Attachments and Loadings Tutorial
Once you have completed the design of your components and supports, you need to input the attachments, contents (including packing and liquid), insulation, applied forces, and wind load diameters of the vessel. This article will walk you through this process.
To begin, click the Vessel button on the Components pane and select "Attachments/Loads" from the menu.
Attachments Tab
The Attachments tab is where any weights and horizontal loads that need to be included in the structural analysis but are not already considered must be entered.
Note: The weights of your subcomponents (nozzles, stiffening rings, and flanges), jacket components, or heat exchanger components, must be entered here to be considered.
Vertical Vessel
Packing Wire Mesh: At an elevation of 150 inches there is packing wire mesh to hold up packing material. The weight of the mesh is 50 pounds and, since the center of gravity of the mesh is the same as the axis of the vessel, the eccentricity is zero. The mesh is in place prior to the hydro test so the "Include for Pressure Test" check box is selected.
Stiffening Ring: At an elevation of 225 inches a stiffening ring is attached to the inside of the vessel. The ring is a complete stiffening ring and is of constant cross section except for a few negligible sized holes for draining. Because the ring is complete and not partial and is basically of constant cross section, the weight of the ring is symmetric around the axis of the vessel and so the eccentricity is zero. Since the ring is in place before the hydro test, the "Include for Pressure Test" check box is selected.
Trays: At an elevation of 350 inches, two separate items exist: an attachment and a horizontal force. The trays are only 50 pounds, but they are not symmetric around the axis of the vessel so they develop an eccentricity which contributes to a bending moment.
The cross-section of the vessel is circular and a plane view of the elevation gives us 360 degrees in which to apply horizontal forces and eccentric weights. As the designer, you can arbitrarily pick your zero reference point. You can select the direction of the uppermost eccentric load or uppermost horizontal force as zero; you can select the direction north as zero. It does not matter what you select as long as you are consistent over the entire height of the vessel.
In this case, the trays are creating a bending moment which is trying to bend the vessel in a direction 15 degrees from the zero reference. At the same elevation, the applied horizontal force is creating a shear force in a direction 45 degrees from the zero reference, or 30 degrees from the direction of the eccentric trays (at lower plane elevations the shear force will have a moment associated with it due to a vertical moment arm). These items were not an issue to be considered in the hydro test so the box was left unchecked.
Horizontal Vessel
In this case, at a distance of 25 inches left of the reference line is an attachment with a weight of 2500 lb and a resultant horizontal force of 18,000 lb at a resultant direction that forms a 60° angle with the longitudinal axis of the vessel. These items will not be included in the Zick Analysis or Saddle design for the hydro test condition since the "Include for Pressure Test" box is not checked.
Some important points:
- The distance from the reference line is here solely for your benefit at this time. It will appear on the Attachment/Loading report, but it will have no effect on the calculations.
- The weight will be divided equally between the saddles; in this case, each saddle will see 1250 lb from this attachment weight.
- The horizontal forces will be separated into a longitudinal and a transverse force with the following relationship:
F is Horizontal Force (18,000 lb in this case) and θ is the Horizontal Resultant Direction (60° in this case). In this example, the longitudinal force component FLF will be 9000 lb and the transverse force component FTF will be 15,588 lb.
The FTF value will always be divided by two to find its effect on each saddle. The FLF value is different, though; its ultimate effect will depend on certain inputs and whether a sliding saddle is used.
Wind Tab
The Wind tab is used to input wind load diameters other than those of the outside diameter of the component.
Note: The wind load diameter will not automatically address expansion joints or jacket components. The information entered here should reflect those items.
Vertical Vessel
The default wind load diameter for cones and formed heads is the largest outside diameter of the component. This tab can be used to reflect increased wind load area due to ladders, stiffening rings, and insulation, or simply to make the calculations more conservative or easier to follow. This tab can also be used to change the wind load diameter for conical sections to the mean diameter. The program calculates the wind area of each section as rectangular by multiplying the height of the section by the wind load diameter; this includes heads and cones.
