UOP Flanges

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(1)Training Services. Flanges. EDS-2004/FL-1.

(2) Purpose . Introduce the common types and uses of flanges, outline the methods to select or design a flange for a given application, describe some of the common reasons for flange leakage, and outline methods for correcting leakage.. EDS-2004/FL-2. The purpose of this presentation is to discuss the common types of flanges and gaskets used in refineries and petrochemical plants. Included is the means used to select an appropriate standard flange for a given service. The means of designing a flange for circumstances where a standard flange cannot be used are briefly introduced. The presentation closes with a discussion of the common causes of and corrections for leakage problems..

(3) Outline . Introduction Standards Materials Flange Selection Flange Facings Gaskets Finishes Flange Design Leakage Causes and Correction EDS-2004/FL-3. The presentation will cover the applicable Standards encountered in the determination of a flange class, materials in terms of product form, specified dimensions of a flange, flanged connection components with their associated tolerances, flange design basis criteria, and some common causes of flange leakage and proposed solutions..

(4) Flanged Joint . . A flanged joint connects piping or equipment by means of bolting, allowing “easy” disassembly and assembly (e.g., valves, instruments, manways) The joint provides a seal against the contained fluid at design conditions –. . Fluid molecule size plays a role (e.g., water is much bigger than hydrogen). A flanged joint is composed of three components -flanges, gasket, and bolts Performance is influenced by another factor, assembly of the joint Because of their cost and the potential for leaks, use flanges only when absolutely necessary EDS-2004/FL-4. The flexibility of a flanged connection comes with a price. The joint is subject to leakage. Providing a seal while maintaining flexibility is the goal of the system design. Fluid molecule size is a factor in determining the difficulty of sealing a joint. It is more difficult to achieve adequate joint tightness to prevent leakage of material with a small molecule size. For example, hydrogen services are common in hydrocarbon processing plants, but are very difficult to seal due to the small size of the hydrogen molecule. Because of leakage concerns (either initially or during service), the use of flanged joints is limited to locations where the ability to easily disassemble the joint is important. Other joints are welded. The contained fluid may be a vapor or a liquid. The design considerations are nearly the same..

(5) Flanged Joint (continued). . . . The gasket provides the seal, bolts provide the forces necessary to seat the gasket and hold the joint together, flanges provide the surfaces for the gasket to seal against and carry the applied forces around the gasket. The joint allows for “easy” disassembly and reassembly of piping or removal of components (e.g., valves and instruments). Because of their cost and the potential for leaks, use flanges only when absolutely necessary.. EDS-2004/FL-5. The gasket provides the seal against the contained fluid. Seating of the gasket involves compressing the gasket so it flows and fills the flange face surface imperfections without being crushed. The resulting seal must be maintained throughout the operating cycle when internal pressure is attempting to separate the flange faces and find a leak path between the gasket and the flange. In elevated temperature services, differential thermal expansion of the joint components and the time dependent effects of creep conspire to create leaks by reducing the forces holding the flanges together. Proper assembly techniques must be observed and alignment of the flange faces must be maintained throughout the operating cycle. Connection by means of bolting allows a joint to be easily and quickly taken apart to accommodate access for installation, removal, maintenance, inspection, or disassembly of a vessel, piping system, or piece of equipment. Examples include vessel manways (for access), valves or expansion joints (for removal or replacement), filters or strainers (to allow removal of the internal element(s)), and unloading nozzles (to allow removal of the vessel contents such as catalyst)..

(6) Stud Bolts with Hex Nuts Gasket. Flange. Gasket – Compressible material providing the seal Bolts – Provide the force to compress the gasket and form the seal Flange – Transmits the force from the bolts to the gasket (must not distort or deflect) PPF-R00-01. EDS-2004/FL-6. A joint consists of two flanges, one on each side of a gasket, and bolts used to squeeze the assembly together. The squeezing force comes from tightening the bolts, which applies force to the opposing flanges. The flanges must remain, essentially, ridged in order to transmit the forces evenly to the gasket surface(s). The gasket is then compressed to provide and maintain the seal. A flanged joint is composed of these three separate and independent, although interrelated, components. Proper controls must be exercised in the selection and application of all three elements to attain a joint which has, and maintains, an acceptable leak tightness. Stud bolts and hex nuts are, by far, the most common bolting configuration. For cast iron flanges, which tend to be brittle, machine bolts are often used because they will fail (break) before the flange.

(7) Flanges . . Flanges may be uniquely designed or selected from standardized designs in a recognized document giving dimensions and pressure – temperature capacities Design methods or standards referenced must be in accordance with the governing code. EDS-2004/FL-7. The flanged system can be uniquely designed for a specific application or selected from industry recognized and accepted standardized code compliant designs. The existence of localized stresses, stress concentrations, and discontinuity stresses of a relatively high order in all pressure equipment is well known. The code accounts for localized stresses by using compensating factors in the design formulas for stress..

(8) Standard Flanges . . Flanges from accepted standards have a proven record of widespread safe, reliable use They are economical because standardized dimensions allow vendors to “tool up” for efficient production Everyone uses the same basis and benefits from economies of scale Users may obtain flanges easily and quickly, and need only stock a limited number of varieties EDS-2004/FL-8. Standardized design avoids the costs and delays associated with customized design and fabrication. Standardized flanges should be used whenever possible. Unique designs are reserved for instances where standard designs are inadequate, e.g. limiting clearance constraints or sizes and design conditions outside of the scope of the available standards. Many flange fabricators have their own “standard” flanges. Taylor Forge’s large diameter Class 175 and Class 350 flanges are examples. The fabricator has the necessary dies and equipment to efficiently produce these flanges, which are not covered by industry standards. These flanges must be checked to insure that they are adequate for the intended service, but significant cost and delivery time savings can be realized if they can be used. Similarly, flanges with industry standard dimensions, but non standard materials, may be suitable. Again, the design must be reviewed for adequacy but, if acceptable, the flange can be easily made with existing dies, etc. Code compliance assures consistent safe engineering practice..

(9) Referenced Standards The following standards are referenced by the Pressure Vessel Code (ASME Section VIII) and the Process Piping Code (ASME B31.3) . ASME B16.5, “Pipe Flanges and Flanged Fittings” Covers flanges from nominal pipe size ½ to 24 inches (12 inches for Class 2500) – Most commonly used standard for refinery and petrochemical plant flanges –. . ASME B16.42, “Ductile Iron Pipe Flanges and Flanged Fittings Classes 150 and 300” –. Used for many ASME pumps (usually in nonhazardous service). EDS-2004/FL-9. ASME (American Society of Mechanical Engineers) Section VIII, Division 1, Pressure Vessels, governs the design and fabrication of the majority of all refinery equipment. ASME B31.3, Process Piping, is the document to which the majority of the piping in a petroleum refinery or chemical plant is designed and fabricated. Flanges must either comply with one of the industry standards incorporated into the applicable Code, or be uniquely designed in accordance with that Code. In most cases, the applicable Code references the design rules/methods in ASME Section VIII, Division 1, Appendix 2 when a special design is necessary. ASME B16.5 is referenced for flange selection by both Section VIII, Division 1 and B31.3. Class 2500 flanges are for use in very high pressure service and have an upper size limit of 12". The concept of flange classes will be discussed later..

