Flanges and Gaskets

1. Table of Contents

1. Table of Contents 1

2. Purpose 1

3. Definitions 1

3.1 Class 1

3.2 Rating 2

4. General 2

5. Flange Class Selection 2

5.1 Referenced Standards 2

5.2 Class Determination Using the Referenced Standards 3

5.3 Class Determination Using the Inflection Point Engineering Tool 4

5.4 Special Cases 7

5.5 Project Consistency 7

6. Flange Materials, Sizes and Designations 7

7. Design Conditions 9

8. Special Conditions and Limitations 10

9. Flange Styles and Facings 11

10. Surface Finish 12

11. Gaskets 12

Attachment 1 Standard Notes 15

Attachment 2 Accommodation of Applied Loads 17

Attachment 3 Tool Error Messages 18

Attachment 4 Guidance on Determining the Applicable Code 22

2. Purpose

This procedure describes the methods used to determine the class(es) and other characteristics specified for flanges used with Schedule A equipment and piping. Information concerning gasket selection and specification is also included.

3. Definitions

3.1 Class

A designation used to describe a set of standardized flange dimensions applicable to each covered size of flange. Sizes are defined in terms of nominal pipe size (NPS). The flanges in each class are adequate for use under a predetermined set of temperature and pressure conditions, depending upon the material of construction. For example, specifying a 3 inch Class 300 (designated CL300) flange defines a precise set of dimensions for the flange. Adding the material of construction defines a table of applicable temperature-pressure ratings.

3.2 Rating

A combination of temperature and pressure for which a particular flange class and metallurgy is adequate. For example, in accordance with ASME B16.5-2003, a carbon steel Class 300 (CL300) flange is rated for 570 psi at 600oF. Rating is not a substitute term for class.

4. General

Flanged connections are provided to allow for assembly and disassembly of piping or equipment joints. The connection consists of a pair of flanges, a gasket, and bolting. The gasket provides the seal between parts of the assembly, the bolts provide the force to achieve and maintain the seal, and the flanges are the means of transmitting the bolt forces to the gasket. Unfortunately, the assemblies are prone to leakage, either immediately or at some point during operation. Leakage is often a safety hazard, frequently an economic concern, and always inconvenient. Therefore, use flanged connections sparingly, i.e., only when needed. When flanges are used, it is important to select materials and flange dimensions compatible with, and adequate for, the conditions to which they are exposed.

5. Flange Class Selection

5.1 Referenced Standards

Select flanges in accordance with the requirements of the Code governing the design of the subject piece of equipment (e.g., vessel, exchanger, pump, instrument) or piping. Based upon the applicable design conditions, the flange class is typically selected from a referenced document. The relevant Codes commonly refer to ASME B16.5, “Pipe Flanges and Flanged Fittings” for sizes up to 24 inches and ASME B16.47, “Large Diameter Steel Flanges NPS 26 through NPS 60” for larger sizes (API 605 is now obsolete). In some cases ASME B16.42 “Ductile Iron Pipe Flanges and Flanged Fittings” or ASME B16.1 “Cast Iron Pipe Flanges and Flanged Fittings, Classes 25, 125, and 250” may be applicable. An example is when ASME pumps of these materials are used in non-process, non-hazardous services. Note that many Codes list the edition of the referenced document that is acceptable. The listed edition may not be (and often has not been) the latest edition. The applicable edition can also vary from code to code. THE FLANGE CLASS MUST NOT ONLY COMPLY WITH THE REFERENCED STANDARD, BUT ALSO THE SPECIFIED EDITION OF THAT STANDARD. Therefore, Inflection Point Engineering Project Specifications shall not call for the use of the latest edition of any flange standard when the subject component is governed by a code, standard, or other document that may call for a specific edition of the flange standard.

5.2 Class Determination Using the Referenced Standards

• Each of the referenced standards contains groupings of standardized flanges for the covered flange sizes. Each grouping is called a Class. Use of standardized flange dimensions simplifies production of the flanges and maintenance/warehousing issues (e.g. compatibility, maintaining an inventory, and obtaining flanges not included in the plant inventory) by limiting the potential number of differing flanges.

• The flange standards contain rating tables organized on the basis of the material of construction. Select the proper class from the applicable rating table using the design temperature and pressure conditions for the flange (see Section 7). Enter the rating table for the material used and move down the left column to the design temperature. Moving along the row defined by the design temperature, find the first pressure greater than the design pressure. The heading of the column defined by this pressure is the applicable flange class.

• Select the lowest flange class with a permitted pressure equal to or greater than the flange design pressure at the design temperature.

• See Section 8 for special conditions and limitations applicable to the flange class selection procedure.

• When the design temperature is between those listed, locate the corresponding pressure rating by straight line interpolation between the values at the next higher and lower temperatures.

• Follow the ratings rigidly. If the pressure is above the rated value at temperature, even if by only a small amount, select a higher flange class. When this occurs, it may be useful to review the design conditions and see if either the temperature or the pressure may be slightly reduced to allow the use of a lower, less costly, flange class.

• ASME B16.5, B16.47, B16.1 and B16.42 each contain their own class selection tables. The tables may differ, so it is possible that a given material and set of design conditions will require a different flange class under each standard.

