 Wall Thickness Calculation of Shells and Tubes Under External Pressure As per para. 304.1.3 Straight Pipe Under External Pressure by ASME B31.3 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) 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 = A53 Gr. A A53 Gr. B A106 Gr. A A106 Gr. B A106 Gr. C A268 TP410 A268 TP430 A333 Gr. 3 A333 Gr. 6 A335 P1 A335 P5 A335 P9 A335 P11 A335 P12 A335 P21 A335 P22 A312 TP304 A312 TP304L A312 TP304H A312 TP316 A312 TP316L A312 TP316H A312 TP309 A312 TP310 A312 TP310H A312 TP317 A312 TP317L A312 TP321 >3/8 thk. (C <0.04%) A312 TP321 >3/8 thk. (C ≥0.04%) A312 TP321 ≤3/8 thk. (C <0.04%) A312 TP321 ≤3/8 thk. (C ≥0.04%) A312 TP321H >3/8 thk. A312 TP321H ≤3/8 thk. A312 TP347 (C <0.04%) A312 TP347 (C ≥0.04%) A312 TP347H A376 TP304 A376 TP304H A376 TP316 A376 TP316H A376 TP321 >3/8 thk. (C <0.04%) A376 TP321 >3/8 thk. (C ≥0.04%) A376 TP321 ≤3/8 thk. (C <0.04%) A376 TP321 ≤3/8 thk. (C ≥0.04%) A376 TP321H >3/8 thk. A376 TP321H ≤3/8 thk. A376 TP347 (C <0.04%) A376 TP347 (C ≥0.04%) A376 TP347H Design Temp. = °C With L/Do and Do/t get Factor A = From ASME Sec. II D Fig. G External Pressure Chart No. = From ASME Sec. II D Figs. CS, HA, HT For values of A falling to the left of the material/ With Factor A get Factor B = temperature line, the factor B is not determined. Go to Step 7. STEP 6 Input data Calculated Value Factor B = Do/t = Using the factor B, calculate the value of the maximum allowable Pa = 4B external working pressure Pa 3(Do/t) Pa = bar STEP 7 Input data Calculated Value Factor A = Do/t = Pa = 2AE Modulus of elasticity,  E = x 10ᶟ Mpa 3(Do/t) 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. Wall Thickness Calculation of Shells and Tubes Under External Pressure As per para. 304.1.3 Straight Pipe Under External Pressure by ASME B31.3 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) STEP 1 Enter the indicated input data Calculated Values Minimum required thickness,  t = in. L/Do = Length between any two sections stiffened,  L = ft. Do/t = Outside diameter,  Do = in. STEPS 2 TO 5 Enter the indicated input data Material = A53 Gr. A A53 Gr. B A106 Gr. A A106 Gr. B A106 Gr. C A268 TP410 A268 TP430 A333 Gr. 3 A333 Gr. 6 A335 P1 A335 P5 A335 P9 A335 P11 A335 P12 A335 P21 A335 P22 A312 TP304 A312 TP304L A312 TP304H A312 TP316 A312 TP316L A312 TP316H A312 TP309 A312 TP310 A312 TP310H A312 TP317 A312 TP317L A312 TP321 >3/8 thk. (C <0.04%) A312 TP321 >3/8 thk. (C ≥0.04%) A312 TP321 ≤3/8 thk. (C <0.04%) A312 TP321 ≤3/8 thk. (C ≥0.04%) A312 TP321H >3/8 thk. A312 TP321H ≤3/8 thk. A312 TP347 (C <0.04%) A312 TP347 (C ≥0.04%) A312 TP347H A376 TP304 A376 TP304H A376 TP316 A376 TP316H A376 TP321 >3/8 thk. (C <0.04%) A376 TP321 >3/8 thk. (C ≥0.04%) A376 TP321 ≤3/8 thk. (C <0.04%) A376 TP321 ≤3/8 thk. (C ≥0.04%) A376 TP321H >3/8 thk. A376 TP321H ≤3/8 thk. A376 TP347 (C <0.04%) A376 TP347 (C ≥0.04%) A376 TP347H Design Temp. = °F With L/Do and Do/t get Factor A = From Subpart 3 ASME Sec. II D Fig. G External Pressure Chart No. = From Subpart 3 ASME Sec. II D Figs. CS, HA, HT For values of A falling to the left of the material/ With Factor A get Factor B = temperature line, the factor B is not determined. Go to Step 7. STEP 6 Input data Calculated Value Factor B = Do/t = Using the factor B, calculate the value of the maximum allowable Pa = 4B external working pressure Pa 3(Do/t) Pa = psi STEP 7 Input data Calculated Value Factor A = Do/t = Pa = 2AE Modulus of elasticity,  E = × 10⁶ psi 3(Do/t) Pa = psi 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 = psi Pa = psi 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 ASME B31.3 Process Piping, paragraph 304.1.3 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 B31.3 Process Piping, paragraph 304.1.3, Straight Pipe Under External Pressure - 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 = the running centerline length between any two sections stiffened in accordance with UG-29. in. (mm). P = external design pressure [see Note in UG-28 (f)]. Pa = calculated value of maximum allowable external working pressure for the assumed value of t, [see Note in UG-28(f)]. t = minimum required thickness of cylindrical shell or tube, or spherical shell, in. (mm)