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Design Calculations,

Section VIII, Division 1

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Pressure Vessel Design

Shall i nclude the requir ements of:

Introduction

Subsection A, General Requirements Subsection B, Methods of

Fabrication

Subsection C, Classes of Materials

Mandatory Appendices

Section II, V, and IX when reference

M ay inclu de:

Code Cases

Nonmandatory Appendices

Other sources which do not conflict with mandatory requirements

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UG-16 General

(b) Minimum thickness of shells and heads is 1/16 in. (1.5 mm) excluding

corrosion allowance (C.A.), after forming & regardless of product form

except:

(1) Heat transfer plates of plate type heat exchangers.

(2) Inner pipe of double pipe heat exchangers and tubes in shell and tube

heat exchangers (where the pipe or tube is NPS 6 [DIN 150] or less.(3) Unfired steam boilers shall be 1/4 in. (6mm) exclusive of corrosion

allowance.

(4) Compressed air, steam or water service vessels of UCS-23 materials

shall be 3/32 in. (2.5mm) excluding corrosion allowance.

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UG-16 General

(c) Mill Under tolerance

Plate material shall not be ordered thinner than the design thickness.

Vessels made of plate furnished with an under tolerance of not more

than the smaller of 0.01 in. (0.25mm) or 6% of the ordered thickness may

be used at the full design pressure for the ordered thickness. When the

material spec, allows a greater under tolerance, the ordered thickness shallbe increased so the material received is within these stated tolerances.

(d) Pipe Under tolerance

If pipe or tube is ordered by its nominal wall thickness, the material

specification manufacturing under tolerance on wall thickness shall be

taken into account (except for nozzle wall reinforcement area

requirements per UG-37).

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After determining the minimum t, the thickness shall be increased

by an amount sufficient to provide the manufacturing under toleranceallowed in the material specification.

UG-16 General

NPS OD SCH 10 SCH 20 SCH

30

SCH

40

SCH

60

SCH

80

SCH

100

SCH

160

6 6.625 - - - 0.280 - 0.432 - 0.718

8 8.625 0.109 0.250 0.277 0.322 0.406 0.500 0.593 0.906

10 10.75 0.134 0.250 0.307 0.365 0.500 0.593 0.718 1.125

The decimal thicknesses listed for the respective pipe sizes represent their nominal or

average wall dimensions and include an allowance of 12.5% under the nominal thickness.

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(e) Corrosion Allowance In Design Formulas All dimensional symbols used in all design formulas throughout

this Division represent dimensions in the corroded condition.

Therefore, material designated for corrosion purposes cannot

contribute to the strength of the vessel. Such material must be

deducted when determining design pressure, and added to the

required thickness to determine design thickness. (Definitions,

Appendix 3)

UG-16 General

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.'.

(b) Special Shapes

Vessels other than cylindrical or spherical and those for which nodesign rules are provided in this Division may be designed under the

conditions set forth in U-2.

U-2(g) This Division of Section VIII does not contain rules to cover

all details of design and construction. Where complete details are not

given, it is intended that the manufacturer, subject to the acceptanceof the Inspector, shall provide details of design and construction

which will be as safe as those provided by the rules of this Division.

UG-19 Special Constructions

(c) No Design Rules

When no design rules are given and the strength of a vessel (or part)

cannot be calculated with a satisfactory assurance of accuracy,Maximum Allowable Working Pressure shall be established in

accordance with the provisions of UG-101. (Proof testing)

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(a) Maximum

Shall not be less than the mean metal temperature under operatingconditions for the part under consideration.

May be determined by computation or measurement from

equipment "in service" under equivalent operating conditions.

UG-20 Design Temperature

(b) Minimum

Is the lowest expected "in service",Determined same as for maximum temperature,

Consideration includes:

Lowest operating temperatures,

Operational upsets,

Auto refrigeration,Atmospheric conditions,

Any other source of cooling.

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(c) Maximum Design temperatures in excess of the maximum temperatures listed

in the tables referenced in UG-23 are not permitted.

In addition, design temperatures for vessels under external pressure

shall not exceed the maximum temperatures given on the external

pressure charts.

UG-20 Design Temperature

(d) The design of zones with different metal temperatures may be

based on their determined temperatures.

(e) Suggested methods for obtaining the operating temperatures of

vessel walls in service are given in Appendix C.

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UG-21 Design Pressure

When determining design pressure, consideration must include thefollowing.

