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Example calculation

Need for Fatigue Analysis of Integral Parts of Vessels

according to ASME 2001 Section VIII Division 2 Part AD

 

Input data:

      Material 1   Material 2    
  Minimum tensile strength       N/mm²
  Design stress intensity       N/mm²
  Coefficient of thermal expansion       ×10−6 1/K
  Modulus of elasticity       N/mm²
  Design fatigue curve of Appendix 5        
  Design pressure     bar
 

Condition A

(a) Expected (design) number of full-range pressure cycles including startup and shutdown      
(b) Expected number of operating pressure cycles in which the range of pressure variation exeeds  bar      
(c) Effective number of changes in metal temperature between any two adjacent points in the pressure vessel for metal temperature differential:        
  28°C to 55°C      
  55°C to 83°C      
  83°C to 139°C      
  139°C to 194°C      
  194°C to 250°C      
  excess of 250°C      
 

Condition B

(a) Expected (design) number of full-range pressure cycles including startup and shutdown      
(b) Expected (design) range of pressure cycles during normal operation     bar
  Specified number of pressure fluctuations with the range higher than  bar      
(c) Temperature difference between any two adjacent points of the vessel during normal operation and during startup and shutdown operation     °C
  Specified number of startup and shutdown cycles      
(d) Change of range of temperature difference between any two adjacent points of the vessel during normal operation     °C
  Specified number of temperature fluctuations with the total algebraic range higher than °C      
(e) Total algebraic range of temperature fluctuation during normal operation     °C
  Specified number of temperature fluctuations with the total excursion higher than °C      
(f) Stress intensity range caused by specified full range of mechanical loads, excluding pressure but including piping reactions     N/mm²
  Specified number of load fluctuations with the total excursion of load stress intensity higher than  N/mm²      
 

Results:

Condition A

 

Fatigue analysis is mandatory, because the specified minimum tensile strength exceeds 552 N/mm².

Condition B

 
  • the requirement (a) is met
  • the requirement (b) is met
  • the requirement (c) is met
  • the requirement (d) is met
  • the requirement (e) is met
  • the requirement (f) is met
 

Fatigue analysis is mandatory, because not all the requirements are met.

 

Conclusion:

 

Fatigue analysis is mandatory.


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