PW is the wind pressure determined from the wind code selection and inputs. EE and SE are the ending and starting elevations, respectively. DW is the wind load diameter for the segment. For this example, assume PW = 0.25 psi at all elevations. The value of FWfor the segment going from 0” to 85” will be 1593.75 lb. The value of FW for the segment going from 85” to 485” will be 6500.00 lb. The value of FW for the segment going from 485” to 511” will be 292.50 lb.
Horizontal Vessel
The values you enter for the wind load diameter will determine the wind load area in both the longitudinal and transverse directions. If a value is not entered here, the wind load areas will be calculated using the vessel outside diameter. The horizontal forces will be separated into a longitudinal and a transverse force with the following relationship:
PW is the wind pressure determined from the wind code selection and inputs. EP and SP are the ending and starting points, respectively. DW is the wind load diameter. For this example, assume PW = 0.5 psi. The longitudinal force component FLW will be 1413 lb and the transverse force component FTW will be 21600 lb. The FTW value will always be divided by two to find its effect on each saddle. The FLW value is different, though; its ultimate effect will depend on certain inputs and whether a sliding saddle is used.
Insulation Tab
The Insulation tab is used to input insulation that may exist on the outside of the vessel. This tab is only available for vertical vessels.
In the above example, the section of the vessel with insulation has an outside diameter of 60 inches (the 60” comes from the component info and is not seen in this screen), so the outside diameter of the insulation is 65 inches. The weight of the insulation is then automatically calculated from this information. The weight of the insulation is calculated using the following formula:
γIns is the specific weight of the insulation: for customary units, the specific weight and density are the same; for metric units, multiply the density times gravity to get the specific weight. EE and SE are the ending and starting elevations, respectively. OD and ID are the insulation outside and inside diameters, respectively. For this example, the insulation weight is 3407 lb.
In this case, the insulation was placed on the vessel prior to the hydro test so the "Include for Pressure Test" box was selected. The column on the far right only applies to vessels supported by skirts. If the elevations considered cross the boundary between the pressure boundary and the skirt (e.g. the bottom head is inside the skirt), specify whether the insulation is on the vessel (pressure boundary) or the skirt. An entry needs to be added to the wind tab to consider the effect of the wind load area of this insulation.
Liquid Tab
The Liquid tab allows for the input of liquids for the operating condition (the hydro condition will flood the vessel with water automatically) based on the starting and ending elevation in the vessel.
Note: This tab and the Summary page in the report are independent from each other. The flooded weight on the Summary Report will not be used in the operating condition calculations for your support design. Any fluid weight you wish to be considered in your operating condition must be entered here.
Vertical Vessel
If different rows are entered, the program will order them so that the least density is on top and the greatest is on the bottom. In the row where the starting elevation is the crown of the bottom head, any value less than or equal to the elevation of the crown of the bottom head will suffice. The software will only calculate the volume of fluid that can possibly exist within the vessel wall. The same is true for the row with the ending elevation of fluid being the crown of the top head - any value equal to or greater than the elevation of the top crown will suffice. In summary, if you wish to simply flood the vessel, enter a 0 for the starting elevation and a rather high value (like 5000) for the ending elevation and the software will take care of the rest. The equation for the weight of liquid between two elevations for a vertical vessel is show below.
γliquid is the specific weight of the liquid: for customary units, the specific weight and density are the same; for metric units, multiply the density times gravity to get the specific weight. EE and SE are the ending and starting elevations, respectively. ID is the inside diameter of the vessel. For this example, the ID is 60”, so the liquid weight is 12,756 lb.
Horizontal Vessel
In the above example, the liquid is slightly more than twice the density of water and it is 15 inches in depth in the vessel during operation. The weight of the liquid for a horizontal vessel is calculated using a more complicated formula than for a vertical vessel because of the nature of partial filling for horizontal vessels.
Packing Tab
The Packing tab is identical to the Liquid tab in function. This tab is only available for vertical vessels.
Limitations
- Wind Load Diameters entered that exist above the top head are not considered.
- Packing, Insulation, and Liquid entered above or below the pressure envelope are not considered.
- Weights and horizontal loads entered above the top head, are not considered in the Tower Analysis
Related articles