., 2016, Evaluation of the fracture parameters for SA-516 Grade 70 Material, Journal of Mechanical and Civil Engineering 13(3): 38-45.