Asme Viii d1 Nma Appendix g

APPEN APPENDIX DIX G SUGGES SUGGESTE TED D GOOD GOOD PRACT PRACTICE ICE REGAR REGARDIN DING G PIPI PIPING NG REAC REACTI TION ONS S AND AND DESI DESIGN GN OF SUPP SUPPOR ORTS TS AND ATTACHM ATTACHMENT ENTS S

G-1

may be local stress concentration. A thicker wall plate at the support may serve to reduce secondary stresses and, if desired, a complete ring of thicker wall plates may be installed. installed. (d)   When When superi superimpo mposed sed forces forces on the vessel vessel wall wall occurring at the attachment for principal struts or gussets and suppor supports ts of any kind kind can produce produce high high bendin bending g stre stress sses es,, and and when when thic thicke kerr wall wall plat plates es do not not seem seem appropria appropriate, te, an oval or circular circular reinforcin reinforcing g plate may be used. used. The attach attachmen mentt of such such reinfo reinforci rcing ng plates plates should should be design designed ed to minimiz minimizee flexing flexing of the plate under under forces forces normal normal to the surfac surfacee of the vessel vessel..

A vessel vessel supported in a vertical vertical or horizontal horizontal position will will have have concen concentra trated ted loads loads impose imposed d on the shell shell in the region region where where the suppor supports ts are attach attached. ed. Primar Primary y and second secondary ary stress stresses es due to other other loadin loadings, gs, such such as the weight weight of water water presen presentt for hydrosta hydrostatic tic test, test, may exceed that due to normal internal pressure. Calculations to resist the forces involved are not given here because they they involv involvee so many many variab variables les depend depending ing upon upon the size and weight of vessels, the temperature of service, the internal pressure, the arrangement of the supporting stru struct ctur ure, e, and and the the pipi piping ng atta attach ched ed to the the vess vessel el as installed.

G-3 G-2

Vertica Verticall vessel vesselss may be suppor supported ted on a number number of  posts without substantial ring girder bracing them around the shell, provided provided they attach attach to the shell where where the latter is reinforced in an equivalent manner by the head of the vessel vessel or by an interme intermedia diate te partiti partition. on.

The The deta details ils of supp suppor orts ts shou should ld conf confor orm m to good good structural practice, bearing in mind the following items (see   Manual for Steel latest edition, edition, by Steel Construc Construction tion,,   latest the American American Institute of Steel Construction). Construction). (a)   All supports should be designed to prevent excessive sive locali localized zed stress stresses es due to temper temperatu ature re change changess in the vessel vessel or deform deformati ations ons produc produced ed by the interna internall pressure. External al stays stays in ring ring girder girders, s, or any intern internal al (b) Extern framing that may support other internal parts, may also exert exert a stiffe stiffenin ning g effect effect on the shell. shell. (c)   Columns supporting field assembled vessels and bear bearin ing g load loadss whic which h may may prod produc ucee high high seco second ndar ary y stress stresses es in the vessel vessel wall wall should should be so design designed ed at the attachment to the wall that no high stress concentration can occur near changes in shape, gusset plates if  any, any, or at ends ends of attachm attachment ent welds. welds. It is prefer preferabl ablee to use details details permitt permitting ing continu continuous ous welds welds extend extending ing completely around the periphery of the attachment and to avoid avoid intermi intermitte ttent nt or deaden deadend d welds welds at which which there there

G-4

Where Where vertic vertical al vessel vesselss are suppor supported ted by lugs, lugs, legs, legs, or brackets attached to the shell, the supporting members under these bearing attachments should be as close to the shell as possible to minimize local bending stresses in the shell. shell.

G-5

For large and heavy vertical vessels to be supported by skirts skirts,, the condit condition ionss of loadin loading g under under hydros hydrostat tatic ic tests, tests, before before pressu pressure re is applied applied,, or for any possib possible le combination of loadings (see UG-22) under the highest 519

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G-5

1998 SECTION VIII — DIVISION 1

expected metal temperature in service for the normal operating pressure, shall be compared in determining the best location for the line of skirt attachment. In applying UG-22 and UG-23(a) to vertical vessels supported on skirts, the following shall be considered in addition to pressure effects: (a)   the skirt reaction: (1)   the weight of vessel and contents transmitted in compression to the skirt by the shell above the level of the skirt attachment; (2)   the weight of vessel and contents transmitted to the skirt by the weight in the shell below the level of skirt attachment; (3)  the load due to externally applied moments and forces when these are a factor, e.g., wind, earthquake, or piping loads. (b)   the stress in the vessel wall due to the effects enumerated in (a) above. Localized longitudinal bending and circumferential compressive stresses of high order may exist in the metal of the shell and skirt near the circle of the skirt attachment if the skirt reaction is not substantially tangent to the vessel wall. When the skirt is attached below the head tangent line, localized stresses are introduced in proportion to the component of the skirt reaction which is normal to the head surface at the point of attachment; when the mean diameter of skirt and shell approximately coincide and a generous knuckle radius is used (e.g., a 2:1 ellipsoidal head), the localized stresses are minimized and are not considered objectionable. In other cases an investigation of local effects may be warranted depending on the magnitude of the loading, location of skirt attachment, etc., and an additional thickness of vessel wall or compression rings may be necessary.

G-9

may be reinforced by stiffening rings at intermediate sections.2

G-7

Large horizontal storage tanks for gases under pressure may be supported by any combination of hangers, with ring girders, stiffeners, and such other reinforcement as may be necessary to prevent stresses in the shell in excess of those allowed by UG-23 and to prevent excessive distortion due to the weight of the vessel when the internal pressure is near atmospheric.

G-8

Certain attachments may serve to mount a pump, compressor, motor, internal combustion engine, mixer, or any other rotating or reciprocating equipment upon a vessel. Such equipment can cause cyclic forces to act upon the attachment, upon the attachment weld to the vessel, upon the vessel shell, and upon the vessel supports. For such cyclic loading, the practices advocated in G-2(c) and (d) above are of particular importance. It is important to avoid resonance between the cyclic forces imposed by the equipment and the natural frequency of the vessel with the equipment in place.

G-9

Additional guidance on the design of supports, attachments and piping reactions may be found in the following references: (a)   British Standard BS-5500, Specification for Fusion Welded Pressure Vessels (Advanced Design and Construction) for Use in the Chemical, Petroleum, and Allied Industries; (b)   Welding Research Council Bulletin #107, Local Stresses in Spherical and Cylindrical Shells Due to External Loadings; (c)   Welding Research Council Bulletin #198, Part 1, Secondary Stress Indices for Integral Structural Attachments to Straight Pipes; Part 2, Stress Indices at Lug Supports on Piping Systems; (d)   Welding Research Council Bulletin 297, Local Stresses in Spherical and Cylindrical Shells Due to External Loadings, Supplement to WRC-107.

G-6

Horizontal vessels may be supported by means of  saddles1 or equivalent leg supports. For other than very small vessels, the bearing afforded by the saddles shall extend over at least one-third of the circumference of  the shell. Supports should be as few in number as possible, preferably two in the length of the vessel. The vessel 1

See “Stresses in Large Cylindrical Pressure Vessels on Two Saddle Supports,” p. 959,  Pressure Vessels and Piping: Design and Analysis,  A Decade of Progress,   Volume Two, published by ASME.

2

See Transactions ASCE, Volume 98 — 1931 “Design of Large Pipe Lines.”

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