Pressure vessels fabrication

Table 1 gives an overview of high pressure processes currently employed and their classification for batch / continuous service. The types of pressure vessels fabricated for these design conditions can be seen in table 2. 

The ASME BPV Code Sec. VIII D.l Part UW describes the requirements for pressure vessels fabricated by welding. Limiting plate thicknesses are specified for each type of weld with the exception of double-welded butt joints. Requirements for radiographic examination of welds are also specified. Section UW-13 of the code specifies the types of welds that can be used to attach heads and tube sheets to shells. Section UW-16 gives rules for attachment of nozzles to vessels. 

The preferred types of joint and recommended designs and profiles are given in the codes and standards. See, for example, ASME BPV Code Sec. VIII D.l, Part UW— Requirements for pressure vessels fabricated by welding. 

Abstract This chapter describes requirements for speciality WWER reactor pressure vessel materials in terms of their chemical composition and mechanical properties. The main principles of manufacturing technology for WWER pressure vessel fabrication are also discussed, including welding and cladding. 

Manufecturer s Data Report for Pressure Vessels Manufacturer s Partial Data Report (A Part of a Pressure Vessel Fabricated 1 One Manufecturer for Another Manufecturer)... 

Suggested Format ftjr Welder/Welding Operator Performance Qualifications (WPQ) Fabricator s Data Report for Fiber-Reinforced Plastic Pressure Vessels (Class I) Fabricator s Partial Data Report (Class I) (A Part of a Fiber-Reinftjrced Plastic Pressure Vessel Fabricated by One Manufacturer for Another Manufecturer) Fabricator s Data Report for Class II Vessels... 

Plastic Pressure Vessel Fabricated by One Fabricator ftjr Another Fabricator)... 

The American Society of Mechanical Engineers (ASME) United Engineering Center 345 East 47th Street New York, NY 10017 The ASME Boiler and Pressure Vessel Code, under the cognisance of the ASME PoHcy Board, Codes, and Standards, considers the interdependence of design procedures, material selection, fabrication procedures, inspection, and test methods that affect the safety of boilers, pressure vessels, and nuclear-plant components, whose failures could endanger the operators or the pubHc (see Nuclearreactors). It does not cover other aspects of these topics that affect operation, maintenance, or nonha2ardous deterioration. 

For flanges of nonstandard dimensions or for sizes beyond the scope of the approved standards, design shall be in accordance with the requirements of the ASME Boiler and Pressure Vessel Code, Sec. T11, except that requirements for fabrication, assembly, inspection testing, and the pressure and temperature hmits for materials of the Piping Code are to prevail. Countermoment flanges of flat face or otherwise providing a reaction outside the bolt circle are permitted if... 

Code Administration The American Society of Mechanical Engineers has written the ASME Boiler and Pressure Vessel Code, which contains rirles for the design, fabrication, and inspection of boilers and pressure vessels. The ASME Code is an American National Standard. Most states in the United States and all Canadian provinces have passed legislation which makes the ASME Code or certain parts of it their legal requirement. Orrly a few jurisdictions have adopted the code for all vessels. The others apply it to certain types of vessels or to boilers. States employ inspectors (usually under a chief boiler inspector) to enforce code provisions. The authorities also depend a great deal on insurance company inspectors to see that boilers and pressure vessels are maintained in a safe condition. 

Inspection Authority The National Board of Boiler and Pressure Vessel Inspectors is composed of the chief inspectors of states and municipalities in the United States and Canadian provinces which have made any pari of the Boiler and Pressure Vessel Code a legal requirement. This board promotes uniform enforcement of boiler and pressure-vessel rules. One of the board s imporiant activities is providing examinations for, and commissioning of, inspectors. Inspeciors so qualified and employed by an insurance company state, municipality, or Canadian province may inspect a pressure vessel and permit it to be stamped ASME—NB (National Board). An inspector employed by a vessel user may authorize the use of only the ASME stamp. The ASME Code Committee authorizes fabricators to use the various ASME stamps. The stamps, however, may be apphed to a vessel only with the approval of the inspector. 

Subsection B This subsection contains rules pertaining to the methods of fabrication of pressure vessels. Part UW is applicable to welded vessels. Service restric tions are defined. Lethal service is for lethal substances, which are defined as poisonous gases or liquids of such a nature that a very small amount of the gas or the vapor of the liquid mixed or unmixed with air is dangerous to life when inhaled. It is stated that it is the user s responsibility to advise the designer or manufacturer if the service is lethal. All vessels in lethal service shall have all butt-welded joints fully radiographed, and when practical, joints shall be butt-welded. All vessels fabricated of carbon or low-aUoy steel shall be postweld-heat-treated. 

Rules for the welded fabrication of pressure vessels cover welding processes, manufacturer s record keeping on welding procedures, welder qualification, cleaning, fit-up alignment tolerances, and repair of weld defects. Procedures for postweld heat treatment are detailed. Checking the procedures and welders and radiographic and ultrasonic examination of welded joints are covered. 

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 ). 

Safety in Design Designing a pressure vessel in accordance with the code will, under most circumstances, provide adequate safety. In the code s own words, however, the rules cover minimum construction requirements for the design, fabrication, inspection, and certification of pressure vessels. The significant word is minimum. The ultimate responsibility for safety rests with the user and the designer. They must decide whether anything beyond code require-... 

Concrete pressure vessels may be used in applications that require large sizes. Such vessels, if made of steel, would be too large and heavy to ship. Through the use of posttensioned (prestressed) concrete, the vessel is fabricated on the site. In this construc tion, the reinforcing steel is placed in tubes or plastic covers, which are cast into the concrete. Tension is applied to the steel after the concrete has acquired most of its strength. 

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. 

Tubular Tubular membranes (Fig. 22-51) are supported by a pressure vessel, iisiiallv perForated or porous. It can be as simple as a wrapped nonw oven Fabric, or as robust as a stainless-steel tube. All rim with tube-side Feed. Thev are rnainlv used For UF, with some RO applications, particularly For Food and daiiw. The primary diameters available are 12 and 25 mm. Tubes are oFten connected in series parallel bundles, gasketed or potted, are also common. 

Low-carbon, low-alloy steels are in widespread use for fabrication-welded and forged-pressure vessels. The carbon content of these steels is usually below 0.2%, and the alloying elements that do not exceed 12% are nickel, chromium, molybdenum, vanadium, boron and copper. The principal applications of these steels are given in Table 3.8. 

These annealed brasses are used for fabrication of pressure vessels. They are cliaracterizcd by the following physical properties ... 

The maximum allowable stress values at normal temperature range for the steel plates most commonly used in the fabrication of pressure vessels are given in Table 12-3. For stress values at higher temperatures and for other materials, the latest edition of the ASME Code should be referenced. 

Most companies have a detailed general specification for the construction of pressure vessels, which defines the overall quality of fabrication required and addresses specific items such as ... 

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