The Design of Stiffening Rings | External Pressure Vessel l Introduction | Part-1

In this video chemical engineering industrial academy will explain
STIFFENERS RING DESIGN ANALYSIS
In the design of stiffening rings, there is no direct procedure or formula to size or design the rings. Instead, the specific size and type of ring are first specified, and then they are analyzed for their moment of inertia and resistance against lateral buckling. If these parameters satisfy the design criteria, the rings' design is then optimized and finalized.
Why there is the need of Stiffening Rings?
If the actual external pressure exceeds the maximum pressure, the vessel can withstand, then the options for reinforcement, include increasing the vessel's thickness, increasing the shell thickness, solely to meet external pressure requirements, may not always be cost-effective or 2nd option is altering its geometry. Geometry of the vessels means the length to diameter ratio and shape of the vessel.
And also, vessel's diameter and length cannot be changed easily, once designed, due to couple of reasons, the obvious reasons may be,
• The designed capacity,
• Position and orientation in plant layout,
• Constraints in instrumentations and operations,
• Cost effectiveness,
• Integration with other equipment, and
• Local machining and fabrication facility constraints for a typical vessel,
and also couple of other reasons may be.
So, what is the solution?
One practical solution is there, that the distance between lines of supports can be changed, or adjusted. This is an alternative solution for strengthening the vessel against external pressure, to utilize external or internal stiffening rings or a combination of them.
But how this works?
Notice here that, reducing the distance between support lines, by adding stiffening ring, enhances the stability of the vessel's shell, the effect is similar to a shorter simply supported beam, that can withstand greater external loads, it is exactly what the stiffening ring do with external pressure vessel.
The required thickness of a shell with a given diameter, under a specified external pressure, can normally be reduced by shortening the shell’s effective length in between the support lines. The length can be reduced by providing stiffening rings at various intervals.
Added Advantages:
Adding Stiffening Rings, also provides an excellent solution, in some stages of design fabrication and operations
 The first one is, due to miss calculation in designing the thickness prior to fabrication,
 In second scenario, it may possible that some changes have been made in process condition, later on, of previously installed vessel,
 The third possibility is that a newly designed vessel has been started, and it has been reached up to such stage of fabrication, that you can do nothing with vessel length, and diameter.
These issues can be solved simply by adding stiffening rings
Let us start the design procedure,
So, where to start?
Let us first take some overview of, some of the main steps, for the design of stiffening rings, and then we will deep dive in one of each step.
I. In first step Select or suggest the type of stiffening ring and determine its cross-sectional area As, so what is the criteria for the selection of stiffening rings, there are different
type of stiffening rings try to choose any standard stiffening rings available in your local market, but standard stiffening rings creates problems in circular bending and fabrication, then the other way is, to choose a flat plate that can be easily bended and welded to the shell even in small several pieces and then take more flat plat and make angle, c channel, or whatever you suited, and in this way bending and fabrication become much easier whatever you suit but each of the them will have different cross-sectional area.

The calculation of cross-sectional area of ring (As) area we will illustrate later on
Now in the 2nd step
II. Assume the required number of rings and distribute them equally between
1-Head lines at 1/3h of its depth of head h
2-Jacketed section,
3-Cone-to-shell junction
And determine dimension, Ls,
We will see all these cases one by one respectively, so, first in case of cylindrical vessel, we are assuming that four stiffening rings of T-bar type have been, Suggested, and installed, between headlines at 1/3h of depth of head, as they are acting as a line of supports, and shortening the simply supported beam. For the sake of better understanding, it is necessary to discuss the concept of Support lines.

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