Standard ASME Vessel Design Criteria

EDITORIAL REVISION May 2009

Process Industry Practices Vessels

PIP VECV1001 Vessel 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.

Process Industry Practices (PIP), Construction Industry Institute, The University of Texas at Austin, 3925 West Braker Lane (R4500), Austin, Texas 78759. PIP member companies and subscribers may copy this Practice for their internal use. Changes, overlays, addenda, or modifications of any kind are not permitted within any PIP Practice without the express written authorization of PIP.

PRINTING HISTORY September 1997 Issued February 1999 Complete Revision August 2000 Revision February 2007 Complete Revision May 2009 Editorial Revision

Not printed with State funds


Process Industry Practices Page 1 of 27

Process Industry Practices Vessels

PIP VECV1001 Vessel Design Criteria

ASME Code Section VIII, Divisions 1 and 2

Table of Contents

1. General Requirements ............... 3 1.1 Purpose .......................................... 3 1.2 Scope ............................................. 3 1.3 ASME Code Requirements ............ 3 1.4 National Board Registration ........... 4 1.5 Jurisdictional Compliance............... 4 1.6 Units of Measurement .................... 4

2. References .................................. 4 2.1 Process Industry Practices ............. 4 2.2 Industry Codes and Standards ....... 5 2.3 Government Regulations ................ 6 2.4 Other References ........................... 6

3. Definitions ................................... 6

4. Responsibilities .......................... 7 4.1 Documentation to be Provided to

the Manufacturer ............................ 7 4.2 Language ....................................... 7 4.3 Designers Responsibility ............... 7

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

Temperature ................................... 8 5.2 Minimum Design Metal

Temperature (MDMT) and Coincident Pressure ....................... 9

5.3 External Pressure Design .............. 9 5.4 Load Combinations ...................... 10 5.5 Wind Load .................................... 12 5.6 Seismic Loads .............................. 12 5.7 Cyclic Service ............................... 12 5.8 Formed Heads .............................. 13 5.9 Nozzles ......................................... 13 5.10 Manways ...................................... 14 5.11 Flanges ......................................... 15 5.12 Vessel Supports ........................... 19 5.13 Anchor Bolts ................................. 21 5.14 Internals ........................................ 22

6. Materials .................................... 22 6.1 General ......................................... 22 6.2 Source of Materials ...................... 23 6.3 Dual (Multiple) Marked Materials . 23 6.4 Corrosion/Erosion Allowance ....... 23 6.5 External Protection of Austenitic

Stainless Steel Equipment from Stress Corrosion Cracking ........... 24

6.6 Support Materials ......................... 24 6.7 External Attachments ................... 25

7. Examination, Inspection and Pressure Testing ...................... 26 7.1 Welded Pressure Joint

Requirements ............................... 26 7.2 Testing .......................................... 26


Page 2 of 27 Process Industry Practices

Appendices Appendix A General Considerations for Pressure Relief Valve Application Appendix B Welded Pressure Joint Requirements Appendix C Equivalent Pressure Formulas for Bending Moment and Axial Tensile Load

PIP VECV1001 EDITORIAL REVISION Vessel Design Criteria May 2009 ASME Code Section VIII, Divisions 1 and 2


1. General Requirements

Note to Readers: This Practice contains design criteria for pressure vessels built to Division 1 or Division 2 of the ASME Boiler and Pressure Vessel Code, henceforth referred to as the Code. Section VIII Division 2 requirements are shown in braces { }.

1.1 Purpose 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.

1.2 Scope 1.2.1 This Practice shall be used in conjunction with PIP VEDV1003 and/or

PIP VEDV1003_EEDS, PIP VEFV1100 (Applicable Details), and PIP VESV1002 in order to comprise a complete vessel purchase specification.

1.2.2 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 shall 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 Standardized pre-designed (off-the-shelf) vessels are not within the scope of this Practice, but are covered in PIP VESSM001.

1.2.4 Vessels with layered construction are outside the scope of this Practice.

1.3 ASME Code Requirements 1.3.1 Pressure vessels within the scope of this Practice shall satisfy all applicable

requirements, including Code symbol stamping.

1.3.2 Applicable Code Scope Exemptions

The Code Scope exemptions that represent across-the-board acceptance are those covered under Code Paragraphs U-1(c)(2)(h) {1.2.4.2 h} and U-1(c)(2)(i) {1.2.4.2 i)}. These exemptions are not intended to prohibit the use of other Scope exemptions in Code Paragraph U-1(c)(2) {1.2.4.2}; however, such use shall be by agreement with the User.

1.3.3 Waste Heat Recovery Vessels

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.

EDITORIAL REVISION PIP VECV1001 May 2009 Vessel Design Criteria ASME Code Section VIII, Divisions 1 and 2


1.4 National Board Registration National Board registration of vessels stamped with the Code U {U2} symbol is required.

1.5 Jurisdictional Compliance 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, or applicable national standards at the point of installation. (See Section 2.3.)

1.6 Units of Measurement US customary (English) units shall be regarded as standard for domestic US locations; metric (SI) units may be included for reference only and shall not be interpreted as a precise conversion.

2. References

Applicable parts of the following Practices, industry codes and standards, and references shall be considered an integral part of this Practice. The edition in effect on the date of contract award shall be used, except as otherwise noted. Short titles are used herein where 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.

