Fabrication welding

Tank Shell. Another example of where thickness is set by minimums for fabricabihty but not for strength is in small-diameter tanks. For example, a water storage tank built using a steel of an allowable stress of 20,000 psi (138 mPa), 9 ft (3 m) in diameter by 21-ft (7-m) high, requires a shell thickness to resist hoop stress of only 0.023-in. (0.58-mm) thick. However, if built to API Standard 650, the shell would be fabricated at least 0.1875-in. (4.76-mm) thick. The code requires this thickness so that when fabrication, welding, and tolerances are considered, a tank of acceptable quaUty and appearance meeting the requirements of most services in most locations is provided. 

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. 

The common wheel types are (1) backward and (2) radial. The types of construction of wheels are milled, fabricated, welded, and cast. See Figures 12-46A-H. 

For both heat-affected zone corrosion (intergranular attack) and knifeline attack the heat flux during welding and the time at temperature can critically affect the severity of the attack. Both these factors may vary from one welder to another, and when preparing pieces for corrosion testing not only should fabrication welding conditions be accurately reproduced, but the work of more than one welder should be evaluated. 

Inspections by owner include inspections, verifications, and audits of the construction of piping systems, which include fabrication, welding, heat treatment, assembly, erection, examination, and testing, in addition to the construction organization s documented procedures, personnel qualifications, and quality control records. 

Post-weld heat-treatment of casing fabrication welds Applicable material specification or ASME VIII, Division 1... 

Fabrication Method Field/shop fabricated, welded, cast forged, multi-layered, etc. 

Standards of pipework fabrication, welding, marking, erection, testing, painting, and cleaning, in complement to the design standard employed. 

Figure 13.7 Waterproof laminated fabrics welded with a Nd YAG laser using the ClearWeld technique. Note the lack of any surface melting—only the interface between the two fabric layers has been melted. (Image illustrating the use of ClearWeld reproduced courtesy ofTWI Ltd.) From TWI (2007).

Standard structural shapes, including pipe, which makes an excellent structural shape, can be used. Electrodes such as the E6OIO-II types are often the welder s first choice for this kind of fabrication welding because of their all-position characteristics. These electrodes, which are not low-hydrogen types, may be used providing the weldability of the steel is such that neither weld cracks nor severe porosity is likely to occur. 

Fifth, it is important to remember that corrosion resistance is not the only criterion when evalnating these new ferritic stainless steels. Welds must also be tough and ductile, and these factors mnst be considered when fabricating welds. 

Shell. Ruggedly fabricated welded steel. Shells 24 in (610 mm) and below are made of SA-106 Gr.B pipe. Larger shells are welded of steel plate of SA-516 Gr.70 normally. Tubesheets are normally of SA-516 Gr.70 material, but are also available in stainlesses, nickel alloys, Hastelloy, etc. 

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