The rules in Appendix 2 apply specifically to the design of bolted flange connections with gaskets that are entirely within the circle enclosed by the bolt holes and with no contact outside this circle, and are to be used in conjunction with the applicable requirements in Subsections A, B, and C of this division.Figure 2 shows an example of what is allowable and what isn’t. I didn’t find any explanation for the reason of why it can’t have contact outside de circle, but I suppose that it may have something to do with the bending generated by the bolt load (if you have any good explanation, please, contact me!).
The design of a flange involves the selection of the gasket (material, type, and dimensions), flange facing, bolting, hub proportions, flange width, and flange thickness. […] Flange dimensions shall be such that the stresses in the flange, calculated in accordance with 2-7, do not exceed the allowable stresses specified in 2-8. Except as provided for in 2-14(a), flanges designed to the rules of this Appendix shall also meet the rigidity requirements of 2-14. All calculations shall be made on dimensions in corroded condition.We’ll talk about the allowable stresses later on. The excpet provided in 2-14(a) is that you can skip the rigidity calculation if you had successful service experience for fluid services that are nonlethal and nonflammable and designed with the temperature range of -20°F (-29°C) to 366°F (186°C) without exceeding design pressures of 150 psi (1035 kPa).The Code, in the item 2-1(e) also says:
The rules of this Appendix should not be construed to prohibit the use of other types of flanged connections provided they are designed in accordance with good engineering pratice and method of design is acceptable to the Inspector. Some examples of flanged connections which might fall in this category are as follows: (1) flanged covers as shown in Fig. 1-6; (2) bolted flanges using full-face gaskets; (3) flanges using means other than bolting to restrain the flange assembly against pressure and other applied loads.So, it basicly tells you that you can design a flange that isn’t interily according to the Code, but uses good engineering pratices (reliable calculation, for example) and is accpetable by the Inspector. One type of flange that come to my mind when I think about it is the swing bolt type, which you can learn how to design it in this website as well!
This type covers those designs in which the flange has no direct connection to the nozzle neck, vessel, or pipe wall, and designs where the method of attachment is not considered to give the mechanical strength equivalent of integral attachment.Integral Type Flanges:
This type covers designs where the flange is cast or forged integrally with the nozzle neck, vessel or pipe wall, butt welded thereto, or attached by other forms of arc or gas welding of such a nature that the flange and nozzle neck, vessel or pipe wall is considered to be the equivalent of an integral structure. In welded construction, the nozzle neck, vessel, or pipe wall is considered to act as a hub.Optional Type Flanges:
This type covers designs where the attachment of the flange to the nozzle neck, vessel or pipe wall is such that the assembly is considered to act as a unit, which shall be calculated as an integral flange, except that for simplicity the designer may calculate the construction as a loose type flange provided none of the following values is exceeded: g0 = 5/8″ (16 mm), B/g0 = 300, P = 300 psi (2 MPa) and operating temperature = 700°F (370°C).