The correct sequence when choosing the right gasket:

Transcription

1 96 SPECMA SEALS HANDBOOK C H O O S I N G T H E R I G H T G A S K E T M A T E R I A L Choosing the right gasket material for a specific application is not always an easy task. All the factors that affect a gasket in a flange joint may seem infinite, but nevertheless they all have to be taken into account in order to achieve optimum seal function. It was sufficient before for the parameters temperature, application, media and pressure to provide enough information to allow the correct gasket to be chosen. Things are not as simple nowadays, as factors such as flange design, flange rotation, sealing surface finish, bolt utilisation ratio etc. can affect the performance of a gasket. In general, it may be stated that the definition of a tight flange joint has dramatically changed over the years. Leakage values have changed. They used to count drops per minute, but now they can be defined using ppm (parts per million). Look for soft gaskets according to their performance: To quickly and easily find the right product in our broad range of soft gaskets, we recommend that you look at our Quick guide on choosing the right soft gasket. This quick guide states the material structure, applications and operating parameters for soft gaskets. Note that data stated for max. pressure and max. temp. cannot normally be combined. Information and values submitted must always be checked by the customer/ consumer as variation in respect of media, equipment, installation and operating conditions can be so great that only the customer/consumer can fully assess the circumstances and maintain control over all data relating to the seal required. The correct sequence when choosing the right gasket: Temperature: In most cases, the temperature of the media to be sealed off must be taken into account first. This allows the number of potential alternatives to be limited considerably, making your choice easier. When the system's operating temperature approaches the max. value for a specific gasket material, it is recommended that you choose a better material instead, with a higher max. temperature limit, so that you have a greater safety margin. Applications: Here, attention must be paid to the flange type and the design of the bolted joint. Bolt quality, the number of bolts and the bolt dimensions determine the available force in the respective flange joints. The gasket's clamped area is determined by the gasket's contact dimensions. The resulting seating stress on the gasket is calculated by dividing the available force by the clamped area expressed in N/ mm 2 (MPa). The technical specifications for the respective products show recommended minimum and maximum values in order to facilitate your choice of gasket. We would be happy to recommend the right material with the aid of a seating stress calculation. Different types of gasket material: Material Product name Max. temp. Cellulose fibre Cellulose fibre jointing +120 C Rubber sheeting Daniel's Ebonite, SBR rubber, NBR rubber, CR/SBR rubber, Vulcopack, Silicone rubber, Viton rubber +70 C to +230 C Rubber gaskets with metal core G-ST-P/S gaskets +70 C Rubber bonded cork NBR rubber bonded cork +120 C Rubber bonded aramid fibre Dixo 4000, Novapress C to +200 C Rubber bonded aramid fibre with graphite Dixo 7000 XP +300 C Rubber bonded mineral fibre 70 Service +250 C Rubber bonded carbon fibre Garlock Style 9850 Extreme +350 C Reinforced PTFE Multiflon Black, Multiflon Blue +180 C Restructured and reinforced PTFE Gylon Style 3501E, Gylon Style 3504, Gylon Style C Glass fibre reinforced PTFE UCAR 323-LC +245 C Expanded PTFE (eptfe) Media: There are thousands of different liquids and gases in industry. Fortunately, however, a relatively limited number of media are actually used in industry. The Applications: section for each gasket type shows the general resistance to media. Further information on resistance to media for the various materials is available from the technical department at Specma Seals. Pressure: Finally, the pipe system's internal operating pressure must be taken into account. The maximum pressure specified for each soft gasket material must be considered as a guide value. If there is a risk of the flange joint being subjected to major dynamic influence and/or pressure surges, an alternative product should be selected. Gore GR, Gore UPG Style 800, Gore DF, Gore Series 500, Gore Series 600, Softseal +270 C without reinforcement Grafex EC, Grafex Crinkle-Tape, FlänsMan, Grafoil TG-281 with reinforcement Grafex EX, Grafex EXP, Elastagraph, Grafex SA, Grafex NR +650 C +650 C Mineral fibre Isoplan C Mica Micapac C The above materials are the most common in the group Non-metallic soft gaskets and essentially cover all normally occurring applications in the process industry. Composite and metal gaskets are dealt with separately in the following section. The stated limit values apply under conditions. Do not utilise more than one maximum value at a time. If in doubt please contact us, we will be happy to offer advice.