At least the most severe condition if coincident pressure and

temperature expected in normal operation.

The operating and test

conditions including themaximum difference in

pressure between

The inside and outside of the

vessel,

Any two chambers of acombination unit.

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UG-98 Maximum Allowable Working Pressure

(a) It is the maximum permissible pressure at the top of thevessel in its normal operating position.

(b) The MAWP for a vessel is the maximum internal or

external pressure, including static head thereon as

determined by the rules and formulas of this Division,

together with the effect of any combination of loadings

listed in UG-22 which are likely to occur for thedesignated coincident temperature, excluding any metal

specified as corrosion allowance (UG-25).

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UG-22 Loadings

The loadings to be considered in designing a vessel shall include

those from:Internal or external design pressure (UG-21).

Weight of the vessel & normal contents under operating or test

conditions (this includes additional pressure due to the static head of

liquids).

- 1 cubic foot of water at 62F = 62.35 lb.

- 62.35 lb. /1728 cubic inches = 0.0361 lb. / cu. inch

- 0.0361 cu. inches x 12 inches = 0.433 lb./foot (for water)

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The maximum allowable tensile stress values permitted for

different materials are given in Subpart 1 of Section II, Part D.

A listing of these materials are included in Subsection C.

Materials meeting more than one specification and/or grade may

be used provided all requirements for the selected specification and/orgrade are met.

UG-23 Maximum Allowable Stress Values

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(a) the user or his designated agent (see U-2) shall specify

corrosion allowances other than those required by this Division.

Where corrosion allowances are not provided, this fact shall be

indicated in the Data Report.

UG-25 Corrosion

(b) vessels or parts subject to thinning by

CorrosionErosion

Mechanical abrasion

shall have provision made for the desired life of the vessel by a

suitable increase in the thickness over that determined by the design

formulas, or by using some other suitable method of protection. (SeeAppendix E).

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(c) Material for these purposes need not be of the same thickness

for all parts of the vessel if different rates of attack are expected for

the various parts.

(d) No additional thickness need be provided when previous

experience in like service has shown that corrosion does not occur or

is of only a superficial nature.

UG-25 Corrosion

(e) Telltale Holes

May be used to provide some positive indication when the thickness

has been reduced to a dangerous degree.

Shall not be used in vessels which are to contain lethal substances

[seeUW-2(a)], except as permitted by ULW-76 for vent holes inlayered construction.

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(e) Telltale Holes

UG-25 Corrosion

(f) Openings for Drains

Vessels subject to corrosion shall be

supplied with a suitable drain opening at

the lowest point practicable in the vessel;

or a pipe may be used extending inward

from any other location to within 1/4 in.

(6mm) of the lowest point.

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(a) The minimum required thickness of shells under internal

pressure shall not be less than that computed by the following

formulas13 except as permitted in Appendix 32 (local thin areas). In

addition, provision shall be made for any of the loadings listed in UG-

22, when such loadings are expected.

The provided thickness of the shells shall also meet the

requirements of UG-16, except as permitted in Appendix 32.

UG-16(b) requires that minimum thickness be determined after

forming and exclusive of any c.a.

UG-16(c) Mill undertolerance

UG-16(d) Pipe Undertolerance

UG-16(e) Corrosion Allowance in Design Formulas

13 Formulas in terms of outside radius and for thicknesses and pressures beyond the limits

fixed in this paragraph are given in 1-1 to 1-3.

UG-27 Thickness of Shells Under Internal Pressure

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(b) The symbols defined below are used in the formulas of thisparagraph.

t = minimum required thickness

P = internal design pressure

R = inside radius of the shell course under consideration

S = maximum allowable stress value (see UG-23 and the stresslimitations specified in UG-24

E = joint efficiency for, or the efficiency of, appropriate joint in

cylindrical or spherical shells, or the efficiency of ligaments

between openings, whichever is less For welded vessels: UW-12,

for ligaments: UG-53


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(c) Cylindrical Shells. The minimum thickness or Maximum

allowable Working Pressure of cylindrical shells shall be the

greater thickness or lesser pressure as given in (1) or (2) below.


(c)(l) Circumferential Stress (Longitudinal Joints)

(c)(2) Longitudinal Stress (Circumferential Joints15)

15 These formulas will govern only when the circumferential joint efficiency is less than

one-half the longitudinal joint efficiency, or when the effect of supplemental loadings

(UG-22) are being investigated.