(10) Referenced Standards (continued). . ASME B16.47, “ Large Diameter Steel Flanges” Covers flanges from 26 to 60 inches, in Classes 150 through 900 – Range of included materials is more limited than in B16.5 (e.g., few nonferritic materials such as Inconel) –. . ASME B16.20, “Metallic Gaskets for Pipe Flanges Ring - Joint, Spiral - Wound, and Jacketed” –. . Unlike its predecessor, API 601, it does not specify default materials.. ASME B46.1, “Surface Texture (Surface Roughness, Waviness, and Lay)” EDS-2004/FL-10. The scope of ASME B16.47 begins where B16.5 ends. B16.47 covers a more limited range of materials than B16.5 (i.e., no high alloys such as Inconel). Two styles are included. Series A flanges are similar to flanges built to MSS-44, a standard often applied to pipelines. They are designed for connection to relatively thin piping and are limited to a maximum temperature of 450°F. Series A flanges may also be found on valve bodies intended for process services. Series B flanges follow the basis used for B16.5 (and the old API 605) and are used for refinery/petrochemical services. Series B is generally more compact than Series A. It is important to note that Series A and Series B flanges are incompatible, i.e., they cannot be bolted together. The edition of each referenced document that is specified (i.e., accepted) by the governing Code must be used. The referenced edition may not be the most recent edition. B16.20 is the standard covering the majority of gasketing used with B16.5 flanges. These are the gaskets commonly found in refineries and petrochemical plants. B16.20 includes gasket dimensions, materials, marking requirements, etc. B46.1 is referenced in B16.5 and B16.47 and defines the flange face surface finish specifications and tolerances..

(11) Obsolete Reference Standards . API 601, “Metallic Gaskets For Raised - Face Pipe Flanges and Flanged Connections (Double - Jacketed Corrugated and Spiral Wound)” – replaced by ASME B16.20.. . API 605, “Large Diameter Carbon Steel Flanges” – replaced by ASME B16.47.. EDS-2004/FL-11. Both of these are obsolete and are not maintained. These have been replaced by B16.20 and B16.47 respectively..

(12) Scope of ASME B16.5 . Materials Pressure - Temperature Ratings Dimensions Tolerances Marking Testing. EDS-2004/FL-12. Subject areas of B16.5 include acceptable flange materials, pressure-temperature ratings for flange class determination, tables of standardized dimensions (based upon flange class), tolerances associated with different components of a flange, required code compliant marking, and the testing required for flanges..

(13) Materials for B16.5 . . Permissible flange materials are listed in Table 1A, bolting materials in Table 1B Flange materials are organized into groups of materials with similar compositions and mechanical properties Ratings are based upon the material in each group with the lowest allowable stress. EDS-2004/FL-13. Materials tables have been grouped to provide compatible flanged joint ratings for materials likely to be used together. Groups frequently have more than one material covered in a respective group. With ratings based on the material in the group with the lowest allowable stress, ratings for some materials within a group are conservative. Material type is also dependent on product form: forging, casting, or plate..

(14) Materials for B16.5 (continued). . Bolt materials are divided into three groups based upon strength High strength (e.g., A193 B7 or B16) may always be used – Intermediate strength (e.g., A193 B8 Class 2) may be used, provided it has the ability to maintain a sealed joint – Low strength (e.g., A307 and A193 B8 Class 1) is limited to Class 150 and Class 300 flanges and certain gaskets –. . Stud bolts with 2 nuts are typically used EDS-2004/FL-14. Bolts must have adequate strength to be able to both seat the gasket and maintain a seal for the specific application throughout the operating cycle. Low strength bolts are used in the lower Class flange applications, which are generally lower temperature and pressure operating conditions. Stainless steel bolts are avoided because of low yield strength and high thermal expansion. Stud bolts, or bolts without heads and threaded over their full length, are used because they are less expensive and can be safer. A nut is used on each end. Two nuts on each end, tack welding of the nuts, or “spiking” (damaging of the bolt thread just outside of the nut) of the thread may be used to prevent backing off or loosening of the nuts when vibration is a concern. Bolt engagement must be enough so that at least two threads show outside of the nut to ensure full engagement. Otherwise, the bolt may project any distance beyond the nut and either nut may be engaged first, either before or after the bolt is inserted through the bolt hole from either direction. Either nut may be tightened to stress the bolt This provides more flexibility in assembly than a headed bolt. Headed bolts are normally used only with studding flanges (see slide 38) where use of a nut on both ends of the bolt is impossible. Even there, a stud bolt with one nut could be used..

(15) Materials for B16.5 (continued). . Flanges may be either forged or cast Forged flanges are preferred due to a lower likelihood of flaws or brittle material Cast flanges are usually provided as an integral part of cast valves and other components In forged and cast construction, the grain tends to be non-directional or circumferential, limiting the potential for large cross grain stresses. EDS-2004/FL-15. Forged flanges are generally considered to be a higher quality product. Cast material can have inclusions or imperfections that can affect material properties, even leading to brittle (sudden) failure. They are permitted as part of valves and other complex components because casting is the accepted (and cost efficient) method of producing these components, including integrated flanges. Rather than weld a separate flange to the component, the flanges are included in the casting. Welding would be more costly, would impose the potential problems found at welds, may require heat treatment, and would often increase the flange face to flange face length of the component,.

(16) Materials for B16.5 (continued). . Only blind and certain reducing flanges (those without hubs) may be made from plate One reason is that a flat plate closely approximates a blind flange’s shape (e.g., there is no raised hub) Another reason is that the directional nature of the grain in these flanges is not a serious additional concern because there will be cross grain bending stresses in blind flanges regardless of how the grain is oriented. EDS-2004/FL-16. Although plate material is listed in ASME B16.5, there are severe limitations placed upon its use. It is rarely acceptable to make a flange out of plate material..

(17) Flange Classes . Flanges are organized into classes for identification Classes used by B16.5 are: Class 150 Class 300 Class 400 Class 600 Class 900 Class 1500 Class 2500. EDS-2004/FL-17. Classes provide an easy method to identify categories of flanges. The dimensions of each size of flange within each class are standardized. The design pressure and temperature for the flange form the required rating. The rating is used to determine the applicable flange class. Flange class and flange rating are not the same. An example of a flange class is the designation “Class 300”. An example of a rating is 250psi at 300°F. A rating of Class 300 is meaningless..

(18) Flange Classes (continued). . . . Class 150 flanges are lightly built and are often avoided, especially when imposed loads (e.g., from piping) or cyclic loads are present Class 150 flanges are not used above a design temperature of 700ºF because they may tend to deform or creep, possibly opening and leaking Class 400 (and sometimes Class 900) flanges are usually avoided because valves and fittings are not commonly available for them. EDS-2004/FL-18. Class 150 flanges are typically used in low temperature and pressure service where their light weight construction is suitable. They are not suitable for cyclic services or where large imposed loads are present. They are inexpensive and very commonly used in refineries and petrochemical plants. Use of Class 400 may be acceptable for systems that do not contain valves or other components not available in the classification. Consider, however, the need to stock a few Class 400 flanges for these lines. It is often cost efficient to use Class 600 even for these instances to avoid the need to have rarely used spare flanges, gaskets, and bolts in the warehouse. As a practical matter, these spares will probably not be found if and when they are needed..

(19) Flange Classes (continued). . . A rating table is provided for each material group For a given material group, temperature, and nonshock pressure, the table indicates the appropriate flange class Each size flange in each class is built to a standard set of dimensions. EDS-2004/FL-19. Ratings are the maximum allowable non-shock working gage pressure at the design temperature for the applicable material. The appropriate flange class is the class with a pressure rating at the design temperature that is greater than the design pressure. Note that B16.5 and B16.47 each have their own set of rating tables. Although these tables are normally identical, there may be differences - especially just after one document’s tables have been revised. It is possible for a different flange class to be required for the same design conditions because of this difference in the selection tables..

