ASME B&PVC sec81$$u10 06-02-99 16:28:04 pd: sec81 Rev 14.04

UG-24 PART UG — GENERAL REQUIREMENTS UG-27

are to be used in vessels to contain lethal substances(UW-2).

(a) Castings of cast iron (UCI-2) and cast ductileiron (UCD-2) are prohibited.

(b) Each casting of nonferrous material permit-ted by this Division shall be radiographed at all criticalsections (see footnote 1, Appendix 7) without revealingany defects. The quality factor for nonferrous castingsfor lethal service shall not exceed 90%.

(c) Each casting of steel material permitted bythis Division shall be examined per Appendix 7 forsevere service applications [7-3(b)]. The quality factorfor lethal service shall not exceed 100%.

(b) Defects. Imperfections defined as unacceptableby either the material specification or by Appendix 7,7-3, whichever is more restrictive, are considered tobe defects and shall be the basis for rejection of thecasting. Where defects have been repaired by welding,the completed repair shall be subject to reexaminationand, when required by either the rules of this Divisionor the requirements of the castings specification, therepaired casting shall be postweld heat treated and, toobtain a 90% or 100% quality factor, the repairedcasting shall be stress relieved.

(c) Identification and Marking.Each casting to whicha quality factor greater than 80% is applied shall bemarked with the name, trademark, or other traceableidentification of the manufacturer and the casting identi-fication, including the casting quality factor and thematerial designation.

UG-25 CORROSION

(a) The user or his designated agent (see U-2) shallspecify corrosion allowances other than those requiredby the rules of this Division. Where corrosion allow-ances are not provided, this fact shall be indicated onthe Data Report.

(b) Vessels or parts of vessels subject to thinningby corrosion, erosion, or mechanical abrasion shall haveprovision made for the desired life of the vessel by asuitable increase in the thickness of the material overthat determined by the design formulas, or by using someother suitable method of protection. (See Appendix E.)

NOTE: When using high alloys and nonferrous materials either forsolid wall or clad or lined vessels, refer to UHA-6, UCL-3, andUNF-4, as appropriate.

(c) Material added for these purposes need not beof the same thickness for all parts of the vessel ifdifferent rates of attack are expected for the various parts.

(d) No additional thickness need be provided whenprevious experience in like service has shown that

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corrosion does not occur or is of only a superficialnature.

(e) Telltale Holes.Telltale holes may be used toprovide some positive indication when the thicknesshas been reduced to a dangerous degree. Telltale holesshall not be used in vessels which are to contain lethalsubstances [see UW-2(a)], except as permitted by ULW-76 for vent holes in layered construction. When telltaleholes are provided, they shall have a diameter of1⁄16

in. to 3⁄16 in. (1.6 mm to 4.8 mm) and have a depthnot less than 80% of the thickness required for aseamless shell of like dimensions. These holes shallbe provided in the opposite surface to that wheredeterioration is expected. [For telltale holes in clad orlined vessels, see UCL-25(b).]

(f) Openings for Drain.Vessels subject to corrosionshall be supplied with a suitable drain opening at thelowest point practicable in the vessel; or a pipe maybe used extending inward from any other location towithin 1⁄4 in. (6 mm) of the lowest point.

UG-26 LININGS

Corrosion resistant or abrasion resistant linings,whether or not attached to the wall of a vessel, shall notbe considered as contributing to the strength of the wallexcept as permitted in Part UCL (see Appendix F).

UG-27 THICKNESS OF SHELLS UNDERINTERNAL PRESSURE

(a) The thickness of shells under internal pressureshall be not less than that computed by the followingformulas.14 In addition, provision shall be made forany of the other loadings listed in UG-22, when suchloadings are expected. (See UG-16.)

(b) The symbols defined below are used in theformulas of this paragraph.

tp minimum required thickness of shell, in.Pp internal design pressure (see UG-21), psiRp inside radius of the shell course under con-

sideration,15 in.Sp maximum allowable stress value, psi (see UG-

23 and the stress limitations specified in UG-24)

14Formulas in terms of the outside radius and for thicknesses andpressures beyond the limits fixed in this paragraph are given in 1-1 to 1-3.15For pipe, the inside radiusR is determined by the nominal outsideradius minus the nominal wall thickness.