PIP VEDV1003 - Vessel Drawing/Data Sheet and Instructions PIP VEDV1003_EEDS - Pressure Vessels Electronic Entry Data Sheet PIP VEFV1100 - Vessel Standard Details (29 Details and Index)

PIP VEFV1105 - Vessel; Horizontal, Saddles Supported on Concrete

PIP VEFV1106 - Vessel; Horizontal, Saddles Supported on Steel

PIP VEFV1116 - Vessel; Manway Hinges PIP VEFV1117 - Vessel; Manway Vertical Davit

PIP VEFV1118 - Vessel; Manway Horizontal Davit PIP VEFV1124 - Vessel; Vortex Breakers PIP VEFV1125 - Vessel; Internal Ladders PIP VEFV1129 - Vessel; Studded Joints

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

PIP VESV1002 - Vessel Fabrication Specification ASME Code Section VIII, Divisions 1 and 2



2.2 Industry Codes and Standards For the following reference documents, if Table U-3 {1.1} of the Code lists an edition or addenda different than the latest edition issued, the edition listed in Table U-3 {1.1} shall be used. For documents not listed in Table U-3 {1.1}, the latest edition or addenda issued at the date of contract award shall be used.

American Petroleum Institute (API) API 650 - Welded Steel Tanks for Oil Storage API 605 - Large-Diameter Carbon Steel Flanges (Nominal Pipe Sizes 26

through 60, Classes 75, 150, 300, 400, 600 and 900) API 579 - Damage Mechanisms Affecting Fixed Equipment in the Refining

Industry American Society of Civil Engineers (ASCE)

ASCE 7 - Minimum Design Loads for Buildings and Other Structures 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 B16.9 - Factory-Made Wrought Buttwelding Fittings ASME B16.11 - Forged Fittings, Socket-Welding and Threaded ASME B16.47 - Large Diameter Steel Flanges, NPS 26 through NPS 60 ASME PCC-1 - Guidelines for Pressure Boundary Bolted Flange Joint

Assembly ASME PCC-2 - Repair of Pressure Equipment and Piping

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

MSS SP-44 - Steel Pipeline Flanges Welding Research Council (WRC)

WRC Bulletin 488 - Damage Mechanisms Affecting Fixed Equipment in the Pulp and Paper Industry

WRC Bulletin 489 - Damage Mechanisms Affecting Fixed Equipment in the Refining Industry

WRC Bulletin 490 - Damage Mechanisms Affecting Fixed Equipment in the Fossil Electric Power Industry



2.3 Government Regulations

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

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

2.4 Other References 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 Wind-Induced Forces, Wind Loads and Anchor Bolt Design for Petrochemical Facilities. (ISBN-0-7844-0262-0)

3. Definitions

Code: ASME Boiler and Pressure Vessel Code Section VIII, Division 1{or 2} and reference section such a Section II and Section IX and any Code Cases accepted by the User. References to Division 2 are identified in braces { }.

construction: An all-inclusive term comprising materials, design, fabrication, examination, inspection, testing, certification (Code stamp and Manufacturers Data Report), {Manufacturers Design Report} and pressure relief

cyclic service: Services that require fatigue analysis per 5.5.2 of ASME Boiler and Pressure Vessel Code Section VIII Division 2. This applies to Division 1 and Division 2 vessels.

Designer: The party responsible for defining and specifying the mechanical design requirements (e.g., Vessel Drawing/Data Sheet {Users 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.

Manufacturer (Supplier): The party entering into a contract with the Purchaser to construct a vessel in accordance with the purchase order. In accordance with the Code definition, the Manufacturer is the party that possesses a valid Certificate of Authorization to manufacturer pressure vessels with the ASME Mark. The Manufacturer may or may not be the Supplier.

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.

Overlay Specification: Technical requirements that supplement or override the provisions of this document, such as a User specification or a project specification.



Owner: The party who owns the facility wherein the vessel will be used. The owner is normally also the User but in certain cases is not.

Purchaser: The party actually placing the order for the vessel or vessel components. This may be the User or the Users Designated Agent.

User: The party responsible for establishing construction criteria consistent with the Code philosophy and service hazards. User refers to the operator of the equipment.

Users Inspector: The person or company authorized by the owner and/or user to inspect pressure vessels to the requirements of this practice and the Users requirements.

4. Responsibilities

4.1 Documentation to be Provided to the Manufacturer The following information shall be provided to the Manufacturer with the purchasing inquiry:

4.1.1 Design requirements to be provided to the Manufacturer shall be per PIP VEDV1003, with additional drawings or details as necessary. PIP VEDV1003_EEDS, Pressure Vessels Electronic Entry Data Sheet, may also be used.

4.1.2 Welded pressure joint requirements, including:

a. Type of Category A, B, C, and D joints (see Appendix B)

b. Type and degree of nondestructive examination to be applied to the joints (see Appendix B)

4.1.3 Quality Overview Plan, as shown in PIP VESV1002, Appendix A.

4.1.4 Documentation Schedule and Manufacturers Data Package, as shown in PIP VESV1002, Appendix B.

4.1.5 {Users Design Specification per 2.2.2}

4.1.6 List of permanent attachments, if any, to comply with OSHA 29 CFR 1910.146, or applicable national standard at the point of installation. (See Section 5.10.8.)

4.2 Language The language of all documents shall be either English or include the English translation.

4.3 Designers Responsibility The Designer is responsible for the design of the vessels in conformance with this Practice and the documents referenced herein. Review of Designers documentation (e.g., design calculations or drawings) by the Purchaser or User does not alter this responsibility.