(20) B16.5 Rating Considerations . Ability to withstand stresses necessary to seat the gasket –. . . Special attention is required for some Class 150 and Class 300 flanges with spiral wound gaskets. Adequate thickness to sustain the stresses due to pressure and other loadings necessary to maintain a fluid seal Distortion due to loadings is transmitted through the piping or bolting. EDS-2004/FL-20. Gasket seating is the application of sufficient force to deform the gasket, causing it to flow into and fill imperfections in the flange surface. The characteristics of the gasket and the flange, i.e., hardness and roughness, must be matched to efficiently produce a seal and not deform the flange. During operation, the forces on the gasket are reduced due to the effects of the internal pressure. Enough force must remain to prevent the internal fluid from flowing between the gasket and the flange, i.e., leaking. As previously mentioned, deformation of the flange itself will affect the ability to produce and maintain a seal. The flange must remain stiff and undistorted..

(21) Use of B16.5 Rating Tables . Determine the applicable group for the material used (Table 1A) Determine the design temperature and pressure (including hydrostatic head) that apply. EDS-2004/FL-21. Material group determination includes consideration of the chemical composition and the product form. Pressure can be considerably different at different locations in a vessel considering liquid head and pressure drops. Temperature can also vary throughout a piece of equipment . Use internal pressure (or the external pressure applied as an internal pressure). External pressure is not a concern because it tends to increase gasket seating forces (and/or reduce the bolt force) and does does not “pry” the flange open as much as internal pressure. If determination of the required flange class considers a reduced design temperature for uninsulated flanges, as permitted by the Piping Code (B31.3), the affected flanges must be clearly identified. Future insulation of these flanges is restricted or prohibited..

(22) Use of B16.5 Rating Tables (continued). . . Enter Table 2 and determine a flange class with a pressure rating equal to or greater than the design pressure for the applicable material and temperature Check the flange for hydrotest conditions (including hydrostatic head) with a maximum permitted pressure of 1.5 times the 100ºF rating rounded up to next multiple of 25 psi. EDS-2004/FL-22. The allowance of a hydrotest maximum permitted pressure of 1.5 times the 100oF (ambient) rating is based on the fact that this is a short-term loading condition, and the material properties are in the elastic range. Excluding the effects of hydrostatic head, hydrotest is not intended to govern the design of a flange. Determination of the test pressure involves the same allowable stress ratio (1.5) used to determine the required flange rating for hydrotest. Hydrostatic head may occasionally result in hydrotesting governing the required class. Section 2.5 of ASME B16.5 states; “Flanged joints and flanged fittings may be subjected to system hydrostatic tests at a pressure not to exceed 1.5 times the 100°F rating rounded off to the next higher 25 psig. Testing at any higher pressure is the responsibility of the user, subject to the requirements of the applicable code or regulation .” Section 8.3 requires flanged fittings to be tested at a minimum pressure of 1.5 times the pressure rating at 100°F, rounded up to the next multiple of 25 psig..

(23) Use of B16.5 Rating Tables (continued). . If the flanges are made of different materials, both must be checked –. . The highest resulting flange Class governs both flanges. Interpolation is permitted between the listed temperatures. EDS-2004/FL-23. Be sure to consider both flanges used in the system - the metallurgy's may differ. One example is a thermowell connection. The thermowell assembly, including the flange, is usually made as one piece using stainless steel. The flange may be paired with a low chrome or carbon steel flange on the vessel. The required flange class for both metallurgy's must be checked, and the greater class used. This may be a different class than is necessary for the remainder of the vessel!.

(24) Use of B16.5 Rating Tables (continued). . . Flanges used to be designated by “Pound” rather than “Class” (e.g., 600 Pound). Previously, this referred to the pressure capacity of a carbon steel flange at 850ºF (500ºF for 150 Pound). This is no longer true; therefore, the word Class is used and, except as noted below, the number is only an identifier.. EDS-2004/FL-24. The “pound” designation has a historical origin based on the empirical testing method development that equated a class with a certain allowable pressure at a standardized reference temperature..

(25) Use of B16.5 Rating Tables (continued). . Rating table pressures for Class 300 and above are based upon the formula: PT = PR x SI / 8750 ≤ PC where:. PT = rated pressure (psi) PR = Class (e.g., 300 for Class 300) SI = material allowable stress at temperature (psi), determined from the rules in Annex D of B16.5 PC = ceiling pressure per Annex D of B16.5 EDS-2004/FL-25. The allowable stresses used are not exactly as listed in other Codes (e.g., B31.3 or Section VIII)..

(26) Use of B16.5 Rating Tables (continued). . . Rating table pressures for Class 150 comply with the formula on the previous slide, except use 115 for PR and limit PT to 320 - 0.3T (T = temperature in ºF) B16.5 ratings originated with experience and were essentially empirical Recently (1996), the ratings have been revised to agree more closely with the formulas. EDS-2004/FL-26.

(27) Class 300 Temperature - Pressure Ratings Material Temp (ºF). 2 ¼ Cr - 1 Mo (psi). 321 S.S. (psi). 100 200 300 400 500. 750 750 730 705 665. 720 645 595 550 515. z z z. z z z. z z z. EDS-2004/FL-27. For each respective material, as the temperature increases, the allowable stress decreases and, accordingly, the allowable pressure (pressure-temperature rating) decreases. This trend of a decreasing allowable stress with an increasing temperature is the same for both materials. However, the magnitude of the decrease is different and dependent on the respective material composition and mechanical properties. Different materials have different capacities at the same temperature. Note that, below the creep range, the allowable pressure for stainless steel flanges declines more rapidly than for low alloy (or even carbon steel) flanges. This is because stainless steel is softer and more ductile than most other materials, hence, it may be more easily deformed and leak..

(28) Class 300. PPF-R01-02 EDS-2004/FL-28. This figure illustrates the decline in allowable pressure with temperature in a graphical form. Stainless steel ratings are generally lower than for many other materials..

(29) Example . Material SA182 - F11 class 2 (1¼ Cr - ½ Mo) Design Pressure PD = 400 psig Design Temperature 1000ºF Allowable Stress (per the Pressure Vessel Code) @ 1000ºF SH = 6,300 psi @ ATM. SC = 20,000 psi Use Class 600 Flange EDS-2004/FL-29. A182-F11 Class 2; Low Chrome (1-1/4 Cr - 1/2 Mo) Forging material -- Use ASME B16.5 material group No. 1.9 to select the required flange class. Allowable stresses at temperature are taken from the governing Code, in this case, the ASME Boiler & Pressure Vessel Code, Section II, Part D - Properties; Table 1A, Maximum Allowable Stress Values S for Ferrous Materials. Allowable stress values are used for the check of hydrotest conditions..

(30) Check for Hydrostatic Test Pressure PT = ( 1.3 ) PD ×. PT = ( 1.3 ) 400 ×. SC SH 20,000 6 ,300. ∴ PT = 1,650 psi < 2 ,250 psi 1,500 * 1.5 Allowable Pressure @ Ambient EDS-2004/FL-30. The purpose of the hydrotest is to confirm the adequacy of the piece of equipment for the service conditions by performing the test at an inflated (elevated) pressure and ambient conditions. The objective is to get to a similar relative stress level (i.e., stress vs allowable stress) as that seen during operation (which has a higher design temperature and lower design pressure), in a controlled, safe, test environment at the low temperature ambient conditions. At the higher design temperature, the material has a lower allowable stress. At the ambient test conditions, the material has a higher allowable stress which is used to adjust the pressure to approach the relative stress level present at operating conditions..