• Use the edition of each flange standard called for by the applicable edition of the governing Code. The user is responsible for determining which code governs and the applicable edition(s) of the code and flange standard(s). See Attachment 4 for guidance.

• The latest edition of each referenced flange standard may be viewed via the Information Handling Services (IHS) website on the Internet. See Employee Handbook for information on accessing and using the IHS website. There are also hard copies of the standards available in many Center libraries. In both cases, be sure the available edition is the one accepted by the applicable code(s).

• Accommodation of potential flange class mismatches due to material or flange standard edition differences (e.g., the piping and vessel interface) is the responsibility of the Contractor. See also, Paragraph 8.1.a.

5.3 Class Determination Using the Inflection Point Engineering Tool

• To simplify the flange class determination process, Inflection Point Engineering has developed Tool . T-800-01 is accessed through the Documentation System Web Interface. The tool selects flanges in accordance with ASME B16.5, B16.47 or B16.42 as applicable. Inflection Point Engineering does not permit cast iron flanges in process service, therefore ASME B16.1 is not included.

• Tool T-800-01 should be used for all flange selection. Other tools may not include as many flange standards and/or may not be updated promptly.

• Follow the standard procedure for use of Inflection Point Engineering Tools, i.e. copy the tool to the users drive, making the user the owner. This gives the user write access. Failing to follow this procedure will result in the save and reset functions becoming inoperable.

• Use of the Tool is self explanatory and requires entry of the following information -

• The design temperature (see Section 7) (select units from a pull down list.)

• The design pressure (see Section 7) (select units from a pull down list.)

• The material of construction (selected from a pull down list).

• Select the material group containing the subject product form.
• Several metallurgies appear more than once on the pull down list. Click on “Click here to see Metallurgy Chemistry and Designations” to display the product forms (i.e. the ASTM material designations) included in each material group.
• If the product form is unknown, and more than one material group contains the subject chemistry, use the material group with “default” marked for the subject chemistry. This group contains the most commonly used flange product form, typically a forging. One exception is a flanged valve, where a cast product form should be selected. Valve flanges are integrally cast with the valve.
• Ductile iron is not included in the pull down list of materials. Select ductile iron by selecting “yes” on the first yes/no input question.

• The code governing the item of which the flange is a part (select Code from a pull-down list). (See Attachment 4).

• Indicate if the flange is ductile iron or mates to a ductile iron flange.

• This results in the use of ASME B16.42 tables rather than B16.5 or B16.47.

• Indicate if the flange is greater than 24” NPS

• This determines whether tables from ASME B16.5 or B16.47 are used.

• If the project has flanges both 26” or greater and 24” or less, the program must be run for each case because they use different look-up tables.

• Indicate if the flange is less than or equal to 12” NPS.

• An error message will be displayed for flanges over 12” if Class 2500 is required. These flanges are not covered by any of the flange standards.

• After confirming that all the required information has been entered, click on the “Determine Flange Class” button.

• The output sheet may be saved by clicking the “Save Output” button. Two options are presented.

• Results may be saved within the tool. After saving, a tab appears at the bottom of the spreadsheet allowing access to the saved results. The input can then be changed, and the new results saved.
• Results may be saved as a file outside of the tool. This option results in saving of the output sheet(s) without saving any of the tool programming. It saves the current calculations and any results previously saved within the tool. After assigned a file name and clicking ok, a message (see Attachment 3, Item 16) appears requesting that the user save the file again, using “save” from the pull down menu. This is necessary to remove the remaining visual basic macros and save only the flange class determination output sheet(s). The tool must be re-entered to input new data and perform another calculation.
• When multiple calculations are to be performed, save each within the tool. After performing the final calculation, save outside of the tool. All of the results saved within the tool will then be saved outside the tool.

• Repeat the above steps for each combination of input information (e.g. if the code, design conditions, or material changes.) The “Reset” button must be clicked before new data can be entered. This removes the previous results, preventing application of the earlier result to the new conditions in the event the “Determine Flange Class” button is not pressed. The “Reset” button gives the user two options; (1) return all inputs to their default values, or (2) retain the most recent input. The latter option facilitates change to only one or two input items (e.g., design pressure, whether flange size exceeds 24 inches).

• The output sheet may be printed from within the tool at any time. This does not save the results.

• The Tool selects the proper flange class based upon the tables in the appropriate standard, interpolating between the values in the table when applicable. It also displays the ratings of other flange classes (using the governing edition of the applicable flange standard) so that the user can see if an alteration of the specified conditions (temperature and/or pressure) would allow use of a lower flange class. The user is alerted if the conditions are within 15 PSI of permitting use of a lower flange class. Warnings and error messages (see Section 7 and Attachment 3) are also displayed when appropriate. The warnings and error messages appear as “pop-up” messages and also in the “required flange class” section of the main screen.

• The selection tables may be viewed and printed if desired. The electronic tool, rather than a copy of the tool’s tables, must be used for flange selection because the Tool will be updated as the flange standards are revised.