2 SPECMA SEALS HANDBOOK 97 Q U I C K G U I D E on choosing the right soft gasket Designation Base material Used for Temperature range Pressure ph Elastagraph Enclosed, corrugated core of stainless steel, faced with expanded graphite. exception of strongly oxidising acids at high temperature. 300 bar Grafex EXP with insert of acidproof expanded metal exception of strongly oxidising acids at high temperature C to +750 C, higher 250 bar, Grafex EX with insert of acidproof expanded metal exception of strongly oxidising acids at high temperature. 250 bar, Grafex SA with insert of smooth acidproof foil. Steam, water, petroleum products, solvents, acids, alkalis etc. i.e virtually all media with the exception of strongly oxidising acids at high temperature. 150 bar, Grafex NR with insert of smooth nickel foil. exception of strongly oxidising acids at high temperature. 200 bar Grafex EC without insert. exception of strongly oxidising acids at high temperature. 100 bar, Grafex Crinkle-Tape Self-adhesive tape of expanded graphite. For sealing of flanges, lids and covers at virtually all media with the exception of strongly oxidising acids in combination with high temperature. 100 bar, FlänsMan Self-adhesive tape of braided expanded graphite fibre. For sealing of flanges, lids and covers at virtually all media with the exception of strongly oxidising acids in combination with high temperature. 45 bar Grafoil TG-281 Self-adhesive foil of expanded graphite. For sealing of flanges, lids and covers at virtually all media with the exception of strongly oxidising acids in combination with high temperature. 100 bar, Garlock Style 9850 Extreme Nitrile rubber bonded carbon fibre. Highly resistant to mineral oils, hot oil, gases, hydrocarbons and other petroleum products. Very suitable as a gasket for gas applications thanks to its excellent sealing properties to prevent diffuse leaks -40 C to +350 C, but +200 C in steam. 100 bar in - Dixo 7000 XP Nitrile rubber bonded aramid fibre with graphite. Ideal for sealing pipe flanges, lids, covers and split casing flanges. The gasket is resistant to steam, water, petroleum products, refrigerants, solvents, gases, weak acids and alkalis etc C to +300 C, higher in certain media, see product sheet. 100 bar in See product sheets Novapress 815 Nitrile rubber bonded aramid fibre with surface facing of nitrile rubber Mainly as a seal in flanges where freon and other gases are present. This gasket is capable of withstanding most freons and can also be used against oils and fuels. Extremely gas-tight. -80 C to +200 C. 50 bar -

