VECV1001 Process industry practice

REVISION August 2000

Process Industry Practices Vessels

PIP VECV1001 Vessel/S&T Heat Exchanger Design Criteria ASME Code Section VIII, Divisions 1 and 2

PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES In an effort to minimize the cost of process industry facilities, this Practice has been prepared from the technical requirements in the existing standards of major industrial users, contractors, or standards organizations. By harmonizing these technical requirements into a single set of Practices, administrative, application, and engineering costs to both the purchaser and the manufacturer should be reduced. While this Practice is expected to incorporate the majority of requirements of most users, individual applications may involve requirements that will be appended to and take precedence over this Practice. Determinations concerning fitness for purpose and particular matters or application of the Practice to particular project or engineering situations should not be made solely on information contained in these materials. The use of trade names from time to time should not be viewed as an expression of preference but rather recognized as normal usage in the trade. Other brands having the same specifications are equally correct and may be substituted for those named. All Practices or guidelines are intended to be consistent with applicable laws and regulations including OSHA requirements. To the extent these Practices or guidelines should conflict with OSHA or other applicable laws or regulations, such laws or regulations must be followed. Consult an appropriate professional before applying or acting on any material contained in or suggested by the Practice.

This Practice is subject to revision at any time by the responsible Function Team and will be reviewed every 5 years. This Practice will be revised, reaffirmed, or withdrawn. Information on whether this Practice has been revised may be found at http://www.pipdocs.org.

© Process Industry Practices (PIP), Construction Industry Institute, The University of Texas at Austin, 3208 Red River Street, Suite 300, Austin, Texas 78705. PIP member companies and subscribers may copy this Practice for their internal use.

September 1997 February 1999 August 2000

Issued Complete Revision Revision

Not printed with State funds.


Process Industry Practices Vessels

PIP VECV1001 Vessel/S&T Heat Exchanger Design Criteria ASME Code Section VIII, Divisions 1 and 2 Table of Contents 1. Introduction .................................. 3 1.1 Purpose ............................................. 3 1.2 Scope................................................. 3

2. References ................................... 4 2.1 2.2 2.3 2.4

Process Industry Practices ................ 4 Industry Codes and Standards .......... 4 Other References .............................. 5 Government Regulations ................... 6

3. Definitions .................................... 6 4. General ......................................... 7 4.1 Applicable PIP Documents ................ 7 4.2 ASME Code Requirements................ 7 4.2.2 Applicable Code Scope Exemptions ................................... 7 4.2.3 Waste Heat Recovery Vessels ..... 7

4.3 4.4 4.5 4.6 4.7

National Board Registration............... 7 Jurisdictional Compliance .................. 7 Units of Measurement ....................... 8 Language........................................... 8 Documentation to be Provided to the Manufacturer...................................... 8

5. Design........................................... 8 5.1 Design Pressure and Temperature ... 8

Process Industry Practices

5.2 MAWP and Coincident Maximum Temperature .................................... 10 5.3 Minimum Design Metal Temperature and Coincident Pressure ................. 11 5.4 External Pressure Design ................ 11 5.5 Cyclic Service .................................. 11 5.5.1 Number of Cycles........................12 5.5.2 Fatigue Analysis ..........................12 5.5.3 Fatigue Loading Data ..................12

5.6 Welded Pressure Joint Requirements .................................. 12 5.7 Postweld Heat Treatment ................ 14 5.8 Wind Load ....................................... 15 5.8.1 User Selections from ASCE 7 .....15 5.8.2 Determination of Wind-Induced Forces .........................................17

5.9 Seismic Loads ................................. 17 5.9.1 General Requirements and Data from ASCE 7 ...............................17 5.9.2 Seismic Loads for GroundSupported Equipment..................18 5.9.3 Seismic Loads for StructureMounted Equipment ....................18

5.10 Design Loads and Load Combinations.......................... 19 5.10.1 Dead Load...................................19 5.10.2 Operating Live Load ....................19 5.10.3 Pressure Load .............................19 5.10.4 Thermal Load ..............................19 5.10.5 Test Load ....................................20 5.10.6 Wind Load ...................................20 5.10.7 Seismic Load...............................20

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5.10.8 Piping and Superimposed Equipment Loads ........................ 20 5.10.9 Load Combinations ..................... 20

5.20.7 Thermal Performance..................50 5.20.8 Hydraulic Performance ................52 5.20.9 Vibration ......................................53

5.11 Wind-Induced Vibration of Vertical Vessels.............................................21

6. Materials ..................................... 53

5.11.1 Vortex Shedding Ranges ............ 22 5.11.2 Corrective Action......................... 22

5.12 Formed Heads .................................23 5.13 Flanges.............................................23 5.13.1 ASME B16.47, Series A .............. 23 5.13.2 ASME B16.47, Series B .............. 23 5.13.3 Custom-Designed Flanges per Code ........................................... 24 5.13.4 Custom-Designed Lap Joint Flanges ....................................... 25 5.13.5 Lap Joint Flanges NPS 24 and Smaller........................................ 27 5.13.6 Slip-on Flanges ........................... 27 5.13.7 Threaded and Socket Weld Flanges ....................................... 28 5.13.8 Flange Facing and Surface Finish ............................. 28 5.13.9 Piping Connections ..................... 29 5.13.10 Quick Opening Closures ............. 29 5.13.11 Flanges - Pass Partition Areas . 29 5.13.12 Flanged Joints .......................... 29

5.14 5.15 5.16 5.17 5.18

Nozzles.............................................29 Manways ..........................................31 Anchor Bolts .....................................32 Internals............................................33 Vessel Supports ...............................34 5.18.1 General ....................................... 34 5.18.2 Vertical Vessels .......................... 34 5.18.3 Horizontal Vessels ...................... 36 5.18.4 Stacked Exchangers ................... 37

5.19 Heat Exchanger Component Design ..............................................38 5.19.1 Tubes .......................................... 38 5.19.2 Tubesheets ................................. 38 5.19.3 Tube-to-Tubesheet Joints ........... 39 5.19.4 Tube Bundles.............................. 40 5.19.5 Expansion Joints......................... 41 5.19.6 Vapor Belts ................................. 42 5.19.7 Exchanger Covers....................... 42 5.19.8 Pass Partition Plates................... 43 5.19.9 Floating Heads............................ 43 5.19.10 Kettle Type Exchangers............ 43 5.19.11 Instrument, Vent, and Drain Connections ...................... 44 5.19.12 Nameplates and Stampings ..... 44 5.19.13 Shell and Bonnet Design .......... 44

6.1 Material Specifications .....................53 6.1.1 External Attachments ..................53 6.1.2 Internal Attachments....................53

6.2 Source of Materials ..........................54 6.3 Corrosion/Erosion Allowance ...........54 6.3.1 Basis............................................54 6.3.2 Corrosion Loss ............................54 6.3.3 Erosion Loss................................54

6.4 Gaskets ............................................55

7. Testing ........................................ 55 7.1 Hydrostatic Test ...............................55 7.1.1 UG-99 Standard Hydrostatic Test..............................................55 7.1.2 Horizontal Vessels.......................55 7.1.3 Vertical Vessels ...........................55 7.1.4 Test Temperature ........................55

7.2 Pneumatic Test ................................56 7.3 Proof Test.........................................56

8. Vessel Rigging Analysis/Lifting Requirements ............................. 56 8.1 8.2 8.3 8.4

Impact Factor ...................................56 Vertical Vessels................................56 Local Stresses..................................57 Welds ...............................................57

Appendices A - General Considerations for Pressure Relief Valve Application B[V] - Welded Pressure Joint Requirements Form B[E] - Welded Pressure Joint Requirements Form C - Equivalent Pressure Formulas for Bending Moment and Axial Tensile Load D - Minimum Clearance for Nozzle Adjacent to Integral Tubesheet

5.20 Heat Exchanger Thermal .................44 5.20.1 Fouling Factors Selection ........... 44 5.20.2 Fluid Side Selection .................... 45 5.20.3 Exchanger Configuration ............ 46 5.20.4 Flow Arrangement....................... 47 5.20.5 Tube Selection ............................ 48 5.20.6 Bundle Design and Tube Layout ................................ 49

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REVISION


August 2000

1.

Introduction Note to Readers: This Practice contains design criteria for pressure vessels and shell-andtube heat exchangers. Corresponding subject matter for pressure vessels and shell-and-tube heat exchangers is covered by paragraphs identically numbered. Paragraphs pertaining to pressure vessels are preceded by [V]. Paragraphs pertaining to shell-and-tube heat exchangers are preceded by [E]. Paragraphs pertaining to both are preceded by [V/E]. In addition, ASME Boiler and Pressure Vessel Code, Section VIII, Division 2 requirements are shown in braces { }. This Practice should be used for pressure vessels built to Division 1 or Division 2 of the ASME Boiler and Pressure Vessel Code, henceforth referred to as the Code. Shell-and-tube heat exchangers are limited to Division 1 in this Practice. 1.1

Purpose [V] The primary focus of this Practice is to communicate vessel design criteria and methodology from the User to a Designer. This Practice is also intended as guidance for the development of purchase specifications covering the construction of new pressure vessels which meet the philosophy and requirements of Section VIII, Division 1 {or 2} of the Code. [E] The primary focus of this Practice is to communicate vessel design criteria and methodology from the User to a Designer. This Practice is also intended as guidance for the development of purchase specifications covering the construction of new shell-and-tube heat exchangers which meet the philosophy and requirements of Section VIII, Division 1 of the Code and TEMA Standards of the Tubular Exchangers Manufacturers Association.

1.2

Scope 1.2.1

[V/E] This Practice must be used in conjunction with PIP VEDST003, PIP VEDV1003, PIP VEFV1100, and PIP VESV1002 in order to comprise a complete vessel purchase specification.

1.2.2

[V/E] Many recognized and generally accepted good engineering construction practices are included herein. However, in light of the many diverse service applications of Code vessels, these practices must be employed with engineering judgment and supplemented as appropriate with requirements related to specific materials of construction, service fluids, operating environments, and vessel geometries. Accordingly, provisions of this Practice may be overridden or supplemented by an Overlay Specification.

1.2.3

[V/E] Standardized pre-designed (off-the-shelf) vessels and heat exchangers are not within the scope of this Practice, but are covered in PIP VESSM001.


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REVISION


2.

August 2000

References The following documents are only those specifically referenced in this Practice. In applications where laws or regulations issued by municipal, state, provincial, or federal authorities cover pressure vessels, those laws or regulations should be reviewed prior to the initiation of design work since the requirements may be different or more restrictive than those covered in this Practice. Short titles will be used herein when appropriate. 2.1

Process Industry Practices (PIP) For the following reference documents, the latest edition issued at the date of contract award shall be used.

2.2

−

PIP VEDST003 - Shell and Tube Heat Exchanger Specification Sheet

−

PIP VEDV1003 - Vessel Drawing/Data Sheet and Instructions

−

PIP VEFV1100 - Vessel/S&T Heat Exchanger Standard Details (27 Details and Index)

–

PIP VESSM001 - Specification for Small Pressure Vessels and Heat Exchangers with Limited Design Conditions

−

PIP VESV1002 - Vessel/S&T Heat Exchanger Fabrication Specification ASME Code Section VIII, Divisions 1 and 2

Industry Codes and Standards For the following reference documents, if Table U-3 {AF-150.1} of the Code lists an edition or addenda different than the latest edition issued, the edition listed in Table U-3 {AF-150.1} shall be used. For documents not listed in Table U-3 {AG-150.1}, the latest edition or addenda issued at the date of contract award shall be used. •

American Institute of Steel Construction (AISC) –

•

•

American National Standards Institute (ANSI) –

ANSI/ASME B36.10M - Welded and Seamless Wrought Steel Pipe

–

ANSI/ASME B36.19M - Stainless Steel Pipe

American Petroleum Institute (API) –

•

API 650 - Welded Steel Tanks for Oil Storage

American Society of Civil Engineers (ASCE) –

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AISC Manual of Steel Construction

ASCE 7 - Minimum Design Loads for Buildings and Other Structures


REVISION


August 2000

•

American Society of Mechanical Engineers (ASME) −

ASME Boiler and Pressure Vessel Code Section I - Power Boilers Section II - Materials, Parts A, B, C, D Section VIII - Pressure Vessels, Divisions 1 and 2 Section IX - Welding and Brazing Qualifications

•

–

ASME B1.1 - Unified Inch Screw Threads (UN and UNR Thread Form)

–

ASME B16.5 - Pipe Flanges and Flanged Fittings, NPS 1/2 through NPS 24

–

ASME B16.11 - Forged Fittings, Socket-Welding and Threaded

–

ASME B16.47 - Large Diameter Steel Flanges, NPS 26 through NPS 60

International Conference of Building Officials (ICBO) –

•

Manufacturers Standardization Society of the Valve and Fittings Industry, Inc. (MSS) –

•

Standards of the Tubular Exchanger Manufacturers Association

Welding Research Council (WRC) –

2.3

MSS SP-44 - Steel Pipeline Flanges

Tubular Exchanger Manufacturers Association (TEMA) −

•

Uniform Building Code (UBC)

WRC Bulletin 107 - Local Stresses in Spherical and Cylindrical Shells Due to External Loadings

Other References –

“Design Equations for Preventing Buckling in Fabricated Torispherical Shells Subjected to Internal Pressure,” G.D. Galletly, Proceedings: Institution of Mechanical Engineers. London: Vol. 200 No. A2.

–

Dynamic Response of Tall Flexible Structures to Wind Loading. Joseph Vellozzi, Ph.D., P.E. U.S. Department of Commerce, National Bureau of Standards, Building Science Series Number 32, 1966.

–

Process Equipment Design. Brownell and Young. Wiley & Sons Publishers, 1959.

–

“Stresses in Large Cylindrical Pressure Vessels on Two Saddle Supports,” L.P. Zick, Pressure Vessels and Piping: Design and Analysis, A Decade of Progress. Vol. 2, 1972.

–

“Wind Loads on Petrochemical Facilities,” ASCE Task Committee on WindInduced Forces, Wind Loads and Anchor Bolt Design for Petrochemical Facilities. (ISBN-0-7844-0262-0)


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REVISION


2.4

Government Regulations •

U. S. Environmental Protection Agency (EPA) –

•

3.

August 2000

Clean Air Act Amendments 1990

U. S. Department of Labor, Occupational Safety and Health Administration (OSHA) –

OSHA 29 CFR 1910.106(b)(5)(ii) - Flammable and Combustible Liquids

–

OSHA 29 CFR 1910.119 - Process Safety Management of Highly Hazardous Chemicals

–

OSHA 29 CFR 1910.146(k)(3)(ii) - Permit-Required Confined Spaces for General Industry

Definitions Code: ASME Boiler and Pressure Vessel Code Section VIII, Division 1{or 2}. References to Division 2 are identified in braces { }. Construction: An all-inclusive term comprising materials, design, fabrication, examination, inspection, testing, certification (Code stamp and Manufacturer’s Data Report), {Manufacturer’s Design Report} and pressure relief Designer: The party responsible for defining and specifying the mechanical design requirements (e.g., Vessel Drawing/Data Sheet {User’s Design Specification}) consistent with User criteria for use by the Manufacturer. The Designer is frequently an engineering contractor, but could be the User, third party consultant, or the Manufacturer. The Designer is also considered the thermal Designer with respect to heat exchanger design. Manufacturer: The party entering into a contract with the Purchaser to construct a vessel in accordance with the purchase order National Board: The National Board of Boiler and Pressure Vessel Inspectors, an organization comprised of chief inspectors of various governmental jurisdictions in the United States and Canada. Vessels meeting requirements of the Code, except those stamped with the Code “UM” symbol, may be registered with the National Board. Overlay Specification: Technical requirements that supplement or override the provisions of this document, such as a User specification or a project specification User: The party responsible for establishing construction criteria consistent with the Code philosophy and service hazards. “User” refers to the owner and/or operator of the equipment. Vessel: This term may be used as a non-specific reference to a pressure vessel or a shell-andtube heat exchanger.

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REVISION


August 2000

4.

General 4.1

Applicable PIP Documents [V/E] All vessels shall be designed in accordance with this Practice, PIP VEDST003, PIP VEFV1100 (applicable details), PIP VEDV1003, and PIP VESV1002.

4.2

ASME Code Requirements 4.2.1

[V/E] Pressure vessels within the scope of this Practice shall satisfy all applicable requirements, including Code symbol stamping.