• There will often be a significant period, perhaps years, between the issue of a new edition of a referenced flange standard and acceptance of that edition by the primary piping and pressure equipment codes (ASME Section I, Section VIII Divisions 1 and 2, B31.1, and B31.3). Although this could be due to Code Committee reservations with the new edition, it’s nearly always due to timing of the Committee meetings followed by elapsed time until publication of the next scheduled revision of the Code. The tool is revised each time a code changes the referenced edition of any flange standard included in the tool.

Special Cases

In some cases Inflection Point Engineering requires a minimum flange class regardless of the design conditions. For example, instrumentation pipe column flanges shall be a minimum of Class 300. Hot Oil Systems also require a minimum of Class 300 where the hot oil contacts the flange. Special cases are identified in the Standard Specification or by the applicable .

Project Consistency

The flange selection criteria shall be consistent throughout each Inflection Point Engineering project. If the Flange Selection Tool and/or the referenced flange standard(s) is revised while a project is underway, the Project Manager shall determine which version of the Tool and/or Standard to use. Superseded versions of the Tool are available for use in these situations.

6. Flange Materials, Sizes and Designations

6.1 Materials are grouped into rating tables based upon chemistry and similar behavior. Each rating table in the applicable flange standard applies only to the listed chemistry and product forms. There may be more than one material group for a given chemistry. Use the material group containing the subject product form. If the product form is not known, use the material group containing the general use forging product form. For example, ASME B16.5 and B16.47 each contain four different rating tables for carbon/killed carbon steel. Use the table containing ASME A105 material unless one of the other listed materials is known to be used.

Each rating table is based upon the worst of the included materials, i.e., the one with the least pressure capacity at the subject temperature. Note that all of the materials included in a table may not be acceptable for use throughout the temperature range of the applicable rating table. These materials and their limiting temperature are identified by footnotes.

6.2 Although forgings, castings and plates are listed, flanges are to be forgings in nearly all cases. Plate materials are permitted for blind flanges, but forgings are superior. Use cast flanges only when they are an integral part of a cast component (e.g., a valve). Otherwise use forgings because castings are prone to the inclusion of flaws and air pockets, leading to brittle behavior. Another benefit of forgings is that the surface of the metal is in compression, resisting the formation and propagation of cracks.

6.3 ASME B16.5 includes tables for many materials, both ferrous and non-ferrous. CL150, CL300, CL400, CL600, CL900, and CL1500 cover flanges through 24 inch nominal pipe size (NPS). CL2500 extends through 12 inch NPS.

6.4 ASME B16.47 includes tables for commonly used ferrous materials but does not include non-ferrous materials. It includes CL150, CL300, CL400, CL600, and CL900 but does not cover CL1500 or CL2500. It also includes Class 75, a class not utilized for process equipment or piping. B16.47 contains two groups of flange dimensions, designated as Series A and Series B (Class 75 is not available in Series A). Although both series comply with the same rating tables the dimensions differ, making them incompatible with each other. Series B, which is based upon the obsolete API 605, is generally used for process applications and Series A, which is based upon MSS SP-44, is generally applicable to pipelines. However, there are many exceptions (e.g., valve bodies often use Series A).

Inflection Point Engineering specifications call for Series B, but note that series A is necessary when connecting to an item using a Series A flange. Series B covers flanges from 26” to 60” in Classes 150 and 300 and 26” to 36” in Classes 400, 600 and 900. Series A covers flanges from 26” to 60” in Classes 150, 300, 400, and 600, 26” to 48” for Class 900.

6.5 ASME B16.42 applies only to flanges made of ductile iron per ASTM A395. It covers sizes from 1 inch to 24 inch NPS. Two classes are included; Class 150 and Class 300. The maximum temperature is 650°F. Inflection Point Engineering permits the use of ductile iron flanges under very limited non-hazardous, non-process circumstances (e.g. when ASME ductile iron pumps are specified and some utility services) and only when Class 150 is adequate.

6.6 Flanges for materials, sizes, or design conditions not covered by the tables must be designed in accordance with the rules of the governing Code. In (nearly) all cases, the referenced rules will be those of ASME Section VIII, Division 1, Appendix 2 and Appendix S. For these cases, indicate that the flange is “Special” on the Project Specification. The contractor or fabricator will design the flange.

When the Schedule A requires design of a specific flange by Inflection Point Engineering, use Kflange, an interactive design tool developed by WJKoves. It’s located on the G:\ drive, at G:\ESE\AppSupport\KFLANGE. Click on the file labeled FLANGE.EXE to start the program. Kflange allows for design according to the Code rules and also for a leakage rate based review. Leakage based criteria are likely to replace the current stress-based criteria in the near future. An alternative is to use the flange design features of AxiPro, a finite element program linked to FEPIPE. See for details.

When flange design is required due to the use of a material not listed in the flange standard, attempt to use flange dimensions of a standardized class. This allows the flange manufacturer to use available dies, machinery and programs (e.g., programs for boring bolt holes), greatly reducing the cost of the special flange.

7. Design Conditions

7.1 For Schedule A purposes, select the required flange class based upon the non-shock design temperature and pressure conditions at the flange’s location. Do not evaluate externally applied loads, gasket seating, and other conditions because they are outside of the Schedule A scope and normally are not known at the time of the Schedule A. Include a note in the Project Specification clarifying the selection basis unless a note is already in the Inflection Point Engineering Standard Specification issued for the equipment or piping. See Attachment 1 for the standard wording of this note. For circumstances where evaluation of externally applied loads is necessary, the straightforward (and conservative) method described in Attachment 2 may be used.

