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ASME B31.3 Pressure Design of Closures

Closures are covered in para. 304.4.1. Listed components, such as ASME B16.9 pipe caps, can be used for closures. The other two options provided in ASME B31.3 are to design the closure in accordance with ASME BPVC Section VIII, Division 1, or to qualify it as an unlisted component in accordance with para. 304.7.2 (see Section 4.15). Specific references to ASME BPVC, Section VIII, Division 1 paragraphs are provided for ellipsoidal, torispherical, hemispherical, conical, toriconical, and flat head.

Openings in closures are covered in para. 304.4.2. These requirements are summarized below:

  • If the opening is greater than one-half of the inside diameter of the closure (as defined in ASME BPVC Section VIII, Division 1, para. UG-36), it should be designed as a reducer per para. 304.6 if the closure is dished and as a flange per para. 304.5 if the closure is flat.

  • Small openings and connections using branch connection fittings that comply with para. 304.3.2(b) or 304.3.2(c) are considered to be inherently adequately reinforced.

  • The required area of reinforcement is determined per the relevant ASME BPVC Section VIII Division 1 requirements [UG-37(b), UG-38, or UG-39], which depend on the type of closure; For example, only one-half of the area requires replacement for a flat head.

  • The available area of reinforcement is calculated per the rules in ASME B31.3, specifically para. 304.3.3 or para. 304.3.4. Note that ASME B31.3 requires that boundaries for a curved closure follow the contour of the closure (versus a chord dimension).

  • Rules for multiple openings follow para. 304.3.3 and para. 304.3.4 rules for multiple openings.


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