Wall Thickness Calculation of Shells and Tubes Under External Pressure  
   
  Section VIII Div 1 - UG 28(c)(1) - Thickness of Shells and Tubes under External Pressure  
  Cylinders having Do/t values ≥ 10  
    (Enter values in yellow cells for calculations and in blue cells as information)  
  STEP 1  
  Enter the indicated input data: Calculated Values  
               
   Minimum required thickness,  t =   mm L/Do =    
  Length between any two sections stiffened,  L =   m Do/t =     
               
  Outside diameter,  Do =  mm        
               
               
  STEPS 2 TO 5  
  Enter the indicated input data:        
               
  Material =          
               
  Design Temp. =  °C        
               
  With L/Do and Do/t get Factor A =    From ASME Sec. II D Fig. G      
               
  With Factor A get Factor B =    From ASME Sec. II D Figs. CS, HA, HT  
        For values of A falling to the left of the material/  
        temperature line, the factor B is not determined.  
        Go to Step 7.  
               
  STEP 6  
    Calculated Value  
  Using the factor B, calculate the value of the maximum allowable        
  external working pressure Pa Pa =   bar  
               
               
  STEP 7  
  Enter the indicated input data: Calculated Value  
               
  Material =          
               
  Design Temp. =  °C        
               
  Modulus of elasticity,  E =   x 10ᶟ MPa Pa =   bar  
  For values of A falling to the left of the applicable material/temperature line.      
               
  STEP 8  
  Compare the calculated value of Pa obtained in Step 6 or Step 7 with P  
  External design pressure, P =   bar Pa =   bar  
        Pa ≥ P      
   If Pa is smaller than P, select a larger value for t and repeat the design procedure until a value of Pa is obtained that is    
  equal to or greater than P.  
               
                 
    Discussion and References
      Information about Wall thickness calculation of straight pipes under external pressure:
      ASME Section VIII Div 1 paragraphs UG-28, UG-29 and UG-30 
    Tables and Standards
  - ASME Section VIII Div 1 paragraph UG-28, Thickness of Shells and Tubes under External Pressure
  - ASME Section VIII Div 1 paragraph UG-29, Stiffening Rings for Cylindrical Shells Under External Pressure
  - ASME Section VIII Div 1 paragraph UG-30, Attachment of Stiffening Rings
  - ASME Sec. II D Fig. G, Geometric Chart for Components Under External or Compressive Loadings (All Materials)
  - ASME Sec. II D Fig. CS, Chart for Determining Shell Thickness of Components Under External Pressure Developed for Carbon or Low Alloy Steel
  - ASME Sec. II D Fig. HA, Chart for Determining Shell Thickness of Components Under External Pressure Developed for Austenitic Steel
  - ASME Sec. II D Fig. HT, Chart for Determining Shell Thickness of Components Under External Pressure Developed for Quenched and Tempered Low Alloy Steel
- ASME Sec. II D Table TM-1 ( Modulus of Elasticity,  E )
  - ASME B36.10M-Welded and Seamless Wrought Steel Pipe
  - ASME B36.19M-Stainless Steel Pipe
    Cylinders having Do/t values ≥ 10    
    Step 1. Assume a value for t and determine the ratios L/Do and Do/t.
    Step 2. Enter Figure G in Subpart 3 of Section II, Part D at the value of L/Do determined in Step 1. For
                 values of L/Do greater than 50, enter the chart at a value of L/Do = 50. For values of L/Do less
                 than 0.05, enter the chart at a value of L/Do = 0.05.
    Step 3. Move horizontally to the line for the value of Do /t determined in Step 1. Interpolation may be
                 made for intermediate values of Do/t; extrapolation is not permitted. From this point of
                 intersection move vertically downward to determine the value of factor A.
    Step 4. Using the value of A calculated in Step 3, enter the applicable material chart in Subpart 3 of
                  Section II, Part D for the material under consideration. (See figures CS for Carbon and Low Alloy
                  Steel and HT for Ferritic Steels with Properties Enhanced by Heat Treatment). Move vertically to
                  an intersection with the material/temperature line for the design temperature (see UG-20).
                  Interpolation may be made between lines for intermediate temperatures. If tabular values in
                  Subpart 3 of Section II, Part D are used, linear interpolation or any other rational interpolation
                  method may be used to determine a B value that lies between two adjacent tabular values for a
                  specific temperature. Such interpolation may also be used to determine a B value at an
                  intermediate temperature that lies between two sets of tabular values, after first determining
                  B values for each set of tabular values.
                  In cases where the value of A falls to the right of the end of the material/temperature line,
                  assume an intersection with the horizontal projection of the upper end of the material/
                  temperature line. If tabular values are used, the last (maximum) tabulated value shall be used.
                  For values of A falling to the left of the material/temperature line, see Step 7.
    Step 5. From the intersection obtained in Step 4, move horizontally to the right and read the value of
                  factor B.
    Step 6. Using this value of B, calculate the value of the maximum allowable external working pressure
                  Pa using the following equation:
                 
    Pa = 4B          
    3(Do/t)          
                 
    Step 7. For values of A falling to the left of the applicable material/temperature line, the value of Pa can be
                  calculated using the following equation:
                 
    Pa = 2AE          
    3(Do/t)          
                 
    If tabular values are used, determine B as in Step 4 and apply it to the equation in Step 6.
    Step 8. Compare the calculated value of Pa obtained in Step 6 or Step 7 with P. If Pa is smaller than P,
                  select a larger value for t and repeat the design procedure until a value of Pa is obtained that is
                  equal to or greater than P.
    The parameters in the wall thickness calculation of straight pipes under external pressure
    equations above are:        
  
    A = factor determined from Figure G in Subpart 3 of Section II, Part D and used to enter the
           applicable material chart in Subpart 3 of Section II, Part D. For the case of cylinders having
           Do/t values less than 10, see (c)(2).
    B = factor determined from the applicable material chart or table in Subpart 3 of Section II,
           Part D  (Figures CS, HA, HT) for maximum design metal temperature [see UG-20(c)]
    Do = outside diameter of cylindrical shell course or tube.
    E = modulus of elasticity of material at design temperature. For external pressure design in
           accordance with this Section, the modulus of elasticity to be used shall be taken from the
           applicable materials chart in Subpart 3 of Section II, Part D. (Interpolation may be made
           made between lines for intermediate temperatures.)
    L =   total length, in. (mm), of a tube between tubesheets, or design length of a vessel section
             between lines of support (see Figure UG-28.1). A line of support is:
    (a)   a circumferential line on a head (excluding conical heads) at one‐third the depth of the
            head from the head tangent line as shown on Figure UG-28;
    (b)  a stiffening ring that meets the requirements of UG-29;
    (c)  a jacket closure of a jacketed vessel that meets the requirements of 9-5;
    (d)  a cone‐to‐cylinder junction or a knuckle‐to-cylinder junction of a toriconical head or
            section that satisfies the moment of inertia requirement of 1-8. 
    P = external design pressure [see Note in UG-28 (f)].
Pa = calculated value of maximum allowable external working pressure for the assumed
              assumed value of t, [see Note in UG-28(f)].
    t = minimum required thickness of cylindrical shell or tube, or spherical shell, in. (mm)