7.2 Frequently, the conditions used for flange selection are the design conditions of the equipment. There are exceptions, however. Because the design conditions are defined as the conditions at the top of the equipment, the actual design conditions at a particular flange location may be greater. A common example is a fractionating column. Due to the tray pressure drop and liquid hydrostatic head, the pressure at the bottom of the vessel may be significantly higher than the pressure at the top. THE ACTUAL DESIGN PRESSURE (AND TEMPERATURE) AT THE LOCATION OF THE FLANGE MUST BE USED TO DETERMINE THE FLANGE CLASS.

7.3 Hot services present a special problem, especially for the bolting. At high temperatures, the allowable stress for the material and therefore the pressure rating of the flange decrease rapidly. This is due to reduced yield and ultimate strength and concerns with creep. Creep deformation is especially devastating for the bolting. Creep deformation results in a reduction of the elastic bolt strain, therefore a lower bolt stress. This results in a lower stress on the gasket. The lower gasket stress reduces the ability of the gasket to maintain a seal and the likelihood of a leak increases.

• The Piping Code contains a provision that may be used to address these problems. It allows the use of a lower design temperature for the flange and bolting if the flange is not insulated. An uninsulated flange may be designed for 90% of the fluid temperature and the bolting may use 80% of the fluid temperature. If the heat loss is acceptable, the lower temperature may allow the use of a lower, less costly, flange class or reduce the effect of creep.

• The Pressure Vessel Code does not have a provision equivalent to the temperature reduction permitted by the Piping Code.

• Uninsulated temperature conditions are typically considered when the design temperature exceeds 800ºF (425ºC). At this point the available bolting materials become limited and the temperature reduction may be significant enough to permit the use of a lower flange class.

• If the uninsulated temperature is used for a piping flange, the flange cannot be insulated at some future time (e.g., to save energy) without a significant reduction in it’s capacity (i.e., rating). For this reason, flanges where the flange class selection was based upon the uninsulated temperature shall be so identified on the Project Specifications and Drawings.

8. Special Conditions and Limitations

8.1 Several other factors impact the final flange class selection.

• Each pair of flanges must be of the same class. If the materials differ, (e.g., thermowells, stainless steel piping joining a low chrome vessel, steel piping connecting to a ductile iron pump, etc.) different class requirements may result. Use the higher class for both flanges. A similar situation may arise when mating flanges are governed by different editions of a flange standard. Again, use the higher class requirement for both flanges. This could occur when different codes govern each assembly, e.g., piping (B31.3) joining to a pressure vessel (Section VIII Division 1). It’s possible for the codes to specify different editions of the same flange standard, possibly requiring different flange classes.

• Do not use CL150 flanges for temperatures above 700oF. This is because CL150 flanges are lightly built, with relatively few bolts, and are susceptible to leakage due to the reduced stress capacity and greater distortion of the material at elevated temperatures.

• Avoid the use of CL400 flanges. It is an uncommonly used class because valves and other components with an equivalent rating are not available. To a lesser extent, the same concerns apply to CL900. The Flange Selection Tool does not permit selection of CL400 flanges.

• CL900 flanges are not available in 2½ inch and smaller sizes, use CL1500 instead.

• Use CL300 flanges, as a minimum, for level gauge/column connections to equipment, including magnetic indicators. CL300 is used because of the weight of the assembly, potential differential thermal expansion between the level gauge/column and the vessel, even people standing on the small nozzles. These and other effects increase the loads applied to the flange. CL300 is used because the flanges are stiffer than CL150 and are more tolerant of the applied loads. This only applies to the vessel connections, not the connections within the level gauge/pipe column assembly.

8.2 Most flanges are intended to be part of a piping system and are dimensioned to join to nominal pipe sizes (NPS). The outside diameter of the pipe is fixed, and the inside diameter varies with the wall thickness. The inside diameter of mating butt-welded flanges must be specified when ordering. (Note ASME B16.5-2003, Section 2.7, limits the permissible bore diameter of welding neck flanges.)

8.3 Vessel nozzles frequently utilize integrally reinforced or long weld neck forgings. In both cases the forging is attached directly to the vessel. Since it is not welded to piping, it need not match a NPS. Therefore, the ID of these forgings equals the specified size; e.g., a 20-inch nozzle has a 20-inch ID. This is useful for manways, instrument connections, or other instances where something passes through the nozzle and a known ID is important. These flanges may be bolted (and gasketed) to any other style of flange. If built-up construction is used for a vessel nozzle, the nozzle neck is a pipe and the flange and nozzle ID match that of the pipe. In all cases, the best approach is to specify the desired ID whenever it is important.

9. Flange Styles and Facings

9.1 Nearly all services utilize raised face welding neck flanges. Integrally reinforced flanges, where the necessary nozzle reinforcement is provided as a thickened portion of the nozzle neck, are common for equipment connections.

9.2 A few specific low pressure, non-hazardous utility services (e.g., potable water and instrument air) use a flat faced flange (see Paragraph 11.5). Flat faced flanges are not accepted by Inflection Point Engineering for process service.