5. Design

5.1 Design Pressure and Temperature 5.1.1 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:

a. Initial startup

b. Normal operations

c. Temporary operations

d. Emergency shutdown

e. Emergency operations

f. Normal shutdown

g. Startup following a turnaround or an emergency shutdown

h. Cleaning, steam out, and decontamination

i. Upset conditions

j. Safety, health and environmental restrictions on material release during a relief event causing increased pressure in the vessel.

5.1.2 The margin above the maximum anticipated operating pressure selected to establish the design pressure and coincident maximum metal temperature shall 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) that will provide containment without actuation of the pressure relief device may be a consideration.

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.

Refer to the Overlay Specification for any margins to be applied to the maximum operating pressure(s) and coincident temperature(s).



5.1.3 In lieu of the requirements of 5.1.2 above, use of Code Case 2211, entitled Pressure Vessels with Overpressure Protection by System Design, Section VIII, Divisions 1 and 2, may be an option. Note that prior jurisdictional acceptance may be required and that this Code Case Number shall be shown on the Manufacturers Data Report.

5.1.4 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 140F (60C), or Steam Service, Section VIII, Divisions 1 and 2, shall be considered.

5.1.5 For multi-chamber vessels, common component(s) of multi-chamber or compartmented vessels shall be designed for the most severe combinations of pressure, temperature, and other loadings which may occur during operation (see above bullet list) and test conditions. Design solely on the basis of simultaneous loading of internal pressure in adjacent compartments is not acceptable.

5.2 Minimum Design Metal Temperature (MDMT) and Coincident Pressure 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 5.1.1 and of the Code rules in Paragraph UG-20(b) {4.1.5.2 e)}. 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) {3.11.2.5}. When atmospheric temperatures govern the metal temperatures during startup or normal operations, the lowest 1-day mean atmospheric temperature at the installation site shall be considered. Figure 4-2 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.

5.3 External Pressure Design In a manner similar to that described in Section 5.1.1, 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.

5.3.1. Non-jacketed vessels

Vessels subjected to operating pressure less than atmospheric shall be designed and Code stamped for full vacuum. Vessels that are subjected to steam-out conditions shall be designed for full vacuum. 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.



5.3.2 Jacketed or compartmented vessels

Jacketed or compartmented vessels that are designed for vacuum in the compartment under consideration shall have the common components designed for an external pressure equal to the sum of internal design pressure of the adjacent compartment plus the vacuum design pressure of the compartment under consideration.

5.4 Load Combinations 5.4.1 Design Loads and Load Combinations

Design loads are defined and classified as follows:

5.4.1.1 Dead Load (L1)

Dead Load is the installed weight of the vessel, including internals, catalyst or packing, refractory lining, platforms, insulation fireproofing, piping, and other permanent attachments.

5.4.1.2 Operating Live Load (L2)

Operating Live Load is the weight of the liquid at the maximum operating level, including that on trays.

5.4.1.3 Pressure Load (L3)

Pressure Load is the MAWP (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 {2.2.2.1 d)1)}). For vessels with more than one independent chamber, see Code Paragraph UG-19(a) {4.1.8}.

5.4.1.4 Thermal Load (L4)

Thermal Loads are the loads caused by the restraint of thermal expansion/interaction of the vessel and/or its supports.

5.4.1.5 Test Load (L5)

Test Load is the weight of the test medium, usually water. Unless otherwise specified, design basis shall consider that the vessel will be field tested in its normal operating position. (See Section 5.2.6 of PIP VESV1002.)

5.4.1.6 Wind Load (L6)

Wind Load shall be determined in accordance with Section 5.5.



5.4.1.7 Seismic Load (L7)

Seismic Load shall be determined in accordance with Section 5.6.

5.4.1.8 Piping and Superimposed Equipment Loads (L8)

Loads caused by piping other than the Dead Load in Section 5.4.1.1 and those caused by superimposed equipment shall be considered as applicable

5.4.2 Load Combinations

Vessels and their supports shall be designed to meet the most severe of the following load combinations, with the controlling load combination indicated in design calculations, unless other combinations are required by the applicable building code at the point of installation: (See Section 5.11.2 of PIP VESV1002 for allowable stresses with wind or seismic loads.)

5.4.2.1 L1+L6 Erected Condition with full Wind Load

5.4.2.2 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)

5.4.2.3 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)

5.4.2.4 L1+(F)L3+L5+(0.25)L6 When specified by User, 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). 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 {allowable stress S} for the test temperature of the vessel to the stress value {allowable stress S} for the design temperature, established the minimum required test pressure at every point in the vessel. Test factor F shall be per appropriate Code for the test medium used. When applicable, Code Case 2055 on pneumatic testing of pressure vessels can be used. The general primary membrane tensile stress in the corroded condition (or when no corrosion allowance is specified) under this load combination shall not exceed 90% of the Specified Minimum Yield Strength at 100F (38C) {that specified in 4.1.6.2 a)}for hydrostatic testing or 80% of the Specified Minimum Yield Strength at 100F (38C) {4.1.6.2 b)} for pneumatic testing. (See examples of design considerations described in 5.2.6 of PIP VESV1002 and testing requirements in Section 7.2.)

5.4.2.5 Lift Condition: See Section 5.8.



5.5 Wind Load 5.5.1 ASCE 7

Unless otherwise specified at the point of installation, wind loads shall conform to ASCE 7.

Note: Local codes or regulations may require compliance with other rules for wind load design.

5.5.2 Force on Vessel Attachments 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 2.4 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.

5.5.3 Wind Induced Vibration 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). See reference document Dynamic Response of Tall Flexible Structures to Wind Loading.

