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
                   
  Material =   Design Temperature =  ᵒC
        Design temp. between −29°C* and 232°C     
        * For temp. below of -29ᵒC see parag. 812    
 External Diameter,  D =  mm Internal design pressure (gauge), Pi =   barg
 KPag
                   
Hoop stress design factor, F1  = 
Water Depth, H =    m
See table A842.2.2-1
Water Density, ɣ =    Kg/m3
External pressure (gauge), Pe =    KPag
  barg
Allow. for corrosion, CA =   mm Temperature derating factor, T = 
optional
See table 841.1.8-1
Select T ≥ tn =   mm Spec. min. yield strength, Sy =   MPa
  After Nominal thickness calculation, tn as per Chapter VIII, it's See table D-1    
  must be selected T̅ ≥ tn from ASME B36.10M or ASME B36.19M.               
           
  CALCULATIONS
Applicable allowable stress value, S = 
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, T =   mm            
  from ASME B36.10M or ASME B36.19M                
  - Additional information for pressure design can be found in API RP 1111, paras. 4.3.1 and 4.3.2.
                 
  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
Material =
Design Temperature =  ᵒF
Design temp. between −20°F* and 450°F
* For temp. below of -20ᵒF see parag. 812
 External Diameter,  D =  in. 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. Temperature derating factor, T = 
optional
See table 841.1.8-1
Select T ≥ tn =   in. Spec. min. yield strength, Sy =  psi
After Nominal thickness calculation, tn as per chapter VIII, it's See table D-1
  must be selected T̅ ≥ tn from ASME B36.10M or ASME B36.19M.               
           
  CALCULATIONS
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, T =   in.            
  from ASME B36.10M or ASME B36.19M                
  - Additional information for pressure design can be found in API RP 1111, paras. 4.3.1 and 4.3.2.
                 
    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.