OhmTech AS | Components Analysis Capabilities

Components Analysis Capabilities

Below is a brief summary of the component analysis capabilities:

	Shells & Heads(dished&flat): under internal and external pressure, calculates the minimum required thickness, maximum allowable pressure in new & cold and hot & corroded conditions and required minimum and maximum allowable hydraulic test pressure.
	Conical Shells: under internal and external pressure, calculates the minimum required thickness, maximum allowable pressure in new & cold and hot & corroded conditions, required minimum and maximum allowable hydraulic test pressure and reinforcement requirements at cone-to-shell junctions.
	Stiffener Rings: Most stiffener geometries consisting of rectangular sections can be defined, and both internal and external rings included. The relevant corrosion allowance is deducted from all surfaces of stiffeners. The stiffener proportions are also checked against code requirements.
	Out off Roundness Check: This module calculates the out of roundness of the shells based on at least 24 measurements of shell radius equally spaced around the circumference of the vessel. If the out-of-roundness of the vessel is greater than 0.5% of the radius measured from the true centre, the allowable external pressure will be recalculated based on the actual out-of-roundness values.
	Nozzles: VVD can accommodate design of any nozzle type, including set in, set on and protruding constructed from plate material, pipe or LWN forgings. The nozzle can be connected to any shell or end, and angled/oblique in any direction. The contributing area along the shell and nozzle will be checked(can also be reduced if required), and distances to discontinuities calculated. Nozzle to shell weld can be included in the design and the minimum weld size calculated. Single sided or double sided reinforcement pads can be included, and the pad limitations on thickness and width will be displayed and checked. Special designs like a nozzle located in the knuckle region of a dished end to EN13445 section 7.7 is also included.
	Groups of Nozzles: A check of nozzle group reinforcement is easily performed in VVD, since the location of all nozzles are known in visual mode no additional input is required. The software will calculate the inter-distance between all nozzles on each major components, and if the nozzle pair is classified as a group, a detailed reinforcement analysis of the nozzle group is performed. Groups of openings are also checked on nozzles located in flat ends.
	Nozzle Loads: for nozzles located in both cylindrical shells and dished ends. Calculates local stresses due to external loads according to PD5500 Annex G and EN13445 section 16 and compare results with calculated allowable stresses. The applicability of the PD5500 Annex G method has been extended to cover the entire range of geometries up to Co/r=0.25 for all values of r/t up to 250 according to the procedure given in reference [46] in Annex G.
	Line Loads: Calculates shell stresses due to line loads in longitudinal and/or circumferential direction to EN13445 section 16.6.
	Flanges: This module includes design of flanges with full face and narrow face flanges for virtually any geometry, subject to both internal and/or external pressure. Also included are reverse flanges, split flanges, lap joints and seal welded flanges. The bolts are designed to produce enough load for gasket seating in the Bolting Up Condition and sustaining both the hydrostatic end force and maintaining sufficient gasket pressure to ensure a leak-free joint in Operating Conditions. The recommended minimum clearance is based on TEMA (Standard of the Tubular Manufacturer Association) TABLE D-5. The program can also calculate the required bolt torque for bolting-up, operating, and hydrotest conditions.
	Skirt, Base Ring, Chairs & Ancor Bolts: The skirt design module calculates the stresses in two sections in the vessel shell adjacent to the skirt and 2 sections in the skirt. In addition this module calculates the stresses in the base ring, the anchor bolts, and the anchor bolt chairs. The method for calculating the stresses in the vessel shell and skirt is according to EN13445 Section 16.12 Vertical Vessels with Skirt. Any number, size and location of openings can be accommodated in the analysis, the system will check all sections and find the location of the maximum weakening. The displacement eps of the neutral axis due to the openings is also calculated to enable calculation of the additional moment due to this displacement. Anchor bolts are designed based on the maximum forces and required bolting area. The VVD database includes dimensions for both metric and imperial bolts. The selection of bolt diameters provides a sizing criteria for the chairs. Two type of chairs are accommodated, skirt with separate chairs and skirt with chairs that has a continuously welded top ring. A table with suggested dimensions for chairs is available to the user, and the chair selection is based on the bolting size. The program will calculate the minimum thickness of the top plate on the chair and the stresses in the vertical stiffeners on the chair based on the bolt loads. The minimum thickness of the basering is based on the bearing pressure taken by the ring, the width and the allowable stresses of the ring.
	Saddle Support: The types of saddle support covered by the program includes plain saddle support, saddle supports with internal stiffening rings in the plane of the saddle and adjacent to saddle, saddle supports with external rings adjacent to saddle, integrated saddle ring and hinged support. The saddle may be subjected to any number loads and any load combinations, including wind, blast, seismic and acceleration loads.