5.6 Seismic Loads Unless otherwise dictated at the point of installation, seismic loads shall conform to ASCE 7.

Note: Local codes and regulations may require compliance with other rules for seismic design.

5.7 Cyclic Service The required service for all vessels shall include consideration by the Designer of cyclic service. Code Paragraph UG-22(e) {4.1.1.4} 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 frequently fall into this category. The following guidelines {5.5.2.3} 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.

5.7.1 Number of Cycles {See 5.5.2.3} Code vessels shall 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:

5.7.1.1 The expected number of full range (design) pressure cycles, including startups and shutdowns

5.7.1.2 The expected number of operating pressure cycles in which the range of pressure variation exceeds 20% of the design pressure

5.7.1.3 The expected number of thermal cycles where the metal temperature differential between any two adjacent points exceeds 50F (28C) {For a definition of adjacent points, see Code Section VIII, Division 2, Paragraph 5.5.2.3 d)1)and 2).}

5.7.2 Fatigue Loading Data The applicable fatigue loading conditions shall be stated on PIP VEDV1003.

5.8 Formed Heads Formed heads in vessels over 2 inches (50 mm) thick typically have hemispherical or 2:1 ellipsoidal heads.

5.9 Nozzles 5.9.1 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.)

5.9.2 For vessels supported by a skirt, the flange of any nozzle in the bottom head shall be located outside the skirt.

Nozzles (including attached piping) within or passing through vessel support skirts shall be adequately supported for the operating conditions and for protection during shipping and handling. Differential thermal expansion between the skirt and nozzle in both the vertical and horizontal directions shall be considered.

5.9.3 In establishing nozzle and manway projections, clearance shall 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 shall be considered when nozzles penetrate insulation or platforms.

Minimum projection from the outside of the vessel wall to the nozzle face shall be:

a. 8 inches (200 mm) for nozzles up to and including NPS 8 (DN 200)

b. 10 inches (250 mm) for nozzles larger than NPS 8 (DN 200)



Round up the dimension from the face of the nozzle to the vessel centerline or reference line to the next larger 1/2-inch (12.7 mm) increment.

5.10 Manways 5.10.1 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 {4.5.16}, Inspection Openings.

5.10.2 Service conditions, size, and configuration of the vessel may justify manways other than (or in addition to) those mandated by the Code.

5.10.2.1 Vessels with mixers/agitators shall be provided with at least one manway that does not require removal of the mixer/agitator.

5.10.2.2 Manways are required on towers with feed and distribution trays. A manway shall also be located about 3 ft (1 m) above the bottom head seam and one at the top, 18 inches (450 mm) above the top tray. Tray towers shall have manways spaced as follows:

a. Short towers (< 60 trays) - Manways spaced 20 trays apart

b. Medium towers (60-120 trays) - Manways spaced 30 trays apart

c. Tall towers (> 120 trays) - Manways spaced 40 trays apart

5.10.2.3 Packed towers shall have manways at all locations where there is feed distribution or redistribution of liquid.

5.10.3 Manways shall be usable from a ladder, platform, or grade.

5.10.4 Vessels 3 feet (1 m) ID and smaller that are subject to internal corrosion, erosion, or mechanical abrasion shall be equipped with inspection openings as described in Code Paragraph UG-46 {4.5.16}. Vessels in this size category may justify the use of body flanges.

5.10.5 Vessels larger than 3 feet (1 m) ID that are subject to internal corrosion, erosion, or mechanical abrasion shall be equipped with one or more flanged and blinded manways.

5.10.6 Manways less than NPS 24 (DN 600) shall not be allowed without written approval from Owner. In no case shall manways be less than NPS 20 (DN 500). Larger diameter manways shall 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.

5.10.7 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. See PIP VEFV1125. Internal ladders shall not be used in corrosive or erosive service.

5.10.8 Consideration should be given by the User for safe access and egress through a manway, including the suitability of a retrieval system at manways for personnel rescue as described in OSHA 29 CFR 1910.146, or equivalent



national standard. Retrieval system as defined by OSHA 29 CFR 1910.146 means the equipment (including a retrieval line, chest or full-body harness, wristlets, if appropriate, and a lifting device or anchor) used for non-entry rescue of persons from permit spaces. Permanent attachments, if any, shall be specified by the User.

5.10.9 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 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. Hinged manways require Owner approval due to potential pinch point.

5.10.10 Consideration may be given for use of suitable process connections as manways and handholes. (Consider both size and location.)

5.11 Flanges 5.11.1 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. Weld neck flanges shall be used except as permitted elsewhere in this specification. Flanges for all flanged vessel nozzles equal to or smaller than NPS 24 (DN 600) 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 (DN 600) and for body flanges of any size, the options available (as follows in Sections 5.11.1.1 through 5.11.1.4) to the User shall be carefully selected as a function of the need.

5.11.1.1 ASME B16.47, Series A (NPS 26 through NPS 60)

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.

5.11.1.2 ASME B16.47, Series B (NPS 26 through NPS 60)

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 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.



5.11.1.3 Custom-Designed Flanges

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 leak-tightness 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 {4.16}. See Code paragraph 2-14 {Table 4.16.10} for Rigidity Index requirements.

5.11.1.4 Custom-Designed Lap Joint Flanges

See paragraph 5.10.9 of PIP VESV1002 for requirements specific to custom designed lap joint flanges.

5.11.2 Lap Joint Flanges NPS 24 (DN 600) and Smaller

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.