9.3 Occasionally an owner will request that ring joint flanges (and gaskets) be used for high pressure or other severe services. Use of these flanges is acceptable if a note is provided requiring flat bottom grooves with a minimum 1/8 inch radius at the intersection of the side and bottom of the groove. This note is included in some Inflection Point Engineering Standard Specifications. If it is not included in the issued Standard Specification, add it to the relevant Project Specification (see Attachment 1 for typical wording). When mating ring joint flanges are of different metallurgies, the effect of differential thermal expansion must be considered. If the flanges expand differently, the grooves no longer align, possibly damaging the gasket and seal. The amount of differential growth is controlled by limiting the flange size for which ring joints may be used; e.g., less than 12" for a Type 321/347 stainless steel flange joined to a low chrome flange at 800ºF (425ºC). A different size limitation may be appropriate for other materials or another temperature.

9.4 Use other flange styles (e.g., slip-on, lap joint) and facings (e.g., tongue and groove, retained gasket) only in special circumstances and if restrictive requirements are met. Some of the requirements are described in the Inflection Point Engineering Standard Specifications.

10. Surface Finish

10.1 Use of the proper surface finish on the flange is critical for proper performance of the assembly. Too rough or too smooth and it will prove difficult, if not impossible, to obtain a seal. Finishes are to be in accordance with ASME B46.1, “Surface Texture (Surface Roughness, Waviness, and Lay)”. Specify finishes by designating an Ra number, which is essentially the roughness average. In the Inflection Point Engineering Specifications, Ra is expressed in microinches.

10.2 The surface finish of a flange is determined by sight and feel, e.g., by use of a comparator, NOT by mechanical means. That is because mechanical means cannot distinguish between a uniform roughness and a very smooth surface with a few very rough areas. Both may have the same average roughness but behave much differently.

10.3 The necessary finish is a function of the gasket style chosen. For spiral wound gaskets the required range is 125 – 250 microinch Ra. A note to this effect is to be in the Schedule A Specifications. If the note is not a part of the applicable Inflection Point Engineering Standard Specification, include it in the Project Specification. See Attachment 1 for the text of the note. If a different style of gasket is used, the flange surface finish shall be within the optimal range for the gasket.

11. Gaskets

11.1 Gaskets are the compressible component of the assembly that, when compressed, form a seal between the flanges. The most commonly used gaskets for refining and petrochemical process applications are spiral wound, jacketed and ring joint. These gaskets are in accordance with ASME B16.20, “Metallic Gaskets for Pipe Flanges – Ring-Joint, Spiral Wound, and Jacketed” (It’s predecessor, API 601, is now obsolete). The gasket style and materials are specified in the applicable Inflection Point Engineering Pipe Class.

11.2 Spiral wound gaskets are, by far, the most frequently used type and are found in nearly all services.

a. They are safe, resilient, forgiving, durable, widely available, easily handled and installed, work well in a wide variety of steady state and transient (e.g., start-up and shut down) atmospheres and operating conditions, and utilize an easily provided, fairly rough flange finish.

b. Spiral wound gaskets are provided with an outer ring. This ring helps stiffen the gasket during handling, fits against the bolts to align the gasket during installation, and retains the filler material and windings during gasket compression. The ring also prevents over compression of the gasket. An inner ring is required for Class 900 and greater flanges, large diameter flanges (over 24 inches), flanges of differing metallurgies and coefficients of thermal expansion operating at elevated temperature, highly corrosive atmospheres, vacuum service and other specific circumstances.

c. Specify the ring, winding, and filler materials.

(1) The normal materials for the ring(s) and windings are Type 304 stainless steel for the windings and inner ring (if required) and carbon steel (protected against corrosion) for the outer ring. In lined areas of the vessel the inner ring (if required) and windings are the same metallurgy as the lining.

(2) The filler is a non-asbestos material (see Procedure ), typically graphite. Teflon is sometimes used in low temperature {less than 400°F (205°C)} services. There is a concern with the deterioration of graphite in a high temperature {greater than 850°F (455°C)} oxidizing environment. In this environment consider using a ceramic or mica filler in the outer windings to protect the inner graphite fiber windings from the oxygen.

• Specialty, usually proprietary, filler materials are available, but very rarely called for on a Inflection Point Engineering Schedule A. They are targeted at a very specific operating environment and may perform very poorly in other circumstances.

• Typical notes specifying gasket materials are included in Attachment 1. The spiral wound note includes a requirement that the inner ring (if present), outer rings, and windings be checked for buckling. These notes are often included in the applicable Inflection Point Engineering Standard Specification, but if they are not they may need to be included in the Project Specification.

11.3 Kammprofile gaskets (some vendors use a different name) have been used in for years and are becoming more popular worldwide. These gaskets utilize a “sandwich” construction with a compressible sealing material above and below a rough metallic filler. They require the same surface finish and sealing surface dimensions as a spiral wound gasket. They seal as well or better than spiral wound, are more forgiving and easier to handle, and the metallic portion can be reused. However, they cost 2 or 3 times as much as a spiral wound gasket. Inflection Point Engineering does not specify these gaskets but they can normally be used wherever a spiral wound gasket is used.

