Analytical Calculations
- Design Calculations.
- Pressure Containers design calculations
- Shaft design Calculations
- Equipment Support and Hold down bolting calculations
- Allowable External nozzle load Calculations
- Seismic Calculations
- Bearing Selection and Bearing life calculations
- Reliability, Availability and Maintainability Study of equipments
- Calculation of Mass Elastic data
1. Design Calculations
1.1 Pressure Containers Design Calculations
Thickness requirements of the Equipment casing, the stuffing box extension and requirements of the casing bolts shall be determined in accordance with the procedures given in the ASME BPVC and Texcelead design practices.
Nozzle wall stresses are calculated using standard engineering equations and evaluation shall be made using ASME Code formula for cylindrical shells.
The required seal gland plate thickness calculation shall be analyzed as a flat head and the gland studs are loaded by the pressure of the Equipment acting on an area bounded by the shaft and the O-ring diameter.
Thread depths for studs are compared to Code required minimums to confirm acceptability. Casing discharge and suction nozzle openings are evaluated for reinforcement as required by the Code.
1.2 Shaft Design Calculations
The shaft of rotating equipment shall be analyzed to determine the mean and alternating stresses that exist during normal and accident operating conditions. The mean and alternating von Misses stresses are calculated based on the uni-axial stress state that exists within the shaft. The von Misses stress values are used to generate modified Goodman diagrams at critical locations on the Equipment shaft.
The Goodman diagrams to show the resultant mean and alternating stresses with respect to the Goodman line and the yield line. The diagrams relate the calculated stresses to the shaft’s endurance limit and tensile strength at critical locations. The critical locations are the areas that have the highest normal and torsional stresses along the length of the shaft.
The shaft is determined to be acceptable if the stress falls below both the Goodman and yield lines. All stresses in the shaft are calculated at the design speed. Both the normal and faulted operating conditions shall be analyzed.
A static analysis is performed for the faulted loading condition to demonstrate structural integrity.
1.3 Equipment Support and Hold Down Bolting Calculations
Well known equations of equilibrium shall be applied to obtain the maximum reactions at the Equipment hold down bolts, motor hold-down bolts and other supporting structures.
The loads that were used to analyze the bolts are due to gravity, motor torque and externally applied loads. The coordinate system in analysis shall be their origins located at the geometric center of the respective bolt patterns.
Equipment support pedestal weld stresses shall be determined considering maximum reaction forces resulting from nozzle loads, dead weight, operational loads and seismic protection loads
1.4 Allowable External Piping Load Calculations
This analysis evaluates the Equipment operability considering the external piping loads, thermal loads and dead weight etc.
The Analysis to determine the loading sources other than piping load causing the excessive stresses or displacement of the Equipment and support structure. Evaluating the potential displacement due to thermal expansion does however the result in displacement which results in angular misalignment that exceeds the manufacturer recommended values.
Flanges and nozzles wall stresses shall be analyzed to qualify the customized piping loads and internal design pressure according to methodology provided in ASME BPVC codes and other standard engineering equations.
2. Seismic Calculations
The equipment shall be analyzed to qualify for the seismic loads in order to meet the requirements of International standards. The seismic factors shall be considered to the analysis according to natural frequency of the system and data of response spectra per customer specification.
The equipment shall be analyzed to determine the natural frequency. Analysis involves the evaluation of self weight, center of gravity, resolving all loads and moments to determine the reaction loads and principal stresses at support to validate with material allowable.
3. Bearing Selection and Bearing Life Calculations
The bearings are recommended based on the magnitude, direction of loads to be carried and physical dimensions of the shaft, the hydrodynamic loads are determined based on Texcelead’s methodology and empirical tests.
Reaction loads at bearing support shall be determined by considering all the rotor component masses, component locations and additional hydrodynamic loads.
The bearing life is determined per international standards and manufacturer recommendations considering additional factors like characteristics of lubrication oil, working temperature and contamination factors etc.
4. Reliability, Availability and Maintainability Study of Equipments
The study of preventive maintenance for the reliability of the equipment’s where safety and reliability is imperative, This study involves the identification of the essential function and critical components to study their failure mode and its effects on the availability of the unit to its allocated function.
The study shall also involve function description of all components, Evaluation of reliability, FMEA and recommendations and analysis of downtime for preventive maintenance, assessments of failure rate of equipment’s and its integral components.
5. Calculation of Mass Elastic Data
Mass elastic data shall be required to represent the rotor system and details of rotor to perform the torsional rotor dynamic analysis, this involves analysis of mass and inertia properties of rotor and its components, torsional stiffness of rotor between the rotor stations and creating rotor train sketch.