Skirt/Intermediate Support

Owned by Former user (Deleted)
Dec 11, 2015

Description: The label given for the component. It will appear in the component pane, the report dialog, the summary pane, and at the top of the component report. This will default to the component type and component number. For example, the third nozzle for the vessel will start with a description of Nozzle 3.

Mark: A shorthand reference for the component. It will also appear in the component report. The default entry will be an abbreviation of the component type and the component number. For example, the second jacket shell for the vessel will start with a mark SJ2.

Skirt/Support Type: Select whether the skirt or intermediate support is cylindrical or conical.

Use Diameter: This option is only available for some components. The user may choose to input dimensions as the inside dimensions or the outside dimensions where this option is available. For some components (such as shell), the use of outside dimensions for internal pressure calculations may result in a slightly higher required thickness.

Temperature: The maximum mean metal design temperature for the skirt/intermediate support.

Diameter: The component diameter in the new condition. The selection in the “Use Diameter” area determines whether this is the inside or outside diameter of the component. In the context of curved heads, this value is specifically the skirt diameter. For circular flat heads, this is the diameter as defined in per the configuration in UG-34.

Top Diameter: For conical skirts and supports, enter the diameter of the top.

Cone Angle: The half-apex angle (half of the included angle) of the conical skirt or support. This field is algebraically connected to the “Diameter”, “Top Diameter”, and “Height” fields. Entering the “Cone Angle” will solve for the “Height”; entering the “Height” will solve for the “Cone Angle.”

Height: The axial length of the conical skirt or support. This field is algebraically connected to the “Diameter”, “Top Diameter”, and “Cone Angle” fields. Entering the “Cone Angle” will solve for the “Height”; entering the “Height” will solve for the “Cone Angle.”

Length: Enter the length of the cylindrical skirt/intermediate support.

Joint Efficiency (Circ.): The joint efficiency of the circumferential joints (girth seams) in the skirt/intermediate support. This may be determined from Table UW-12 for welded joints, however several references would limit this value to 70% depending on how it is attached to the vessel wall and/or base ring.

Nominal Thickness: The skirt thickness in the new condition.

CA: Corrosion allowance on the inside of the component (concave side).

Long. Factor A: This is the Factor A that is determined in Step 1 of UG-23(b)(2). Factor A is determined using the corroded dimensions. For pipe, this is based on nominal thickness as opposed to minimum thickness.

Long. Factor B: The allowable longitudinal compressive stress determined in Step 2 of UG-23(b)(2) as B. Factor B is determined at the temperature listed for the internal pressure condition. Note that this is not the same Factor B that is determined for external pressure strength; the modulus value that is sometimes used in these calculations is from the external pressure chart, not from the TM tables.

Skirt/Intermediate Support 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.

Modulus of Elasticity: 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 and the skirt temperature. In cases where the skirt 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. Manually editing this field will sever the connection to the material in the database as indicated by the “Unlisted Material” caption.

Stress (Hot): The material allowable stress at the skirt temperature. 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 skirt temperature exceeds the highest temperature entry for this material’s stress line, the value will be zero. Manually editing this field will inform the software that the user is defining the material differently than what is stored in the database and the connection to the material in the database will be severed. This is indicated by the “Unlisted Material” caption.

Stress (Cold): The material allowable stress at 70 °F (20 °C). 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. Manually editing this field will sever the connection to the material in the database as indicated by the “Unlisted Material” caption.

Factor 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.

Yield Strength: The material yield strength at the skirt temperature listed for the internal pressure condition. This value comes from Section II, Part D, Table Y-1. In cases where the skirt 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. Manually editing this field will inform the software that the user is defining the material differently than what is stored in the database and the connection to the material in the database will be severed. This is indicated by the “Unlisted Material” caption.