4.2.2

Applicable Code Scope Exemptions [V/E] The Code Scope exemptions that represent across-the-board acceptance are those covered under Code Paragraphs U-1(c)(2)(h) {AG-121(h)} and U-1(c)(2)(i) {AG-121(i)}, as follows: 4.2.2.1

[V/E] U-1(c)(2)(h) {AG-121(h)}: Vessels not exceeding 15 psig, with no limitation on size [see Code Paragraph UG-28(e) {AD-300}]

4.2.2.2

[V/E] U-1(c)(2)(i) {AG-121(i)}: Vessels having an inside diameter, width, height, or cross-section diagonal not exceeding 6 inches, with no limitation on length of vessel or pressure Note: The 6-inch dimension is in the corroded condition.

The above is not intended to prohibit the use of other Scope exemptions in Code Paragraph U-1(c)(2); however, such use shall be by agreement with the User. 4.2.3

Waste Heat Recovery Vessels [V/E] Steam generating vessels associated with waste heat recovery operations shall be constructed and stamped with the Code “U” symbol in accordance with Code Section VIII, Division 1. Dual Code symbol stamping of such vessels (both Section I “S” symbol and Section VIII, Division 1 “U” symbol) is not permitted.

4.3

National Board Registration [V/E] National Board registration of vessels stamped with the Code “U” {“U2”} symbol is required.

4.4

Jurisdictional Compliance [V/E] All aspects of the work shall comply with applicable local, county, state, and federal rules and regulations. This includes, but is not limited to, the rules and standards established by EPA and OSHA. (See Section 2.4.)


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REVISION


4.5

August 2000

Units of Measurement [V/E] U.S. customary (English) units shall be regarded as standard; metric (SI) units may be included for reference only and shall not be interpreted as a precise conversion.

4.6

Language [V/E] The language of all documents shall be either English or include the English translation.

4.7

Documentation to be Provided to the Manufacturer [V/E] The following information shall be provided to the Manufacturer with the purchasing inquiry:

5.

4.7.1

[V] Design requirements to be provided to the Manufacturer shall be per PIP VEDV1003, with additional drawings or details as necessary.

4.7.2

[E] Design requirements to be provided to the Manufacturer shall be per PIP VEDST003, with additional drawings or details as necessary.

4.7.3

[V/E] Welded pressure joint requirements, including: •

Type of Category A, B, C, and D joints (see Appendix B[V] or B[E])

•

Type and degree of nondestructive examination to be applied to the joints (see Appendix B[V] or B[E])

4.7.4

[V/E] Quality Overview Plan, as shown in PIP VESV1002, Appendix A.

4.7.5

[V/E] Documentation Schedule and Manufacturer’s Data Package, as shown in PIP VESV1002, Appendix B.

4.7.6

[V] {User’s Design Specification}

Design 5.1

Design Pressure and Temperature [V/E] The design pressure and coincident maximum metal temperature shall be determined by the Designer by carefully considering all operating phases and associated loadings (e.g., liquid head and other sources of pressure variation, such as that resulting from flow) that the vessel may experience during the specified project life, such as:

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•

Initial startup

•

Normal operations

•

Temporary operations

•

Emergency shutdown

•

Emergency operations


REVISION


August 2000

•

Normal shutdown

•

Startup following a turnaround or an emergency shutdown

•

Cleaning, steam out, and decontamination

•

Upset conditions

•

Environmental restraints on relief venting

•

[E] Tube failure [Code Paragraph UG-133(d)]

[V/E] The margin above the maximum anticipated operating pressure selected to establish the design pressure and coincident maximum metal temperature must be carefully considered for each vessel component as a function of the overall objective with respect to pressure relief, coupled with the uncertainties in determining what actual pressures will be developed. For example, where minimization of severely flammable or acutely toxic environmental hazards is a controlling design requirement, the establishment of a design pressure and associated Maximum Allowable Working Pressure (MAWP) {MAWP replaced by Design Pressure in Division 2, AD-121.1} that will provide containment without actuation of the pressure relief device may be a consideration. [V/E] As will be noted with reference to Appendix A, this margin is also dependent upon the operational characteristics of the pressure relief device. For example, when the maximum anticipated operating pressure of a gas/vapor service can be identified with confidence, and when metal-seated, direct spring-operated valves will be used, the design pressure is frequently established by dividing the maximum anticipated operating pressure by 0.90. However, when a pilot-operated pressure relief device is used, the design pressure is sometimes established by dividing the maximum anticipated operating pressure by a factor as high as 0.98. [V/E] Refer to the Overlay Specification for any margins to be applied to the maximum operating pressure(s) and coincident temperature(s). [V/E] Also use of Code Case 2211, entitled “Pressure Vessels with Overpressure Protection by System Design, Section VIII, Divisions 1 and 2,” may be an appropriate option. Note that prior jurisdictional acceptance may be required and that this Code Case Number shall be shown on the Manufacturer’s Data Report. Likewise, with permission from the authority having legal jurisdiction over the installation of pressure vessels (should one exist), the advantages of using the provisions of Code Case 2203, entitled “Omission of Lifting Device Requirements for Pressure Relief Valves on Air, Water over 140° F, or Steam Service, Section VIII, Divisions 1 and 2,” should be considered. [E] The shell side and tube side design pressures and temperatures shall be reviewed to determine extreme conditions that may be encountered. During transients (startup, pressure relief, or shutdown, etc.), the shell side or tube side fluid may be absent, not flowing, or auto-refrigerating with design pressure in the other chamber. For components subjected to both shell side and tube side conditions, the more severe condition shall control. The following additional conditions shall be considered:


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5.2


5.1.1

[E] The exchanger shall be designed for full pressure on either side with atmospheric (or full vacuum if specified) on the other side. If an exchanger is designed for differential pressure, the Data Sheet and nameplate shall so indicate.

5.1.2

[E] Fixed tubesheet exchangers cannot generally be operated at the coincident nameplate temperature-pressure conditions. The basis for differential thermal expansion used in the design shall be defined and shall become a fabrication drawing requirement. (See PIP VEDST003.)

MAWP {Design Pressure} and Coincident Maximum Temperature 5.2.1

[V/E] The MAWP {Design Pressure} to be marked on the Code nameplate is defined as the maximum gauge pressure permissible at the top of a completed vessel in its normal operating position at the designated coincident metal temperature for that pressure. (See Code Appendix 3 {AD-121} for definitions of MAWP and Design Pressure.) This MAWP may be determined from the design pressure or from calculations based on the specified nominal component thickness, but reduced by the specified corrosion allowance. [V/E] The maximum permissible set-to-operate pressure of a single safety relief device cannot be higher than the MAWP {Design Pressure}. (See Code rules when multiple safety relief devices are employed.) [V/E] See Code Paragraph UG-20(a) {AD-121} for Code rules relative to determining the coincident maximum metal temperature to be stamped on the nameplate. A suitable margin consistent with the uncertainties with which the true maximum mean-metal temperature can be determined should be included. The maximum design temperature rating shall be increased to the highest temperature possible without affecting the thickness of the shell or heads and without changing the pressure class for nozzle flanges. When appropriate, a vessel may be designed and Code stamped for more than one pressure/coincident maximum metal temperature condition.

5.2.2

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[V/E] To provide for future field tests, the vessel and foundation (provided by others) shall be designed so that any component in the corroded condition will withstand the combination of hydrostatic test pressure at the top of the vessel (as defined in Code Paragraph UG-99 {Article T-3}) and the hydrostatic head of the vessel full of water when the vessel is in its operating position without exceeding the stress levels defined in Section 5.10.9(4). Vessel designs that include such features as conical sections without knuckles, torispherical heads with an inside crown radius/head thickness (L/t) ratio greater than 500, openings in the shell that exceed the dimensional limits given in Code Paragraph UG-36(b)(1) {Not Division 2 Applicable}, thermal gradients, or body flanges may require special analysis for future tests. Refer to Section 5.10 for additional requirements that apply. Note that the equipment foundation must also be designed to support the loading of a future test.


REVISION


August 2000

5.3

Minimum Design Metal Temperature (MDMT) and Coincident Pressure [V/E] The MDMT and coincident pressure to be marked on the Code nameplate shall be selected by the Designer in consideration of the operating phases such as those listed in Section 5.1 and of the Code rules in Paragraph UG-20(b) {Not Division 2 Applicable}. Reliable administrative procedures to control the pressure/coincident temperatures during transient operations (e.g., startup and shutdown) are often appropriate from a materials of construction selection point of view. For example, when considering the effects of auto-refrigeration on carbon and low-alloy steels, such procedures make it appropriate to consider operations below the MDMT stamped on the nameplate, provided the reduction in MDMT for the coincident general primary membrane tensile stress results in a temperature that is no colder than that permitted in Code Paragraph UCS-66(b) {AM-218.1}. When atmospheric temperatures govern the metal temperatures during startup or normal operations, the lowest 1-day mean atmospheric temperature at the installation site must be considered. Figure 2-2 from API 650 may be used to establish the lowest 1-day mean temperatures insofar as applicable. The mean metal temperature during shop and future field pressure testing shall also be considered during the vessel design stage. During the pressure test, the pressure-resisting components and attachments, that when welded to pressure-retaining components are judged to be essential to the vessel’s structural integrity, shall have a temperature at least 30ºF warmer than the MDMT to be stamped on the nameplate, but shall not exceed 120ºF. (See Section 6.1.)

5.4

External Pressure Design [V/E] In a manner similar to that described in Section 5.1, the Designer shall establish the external design pressure and coincident temperature by determining requirements for external pressure based on the expected operation of the vessel and adding a suitable operating margin. [V/E] If the vessel is not designed for full vacuum, and if the use of vacuum relief devices is selected, consideration must be given to the effects of introducing air into the vessel. Vessels in steam service shall be designed for full vacuum, and consideration shall also be given for vessels in services that may be subject to steam out. Consideration shall also be given to external pressures caused by sudden cooldown of gases or vapors in the vessel or by the sudden emptying of the vessel contents. [V/E] Code-required stiffening rings for shells under external pressure shall be placed on the outside of the vessel, shall have a thickness not less than 3/8 inch, and shall have a ring width-to-thickness ratio no greater than 10. Stiffening rings shall be attached by continuous fillet welds on both sides of the ring.

5.5

Cyclic Service [V/E] The required service for all vessels shall include consideration by the Designer of cyclic service. Code Paragraph UG-22(e) {AD-160} mandates that cyclic and dynamic reactions from any mechanical or thermal loading source be considered in design. Batch operation vessels and vessels having agitators, for example, quite


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frequently fall into this category. The following guidelines {AD-160} are recommended as a starting point when determining if cyclic analysis will be required. The need for a fatigue analysis by the Manufacturer shall be stated on the Data Sheet by the Designer. 5.5.1

Number of Cycles {See AD-160.2} [V/E] Code vessels should be considered to be in cyclic service when the total number of cycles in the following three items (1.+2.+3.) exceed 1000 cycles in the desired design life of the vessel: 1. The expected number of full range (design) pressure cycles, including startups and shutdowns 2. The expected number of operating pressure cycles in which the range of pressure variation exceeds 20% of the design pressure 3. The expected number of thermal cycles where the metal temperature differential between any two adjacent points exceeds 50ºF (For a definition of adjacent points, see Code Section VIII, Division 2, Paragraph AD-160.2, footnote 3.)

5.5.2

Fatigue Analysis [V/E] In cases where the preliminary guidelines in Section 5.5.1 indicate that a fatigue analysis may be required, the rules in Code Section VIII, Division 2, Paragraph AD-160, “Fatigue Evaluation,” are recommended for use with sound engineering judgment as a guideline for establishing further action. A fatigue analysis shall always be performed for agitator mounting nozzles and their attachment to the vessel. (See Sections 5.12.2 and 5.14.1.)

5.5.3

Fatigue Loading Data [V/E] The applicable fatigue loading conditions shall be stated on PIP VEDV1003 and PIP VEDST003.

5.6

Welded Pressure Joint Requirements 5.6.1

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[V/E] Consistent with the service-specific needs of each vessel, consideration must be given to the type of welded pressure joints to be furnished in the pressure-boundary components. Consideration shall also be given to the type/degree of nondestructive examination to be applied to these joints. (See User’s responsibilities under the Code as outlined in the Code Foreword. See also Code Paragraph U-2(a) {AG-301}.) As a minimum, specific Code requirements must be met. In order to provide a means of communicating the requirements to the prospective manufacturers in a manner that is not open to dispute, the Code has provided the Welded Joint Category system in Code Paragraph UW-3 {AD-400}. A Welded Pressure Joint Requirements Form for documenting and transmitting the needed information for each welded joint category (location) is included in Appendix B[V] or B[E]. Also included in these Appendices is a completed form showing the requirements described in Section 5.6.2, illustrating the use and usefulness of this form for communicating welded pressure joint


REVISION


August 2000

requirements to manufacturers for quotations and purchase specifications. Notes A through C of the Nondestructive Examination Notes (Page 2 of the Form) are standard examination notes that may be selected by the User. The remaining options or User-defined options may be added as appropriate. 5.6.2

[V/E] The welded pressure joint requirements are to be selected consistent with service-specific needs; however, the following shall apply as a minimum: 5.6.2.1

[V/E] Welded joints of Categories A, B, and, when used, butt-type Categories C and D shall be Type No. 1 of Code Table UW-12 {AF-221}. Note that this excludes the use of permanent weld joint backing strips and the use of butt welds with one plate offset [Code Figure UW-13.1(k)]. (See Section 5.6.2.3.)

5.6.2.2

[V/E] Non-butt joints that connect nozzles (including manways and couplings) to the vessel wall (Code Category D joints) shall be full penetration welds through the vessel wall and through the inside edge of reinforcing plates, when used. Nozzle necks designated to extend beyond the inside surface of the vessel wall shall have a fillet weld at the inside corner. (See Section 5.6.2.4.)

5.6.2.3

[V/E] {Not Division 2 Applicable} The minimum degree of examination of welded butt joints shall be spot radiography per Code Paragraph UW-52, such that, in combination with the requirements of Section 5.6.2.1, a joint efficiency not lower than 0.85 will result. In applying the rules of Code Paragraph UW-52, the increments of weld shall be selected so as to include all Category A, B, and C butt welds, except Category B or C butt welds in nozzles and communicating chambers that exceed neither 10 inches nominal pipe size nor 1-1/8 inches wall thickness.

5.6.2.4

[V/E] The need for examining the accessible surfaces of the completed Category D corner joint welds by magnetic particle, liquid penetrant, ultrasonic, or other nondestructive methods shall be considered on a case-by-case basis. For example, see optional Note E in the Nondestructive Examination Notes of the Welded Pressure Joint Requirements Form.

5.6.2.5

[V/E] Use either Appendix B[V] or B[E] to document specified requirements.

5.6.2.6

[E] Tubesheet-to-shell (or channel) weld joints shall be any full penetration weld permitted by Code Figure UW-13.2 or Figure UW 13.3, except as follows: 5.6.2.6.1


[E] Weld joints that employ a permanent backing strip are not permitted.

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REVISION


5.6.2.7

August 2000

5.6.2.6.2

[E] To avoid the potential for crevices generated during fabrication, Code Figures UW-13.2 (d), (e-2) and (i) are not permitted.

5.6.2.6.3

[E] Exchangers having any of the following design conditions shall employ tubesheet-to-shell (or channel) weld joints per Code Figures UW-13.2 (a), (f) or (k), or Figure UW-13.3: •

Tube side MAWP exceeding 600 psig

•

Shell side MAWP exceeding 1000 psig

•

MDMT colder than minus 20°F

•

High-alloy tubesheet and adjoining shell (or channel) with the weld joint exposed to the process fluid

•

Shell (or channel) inside diameter (ID) larger than 48 inches with carbon steel, low-alloy steel, or clad steel tubesheet material; or larger than 30 inches with high-alloy or nonferrous tubesheet material

[E] For the purpose of determining required tubesheet-to-shell (or channel) weld sizes in accordance with Code requirements, a fixed tubesheet shall be considered supported (not less than 80% of the pressure load is carried by the tubes) if: [(AtEt)/(AsEs)] ≥ 4.0

Where: Total cross-sectional metal area of tubes, sq. in. Et = Modulus of Elasticity of tube material at mean metal temperature, psi As = Cross-sectional metal area of shell based on actual thickness less corrosion allowance, sq. in. Es = Modulus of Elasticity of shell material at mean metal temperature, psi At =

5.7

Postweld Heat Treatment (PWHT) 5.7.1

Page 14 of 58

[V/E] Vessels shall be postweld heat treated per applicable sections of the Code in accordance with material specifications or when specified by the User due to service such as ammonia, caustics, amines, or wet hydrogen sulfide. Requirements for PWHT of carbon and low-alloy steels are provided in Table UCS-56 {AF-402.1} of the Code. Alternative PWHT requirements of Code Table UCS 56.1 {AF-402.2}, “Alternative Postweld Heat Treatment Requirements for Carbon and Low-Alloy Steels,” shall not be employed.


