Tubesheet - Conditions

Owned by Former user (Deleted)
Last updated: Feb 03, 2021 by Mike Clark
8 min read

Last Updated: 2020.6

(Fixed, Floating, and U-Tube)

The conditions grid is a repository for tubesheet design cases. Values entered here will overrule values entered on previous tabs. For example, if shell pressure on this tab is 15 PSI and shell pressure on the shell tab is 50 PSI, 15 PSI will be used in the calculations; however, a value entered on the conditions grid will not change the value on any other tab.

The values entered on this tab default based on settings from other tabs. If temperatures, pressures, or materials are changed on the other tabs, the values on this tab will only reflect those changes for new rows that are added. If the values on this grid are manually changed, they will not be updated by changes to the other tabs. 

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Thermal Case: This field is only available for the 2013 code year and later. If this box is selected, thermal loads will be considered and the case treated as an operating case.

Loading Type: There are several options here including Design, Operating, Startup, and Shutdown. All of these Loading Types should be considered and are ultimately defined by the designer. The 2010 and 2011 code year defines thermal expansion by the Loading Case (1-3 do not consider it and 4-7 do). The 2013 code year and later uses thermal expansion when the Thermal Case check box is selected. U-tube Tubesheet designs do not consider thermal expansion; however, these other Loading Types may still need to be considered. For thermal loadings plus pressure cases, the operating temperatures may be used to determine the material properties.

Loading Case: For the 2010 Code Edition and the 2011 Code Addenda, the loading case options are 1 – 7 (limited to 1 – 3 for U-Tube Tubesheet design).

The 2010 and 2011 code year defines the load cases as follows:

  1. Tube Side internal pressure and/or Vacuum; Shell Side Pressure set to 0; no thermal expansion
  2. Tube Side Pressure set to 0; Shell Side internal pressure and/or Vacuum; no thermal expansion
  3. Tube Side internal pressure and/or Vacuum; Shell Side internal pressure and/or Vacuum; no thermal expansion
  4. Tube Side Pressure set to 0; Shell Side Pressure set to 0; thermal expansion
  5. Tube Side internal pressure and/or Vacuum; Shell Side Pressure set to 0; thermal expansion
  6. Tube Side Pressure set to 0; Shell Side internal pressure and/or Vacuum; thermal expansion
  7. Tube Side internal pressure and/or Vacuum; Shell Side internal pressure and/or Vacuum; thermal expansion

For the 2013 Edition, the options are 1-4. The 2013 code year defines the load cases as follows (thermal is defined by Thermal Case check box):

  1. Tube Side highest pressure; Shell Side vacuum pressure if a Design Case, Shell side zero pressure if a Thermal Case
  2. Tube Side vacuum pressure if a Design Case, Tube side zero pressure if a Thermal Case; Shell Side highest pressure
  3. Tube Side highest pressure; Shell Side highest pressure
  4. Tube Side vacuum pressure if a Design Case, Tube side zero pressure if a Thermal Case; Shell Side vacuum pressure if a Design Case, Shell side zero pressure if a Thermal Case

For the 2015 Edition and later, the options are 1-4. The 2015 code year and later defines the load cases as follows (thermal is defined by Thermal Case check box):

  1. Tube Side highest pressure; Shell Side vacuum pressure
  2. Tube Side vacuum pressure; Shell Side highest pressure
  3. Tube Side highest pressure; Shell Side highest pressure
  4. Tube Side vacuum pressure; Shell Side vacuum pressure

CA: This option allows you to consider corrosion allowance, to not consider corrosion allowance, or to check both the corroded and uncorroded cases. UHX in Section VIII-I and 4.18 in Section VIII-II both require that both the corroded and uncorroded conditions be considered. All new rows in the conditions grid will default to Both. It may be valid to only consider certain cases as corroded or uncorroded. For example, the hydrotest Loading Type may only require the uncorroded condition.

Vacuum: If “Yes” is selected, then the number of permutations of calculations for this row in the grid will double for code years 2010 and 2011. For example, if loading case 1 is specified for Code year 2010 or 2011, and “Yes” is picked for this value, the calculations will be run with the tube side pressure set to the internal pressure and again with the tube side pressure set to the negative tube vacuum pressure. This same logic applies for the 2013 and later years for the thermal cases only. This is ignored for the non-thermal cases in years 2013 and later.

Radial Diff. Thermal Calcs.: This column is only available for Fixed and Floating tubesheet designs. It only affects the thermal loading conditions/cases. If “Yes” is picked, it will consider the effect of Radial Thermal Expansion in addition to the axial thermal expansion that is already considered in the thermal loading conditions/cases.

Shell Pressure: The shell side internal design pressure for Design Cases. This may be an operating pressure for the thermal cases.

Shell Vacuum: The shell side external design pressure for Design Cases. This may be an operating external pressure for the thermal cases.