	Vertical Vessels with Bracket Support: Several different bracket geometries are included. The software will calculate the stresses in the vessel wall due to loads on the bracket. Two different load cases are generated by default (operating/design and test condition), however any number of load cases can be included.
	Vertical Vessels with Leg Support: Covers design of both straight/vertical legs and legs with and angle between leg axis and vertical axis. The software will check the stresses in the attaching vessel end and also stresses in the legs and perform a check of buckling. Two different load cases are generated by default (operating/design and test condition), however any number of load cases can be included.
	Tubesheets: covers design of floating heads, U-tube bundle and fixed tubesheets with and without expansion bellow. This module calculates the required thickness of the tubesheet and flanged extension, determines the tube stresses, tube-to-tubesheet joint loads and allowable loads. Corrosion allowance on both sides and pass partition grooves are considered in the tubesheet design.
	Tube Bundle: Checks the tubes for internal (tubeside) & external (shellside) pressures, calculates weight and CG of tube bundle. Also enables drawing generation of tube bundle.
	Floating Heads: includes design of the spherical domed end and the flange section of the floating head. Design of both narrow faced flanges and full-faced flanges are included. The domed end and flange are designed for both internal pressure and external pressure. The methods included are: PD5500: Section 3.5.6 Spherically domed and bolted ends of the form shown in figure 3.5-36 and EN13445: Section 12: Bolted Domed Ends
	Lifting Lugs: Includes design of lifting lugs and lifting trunions. Calculates the stresses in the shell and in the lug/trunions to verify stress values to be within code acceptance limits.
	User Specified Components: The user specified components are used to include any additional components that are not yet included in the standard/software. By specifying the mass, volume, CG and projected surfaces in x, y and z direction, the software will be able to accommodate any internal or external component/structure(ladders, platforms etc.) and include it in the calculation of vessel weight, volume, CG, external loadings (seismic, wind, blast etc.), vessel deflection, and in calculation of natural frequency for tall towers.
	Fatigue Analysis: The fatigue analysis module can accommodate both constant amplitude loading and variable amplitude loading. Based on the loading data and data for the different components included in the analysis, the allowable number of cycles will be calculated for each component. In the case of variable amplitude loading the total fatigue damage index due to the cumulative effect of the cycles that form the design stress range spectrum will be calculated. Default values for all the input data in the components input table can be automatically generated based on previous calculation data for each component..
	Tall Tower Analysis: VVD calculates the static effects of external loads on tall towers/vertical vessels. The software can accommodate any type of loads and include the effects of wind, blast, seismic, weights, operating liquid heads, internal & external pressures, and the user can add any additional loads. User Specified components are used to include additional loads to accommodate trays, external piping, ladders and platforms. The system generates by default 7 loads and 5 different load cases covering Erection, Hydrotest, Transportation, and Operation in combination with Blast condition and Seismic. The loading on external vessels are calculated at discrete intervals along the vessel centreline (z-axis). Seismic and accelerations loads consider elemental weight and shear calculations along the vessel length. The stresses are calculated at the base of each component (shell, end or cone section), except for conical shells were the stresses also are checked at the top section. The stresses are also checked in the section of the vessel just below the skirt. In this section the weight of the content of the vessel causes tensional stresses. Both the internal and external pressure cases are checked. The external pressure case will add compressive stresses and may govern the design analysis. The internal pressure is the pressure at the top increased by the static head of test/operating liquid at the elevation considered. Stresses are calculated in all components for all load cases. For the code PD5500 the stress calculations and stress limits are in accordance with Annex A3.5 & A3.6 and Annex B. For the code EN13445 the stress calculations and stress limitations are in accordance with sections 16.14.6 (internal pressure case) and section 16.14.7 (external pressure case). The deflection is calculated for each loading case. The system will accommodate any vessel geometry with variations in thickness, diameters and unevenly weight distribution and flexibility. A numerical integration is carried out along the vessel centreline (z-axis) to determine the shear forces, moments and deflection. The software will plot shear forces, moments and deflection along the z-axis of the vessel in both the x- and y- directions. The maximum values are calculated by vectorial additions. For vertical vessels the first natural period/resonance frequency of vibration is calculated for each loading case, and compared against the actual wind loading to determine if wind induced vibration is a potential problem.