For certain of the smaller sizes in each pressure class, the length-through-hub (dimension Y) of the slip-on flange and the lapped flange are the same. (This is true through NPS 12 (DN 300) for Class 150, through NPS 8 (DN 200) 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.

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.

5.11.3 Slip-on Flanges

Slip-on flanges are limited to use under the following conditions:

5.11.3.1 ASME B16.5 standard forged flanges for design pressures and coincident temperatures not exceeding the pressure-temperature ratings for Class 150 flanges as specified in ASME B16.5, except that the maximum design temperature shall not exceed 450F (230C)

5.11.3.2 Custom-designed flanges per Code Figure 2-4(8), (8a), (9), (9a), (10), or (10a){Figure 4.16.5 (a) or (b)} for design temperatures not exceeding 650F (345C); and for flange thickness not exceeding 3 inches (75 mm)

5.11.3.3 Corrosion allowance does not exceed 1/16 inch (1.5 mm)

5.11.3.4 Carbon or low-alloy steel flanges attached to solid high-alloy necks are limited to design temperatures no higher than 450F (230C), unless a higher temperature is justified by a complete stress analysis and approved by the User

5.11.3.5 MDMT is not colder than minus 20F (-29C) for carbon and low-alloy steels

5.11.3.6 Vessel is not for lethal service (Code requirement)

5.11.3.7 Vessel or nozzle is neither for cyclic pressure or temperature service nor subjected to cyclic loadings from associated equipment

5.11.3.8 For vessels not in hot hydrogen service [Hot hydrogen service is defined as hydrogen partial pressure exceeding 100 psia (700 kPa-a), with a corresponding coincident temperature exceeding 400F (205C).]

5.11.4 Threaded and Socket Weld Flanges

Threaded and socket weld flanges shall not be used. (See Section 5.11.6.)

5.11.5 Flange Facing and Surface Finish

5.11.5.1 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 5.11.5.3. The height of a raised face shall be 1/16 inch (1.5 mm) 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.



5.11.5.2 For standard flanges and for custom flanges and shop-fabricated and factory made 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 inch (3.2 6.4 m) average roughness.

5.11.5.3 Confined Gaskets

For any of the following conditions, gasketed flange joint designs (body flange and nozzle joints) larger than NPS 24 (DN 600) shall provide outer confinement of the gasket:

a. Design pressure 300 psi (2 MPa) or higher

b. Design temperature hotter than 500F (260C)

c. MDMT colder than minus 20F (-29C) d. Cyclic pressure or temperature service

e. 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.

5.11.6 Piping Connections

All piping connections to vessels shall be either flanged or butt-welded. The minimum size shall be NPS 1-1/2 (DN 40). 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 (DN 20) Schedule (Sch) 160 or 6000# coupling. (See ASME B16.11.) Nozzle sizes NPS 1-1/4, 2-1/2, 3-1/2, 5, and 22 (DN 32, 65, 90, 125, and 550) shall not be used.

5.11.7 Quick Opening Closures

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. See Code paragraph UG-35.2 and Appendix FF {4.8 and Annex 4.B}

5.11.8 Lap Joints

Flanged joints for stainless steel and nonferrous alloy components may be of the lap-joint type with carbon or low-alloy steel flanges when the nominal diameter of the vessel component does not exceed NPS 24 (DN 600) and the maximum temperature stamped on the Code nameplate is not warmer than 300F (150C).

5.11.9 Flanged Joints with Dissimilar Metals

Austenitic stainless steel or nonferrous alloy flanges may be bolted to carbon steel flanges provided that the differential diametrical expansion will not result in diametrical interference of recessed (e.g., tongue and groove) joints and does not exceed 1/32 inch (0.8 mm). Bolting joining a carbon steel



flange to a stainless steel or nonferrous alloy flange shall be of low-alloy steel.

5.11.10 Bolting Considerations for Studding Connections

When studded connections are used, the holes in the studded connection and the studs may be machined per PIP VEFV1129. Indicator type studs for studded connections, when used, shall be in accordance with ASME PCC-1 Figures 1 and 2. A spacer ring of the same material as the nozzle flange may be provided behind the flange to increase the effective stud length (see note on PIP VEFV1129). When used, the thickness of the spacer ring shall be at least as thick as the mating flange thickness. The Manufacturer shall furnish the studs and spacer ring (when required) for each studded connection on the vessel. The studded connection shall be checked to assure the remaining thickness of the drilled holes complies with UG-43(d){4.5.3.1 b)}.

5.12 Vessel Supports 5.12.1 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 5.2.)

5.12.2 Vertical Vessels

5.12.2.1 Skirts shall have a minimum thickness of 1/4 inch (6 mm).

5.12.2.2 Vertical vessels shall normally be designed as self-supporting units and shall resist overturn based upon wind or earthquake loadings loadings per Paragraph UG-22 {4.1.5.3} of the Code.

5.12.2.3 Skirts or lugs shall be used to support towers or large vertical vessels and are preferred for vessels having top-entering agitators.

5.12.2.4 Leg supports shall be limited to spherical and cylindrical vessels that meet the following:

a. Operating temperature does not exceed 450F (230C) b. Service is noncyclic and nonpulsating (See Note 1.)

c. 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.

5.12.3 Horizontal Vessels

5.12.3.1 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 2.4 and Code Appendix G-6 {4.15.3}).

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.

