Pipe thickness as ASME/IBR

Dear friends....

As we are aware of the pipe thickness formulae as

1)     According ASME/ANSI B31.3  clause 304.1.2
      |----------+----+---+----------------------------------------------------|
      |          | t  | = |        PD      + C                                 |
      |          |    |   |2 ( SE  +  PY )                                     |
      |----------+----+---+----------------------------------------------------|
      | where :  | t  | = | pressure design thickness                          |
      |----------+----+---+----------------------------------------------------|
      |          |P   |=  |internal design gage pressure                       |
      |----------+----+---+----------------------------------------------------|
      |          |D   |=  |outside diameter of pipe                            |
      |----------+----+---+----------------------------------------------------|
      |          |S   |=  |allowable  stress  of  material  from  table  A-1 of|
      |          |    |   |B31.3                                               |
      |----------+----+---+----------------------------------------------------|
      |          |E   |=  |quality factor from table A-1A or A-1B of  B31.3    |
      |----------+----+---+----------------------------------------------------|
      |          |Y   |=  |coefficient from table 304.1.1 of  B31.3            |
      |----------+----+---+----------------------------------------------------|
      |          | C  | = | Corrosion, erosion allowances and mill tolerance   |
      |----------+----+---+----------------------------------------------------|
      |          |    |   |                                                    |
      |          |    |   |                                                    |
      |----------+----+---+----------------------------------------------------|





    2)  But in India Pipe Wall Thickness Calculations for all IBR (Indian
           Boiler regulation) for for Steam Line   pipes, governs
              ( line pressure >3.5 kg/cm2 or line size above 10")

       According to IBR Regulation No. 350
     


|----------+-----+----+----------------------------------------------------|

      |          | t   | =  |     P  x  D        + c’
|
      |          |     |    |(2 x f x e + P)                                    
|
     


|----------+-----+----+----------------------------------------------------|

      | where:   | t   | =  | minimum thickness required                        
|
     


|----------+-----+----+----------------------------------------------------|

      |          |P    |=   | working pressure                                  
|
     


|----------+-----+----+----------------------------------------------------|

      |          |D    |=   | outside diameter of pipe                          
|
     


|----------+-----+----+----------------------------------------------------|

      |          |C    |=   | Piping class corrosion allowance                  
|
     


|----------+-----+----+----------------------------------------------------|

      |          |c’   |=   | 0.75mm   is  constant factor
|
      |          |     |    |                                                   
|
     


|----------+-----+----+----------------------------------------------------|

      |          |e    |=   | efficiency factor (for seamless pipe e = 1)       
|
     


|----------+-----+----+----------------------------------------------------|

      |          |f    |=   | allowable stress as determined from regulation 271
|
     


|----------+-----+----+----------------------------------------------------|

      |          |     |    | 1) for temperatures at or below 454 deg. C, the   
|
      |          |     |    | lower of:                                         
|
     


|----------+-----+----+----------------------------------------------------|

      |          |     |    | a) Et / 1.5B)  R.2.7                              
|
     


|----------+-----+----+----------------------------------------------------|

      |          |     |    | 2)  for  temperatures  above  454 deg. C, the
lower|
      |          |     |    | of:                                               
|
     


|----------+-----+----+----------------------------------------------------|

      |          |     |    | a) Et / 1.5b) SR /1.6c)  Sc                       
|
     


|----------+-----+----+----------------------------------------------------|

      | where:   | Xt  | =  | Working metal temperature                         
|
     


|----------+-----+----+----------------------------------------------------|

      |          |R    |=   | Specified minimum tensile strength                
|
     


|----------+-----+----+----------------------------------------------------|

      |          |Et   |=   | Yield point (0.2% proof stress) at temperature Xt 
|
     


|----------+-----+----+----------------------------------------------------|

      |          |Sc   |=   | Average stress to produce elongation of 1& (creep)
|
      |          |     |    | in                                                
|
      |          |     |    |                                                   
|
      |          |     |    |                                                   
|
      |          |     |    | 100,000 hours at temperature Xt                   
|
     


|----------+-----+----+----------------------------------------------------|

      |          |SR   |=   |Average  stress  to produce rupture in 100,000
hours|
      |          |     |    |at  temperature  Xt  and  in  no case more than
1.33|
      |          |     |    |times  the  lowest  stress to produce rupture at
the|
      |          |     |    |temperature.                                       
|
     


|----------+-----+----+----------------------------------------------------|

      |          |     |    | Note:  Should  ‘Sc’  values  not  be  available
in|
      |          |     |    | material  standards   although  such  materials
are|
      |          |     |    | known  to  have  been  used  in boilers in India
or|
      |          |     |    | abroad,  then  for  such  materials  the 
allowable|
      |          |     |    | stress may be taken as the lower of:              
|
      |          |     |    |                                                   
|
      |          |     |    |                                                   
|
      |          |     |    |                                Et  / 1.5      or
SR|
      |          |     |    | / 1.5                                             
|
     


|----------+-----+----+----------------------------------------------------|









      IBR Rules doesn't say any thing  about the Piping class corrosion
      allowance.


      Should we add above this calculation.


      I wish that this forum should comments / have some discussion on these
      formulae.





      Animesh Singh


      Piping -Project


      Reliance Engineering associates limited


      Mumbai,India



      DAKC, C block, Gr floor

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