REVISION


August 2000

5.7.2

5.8

[V/E] PWHT provides reduction of residual stresses due to forming and welding and softens heat-affected zones. Some steels can be damaged within certain temperature zones below PWHT temperature. A materials engineer shall be consulted regarding the need for PWHT beyond the requirements of the Code and dependent on service conditions. The resulting recommendation shall be included on the Data Sheet, PIP VEDV1003, or PIP VEDST003.

Wind Load 5.8.1

User Selections from ASCE 7 (References are to ASCE 7-95, unless otherwise specified) Note: Local codes or regulations may require compliance with UBC or other rules for wind load design. [V/E] Wind load design requirements that shall be used for U.S. locations are covered in ASCE 7; however, simply specifying wind loads in accordance with ASCE 7 is an incomplete specification since choices exist within ASCE 7 that the Designer must make. The Designer shall determine and specify on the Data Sheet, PIP VEDST003, or PIP VEDV1003 the following items: 5.8.1.1 Classification Category (from Table 1-1)

[V/E] There are four Classification Categories. This selection allows the Designer to determine the Importance Factor, I, from Table 6-2. The Importance Factor is needed to determine the Velocity Pressure. Category II (formerly Category I in ASCE 7-93 and earlier editions) has been the industry standard; however, in some cases it may be appropriate to select Category III. 5.8.1.2 Basic Wind Speed (from Figure 6.1)

[V/E] The Designer shall make this determination by knowing the geographic location of the equipment’s point of installation. [V/E] There are different units of measurement for wind speed that must be recognized for design. The basic wind speed in ASCE 7 is in terms of a 3-second gust. This is the mean wind speed averaged over 3 seconds. All U.S. codes before ASCE 7-95 use wind speed in terms of the fastest mile. These wind speed numbers cannot be used interchangeably in design. Interchanging these wind speed values can produce results that may be 40% or more in error. 5.8.1.3 Exposure Category (from Paragraph 6.5.3)

[V/E] There are four Exposure Categories from which to select. Velocity Pressure Coefficients, Kz, are provided in Table 6-3 as a function of the selected Exposure Category. Exposure Category C should be selected for most Gulf Coast sites. For other than coastal plant sites, Exposure Category B is often selected. The Designer


Page 15 of 58



shall make this determination by knowing the geographic location of the equipment’s point of installation. 5.8.1.4 Topographic Factor, Kzt (from Paragraph 6.5.5 and Figure 6-2)

[V/E] Wind speed-up over isolated hills and escarpments must be considered for Exposure Category B, C, or D where the upwind terrain is free of such topographic features for a distance of 1 mile or 50 times the height of the hill or escarpment, whichever is less. Wind speed-up over isolated hills and escarpments must also be considered for structures situated on the upper half of hills or near the edge of escarpments. For Exposure Categories B and C, wind speed-up does not need to be considered when the height of hills or escarpments is less than 30 feet and 60 feet respectively, which would be typical for the Gulf Coast region. 5.8.1.5 Gust Effect Factor

[V/E] For flexible structures such as a tall vertical process vessel, a Gust Effect Factor, Gf , is another essential variable needed to determine the wind forces involved. The instructions in ASCE 7 in this regard are as follows: • [V/E] Gust Effect Factors for main wind-force resisting systems of flexible buildings and other structures shall be calculated by a rational analysis that incorporates the dynamic properties of the main wind-force resisting system. • [V/E] For flexible vertical vessels, defined as vessels with a fundamental (natural) frequency of vibration less than 1 Hertz [including vessels with a height-to-diameter (h/D) ratio greater than 4, where h is the total height of the vessel and D is the vessel diameter measured to the mid-thickness of the vessel wall], the recommendation is that Gf be determined using either the analysis method given in Paragraph 6.6 of the Commentary Section of ASCE 7 or some other rational analysis method that incorporates the dynamic properties of the main wind-force resisting system. When employing equation C6-9 in Paragraph 6.6, use 0.01 as the damping ratio, β, for steel construction.

Page 16 of 58


REVISION


August 2000

5.8.1.6 Force Coefficients

[V/E] Force Coefficients, Cf, formerly called “Shape Factors,” are also needed to determine wind-induced forces acting on the vessel. Typical factors are provided in Table 6-7. The following are recommendations for Cf to be used in design: Vessel Description A. For all horizontal vessels and for vertical vessels having an h/D ratio not greater than 1

5.8.2

Cf 0.5

B. For vertical vessels having an h/D ratio greater than 1 (applies to that portion of vessel without spoilers)

See Table 6-7 for moderately smooth surfaces

C. For that portion of vertical vessels provided with spoilers as recommended in Section 5.11.2.1 or 5.11.2.2 of this Practice

See Table 6-7 for very rough surfaces

Determination of Wind-Induced Forces [V] ASCE 7 does not provide the complete methodology needed to account for wind-induced forces on common appurtenances to pressure vessels such as ladders, platforms, handrails, piping, etc. The report entitled “Wind Loads on Petrochemical Facilities” (see Section 2.3 of this Practice) provides guidelines and examples for the determination of the total wind-induced forces on pressure vessels, including those from appurtenances. If most detail items (ladders, platforms, piping, etc.) of the vessel are known or can be estimated with reasonable accuracy, the Detailed Method described in this report shall be used for the vessel design. [E] See PIP VEDST003 for specific loading information, when applicable.

5.9

Seismic Loads Note: Local codes and regulations may require compliance with UBC or other rules for seismic design. 5.9.1

General Requirements and Data from ASCE 7 (References are to ASCE 7-95, unless otherwise specified) [V/E] The seismic design requirements and the specification of criteria variables for the calculation of seismic response loads for the design of vessels are in ASCE 7. The calculation of seismic forces for vessels is governed by one of two methods. For vessels mounted on the ground, see Section 5.9.2 of this Practice. For vessels mounted above grade within a structure, see Section 5.9.3 of this Practice. The first step in an analysis is to perform an eigenvalue analysis of the vessel in order to calculate its first natural period (horizontal direction, in the installed position). This is done by dividing the vessel into an appropriate number of mass and stiffness


Page 17 of 58

REVISION


August 2000

elements per the theory of structural dynamics. For long pieces of equipment, more elements are normally required for an accurate analysis. A general rule is to use the diameter of the vessel as the minimum longitudinal length of each element. For vertically-oriented vessels, the mass points are numbered starting at the first point above grade. For horizontally oriented vessels, only one mass point is normally required because the vessel has the center of gravity of the majority of its mass concentrated at one level above the ground. For vessels that can be shown to have uniform properties in mass and stiffness, the closed form handbook solution for natural period may be used. [E] See PIP VEDST003 for specific loading information, when applicable. [V/E] The design of pressure retaining elements (both internal and external) shall permit allowable stress multiplying factors which do not exceed those found in Code Paragraphs UG-23(c) and (d) {Table AD-150.1}. The load combination factors of ASCE 7, Paragraphs 2.4.3 and 2.4.4, are not permitted. The design of supports shall meet the requirements in Section 5.18 of this Practice. 5.9.2

Seismic Loads for Ground-Supported Equipment [V/E] The governing equation for horizontal seismic base shear of groundsupported equipment is: V = CsW where: Cs = 1.2Cv/(RT2/3) Cs (seismic design coefficient) should not be less than 0.5Ca , but need not be greater than 2.5Ca/R. Cv , Ca are site-specific coefficients based on Soil Profile Type and values of Av and Aa as determined from the corresponding contour maps. R is Response Modification Factor based on nonbuilding structure type and vessel contents if applicable (ASCE 7 Table 9.2.7.5). T is the first natural period of the equipment to be calculated W is the operating weight of the equipment. The lateral horizontal seismic forces induced at the levels or mass points of the equipment and in the direction causing the highest stresses shall be determined from the rules in ASCE 7. The Designer shall specify the sitespecific values on the Data Sheet, PIP VEDV1003, or PIP VEDST003. Note: ASCE 7, Section 9.2.7.2, requires that the calculated shear be increased for vessels with hazardous contents, if they are supported by structures similar to buildings. Other special requirements may apply for special cases such as vessels with fundamental period T, less than

Page 18 of 58


REVISION


August 2000

0.06 sec, storage tanks, and irregular equipment structures. The designer shall be responsible for such special analysis and design requirements. 5.9.3

Seismic Loads for Structure-Mounted Equipment [V/E] For equipment mounted in a structure above grade, the governing equation for seismic force is: Fp = 4.0 Ca Ip Wp where: Ca = seismic coefficient Ip = component importance factor = 1.5 Wp is the operating weight of the equipment. Fp is the horizontal seismic force applied at the center of gravity of the equipment and in the direction causing the highest stresses. If the above method of calculating the floor-mounted equipment seismic force is too conservative, the alternate method may be used. See equations 9.3.1.2-2 through -5 in ASCE 7. Note that this method requires the calculation of the fundamental period T of the structure that the equipment is mounted in.

5.10

Design Loads and Load Combinations [V/E] The Designer shall determine the following loads and specify them on the Vessel Drawing/Data Sheet. Design loads are defined and classified as follows: 5.10.1 Dead Load (L1) [V/E] Dead Load is the installed weight of the vessel, including internals, catalyst or packing, refractory lining, platforms, insulation fireproofing, piping, and other permanent attachments. 5.10.2 Operating Live Load (L2) [V/E] Operating Live Load is the weight of the liquid at the maximum operating level, including that on trays. 5.10.3 Pressure Load (L3) [V/E] Pressure Load is the MAWP {Design Pressure} (internal or external at the coincident temperature) considering the pressure variations through the vessel, if any. MAWP may be equal to the design pressure (see Code footnote 34). For vessels with more than one independent chamber, see Code Paragraph UG-19(a) {AD-102}. 5.10.4 Thermal Load (L4) [V/E] Thermal Loads are the loads caused by the restraint of thermal expansion/interaction of the vessel and/or its supports.


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REVISION


August 2000

5.10.5 Test Load (L5) [V/E] Test Load is the weight of the test medium, usually water. Design basis shall consider that the vessel will be tested in its normal operating position. (See Section 5.2.2.) 5.10.6 Wind Load (L6) [V/E] Wind Load shall be determined in accordance with Section 5.8. 5.10.7 Seismic Load (L7) [V/E] Seismic Load shall be determined in accordance with Section 5.9. 5.10.8 Piping and Superimposed Equipment Loads (L8) [V/E] Loads caused by piping other than the Dead Load in Section 5.10.1 and those caused by superimposed equipment shall be considered as applicable. 5.10.9 Load Combinations [V/E] Vessels and their supports shall be designed to meet the most severe of the following load combinations: (See Section 5.18 for vessel supports.) 1. L1+L6

Erected Condition with full Wind Load

2. L1+L2+L3+L4+L6+L8 Design Condition with full Wind Load (include both full and zero pressure conditions (L3) for check of maximum longitudinal tensile and compressive stress) 3. L1+L2+L3+L4+L7+L8 Design Condition with Seismic Load (include both full and zero pressure conditions to determine L3 for check of maximum longitudinal tensile and compressive stress) 4. L1+(F)L3+L5+(0.25)L6 Initial (New uncorroded) Hydrostatic Test Condition and Future (corroded) Hydrostatic Test Condition with vessel in normal operating position and with 50% of design wind velocity (25% of Wind Load)

Page 20 of 58


REVISION


August 2000

F is the appropriate Code test factor that, when multiplied by the lowest ratio (for the materials of which the vessel is constructed) of the stress value S {stress intensity value Sm} for the test temperature of the vessel to the stress value {stress intensity value Sm} for the design temperature, established the minimum required hydrostatic test pressure at every point in the vessel. Following are the Division 1 Code hydrostatic test factor requirements in UG-99, UG-101(c), Code Case 2046, and Code Case 2055-1: •

1.5 for contruction to 1998 and earlier editions (4.0 design margin)

•

1.3 for construction to 1999 and later addenda/editions (3.5 design margin)

For Division 2, the hydrostatic test factor is 1.25. The general primary membrane tensile stress in the corroded condition (or when no corrosion allowance is specified) under this load combination shall not exceed {AD-151.1}: •

90% of the Specified Minimum Yield Strength at 100°F for carbon and low-alloy steels

•

The Specified Minimum Yield Strength at 100°F for austenitic stainless steels

(See examples of design considerations described in Section 5.2.2 and testing requirements in Section 7.) 5. Lift Condition: See Section 8. 5.11

Wind-Induced Vibration of Vertical Vessels [V/E] Vertical vessels having an h/D ratio (not including insulation thickness, but including skirt height) greater than 15 may vibrate due to vortex-excited resonance unless sufficient external appurtenances or wind spoilers are present to disrupt the airflow over the vessel, thereby preventing the generation of the vortices with the undesirable predominant frequency. (In general, the addition of spoilers is typically more feasible than changing the natural frequency of the vessel or providing supplementary damping.) In the case of cylindrical pressure vessels that have been determined to be candidates for wind-induced vibration, it has been found that spoilers are only required for the top third of the vessel height and that normal attachments in this region (e.g., ladders and piping) will be effective as spoilers provided the maximum circumferential distance between them is 108 degrees (30% of the vessel circumference). [V/E] Vessels with an h/D ratio of 15 or greater that do not have a significant number of effective attachments shall be investigated for dynamic behavior due to wind excitation as described by Vellozzi (see Section 2.3) and Sections 5.11.1.1, 5.11.1.2, and 5.11.1.3. Other similar proven evaluation methodology may be used.


Page 21 of 58



5.11.1 Vortex Shedding Ranges [V/E] Vessels may vibrate in any of three vortex shedding ranges. 5.11.1.1 [V/E] Lower Periodic Vortex Shedding Range: When the Reynolds number is less than 300,000 and the Strouhal number is approximately 0.2, vibration due to periodic vortex shedding may occur with tall slender vessels that have very low fundamental frequencies. 5.11.1.2 [V/E] Random Vortex Shedding Range: When the Reynolds number is between 300,000 and 3,500,000, random vortex shedding occurs. When the Strouhal number is approximately 0.2, the random vortex oscillations may lock-in and become periodic, causing the vessel to vibrate. 5.11.1.3 [V/E] Upper Periodic Vortex Shedding Range: When the Reynolds number is above 3,500,000 and the Strouhal number is approximately 0.2, self-excited vibration will occur when the natural frequency of the vessel corresponds with the frequency of vortex shedding. 5.11.2 Corrective Action [V/E] When it has been determined that a vessel may vibrate and the attributes of the vessel (e.g., normal attachments) cannot be changed to put it in a range where vibration will not occur, wind spoilers in accordance with Section 5.11.2.1 or 5.11.2.2 shall be added to the top-third of the vessel. 5.11.2.1 [V/E] Helical Spoilers: Use a three-start system of spoilers in a helical pattern on the top third of the vessel. An optimum configuration consists of spoilers with an exposed width beyond insulation of 0.09D and a pitch of 5D, where D is the diameter of the top third of the vessel. The spoiler system may be interrupted to provide clearance at vessel appendages. 5.11.2.2 [V/E] Short Vertical Spoilers: Use a three-start system of short vertical spoilers arranged in a helical pattern on the top-third of the vessel. The exposed width beyond insulation of the spoilers should be 0.09D and the pitch (height of one helical wrap) between 5D and 11D. There should be a minimum of eight (8) spoilers over the pitch distance (each complete helical wrap) and a minimum of 1.5 helical wraps over the top-third of the vessel. The spoiler system may be interrupted to provide clearance at vessel appendages. 5.11.2.3 [V/E] Projected Area: When spoilers as described in Sections 5.11.2.1 and 5.11.2.2 are added to a vessel, the column projected area normal to wind, Af, and the corresponding force coefficient, Cf, for the column height where spoilers have been added (see Section 5.8.1.6) shall be used when designing the vessel and supporting structure to calculate the overturning load. The column projected area shall be calculated using the projected diameter

Page 22 of 58


REVISION


August 2000

taken at the outside edge of the spoilers multiplied by the height of the section under consideration. 5.12

Formed Heads 5.12.1 [V/E] Design rules to prevent buckling of thin fabricated torispherical heads subjected to internal pressure are not yet available in Division 1 or Division 2 of the Code. Accordingly, for L/t ratios greater than 500, design checks of the Code-required thickness should be made based on equations for perfect torispheres that have been modified to reflect experimental results on fabricated models (see Section 2.3, Galletly). This check may reveal the need for a head thickness greater than the Code-required minimum thickness. Note: L is the inside spherical or crown radius and t is the minimum required thickness of the head after forming (corroded condition). 5.12.2 [V/E] When an agitator is mounted on a nozzle (or studding outlet), in a formed head, the head thickness determined from Code formulas for pressure loadings and static local loadings analysis is often not sufficient to provide the rigidity and stress levels acceptable for the dynamic loadings that will be applied. Before ordering the head, the agitator manufacturer shall be consulted regarding the recommended minimum head thickness for the agitator installation under consideration.

