From this point there are two possibilities:
- complete all information per individual part
- use the design module for heat exchangers in the VES application
We will start with the design module and use the detail input possibility later for the modifications. The design module is the most efficient method when for example the design temperature and design pressure will be set for a new equipment. The design pressure and temperature is applicable for a number of parts and will be entered for all parts at the same time.
The design module will facilitate the data input for the exchanger. Input data necessary for the different parts of the heat exchanger will be completed in the database by the design module.
After double clicking the 'Heat exchanger design module' in the 'Equipment part list', the design module screen will be opened. For the full data sheet content refer to the appendices.
Figure 7 - Heat exchanger design data sheet
The following data can be entered of which most is necessary for the calculation unless indicated otherwise.
- NominalOD and the length of the shell, both of these figures are optional and are for indication of the equipment size only
- Connection is an indication of the location of the exchanger. It can be used to indicate a installation in series or parallel. This will provide the designer of the plant information whether exchangers can be stacked.
- The Tema class entrance can be R,C or B as per the Tema code. The selected option is use in the Tema to set the minimum allowed wall thicknesses that can be used in the heat exchanger design. The design option for Tema can be de-activated by selecting in the menu edit > options. At the tab 'General' unselect the 'Check Tema – Minimum' check box. The dialog 'Options' will be explained in the next sections.
- Select the allowable stress option as per code, 0 = ASME, 1 = RtoD, 2 = ADM
- Complete the data for the exchanger, design pressure, test pressure, vacuum pressure, design temperature, insulation thickness, number of passes, etc.
- The test pressure is not used in the calculations and is for completing the datasheet only
- The insulation thickness is used in the application to determine the stand-out required for the nozzles
- Use '1' for the joint efficiency to start the calculation. This value can be altered when the none destructive testing (NDT) details are determined. With the use of '1' the total strength of the material is taken into account in the calculations.
- The material code instructs, depending the Tema code, the program to use the specific 'Minimum Shell Thickness' Table in the Tema code
The buttons 'Nozzle list', 'Material list' and 'Options' in this section are to edit the nozzles, materials and design details. These buttons will be discussed later in this document.
Design data cylinders:
- The inside diameters can be entered by hand. Alternatively the user can use the buttons next to the input fields to select pipe size and schedules when the shells are made of pipe
- The wall thicknesses are optional. The minimum wall thickness is calculated by the program and/or are determined by the Tema code. Otherwise the optional values are used for the calculations
- The nozzle pads can be allowed Yes/No. If nozzle pads are not allowed the program will increase during the design the shell thickness for the minimum required strength. In hydrogen service nozzle pads (reinforcements) are usually not allowed.
- The nozzle pad default width and default thickness are optional and otherwise calculated by the program
Design data girth flanges:
The girth flanges are the flanges at channel and shell side, they are so-called body flanges. Select the type of flange: Straight (S) or Tapered (T). The Straight type is usually preferred since they are cheaper to manufacture.
- The Tema gives a standard gasket width of 3/8” (10 mm) up to a nominal outside diameter of 23” and ½ “ (13 mm) above 23” outside diameter of the shell
- The gasket thickness is not determined by the program. It is usually depending on the vendor used for the gasket, in this case we use 4 mm
- The button next to the 'Gasket Number' will open a new window for the selection of the gasket type. In this window, which will be discussed later, the selection will set the gasket number (for reference in the database only), the facing sketch and the material properties. The thickness, number and facing sketch can also be set manually. For the facing sketch refer to table 2-5.2 of ASME VIII Div 1. 'Effective gasket width”. ( In this table the applicable column needs to be selected depending the type of gasket. It will define the specific width factor toe determine the 'Effective gasket width'.)
- The seating pressure 'y' is determined via the gasket type settings but can be overwritten.
- The gasket factor 'm' is determined via the gasket type settings but can be overwritten.
- The partition factor is depending the number of passes, for example for a two pass there is a 30% more gasket area which needs therefore 130% of bolt tensioning to get to the required seating pressure on the gasket.
Design data tube sheet and bundle:
- The tubesheet thickness is optional, it can be set by the user or will be calculated
- The total allowance is the maximum of the (partition) groove depth and the corrosion allowance at the channel side, plus the corrosion allowance at the shell side see below figure. Tubesheet thickness and the allowance determines the thickness of the tubesheet for the calculations.
- The total tube length is including the extended parts. If the tubes are not up to the end of the tubesheet this factor can also be negative. The tubesheet extension is set by selecting in the menu edit > options and tab tubesheet which will open a new window. This window will be discussed later in detail.
- The number of tube holes are the actual holes in the tubesheet. There are two (2) holes per tube in a U-tube type exchanger.
- The outside diameter of the tubes is the nominal dimension for the diameter of the tubes.
- The thickness of the tube wall is usually based on the tables of the Birmingham Wire Gage (BWG), refer to section 9 table D-7M of the Tema Standard.
- The tube hole pitch is the distance between the centerlines of the tubes
- The pitch arrangement is the layout arrangement of the tubes. The layout can be triangular (three tubes on the corners of a triangle) or square (four tubes on the corners of a square).
- The perimeter bundle is the length of the line through the centerlines of the outside tubes. This factor is used to calculate the shear stress between the tubes and the tubesheet, refer to Tema section 5 paragraph RCB 7.133. The factor C will be used to calculate the equivalent diameter DL. The DL is used to calculate the effective (minimum required) tubesheet thickness for shear.
- Enclosed area A is determined by the perimeter C and is calculated by the software
- Largest bend radius is only applicable for U-tubes. The bend radius is used to set the distance and overall dimensions at the end of the bundle.
Figure U-Tube radius and end distance
- Smallest bend radius (only for U- tube) is the minimum allowable radius. An excepted value for the smallest bend radius is 1.0 * diameter of the tube, for spacing requirements at the end head of the heat exchanger.
- The mechanical datasheet usually gives the number of baffle spacings. This value is important for the calculation for the buckling length of the tubes. This is not applicable for the U-tube heat exchangers.
Figure baffle spacing
- The central baffle spacing is the distance between the central baffles as indicated in the figure
- The baffle spacing tubesheet is the the distance between the stationary tubesheet and the first baffle
- The spacing between the last baffle and the support plate is only applicable for the U-tube heat exchangers. This value will be calculated by the software and is shown on the overall settingplan.
- The thickness of the baffles is required for the calculation of the weights only.