Solid-wall 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 ... 

The term solid-wall or monobloc vessel is applied to all components where the cylindrical wall consists of a single layer. Solid-wall vessels are suitable for all types of pressure vessels, in particular for those operated under high temperatures. Thermal stresses arising during heating or cooling are smaller than in multilayer vessels because of the good thermal conduction across the wall. Therefore solid-wall vessels are especially suitable for batchwise operation. 

Solid-wall vessels can be manufacured by different methods ... 

A solid-walled vessel, produced by forging or by boring a solid rod of metal, is most commonly used for vessels less than 12 in. in diameter or when the pressure exceeds 7,000 psi. 

A multi-layer vessel is a vessel in which the cyhndrical portion is made up of two or more contacting bands or layers. The inner shell is the innermost band of a multilayer vessel and is made in the same manner as any solid wall vessel. The inner shell can be of any suitable material to resist corrosion by the contents. This is one of the unique advantages of a multi-layer vessel. Subsequent layers are added on top of this inner layer by a variety of techniques to achieve the ultimate wall thickness required. 

Figure 8.1 summarises the most important methods of pressure vessel construction [1]. In this figure a distinction is first drawn between vessels with solid walls and those with compound (or layered) walls. Solid-walled vessels are normally produced as single forgings. In this method of construction the... 

The technological limitations of weight and size imposed by the above construction methods for solid-walled vessels may be overcome to a large extent by using vessels with laminated walls. A number of designs for such vessels are illustrated in Table 8.2 [2]. 

Relative merits of multilayer and thick solid Walled vessels [4]... 

Figures 8.5 and 8.6 show two pressure vessels which are used as extractors. The solid-walled vessel (Figure 8.5) has an inner volume of 2 m and is used for the extraction of hops. A special feature of this extractor is the inner...

Today most layered vessels arc constructed in accordance with the ASME Code, Vni-1, Division 2. The majori of the design equations given in the code for solid wall vessels are applicable to layered vessels. For fabrication, the ASME Code, VHI-l, Division 2, gives additional rules for layered-vessel constmetion. One criterion for controlling wrapping tightness of layered shells is that the area of any gap between two adjacent layers, as measured from the end of a shell section, must not exceed the thickness of a layer expressed in square inches. This is illustrated in Fig. 15.7. 

In this section, the phenomenon of BLEVE is discussed according to theories proposed by Reid (1976), Board (1975), and Venart (1990). Reid (1979, 1980) based a theory about the BLEVE mechanism on the phenomenon of superheated liquids. When heat is transferred to a liquid, the temperature of the liquid rises. When the boiling point is reached, the liquid starts to form vapor bubbles at active sites. These active sites occur at interfaces with solids, including vessel walls. 

It is well known that during liquefaction there is always some amount of material which appears as insoluble, residual solids (65,71). These materials are composed of mixtures of coal-related minerals, unreacted (or partially reacted) macerals and a diverse range of solids that are formed during processing. Practical experience obtained in liquefaction pilot plant operations has frequently shown that these materials are not completely eluted out of reaction vessels. Thus, there is a net accumulation of solids within vessels and fluid transfer lines in the form of agglomerated masses and wall deposits. These materials are often referred to as reactor solids. It is important to understand the phenomena involved in reactor solids retention for several reasons. Firstly, they can be detrimental to the successful operation of a plant because extensive accumulation can lead to reduced conversion, enhanced abrasion rates, poor heat transfer and, in severe cases, reactor plugging. Secondly, some retention of minerals, especially pyrrhotites, may be desirable because of their potential catalytic activity. 

The vessels are used as monobloc resp. solid-wall or multilayer features with appropriate connections, mainly consisting of endpieces and covers (Fig. 4.3-1). 

Put into a vessel, liquid helium will not only wet the walls but will also—in a gravity-defying act—form macroscopically thick films on the walls. The polarizability of liquid helium is greater than that of air (em > air) but less than that of the walls (em < Waii). As a result, the liquid tries to put as much of itself as possible near solid walls, to create an ever-thicker film to the extent that van der Waals energy can pay for this mass displacement against gravity. There is not actually any repulsion. Rather, there is attraction to the wall. Its effect is to thicken the helium "medium" and make it move up the attractive wall. 

The kinetic theory of gases was first propounded by Daniel Bernoulli in 1738. It was rediscovered and worked out in detail about the middle of the nineteenth century by Kr5nig, Waterston, Maxwell, and above all by Clausius. According to the kinetic theory the molecules of a gas move in straight lines unless they are deflected from their path by impacts with other molecules or with the walls of the containing vessel. They, therefore, exert on every solid wall a pressure which is measured by the momentum which the molecules impart to the wall in unit time. As this momentum is proportional to the number of collisions per unit of timclosed vessel is proportional to the square of the velocity of its molecules. It is assumed in this that all the molecules have the same velocity. When this is not the case, the pressure can be shown to be proportional to the mean square of the velocity. In any case we may write... 

The solid wall can be the wall of the evaporator itself, as in jacketed evaporators. The area available for heat transfer in jacketed vessels, however, is quite limited. Jacketed vessels frequently incorporate some sort of internal agitator. 

Typical U.S. materials for solid-wall ammonia converter shells have been A516 Gr. 70, A212 Gr. B and A302 Gr. C (Mn-Mo-Ni) and nickel-vanadium steel for multilayer vessels. For similar conditions, most European fabricators have selected alloy material WSB 62, 24-CrMo 10 and Ducol W30, for example. 

The determination of AH is, in principle, similar to that for other enthalpy changes. In practice, the fuel (or food) is mixed with an oxidizing agent (such as solid sodium peroxide (Na202) or pure oxygen gas) and sealed in a steel-walled vessel called a bomb calorimeter. The mixture is ignited by an electric current and the temperature rise recorded. The combustion reaction in a bomb calorimeter is not taking place at constant pressure, but this is easily allowed for in the final calculations. 

A Chinese manufacturing firm developed a ribbon wound technique for multi-layered vessel construction in the 1960s and has subsequently produced over 7,000 ribbon wound vessels. Kobe Steel in Japan, was originally a multi-layer vessel manufacturer and produced approximately 1,000 units of the concentrically wrapped types. They currently do not produce multi-layer vessels any longer but still engage in solid wall, monobloc construction. 

In general, the thicker the vessel, and the longer the vessel, the more attractive the multi-layer option becomes. It is usually more economical to design a multi-layer vessel with a large L/D ratio for a given volume. The selection of the multi-layer option is usually determined by economics. However, once the practical manufacturing limits of solid wall construction are exceeded, multi-layer may be the only option. 

Examples of solid-walled and multilayer extraction vessels... 

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