(31) Flange Material: A B C , SA182-F11 class 2 (1¼ Cr - ½ Mo) D , SA182-F316 (16 Cr-12 Ni-2 Mo). B A. Design Pressure: PD = 850 psi Design Temperature: T = 850°F Allowable Stress (per the Pressure Vessel Code): A182-F11 @ 850°F : SH = 18,700 psi @ ATM. : SC = 20,000 psi A182-F316 @ 850°F : SH = 11,600 psi @ ATM. : SC = 20,000 psi For A & B, Use Class 600 For C & D, Use Class 900. C. D. PPF-R00-03 EDS-2004/FL-31. A182-F11 Class 2; Low Chrome (1-1/4 Cr – ½ Mo) Forging material -- Use ASME B16.5 material group No. 1.9 for selection of the required flange class. Allowable stresses at temperature are taken from the ASME Boiler & Pressure Vessel Code, Section II, Part D - Properties; Table 1A, Maximum Allowable Stress Values S for Ferrous Materials. A182-F316; Stainless Steel Forging material -- Use ASME B16.5 material group No. 2.2 for selection of the required flange class. The class of the low chrome flange C is increased to match the Class 900 required for the mating stainless steel flange D. By itself, the pressure-temperature rating of the low chrome flange C for Class 600 would be acceptable. In this case, the higher resulting flange class of the mating flanges governs both flanges. This is necessary so that the bolt size and locations for the two flanges match, and the sealing surfaces and gasket requirements are compatible..

(32) Check for Hydrostatic Test Pressure. PT = (1.3) PD ×. SA 182-F11 PT = (1.3) 850 x. SC SH. 20,000 18,700. PT = 1,182 psi < 2,250 psi. EDS-2004/FL-32.

(33) Check for Hydrostatic Test Pressure (continued). SA 182 - F 316 PT = (1.3) 850 ×. 20,000 11,600. PT = 1,905 psi < 3,250 psi 2,160 * 1.5 Allowable Pressure @ Ambient EDS-2004/FL-33.

(34) Flange Types . Integral Flanges (flange is part of or buttwelded to the piping or vessel so the system acts as an integral structure) – – – – – –. Welding neck Long welding neck Integrally reinforced Ring Studding Specialty joints such as exchanger closures. EDS-2004/FL-34. This classification covers types of construction where the flange is integral (i.e., part of the same piece) with the neck or vessel wall, butt-welded to the neck or vessel wall, or attached to the neck or vessel wall by any other type of welded joint that is considered to be the equivalent of an integral structure. In welded construction, the neck or vessel wall is considered to act as a hub. The whole system acts as one..

(35) Integral Flanges. Welding Neck. Weld Neck. Ring PPF-R00-04 EDS-2004/FL-35. Welding neck is the most common type of an integral flange. They are designed so that the outside diameter at the junction to the pipe matches the outside diameter of the joining pipe. The inside diameter must be specified. They are used where joining to a pipe. Ring weld is a ring butt-welded onto the end of a pipe. This is typically used only in low pressure service..

(36) Integral Flanges (continued). Long Welding Neck. PPF-R00-05 EDS-2004/FL-36. Long welding neck flanges are usually dimensioned by their inside diameter. The outside diameter varies with their wall thickness. They are one piece nozzles that provide much of the required reinforcement for the vessel opening in their neck. Because their dimensions do not match those of standard pipes, they are not suitable for welding to a pipe. They are normally welded to the vessel and used where control of the inside diameter is important. Two examples are manways and small nozzles through which instruments are inserted. They can use a constant ID and a varying OD because they do not attach to a pipe, hence they do not need to match a pipe’s OD..

(37) Integral Flanges (continued). Allow room for the nuts on the bolts (bolts are removed through the mating flange). Integrally Reinforced PPF-R01-06 EDS-2004/FL-37. These flanges have a thick nozzle neck. The reinforcement for the vessel opening is integral to the flange. The reinforcement is provided by thickening the nozzle neck, sometimes to a greater dimension than the outside diameter of the flange itself! The thick hub makes them unsuitable for connection to piping. Therefore, they are dimensioned by their inside diameter for the same reason as a long welding neck flange, and welded directly to the vessel. Integral reinforcement is preferred over built-up pad reinforcement for several reasons: • • •. •. The reinforcement is concentrated near the nozzle/shell junction, where local stresses are at their maximum The reinforcement is one piece, stresses and forces do not transfer from piece to piece across welds There are far fewer welds to make. Welds are costly, are prone to flaws, create residual thermal stresses, create heat affected zones with related metallurgical concerns, and can cause warpage of the joined pieces. There is no flange to pipe weld. This weld would be in a high stress zone caused by the flange rotation and local stresses , as the bolts are tightened.. On the other hand, integral nozzles are machined from a large forging, itself an expensive undertaking.

(38) Flared Nozzle. R Weld. PPF-R00-94 EDS-2004/FL-38. Often a “flare” is provided at the base to move the vessel/nozzle weld away from the stress concentration zone at the junction of the shell and nozzle. This places the stress concentrations due to geometry and stresses due to welding at different locations. The detail also allows a contoured, controlled junction geometry to be more easily provided because the transition is part of the forging, not the weld. Additionally, the “flared” detail provides the needed clearance to adequately radiograph the welded joint.. Although a clearly better detail than a conventional integral nozzle, flared nozzles are more costly than conventional integral nozzles. The differential becomes greatest when the flared portion extends beyond the flanged portion. This requires an increase in the initial forging size and additional machining to arrive at the required geometry. UOP uses the flared detail in high temperature services (i.e., the creep range of the material) where differing stresses and creep rates may redistribute (and concentrate) stresses to the weld. Significant cracking has been detected in services such as catalytic reforming. Flared nozzles are also used in high pressure, heavy wall (greater than 4 inches (100 mm)) services. Here the stresses are high and it’s difficult to ensure the proper material properties throughout the thickness. The ability to radiograph the joint is also important. Cyclic or fatigue services are another instance where UOP uses a flared nozzle detail..

(39) Integral Flanges (continued). Studding. PPF-R01-07 EDS-2004/FL-39. These flanges set into a vessel head or shell where clearance is critical. The design allows for compact installation applications. They are dimensioned by their inside diameter. This type of flange allows a low projection from the mating vessel shell. Often this design includes the nozzle reinforcement as part of the flange. When determining the flange dimensions to provide sufficient opening reinforcement, the effect of the bolt holes must be considered because they project into the area providing the reinforcement. A danger with this type of nozzle is that the bolt engagement is within the flange and is not visible. Use of a short, or wrong diameter, bolt is not visually apparent. A flange failure due to insufficient thread engagement is possible. When stud bolts are used with a through bolted flange, a short bolt is easily seen. A small diameter stud bolt may be seen by comparison with the bolt hole. If the bolt size is still adequate, nuts of the proper size may be used and the bolt will be fully engaged and will work. The thread size in a studded outlet cannot be adjusted to fit a bolt of the wrong size (e.g., only the tip of the threads may be engaged). UOP uses studded outlets only where there is a severe space or clearance problem in a low pressure service (e.g., CCR’s)..

(40) Flange Types . Loose Flanges (no direct attachment between the flange and piping or vessel, does not act as one integral structure) Slip-on – Lap joint –. . Blind Flanges (closures) –. Flat, solid discs used to close an opening (e.g., a manway cover). Generally thick because they are flat, spanning the opening like a beam, developing through thickness bending moments EDS-2004/FL-40. Loose flanges cover types of flanged construction where there is no direct attachment between the flange and the pipe, neck, or vessel wall and where the means of attachment between the flange and pipe, neck, or vessel wall is not considered to be equivalent to an integral structure. In these cases, the pipe, neck, and/or vessel wall has less influence upon the response of the flange to applied and pressure loadings than in an integral design..

(41) Loose Flanges. Vent. Slip-on. Lap Joint PPF-R01-08 EDS-2004/FL-41. A lap joint flange rests on the lap or stub of the piping. Slip-ons slide onto the end of a pipe and are welded to the pipe, usually after the flanges are bolted together. Slip-ons provide some ability to adjust the axial location of the flange. They are limited to low pressure, non-hydrogen, services with no applied moments or forces. Both types of flange may be rotated in place so that the bolt holes of the mating flanges line up. This is not possible with welded in place welding neck flanges (unless the butt welds are made insitu)..