5.12.3.2 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 (6 mm) larger than the bolt diameter. The length of the slot shall be: 2DLT where:

= Coefficient of thermal expansion of shell material, in/in/F (mm/mm/C)

DL = Length between saddle supports, measured to centerline of anchor bolts, inches (mm)

T = Greatest absolute value of: ambient temperature at installation [but not warmer than 70F (20C)] minus the maximum or minimum shell temperature to be stamped on the Code nameplate, F (C)

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, when the operating temperature exceeds 250F (120C) or the calculated thermal expansion exceeds 1/4 inch (6 mm). 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.

5.12.3.3 The bottom of the saddle supports may extend at least 1 inch (25 mm) below nozzles or other projecting vessel components. Otherwise, a temporary member shall be attached at each support to provide necessary extension until the vessel is placed in permanent position.

5.12.3.4 Saddles to be used in conjunction with weigh cells or slide plates require design considerations to accommodate the applicable loadings.



5.13 Anchor Bolts 5.13.1 Materials for anchor bolts shall be selected from one of the following:

1. Carbon steel: A-36, A-307 Grade B, or F-1554 Gr 36

2. Low-alloy steel: A-193 B7. (Note: Some users have reported environmental cracking of B7 anchor bolts as a result of the hydrogen from the corrosion process.)

3. For corrosive conditions, stainless steel or other high alloy materials may be used, with due consideration for possible chloride exposure, as well as the yield strength.

5.13.2 The allowable design stress, as calculated using the tensile stress area of the threaded portion, shall not exceed the following (see the following Note):

a. Carbon or stainless steel: 20,000 psi (138 MPa) b. Low-alloy steel: 30,000 psi (207 MPa)

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. Also, other local codes may be more stringent than these values, in which cases shall govern. Allowable stresses used in the final design shall be agreed to by the structural engineer.

5.13.3 Anchor bolts shall be selected with the following threads and the tensile stress area shall be selected accordingly:

a. Bolts 1 inch (25 mm) and smaller in diameter: Coarse thread series, ASME B1.1

b. Bolts larger than 1 inch (25 mm) in diameter: 8 thread series, ASME B1.1

5.13.4 For vessels on concrete foundations, the design concrete bearing stress used shall be 1658 psi (11.4 MPa).

Note: This value is based on the use of concrete with an ultimate strength, f'c, of 3000 psi (20.7 MPa) for which the minimum allowable bearing is (0.65)(0.85)f'c [approximately 1658 psi (11.4 MPa) for 3000 psi (20.7 MPa) concrete].

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 2.4, 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.



5.13.5 Anchor bolts embedded in concrete foundations shall be zinc-coated (hot dip galvanized or mechanically zinc-coated), unless the bolts are stainless steel, so that the addition of a corrosion allowance is not required. If J-bolts are used, they shall be fully stress relieved at 1100F (595C) for one hour per inch of diameter prior to hot dip galvanized coating. Threaded J-bolts in the bent area are not allowed.

5.13.6 Anchor bolts for vessels shall not be less than 3/4 inch (19 mm). Anchor bolts shall straddle normal centerlines. (See PIP VEDV1003, Section 3.3.2(d) and (l).) The anchor bolt circle shall be selected to provide radial clearance for the bolt tensioning device when low-alloy steel bolting is required.

5.13.7 Anchor bolting shall be furnished and installed by the User.

5.14 Internals Process design of trays and other removable internals are outside the scope of this Practice.

5.14.1 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.

5.14.2 Vessel internals such as distributors, dip tubes, baffles, and thermowells shall not be located near manways in a manner that would interfere with personnel access or rescue. Special consideration shall 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.

5.14.3 Unless otherwise specified on the data sheet, the material for internal attachments shall be the same nominal composition as the cladding, weld overlay, or alloy shell.

6. Materials

6.1 General 6.1.1 Care shall be taken to comply with the temperature limitations for the

material. (See applicable General Notes to the allowable stress tables in Section II, Part D, Notes in Table 2 of B16.5, etc.)

6.1.2 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 30F (17C) during the test] shall be a consideration when selecting the materials of construction and the associated MDMT to be stamped on the vessel.



6.2 Source of Materials If the User restricts sources of fabrication materials, the prospective manufacturers shall be informed at the time of bidding. Some reasons for restrictions may include but are not limited to:

a. Maintenance of a specific alloy composition

b. Compliance with government requirements

c. Compatibility with existing equipment

d. Compliance with User procurement policies

6.3 Dual (Multiple) Marked Materials ASME guidelines for dual or multiple marking of materials are given in Appendix 7 of Section II Part D of the Code. Under these ASME guidelines, dual or multiple marking signifies that the material so marked meets all of the requirements of all of the specifications, grades, classes, and types with which it is marked. Therefore, this means, for example, that the allowable stress values given in Section II Part D of the BPV Code for a regular grade of Type 304 stainless steel plate may be used in design for SA-240 plate material with a dual marking of 304/304L. By the same standard, the rating for an SA-182 GR F304 B16.5 flange may be used when it is dual marked SA-182 GR F304/F304L. However, the following requirements apply for dual-marked materials and Standard pressure parts that comply with Code requirements (e.g., flanges and pipe fittings per UG-44) {3.2.8.2}:

6.3.1 The Purchaser shall specify if dual marked materials may be used.

6.3.2 When using only one set of allowable stress values for the dual-marked Grade designation, the material listed on the Manufacturers Data Report Forms shall be the material grade chosen from the allowable stress or ratings tables. For example, if the allowable stresses for SA-240 Type 304 are used in design for the shell and heads, the material listed in the Manufacturers Data Report Form shall be SA-240 Type 304. However, a note in the Remarks section of the Manufacturer's Data Report Form may contain the phrase: The shell and head material meet all of the requirements of SA-240-304 and SA-240-304L. (See Code Interpretation VIII-1-92-166). By the same standard, this same material information shall be included on the Data sheet and/or drawings covering the pressure parts involved, as appropriate, since this is the source of the information used by the Manufacturer.

