Procedure 9-7 Field-Fabricated Spheres

Spheres are built according to ASME, Section VIII, Division 1 or 2, API 620 or BS 5500. In the United States, ASME, Section Vm, Division 1 is the most commonly used code of construction. Internationally spheres are often designed to a higher stress basis upon agreement between the user and the jurisdictional authorities. Spheres below 15 psig design pressure are designed and built to API 620. 

The allowable stresses for the design of the supports is based on either AWWA D100 or AISC. 

Typical materials are carbon steel, usually SA-516-70. High-strength steels are commonly used as well (SA-537, Class 1 and 2, and SA-738, Grade B). SA-516-60 may be used to eliminate the need for PWHT in wet H2S service. For cryogenic applications, the full range of materials has been utilized, from the low-nickel steels, stainless steels, and higher alloys. Spheres of aluminum have also been fabricated. 

Liquified gases such as ethylene, oxygen, nitrogen, and hydrogen are typically stored in double-wall spheres, where the inner tank is suspended from the outer tank by 

Standard sizes range from 1000 barrels to 50,000 barrels in capacity. This relates in size from about 20 feet to 82 feet in diameter. Larger spheres have been built but are considered special designs. In general, thicknesses are limited to 1.5 in. to preclude the requirement for PWHT, however PWHT can be accomplished, even on very large spheres. 

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Procedure 6-3 Design of Square and Rectangular Platforms, 304 Procedure 6-4 Design of Pipe Supports, 309 Procedure 6-5 Shear Loads in Bolted Connections, 317 Procedure 6-6 Design of Bins and Elevated Tanks, 318 Procedure 6-7 Agitators/Mixers for Vessels and Tanks, 328 Procedure 6-8 Design of Pipe Coils for Heat Transfer, 335 Procedure 6-9 Field-Fabricated Spheres, 355 References, 364... 

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