Plastic Limit Pressure Research Articles

Approximate Analysis of the Plastic Limit Pressures of Nozzles in Cylindrical Shells

An estimate of the limit pressure for cylindrical nozzles in cylindrical shells is derived from an upper bound analysis based on an assumed velocity distribution. The analysis is restricted to nozzle/shell diameter ratios of 1/2 or less. Comparisons with other theoretical approaches and the results of a single experiment are shown. Design graphs based on the analysis have been prepared to indicate the amount of nozzle or shell thickening required to make the limit pressure of the nozzle-cylinder structure approximately equal to the yield pressure of the imperforated cylinder.

Experimental Investigation of the Behaviour beyond the Elastic Limit of Flush Nozzles in Cylindrical Pressure Vessels

Eleven tests have been carried out on mild steel cylindrical pressure vessels with flush nozzles. The cylindrical vessel was 18-in outside diameter x 3/8-in thick and the nozzles covered a range of outside diameters from 2 1/2 in to 6 in and thicknesses from 1/8 in to 3/8 in. The nozzle-vessel weld was in all cases to B.S. 1500, Fig. 32 e. Two plain cylindrical vessels 18-in o.d. x 3/8-in thick were also tested to establish datum curves for the vessels with nozzles. Clock gauges and strain gauges capable of measuring up to 2 per cent strain were used to measure the strain and change of geometry in the vicinity of the nozzle-cylinder intersection. Measurements were also made of the pumped water volume as the pressure was increased. After pressurizing until the main vessel had yielded the instrumentation was removed and all vessels were tested to rupture. The results do not show a well defined plastic limit pressure as normally understood but it has been possible to define from the experiments a series of pressures for each specimen at which consistent patterns of stress, strain and deflection are evident. One of these pressures is chosen to derive an empirical relationship which can be used in formulating a minimum design requirement.