11.4 Jacketed gaskets were once the industry standard, but now they are rarely used because they are less effective than spiral wound gaskets. ASME B16.5 cautions against their use in CL150 flanges (see Paragraph 5.4.3 of B16.5.) However, there are a couple of cases where they may be seen. When the surface to be sealed is a large diameter, jacketed gaskets are occasionally used because they are easier to handle than spiral wound gaskets. Jacketed gaskets are also used when the surface to be sealed is “non-circumferential” (e.g., it includes a chord) because spiral wound gaskets are not easily fabricated to these shapes. An example is the channel of an exchanger where the baffle between passes must be sealed along with the flange itself. When jacketed gaskets are used, the corrugated double-jacketed style is specified. A jacketed gasket may not maintain a seal if it is subjected to shearing forces from differential radial movements. Jacketed gaskets require a smoother surface finish (63-80 microinch Ra) than spiral wound gaskets.

11.5 A few low pressure, non hazardous utility services (e.g., potable water and instrument air) use cast iron flanges. Flat, full face gaskets must be used with cast iron flanges (e.g., ASME B16.1) to avoid overstressing, even cracking, the flange. Although the gasket has much more loaded area than a spiral wound gasket, the required stress is far lower, giving a lower total seating force. The moment arm between the bolting and the gasket reaction is also shorter than if a spiral wound gasket were used. The result is much lower flange stresses with a flat, full face gasket than if a spiral wound gasket is used. Low strength bolts are also required for these flanges unless the gasket extends beyond the bolt holes, to the flange OD. (See ASME B16.5, Paragraph 5.3.5). Flat, full face gaskets are soft and do not provide a low leakage seal.

11.6 Ring joint gaskets (and compatible flanges) are used by some owners for high pressure and other severe services. Inflection Point Engineering specifies raised face flanges for all services however, when requested by the owner, ring joints may be specified on the Schedule A. Ring joint gaskets are metallic, normally either iron or stainless steel. Use an oval ring because it will seal in the current flat bottom and the old oval grooves.

Attachment 1 Standard Notes

Several notes relating to flanges and gaskets must be included in the specifications issued with each piece of equipment or piping that contain(s) flanges. These notes describe the basis used for the selection of the flange class and highlight any areas that must be evaluated by the Contractor. These notes are often included in the Inflection Point Engineering Standard Specifications applicable to the component. If so, no further action is required. If not, the notes must be added to the Project Specification(s). Typical notes to be included are as follow:

1) Flange classes are specified in accordance with ASME B16.5 or ASME B16.47 Series B (Series A is required if connected to an item furnished with Series A flanges). Flange classes listed in the Inflection Point Engineering Project Specifications are based upon design pressure and temperature conditions only, and do not account for other loads. The final design of all flanges shall account for gasket seating and external loads. Differential thermal expansion, including joints between dissimilar materials, and transient thermal conditions such as start-up/shut down and operational upset shall be accommodated.

2) Flanges that are intended for use with spiral wound gaskets shall have a flange surface finish of 125 microinch Ra minimum to 250 microinch Ra maximum. Flanges intended for use with other gaskets shall have a flange surface finish within the optimal range for the specified gasket. Finishes shall be judged by visual comparison with surface finish roughness standards conforming to ASME B46.1. Flange finishes shall be protected from damage during fabrication, heat treatment, shipping, storage, and installation.

• Gaskets shall conform to the requirements of the Inflection Point Engineering Pipe Class specified on the Inflection Point Engineering Piping and Instrument Diagram (P&ID). The applicable Inflection Point Engineering Pipe Class is that specified for the connected piping. When there is no connected piping (e.g., a vessel manway), use the miscellaneous connections Pipe Class specified for the vessel on the Inflection Point Engineering P&ID.

• Gaskets for use with raised face flanges shall be spiral wound, per ASME B16.20, with a non-asbestos filler material. In lined portions of the equipment, the winding material shall be the same as the equipment lining. In unlined portions of the equipment, the winding material shall be a minimum of ASTM A 240 Type 304. Gaskets shall include an outer retainer ring. The outer ring may be carbon steel, protected against corrosion. Gaskets for Class 900 and greater flanges, flanges over 24 inch NPS, and gaskets in vacuum service shall have an inner retainer ring of the same material as the windings. Gaskets with an inner retainer ring shall also be used between flanges of different metallurgies with different coefficients of thermal expansion when they operate at an elevated temperature. The contractor shall verify the adequacy of all gaskets considering potential buckling of the outer or inner retaining ring(s) and the windings.

• The use of corrugated, double jacketed gaskets per ASME B16.20 may be considered for large diameter openings (over NPS 24 inch), especially when the sealing surface is vertical or when the surface to be sealed is not round (e.g., multi-pass exchanger channel to shell closure gaskets).

• Ring joint gaskets shall be per ASME B16.20.

• Ring joint flanges shall have a flat bottom groove with the intersection between the bottom and sides of the groove machined to a smooth 1/8 - inch (3 mm) minimum radius.

• Flanges and bolts shall be analyzed to ensure that they are not overstressed during gasket seating. Overstressing is more likely to occur when Class 300 and lower flanges are used with spiral wound or metal gaskets.