5.13

Flanges (see PIP VESV1002, Section 6.3.16) [V/E] The Designer is responsible for ensuring that the facings, bolt circle, number of bolts, and size of bolts of vessel nozzles match the mating piping flanges. Flanges for all flanged vessel nozzles equal to or smaller than NPS 24 shall meet the requirements of ASME B16.5. Body flanges in this size range may be either per ASME B16.5 or custom-designed per the Code. For nozzles larger than NPS 24 and for body flanges of any size, the options available (as follows in Sections 5.13.1 through 5.13.4) to the User must be carefully selected as a function of the need. 5.13.1 ASME B16.47, Series A (NPS 26 through NPS 60) [V/E] These are standard carbon, low-alloy, and austenitic stainless steel flanges of the integral hub, welding neck style that are dimensionally the same as MSS SP-44 flanges. The materials covered are identical with those in Materials Groups 1 and 2 of ASME B16.5. Line valves and machinery nozzles may be provided with flanges of MSS SP-44 dimensions. Therefore, vessel nozzle flanges that meet the dimensions of Series A flanges may be either necessary or desirable. Series A and Series B flanges are not dimensionally compatible in all sizes. 5.13.2 ASME B16.47, Series B (NPS 26 through NPS 60) [V/E] These are standard carbon, low-alloy, and austenitic stainless steel flanges of the integral hub, welding neck flange style that are dimensionally the same as flanges covered under the now obsolete API 605. The materials covered are identical with those in Materials Groups 1 and 2 of ASME B16.5. Machinery nozzles may be provided with flanges of Series B


Page 23 of 58

REVISION


August 2000

dimensions. Therefore, vessel nozzle flanges that meet the dimensions of Series B flanges may either be necessary or desirable. Series A and Series B flanges are not dimensionally compatible in all sizes. 5.13.3 Custom-Designed Flanges per Code 5.13.3.1 [V/E] Custom-designed flanges may be required when: a. Materials of construction covered in ASME B16.5 or ASME B16.47 are not appropriate for the service conditions. b. For NPS 26 through NPS 60, the desired flange style is other than the welding neck type (e.g., lap joint, slip-on) covered in ASME B16.47. c. Design conditions for the intended service application exceed the pressure-temperature ratings of ASME B16.5 or ASME B16.47 flanges. d. Service requirements result in significant mechanical loadings other than pressure. The pressure-temperature ratings of both ASME B16.5 and ASME B16.47 are based primarily on pressure loadings and accordingly, the flanges may not be suitably designed for externally applied moment or axial thrust loadings (e.g., as imposed by mating piping, weight, wind, or seismic loadings), resulting in leaktightness problems. See Appendix C for the method usually employed for considering such mechanical loadings. e. Rigidity requirements of ASME B16.47 flanges are sometimes below recommended guidelines, even when flanges are subjected only to pressure loadings within the pressure-temperature ratings, or for those flanges designed in accordance with Code Appendix 2 {Appendix 3}. See Code Appendix S-2 {Appendix M} for Rigidity Index guidelines.

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REVISION


August 2000

5.13.3.2 [V/E] Recommended minimum gasket contact widths are shown in the following table: Vessel OD (inches)

Gasket Contact Width (inches)

≤ 36

1

36 < OD ≤ 60

1-1/4

OD > 60

1-1/2

Notes: 1. Gasket Contact Width is the recommended minimum width of the gasket in contact with both flange faces. 2. For 3-ply corrugated metal gaskets, the gasket OD shall be a minimum of 1/4 inch less than the raised face or lap ring OD. (See Section 5.13.4.4.)

5.13.3.3 [V/E] Design flanges not only for the design pressure, but also for other loadings that will be applied to the joints during the project life (e.g., externally applied bending moment and axial thrust loadings.) [See Section 5.13.3.1(d).] 5.13.3.4 [V/E] Select flange thickness so that, considering all loadings that will be applied [see Section 5.13.3.1(d)], the Rigidity Index as defined in Appendix S-2 {Appendix M} of the Code is ≤ 1.0, based on the recommended value of KL of 0.2 or K1 of 0.3, as applicable. 5.13.3.5 [V/E] Flange bolts shall not be less than 3/4 inch nominal diameter. Flange bolt holes shall be 1/8 inch larger than the diameter of the bolts. 5.13.3.6 [V/E] Nubbins are permitted only by agreement with the User. 5.13.4 Custom-Designed Lap Joint Flanges [V/E] Practices relative to lap joint flanges that experience has shown will result in a level of damage tolerance, leak-tightness integrity, and gasket replacement capability equivalent to the welding neck style are as follows:


Page 25 of 58

REVISION


August 2000

5.13.4.1 [V/E] The recommended radial lap width is as shown in the following table: Nozzle Vessel OD (inches)

Radial Lap Width (inches)

OD ≤ 18

1

18 < OD ≤ 36

1-1/2

36 < OD ≤ 60

1-3/4

OD > 60

2

Note: Radial Lap Width shall be measured from the toe of the lap-to-shell attachment weld to the outer edge of the lap ring. (See Section 5.13.4.4.)

5.13.4.2 [V/E] The gasket contact width is as shown in the Table in Section 5.13.3.2. 5.13.4.3 [V/E] Finished lap ring thickness is a minimum of 3/16 inch greater than the nominal wall thickness of the nozzle/shell to which it is attached. This thickness will allow possible future re-machining of the lap and should be sufficient to allow the laps to be machined front and back, if necessary to maintain parallel surfaces after repair. 5.13.4.4 [V/E] If the values in the Tables in Sections 5.13.3.2 and 5.13.4.1 are not used, the gasket/lap/flange design shall be configured so that the gasket load reaction on the lap (defined as “G” in Code Appendix 2 {Appendix 3}) is as close as practicable to being coincident with the reaction of the flange against the back of the lap (taken at the midpoint of contact between the flange and lap). The Code does not treat the gasket reaction and flange/lap reaction independently [see Code Figure 2-4(1) {Figure 3-310.1(a)}]. However, this recommended configuration is believed to promote improved joint performance because it minimizes the amount of bending in the lap ring resulting from applied forces. 5.13.4.5 Lap Type Flange-to-Shell Clearance

[V/E] The difference between the flange inside diameter (ID) and the shell OD shall not exceed: •

1/16 inch for nominal diameters up to and including NPS 12

•

1/8 inch for nominal diameters over NPS 12 through 48 inches OD

•

3/16 inch for nominal diameters over 48 inches OD

5.13.4.6 Flange Bevel and Lap Ring Weld

[V/E] The fillet weld attaching the lap ring to the shell shall be an equal leg fillet weld with the leg dimension equal to the nominal shell thickness (+1/16 inch, -0). The difference between the diameter of the flange bevel where the lap ring contacts the surface of the

Page 26 of 58


REVISION


August 2000

flange and the nominal diameter at the toe of the lap ring attachment weld at the back of the lap ring shall be 1/8 inch (+1/16 inch, -0). 5.13.5 Lap Joint Flanges NPS 24 and Smaller [V/E] When ASME B16.5 lapped flanges are specified, the User is cautioned to make the checks/inspections necessary to ensure that the flanges actually are ASME B16.5 lapped flanges. [V/E] For certain of the smaller sizes in each pressure class, the lengththrough-hub (dimension Y) of the slip-on flange and the lapped flange are the same. (This is true through NPS 12 for Class 150, through NPS 8 for Class 300, etc.) Accordingly, since the slip-on flange is more commonly used, flange manufacturers typically modify the small slip-on flanges to make the lapped style. This modification consists of machining the corner radius of the bore as specified in ASME B16.5 (dimension r) and removing the raised face. The latter change is permitted in Interpretation 3-5 of ASME B16.5, provided the resulting flange meets the requirements for a lapped flange, including flange thickness, or a length-through-hub dimension. [V/E] The caution is focused on larger sizes where the length-through-hub (dimension Y) for lapped flanges is greater than that of the slip-on style. Some flange manufacturers have furnished the modified versions of these slip-on flanges as lapped flanges, calling them short-hubbed lapped flanges. These flanges do not comply with ASME B16.5 and, as a result, do not comply with either the Code or OSHA when Code construction is mandated. The strength of the short-hubbed flanges cannot generally be justified by Code calculations. 5.13.6 Slip-on Flanges [V/E] Slip-on flanges are limited to use under the following conditions:


1.

[V/E] ASME B16.5 standard forged flanges for design pressures and coincident temperatures not exceeding the pressuretemperature ratings for Class 150 flanges as specified in ASME B16.5, except that the maximum design temperature shall not exceed 650°F

2.

[V/E] {Not Division 2 Applicable} Custom-designed flanges per Code Figure 2-4(8), (8a), (9), (9a), (10), or (10a) for design temperatures not exceeding 650ºF; and for flange thickness not exceeding 3 inches

3.

[V/E] Corrosion allowance does not exceed 1/16 inch (1.6 mm)

4.

[V/E] Carbon or low-alloy steel flanges attached to solid highalloy necks are limited to design temperatures no higher than 450ºF, unless a higher temperature is justified by a complete stress analysis and approved by the User

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5.

[V/E] MDMT is not colder than minus 20ºF for carbon and lowalloy steels

6.

[V/E] Vessel is not for lethal service (Code requirement)

7.

[V/E] Vessel or nozzle is neither for cyclic pressure or temperature service nor subjected to cyclic loadings from associated equipment

8.

[V/E] For vessels not in hot hydrogen service (Hot hydrogen service is defined as hydrogen partial pressure exceeding 100 psia, with a corresponding coincident temperature exceeding 400ºF.)

5.13.7 Threaded and Socket Weld Flanges [V/E] Threaded and socket weld flanges shall not be used. (See Section 5.13.9.) 5.13.8 Flange Facing and Surface Finish 5.13.8.1 [V/E] Flanges, except for lapped flanges, shall either have a raised face or shall have a construction that provides outer confinement to the gasket if required by Section 5.13.8.3. The height of a raised face shall be 1/16 inch or a greater height when required by ASME B16.5 or ASME B16.47, or as specified by the User. For some User-designated services, flat-face flanges or ring joint facings may be required. 5.13.8.2 [V/E] Standard flanges and factory-made lap joint stub ends shall have a surface finish in accordance with ASME B16.5 or ASME B16.47, as applicable. For standard flanges in services requiring special consideration (e.g., hydrogen) and for custom flanges and shop-fabricated lap joint stub ends, the gasket contact surface shall have either a serrated concentric or serrated spiral finish having a resultant surface finish from 125 - 250 µ inch average roughness. 5.13.8.3 Confined Joints

[V/E] For any of the following conditions, gasketed flange joint designs (body flange and nozzle joints) larger than NPS 24 shall provide outer confinement of the gasket: • Design pressure 300 psi or higher • Design temperature hotter than 500°F • MDMT colder than minus 20°F • Cyclic pressure or temperature service • Joint requires metallic gasket Note: Robust metal reinforced gaskets (e.g., spiral-wound with outer gauge ring, double-jacketed corrugated metal gaskets with a corrugated metal filler, etc.) are exempted.

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5.13.9 Piping Connections [V/E] All piping connections to vessels shall be either flanged or buttwelded. The minimum size shall be NPS 1-1/2. The use of threaded connections is not recommended because of the potential for crevice corrosion and notch sensitivity. Threaded connections for vents and drains or instrument connections are permissible when specified by the User. When used, the minimum size shall be NPS 3/4 Schedule (Sch) 160 or 6000# coupling. (See ASME B16.11.) Nozzle sizes NPS 1-1/4, 2-1/2, 3-1/2, and 5 shall not be used. 5.13.10 Quick Opening Closures [V/E] Swing bolts (eye bolts) shall be of one-piece construction without welding. Hinge pins shall be solid (not rolled) and of the same material as the swing bolts. 5.13.11 Flanges - Pass Partition Areas [E] In multi-pass heat exchangers, the total gasket sealing areas of the pass partition plate(s) shall be included when calculating the minimum initial bolt load required to seat the gasket (Wm2). 5.13.12 Flanged Joints [E] Removable channels or bonnets, channel covers, and floating head covers shall be attached with through-bolted flanged joints, except TEMA Type D stationary head designs. 5.14

Nozzles 5.14.1 [V/E] Nozzles supporting agitators, pumps, or other mechanical equipment shall be suitably reinforced to withstand the mechanical loadings specified by the device manufacturer. Likewise, nozzles for pressure relief devices shall be designed and reinforced for thrust reaction. Use of heavier nozzle necks, conventional reinforcing pads with properly contoured fillet welds, and formed heads of appropriate stiffness are the elements that result in a design suitable for an infinite number of cycles. Gussets shall not be used to strengthen, stiffen, or reinforce nozzles, unless demonstrated by calculations to be suitable for the specified cyclic life or thermal condition. For such nozzles, consideration shall be given to the dimensional requirements of the device as supplied by the device manufacturer (e.g., tolerances). 5.14.2 [V/E] Surface-attached nozzles as shown in Code Figures UW-16.1(a), (a-1), (a-2), (a-3), and (b) {Figures 610.1(a) and (b)}, and those with internal reinforcing pads, are not permitted. 5.14.3 [V/E] Nozzle locations (including manways) and their reinforcing pads, if necessary, shall preferably not interfere with or cover pressure vessel weld seams [see PIP VESV1002, Section 5.2.2(c)]. When located in heads other


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August 2000

than hemispherical heads, all the nozzle reinforcing shall preferably be within the spherical portion of the head. 5.14.4 [V/E] Vessels shall be provided with sufficient connections to permit purging, pumpout, venting, decontamination, pressure relieving, and draining. Vortex breakers shall be provided on pump suction nozzles. (See PIP VEFV1124.) 5.14.5 [V/E] For vessels supported by a skirt, the flange of any nozzle in the bottom head shall be located outside the skirt. 5.14.6 [V/E] In establishing nozzle and manway projections, clearance should be provided for removing flange stud bolts from between the flange and vessel and for accessing flange stud nuts. Clearance for flange studs and nuts should be considered when nozzles penetrate insulation or platforms. Minimum projection from the outside of the vessel wall to the nozzle face shall be: •

8 inches for nozzles up to and including NPS 8

•

10 inches for nozzles larger than NPS 8

Round up the dimension from the face of the nozzle to the vessel centerline or reference line to the next larger 1/2-inch increment. 5.14.7 [V/E] Minimum nozzle neck nominal thickness for carbon steel nozzles shall be per Code Paragraph UG-45, except in no case shall the nominal thickness selected for NPS 3 and smaller be thinner than Sch 80. 5.14.8 [V/E] Minimum nozzle neck nominal thickness for high-alloy and nonferrous alloy nozzles shall be per Code Paragraph UG-45, except in no case shall the nominal thickness selected for NPS 3 and smaller be thinner than Sch 40S. 5.14.9 [V/E] {Not Division 2 Applicable} When there is concern that an overstress condition may exist, the local membrane and surface stresses due to local loads (e.g., piping loads, platform loads, etc.) shall be determined using the WRC Bulletin 107 procedure, or other local stress analysis procedures. For local loads and pressure, the allowable stresses are 1.5S for local primary membrane stress and 3S for primary membrane plus secondary bending stress at nozzles, platform lugs, etc. S shall be the Code-allowable stress at the design temperature. 5.14.10 [E] Nozzles shall not be located closer to an integrally attached tubesheet, either shell side or tube side, than shown in Appendix D. 5.14.11 [V/E] Openings exceeding the size limits stated in Code Paragraph UG-36(b)(1) shall meet the supplemental rules of Code Appendix 1-7(a) and (b). (Code Case 2236 covering alternative design rules for large openings shall only be used with User’s agreement.) 5.14.12 [V/E] A minimum of three safety retainer clips shall be welded to the nozzle neck at the back of NPS 4 and larger lap joint flanges that face upward.

