Tubesheet - Tube
(Fixed, Floating, and U-Tube)
Several of these fields will be automatically completed based on the host tube information when the Custom Tube Browser is used. The content of those fields will be locked.
Tube Information
Design Pressure (Pt): The tube side internal design pressure.
Design Pressure (Pt,vac.): The tube side external design pressure. This is not the external design pressure on the tubes themselves.
Temperature: The maximum mean metal design temperature for the internal pressure case as defined in UG-20(a).
Liquid Density: Refers to the shell side liquid. This is for information only.
Nominal Pitch: The center to center distance between adjacent tubes. The calculations assume that this value is uniform.
Length: The tube length between outer tubesheet faces.
Number of Tube Holes: For fixed and floating tubesheet exchangers, this value matches the number of tubes and is consistent for both tubesheets in the exchanger. For U-Tube tubesheet exchangers, this value is the number of U-tubes multiplied by two.
Nominal Tube OD: The nominal outside diameter of the tube.
Wall Thickness: The new wall thickness of the tube.
Tube to Tubesheet Intersection: Select the location where the tube intersects the tubesheet.
Inside Corrosion: The corrosion allowance for the inside of the tubes.
External Corrosion: The corrosion allowance for the outside of the tubes.
Tube hole diameter: When the "Tube to Tubesheet Intersection" is Backside of tubesheet, this is the diameter of the tube hole in the tubesheet.
Ap: Total area on the tubesheet that is enclosed by the step-wise perimeter, Cp.
Cp: Perimeter of the tube layout measured in stepwise increments from center-to-center of the outer-most tubes. See figure UHX-12.2 for reference.
Pattern: Select whether the hole pattern is an equilateral triangle or a square.
Span
Largest Unsupported Span: If there are no tube supports, enter the length of tubes between tubesheets. If only one tube support exists, enter the greater of the lengths between the tubesheets and the tube support. If there are multiple tube supports, compare the longest length of tube between two tube supports to the longest length of tube between a tubesheet and a tube support multiplied by 0.8. If the former is greater, enter that value; if the latter is greater, enter the actual length between the tubesheet and tube support (do not multiply it by 0.8).
As an example, consider a design with three tube supports; the distances between the tube supports are 5 inches and 10 inches and the spans between the tubesheets and adjacent tube supports are 15 inches and 11 inches. Compare 10 inches to 0.8*15 inches. As 12 is greater than 10, the span of 15 inches will be the value entered in this field. In addition, Tubesheet and Tube Support would be chosen in the "Unsupported Span is Between" field for this example.
Unsupported Span is Between: Select the location of the largest unsupported span.This is for the purpose of determining the constant k which has a value of 0.6 for unsupported spans between two tubesheets, 0.8 for unsupported spans between a tubesheet and a tube support, and 1.0 for unsupported spans between two tube supports.
Expansion Ratio
Tube Expansion Depth Ratio: The ratio of tube expansion length in the tubesheet to the tubesheet thickness. This value is based on the new dimensions. If the tube is not expanded to the tubesheet, enter 0.
Exp. Length of Tube in Tubesheet: Select the box to enable this field. Clear the box to enable the "Tube Expansion Depth Ratio" field. When this box is selected, enter the length the tube is expanded into the tubesheet in the new condition.
Tube Material
Material: A brief description of the component material. When the material selection dialog is used, the default description is based on settings on the Materials-Misc. tab under Tools > Defaults. For example, if the settings are for Spec and Type/Grade and the material is SA-516 Grade 70, this field will show SA-516 Gr. 70. If the settings are instead just for Spec, the field will show SA-516. The field may be edited by the user to say anything without breaking the relationship to the material database; while this flexibility can be very helpful, the user must take care to enter correct information.
Condition: A brief description of the component material. Similar to the "Material" field, the description will default a certain way based on settings on the Materials-Misc. tab under Tools > Defaults when the material selection is used. This field may be edited by the user without breaking the relationship to the material database. As with the “Material” field, the user must take care to enter correct information.
Density: The material density based on table PRD from Section II, Part D. For those materials that did not have a clear match in this table, every effort was made to assign conservative values. Manually editing this field will sever the connection to the material in the database as indicated by the "Unlisted Material" caption.
B-Table: The external pressure table assigned to the material in the allowable stress tables in Section II, Part D. The table is used to determine the external pressure strength of the component and also the longitudinal compressive strength. Selecting a Factor B table other than the one assigned to the material will sever the connection to the material in the database as indicated by the “Unlisted Material” caption.
Poisson: Poisson's ratio for the selected material.
(Ttm): The mean tube temperature along the tube length as expected during operation; this considers the entire tube bundle. It is generally not conservative to substitute the tube design temperature for Ttm.
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