Attachment 2 Accommodation of Applied Loads

The method for determining the required flange class described in this procedure considers only the design temperature and pressure conditions to which the flange is subjected. In addition, the flange may be subjected to applied loads from thermal expansion, weight, expansion joints, and other factors. There are a number of methods available to include the effect of these loads when selecting the required flange class. None of these methods is precise. Often a simple, but conservative, approach is best. One of the most common, and certainly straightforward, methods is to convert the applied loads into an equivalent internal pressure via the following formula:

where

G = Diameter at the gasket reaction

F = Resultant applied axial force, considered to be positive if pulling the flanges apart and negative if pushing the flanges together. Negative (compressive) forces are normally ignored because they increase the gasket sealing pressure.

M = Resultant applied bending moment

In this method, torsion and shear loads applied to the joint are not considered to affect the required flange class, but they do affect the bolts and must be considered when selecting the number, size, and material of the bolts. Normally, the standard bolting is adequate.

The equivalent internal pressure determined by the above formula is added to the design pressure, giving an effective design pressure. The flange class determined from consideration of only the design conditions (temperature and pressure) is rechecked for adequacy at the effective design pressure. If it is adequate, no further work is necessary. If it is not adequate, there are two choices. One is to use a higher flange class that is adequate. Because the equivalent pressure method is very conservative, this may result in unnecessary expense for the higher flange class. A more rigorous analysis of the flange subjected to external loads is generally warranted. The flange class determined from the design conditions (temperature and pressure) will often prove to be adequate.

Attachment 3 Tool Error Messages

The Inflection Point Engineering Flange Class Determination Tool displays the following error messages as pop-up’s, below the point where the required flange class is indicated, or both.

• “Verify that the correct metallurgy and governing Code are selected. If the flange is mating with a ductile iron flange and you have selected “yes” to this question in the input section then a metallurgy selection is not required.”

This message appears if the “Determine Flange Class” button is clicked before the metallurgy, code, or both has been selected. Ensure that a metallurgy and code have been selected and all other input completed; then re-click the “Determine Flange Class” button. Ductile iron is not included in the metallurgy pull-down list, but is covered by the first yes/no input question.

• “The design temperature or pressure is outside the scope of the tables. This flange must be designed per ASME Code”.

The rating tables in the applicable flange standard have an upper temperature limit. They also have an upper pressure limit, as defined by the pressure rating of the highest included flange class at the input temperature. Class 2500 is the highest class included in ASME B16.5. ASME B16.47 includes flanges through Class 900. If either the temperature limit or the pressure limit at the input temperature of the applicable rating table is exceeded, the flange must be designed.

3) “Specific product forms of the selected material have a lower maximum temperature. See the referenced standard for the affected product forms and their temperature limit. Results shown are for the full temperature range of the material category.”

In some cases, all of the materials covered by a specific rating table in the applicable flange standard are not acceptable for use to the table’s maximum temperature. The new lower maximum temperature is noted in a footnote to the table. If this message appears, check if the material used is subject to a lower maximum temperature. If so, and the design temperature exceeds this maximum, the flange must be designed. Materials with a lower temperature limit than the range of the table are identified by an asterisk (*) in the metallurgical list. This note appears only if the input temperature exceeds the limit of any of the included materials.

• “The design temperature is below the range included in the standard. This is acceptable if sufficient material toughness at the design temperature is confirmed. The pressure rating is the same as at the lowest temperature listed in the standard.”

At temperatures below the lowest temperature included in the flange standard’s rating table, brittle material behavior becomes a concern. If sufficient toughness at the design temperature can be confirmed (generally via Charpy impact testing), flange standards allow use of the flange below the lowest listed temperature. They require that the pressure rating be no greater than the rating at the lowest listed temperature.

• “When selecting Carbon or Killed Carbon Steel use the default material listed for typical cases. Only select other materials when you are certain that it is the correct option.”

or

“If you are choosing Type 304L, then you have not chosen the default type. Please verify that your selection is correct”.

When a chemistry is included in more than one material group, the group with the most commonly used product form is identified as the default group. The above message appears when the user selects one of the material groups that does not include the default product form. These groups are to be used only when it is known that the flange is made of one of the included product forms. A wording similar to the above notes is used for other chemistries included in more than one material group.

• “The selected material is not included in ASME B16.47 - Large Diameter Flanges. This flange must be designed per ASME Code.”

The selected material is not included in ASME B16.47; therefore the flange must be individually designed. B16.47 does not include non-ferrous materials. The selected material may be included in B16.5, permitting use of a standard flange for sizes 24 inch NPS and below.

• “The selected material is only available in ASME B16.5-2003”

This material (i.e. chemistry) is not included in the 1996 edition of ASME B16.5, nor is it included in the 1996 edition of ASME B16.47. A flange of this material must be designed if these flange standards are specified. The material is included in the 2003 edition of ASME B16.5.

• “Specific product forms of the selected material are only available in ASME B16.5-2003. See the metallurgical list for the product forms”.

One or more product forms of this material are not included in the 1996 edition of ASME B16.5, nor are they included in the 1996 edition of ASME B16.47. A flange of these product forms must be designed if these flange standards are specified. The product forms are included in the 2003 edition of ASME B16.5

• “Specific product forms of the selected material are only available in ASME B16.5-1996. See the metallurgical list for the product forms”.