6.4 Corrosion/Erosion Allowance 6.4.1 Basis

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 shall examine the process and make judgment on the expected corrosion rate. Corrosion allowance shall not be arbitrary; rather, it shall be compatible with design life requirements.



6.4.2 Corrosion Loss Additional metal thickness shall be added to compensate for anticipated loss due to metal reacting with the environments to which it is subjected (including cleaning operations, shutdowns, etc.).

6.4.2.1 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.

6.4.2.2 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).

6.4.3 Erosion Loss Additional metal thickness shall 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:

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

b. Addition of a welded wear plate with the intent that the plate is sacrificial

Note: Use caution when using this method in hydrogen service.

c. Internal refractory linings, if appropriate

d. Increase of inlet nozzle size

6.4.4 References for Damage Mechanisms The User, when selecting the materials of construction, shall consider all damage mechanisms associated with the service fluid at design conditions. Informative and non-mandatory guidance regarding metallurgical phenomena is provided in Section II, Part D, Appendix A, API RP 571, and WRC Bulletins 488, 489 and 490.

6.5 External Protection of Austenitic Stainless Steel Equipment from Stress Corrosion Cracking Insulated austenitic stainless steel equipment that is susceptible to atmospheric chloride stress corrosion cracking shall be protected by a suitable external protective coating and the use of a low chloride insulation.

6.6 Support Materials

6.6.1 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 450F (230C). The length of this high-alloy steel portion of the skirt shall be )(2 Rt , but not less than 12 inches (300mm),



where R is the mean skirt radius and t is skirt thickness. 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 between -20F (29C) and 450F (230C), 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.

6.6.2 For vessels with a design temperature lower than -20F (-29C), the skirt shall be the same material as the head for a minimum length of )(2 Rt , but not less than 12 inches (300 mm).

6.6.3 Corrosion allowance for the skirt and base ring shall be specified separately from the vessel corrosion allowance.

6.7 External Attachments As a minimum, the attachments shall be of the same type material (ASME Code P-number) as the pressure part to which attached except austenitic stainless steel external welded attachments may be any 300-series stainless steel. Carbon and low-alloy steel attachments welded to pressure-retaining components shall be considered as being essential to the structural integrity of the vessel; accordingly, for purposes of establishing the attachment impact test requirements, the level of applied general primary membrane stress shall be considered to be the same as the maximum level applied to the pressure boundary component to which they are attached. The Manufacturer may propose other materials for the attachments with due consideration being given to the following:

a. Potential problems associated with welding dissimilar materials

b. Compatibility with the Code nameplate maximum and minimum design metal temperatures

c. Whether or not the attachment is essential to the structural integrity of the vessel (see Code Paragraph UCS-66(a) {3.11.2.3 c)})

d. Differential thermal expansion characteristics and associated stresses

e. Corrosion resistance

f. Painting requirements

g. Suitability for the anticipated loadings



7. Examination, Inspection and Pressure Testing

7.1 Welded Pressure Joint Requirements Consistent with the service-specific needs of each vessel, consideration shall 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 Users responsibilities under the Code as outlined in the Code Foreword. See also Code Paragraph U-2(a) {2.2.2.2}.) As a minimum, specific Code requirements shall 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 {4.2.5}. A Welded Pressure Joint Requirements Form for documenting and transmitting the needed information for each welded joint category (location) is included in Appendix B. Also included in these Appendices is a completed form showing the requirements described in Sections 7.5.1, 7.5.2, 8.1.3 and 8.1.4 of PIP VESV1002, illustrating the use and usefulness of this form for communicating welded pressure joint 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.

Use the Welded Pressure Joint Requirement form Appendix B to specify the welded pressure joint type and associated nondestructive examination requirements.

7.2 Testing The following paragraphs provide guidance and references to design and execution considerations relative to hydrostatic and pneumatic pressure testing.

7.2.1 Hydrostatic Test 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.

7.2.2 Pneumatic Test Caution: Pneumatic testing presents hazards that require careful

attention as part of the engineering design of the pressure vessel to ensure personnel safety during the test.

(Reference Code Paragraph UG-100 {8.3}, Pneumatic Test and Code Paragraph UW-50 {Not Division 2 Applicable}, Nondestructive Examination Of Welds On Pneumatically Tested Vessels.)

Due to the additional hazards of pneumatic testing, vessels shall be manufactured and inspected 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.

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 over design of the vessel and foundation only to support a water full test may be considered for pneumatic testing.

Acoustic emissions monitoring during pneumatic testing may successfully locate flaws in the vessel and shall be considered for field erected vessels.

ASME PCC-2 Article 5.1 provides guidance on energy calculations for pneumatic tests and safe distances for personnel during the test.

7.2.3 Proof Test (Code reference - Paragraph UG-101, Proof Tests To Establish Maximum Allowable Working Pressure.{not Div.2 applicable}) Proof tests are highly individualized and are not included in this Practice.

