Design Constraints (Global Settings in PV Elite) - PV Elite - Installation - Hexagon PPM

PV Elite Quick Start (2020)

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Use the Design Constraints Tab to set the default values for the entire vessel. By entering the pressures and temperatures in these first four fields, PV Elite will use these values as the default values for the whole vessel. This saves time later.

Some of the other design constraints that you might what to consider are discussed below.

Datum Line Options

  1. Click the 3D View tab.

    PV Elite has located the datum line at the tangent line of the bottom head. We can change the location of the datum line at any time to move it to a more convenient location.

  2. Click Browse at the end of the Datum Line Options field.

  3. Type 3 for the Vertical Vessels offset, and then click OK. This sets the datum line to 3 feet up from its current location.

    After you have a skirt attached to the bottom of the vessel, you might want to move the datum line to the bottom of the skirt.

Hydrotest Type and Position of the Hydrotest

Select the type of hydrotest. For Division 1, the software provides the following methods to determine hydrotest pressure. Select one of the following:

  • UG-99b - ASME UG-99 (b), Division 1. The hydrotest pressure is 1.3 times (1.5 for pre-99 addenda) the maximum allowable working pressure for the vessel multiplied by the lowest ratio of the stress value S for the test temperature to the stress value S for the design temperature. This type of hydrotest is normally used for non-carbon steel vessels for which the allowable stress changes with temperature, starting even at a somewhat low temperature.

  • UG-99c - ASME UG-99(c), Division 1. The hydrotest pressure is determined by multiplying the minimum MAP by 1.3 (1.5 for pre-99 addenda) and reducing this value by the hydrostatic head on that part. The hydrostatic head is calculated based on the dimensions of the vessel and by values for Projection from Top, Projection from Bottom, and Projection from Bottom Ope. In addition, Pressure Test Position is used to determine the head pressure.

  • UG-99b(36) - ASME UG-99(b), footnote 36, Division 1. The hydrotest pressure is 1.3 times (1.5 for pre-99 addenda) the design pressure for the entire vessel, multiplied by the lowest ratio of the stress value Sa for the test temperature to the stress value S for the design temperature.

  • UG-100 - ASME UG-100 pneumatic test. The test pressure is 1.1 times (1.25 for pre-99 addenda) the maximum allowable working pressure for the entire vessel, multiplied by the lowest ratio of the stress value Sa for the test temperature to the stress value S for the design temperature.

    The stress ratio mentioned above includes bolt allowable stresses for flanges that are designed according to Appendix 2. This allowance usually results in a ratio of 1. See ASME Interpretation VIII-1-83-260 for more information. Click Tools > Configuration to turn off this option, resulting in a ratio greater than one in cases in which the operating and ambient stresses for the vessel parts are not the same.

  • No Hydro - No hydrotest pressure.

  • User Entered Pressure

  • 1.43 * MAWP (PED)

  • App. 27-4 - ASME Appendix 27-4, Division 1. The hydrotest pressure is 1.3 times the maximum allowable working pressure for the vessel multiplied by the lowest ratio of the stress value S for the test temperature to the stress value S for the design temperature. This type of hydrotest is normally used for glass-lined vessels.

For Division 2, the software provides the following methods to determine hydrotest pressure. Select one of the following:

  • AT-300 - ASME AT-300, Division 2, based on vessel design pressure. The hydrotest pressure is 1.25 times the design pressure marked on the vessel, multiplied by the lowest ratio of the stress intensity value Sm for the test temperature to the stress intensity value Sm for the design temperature. This type of hydrotest is normally used for non-carbon steel vessels for which the allowable stress changes with temperature starting even at a somewhat low temperature.

  • AT-301 - ASME AT-301, Division 2, based on calculated pressure. A hydrostatic test based on a calculated pressure is allowed by agreement between the user and the manufacturer. The hydrostatic test pressure at the top of the vessel is the minimum of the test pressures calculated by multiplying the basis for calculated test pressure for each element by 1.25 and then reducing this value by the hydrostatic head on that element.

  • AT-410 - ASME AT-410, Division 2, based on vessel design pressure. The pneumatic test pressure shall be no less than 1.15 times the design pressure multiplied by the lowest ratio of the stress value S for the test temperature to the stress value S for the design temperature.

  • Hydrostatic

  • Pneumatic

  • No Hydro - No hydrotest pressure.

User Entered Pressure

The next box lets you specify which position the vessel will be during the hydrotest:

Select a hydrotest position. This input is required so that the total static head can be determined and subtracted when UG-99c is selected for Pressure Test Type. This value is used in conjunction with Projection from Top, Projection from Bottom, and Flange Distance to Top to determine the total static head. Select from the following:

  • Vertical - The vessel is tested in the upright or vertical position. This is not common.

  • Horizontal - The vessel is tested in the horizontal position. This is common for most vessels. The vessel is on its side (in the case of a vertical vessel) or in its normal position (for a horizontal vessel).