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(Facing upward is defined as inclination of the nozzle from the horizontal at an angle of 30 degrees or greater.) These clips shall be located so that a spacing of one length-through-hub dimension (dimension Y in ASME B16.5) will exist between the back of the lap and the face of the flange. This will allow for future painting of the nozzle neck in this region. 5.15

Manways [V/E] The location, quantity, and size of manways and internal ladder rungs shall be specified to ensure that all interior areas are accessible as required. Minimum requirements regarding manway and inspection openings are covered in Code Paragraph UG-46 {Article D-10}, “Inspection Openings.” 5.15.1 [V/E] Service conditions, size, and configuration of the vessel may justify manways other than (or in addition to) those mandated by the Code. 5.15.1.1 [V] Vessels with mixers/agitators shall be provided with at least one manway that does not require removal of the mixer/agitator. 5.15.1.2 [V] Unless other provisions (e.g., body flanges) are made for tray removal, trayed towers shall have at least two manways, one at the top and one at the bottom. Additional manways shall be as specified by the User. 5.15.2 [V/E] Manways shall be usable from a ladder, platform, or grade. 5.15.3 [V] Vessels smaller than 3 feet ID that are subject to internal corrosion, erosion, or mechanical abrasion shall be equipped with inspection openings as described in Code Paragraph UG-46 {Article D-10}. Vessels in this size category may justify the use of body flanges. 5.15.4 [V] Vessels 3 feet ID and larger that are subject to internal corrosion, erosion, or mechanical abrasion shall be equipped with one or more flanged and blinded manways. 5.15.5 [V/E] The nominal recommended manway size is NPS 24 with a finished ID not less than 23 inches. Manways shall not be smaller than NPS 18 or have a finished ID of less than 17 inches. Larger diameter manways should be used to satisfy additional needs such as, but not limited to, installation of internals/catalyst, packing, maintenance requirements, long projection due to thick insulation, etc. 5.15.6 [V/E] To provide utility for entry and exit, vessel geometry, and location of access platforms shall be considered when locating manways. Internal ladders or grab rungs may be needed at manway locations for entry and exit. 5.15.7 [V/E] Provisions shall be made for lifting devices (fixed or portable) at manways for personnel rescue as described in OSHA 29 CFR 1910.146. 5.15.8 [V/E] Manways shall be equipped with either a davit or a hinge to facilitate handling of the blind flange. Manways oriented with the nozzle neck axis in a horizontal plane shall be equipped with a hinge in accordance with PIP VEFV1116 or a davit in accordance with PIP VEFV1117. Attach the


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davit-socket bracket to the nozzle neck when lap joint flanges are employed. Manways on the top of vessels oriented with a vertical nozzle neck axis shall be equipped with a davit in accordance with PIP VEFV1118. 5.15.9 [V/E] Consideration may be given for use of suitable process connections as manways and handholes. (Consider both size and location.) 5.15.10 [V/E] When approved by the User, flanges and their pressure-retaining covers for manways may be custom-designed, with due consideration being given to providing a Rigidity Index in accordance with the recommendations in Code Appendix S-2 {Appendix M}. A detail sketch describing the flange, cover, bolting, and gasket, as well as Code calculations supporting the design, shall be provided. 5.16

Anchor Bolts 5.16.1 [V/E] Materials for anchor bolts shall be selected from one of the following: 1. Carbon steel: A-36 or A-307 Grade B 2. Low-alloy steel: A-193 B7. The User’s written approval shall be obtained for the use of this low-alloy material. 5.16.2 [V/E] The allowable design stress, as calculated using the tensile stress area of the threaded portion, shall not exceed the following (see Note): •

[V/E] Carbon steel: 20,000 psi

•

[V/E] Low-alloy steel: 30,000 psi Note: For vessels on concrete foundations, the allowable stress of anchor bolts may be limited by the strength and dimensions of the concrete for the bolt spacing selected. Allowable stresses used in the final design shall be agreed to by the structural engineer.

•

[V/E] Anchor bolts selected shall not be smaller than 3/4 inch, shall be selected in multiples of 4, and shall straddle normal centerlines.

•

[V/E] Anchor bolting shall be furnished and installed by the User.

5.16.3 [V/E] Anchor bolts shall be selected with the following threads and the tensile stress area shall be selected accordingly: •

[V/E] Bolts 1 inch and smaller in diameter: Coarse thread series, ASME B1.1

•

[V/E] Bolts larger than 1 inch in diameter: 8 thread series, ASME B1.1

5.16.4 [V/E] For vessels on concrete foundations, the allowable concrete bearing stress used in design shall be 1800 psi. Note: This value is based on the use of concrete with an ultimate strength, f'c, of 3000 psi for which the minimum allowable bearing is (0.7)(0.85)f'c (approximately 1800 psi for 3000 psi concrete).

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Higher values may be used consistent with the ulitmate strength chosen (if known) and other provisions of state-of-the-art concrete foundation design. The design loadings for anchor bolts embedded in concrete may be determined by either the simplified method (neutral axis of bolt pattern at centerline of vessel) or the shifted neutral axis method (See Section 2.3, Brownell and Young). However, the use of the latter method is recommended for large vertical vessels because of the economic benefit. Note: The neutral axis shift method does not apply for vessels supported by steel structures. 5.16.5 [V/E] Anchor bolts embedded in concrete foundations shall be zinc-coated (hot dip galvanized or mechanically zinc-coated) so that the addition of a corrosion allowance is not required. 5.17

Internals [V/E] Functional design of trays and other removable internals are outside the scope of this Practice. 5.17.1 [V/E] Removable internals shall be sized to pass through designated vessel openings. On vessels with internals where a vessel manway is not located in the top head, internal rigging clips shall be provided to facilitate handling of the internals. 5.17.2 [V/E] Vessel internals such as distributors, dip tubes, baffles, and thermowells should not be located near manways in a manner that would interfere with personnel access or rescue. Special consideration should be given to the area directly below manways and to head knockers above manways. In some circumstances, the addition of grab rungs may be necessary. 5.17.3 [V/E] In services the User has defined as corrosive, welding of vessel internals attached to a pressure boundary component shall be continuous on all surfaces in order to eliminate corrosion pockets. All seams and corner joints shall be sealed. 5.17.4 [V/E] Internal piping and baffles shall be mounted in a manner that will not unduly restrict thermal expansion. Consideration shall be given to vibration and the possibilities of fatigue failure. Where vibration and fatigue are governing design requirements, internal non-pressure parts (e.g., baffles that may be subject to vibration or cyclic loading) shall be continuously welded. 5.17.5 [V/E] Internal bolting in vessels, especially where vibration is expected (e.g., where agitators are installed), shall either be double nutted, tackwelded to the clip (or baffle), or have a lock wire placed in the nut/bolt or other supports. 5.17.6 [V/E] The nominal chemical composition of internal non-pressure piping shall be compatible with that of the inside surface of the vessel and the process. Flanges for internal non-pressure piping may be fabricated from plate but must conform to ASME B16.5 Class 150 bolting dimensions.


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5.17.7 [V/E] Vessel internals and all portions of each vessel shall be self-draining to ensure complete elimination of liquid from the vessel when drained. 5.17.8 [V/E] For integrally clad and/or weld overlayed vessels, lightly loaded (as defined in Code Section VIII, Division 2, Paragraph AD-912, footnote 4) supports, such as those for trays, baffles, etc., may be welded directly to the alloy clad or weld overlay. Where supports are carrying an appreciable load (> 25% of the allowable stress for fillet welds), such as packing bed support rings, the Designer shall determine and specify whether the support shall be welded directly to the base metal. 5.18

Vessel Supports 5.18.1 General 5.18.1.1 [V/E] Code-allowable stresses {design stress intensity} shall be used for vessels and their supports. For combinations of earthquake or wind loadings with other loadings listed in Code Paragraph UG-22 {AD-110}, the allowable stresses {design stress intensity} may be increased as permitted by Code Paragraph UG23(c) {AD-151.1}. See Section 5.10.9 for load combinations to be considered. See also Code Appendix G {AD-940}. 5.18.1.2 [V/E] For structural-shape support members in compression where slenderness ratio is a controlling design consideration, no increase in the allowable compressive stress is permitted. 5.18.1.3 [V/E] For supports outside the scope of the Code, either Codeallowable stresses {design stress intensity} or, for structural shapes, those in the AISC Manual of Steel Construction may be used. 5.18.1.4 [V/E] The MDMT for the vessel support assembly shall not be warmer than the lowest 1-day mean atmospheric temperature at the installation site. (See Section 5.3.) 5.18.1.5 [V/E] Localized shell stresses at all support-to-shell locations shall be considered, as applicable, for wind load, earthquake, and all other loadings described in Paragraph UG-22 {AD-110} of the Code. (See Sections 5.8, 5.9 and 5.18.2.5.) 5.18.1.6 [V/E] Where reinforcing pads are used under supports, consideration shall be given to stresses due to possible temperature differentials among the vessel, pads, and supports. 5.18.2 Vertical Vessels 5.18.2.1 [V/E] Vertical vessels shall normally be designed as selfsupporting units and shall resist overturn based upon wind or earthquake loadings (as described in Sections 5.8 and 5.9) and other applicable loadings per Paragraph UG-22 {AD-110} of the Code.

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5.18.2.1.1 Skirts or lugs shall be used to support towers or large vertical vessels and are preferred for vessels having top-entering agitators. 5.18.2.1.2 Leg supports shall be limited to spherical and cylindrical vessels that meet the following: •

Design temperature does not exceed 450°F

•

Service is noncyclic and nonpulsating (See Note 1.)

•

Vessel h/D ratio does not exceed 5 (Height is the distance from base of support to the top tangent line of the vessel.) (See Note 2.) Note 1: Vessels having agitators experience transient transverse forces due to dynamic bending moments from the agitator and sloshing of the liquid. Therefore, the design of leg-supported vessels with agitators requires the application of experience-based engineering judgment to ensure that displacement stiffness and stress levels essential to satisfactory operation are provided. Note 2: Caution is advised for leg-supported vessels that may be within h/D ≤ 5 but could have excessive axial and/or bending loads on the legs or an overstress condition in the vessel wall.

5.18.2.2 [V/E] Skirts shall be attached to the bottom head by a continuous weld sized so as to provide for the maximum imposed loadings. The preferred skirt attachment detail shall be butt type (skirt butted to knuckle portion of head such that the centerlines of the skirt plate and the head flange are the same diameter, or such that the OD of the shell and the OD of the skirt coincide). A lapped type skirt design (skirt lapped to straight flange of head) may also be used. See Figure AD-912.1 of Division 2 of the Code for some illustrative weld attachment details and associated minimum weld sizes. All butt weld joints within the skirt shall be Type No. 1 of Code Table UW-12 {AF-221}. Alignment tolerance at plate edges to be butt-welded shall be per Code Paragraph UW-33 {AF-140.2}. The type of skirt attachment detail, the style of anchor ring assembly (e.g., single ring with gussets, single ring with chairs, double ring with gussets, etc.), and the type/degree of nondestructive examination of the skirt assembly welds shall be a matter of agreement between the User and the Designer.


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5.18.2.3 [V/E] Skirt diameter permitting, one or more 24-inch diameter or larger openings shall be provided to allow free access for inspection and/or maintenance work inside the skirt. Other opening geometries are acceptable and are a matter of agreement between the User and the Designer. 5.18.2.4 [V/E] When the skirt is to be provided with insulation or fireproofing, all openings shall be provided with rings or collars projected to equal the insulation or fireproofing thickness. Sleeves shall be of sufficient size to provide clearance for painting, insulation, and expansion. Sleeve material shall be the same material composition as that portion of the skirt and shall be continuously fillet-welded inside and outside. 5.18.2.5 [V/E] The skirt for stainless steel or other high-alloy steel vessels shall be of a material with essentially the same coefficient of expansion as the head to which it is attached when the maximum temperature stamped on the Code nameplate is hotter than 450°F. The length of this high-alloy steel portion of the skirt shall not be less than 2 ( Rt ) , where R is the mean skirt radius and t is skirt thickness, in inches. The lower portion of these skirts may be constructed of carbon or low-alloy steel. When the maximum temperature stamped on the Code nameplate is 450°F or colder, the entire skirt may be made of carbon or low-alloy steel. In all cases, the materials and thicknesses selected shall be suitable for the maximum and minimum design metal temperatures and the imposed loadings. 5.18.2.6 [V/E] Corrosion allowance for the skirt and base ring shall be specified separately from the vessel corrosion allowance. 5.18.3 Horizontal Vessels 5.18.3.1 [V/E] Horizontal vessels shall be designed for two saddle supports attached by welding. Design of saddle supports and calculation of localized shell stress may be determined by the L. P. Zick method. (See Section 2.3 and Code Appendix G {AD-940}). The minimum saddle support contact angle shall be 120 degrees. For vessels, saddle supports shall be located a maximum distance of Ro/2 from the head tangent line, where Ro is the shell outside radius. 5.18.3.2 [V/E] Saddle wear plates, when required, shall have the following proportions: •

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Thickness: Established by design, but not less than the smaller of shell thickness or 3/8 inch


REVISION


August 2000

•

Width: Width of saddle plus 5t each side of the saddle, where t = cylindrical shell thickness in the corroded condition

•

Extension Beyond Horn of Saddle: r/10, where r = radius of cylindrical shell in corroded condition The wear plates shall have a minimum radius of 2 inches on the corners, shall be continuously welded to the shell, shall be provided with one 1/4 inch drilled telltale hole (or equivalent venting) per segment, and shall be vented to the atmosphere. Vent holes shall be located at the low point of the wear plate and shall not be plugged during hydrostatic testing. 5.18.3.3 [V/E] One of the saddles shall be designated as the fixed saddle in which holes shall be provided to receive the anchor bolts. The other saddle shall be designated as the sliding saddle in which slotted holes shall be provided. The diameter of the bolt holes and width of the slot shall be 1/4 inch larger than the bolt diameter. The length of the slot shall be: 2αDL∆T Where: α = Coefficient of thermal expansion of shell material, in/in °F DL = Length between saddle supports, measured to centerline of anchor bolts, inches ∆T = Greatest absolute value of: ambient temperature at installation (but not warmer than 70°F) minus the maximum or minimum shell temperature to be stamped on the Code nameplate, °F The anchor bolts are to be located at the center of the bolt holes (fixed saddle) or the midpoint of the slot (sliding saddle). All sliding saddles shall be provided with slide plates. Slide plates are to be furnished by others. Examples of standard details that may be used (non-mandatory) are shown on PIP VEFV1105 and PIP VEFV1106. 5.18.3.4 [V/E] The bottom of the saddle supports shall extend at least 1 inch below nozzles or other projecting vessel components. Alternatively, a temporary member shall be attached at each support to provide necessary extension until the vessel is placed in permanent position. 5.18.3.5 [V/E] Saddles to be used in conjunction with weigh cells or slide plates require design considerations to accommodate the applicable loadings. 5.18.4 Stacked Exchangers 5.18.4.1 [E] Stacked exchangers shall have the lower shell(s) designed to withstand the superimposed load of the upper exchanger(s) filled


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with water or operating fluid (whichever is greater) without distorting the shell in a manner that could cause binding of tube bundle(s). 5.18.4.2 [E] When two or more exchangers are stacked, a 1/2-inch shimming allowance shall be provided between intermediate supports. 5.18.4.3 [E] The lower fixed support of stacked exchangers shall be designed for the full bundle pulling load for removal of any upper bundle. 5.18.4.4 [E] Consideration shall be given to the effects of differential thermal expansion between exchangers. 5.18.4.5 [E] Component (i.e., bonnet, cover, etc.) lifting lugs shall be given special consideration. Two or more lifting lugs located at 45 degrees from the top centerline shall be provided to permit removal of the component without difficulty. 5.19

Heat Exchanger Component Design 5.19.1 Tubes (See Section 5.20.5 for additional information.) 5.19.1.1 [E] Tubes may be either welded or seamless. 5.19.1.2 [E] Corrosion allowance need not be added to tubes. 5.19.2 Tubesheets 5.19.2.1 [E] Tubesheets shall be designed for full design pressure on either side, with atmospheric pressure or specified vacuum on the other side. Differential pressure design may only be used when approved by the User. 5.19.2.2 [E] Manufacturer shall calculate the value of Xa (the ratio of the tube bundle axial stiffness to the tubesheet bending rigidity) as defined in Code Paragraph AA-2.4. These calculations shall be submitted with the mechanical design calculations. 5.19.2.2.1 [E] If the value of Xa is less than 3.0, the tubesheet shall be designed in accordance with Code Appendix AA rules or the methods provided in the references in TEMA RGP-RCB-7. For values of Xa equal to or greater than 3.0, the tubesheet may be designed in accordance with TEMA, Code rules, or the references in TEMA RGP-RCB-7. 5.19.2.2.2 [E] Tubesheets exceeding the scope of TEMA shall be designed in accordance with Code rules or TEMA RGP-RCB-7 references, regardless of the value of Xa.