(42) Types of Flange Facing Flat Face. Inexpensive Used with a full face gasket in low temperature/pressure services Easily sealed (i.e., containment of large molecules), non-dangerous, noncyclic services that require low bolt loads and sealing pressures ASME non-process pumps and utilities such as cooling water are examples . PPF-R00-09 EDS-2004/FL-42. This style of flange may be used in refineries for low pressure utility lines and low pressure/temperature process services where ASME pumps are acceptable. This is especially true when the pumps are cast iron, which tends to be brittle. Flat face flanges and full face gaskets are used to reduce the imposed bending moment stresses by moving the bolt force and resultant gasket force closer together. Tightening of the bolts is likely to deflect the flange surfaces towards each other. This causes a non-uniform application of load to the gasket, possibly interfering with the ability to seat and/or seal the gasket. If the deflected flanges contact each other, a portion of the bolt forces will transfer directly from one flange to another without further seating/sealing the gasket. The large gasket surface area, coupled with the limited force available from the bolts, means that the gasket seating/sealing stress that can be achieved is limited. Therefore, these flanges are not applicable for gasket systems requiring “high” seating or sealing forces..

(43) Types of Flange Facing Tongue and Groove. Mating flanges are different - one with a 3/16 inch recess, the other with a ¼ inch raised portion The gasket is confined on both edges and partially protected from the internal environment The projecting sealing surface is subject to damage Reduced bolt load when compared to raised face, due to the smaller gasket area . PPF-R00-10 EDS-2004/FL-43. The gasket is contained in the mating flange’s groove. A potential detriment to this type of flange facing is that the small protruding portion on one of the flanges can be subject to damage during handling, reducing or destroying the ability to subsequently effect a seal..

(44) Types of Flange Facing Male-Female. . . . Similar to tongue and groove except the gasket is confined only against blowout The sealing surface is not protected from the internal environment Projecting portion is larger and less likely to be damaged than on the tongue and groove style. PPF-R00-11 EDS-2004/FL-44. Blowout is the internal pressure force that directionally acts to push the gasket radially outward. Although the projecting portion of the flange is much sturdier than on the tongue and groove type, it can still be damaged. Even a radial scratch will affect sealing..

(45) Types of Flange Facing Lap Joint. . Stub end fitting. . Allows use of a different metallurgy for the flange than for the piping Is not welded Avoid in cyclic or services other than low pressure Compensates for some misalignment Limit to low temperature services to avoid differential thermal expansion problems Sealing may be more difficult because the flange and sealing surface (stub) are independent PPF-R00-12 EDS-2004/FL-45. Because the flange rests on the lap (stub end) of the piping, it does not see the internal service fluid. This potentially allows different materials to be used for the flange and pipe/stub. The flange may be a lower grade of material (e.g., low chrome) that is acceptable for the temperature and pressure, but not the internal atmosphere. A higher grade piping material (e.g., Inconel) is required because it is directly exposed to the corrosive environment. Very significant cost savings can be realized in these cases if this style of flange is acceptable. Lap joint flanges are limited to low pressure, non-cyclic services where there are no external loads. These flanges are subject to severe distortion because the end of the hub is not restrained. Distortion or flange rotation under imposed loads or during gasket seating is likely and can reduce the seating and sealing pressures on the gasket, leading to leakage. Differential thermal expansion between the flange and the pipe can also pose a big problem. The differential expansion may be due to differing coefficients of thermal expansion between the two materials, and/or differing temperatures because the flange and stub are not directly connected, thereby limiting heat transfer..

(46) Types of Flange Facing Slip-On. . Vent. . . Allows adjustment of the flange position(s) in situ Must be double welded and vented Not used above Class 150 (except for manways and some reducing flanges) or 500°F Not used in hydrogen atmospheres and cyclic services. PPF-R02-13 EDS-2004/FL-46. The enclosed space between the flange and the pipe must be vented to relieve any trapped vapor. The vapor may come from gasses released during welding, or may gather from diffusion of the contained materials through the pipe or weld into the open space between welds. There, it can combine into molecules too large to get out. Hydrogen is a prime example of this phenomenon. If not vented, the trapped gas can crack the welds. Hydrogen accumulation may also cause blistering and hydrogen embrittlement. The system depends upon a couple of fillet welds to hold it together and prevent leakage between the flange and the pipe. Thermal stresses, piping movements, and the forces/moments developed when the flange is bolted together can damage, even break, one or both of the welds, permitting leakage, and/or rotation of the flange, reducing the gasket sealing forces also leading to leaks. UOP restricts the use of slip-on flanges to Class 150 in low temperature (<500°F), noncyclic, non-hydrogen, services that are not subject to severe corrosion or external loads and do not require postweld heat treatment due to process or material characteristics. This is because of their poor fatigue life, potentially large distortions and internal stresses, and susceptibility to thermal cracking at the fillet weld attachments due, in part, to the stress concentrations at the notch at the edges of the fillet welds. Externally applied loads are also a concern because a pair of fillet welds does not provide the smooth stress flow or dependability of a butt weld. The fillet welds are also small, limited by the pipe and flange hub thicknesses, and subject to stress concentrations, undercuts, and cracking at the inside base. This area cannot be inspected, backgouged, or ground. Inspection of the fillet welds is difficult at best. Cracking or internal corrosion cannot be seen..

(47) Types of Flange Facing Ring Joint. . . . The gasket is confined within grooves provided in the mating flange faces Historically used for high pressure, high temperature services, or aggressive operating conditions Expensive. PPF-R02-14 EDS-2004/FL-47. Most commonly used in very severe or aggressive service. The confined gasket will not be displaced by high internal pressures, and tends to be self sealing. A higher internal pressure forces the gasket more tightly against the outer portion of the groove, increasing the seal at that point. Because of their infrequent, specialty use (requiring stocking of a few flanges and gaskets not generally used in the plant), the drawbacks and other points noted on the following slides, and experience that shows other flange and gasket styles (notably raised face with spiral wound gaskets) are as safe and reliable, ring joints are being specified and used less frequently. Still, some refiners mandate their use because of their self sealing characteristics and their intrinsic resistance to blow out. Ring joint flanges are expensive. Both flanges must be machined to create the grooves in the respective flange. The grooves in mating flanges must align with each other. The height of the raised portion of the flange must be such that the groove does not project into the portion of the flange relied upon to carry the imposed stresses. Unlike male and female and tongue and groove flanges, both mating flanges are identical..

(48) Ring Joint Flanges . . . The seal is provided by pressure against the sides of the groove (the gasket does not contact the bottom of the groove) Two narrow sealing surfaces are formed, one on each side of the groove, with very high imposed stresses One sealing surface is protected from the internal atmosphere and possible corrosion The sealing surfaces are small and sheltered, protecting them from damage (e.g., when the flange is open(ed) during a turnaround) EDS-2004/FL-48. The seating surfaces for the gasket are small, resulting in very high seating pressures (high unit load per surface area). The gasket seals along a line on either side of the groove. An added advantage is that the outside sealing surface is isolated from the possibly damaging effects of the internal atmosphere (e.g., corrosion). The recessed groves are also less likely to be damaged when the flange is exposed or handled, although foreign material (e.g., dirt, moisture) can gather in them and must be thoroughly removed before the flange is closed. Cleaning is necessary for any flange; it is even more critical for ring joints. Because of the small, narrow, sealing surface, debris or damage (e.g., scratches) on the surface will have an even greater effect. The gaskets are typically a soft metal material (e.g., iron) suitable for the internal atmosphere. Good resulting seal with applications for hydrogen service and high pressure service..