Appendices Appendix A General Considerations for Pressure Relief Valve Application Appendix B Welded Pressure Joint Requirements Form Appendix C Equivalent Pressure Formulas for Bending Moment and Axial Tensile Load

Appendix A

General Considerations for

Pressure Relief Valve Application


Page A-2 Process Industry Practices

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 shall be known by the User as well as the Designer. Direct spring and pilot-operated relief valves are available for use on applications that are required to 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.

Appendix B

Welded Pressure Joint Requirements Form


Page B-2 Process Industry Practices

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{4.2.5)

TYPE OF JOINT NDE (SEE LETTERED NOTES)

CATEGORY A (SEE NOTE 5) TYPE NO. (1) OF TABLE UW-12{4.2.2}

CATEGORY B

HEAD -TO-SHELL TYPE NO. (1) OF TABLE UW-12{4.2.2}

OTHER

CATEGORY C

BODY FLANGES

NOZZLE FLANGES FIGURE 2-4 {TABLE 4.2.9 and FIGURES 4.16.1, 4.16.2 & 4.16.5}

CATEGORY D SEE GENERAL NOTE (6)

GENERAL NOTES: 1) Unless otherwise indicated, all references on this form are to ASME Code Section VIII, Division 1 paragraphs, tables, and figures.

Comparable ASME Code Section VIII, Division 2 references are shown in brackets { }.All nondestructive examination shall meet or exceed ASME Code requirements and 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 UW51{7.5.3} before forming. After forming, the spin hole, if it remains in the final construction, shall be closed in accordance with UW-34 {6.1.2.9} 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{Tables 4.2.10, 4.2.11, 4.2.13} 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.

ITEM NUMBER: ____________________________________

WELDED PRESSURE JOINT REQUIREMENTS PRESSURE VESSELS

VESSEL ASSEMBLY DWG.: __________________________ DRAWN BY CHECKED BY DATE DRAWING NUMBER

PAGE 1 OF 2


Process Industry Practices Page B-3

Nondestructive Examination Notes

A. Full radiography shall be per Paragraph UW-51{7.5.3}. For welded pipe components, this applies only to Categories B and C butt joints. For exclusions, see Paragraph UW-11(a)(4){Table 7.2}.

B. Spot radiography shall be per Paragraph UW-52{7.4.1, 7.4.2, 7.4.3 & 7.5.3 }. For welded pipe components, this applies only to Categories B and C butt joints. For exclusions, see Paragraph UW-11(b) {Table 7.2}.

C. Spot radiography shall be per Paragraph UW-52{Table 7.2}. Rules of UW-11(a)(5)(b) {not Division 2 applicable}shall 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 {7.4.3.5}]

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 (50 mm), examine (using MT or PT) the root pass after back-chipping 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. Examination (using MT or PT) of completed welds shall be made after PWHT for the following:

1. Vessels or vessel parts for which impact testing is required 2. Welds joining non-impact tested low-alloy steels thicker than 1-1/4 inches (32 mm) 3. Welds joining carbon steels thicker than 2 inches (50 mm) 4. When required by Code

G. Butt welds exempt from radiography by Paragraph UW-11(a)(4) {Table 7.2} shall have accessible surfaces of completed welds MT or PT examined. (Only applies to designs employing impact-tested 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-4 Process Industry Practices

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 7.5.1.1, 7.5.1.2, 8.1.3, and 8.1.4 of PIP VESV1002. 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_______

WELDED PRESSURE JOINT REQUIREMENTS

JOINT LOCATION PARAGRAPH UW-3{4.2.5}

TYPE OF JOINT NDE (SEE LETTERED NOTES)

CATEGORY A (SEE NOTE 5) TYPE NO. (1) OF TABLE UW-12{4.2.2}

B

CATEGORY B

HEAD -TO-SHELL TYPE NO. (1) OF TABLE UW-12{4.2.2}

B

OTHER B

CATEGORY C

BODY FLANGES

--

NOZZLE FLANGES FIG. 2-4 {TABLE 4.2.9, and FIGURES 4.16.1,4.16.2, & 4.15.5 }

B

CATEGORY D SEE GENERAL NOTE (6) --

GENERAL NOTES: 1)) Unless otherwise indicated, all references on this form are to ASME Code Section VIII, Division 1 paragraphs, tables, and figures.

Comparable ASME Code, Division 2 references are shown in brackets { }. All nondestructive examination shall meet or exceed ASME Code requirements and 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 UW51{7.5.3} before forming. After forming, the spin hole, if it remains in the final construction, shall be closed in accordance with UW-34 {6.1.2.9}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{Table 4.2.10, 4.2.11, 4.2.13} 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.

ITEM NUMBER: ________PIP 123456___________________

WELDED PRESSURE JOINT REQUIREMENTS PRESSURE VESSELS

VESSEL ASSEMBLY DWG.: ___PIP 123456______________

DRAWN BY CHECKED BY DATE DRAWING NUMBER

PAGE 1 OF 2

Appendix C

Equivalent Pressure Formulas for Bending Moment and Axial Tensile Load


Page C-2 Process Industry Practices

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 shall be replaced by the following design pressure:

PFLG = P + PEQ

The equivalent pressure PEQ is determined as follows:

PEQ = 16MG

4F

G3 2 +

Where: M = Sustained bending moment applied across full section at flange during the design

condition, in-lb F = Sustained axial tensile force applied at flange, lb

G = Diameter at location of gasket load reaction, in (See Appendix 2-3 {4.16.6.1 c), and 4.16.12} 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:

H = 0.785 G2 PFLG Dynamic Bending Moment

PEQ = 8MG3

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

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Standard ASME Vessel Design Criteria