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5.19.2.3 [E] Tubesheets welded to a carbon steel shell or channel shall be of carbon steel or clad carbon steel. Solid alloy tubesheets may be welded to a carbon steel shell or channel, provided one of the following is met: 1. [E] The thermal coefficients of expansion do not vary more than 15% from the tubesheet to the shell or channel over the operating temperature range. 2. [E] A stress analysis is performed by the Manufacturer and approved by the User for the joint between the tubesheet and the shell or channel. 3. [E] The tubesheet is welded to a relatively short cylindrical section of the same material, and a stress analysis of the junction of the alloy and carbon steel cylindrical section is performed and approved by the User. 5.19.2.4 [E] In addition to TEMA requirements for tubesheet cladding, consideration shall be given to providing adequate cladding thickness under pass partition and gasket grooves. 5.19.2.5 [E] Loose liners and plug-welded strip liners are not permitted. 5.19.2.6 [E] Confining gasket grooves shall be provided for all exchangers with gasketed pass partition joints. 5.19.3 Tube-to-Tubesheet Joints 5.19.3.1 [E] When the type of joint is not specified, expanded joints with grooves shall be used for tubesheets of homogeneous material. Expansion may be by roller, hydraulic pressure, or other User approved method. 5.19.3.2 [E] If tube-to-tubesheet leakage is deemed to be detrimental to the process, seal-welded and expanded joints are to be used. Transient operations may also warrant seal-welded and expanded tube joints. Seal-welded and expanded joints with grooves shall be used for integrally clad tubesheets. 5.19.3.3 [E] Strength-welded tube-to-tubesheet joints are to be used when expanded joints cannot carry the expected tube load or when the residual interface pressure due to expansion (tube rolling or hydraulic expansion) is compromised during operation. The loss of residual interface pressure can occur with high temperature applications or when significant differential thermal expansion occurs between the tube and the tubesheet. 5.19.3.4 [E] The special close fit tolerances for tube holes as stated in TEMA shall be mandatory for: •


Austenitic tubes with expanded and grooved tube-totubesheet joints

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REVISION


•

August 2000

Seal-welded or strength-welded tube-to-tubesheet joints

• Hydraulically expanded tube-to-tubesheet joints 5.19.4 Tube Bundles 5.19.4.1 [E] The minimum mean bend diameter of U-tubes shall not be less than 3 times the nominal tube OD. 5.19.4.2 [E] The end baffle spaces shall be equal to or greater than the central baffle space. 5.19.4.3

[E] 1. Cross-baffle metallurgy and thickness shall be selected considering the corrosivity of the shell side fluids and the intended design life. 2. Cross baffles that resist corrosion shall have a thickness no less than the greater of that specified by TEMA or 1/8 inch. 3. Cross baffles susceptible to corrosion shall have a thickness not less than the greater of the TEMA minimum, 2 times the corrosion allowance, or 3/16 inch.

5.19.4.4 [E] Each support plate and baffle in horizontal exchangers shall be provided with a 1/2 inch x 90 degree notch in the bottom for draining. 5.19.4.5 [E] All TEMA Type S and T (with removable shell cover) exchangers shall have a floating head support plate located 4 to 6 inches from the inside face of the floating tubesheet. 5.19.4.6 [E] Except for shell side isothermal boiling, isothermal condensing, or kettles, bypass sealing devices shall be provided as follows: • Seal strips are required when the radial clearance between shell and the outer tubes exceeds 5/8 inch. • Exchangers with vertical cut baffles (baffle cut parallel to shell side nozzle centerline) shall have seal strips installed to seal the bypass areas caused by the omission of tubes. • Dummy tubes, rods, or seal strips shall be provided for any pass partition lanes that are parallel to the shell side flow. • Seal strip thickness shall not be less than the greater of 75% of baffle thickness or 1/4 inch. • For vertical cut baffles (baffle cut parallel to shell side nozzle centerline), seal strips shall not extend into the inlet or outlet baffle spaces. For horizontal cut baffles (baffle cut perpendicular to shell side nozzle centerline), seal strips shall extend from the front or stationary tubesheet to the last baffle or support plate.

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REVISION


August 2000

• One pair of seal strips or one dummy tube shall be provided for each five(5) tube rows between baffle cuts. Minor adjustments may be made to suit actual tube layout. 5.19.4.7 [E] Exchangers with removable tube bundles weighing 20,000 pounds or more shall have bundle skid bars. 5.19.4.7.1 A minimum of two skid bars shall be provided. The bars shall be 1/2 inch minimum thickness by 1-1/2 inch minimum height flat bar. The skid bars shall be located no more than 30 degrees from the vertical centerline. 5.19.4.7.2 The skid bars shall extend from the stationary tubesheet to floating head support plate (TEMA Types S and T) or end baffle (TEMA Types P, U, and W). 5.19.4.7.3 When skid bars interfere with nozzle openings, the skid bars shall be terminated at the baffle or support plate adjacent to the nozzle. A tie rod/spacer of adequate strength to carry the bundle pulling load shall be located close to the tube field and within 3 inches of the skid bar and shall extend from the tubesheet or baffle/support plate on one side of the nozzle to the baffle/support plate on the other side of the nozzle. 5.19.4.8 [E] Perforated or slotted impingement plates shall not be used. 5.19.4.9 [E] Multiple exchangers of the same TEMA size and material, either stacked or parallel, shall have interchangeable components to the maximum extent possible. 5.19.5 Expansion Joints 5.19.5.1 [E] Shell expansion joints shall be of the “thick wall” flanged and flued type or flanged only type. “Thin wall” bellows type shall only be used by User agreement, shall conform to Code Appendix 26, and shall have the welding stubs of the same material as the shell. 5.19.5.2 [E] The design of expansion joints shall be performed by any method of stress analysis (e.g., finite element analysis), including TEMA Paragraph RCB-8, which can be shown to be applicable to expansion joints. The allowable stresses and cycle life for design shall conform to Code Appendix CC. The need for and design of expansion joints shall satisfy the following condition: • Differential thermal expansion encountered in the most adverse combination of temperature combinations anticipated and specified by the User – for all normal operating (including shutdown and startup) and upset


Page 41 of 58

REVISION


August 2000

conditions or operation based on metal temperatures rather than fluid temperatures and MAWP rather than operating pressures 5.19.5.3 [E] Shell expansion joints shall be ventable and drainable in the operating position. 5.19.5.4 [E] Expansion joints for single pass floating head units may be of the “thin wall” bellows type. The expansion joint manufacturer shall provide the bellows with welding stubs of the same material as the tail pipe material. The design of the expansion joint shall conform to Code Appendix 26. 5.19.5.5 [E] The expansion joint-to-shell weld shall not be located less than 2 ( Rt ) from the back of the tubesheet, where R is the outside radius of the shell, in inches, and t is the actual thickness of the shell less corrosion allowance, in inches. 5.19.6 Vapor Belts 5.19.6.1 [E] The design of vapor belts shall include: •

Effect of pressure loads

•

Longitudinal stresses produced by operating and test pressures (in other than fixed tubesheet designs)

•

Consideration of flexibility produced when designing the exchanger shell, tubes, and tubesheet. When a sleeve type vapor belt is used, the design shall be considered flexible and designed per Section 5.19.5.1.

5.19.6.2 [E] Vapor belts may be used as expansion joints provided all requirements of Section 5.19.5 are met. Whether or not vapor belts are used as expansion joints, vapor belt flexibility shall be considered in the design of exchanger shell, tubes, and tubesheets. 5.19.7 Exchanger Covers 5.19.7.1 [E] TEMA Type T exchangers (except kettle type reboilers) shall have removable shell covers. 5.19.7.2 [E] When full diameter tubesheets are specified on exchangers with removable tube bundles, the following shall apply: 1. Retaining studs are recommended to maintain the gasket seal on the shell side of the tubesheet with the channel (or bonnet) removed. Retaining studs shall be installed in 25% of the boltholes (four minimum). 2. The tubesheet shall be designed to withstand shell side or tube side hydrostatic test pressure with bonnet/channel or shell removed.

Page 42 of 58


REVISION


August 2000

5.19.7.3 [E] Mitered 90 degree reducing elbows for thermosyphon reboiler outlet heads shall conform to the following requirements: 1. No less than three (3) changes in direction at the inside and outside contour 2. Cyclic loading is not a governing design requirement. 3. Meridian (change of direction) angles between adjacent sections shall be approximately equal for gradual flow transition. 4. The general contours shall be similar to those of commercial forged reducing elbows. 5.19.8 Pass Partition Plates [E] Drain holes shall not be provided in pass partition plates. 5.19.9 Floating Heads 5.19.9.1 [E] Floating heads shall be designed and dimensioned in accordance with Code Figure 1-6(d). 5.19.9.2 [E] Nubbins shall only be used by agreement with the User. 5.19.9.3 [E] Floating heads shall be designed with respective corrosion allowance applied to the inside and outside of the floating head and flange. Corrosion allowance on the OD of the flange shall be added to the recommended edge distance for the selected bolt size. 5.19.10 Kettle Type Exchangers 5.19.10.1 [E] If a weir plate is required, the weir plate shall be continuously welded all around to the shell and shall be of sufficient height to flood the top row of tubes with a minimum of 2 inches of process fluid during normal operation. 5.19.10.2 [E] Consideration shall be given to draining both sides of the weir. 5.19.10.3 [E] Rails shall be provided to support and guide the tube bundle. Rails shall be welded to the shell. A hold down bar or angle shall be provided directly above the floating head or the last Utube support plate. 5.19.10.4 [E] All kettle type exchangers shall either have a 3-inch minimum length cylindrical section (includes flanged hub, if any) between the shell flanges and conical transitions or be provided with other alternatives for cone-to-flange fit-up and bolting clearance. For kettle type exchangers with tubesheets integral with the shell, the minimum length of cylindrical section between the tubesheet and the conical transition shall be the


Page 43 of 58

REVISION


August 2000

greater of 3 inches or ( Rt ) , where R is the mean radius of the cylindrical section and t is the thickness of the section. 5.19.11 Instrument, Vent, and Drain Connections 5.19.11.1 [E] Additional connections (such as specified by TEMA) shall not be provided in the nozzle necks. 5.19.11.2 [E] Consideration should be made to placing vents in the tubesheet to meet specific process needs. When vents/drains are specified to be in the tubesheet, installation shall be per standard details. (See PIP VEFV1127.) 5.19.12 Nameplates and Stampings 5.19.12.1 [E] Required nameplate markings shall not be stamped directly on the exchanger. 5.19.12.2 [E] In addition to required Code information, the following information shall be stamped on the nameplate: •

User’s equipment item number

•

Initial test pressures

•

Purchase order number

5.19.12.3 [E] Exchanger nameplates shall be located on the shell in an accessible location. Manufacturer shall show the nameplate location on the dimensioned outline drawing. 5.19.13 Shell and Bonnet Design [E] The use of commercially produced NPS pipe for shell and bonnet sections NPS 24 and smaller is recommended. When specifying NPS pipe as an acceptable option for rolled plate, consider Manufacturer’s tolerance when specifying inside diameters if internals such as minimum tube counts are critical. 5.20

Heat Exchanger Thermal [E] Thermal design of shell-and-tube heat exchangers must consider safety, operation, maintenance, and initial cost aspects of the intended service. Each heat exhanger unit requires independent design. The thermal design method to be used must be acceptable to User and Designer. The Designer shall be sufficiently trained to perform the calculations and properly interpret the results. 5.20.1 Fouling Factors Selection 5.20.1.1 [E] An arbitrary rule to distinguish between clean and dirty service is to define a service as dirty when the fouling factor equals or exceeds 0.002 hr ft2 °F/BTU. A lower fouling factor implies a clean service.

Page 44 of 58


REVISION


August 2000

5.20.1.2 [E] Fouling factors should be supplied from previous experience or similar service. If not available, the fouling factors for each fluid should be selected from TEMA. The fouling factor is based on the heat transfer surface contacting the fluid. The total fouling factor is the sum of the outside fouling factor and the inside fouling factor related to the outside surface. Do not use arbitrarily high fouling factors to provide thermal overdesign or to compensate for uncertainties in thermal properties or process design. High heat transfer coefficients should not be expected when high fouling factors are used; low heat transfer coefficients should not be expected when low fouling factors are used. The percentage of surface area added as a result of the fouling factor should be reviewed. 5.20.1.3 [E] The service overall heat transfer coefficient divided by the clean overall heat transfer coefficient determines the fraction of surface required for the heat exchanger to meet the process requirements when the exchanger is “clean.” The balance of the surface exists for fouling. Excessive surface available for fouling can be expensive, promote fouling, and make the exchanger difficult to control when it is clean. A review of the clean exchanger performance is required. Note: A “clean” reboiler with low-pressure steam may require a wide range control valve or low outlet pressure for control. 5.20.2 Fluid Side Selection [E] When the fluids have not been assigned a side, the following guidelines may be used to select the fluid side: (Consideration shall be given to the maintenance, operation, size, and cost.) 5.20.2.1 Favoring Shell Side Fluid Placement

•

More viscous services

•

Lower flow rate service

•

Low available pressure drop

•

Clean service

5.20.2.2 Favoring Tube Side Fluid Placement


•

Cooling water service

•

Slurry service

•

High-pressure service

•

Higher fouling service

•

Service requiring more expensive materials

Page 45 of 58

REVISION


August 2000

5.20.3 Exchanger Configuration [E] The various configurations have certain advantages and disadvantages with regard to maintenance, operation, and cost. Selection of the proper configuration is of prime importance and affects the thermal design characteristics significantly. The various configurations are defined in TEMA. 5.20.3.1 Fixed Tubesheet Units

[E] Advantages: • Typically lowest cost design • No gasketed joint between tube side and shell side fluids • Shell side has no gasketed girth joints • Can handle temperature crosses with counterflow designs • Low circumferential bypass area around the bundle • Straight tubes allow mechanical tube side cleaning [E] Disadvantages: • Shell side cannot be mechanically cleaned • Limited access for internal shell inspection • Limited differential thermal expansion allowed without the use of an expansion joint 5.20.3.2 U-Tubes

[E] Advantages: • Typically lowest cost removable bundle design • No thermal expansion problems between shell and tubes • Removable bundle for shell side mechanical cleaning • Allows for internal shell inspection • Low circumferential bypass area • For tube side high-alloy and high-pressure, typically lower cost than fixed tubesheet • No gasketed joint between tube side and shell side fluids [E] Disadvantages: • Tube side not easily mechanically cleaned • Only tubes at bundle periphery can be easily replaced • Can have large pass lane bypass area under certain baffle arrangements

Page 46 of 58


REVISION


August 2000

• U-Bends are susceptible to vibration problems, unless properly supported 5.20.3.3 TEMA Type S (non-pull through floating head)

[E] Advantages: • Removable bundle for shell side mechanical cleaning • No thermal expansion problems between shell and tubes • Straight tubes allow mechanical tube side cleaning • Allows for internal shell inspection [E] Disadvantages: • Higher cost • Internal gasketed joint • Larger circumferential bypass area • Labor intensive to pull bundle 5.20.3.4 TEMA Type T (pull through floating head)

[E] Advantages: • Removable bundle for shell side mechanical cleaning • No thermal expansion problems between shell and tubes • Straight tubes allow mechanical tube side cleaning • Allows for internal shell inspection [E] Disadvantages: • Highest cost • Internal gasketed joint • Largest circumferential bypass area around the bundle 5.20.3.5 TEMA Type F (two pass shell)

[E] Use of the TEMA Type F shell requires User’s approval. Consideration should be given to differential pressure and temperature across the longitudinal baffle, heat transfer through the longitudinal baffle, and flow bypassing around the removable longitudinal baffles. 5.20.4 Flow Arrangement 5.20.4.1 [E] Liquids, in general, are to be arranged in an upward flow direction in order to facilitate liquid filling without gas pockets. Particulate-laden liquids, such as boiler water blowdown, may be considered for a downward flow arrangement to assist in the exhaustion of solids when velocities warrant such arrangement.


