External pressure Code Case

In 1998, Code Case 2286 Alternative Rules for Determining Allowable External Pressure and Compressive... 

There are several differences between Code Case 2286 and the older vacuum chart method. One difference is the upper limit of temperatures that each method has. Code Case 2286 has a limit of 800F for carbon steels found in UCS-23.1 and 800F for stainless steels in UHA-23, whereas the vacuum charts have higher limits for the more common carbon steels and stainless steels (except in a few cases). See Section II, Part D, Mandatory Appendix 3 for criteria and figures with temperature limits for various classes of materials under external pressure and axial compression. It should be noted that neither method has accounted for the effects of creep on buckling. A complete list of what 2286 covers that the... 

The procedure for designing a simple cylindrical vessel to Code Case 2286 or Section VIII, Division 2 is to first establish geometry as weU as determine shell thickness values to begin with. Typically, some thickness is estab-hshed from, say, internal pressure and those thickness values are used for starting the procedure in Code Case 2286. External loads from wind and seismic design criteria must be estabhshed to complete the procedure. 

The effect of combining intemal/external pressure with axial tension/compression may be represented by an ellipse created using a yield criterion. In the four quadrants created by the yield criterion, four combinations of the internal/extemal pressure with axial tension/compression may be represented. In the case of external pressure, quadrants three and four (external pressure and axial compression, and external pressure and axial tension) are representative of what is discussed here. Furthermore, only quadrant three is evaluated in Code Case 2286 and Section VIII, Division 2, Part 4 since the topic of internal pressure is not addressed. 

Pipe-Wall Thickness. Once the design pressure and temperature have been established and the pipe material and size selected, the wall thickness is calculated using the appropriate section of the code. In rare cases, a thin pipe must be made thicker to withstand handling. Occasionally the thickness is affected by external loads or vibrations. All codes prescribe essentially the same design formula for metallic hoUow circular cylinders under internal pressure ... 

If a CRM lined pressure vessel is to be designed for below -20°F (-29°C) for reasons other than seasonal atmospheric temperature. Section VIII, Division 1 of the ASME Code requires that the materials and fabrication practices meet minimum notch toughness requirements (Paragraph UG-84). Paragraphs UCS-65, 66 and 67 cover the requirements for vessels operating below -20°F. The use of SA-36 or SA-283 is not permitted. Impact tests are required except for seasonai temperature excursions beiow -20°F (-29°C) or when exempted by paragraph UCS-66 (c) which states that "no impact test is required for materials used for metal temperatures below -20°F (-29°C) when the minimum thickness is the greater of those determined under the most severe conditions of coincident pressure (external or internal) and temperature in accordance with UG-21 for temperatures of (a) -20°F (-29°C) and above and (b) below -20°F (-29°C), in which case the coincident pressure (internal if above atmospheric pressure and external if below atmospheric pressure) shall be multiplied by 2%."... 

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