High pressure vessel construction types

The rules of Section V111 -2 [ 2] do not specify a pressure limitation but are applicable to all types of high-pressure vessel constructions. Therefore, some additional considerations to these rules may be necessary to meet the design principles and construction practices essential to very high-pressure vessels. As an alternative to Division 2 [2], Division 3 should be considered for the construction of vessels intended for operating pressures exceeding 68.95 MPa (see the following section). 

In the construction of the wet oxidation unit, several areas of safety were considered. Of utmost importance was that of personal safety. Since this type of operation demands the use of high pressures and temperatures, operator contact with the high pressure vessels had to be limited. To accommodate this criterion, a barrier was constructed to shield the operator from any unforeseen releases from the reactor. This barrier was constructed from 1/4 inch steel and is desig ied in a manner that will fully contain any releases. This barrier is also equipped with two explosion vents to direct the force of any explosions away from the main walls and into a safe area. To further maximize personnel safety, all operator assisted controls are mounted on the outside of the unit. 

In the design of high-pressure vessels, both the size and the pressure involved will dictate the type of construction used. In general the following four types are used. 

For high pressure vessels, the nozzles are t5rpically loeated in the end elosures, and not in the shells. Frequently they have eenirally located openings with either integral or non-integral (loose) attachments for nozzles. This procedure provides for the design of both types of construction. 

A similar construction type is winding of a corrugated band in a helix on the core shell to form a high-pressure vessel. The additional advantage of the corrugation is the capability to transmit longitudinal forces from one layer to another, which allows... 

A relatively recent addition to the code is Part ULW, which contains requirements for vessels fabricated by layered construction. This type of construction is most frequently used for high pressures, usually in excess of 13,800 kPa (2000 Ibf/in ). 

Vessels for high-temperature serviee may be beyond the temperature hmits of the stress tables in the ASME Codes. Sec tion TII, Division 1, makes provision for construction of pressure vessels up to 650°C (1200°F) for carbon and low-alloy steel and up to 815°C (1500°F) for stainless steels (300 series). If a vessel is required for temperatures above these values and above 103 kPa (15 Ibf/in"), it would be necessaiy, in a code state, to get permission from the state authorities to build it as a special project. Above 815°C (1500°F), even the 300 series stainless steels are weak, and creep rates increase rapidly. If the metal which resists the pressure operates at these temperatures, the vessel pressure and size will be limited. The vessel must also be expendable because its life will be short. Long exposure to high temperature may cause the metal to deteriorate and become brittle. Sometimes, however, economics favor this type of operation. 

One solution to this issue is to use automation wherever possible and to use continuous (more properly referred to as steady-state) reactions rather than batch ones. Doing so, of course, is likely to increase the capital cost of the plant and reduce the versatility of the process and so the optimum balance must be found. The use of hazardous materials or high pressures will also increase the cost of the plant. In the former case, the materials of construction and the safety precautions will add to the cost. In the latter, the vessels must be stronger, hence usually thicker-walled and with additional safety features, again resulting in higher costs. The capital cost is usually depreciated over a set time, determined by the average lifetime of the type of plant in question. For example, if a plant costs 1,000,000 and is expected to last for 10 years, the annual depreciation would be 100,000. If the output is 10 ton per annum, then the capital depreciation will add 10 per kg to the cost of the product. 

When bisphenol A is used in conjunction with fumaric acid, a bis-A fumarate resin is produced. The best known trade marks for this type of resin are the Crystic 600 series supplied by Scott Bader, and the Atlac series, commercialized by DSM-BASF. This type of resin is noted for its excellent chemical and thermal resistance. It performs particularly well in contact with high pH solutions, and to a lesser extent with acids. It is, however, rather brittle, with only 2-3% tensile elongation at break, making it difficult to use for the construction of pressure vessels. Bis-A fumarates retail at around 4DMkg ... 

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