3 98 SPECMA SEALS HANDBOOK Designation Base material Used for Temperature range Pressure ph 70 Service Nitrile rubber bonded mineral fibre. Low pressure steam, LPG, oil, petrol, weak acids and alkalis, solvents and jet fuel -100 C to +250 C continuously, briefly up to +370 C. 70 bar - Dixo 4000 Nitrile rubber bonded aramid fibre. Water, weak acids and alkalis, oils, fuels, solvents, gases etc C to +120 C continuously, briefly up to +200 C. 50 bar - Gylon Style 3501E Gylon Style 3510E Restructured PTFE with reinforcement. Flanges, lids, covers and split casing flanges in chemical, pharmaceutical and food industries, where stringent demands are made of tightness, safety and cleanliness C to +260 C. 80 bar, Multiflon Black PTFE reinforced with carbon. Flanges, lids, covers and split casing flanges Suitable for a wide spectrum of media, such as acids, alkalis, solvents, hydrogen peroxide 50%, chlorine dioxide 23 g/l, petroleum products etc C to +180 C. 40 bar, Multiflon Blue PTFE reinforced with glass fibre. Flanges, lids, covers and split casing flanges. Suitable for a wide spectrum of media, such as acids, alkalis, solvents, chlorine, chlorine dioxide, petroleum products etc C to +180 C. 40 bar, Multiflon White PTFE without reinforcement. Limited application, see product sheet C to +180 C. 6 bar UCAR 323-LC Glass fibre reinforced PTFE. Flanges, lids, covers and split casing flanges. Very suitable for demanding applications in the process industry, where conventional PTFE-based soft gaskets with large cold deformation properties and high compression in heat tend to cause leakage C to +245 C. 40 bar, GORE GR Biaxially expanded PTFE. Specially designed for metal flanges and large flanges, flanges which are difficult to access and flanges with complex shapes. Suitable for foods and pharmaceuticals, drinking water, oxygen etc C to +270 C, up to +315 C under ideal conditions. max. 40 bar GORE Joint Sealant DF Sealing tape of monoaxially expanded PTFE. The majority of types of flange and manhole. Suitable for foods and pharmaceuticals, drinking water, oxygen etc C to +270 C, up to +315 C under ideal conditions. 40 bar GORE Series 500 Series 600 Sealing tape of biaxially expanded PTFE. Heat exchangers, air coolers, pressure vessels, columns etc. Suitable for flanges, lids, covers and parting lines. Suitable for a broad range of media, e.g. acids, alkalis, solvents etc. (not suitable for molten alkali metals and fluorine) C to +270 C, up to +315 C under ideal conditions. max. 40 bar max. 6 bar GORE UPG Style 800 Biaxially expanded PTFE. Plastic flanges, enamelled flanges, PTFE and rubber-faced flanges. Particularly well suited to extremely aggressive solutions or in cases where the flanges are weak C to +270 C, up to +315 C under ideal conditions. max. 40 bar Softseal Sealing tape of monoaxially expanded PTFE. Flanges, lids, covers, split casing flanges, also for enamelled flanges and plastic flanges. Softseal is resistant to all gases and fluids with the exception of fluorine and molten alkali metals C to +270 C. 40 bar, The stated limit values apply under conditions. Do not utilise more than one maximum value at a time. If in doubt please contact us, we will be happy to offer advice.

4 SPECMA SEALS HANDBOOK 99 Designation Base material Used for Temperature range Pressure ph G-ST-P/S Rubber/steel gaskets Nitrile rubber with steel core. Pipe flanges of steel, plastic or rubberised for water, air, gas, oils, petroleum products etc. Approved by DVGW for use in gas pipes. Recommended by KTW for drinking water. -25 C to +70 C. 40 bar - Daniel's Ebonite Synthetic special rubber without. Very good resistance to alkalis, chlorine solutions, chlorine dioxide, green liquor, saline solutions, solvents, oils, low pressure steam, water etc. -60 C to +150 C, 40 bar 2-14 SBR rubber with or without Styrene butadiene rubber with or without. For general applications where no specific demands are made, e.g. for water. Not oil resistant. -15 C to +80 C. 10 bar - NBR rubber with or without Nitrile rubber with or without. Synthetic NBR rubber for oils, fuels and non-oxidising acids. -15 C to +70 C. 10 bar - White NBR rubber without White nitrile rubber without. White synthetic NBR rubber for food applications -30 C to +85 C. 10 bar - CR/SBR rubber with or without Chloroprene rubber with or without. Synthetic rubber with good resistance to the elements, ozone, non-oxidising acids. Limited resistance to oil products. -25 C to +100 C. 10 bar - Vulcopack Specially vulcanised EPDM rubber without. Superheated and hot water, low pressure steam, acids and alkalis. Very good weather/ozone resistance and wear strength. Excellent gasket for manholes etc. -40 C to +140 C. 25 bar - Silicone rubber without Silicon rubber without. Synthetic rubber for high and low temperatures with good resistance to the elements, ozone. Limited resistance to oil products and chemicals in general. -60 C to +230 C. 10 bar - Viton rubber Fluoride rubber without. Excellent resistance to oils, acids, chemicals. Less suitable for esters, ketones, water vapour and alkalis at high temperatures. -30 C to +200 C. 10 bar Rubber bonded cork Fine-granulated cork bonded with nitrile rubber. Primarily suitable for oil, fuels, solvents and water. Seals at low seating stresses. -30 C to +120 C. 10 bar - Cellulose fibre gasket Glycerineimpregnated cellulose fibres. Flanges, lids and covers in cooling machines, air lines, paper machines, transformers etc. Able to withstand engine fuels, mineral and diester oils, water and other media. Not suitable for steam. -60 C to +120 C. 10 bar - Isoplan 1000 Mineral fibres. The steel and glass industries for furnaces, boilers, fireproof doors, fireplaces, drying equipment, fire protection etc. max C. 3 bar - Micapac 1000 Mica. High temperature applications. Extremely good chemical resistance. Particularly suitable for aggressive acids at high temperature. max C. 5 bar