One or more product forms of this material are not included in the 2003 edition of ASME B16.5. A flange of these product forms must be designed if these flange standards are specified. The product forms are included in the 1996 edition of ASME B16.5.

10) “Inflection Point Engineering specifies that the maximum temperature for Class 150 is 700 F. Therefore, Inflection Point Engineering requires Class 300 for this case.”

Although the flange standard permits the use of Class 150 flanges for this design temperature, Inflection Point Engineering policy does not. A similar note appears when Celsius temperatures are used.

11) “You are within 15 psi of using a lower flange class. Lowering design temperature or pressure may accomplish this.”

Permitted flange ratings are rigidly followed. If the design conditions are just above the permitted rating of a class, the next higher class is selected. The flange costs will increase. A small adjustment to the design conditions may result in significant cost savings by permitting the use of a lower flange class. A similar note appears when using other pressure units.

12) “Class 2500 is limited to 12” and smaller. This flange must be designed per ASME Code.”

ASME B16.5 includes Class 2500 flange dimensions for sizes through 12” NPS. ASME B16.47 does not include Class 2500. Flanges larger than 12” that would require Class 2500 must be individually designed.

13) “Inflection Point Engineering permits the use of ductile iron only when Class 150 is sufficient.”

Although Class 300 is included in ASME B16.42, Inflection Point Engineering policy, as described by the acceptable design conditions, permits only CL150 ductile iron flanges.

14) “ASME B16.47-1996 covers flanges within the following size ranges: Series B (Inflection Point Engineering Default) [26 in – 60 in Class 150, 300] [26 in – 36in Class 400, 600, 900] Series A [26 in – 60 in Class 150, 300, 400, 600] [26 in – 48 in Class 900]. Flanges larger than the covered sizes must be designed per ASME Code.”

ASME B16.47 does not include flanges larger than 60 inches and does not cover up to 60 inches for all of the covered classes. Flanges outside the scope of ASME B16.47 must be designed in accordance with the governing Code. A few abbreviations are used in the caution message listing to accommodate the limitation on the total number of characters.

15) “The cell or chart you are trying to change is protected and therefore read only. To modify a protected cell or chart, first remove protection using the unprotect sheet command (Tools Menu, Protection Submenu). You may be prompted for a password”.

This is an Excel based error message. It appears if any attempt is made to change input data without clicking on the reset button after completing an earlier calculation. Click on the reset button, rather than follow the Excel procedure to enable modification of input data used for an earlier calculation. Following the Excel procedure will cause the “Determine Flange Class” button to disappear.

16) “Please resave the file after hitting OK to complete programming removal. Use the Save function under the File menu, click on the Save icon, or press Ctrl +S to resave the file. To perform another flange class calculation, the tool must be reopened.”

This is not an error message but is intended as guidance to the user. This procedure clears all remnants of Visual Basic macros from the saved file, leaving only the flange class determination output sheet. Saving output outside of the tool results in exiting from the tool. The tool must be re-entered to perform additional calculations.

Attachment 4 Guidance on Determining the Applicable Code

The user is accountable for selecting the proper code. The tool determines the required flange class based upon the edition of the applicable flange standard referenced by the latest edition and addenda of the selected code. The tool output indicates the flange standard and edition used. If a different edition of the code applies, the user must determine the required flange class in accordance with the procedures of Section 5.2.

Accommodation of potential flange class mismatches due to material or flange standard edition differences, for example where piping and vessels interface, is the responsibility of the Contractor.

Guidance on determining the applicable Code follows. The user is cautioned that special circumstances or rules (e.g., Inflection Point Engineering policies or superceding requirements within the Code) may take precedence over these guidelines.

Instance	Governing Code	Comment
Vessels and some piping that are part of a steam generating system	ASME Section I	The Code contains further guidance on the scope of Section I
Most pressure vessels (design pressure exceeds 15 psig)	ASME Section VIII, Division 1
Vessels requiring a thick shell (over 2 inches) or with a high design pressure (over 1000 psig)	May be governed by ASME Section VIII, Division 2	See Procedure for further information
Steam system piping	ASME B31.1
Process piping (Design pressure exceeds 15 psig)	ASME B31.3
Fired heaters, with the exception of a steam generation section	ASME B31.3	Steam generation sections are governed by ASME Section I
Pumps and compressors	ASME Section VIII, Division 1 or, occasionally, Division 2	See Procedure for further information
Exchangers (shell and tube, air cooled, hairpin, and other types)	ASME Section VIII, Division 1, or occasionally, Division 2	See Procedure for further information
Steam generators	ASME Section I
Instruments	Code that governs the item to which the instrument is attached
Pressure Relief Valves	ASME Section VIII, Division 1 or, occasionally, Division 2	See Procedure for further information
Low PressureTanks	No governing Code	API 620, Section 5.20 requires Class 150 flanges or design per ASME Section VIII
Atmospheric Tanks	N/A	API 650, Table 3-8, provides dimensions for all flanges

When no governing Code applies, where reference is made to the latest edition of the flange standard, or no edition of the flange standard is specified, use the latest edition of the flange standard. Select “No Governing Code” from the Tool pull down list. Low pressure tanks are an example.