Shell Ts: The shell material maximum mean metal design temperature for Design Cases. This may be an operating temperature for the thermal cases.  This temperature is used to determine the shell material properties for the row under consideration, with the exception of the alpha values.  It is conservative to use a higher value here and this will typically match the design temperature for the shell side, though the operating temp may be used in the thermal cases as mentioned.

Shell Tsm: The mean shell temperature along the shell length as expected during the case under consideration (e.g., Operating, Startup, Shutdown, etc). It is generally not conservative to substitute the shell design temperature for Tsm as a higher delta between Tsm and Ttm is what is considered conservative.

Shell T's: The metal temperature of the shell at the tubesheet rim as expected during the case under consideration (e.g., Operating, Startup, Shutdown, etc). It is usually not conservative to substitute the shell design temperature for T's. This value is only required for radial differential thermal expansion calculations.

Tube Pressure: The tube side internal design pressure for Design Cases. This may be an operating pressure for the thermal cases.

Tube Vacuum: The tube side external design pressure for Design Cases. This may be an operating external pressure for the thermal cases.

Tube Tt: The tube material maximum mean metal design temperature for Design Cases. This may be an operating temperature for the thermal cases.  This temperature is used to determine the tube and channel material properties for the row under consideration, with the exception of the alpha values and the tube values @ Tts.  It is conservative to use a higher value here and this will typically match the design temperature for the tube side, though the operating temp may be used in some cases as mentioned.

Tube Ttm: The mean tube temperature along the tube length as expected during the case under consideration (e.g., Operating, Startup, Shutdown, etc); this considers the entire tube bundle. It is generally not conservative to substitute the tube design temperature for Ttm as a higher delta between Tsm and Ttm is what is considered conservative.

T'c: The metal temperature of the channel at the tubesheet rim as expected during the case under consideration (e.g., Operating, Startup, Shutdown, etc). It is generally not conservative to substitute the channel design temperature for T'c. This value is only required for radial differential thermal expansion calculations.

T': The metal temperature of the tubesheet at the rim as expected during the case under consideration (e.g., Operating, Startup, Shutdown, etc). It is usually not conservative to substitute the tubesheet design temperature for T'.  This value is only required for radial differential thermal expansion calculations.

Stress: The material allowable stress. When a 3.5:1 safety factor is specified in the vessel screen, this value comes from Section II, Part D (Table 1A for Ferrous Materials, Table 1B for Non-Ferrous Materials, and Table 3 for Bolting). If a 4:1 safety factor is specified, this value is calculated based on the ultimate strength from Table U in Section II, Part D; furthermore, the value is limited to the values listed in the allowable stress tables for yield and creep governed cases. In cases where the temperature exceeds the highest temperature entry for this material’s stress line, the value will be zero. Shell Stress and Shell Band Stress are based on Ts. Tube Stress is based on Tt. Tube Stress @ Tts is based on Tts. Stationary Channel Stress and Floating Channel Stress are based on Tc. Tubesheet Stress is based on Tts.

Yield: The material yield strength based on Section II, Part D, Table Y-1. In cases where the temperature exceeds the highest temperature entry for this material’s yield line, the value will be zero. There are several materials that do not have clear matches in these tables. When a clear match cannot be found by the software’s assignment criteria, the software will calculate the yield strength using the external pressure chart and the method described in UG-28(c)(2) Step 3. This is more common with non-ferrous materials. If no match is found and the software cannot perform the described calculation, this value will be zero. Shell Yield and Shell Band Yield are based on Ts. Tube Yield is based on Tt. Tube Yield @ Tts is based on Tts. Stationary Channel Yield and Floating Channel Yield are based on Tc. Tubesheet Yield is based on Tts.

Modulus: The material modulus of elasticity based on the TM tables from Section II, Part D. The value shown here is based on the applicable TM table. In cases where the temperature exceeds the highest temperature entry for this material’s TM table, the value will be zero. There are several materials that do not have clear matches in these tables. When a clear match cannot be found by the software’s assignment criteria, the software will instead retrieve the modulus of elasticity from the external pressure chart assigned to the material. If this attempt also fails, then the value will be zero. This is more common with non-ferrous materials. Shell Modulus and Shell Band Modulus are based on Ts. Tube Modulus is based on Tt. Tube Modulus @ Tts is based onTts. Stationary Channel Modulus and Floating Channel Modulus are based on Tc. Tubesheet Modulus is based on Tts.

Alpha: The material mean coefficient of thermal expansion based on the TE tables from Section II, Part D; column B is used in those tables. There are several materials that do not have clear matches in these tables. When a clear match cannot be found by the software’s assignment criteria, this value will be zero. Shell Alphas,m and Shell Band Alphas,m1 are based on Tsm. Shell Alpha' s is based on T's. Tube Alphat,m is based on Ttm. Stationary Channel Alpha'c and Floating Channel Alpha'c are based on T'c. Tubesheet Alpha’ is based on T’.