Page 47 of 58

REVISION


August 2000

5.20.4.2 [E] Two phase flows, in general, are to have the hot stream (condensing) flow downward and the cold stream (boiling) upward. Exceptions are “falling film evaporation” and “reflux condensation,” which will have downward liquid and upward vapor flows. Mist flow may warrant flow in either direction. 5.20.4.3 [E] Gases may flow down or up consistent with the Log Mean Temperature Difference (LMTD) calculation. 5.20.5 Tube Selection (See Section 5.19.1 for additional information.) 5.20.5.1 Diameter

[E] The preferred tube size for use in heavy tube side fouling (dirty service) (0.002 hr ft2 °F/BTU or greater) is 1 inch OD. For light tube side fouling (clean service), 3/4 inch OD tubes are preferred. 5.20.5.2 Length

[E] Specify commonly used tube lengths, if practical. 5.20.5.3 [E] Recommended Tubewall Thickness Tube Material

Tube Wall Thickness BWG

inches

mm

Carbon steel, low-alloy steel, aluminum, and aluminum alloys

14*

0.083*

2.1*

Copper and copper alloys

16*

0.065*

1.7*

High-alloy steel and other nonferrous materials

16**

0.065**

1.7**

Titanium BWG = Birmingham Wire Gauge * = minimum ** = average

20**

0.035**

1.2**

5.20.5.4 [E] Enhanced Surface Tubes and Turbulence Promoters

The use of enhanced surface tubes or tube inserts requires an agreement between the User and the Designer. Enhancements may be quite effective in one process, but not effective in another. Designers may offer enhancements as an alternate. Enhanced surfaces are available in many forms such as low fin, sintered metal, oval or deformed tubes, or tubes with longitudinal fins. Inserts are used to promote turbulence. Spiral inserts may also reduce fouling buildup. Low fin tubes may be used under the following conditions: •

Page 48 of 58

Deposition of solid matter on the tube surface from the shell side stream is not a problem.


REVISION


August 2000

•

Tube side inlet temperatures are well above the shell side stream pour-point temperature.

•

Surface tension will not “hold” the condensate in the fins.

•

Tube external corrosion is not expected.

5.20.6 Bundle Design and Tube Layout 5.20.6.1 Tube Layout

5.20.6.1.1 [E] Removable bundle designs and square (or rotated square) tube pattern should be considered for dirty shell side service. (See Section 5.20.1.2.) Cleaning lanes of 1/4 inch minimum are to be maintained throughout the bundle. 5.20.6.1.2 [E] Triangular pattern can be used for clean shell side services, independent of whether the bundle is removable or not. An expanded pitch triangular design can be used in dirty services only when sufficient cleaning lanes are provided by the tube layout and when approved by User. 5.20.6.2 Baffles

5.20.6.2.1 [E] In horizontal exchangers, the horizontal cut (baffle cut perpendicular to shell nozzle axis) single segmental baffles are the most commonly used and generally preferred for single-phase shell side service. In horizontal exchangers, vertical cut (baffle cut parallel to shell nozzle axis) baffles may be used to minimize liquid pooling in two-phase service. Vertical exchangers should have baffles cut perpendicular to the inlet flow path. To avoid flow-induced tube vibration, the tube field may be modified to provide “no tubes in the baffle window.” Intermediate tube supports may be provided to further reduce vibration probability. 5.20.6.2.2 [E] Multi-segmental baffles (usually double, occasionally triple segmental) are used to reduce the shell side pressure drop. 5.20.6.2.3 [E] Special baffle designs (e.g., rod, disk and donut, longitudinal, spiral baffles, etc.) require User’s approval.


Page 49 of 58

REVISION


August 2000

Baffles utilizing rods are used to reduce shell side pressure drop and probability of flow-induced tube vibration. Longitudinal baffles (TEMA Type F shell) allow the maximum LMTD correction factor. “De-tuning” baffles are used in gas service shell side when required to prevent acoustic vibration. 5.20.6.2.4 [E] U-tube bundles: The baffle adjacent to the tube bends shall be located in the straight portion of the tubes not more than 2 inches from the tangent line of the bends. 5.20.6.2.5 [E] Tie rods and spacers: Peripheral tie rods and spacers for positioning baffles shall be located so that the outside of the spacers coincides with the outer periphery of the baffles. The ID of the spacer shall not be greater than the OD of the tie rod plus 1/8 inch. 5.20.7 Thermal Performance 5.20.7.1 [E] Condensing Heat Transfer

For accurate condenser design, the temperature difference should be calculated incrementally. The temperature and heat transfer of the condensing vapor mixtures will vary with the fraction condensed. Even with pure components, the condensing temperature will not be constant if there is significant pressure drop. The effect of delta P on delta T should be checked, especially if the overall delta T is small. For rough calculations, a straight line temperature may be used for the condensing zone. For final design, the results should always be checked using stepwise increments. When the vapor entering a condenser is superheated (temperature above the dew point) or when the condensate is subcooled (temperature below the bubble point), special considerations are required. If the temperature of the heat transfer surface (tube wall temperature) encountered is less than the dew point of the vapor, the vapor will begin to condense on contact and a wet wall condition will occur. In such cases, a condensing heat transfer coefficient is used (just as in the case of saturated vapor) and the Mean Temperature Difference (MTD) is based on the dew point temperature rather than the superheated vapor temperature. If the tube wall temperature is greater than the dew point of the vapor, a dry wall condition occurs. In such cases, the single phase gas heat transfer coefficient is used and the actual vapor

Page 50 of 58




temperature is used to calculate the MTD for the increment of the exchanger at dry wall conditions. Some subcooling of condensate usually occurs in total condensers. Condensers can sometimes be designed to accommodate subcooling by flooding a portion of the shell with condensate. However, the accuracy of predicting subcooling performance is low because the true liquid level and subcooling MTD are almost impossible to determine. If required, significant subcooling duty should be done in a separate liquid cooler. 5.20.7.2 Water Cooled Services (Cooling Water on Tube Side)

[E] When the cooling water is on the tube side, water velocity significantly affects the fouling rate, erosion, corrosion, and resulting maintenance of installed equipment. The Designer should therefore attempt to select an optimal velocity with considerations given to installed and maintenance cost. The following tabulated values for minimum and maximum velocities and maximum tube wall temperature provide accepted practical limitations. Site-specific water quality and treatment practices may justify deviations from these limits.


Page 51 of 58

REVISION


August 2000

Minimum Velocity Ft/sec Material

CTW

Closed loop

Brackish

Raw surface

Seawater

Ferrous

5*

3

---

---

---

Nonferrous

5*

3

4

5

5

* Lower minimum velocities may be necessary in some cases due to hydraulic limitations. Consideration should be given to the water quality and higher fouling factors for these cases.

Maximum Velocity Ft/sec Material

CTW

Closed loop

Brackish

Raw surface

Seawater

Ferrous

10

16

---

---

---

Admiralty

8

---

---

---

---

Al-Brass

8

---

6

---

---

CuproNickel

12

---

7

7

7

Aust. SS

---

16

---

---

---

Monel

16

16

14

14

14

Titanium

16

16

16

16

16

Maximum Contacted* Metal Surface Temperature, °F Material All Material

CTW

Closed loop

Brackish

Raw surface

Seawater

140

No Limit

140

120

140

* Beneath any fouling layer on the waterside when there is no fouling on the hot side.

Blanks in the above tables indicate that the listed material is generally not specified for the application. 5.20.8 Hydraulic Performance [E] The requirement for thermal design described in Section 5.20 also applies to the hydraulic design. [E] The User and the Designer shall agree on the pressure drop design factors. Pressure drop considerations include:

Page 52 of 58

•

Mill tolerance of tubes

•

Fouling build up on tube side and shell side

•

Piping between exchangers in series

•

Piping for thermosyphon reboilers


REVISION


August 2000

5.20.9 Vibration [E] The Designer shall include a check for flow-induced tube vibration. The method of vibration analysis shall be acceptable to the User. The vibration analysis shall consider, as a minimum, vortex shedding, fluid elastic instability, turbulence excitation (buffeting), and acoustic resonance. Generally, the natural frequency (or harmonics) of the tubes should not be within 20% of the predicted flow vibration frequency produced by any excitation mode, unless the vibration amplitude is within accepted practices.

6.

Materials 6.1

Material Specifications [V/E] Materials not specified by the User shall be selected based on known or anticipated process conditions and approved by the User. [V/E] The cost of heating the test fluid for shop or future field hydrostatic tests (so that the temperature of the pressure-resisting components is MDMT plus 30°F during the test) should be a consideration when selecting the materials of construction and the associated MDMT to be stamped on the vessel. 6.1.1

External Attachments [V/E] External attachments welded to pressure-resisting components shall be made of Code-approved materials. (External attachments such as nozzle reinforcing pads and stiffening rings are, by Code definition, pressureresisting components.) The material selected is often the same type as the pressure-resisting component to which it is attached. The selection of the type of external attachment material and the specific ASME SA material specification should be made with due consideration being given to the following: 1. Potential problems associated with welding dissimilar materials 2. Compatibility with the Code nameplate maximum and minimum design metal temperatures 3. Whether or not the attachment is essential to the structural integrity of the vessel (see Code Paragraph UCS-66 {AM-204}) 4. Differential thermal expansion characteristics and associated stresses 5. Corrosion resistance 6. Painting requirements 7. Suitability for the anticipated loadings

6.1.2

Internal Attachments [V/E] See Section 5.17 for commentary.


Page 53 of 58


6.2


Source of Materials [V/E] If the User restricts sources of fabrication materials, the prospective manufacturers must be informed at the time of bidding. Some reasons for restrictions may include but are not limited to:

6.3

•

Maintenance of a specific alloy composition

•

Compliance with government requirements

•

Compatibility with existing equipment

•

Compliance with User procurement policies

Corrosion/Erosion Allowance 6.3.1

Basis [V/E] The required design life shall be based on written agreement between User and Engineering Contractor. Allowances specified by the Designer shall be based on need and can best be determined by past experience in similar operating environments. If no past experience is available, such as with a new process, a materials engineer should examine the process and make judgment on the expected corrosion rate. Corrosion allowance should not be arbitrary; rather, it should be compatible with design life requirements.

6.3.2

Corrosion Loss [V/E] Additional metal thickness must be added to compensate for anticipated loss due to metal reacting with the environments to which it is subjected (including cleaning operations, shutdowns, etc.).

6.3.3

6.3.2.1

[V/E] Internal corrosion loss due to the process conditions affects all pressure-containing parts. Internal structural parts may experience corrosion loss on more than one surface. Bolted parts are frequently constructed of different materials and need to be assessed separately.

6.3.2.2

[V/E] External corrosion may result from exposure of bare metal to the atmosphere, especially in coastal areas and under insulation. Other equipment operating nearby may influence corrosion (e.g., cooling towers).

Erosion Loss [V/E] Additional metal thickness must be added in specific locations where metal loss is expected due to stream flow that is of high velocity or abrasive for any reason. Erosion loss usually occurs within a definable area, and compensation can be made as follows: •

Page 54 of 58

Weld overlay of the area with the intent that the overlay is sacrificial


REVISION


August 2000

•

Addition of a welded wear plate with the intent that the plate is sacrificial Note: Use caution when using this method in hydrogen service.

6.4

•

Internal refractory linings, if appropriate

•

Increase of inlet nozzle size

Gaskets [V/E] In no case shall the nominal thickness of sheet or laminate service gasketing be greater than 1/16 inch.

7.

Testing [V/E] All new pressure vessels shall be pressure tested prior to being placed in service. The following paragraphs provide guidance and references to design and execution considerations relative to hydrostatic and pneumatic pressure testing. 7.1

Hydrostatic Test 7.1.1

UG-99 Standard Hydrostatic Test [V/E] All provisions of this Code paragraph must be met when the hydrostatic test is employed. Paragraph UG-99(b) {AT-302}, including footnote 34 {Not Division 2 Applicable}, shall be considered to be the standard hydrostatic test. The test pressure or applicable Code paragraph number shall be specified on the Data Sheet.

7.1.2

Horizontal Vessels [V/E] A horizontal vessel designed to support a full weight load of water shall be tested while resting on its support saddles, without additional supports or cribbing.

7.1.3

Vertical Vessels 7.1.3.1

[V/E] Short vertical vessels may be shop-tested in the erected position, depending on their height and the shop capability.

7.1.3.2

[V/E] Tall vertical vessels may be shop tested in the horizontal position. These vessels must be adequately supported during the test to prevent damage. Note: Design shall be per Section 5.10.9(4) regardless of test orientation.

7.1.3.3

7.1.4

[V/E] Vertical vessels being tested in the erected position, whether shop or field, shall have consideration given to the additional pressure and weight due to the fluid head. (See Section 5.2.2.)

Test Temperature [V/E] See PIP VESV1002, Section 6.3.8.


Page 55 of 58


7.2


Pneumatic Test [V/E] Caution: Pneumatic testing presents hazards that must be addressed as part of the engineering design of the pressure vessel. (Reference Code Paragraph UG-100 {AT-400}, “Pneumatic Test” and Code Paragraph UW-50 {Not Division 2 Applicable}, “Nondestructive Examination Of Welds On Pneumatically Tested Vessels.”) [V/E] Due to the additional hazards of pneumatic testing, vessels shall be designed to minimize the possibility of failure during the test. The vessels shall be constructed of materials that ensure fracture toughness during the test. Additional nondestructive examination may be required of main seams, nozzle attachments, and some structural attachments. All such nondestructive examination shall be performed in accordance with Code methods and acceptance criteria. [V/E] Large diameter low-pressure designs, vessels with exceptionally large volume, service that would not allow residual water in the process, and designs that would force great overdesign of the vessel and foundation only to support a water full test may be considered for pneumatic testing.

7.3

Proof Test [V/E] (Code reference - Paragraph UG-101, “Proof Tests To Establish Maximum Allowable Working Pressure.”) Proof tests are highly individualized and are not included in this Practice.

8.

Vessel Rigging Analysis/Lifting Requirements 8.1

Impact Factor [V/E] Unless otherwise specified by the User, a minimum impact factor of 1.5 shall be applied to the lift weight for designing lifting devices. The basis for the lift weight must be established during the design phase of the vessel so that the design of lifting devices includes all components to be included in the lift (e.g., trays, ladders/platforms, insulation, additional piping with insulation, etc.).

8.2

Vertical Vessels [V/E] Vertical vessels having h/D ratios greater than 8 and weighing more than 25,000 pounds shall have bending stresses in the vessel shell/skirt checked from the loadings imposed during the lift from the horizontal to vertical position. Calculated general primary membrane tensile stress shall not exceed 80% of the material’s specified minimum yield strength at 100ºF. Calculated compressive stress shall not exceed 1.2 times the B factor obtained from the Code. Vessel lifts are recommended to be made when wind speeds are less than 33% of design wind velocity and the resulting wind load (at 33% design wind velocity) is included in the consideration of the lift.

Page 56 of 58


REVISION


August 2000

8.3

Local Stresses [V/E] Local stresses in the vessel shell/head/skirt/base rings from the lifting attachments (e.g., lugs, trunnions, etc.) shall be determined for the imposed loadings using local stress analysis procedures such as WRC Bulletin 107 or other accepted local stress analysis procedures (e.g., finite element analysis). For the rigging condition, the allowable stresses as shown in Section 5.14.9 shall be used.

8.4

Welds [V/E] Shear stresses for fillet welds on the lifting attachments to the vessel shell/head shall not exceed 0.55 times the Code-allowable stress {design stress intensity} at 100ºF for the material selected.