ASME B&PVC sec81$$u10 06-02-99 16:28:04 pd: sec81 Rev 14.04

UG-27 1998 SECTION VIII — DIVISION 1 UG-28

Ep joint efficiency for, or the efficiency of, appro-priate joint in cylindrical or spherical shells, orthe efficiency of ligaments between openings,whichever is less.

For welded vessels, use the efficiency speci-fied in UW-12.

For ligaments between openings, use the ef-ficiency calculated by the rules given in UG-53.

(c) Cylindrical Shells.The minimum thickness ormaximum allowable working pressure of cylindricalshells shall be the greater thickness or lesser pressureas given by (1) or (2) below.

(1) Circumferential Stress (Longitudinal Joints).When the thickness does not exceed one-half of theinside radius, orP does not exceed 0.385SE, thefollowing formulas shall apply:

t pPR

SE− 0.6Por P p

SEt

R + 0.6t(1)

(2) Longitudinal Stress (Circumferential Joints).16

When the thickness does not exceed one-half of theinside radius, orP does not exceed 1.25SE,the followingformulas shall apply:

t pPR

2SE+ 0.4Por P p

2SEt

R − 0.4t(2)

(d) Spherical Shells.When the thickness of the shellof a wholly spherical vessel does not exceed 0.356R,or P does not exceed 0.665SE, the following formulasshall apply:

t pPR

2SE− 0.2Por P p

2SEt

R + 0.2t(3)

(e) When necessary, vessels shall be provided withstiffeners or other additional means of support to preventoverstress or large distortions under the external loadingslisted in UG-22 other than pressure and temperature.

(f) A stayed jacket shell that extends completelyaround a cylindrical or spherical vessel shall also meetthe requirements of UG-47(c).

(g) Any reduction in thickness within a shell courseor spherical shell shall be in accordance with UW-9.

16These formulas will govern only when the circumferential jointefficiency is less than one-half the longitudinal joint efficiency, orwhen the effect of supplementary loadings (UG-22) causing longitudi-nal bending or tension in conjunction with internal pressure is beinginvestigated. An example illustrating this investigation is given inL-2.1 and L-2.2.

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UG-28 THICKNESS OF SHELLS ANDTUBES UNDER EXTERNALPRESSURE

(a) Rules for the design of shells and tubes underexternal pressure given in this Division are limited tocylindrical shells, with or without stiffening rings, tubes,and spherical shells. Three typical forms of cylindricalshells are shown in Fig. UG-28. Charts used in determin-ing minimum required thicknesses of these componentsare given in Subpart 3 of Section II, Part D.

(b) The symbols defined below are used in theprocedures of this paragraph:

Ap factor determined from Fig. G in Subpart 3 ofSection II, Part D and used to enter the applica-ble material chart in Subpart 3 of Section II,Part D. For the case of cylinders havingDo/tvalues less than 10, see UG-28(c)(2).

Bp factor determined from the applicable materialchart in Subpart 3 of Section II, Part D formaximum design metal temperature, psi [seeUG-20(c)]

Dop outside diameter of cylindrical shell course ortube, in.

Ep modulus of elasticity of material at design tem-perature, psi. For external pressure design inaccordance with this Section, the modulus ofelasticity to be used shall be taken from theapplicable materials chart in Subpart 3 of Sec-tion II, Part D.17 (Interpolation may be madebetween lines for intermediate temperatures.)

Lp total length, in., of a tube between tubesheets,or design length of a vessel section betweenlines of support (see Fig. UG-28.1). A line ofsupport is:

(1) a circumferential line on a head (ex-cluding conical heads) at one-third the depth ofthe head from the head tangent line as shownon Fig. UG-28;

(2) a stiffening ring that meets the require-ments of UG-29;

(3) a jacket closure of a jacketed vesselthat meets the requirements of 9-5;

(4) a cone-to-cylinder junction or aknuckle-to-cylinder junction of a toriconicalhead or section which satisfies the moment ofinertia requirement of 1-8.

Pp external design pressure, psi [see Note inUG-28(f)]

17Note that the modulus of elasticity values listed in UF-27 of thisDivision shall not be used for external pressure design.

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