Pressure vessels thick-walled

Figure 9.4 A thick-walled pressure vessel might be economical when compared with a thin-walled vessel and its relief and venting system.

Creep of Thick-walled Cylinders. The design of relatively thick-walled pressure vessels for operation at elevated temperatures where creep caimot be ignored is of interest to the oil, chemical, and power industries. In steam power plants, pressures of 35 MPa (5000 psi) and 650°C are used. Quart2 crystals are grown hydrothermaHy, using a batch process, in vessels operating at a temperature of 340—400°C and a pressure of 170 MPa (25,000 psi). In general, in the chemical industry creep is not a problem provided the wall temperature of vessels made of Ni—Cr—Mo steel is below 350°C. 

Jasper, McL, T. and Scudder, C. M. (1941) Trans. Am. Inst. Chem. Eng. 37, 885. Multi-layer constmction of thick wall pressure vessels. 

The bodies of thick-walled pressure-vessels with an outer- to inner-diameter ratio d /dj > 1.2 can either be manufacured as monobloc (solid-wall vessels) or be constructed of several layers (multi-wall vessels). During the process of design and fabrication of such vessels some significant and common rules must be observed ... 

An intermediate form of isostatic pressure sintering, sometimes referred to as pseudo-isostatic hot-pressing, uses uniaxial hot-pressing apparatus but immerses the object to be sintered in a refractory non-interacting powder within the die and punches. This avoids the very considerable expense of building a furnace inside a thick-walled pressure vessel but the results are inferior to those achieved with true isostatic hot-pressing. 

Y. Murakami, T. Nomura, J. Watanabe, MPC/ASTM Symposium on the Application of 21/4 Cr-1 Mo Steel for Thick Wall Pressure Vessels, Denver, Col. 1980. J. Watanabe et al.,... 

P(R + 0.5t)/t. Values obtained from the use of this form of the equation provide stress values within 2% of the values calculated using the more exact thick-walled pressure vessel formulas. 

ASME Section VIII, Division 1 requirements to prevent brittle fracture are 15 ft. -lb. Charpy Keyhole applied only below -20°F. Until recently, these requirements were thought to protect against brittle fracture. In the past few years, however, a considerable number of catastrophic brittle fractures in thick-wall pressure vessels have occurred throughout all industry. In each instance, the code impact values seemed to have been met or exceeded. 

The design and construction of small-scale pilot-plant units for processing under extreme conditions of pressure and temperature have been described. This description includes material on constructing barricades, thick-walled pressure vessels, and pumps as well as information on the selection of alloys and the effects of hydrogen on the properties of metals. 

From the perspective of engineering mechanics, the ventricles are three-dimensional thick-walled pressure vessels with substantial variations in wall thickness and principal curvatures both regionally and temporally through the cardiac cycle. The ventricular walls in the normal heart are thickest at the equator and base of the left ventricle and thinnest at the left ventricular apex and right ventricular free wall. There are also variations in the principal dimensions of the left ventricle with species, age, phase of the cardiac cycle, and disease (Table 54.3). But, in general, the ratio of wall thickness to radius is too high to be treated accurately by all but the most sophisticated thick-waU shell theories [1]. 

Moulds must resist high pressures without distortion, and resist wear over 10 cycles or more they are usually made from forged blocks of low-alloy steel, air-hardened after machining. Moulds act as thick-walled pressure vessels, with high tensile stresses in the walls. For a melt pressure of 50 MPa and a cavity diameter that is four times the wall thickness, the average hoop stress in the wall is 100 MPa from Eq. (C.21). Concave corners in the mould cavity act as stress concentrating features, so to... 

Hie major methods for manufacture of thick-walled pressure vessels are as follows ... 

The reaction space itself is enclosed by an inner shell with relatively thin walls which is accommodated inside the thick-walled pressure vessel. The space between the inner and outer shells is filled with boiling water to cool the inside. This boiling water is pressurized to a level slightly higher than the reactor pressure it is used to generate steam which can be added to the gasifying agent. 

Two basic modes of failure are assumed for the design of pressure vessels. These are (a) elastic failure, governed by the theory of elasticity and (b) plastic failure, governed by the theory of plasticity. Except for thick-walled pressure vessels, elastic failure is assumed. When the material is stretched beyond the elastic limit, excessive plastic deformation or rupture is expected. The relevant material properties are the yield strength and ultimate strength. In real vessels we have a multiaxial stress situation, where the failure is not governed by the individual components of stress but by some combination of all stress components. 

If the Cockenzie drum had survived this hydraulic pressure test (the seventh and last) it would have entered service. Sometime later, when pressurized with steam, it would have failed, and the explosion would have caused massive damage, and probably injuries and deaths. The question is this How can we be really sure that there are no significant cracks in thick-walled pressure vessels ... 

High reactor coolant temperatures are required to produce electricity efficiently. Removing this constraint allows the development of very safe concepts. Although revenue from the sale of electricity is lost, capital costs are reduced by eliminating turbines, generators, some support facilities, some backup safety systems, and a thick-walled pressure vessel. Reactor containment costs are reduced. Reactor design becomes simpler and more flexible, which also reduces costs. The mission of destroying plutonium is not impeded by electricity load demand concerns and delays caused by maintenance of electrical systems. 

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