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(c)(l) Circumferential Stress (Longitudinal Joints)

(c)(2) Longitudinal Stress (Circumferential Joints)


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Example: Assume P = 150PSI S = 17, 500

R = 24 inches E=1.0

(c)(l) Circumferential stress (Longitudinal Joints)

(c)(2) Longitudinal Stress (CircumferentialJoints)


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(a) The required thickness at the thinnest point after forming of

ellipsoidal, torispherical hemispherical, conical and toriconical

heads under pressure on the concave side (plus heads) shall be

computed by the appropriate formulas in this paragraph, except

as permitted in Appendix 32 (Localized Thin Areas).

UG-32 Formed Heads and Sections, Pressureon the Concave Side

(a) In addition, provision shall be made for any of the loadings

listed in UG-22. The provided thickness of the heads shall also

meet the requirements of UG-16, except as permitted in Appendix

32. (b) The thickness of an unstayed ellipsoidal or torispherical

head shall in no case be less than the required thickness of aseamless hemispherical head divided by the efficiency of the head

to shell joint.

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(c) The symbols defined below are used in the formulas of thisparagraph.

t = minimum required thickness of the head after forming

P = internal design pressure

D = inside diameter of the head skirt; or inside length of a major

axis of an ellipsoidal head; or inside diameter of a conical head at thepoint under consideration, measured perpendicular to the longitudinal

axis.

Dt = inside diameter of the conical portion of a toriconical head at

its point of tangency to the knuckle, measured perpendicular to the

axis of the cone. [ = D- 2r(l-cos a)]


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r = inside knuckle radiusS = maximum allowable stress value in tension as given in the

tables referenced in UG-23, except as limited in UG-24 and (e) below

E = lowest efficiency of any joint in the head; for hemispherical

heads this includes head-to-shell joint; for welded vessels, use the

efficiency specified in UW-12L = inside spherical or crown radius. The value of L for elliptical

heads shall be obtained from Table UG-37

a = one-half of the included (apex) angle of the cone at the center

line of the head (see fig. 1-4)


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(d) Ellipsoidal Headswith t/L >0.002.The required thickness of a dished

head of semi-ellipsoidal form, in

which half the minor axis (inside

depth of head minus head skirt) equals

one-fourth of the inside diameter of

the head skirt, shall be determined by:


NOTE: For ellipsoidal heads with t/L< 0.002, the rules of l-4(f)

shall also be met.

An acceptable approximation of a 2:1 ellipsoidal head is one witha knuckle radius of 0.17D and a spherical radius of 0.90D.

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(e)Torispherical Heads with t/L >0.002.The required thickness of a torispherical

head for the case in which the knuckle

radius is 6% of the inside crown radius and

the inside crown radius equals the outside

diameter of the skirt [see (j) below], shall

be determined by:


Note: For torispherical heads with t/l

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(f) Hemispherical Heads. When the

thickness of a hemispherical head

does not exceed 0.356L, or P does not

exceed 0.665SE, the following

formula shall apply:


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(g) Conical Heads and Sections

(Without Transition Knuckle).

The required thickness of conical

heads or conical shell sectionsthat have a half apex-angle a not

greater than 30 deg shall be

determined by:


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(h) Toriconical Heads and Sections

The required thickness of the

knuckle shall be determined by

formula (3)of l-4(d)in which:


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(i) When an ellipsoidal, torispherical, hemispherical conical ortoriconical head is of a lesser thickness than required by the rules of

this paragraph, it shall be stayed as a flat surface according to the

rules of UG-47 for braced and stayed flat plates.


(o) If a torispherical, ellipsoidal, or hemispherical head is formedwith a flattened spot or surface, the diameter of the flat spot shall

not exceed that permitted for flat heads as given in Formula (1) in

UG-34, using C = 0.25.

(p) Openings in formed heads under internal pressure shallcomply with the requirements of UG-36 through UG-47.

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(a) The minimum thickness of unstayed flat heads, cover plates and

blind flanges shall conform to the requirements of this paragraph.

Some acceptable types of flat heads and covers are shown in Fig.

UG-34.

In this figure, the dimensions of the component parts and the

dimensions of the welds are exclusive of extra metal required for

corrosion allowance.

UG-34 Unstayed Flat Heads and Covers

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(c) The thickness of flat unstayed heads, covers and blind flangesshall conform to one of the following three requirements.

