Stiffening rings

For short closed vessels, and long vessels with stiffening rings, the critical buckling pressure will be higher than that predicted by equation 13.51. The effect of stiffening can be taken into account by introducing a collapse coefficient , Kc, into equation 13.51. 

Any stiffening rings used must be spaced closer than Lc. Equation 13.52 can be used to determine the critical buckling pressure and hence the thickness required to resist a given external pressure see Example 13.2. A factor of safety of at least 3 should be applied to the values predicted using equation 13.52. 

Figure 13.15. Effective length, vessel under external pressure (a) Plain vessel (b) With stiffeners (use smaller of 1J and Ls) (c) I — section stiffening rings (d) Jacketed vessel...

In vacuum distillation columns, the plate-support rings will act as stiffening rings and strengthen the vessel see Example 13.2. 

A vacuum distillation column is to operate under a top pressure of 50 mmHg. The plates are supported on rings 75 mm wide, 10 mm deep. The column diameter is 1 m and the plate spacing 0.5 m. Check if the support rings will act as effective stiffening rings. The material of construction is carbon steel and the maximum operating temperature 50° C. If the vessel thickness is 10 mm, check if this is sufficient. 

FIG. 10-186 Cost of large field-erected tanks in mid-1990, including stairs, platforms, and a normal complement of nozzles curve for carbon steel API Standard 650 tanks in quantities of three or more at a Gulf Coast site. For type 304 stainless steel, multiply cost by 2.5 and for type 316 stainless steel, multiply cost by 3.5. Allowances should be added to the factored costs as follows 10 percent for stiffener rings, 20 percent for API Standard 620, 15 percent for quantity of one tank, 10 percent for quantity of two tanks, and 15 percent of carbon steel cost for a congested working area. To convert gallons to cubic meters, multiply by 3.785 X 10- ... 

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