Solution Overview - TANK - Help - Hexagon PPM

The major steps performed in the solution phase are discussed in this section. Refer to codes API-650 and API-653 for additional details.

1. Wind effect - The specified wind speed is used to determine the applied wind pressure, the velocity factory, and the overturning moment. These values are used later in the computations for the wind girders and Appendix F considerations.

2. Allowable stresses for both the design and test cases - The material control routine includes considerations for reductions due to temperature from Appendix M and if necessary Appendix S and API-653 Section 2 requirements. The allowables for each shell course are determined individually based on the specified course materials.

3. Required shell course thicknesses - This thickness is based on the specified design method, either one-foot, variable point, or Appendix A. The appropriate sections of the code are implemented using the material properties to determine the thicknesses for each course for the design and test cases. Each thickness computation is then followed by a check of API-650 Section 5.6.1.1 to insure that the minimum thickness requirements of the code are met. If the input indicates that the software is to operate in analysis mode to rate an existing tank, the design and test thicknesses just computed are replaced with the users input thicknesses for subsequent computations. A note to this effect appears in the output below the thickness table when required.

4. Allowed fluid heights - This procedure involves the use of the same code sections used in the thickness determination. In the case of the variable point method, this is an iterative process.

5. Shell weight and center of gravity - The weight/center of gravity routine compares the computed shell weight with that specified by the user, and selects the maximum of the two for subsequent computations in Appendix E.

6. Overturning stability - This value is checked according to Section 5.11.

7. Wind girder requirements - The number of girders, their section moduli, and their locations are determined according to API-650 Section 5.9. Wind girder detail and size is then selected from API-650 Table 5-22.

This concludes the general computations performed for each tank input data set. All subsequent computations are optional depending on user specification.

• Roof Data - If the roof data has been specified, the software evaluates, analyzes, or designs the roof. Roof evaluation involves weight summations, required thicknesses and net areas according to API-650 Sections 5.10.5 or 5.10.6. The analysis or design of a supported cone roof applies the procedures outlined in Brownell & Young. Following the roof design, the Section 5.10.3 checks are implemented.

• API-650 Appendix F requirements - After the actual roof computations are completed, the API-650 Appendix F requirements are evaluated.

  Also note that the roof weights computed from a design are used in subsequent (seismic) computations.

• Seismic requirements of API-650 Appendix E - The guidelines of this appendix are applied to the tank in three conditions: design, test, and empty.

• Nozzle flexibility calculations as outlined in API-650 Appendix P - This appendix also offers guidelines on the maximum allowed nozzle loads. The software determines the flexibilities and limiting loads on up to fifteen nozzles for all three sets of shell course thicknesses (design, test, and user input).

• Grillage computations - These computations conform to the rules of API-650 Appendix I, Section 7.

• Settlement limits as set forth in API-653 Appendix B - These computations use an iterative procedure to determine the optimum cosine curve which most closely represents the user's measured values of shell settlement. After the cosine curve is known, the out-of-plane settlement and out-of-plane deflection can be determined.

• Service/maintenance computations - These computations are based on API-653 Section 2.

• API-2000 Venting calculations.

After all sizing, roof, and seismic computations have been completed, the evaluation for the permitted cycle life according to Appendix M, Section M.4 begins.

Following the cycle life calculations, the bolting requirements are checked. This procedure evaluates each of the load cases defined in Section 5.12 and determines, if necessary, the required number of bolts and the bolt size. A second pass is then made to determine the governing condition and to report a single bolt size and quantity, with the corresponding stress for each load case.