(49) Ring Joint Flanges (continued). . Internal pressure tends to increase the sealing pressure on the outside of the gasket Due to flange distortion during operation, the groove, and the gasket contained in it, may become non circular –. . The gasket cannot then be (easily) replaced with a new one. Grooves have flat bottoms Flat is used to insure the gasket touches only where desired – Groove dimensions are standardized in B16.5 and identified by a groove number –. EDS-2004/FL-49. The gasket behaves like a self actuated gasket. In other words, higher contained pressures increase the gasket seal by pressing the gasket against the side of the groove. During regular service, flanges tend to distort, even on a small scale, which can be a maintenance concern causing difficulty replacing the gasketing..

(50) Ring Joint Flanges (continued). . . A generous radius (1/8 inch or 3mm) is provided at the intersection of the flat bottom and the sloped sides to prevent initiation of a crack Where differential expansion occurs, do not use for flanges over 10 inch NPS Very sensitive to scratches in the sealing area of the grooves Grooves must be machined into the flange – an additional cost Grooves of mating flanges must match each other and the gasket EDS-2004/FL-50. The junction of the groove side and bottom is a discontinuity which results in stress concentrations. The junction is susceptible to cracking, with cracks observed to extend deep into the flange body. UOP specifies a larger radius for the corners of the groove than is required by B16.5 to reduce the stress intensification at this location. Different mating flange materials thermally expand at different rates, offsetting the grooves and setting up a shearing of the gasketing. The limitation on flange size (10-inch) keeps the magnitude of the differential movement within acceptable bounds. Because of the very small width of the sealing surface (little more than a wide line), and the fact that ring joints are most frequently used for elevated pressure systems, even a small scratch can allow leakage around the gasket. As noted earlier, the flange must be thick enough that the groove depth does not infringe upon the portion of the flange considered to be carrying the stresses. This may require a thicker flange than necessary for other types of flange facings. Another potential concern is that small amounts of process fluid may remain in the groove, a potentially dangerous situation when the flange is opened..

(51) Types of Flange Facing Raised Face. The sealing surface is raised 0.06 inch (1mm) for Class 150 and Class 300 flanges and 0.25 inch (6 mm) for other flanges Raised faces help prevent contact of the flange edges due to rotation from high bolt loads The most common type of facing in refineries The sealing surface is exposed and susceptible to damage when opened during a turnaround . PPF-R00-15 EDS-2004/FL-51. Raised face flanges are the most common type of refinery/petrochemical flange. The protruding portion of the flange is the raised face. There are standard dimensions to the raised faces and the associated tolerances are specified in B16.5. The raised face concept arose from the rotation problem discussed for flat faced flanges. Using a raised, or protruding, sealing surface moved the flange extremities, where the bolt forces are applied, further apart. If the flange did deform a bit, the increased separation kept the flanges from coming into contact. The raised face also adds a bit more metal to the flange, increasing its bending stiffness. Flanges with raised faces are extensively used because of their simplicity of design and they are adequate for average and most severe services. Gasket replacement is simple because the gasket rests on the flat, raised surface. It does not need to fit into a groove, which may become distorted, or otherwise align with any features of the flanges. Another useful feature is that the two flanges are identical, they are not a matched pair. This eases the warehousing problem. In a few instances, a groove has been machined into one of the flanges into which a thicker gasket was placed. The idea is to provide gasket confinement or retention, as well as a somewhat self actuating performance. This has been viewed as a safety enhancement. Unlike tongue and groove or male/female flanges, there is no projecting portion of the flange to be damaged by handling. On the other hand, the flanges are no longer identical, the gasket has to be thicker, and it cannot have inner or outer stiffening rings. The thicker gasket is more compressible and more difficult to seal. All in all, this design has not achieved wide usage. The gasket styles normally used provide blow out resistance, eliminating the groove’s perceived benefit..

(52) Specialty Types . Generally developed to make the joint smaller and lighter Normally proprietary and, therefore, more expensive May be less tolerant of mis-alignment and applied forces Components are matched and may not be interchangeable. EDS-2004/FL-52. Because of the added cost and the need to stock non standard components in the plant warehouse, specialty flanges are used only where they provide a significant advantage. Two of the most common uses are where space and access are limited, requiring either a smaller flange or a different joining (bolting) method than is used for the typical flange, and for systems requiring rapid assembly and disassembly..

(53) Specialty Types (continued). . Examples are: Dur O Lok • Uses a coupling style system with a self energized gasket – Graylock • Clamping style system using two clamps with the bolts oriented parallel to the piping diameter –. EDS-2004/FL-53. There are many other types of specialty flanges..

(54) DUR O LOK Couplings ®. Changing the Load Path Reduces Size and Eliminates Leaks 10-1/2" Dia.. 4-3/4" Dia.. Small offset in load path and multi-grooved couplers insure positive gasket seal and consistent assembly dimensions under all conditions.. Large offset in load path leads to leakage under stress, temperature changes and bolt relaxation.. Load path through a bolted flange.. Load path through DUR O LOK coupling.. Three Inch Class 300 Joint. PPF-R01-16 EDS-2004/FL-54. A full encirclement multiple-groove design distributes the holding force around the entire pipe perimeter without excessive stress concentration. The load path through the flange is nearly straight, minimizing the bending imposed on the system. The offset bolting used for standard flanges creates large internal bending loads. The compact design reduces cross-sectional area by 60% compared to flanges -- twice as many lines can fit in same rack space Weight is as little as one-tenth that of a standard flange, saving material, transportation, and support costs. Boltless, threadless design means pipelines can run close to walls or to each other because wrench swing room is not a factor. Assembly and disassembly is faster and easier. Good for low pressure drop services and catalyst transfer (there is no inner “lip” to create catalyst fines). Also good to reduce the turbulence caused by the internal ledges of conventional flanges. The components are supplied as a matched set and may not be interchangeable. With Dur-O-Lok flanges, the piping must be assembled with a near perfect fit because it is not possible to use the bolts to pull or bend the system into alignment. They are also not suitable where external loads and moments are imposed. Dur-O-Loks are currently available through 20-inch NPS. Larger flanges are possible, but the manufacturer is not set up to make larger flanges..

(55) DUR O LOK Couplings ®. Tapered Retaining Ring Split Coupler Lock Device & Assembly Prover Hub. Seal Cavity. PPF-R00-17 EDS-2004/FL-55. The smooth interior surface with no lips, edge, or burrs prevents damage to catalyst during transport, prevents leaks in liquid service. The interlocking grooves transmit forces evenly across the seal cavity to provide dimensional stability..

(56) DUR O LOK Couplings ®. Tapered Retaining Ring Hub Self energized Seal Split Coupler. Seal Cavity Multiple Matched Grooves Split Coupler Lock Screw Groove Hub. PPF-R00-18 EDS-2004/FL-56. This Dur-O-Lok Coupling has a simple, 7-part (counting the locking device) assembly process. A standard ASME flange has bolts, each with a nut on each end, two flanges, and a gasket. The Dur-O-Lock assembly process is easier than a standard flange - there is no concern with the order or amount of bolt tightening. The self energizing seal uses the internal pressure to add to the sealing force. Orings are used for low temperatures (up to about 450°F) and a proprietary design is used for more elevated temperatures..

(57) Grayloc Assembly Seal Ring (Install Prior to Start-Up). Grayloc Clamp Half (Typical) Bolting Centerline 4-Places (Typical). Grayloc Hub beveled for attachment to piping. Temporarily Installed Gasket Plate. Do not remove until welding of hubs to piping is completed and seal rings are ready to be installed. (Save for future use.). "O" Ring. Valve. Grayloc Hub. Studbolt (Typical) Studbolt Nut. PPF-R04-19 EDS-2004/FL-57. The hubs are clamped together and then bolted. This design uses far fewer bolts than a standard flange. The bolts are oriented perpendicular to the pipe axis. The standard flange bolt orientation is parallel to the pipe axis. As with the Dur-O-Lok, this is an easy system to assemble and disassemble, and it requires less space than a traditional flange. There must, however, be bolt removal clearance perpendicular to the pipe, and the two sides of the connection cannot be pulled into alignment by the bolting process..

