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ASME PVHO-1-2002 pdf download

(2) Local Shell Tolerances (a) The maximum plus or minus deviation from the true spherical form, measured radially on the outside or inside of the vessel, shall not exceed 0.5% of the nominal outside radius of the spherical shell and shall not be abrupt. Measurements shall be made from a segmental template having the design inside or outside radius (depending where the measurements are taken) and a chord length L, equal to the arc length determined as follows. (b) From the required minimum ratio of thick- ness to outside radius tlR, obtained in Step 3 of (b), move vertically upward on Fig. 1.4-1 to the intersection of the dashed line. Move horizontally to the right from the dashed line and determine the ratio of critical arc length to outside radius LJR,. The chord length L, is obtained by multiplying this ratio by the outside radius R,. (d) Limitations. The following limitations apply to PVHOs designed in accordance with para. 1.4.7. For PVHOs not conforming to the following limitations, the external pressure design shall be as required by the specified Division of Section VI11 of the Code. (1) The maximum outside radius R, shall not exceed 60 in. (1500 mm). (2) The maximum shell thickness, including corro- sion allowance, shall not exceed 2 in. (50 mm). (3) The minimum shell thickness, excluding corro- sion allowance, shall not be less than “/s in. (10 mm). (4) The maximum external design pressure shall not exceed 900 psig (6.2 MPa gage). (5) The fabricated vessel, regardless of thickness, shall be postweld heat treated in accordance with the requirements of Section VIII, Part UCS (Division 1 design) or Article F-4 (Division 2 design). The PWHT shall be accomplished prior to conducting the external pressure test. (6) Materials of construction are limited to ferrous materials. (7) These rules are applicable only for spheres and spherical segments and are not applicable to cylindrical vessel parts and forms of other shapes. (e) External Pressure Test ( I) Test Pressure. All spherical vessels and vessels with spherical segments designed in accordance with para. 1.4.7 shall be subjected to an external hydrostatic pressure test that subjects every part of the vessel to an external pressure PT not less than 1.25P, to be marked on the vessel. (2) Post Test Measurements. Measurements for determining the deviations specified in (c), Tolerances, shall be taken after the external pressure hydrostatic test. Any deviations exceeding the limits of (c) Toler- ances, shall be corrected and the external pressure test repeated. 1.4.8 Windows (a) The design pressure and temperature of the trans- parent materials shall meet, or exceed, the design pressure and temperature of the chamber. (b) The design of transparent materials and their attachments to the chamber shall meet the requirements of Section 2 of this Standard. (c) The transparent materials shall be fabricated by processes specified in Section 2 of this Standard. (d) The designer shall consider all loadings, includ- ing, but not limited to, internal, external, hydrodynamic, hydrostatic, and thermal forces on the vessel. 1.4.9 Hatch Design. Hatches that do not use bolts (02) for attachments may be designed in accordance with the requirements of Division 1, appendix 1-6(g) with the following conditions: (a) the circular centerline of the spherically dished head shall pass through the centroid of the flange; (6) the connection of the dished head to the flange shall include fillet(s) of radius not less than 10 mm; (c) if an O-ring seal is specified, it shall be located at the mean radius of the flange; (d) hatch construction shall be from ferrous materials that meet ASMEPVHO requirements; and (e) if the hatch is convex to pressure, the minimum thickness of the head shall be the greater of that determined in Division 1, appendix 1-6(g) and that calculated from para. 1.4.7. 1.4.10 Rectangular Door Design. If rectangular openings are employed in either Division 1 or 2 con- struction, a detailed analysis of the interaction of the entire assembly (i.e., door, door frame, adjacent shell, and relevant appurtenances) shall be performed to ensure the design is adequate for the intended application. For Division 2 vessels, the analysis shall be performed in accordance with appendix 4.

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