(c)(l) Circular blind flanges conforming to the standards referenced

in Table U-3, when the blind flange is of the types shown in Fig. UG-

34 sketches (j) and (k).


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(c) Flat unstayed heads, covers and blind flanges shall be

calculated by the following formula:

(c)(2)Circular

(c)(3) square, rectangular, elliptical, obround, segmented orotherwise noncircular


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(c)(2)(a) Openings in Cylindrical or conical shells, or formed

heads shall be reinforced to satisfy the requirements of UG-37

except as given in (3) below.

(c)(2)(b) Openings in flat heads shall be reinforced as required by

UG-39.

UG-36 Openings in Pressure Vessels

(c)(3) Openings in vessels not subject to rapid fluctuation in

pressure do not require reinforcement other than that inherent in theconstruction under the following conditions:

(a) welded, brazed or flued connections with a finished opening

not larger than:

3 1/2 in. (89mm) dia. in vessel shells or heads with a required

minimum thickness of 3/8 in. (10mm) or less 2 3/8 in. (60mm) dia. in vessel shells and heads over a minimum

required thickness of 3/8 in (10mm).

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UG-36(c) exemptions to reinforcement consideration, continued... UG-36(c)(3)(b) threaded, studded or expanded connections in

which the hole cut in the shell or head is not greater than 2 3/8 in.

(60mm) dia.


UG-36(c)(3)(c) no two unreinforced openings, in accordance with

(a) or (b) above, shall have their centers closer to each other than thesum of their diameters

example

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(d) Openings Through Welded Joints

Additional provisions governing openings through welded joints are

given in UW-14.

UW-14 (a) Any type of opening that meets the requirements for

reinforcement given in UG-37 or UG-39 may be located in a welded

joint.

UW-14(b) Single openings meeting the requirements given in UG-36(c)(3) may be located in head-to-shell or Category B or C butt

welded joints, provided the weld meets the RT requirements of UW-51

for a length equal to three times the diameter of the opening with the

center of the hole at midlength.

Defects that are completely removed in cutting the hole shall not beconsidered in judging the acceptability of the weld.


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UW-14(c) In addition to meeting the radiographic requirements of(b) above, when multiple openings meeting UG-36(c)(3) are in line in

head-to-shell or Category B or C butt welded joints, the requirements

of UG-53 (ligaments) shall be met or the openings shall be reinforced

in accordance with UG-37 through UG-42.

UW-14 Openings in or Adjacent to Welds

UW-14(d) Except when the adjacent butt weld satisfies therequirements for radiography in (b) above, the edge of openings in

solid plate meeting the requirements of UG-36(c)(3) shall not be

placed closer than 1/2 in. (13mm) to the edge of a Category A, B, or

C weld for material 1 1/2 in. (38mm) thick or less.

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(b) General. The rules of this paragraph apply to all openings other

than:

Small openings, UG- 36(c)(3)

Openings in flat heads, UG-39

Openings designed as reducer sections, UG-36(e)

Large head openings, UG-36(b)(2)Tube holes with ligaments, UG-53

Reinforcement shall be provided in amount and distribution such

that the area requirements for reinforcement are satisfied for all

planes through the center of the opening and normal to the vessel

surface.

UG-37 Reinforcement Required For Openings inShells and Formed Heads

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Fig. UG-37.1

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Design Review

Design parameters can be reviewed, such as

Code Edition and Addenda

Pressure and Temperature

Materials

Size

Loadings and Service Conditions

Based upon the design parameters, fabricationrequirements can be reviewed such as:

Welding

Nondestructive Examination

Heat Treatment

Impact Testing

Forming and Bending Limitations

Pressure Testing

Data Reports and Stamping

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Based upon a review of design parameters and fabrication

requirements, you are in a better position to determine meaningful

inspection involvements using documents such as:

Calculations

Drawings & Bills of Material

Purchase & Receiving Documents

Process Control DocumentsSpecial Process Procedures (WPS, NDE, HT, etc.)

Design Review

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Design Review Tips

Has the correct construction Code Section been selected

and used?

Is the Code Edition/Addenda correct?

Have the required calculations been prepared?

Do the design documents include criteria as supplemented

by the QC system?

Are design documents reviewed/approved by appropriate

personnel?

Are you reviewing the latest revision to the design/fabrication

document?

If the design work is computer generated, have the computer

program capabilities and results been verified as accurate?