Page 57 of 58



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Page 58 of 58


APPENDIX A General Considerations for Pressure Relief Valve Application

REVISION


August 2000

General Considerations for Pressure Relief Valve Application A general comparison of operational characteristics is given for the different types of pressure relief valves in common industrial use. The influence on operating margin, from set pressure, is considered. Operational characteristics of direct spring-operated and pilot-operated pressure relief valves should be known by the User as well as the Designer. Direct spring and pilot-operated relief valves are available for use on applications that must meet Code requirements. The approximate reseating pressure for direct spring-operated valves is 93% of the set pressure in gas or vapor service and 85% of set pressure for National Board tested safety relief valves in liquid service. Many older liquid service safety valves, requiring 25% overpressure to be full open, have a reseating pressure as low as 70% of the set pressure. The reseating pressure for pilot-operated valves is typically specified in the same range as the direct spring valves. However, the reseating pressure of pilot-operated valves can be lowered to a value slightly above atmospheric by adding a manual blowdown connection which can be operated either locally or remotely. Pilot-operated valves are used in this fashion as remote, manual, emergency, blowdown valves. The versatile pilot-operated valve has some significant application limitations. Pilot-operated pressure relief valves are supplied with filters to protect against foreign matter and are generally recommended for relatively clean service. A summary detailing when, and when not, to use pilot-operated valves is given below. USE

DO NOT USE

•

Clean gas or vapor service

•

Corrosion of wetted part is possible

•

Clean liquid service

•

Polymerization process

•

Coking service

•

Abrasive or dirty service

•

Freezing of contents at ambient temperature is possible

The point where leakage begins to be a concern when using direct spring-operated valves depends on the disk seat design. Metal-to-metal contact seats will begin to leak at about 90% of set pressure. O-ring soft seat disk type direct spring-operated valves will not leak below 95% of set pressure. Pilot-operated valves will not leak below 98% of set pressure. The recommended maximum equipment operating pressure is slightly below, but many times considered to be equal to, the start-to-leak limit for the valve.

Page A-2


APPENDIX B [V] Welded Pressure Joint Requirements Form

REVISION


August 2000

Welded Pressure Joint Requirements DESIGN BASIS SHELL AND CONE THICKNESS BASED ON: JOINT EFFICIENCY E = _________

DISHED HEAD THICKNESS BASED ON: JOINT EFFICIENCY E = _________

WELDED PRESSURE JOINT REQUIREMENTS JOINT LOCATION PARAGRAPH UW-3 CATEGORY A

(SEE NOTE 5)

TYPE OF JOINT

NDE (SEE LETTERED NOTES)

TYPE NO. (1) OF TABLE UW-12

HEAD -TO-SHELL CATEGORY B

TYPE NO. (1) OF TABLE UW-12 OTHER BODY FLANGES

CATEGORY C NOZZLE FLANGES CATEGORY D

FIGURE 2-4 SEE GENERAL NOTE (6)

GENERAL NOTES: 1) Unless otherwise indicated, all references on this form are to ASME Code paragraphs, tables, and figures. All nondestructive examination shall be performed per Code methods. 2) Joints supplied shall be either detailed or identified by use of standard AWS welding symbols on the vessel Manufacturer's drawings. 3) Permanent weld joint backing strips are not permitted. 4) Separate internal nozzle reinforcing plates are not permitted. 5) The flat plate from which formed heads are to be made shall be either seamless or made equivalent to seamless in which all Category A welds are Type (1) and fully radiographed per UW−51 before forming. After forming, the spin hole, if it remains in the final construction, shall be closed with a metal plug which is butt-welded in place with the weld meeting the Category A weld joint requirements shown in the table. 6) Category D welds shall be per Figure UW-16.1 using full penetration welds through vessel wall and through inside edge of external reinforcing plates, when used. Nozzle necks designated to extend beyond the inside surface of the vessel wall shall have a fillet weld at the inside corner.

WELDED PRESSURE JOINT REQUIREMENTS PRESSURE VESSELS EXCLUDING HEAT EXCHANGERS

ITEM NUMBER: ____________________________________

VESSEL ASSEMBLY DWG.: __________________________

DRAWN BY

CHECKED BY

DATE

DRAWING NUMBER

PAGE 1 OF 2

Page B[V]-2




Nondestructive Examination Notes A. Full radiography shall be per Paragraph UW-51. For welded pipe components, this applies only to Categories B and C butt joints. For exclusions, see Paragraph UW-11(a)(4). B. Spot radiography shall be per Paragraph UW-52. For welded pipe components, this applies only to Categories B and C butt joints. For exclusions, see Paragraph UW-11(b). C. Spot radiography shall be per Paragraph UW-52. Rules of UW-11(a)(5)(b) must be satisfied. The Manufacturer is cautioned to select the appropriate increments of weld for establishing the spot radiography requirements for the vessel. [See UW-52(b)(4).] General Note: Notes D through H are examples of user options that are sometimes selected for critical services. Other options may be provided as appropriate. D. When joint thickness exceeds 2 inches, examine (using MT or PT) the root pass after backchipping to sound metal and all accessible surfaces of completed welds of Categories A, B, C, and D butt type joints. E. When design is based on a joint efficiency of 1.00, examine (using MT or PT) Categories C and D non-butt type joints after back-chipping or gouging root pass to sound metal and accessible surfaces of completed weld. F. When nozzles are attached with a full penetration weld through the nozzle wall, the cut edge of the opening in vessel walls thicker than 1/2 inch shall be examined using MT or PT. The examination shall be made before nozzle attachment and a re-examination shall be made after attachment, when accessible. G. Examination (using MT or PT) of completed welds shall be made after PWHT for the following: 1. 2. 3. 4.

Vessels or vessel parts for which impact testing is required Welds joining non-impact tested low-alloy steels thicker than 1-1/4 inches Welds joining carbon steels thicker than 2 inches When required by Code

H. Butt welds exempt from radiography by Paragraph UW-11(a)(4) shall have accessible surfaces of completed welds MT or PT examined. (Only applies to designs employing impacttested steels when Category A joints are based on a joint efficiency of 1.00.)

Item Number: Vessel Assembly Dwg.: Reference paragraphs are contained in Division 1 of the ASME Code. MT = Magnetic Particle Examination PT = Liquid Penetrant Examination PAGE 2 OF 2


Page B[V]-3

REVISION


August 2000

EXAMPLE Use Of Welded Pressure Joint Requirements Form To illustrate the use and usefulness of the Welded Pressure Joint Requirements form for communicating welded pressure joint requirements to manufacturers for quotation and purchase specification purposes, the following completed form shows the requirements described in Sections 5.6.2.1, 5.6.2.2, 5.6.2.3, and 5.6.2.4. With reference to the lettered Nondestructive Examination Notes (page 2 of the form), note that other options are available for convenient use or may be provided.

DESIGN BASIS SHELL AND CONE THICKNESS BASED ON: JOINT EFFICIENCY. E = __0.85_______

DISHED HEAD THICKNESS BASED ON: JOINT EFFICIENCY. E = __0.85_______


(SEE NOTE 5)

TYPE OF JOINT


TYPE NO. (1) OF TABLE UW-12 B

HEAD -TO-SHELL CATEGORY B


B

OTHER B BODY FLANGES CATEGORY C

-NOZZLE FLANGES

FIG. 2-4 (6) B

CATEGORY D

SEE GENERAL NOTE (6) --

GENERAL NOTES: 1) UNLESS OTHERWISE INDICATED. ALL REFERENCES ON THIS FORM ARE TO ASME CODE PARAGRAPHS. TABLES AND FIGURES. ALL NONDESTRUCTIVE EXAMINATION SHALL BE PERFORMED PER CODE METHODS. 2) JOINTS SUPPLIED SHALL BE EITHER DETAILED OR IDENTIFIED BY USE OF STANDARD AWS WELDING SYMBOLS ON THE VESSEL MANUFACTURER'S DRAWINGS. 3) PERMANENT WELD JOINT BACKING STRIPS ARE NOT PERMITTED. 4) SEPARATE INTERNAL NOZZLE REINFORCING PLATES ARE NOT PERMITTED. 5) THE FLAT PLATE FROM WHICH FORMED HEADS ARE TO BE MADE SHALL BE EITHER SEAMLESS OR MADE EQUIVALENT TO SEAMLESS IN WHICH ALL CATEGORY A WELDS ARE TYPE (1) AND FULLY RADIOGRAPHED PER UW−51 BEFORE FORMING. AFTER FORMING, THE SPIN HOLE, IF IT REMAINS IN THE FINAL CONSTRUCTION, SHALL BE REPAIRED WITH A METAL PLUG THAT IS BUTT-WELDED IN PLACE WITH THE WELD MEETING THE CATEGORY. A WELD JOINT REQUIREMENTS SHOWN IN THE TABLE. 6) CATEGORY D WELDS SHALL BE PER FIG. UW-16.1 USING FULL PENETRATION WELDS THROUGH VESSEL WALL AND THROUGH INSIDE EDGE OF EXTERNAL REINFORCING PLATES WHEN USED. NOZZLE NECKS DESIGNATED TO EXTEND BEYOND THE INSIDE SURFACE OF THE VESSEL WALL SHALL HAVE A FILLET WELD AT THE INSIDE CORNER.

WELDED PRESSURE JOINT REQUIREMENTS PRESSURE VESSELS EXCLUDING HEAT EXCHANGERS

ITEM NUMBER: ________PIP 123456___________________ VESSEL ASSEMBLY DWG.: ___PIP 123456______________

DRAWN BY

CHECKED BY

DATE

DRAWING NUMBER

PAGE 1 OF 2

Page B[V]-4


APPENDIX B [E] Welded Pressure Joint Requirements Form

REVISION


August 2000

Welded Pressure Joint Requirements DESIGN BASIS SHELL THICKNESS BASED ON: JOINT EFFICIENCY E = _________(SHELL)

DISHED HEAD THICKNESS BASED ON: JOINT EFFICIENCY E = _________(SHELL)

JOINT EFFICIENCY E = _________(CHANNEL)

JOINT EFFICIENCY E = _________(CHANNEL)


SHELL

(SEE NOTE 5)

TYPE OF JOINT



HEAD-TO-SHELL CATEGORY B

SIDE

TYPE NO. (1) OF TABLE UW-12 OTHER

CATEGORY C

TUBESHEETS

FIGURE UW-13.2

NOZZLE FLANGES

FIGURE 2-4

CATEGORY D CATEGORY A

TUBE

SEE GENERAL NOTE (6) (SEE NOTE 5)


HEAD-TO-CHANNEL CATEGORY B

SIDE

TYPE NO. (1) OF TABLE UW-12 OTHER

CATEGORY C BODY FLANGES

FIGURE 2-4

NOZZLE FLANGES

FIGURE 2-4

CATEGORY D

SEE GENERAL NOTE (6)

GENERAL NOTES: 1) Unless otherwise indicated, all references on this form are to ASME Code paragraphs, tables, and figures. All nondestructive examination shall be performed per Code methods. 2) Joints supplied shall be either detailed or identified by use of standard AWS welding symbols on the vessel Manufacturer's drawings. 3) Permanent weld joint backing strips are not permitted. 4) Separate internal nozzle reinforcing plates are not permitted. 5) The flat plate from which formed heads are to be made shall be either seamless or made equivalent to seamless in which all Category A welds are Type (1) and fully radiographed per UW−51 before forming. After forming, the spin hole, if it remains in the final construction, shall be closed with a metal plug which is butt-welded in place with the weld meeting the Category A weld joint requirements shown in the table. 6) Category D welds shall be per Figure UW-16.1 using full penetration welds through vessel wall and through inside edge of external reinforcing plates, when used. Nozzle necks designated to extend beyond the inside surface of the vessel wall shall have a fillet weld at the inside corner.

WELDED PRESSURE JOINT REQUIREMENTS SHELL AND TUBE HEAT EXCHANGERS

ITEM NUMBER: ____________________________________ VESSEL ASSEMBLY DWG.: __________________________

DRAWN BY

CHECKED BY

DATE

DRAWING NUMBER

PAGE 1 OF 2

Page B[E]-2




Nondestructive Examination Notes A. Full radiography shall be per Paragraph UW-51. For welded pipe components, this applies only to Categories B and C butt joints. For exclusions, see Paragraph UW-11(a)(4). B. Spot radiography shall be per Paragraph UW-52. For welded pipe components, this applies only to Categories B and C butt joints. For exclusions, see Paragraph UW-11(b). C. Spot radiography shall be per Paragraph UW-52. Rules of UW-11(a)(5)(b) must be satisfied. The Manufacturer is cautioned to select the appropriate increments of weld for establishing the spot radiography requirements for the vessel. [See UW-52(b)(4).] General Note: Notes D through L are examples of user options that are sometimes selected for critical services. Other options may be provided as appropriate. D. When joint thickness exceeds 2 inches, examine (using MT or PT) the root pass after backchipping to sound metal and all accessible surfaces of completed welds of Categories A, B, C, and D butt type joints. E. When design is based on a joint efficiency of 1.00, examine (using MT or PT) Categories C and D non-butt type joints after back-chipping or gouging root pass to sound metal and accessible surfaces of completed weld. F. When nozzles are attached with a full penetration weld through the nozzle wall, the cut edge of the opening in vessel walls thicker than 1/2-inch shall be examined (using MT or PT). The examination shall be made before nozzle attachment and a re-examination shall be made after attachment, when accessible. G. Examination (using MT or PT) of completed welds shall be made after PWHT for the following: 1. 2. 3. 4.

Vessels or vessel parts for which impact testing is required Welds joining non-impact tested low-alloy steels thicker than 1-1/4 inches Welds joining carbon steels thicker than 2 inches When required by Code

H. Butt welds exempt from radiography by Paragraph UW-11(a)(4) shall have accessible surfaces of completed welds MT or PT examined. (Only applies to designs employing impacttested steels when Category A joints are based on a joint efficiency of 1.00.) J.

Non-butt type joints attaching tubesheets shall be MT or PT examined (usually on exchangers larger that NPS 24, or any size having design pressure on the tubesheet attachment side exceeding 300 psi) as follows: 1. Before welding, examine the cut surfaces per Paragraph UG-93(d)(4). 2. For joints per Figure UW-13.2(f), (j), or (k), examine the deposited groove weld surfaces after machining weld flush with tubesheet. 3. For double-welded joints, after back chipping the reverse side of weld metal first deposited and before additional welding, examine the back-chipped surfaces. 4. Examine all accessible surfaces of completed weld. 5. After welding, re-examine all cut edges examined per Item 1 above that remain exposed.

K. Tubesheet stock material exceeding 3 inches in thickness shall be ultrasonically examined after cutting to final size per ASME SA-578 Acceptance Level 1, Supplementary Requirement S1 (applies to nonclad material).


Page B[E]-3



L. Clad tubesheet material shall be ultrasonically examined after cutting to final size per ASME SA-578 Acceptance Level 1, Supplementary Requirement S7 (applies to clad material of any thickness).

Item Number: Vessel Assembly Dwg.: Reference paragraphs are contained in Division 1 of the ASME Code. MT = Magnetic Particle Examination PT = Liquid Penetrant Examination PAGE 2 OF 2

Page B[E]-4


APPENDIX C Equivalent Pressure Formulas for Bending Moment and Axial Tensile Load



Equivalent Pressure Formulas for Bending Moment and Axial Tensile Load When sustained bending moments or axial thrust loadings are applied to the flanged joint during operation in sufficient magnitude to warrant consideration in the flange design, the design pressure, P, used in the calculation of total hydrostatic end load, H, in the flange design calculations should be replaced by the following design pressure: PFLG = P + PEQ The equivalent pressure PEQ is determined as follows: PEQ = Where: M= F= G=

16M

πG3

+

4F

πG2

Sustained bending moment applied across full section at flange during the design condition, in-lb Sustained axial tensile force applied at flange, lb Diameter at location of gasket load reaction, in (See Appendix 2 {Appendix 3} of the Code for full definition.) Note: Experience has shown that axial tensile forces resulting from a properly designed piping system have no significant effect on the flange design and hence are typically not included in the PEQ determination.

Therefore, the hydrostatic end load, H, used in the flange calculations is determined as follows: 2

H = 0.785 G PFLG

Dynamic Bending Moment PEQ =

8M

πG3

Where: M=

Bending moment, as defined above, but including dynamic bending moment (e.g., seismic moment) applied across full section at flange during the design condition, in-lb

Other Terms = Same as above

Page C-2


APPENDIX D Minimum Clearance for Nozzle Adjacent to Integral Tubesheet

VECV1001 Process industry practice

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