Wall Thickness Calculation of Straight Pipes on Offshore Gas Transmission
 
  Calculation as per Chapter VIII by ASME B31.8 for D/t ≥ 30
                     
  (Enter values in yellow cells for calculations and in blue cells as information)
  DATA INPUT
                     
  Diameter Nominal,  DN =
 mm Materia  =
 
                     
   External Diameter,  D =  mm Design Temperature =  ᵒC  
        Design temp. between −29°C* and 232°C       
  Location  =  
* For temp. below of -29ᵒC see parag. 812      
  See table A842.2.2-1     Internal design pressure (gauge), Pi =   barg  
                 KPag  
  Hoop stress design factor, F1  =                 
See table A842.2.2-1
Water Depth, H =   m
Water Density, ɣ =   Kg/m3
  Allow. for corrosion, CA =   mm External pressure (gauge), Pe =   KPag  
  optional              barg  
                     
        Temperature derating factor, T =     
        See table 841.1.8-1      
    Spec. min. yield strength, Sy =  MPa  
        See table D-1      
                     
                     
  CALCULATIONS
               Check for Applicability    
  Applicable allowable stress value, S =   MPa       D/t =    
               D/t ≥ 30    
                     
  Nominal thickness as per chapter VIII, t =   mm t = (Pi-Pe)D          
  Minimum thickness required     2000S          
                     
  Nominal thickness + Corr. Allow., tn =   mm  tn = t + CA        
                     
   Nom. pipe wall thickness T̅ ≥ tn =  mm              
  From ASME B36.10M (Thickness most commonly used)                
  SCH =  (Minimum acceptable when applicable)      
                   
  Wall Thickness Calculation of Straight Pipes on Offshore Gas Transmission
 
  Calculation as per Chapter VIII by ASME B31.8 for D/t ≥ 30
                     
  (Enter values in yellow cells for calculations and in blue cells as information)
  DATA INPUT
                     
  Nominal Pipe Size,  NPS =
 in. Materia  =
 
                     
   External Diameter,  D =  in. Design Temperature =  ᵒF  
        Design temp. between −20°F* and 450°F      
  Location  =  
* For temp. below of -20ᵒF see parag. 812      
  See table A842.2.2-1     Internal design pressure (gauge), Pi =   psig  
                     
  Hoop stress design factor, F1  =   Water Depth, H =   ft  
See table A842.2.2-1
Water Density, ɣ =   lb/ft³
External pressure (gauge), Pe =   psig
  Allow. for corrosion, CA =   in.              
  optional     Temperature derating factor, T =     
        See table 841.1.8-1      
    Spec. min. yield strength, Sy =  psi  
        See table D-1      
                     
                     
  CALCULATIONS
               Check for Applicability    
  Applicable allowable stress value, S =   psi       D/t =    
               D/t ≥ 30    
                     
  Nominal thickness as per chapter VIII, t =   in. t = (Pi-Pe)D          
  Minimum thickness required     2S          
  Nominal thickness + Corr. Allow., tn =   in.  tn = t + CA        
                     
   Nom. pipe wall thickness T̅ ≥ tn =  in.              
  From ASME B36.10M (Thickness most commonly used)                
  SCH =  (Minimum acceptable when applicable)      
                 
    Discussion and References
      Information about Wall thickness calculation of straight pipes on Offshore Gas Transmission:
      ASME B31.8 Gas Transmission and Distribution Piping Systems, chapter VIII.
    Tables and Standards
     Table D-1 Specified Minimum Yield Strength for Steel Pipe Commonly Used in Piping Systems
     Table A842.2.2-1 Design Factors for Offshore Pipelines, Platform Piping, and Pipeline Risers
 Table 841.1.8-1 Temperature Derating Factor, T, for Steel Pipe
     ASME B36.10M-Welded and Seamless Wrought Steel Pipe  
     ASME B36.19M-Stainless Steel Pipe    
                 
    Equations for Wall thickness calculation of straight pipes on Offshore Gas Transmission (chapter VIII):
For D/t ≥ 30, the wall thickness should be calculated by the equations:
                 
    t = (Pi-Pe)D     (U.S. Customary Units)    
    2S        
                 
    t = (Pi-Pe)D     (SI Units)    
    2000S        
                 
     tn = t + CA   Corrosion allowance is not included in the chapter VIII
            It is optional to the designer its inclusion in the calculation.
                 
    The parameters in the wall thickness calculation of straight pipes on Offshore Gas Transmission
    equations above are:      
    Pe = external pressure, psig (kPag).
    Pi = internal design pressure, psig (kPag).
    D = external diameter, in. (mm).
    CA = sum of corrosion allowance, slots, threads and safety in special areas, in. (mm).
    t = nominal thickness, in. (mm) as per chapter VIIII.
    S = Applicable allowable stress value, psi (MPa), as determined by the following equation:
                 
    S = F₁(Sy)T        
                 
Where:
     F₁ = Design Factors for Offshore Pipelines, Platform Piping, and Pipeline Risers. Table A842.2.2-1 
    Sy = specified  minimum  yield  strength, psi (MPa) 
    T = temperature derating factor obtained from Table 841.1.8-1
    * Additional information for pressure design can be found in API RP 1111, paras. 4.3.1 and 4.3.2.