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- B31.1 Power Piping: Y Factor in Pressure thickness formula 3A - Thursday, July 29, 2010 - Salman [1088]
  My questions is based on Pressure thickness formula 3 & 3A in B31.1 referring to 2007 edition.
  
  For ferritic allow steel the y factor is 0.4 for temperatures 482 degC and it increases to about 0.7 at 538 degC and remains 0.7 for any values of temperature above.
  In General Notes: b of figure: 104.1.2A [y factor table], code says
  For pipe with a Do /tm ratio less than 6, the value of y for ferritic and austenitic steels designed for
  temperatures of 900Â°F 480Â°C and below shall be taken as:
  y d/d+Do
  
  Question is what is d stands for in the above formula. Code mentions this small d in Nozzle re-inforcement area calculation as the dia of branch where Do is the dia of header. Calculation of thickness is independant of branch and header configuration combined i.e. We have to calculate pressure thickness/min thickness by NOT considering what branch or header configuration it is. This d must be something else or ID may be but I need the confirmation on Notes: b as of where we would take this d value from?
- - Re: B31.1 Power Piping: Y Factor in Pressure thickness formula 3A - Thursday, July 29, 2010 - Murphy [21]
    The little d is inside diameter. The custom or practice for piping is to consider little to be ID of pipe. Also, the little d is the pipe or header size up to 12-inches then at 14-inches the big D is the pipe size.
    
    Thickness calculation is a primary stresses and a secondary stress is a bending issues at the branch connection. These are both a priority and one is not more important than the other.
    
    The y coefficient is a carryover from the BPV Code and is dependent on the material group and temperature. Basically, y is a dimensionless factor that thins the code minimum wall when the y value increases which is at higher temperatures.

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