Pressure vessels high-strength steels

ASTM A 517, Specification for Pressure Vessel Plates, Alloy Steel, High-Strength, Quenched and Tempered... 

For BHWRs of large output, steel vessels welded on site or prestressed concrete pressure vessels have to be chosen and the latter give the lowest calculated cost. They are discussed in more detail In paras 31 to 36. For the steel vessel case. Improved high strength steels with Improved site welding and properties and reduced heat treatment requirements have been developed and are expected to be commercially available soon. 

The fifth component is the stmcture, a material selected for weak absorption for neutrons, and having adequate strength and resistance to corrosion. In thermal reactors, uranium oxide pellets are held and supported by metal tubes, called the cladding. The cladding is composed of zirconium, in the form of an alloy called Zircaloy. Some early reactors used aluminum fast reactors use stainless steel. Additional hardware is required to hold the bundles of fuel rods within a fuel assembly and to support the assembhes that are inserted and removed from the reactor core. Stainless steel is commonly used for such hardware. If the reactor is operated at high temperature and pressure, a thick-walled steel reactor vessel is needed. 

Concrete nuclear reactor vessels, of the order of magnitude of 15-m (50-ft) inside diameter and length, have inner linings of steel which confine the pressure. After fabrication of the liner, the tubes for the cables or wires are put in place and the concrete is poured. High-strength reinforcing steel is used. Because there are thousands of reinforcing tendons in the concrete vessel, there is a statistical factor of safety. The failure of 1 or even 10 tendons would have little effec t on the overall structure. 

The important property of high mechanical strength of duplex stainless steels has been profitably used in the fabrication of pressure vessels, and storage tanks. The digesters in the pulp and paper industry are made of duplex stainless steels of wall thickness of 19-21 mm compared with 31 mm thickness of carbon steel. Some typical wall thickness values of steels calculated for pressure vessels are noted below ... 

The pressure vessels are hollow cylinders, of 100- to 10,000-liter capacity, having a flange onto which the cover is fastened by means of bolts and nuts. The bottom of die vessel is usually hemispherical for greater strength. Autoclaves are almost always made of iron, either cast steel or cast iron, the former being safer to use at high pressures. Sheet iron is also used, in wall thicknesses up to 40 mm., in either riveted or welded construction. The reluctance in many dye plants to use welded autoclaves is entirely unjustified and has arisen simply because in the early days of the industry welding processes had not been perfected. 

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