Tall towers for example, are usually hydrotested in the horizontal position. PV Elite has to compute the hydrostatic pressure from the water in the vessel at hydrotest time. If the vessel is tested in the vertical positions, the pressure at the bottom of the vessel will be greater than if the vessel is tested in the horizontal position. Carefully consider the position that is appropriate to your situation.

Miscellaneous Weight %

Click to open the Miscellaneous Weight Percent Inclusion dialog box. This dialog box lets you specify to increase the mass of various elements and their details. There are three methods for applying the percentage of extra weight to use:

  1. Use a single percentage for all components - Increases all metallic elements of the vessel by a certain percentage. In the Miscellaneous Weight Percent for all Items box, type a percentage value to include additional weight which accounts for vessel attachments and internal items not otherwise included in the vessel. Typical values are 3.0 or 5.0. The software multiplies the total weight of the vessel by 1.0 plus this value converted to a decimal value (such as 1.03 or 1.05). Type 0 if no additional weight is needed.

  2. Use individual percentages for the different components - Increases the weight of an item by the percentage specified for the item in the Miscellaneous Weight Percentages section.

  3. Add percentages to increase weights of shells and heads - Increases the weights of the shells and heads by the sum of the percentage increase for nozzles, clips, and piping.

    If you use this option and model the nozzles or clips, the weight will be excessive.

    When using this option, the software calculates the weight of platforms automatically. You only need to specify the following information:

    • Is There a Top Head Platform? - Enables the additional weight fields.

    • Top Head Platform Uniform Weight - Specifies the grating weight from which the top head platform is constructed.

    • Circular Platform Uniform Weight - Specifies the grating weight from which the circular platforms are constructed.

    • Ladder Uniform Weight - Indicates the weight of the ladder per unit length.

      The top head platform, if specified, is square. The width the software uses to calculate the area is the larger of 4.5 feet (1.3716 meters) or the vessel inside diameter at the top head. Ultimately, the software adds the weight of the platform to the weight of the top head.

      Circular platforms are placed every 20 feet (6.096 meters) along the height of the vessel. The platforms are 3.5 feet (1.0668 meters) wide and sweep 180 degrees. PV Elite calculates the weights of the platforms. The software then adds the value to the mass of the element on which the platforms would theoretically exist, based on the dimension from the base of the skirt.

The software also calculates the total weight of ladders along the vessel. In addition, PV Elite proportions the total ladder weight to each element based on the element's length.

Design Code

PV Elite allows the user to perform vessel calculations in several pressure vessel codes. Use the Design Code field on the Home tab in the Units/Code panel to change the design code.

PV Elite supports the following design codes:

  • ASME Section VIII, Division 1

  • ASME Section VIII, Division 2

  • British Code PD 5500

  • European Code EN 13445

After you select a code, you will have to re-select the materials because each code has its own design stress tables.

Is this a Heat Exchanger

If the Dimensional Solutions 3D file interface button is selected, also select this option to write geometry and loading information for this vessel design to the <jobname>.ini file created in the current working directory. See Dimensional Solutions for more information about the Dimensional Solutions product line. This entry is optional.

To completely define an exchanger it is necessary to enter in the required information regarding the tubes, tubesheets and the floating head (if any). With the exchanger data, PV Elite can then compute the weights and required thicknesses of the exchanger components. For more information, see Tubesheet Analysis.

This check box is optional.

ASME Steel Stack

Select to perform an ASME steel stack analysis, based on the ASME recommended guidelines for Steel Stacks STS-2000 with addenda. This analysis is for circular stacks that meet the design requirements in the steel stack guidelines. The results are shown in the ASME STS Stack Calculations report. If Design Code is not set to Division 1 (ASME VIII-1), the stack analysis is not performed.

Also select this option if you are analyzing a steel stack and want to check it against ANSI/ASME STS-2000/STS-1a-2003. After the software completes the calculation, the program generates the Stress Due to Combined Loads report with a listing of the stack calculations. Compressive allowables in the report are calculated based on Section 4.4.

When selected, expand ASME Steel Stack and enter values for ASCE Wind Exposure, Factor of Safety, Mean Hourly Wind Speed, Is the Stack Lined?, and Importance Factor.

Read and understand the ASME stack guidelines. This is not a code like ASME Division 1 or 2, but a set of design guidelines for designers and engineers.

The following paragraphs from the stack guidelines are addressed:

  • 4.4 Allowable Stresses

  • 4.4.1 Longitudinal Compression, equations 4.7,4.8 and 4.9

  • 4.4.2 Longitudinal Compression and Bending

  • 4.4.3 Circumferential Stresses

  • 4.4.4 Combined Longitudinal and Circumferential Compressive Stresses

  • 4.4.5 Circumferential Compression in Stiffeners, equations 4.14, 4.15, 4.16

  • 4.4.7 Minimum Structural Plate Thickness

  • 5.2.2 Wind Responses, equations 5.3, 5.4 and (1),(2) and (3), (b) equations 5.5, 5.6 and 5.7

Design Modification

If any of the modifications is set to yes, PV Elite will correct the item should it fail in the analysis. For example, if Select Wall Thickness for Internal Pressure was set to Yes, PV Elite will automatically increase the thickness of a component should it not be thick enough.