(58) Gaskets . . Gaskets create a static seal between two members of an assembly and maintain the seal during operating conditions that may fluctuate The seal is provided by gasket material flowing into imperfections in the mating surfaces The force to effect the seal is provided by the bolting compressing the gasket. EDS-2004/FL-58. Gaskets are the component of a flanged joint that provides the seal against leakage. Compression of the gasket is introduced by bolt-up of the flange, causing the gasket to “flow” and fill the irregularities in the flange surface. This is called seating the gasket. The force must not be too high, however, because it can crush the gasket. The compressive force is applied perpendicular to the face of the gasket. The gasketing flow characteristics and the amount of force/stress needed to seat the gasket are dependent on the gasketing material..

(59) Gaskets. (continued) . . . Sufficient initial force is necessary to deform the gasket into the imperfections, thus “seating” the gasket For gasket design, the necessary compressive stress depends upon the gasket style and materials and is called “Y” Sufficient force must be present during operation to maintain the seal against the internal pressure, preventing leakage For gasket design, the required ratio of gasket compressive stress to internal pressure depends upon the gasket style and materials and is called “M” EDS-2004/FL-59. Different types and styles of gaskets have unique flow characteristics. The force to seat the gasket is the stress in pounds per square inch required to compress or deform and flow the gasket material. Sufficient force must also be maintained during operation to seal against internal pressure. The magnitude of this net force is quantified by a ratio termed “M” as described above. The stress on the gasket will be reduced during operation because the internal pressure tends to try to force the flanges apart. Resisting this force uses some of the force imposed by the bolts, leaving less available to compress the gasket..

(60) Gaskets. (continued). . “Y” and “M” have no theoretical basis but are empirical, developed from experience. Gasket material must be suitable for the temperatures, pressures, and environment to which it is exposed. Gasket filler material was asbestos, now it’s generally graphite or, sometimes, Teflon or another non-asbestos, compressible material. Teflon is generally used in acid services below 400 ºF.. EDS-2004/FL-60. Asbestos was used for years in nearly all services. Asbestos has excellent resistance to nearly every conceivable refinery atmosphere and flowing stream content and is suitable for use at all temperatures encountered in these plants. However, in the past 10 or 15 years, health concerns related to the inhalation of asbestos fibers have reduced its use. Graphite is now a commonly used filler material. It is inert in a reducing atmosphere up to 3000°F; however it has a limitation of 850°F in an oxidizing atmosphere. Teflon is also resistant to the great majority to atmospheres in refineries, but it is only good for low temperature service, up to about 450°F. Many other proprietary materials are available, most of which are tailored for a specific application or set of circumstances. These materials are a complex combination of components and binders and are not suitable for services outside of those for which they were developed. If used in other services, they may fail very rapidly..

(61) Representative “M” and “Y” Values. Spiral Wound Corrugated & Jacketed Flat & Jacketed Ring Joint Flat Face Asbestos Elastomers Metal. “M” 2.5 - 3 2.5 - 3.5 3.25 - 3.75 5.5 - 6.5. “Y” (psi) 10,000 2900 - 6500 5500 - 9000 18,000 - 26,000. 2 - 3.5 1 - 2.75 4 - 6.5. 1600 - 6500 400 - 3700 8800 - 26,000. EDS-2004/FL-61. Spiral wound gaskets are the most commonly used. Ring joints can be seen to require a large seating force (“Y”) and must also maintain a large compressive stress vs contained stress ratio. Because they are most often applied to high pressure services, the large “M” value (5.5 - 6.5) means the sealing stress must also be very high. This can may make it more difficult to maintain a seal during operation when using a ring joint gasket than with other types of gasket. This is not usually a concern because the required seating stresses (“Y”) are very high to begin with and the sealing area is small, resulting in continuously high stresses. Neither “M” nor “Y”values have theoretical standing, and those now in use are based on practical experience and some formal experimentation..

(62) Types of Gaskets Flat Face. Metallic Nonmetallic Corrugated Metal. Covers most of the face to minimize flange rotation and possible contact Low seating stresses due to the large gasket area Used only in limited, non-hazardous services Nonmetallic gaskets are made of a suitable, compressible material held together with a binder. Asbestos was common, most are now proprietary materials PPF-R00-20 . EDS-2004/FL-62. Flat ring gaskets are widely used wherever service conditions permit because of the ease with which they may be cut from flat sheets and installed. With a large seating surface, the seating load is spread over a large area and, as a result, it is difficult to obtain a high sealing pressure and “solid” seal. Therefore, these gaskets are used for low pressure services and services where small leakage is not a hazard (e.g., water and air). They are also used where piping joins to an ASME pump (used only in low pressure/temperature services) with a flat face flange..

(63) Types of Gaskets Jacketed and Filled. Jacketed Double Jacketed Corrugated Double Jacketed This was the standard refinery gasket Still common for large diameters and applications with more than circumferential sealing surfaces Soft compressible filler material is contained within a thin “wrapper” Corrugations provide the seal, and a labyrinth leak path . PPF-R00-21 EDS-2004/FL-63. The outer “wrapper” on a jacketed gasket makes the gasket more rugged by protecting the soft inner material from damage. It also provides some resistance to blow out. Corrugated jackets are more rugged than flat jackets because the deformations add strength to the system. They also can provide a better seal because the sealing force is concentrated at the peaks of the corrugations; it is not spread over the gross surface of the gasket. The “labyrinth” path referred to means that it is a complex path with a lot of twists and turns, difficult to pass through. If the fluid finds its way past one corrugation, there is another waiting. Jacketed gaskets, especially the corrugated style, require less seating force than spiral wound gaskets. This type of gasket is sometimes used in large diameter, often low pressure applications, where a spiral wound gasket may tend to unravel or “spring” apart during handling. The problem is particularly acute for vertical sealing surfaces. When the spiral wound gasket is removed from its backing cardboard, it’s quite unstable. For a horizontal sealing surface, the gasket can lie atop one of the flanges. Regeneration Tower body flanges and large diameter access openings on FCC Reactor and Regenerators are examples of where they are used. Jacketed gaskets are also used for specialty exchanger gaskets, such as channel gaskets that also seal at the baffle between passes. It would be difficult, if not impossible, to wind a spiral wound gasket to include the diametrical piece..

(64) Types of Gaskets Kammprofile. . A serrated metallic filler sandwiched between two layers of sealing material Upon bolt-up the sealing material deforms into and is held by the serrations Seal stress is concentrated at the peaks of the serrations, while the valleys prevent the sealing material from flowing Metallic filler can be reused Becoming more popular, especially in Europe PPF-R00-22. EDS-2004/FL-64. The serrated filler is fabricated of solid metal and has concentric grooves machined into the faces. This greatly reduces the gasket contact area on initial tightening, thereby reducing the total required bolt load. The gasket material flows into the serrations of the metallic filler which holds the gasket in place. Blow-out of this style gasket is nearly impossible, and no special flanges (e.g., with grooves) are necessary. The assembly is mostly metal, hence it is rugged and requires less careful handling than other gaskets. No grooves or projections on the flange are necessary. The soft gasket material must be changed each time the flange is opened..

(65) Types of Gaskets Self Actuated. Seal Pressure. O-Ring. Seal. Seal Pressure. K-Ring. Seal. Gaskets for which an increase in the pressure to be contained increases the sealing pressure. Examples are O-rings, K-rings, and to a lesser degree, gaskets for ring joint flanges. Gasket material must be soft and deformable. Acceptable materials have low limiting temperatures (200-400°F). . PPF-R00-23 EDS-2004/FL-65. This the type of gasket used in the Dur-O-Lok coupling. The seal with this style of gasket is based on the internal pressure. Internal pressure deforms the gasket and seals it against the outside of the groove. The greater the pressure, the greater the provided seal. Self actuated gaskets must be changed every time the flange is opened because they are soft and depend upon the ability to plastically deform. After use, they cannot be reliably removed and then re-deformed into another, slightly different, configuration to seal the flange again..

(66) Types of Gaskets Ring Joint . . . Ring joint gaskets are either oval or octagonal (oval is preferred because it works in the current and old groove shapes) Made of a variety of hard metallic materials to avoid distortion Must be compatible with the internal atmosphere and softer than the flange material Must be no rougher than 63 microinch Ra Hard to handle PPF-R00-24 EDS-2004/FL-66. The rings are fabricated of solid metal, usually soft iron, soft steel, Monel, 4-6 percent chromium, or stainless steels. Oval rings will work in the current octagonal grooves and the older oval grooves. Octagonal gaskets only work in octagonal grooves. The alloy steel rings must be heat treated to soften them. The gasket must be softer than the flange material to insure that it is the gasket that flows and fills imperfections, i.e., the gasket distorts upon use. The gasket can be replaced, although they are frequently reused. One reason for reuse is that if the flange or groove distorts during operation, the existing gasket (which also distorted) will continue to provide a seal. A new gasket may not function as well because it may not fit well into the distorted grooves. The second reason is that the gasket is made of soft metal that is not crushed or strained well beyond its yield point as other gasket materials and styles are. The gasket can, therefore, function as well on reuse as the initial use. The gaskets are wedged into the grooves in the flanges. They fit against the sides of the groove and do not touch the bottom. An internal ceramic rope is frequently provided to shield the gasket from the worst of the internal atmosphere..

(67) Types of Gaskets Spiral Wound. Composed of alternating layers of compressible filler material and metal rings wound in a spiral, forming a labyrinth leak path sealed at the peaks Most common type of gasket in refinery service . PPF-R00-25 EDS-2004/FL-67. The upper picture has an outer ring. The lower picture has an inner and an outer ring. The sealing portion of the gasket is formed by layers of thin metal windings, as shown in the figures, alternating with the compressible gasket material. Spiral wound construction creates a very difficult labyrinth leak path which gives good sealing characteristics. The spiral metal windings greatly enhance the resistance of the gasket to blow-out, to the point where it essentially never occurs. They act to resist any inner pressure via circumferential tensile stress in the same way a pressure vessel shell acts..

(68) Spiral Wound Gaskets . . Commonly used in refineries due to excellent sealing performance through a wide range of temperatures, pressures, liquid or gaseous atmospheres (including hydrogen), and flange finishes Layers provide many sealing surfaces and a labyrinth path in the direction of leakage Forgiving to seal stress variations (e.g., overstress) and less prone to relax over time. EDS-2004/FL-68. Spiral wound gaskets are forgiving to flange surface finish variation and fit-up. The metal windings stiffen the gasket (hence the higher required seating stresses) and make it less susceptible to crushing than gaskets where the entire bolt load is carried by the compressible gasket material. There are few, if any, welds in the gasket assembly..

(69) Spiral Wound Gaskets (continued). . Asbestos used to be the “universal” filler material Filler materials are now commonly a non asbestos material Graphite and sometimes Teflon (for low temperature applications) are the most common – Specialty materials are available for particular conditions –. . Filler material must be specified for each gasket (there is no default) Windings are commonly 304 Stainless Steel –. Must be compatible with the internal atmosphere EDS-2004/FL-69. These gaskets are now specified in accordance with ASME B16.20. Up until the early 1990’s, API 601 governed gasket design and characteristics. Most API 601 requirements have been incorporated into ASME B16.20, so little was lost by the change. One notable difference is that API 601 specified default materials. If nothing else was called for, they were required. B16.20 does not have default materials so the designer must be careful to call out the filler, winding, and ring material for every gasket. Type 304 stainless steel was the default winding material specified by API 601. It is still the most common material and is recommended for general use. Type 316L, or stabilized (Type 321 or 347) stainless steel may be required where sensitization, and intergranular stress corrosion cracking, is a concern. Graphite windings may be unsuitable for oxidizing atmosphere services over 800°F because the graphite “dissolves”. For spiral wound gaskets, consider using another material, e.g., ceramic or mica, for the first few windings, where oxygen exposure is possible. The remaining windings may then be graphite. Specialty filler materials are often tailored for a specific type of application. They may not work well, and may even be outright dangerous, in another service. They are often a blend of a number of components, and sensitive to variations in the proportions or quality of those materials..

(70) Spiral Wound Gaskets (continued). . . Gaskets have an outer ring for stability By using the flange bolts as a guide, the outer ring is used to center the gasket The outer ring also helps resist blowout and acts as a limit stop, preventing crushing of the outer windings from overbolting The outer ring is normally carbon steel, protected against corrosion. EDS-2004/FL-70. Stability refers to handling for installation. The outer ring aligns the gasket by fitting against the inside edge of the flange bolts. As noted in the jacketed gasket discussion, handling of large spiral wound gaskets can be difficult - they can “spring” apart and wobble around. Jacketed gaskets are sometimes specified for large diameter, low pressure services..

(71) Spiral Wound Gaskets (continued). . . An inner ring is provided for additional (handling) stability for large gaskets An inner ring is also used to protect the flange surface from corrosion due to the internal atmosphere Use the same material as for the windings An inner ring is frequently used for Class 900 and higher flanges to resist inner deflection and possible gasket buckling due to the high bolt loads present –. The bolt load tends to squeeze the outer portion of the gasket and push the gasket inward EDS-2004/FL-71. As describer on slide 63, large diameter spiral wound gaskets are difficult to handle, especially in a vertical orientation. An inner ring helps keep them from unraveling. Use of a jacketed gasket is also often considered. The inner ring also assists in maintaining the integrity of the ID of the gasket as the flanges rotate about the outer edge of the gasket and tend to push the gasket inward. It also provides additional gasket strength to resist blowout. For some filler materials (e.g., Teflon), an inner ring may be required by the governing standard (ASME B16.5). Inner rings are also advisable when the mating flanges are different metallurgy's with differing coefficients of thermal expansion. As the system heats and cools, the differing movements may put the gasket into shear. ASME B16.5 requires inner rings for some gaskets in high pressure services (≥ 24 inch Class 900, ≥ 12 inch Class 1500, and ≥ 4 inch Class 2500). UOP’s criteria is to provide an inner ring for all Class 900 and higher flanges..

(72) Spiral Wound Gaskets (continued). . . Graphite (and Teflon) filler materials act as incompressible fluids as the flanges press upon the gasket As the gasket is squeezed, the filler material presses outward into the windings and ring This can cause bucking of the windings and a failure of any gasket Asbestos is a system of compressible fibers and does not create radial forces as it is compressed All winding and ring materials must be specified (is no default) EDS-2004/FL-72. When the bolts for high pressure flanges are tightened, the large forces present may slightly deform the flanges and create a inward component of the force acting on the gasket. As noted on the slide, an incompressible filler material, such as graphite or Teflon, can lead to a similar problem. Asbestos, on the other hand, is a fibrous, compressible, material. Compression of the gasket does not create radial forces on the windings or ring. The gasket inner ring needs to be checked to insure that this force will not damage the gasket (i.e., buckle the inner ring). Outer rings, and even the windings, may also be subject to buckling. This is the reason that, in high pressure service, the outer ring often has a wavy (non-planar) appearance. The inner ring and winding material must be compatible with the internal atmosphere of the vessel or piping. As noted previously for the filler material, ASME B16.20 does not specify default materials for the ring(s) and windings. The designer must be careful to call them out. Often the outer ring is made of a low alloy material (carbon steel if the temperature is below 1000°F) because it is not exposed to the internal atmosphere..

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