5 100 SPECMA SEALS HANDBOOK F U N C T I O N P R I N C I P L E F O R F L A N G E J O I N T S Flange joints are normally divided into two main types with a load-bearing gasket and with metal-to-metal contact. 1. Flange with load-bearing gasket With this type of flange joint, there is no contact between the flanges: the gasket takes the entire load. It is possible to compress the gasket further if the system pressure increases, in order to compensate for the increased seating stress then required by the gasket. However, you should take into account the fact that increased prestressing of bolts also increased the risk of flange rotation (bending). Most commonly occurring in flat flanges with or without a raised sealing face (type IBC or type FF) and in flanges with tongue and groove or spigot/recess (type TG or type SR). 2. Flange with metal-to-metal contact In a flange joint where there is contact between the two flange faces, it is not possible to further increase the seating stress on the gasket once contact has been made between the flanges. The gasket is enclosed in a groove with a well defined depth, which is determined by the gasket's degree of compression in relation to its original thickness. This type of flange system requires careful control over the gasket's compressibility and its recommended min. seating stress. Bolt force Gasket seating stress in service The influence of force in a flange joint: The total force generated by all the bolts in the bolted joint on tightening is transmitted to the gasket of the flanges. The force is distributed across the clamped area of the gasket, at which point the seating stress generated compresses the gasket so that it fills out irregularities and also compensates for distortion in order to achieve max. sealing capability. The gasket in the above example is centred within the bolts, known as an IBC gasket ( inside bolt circle ). When the system is pressurised, a hydrostatic force occurs which attempts to separate the flanges, which in turn results in reduction of the seating stress on the gasket. The remaining seating stress on the gasket is the pressure to which the gasket is subject during operation and is crucial to an optimum flange sealing function. Under Technical data for each gasket type, recommended min. and max. values are stated for the seating stress. Flange rotation (bending) It is worth noting that in the case described above with flanges with a raised sealing face, there is a risk of the flange potentially being subject to rotation (bending). The degree of flange rotation is dependent on bolt forces, flange geometry and material. In the event of flange rotation occurring in a flange, the seating stress on the gasket will be greatest at the outermost point of the raised sealing face and smallest in towards the medium (see diagram). This should be taken into account when choosing a soft gasket material as there is a risk of the gasket being partially subject to excessively high seating stress and hence potentially being crushed. Hydrostatic force Clamped area If you use a flat flange without a raised sealing face and an FF gasket ( full face ) covering the entire flange face complete with bolt holes, this eliminates the chances of flange rotation. The disadvantage of this design is that the collective force of all bolts in the joint is distributed across more or less twice the area than is the case with an IBC gasket, which in turn means that the seating stress on the gasket is essentially half as great. Seating stress calculation: To ensure that our gaskets have the best possible chances of working optimally, we help our customers with seating stress calculation for flanges. The Seating stress calculation enquiry form can be found in section entitled Questionnaires, and also on our website at The stated limit values apply under conditions. Do not utilise more than one maximum value at a time. If in doubt please contact us, we will be happy to offer advice.

6 SPECMA SEALS HANDBOOK 101 Summary of sealing surface types on flanges as per EN 1514 and suitable for soft gaskets. The most common flange types with regard to sealing surface design: Type A: Plan flange without raised sealing surface Type B: Flange with raised sealing surface Type C: Flange with tongue Type D: Flange with groove Type E: Flange with spigot Type F: Flange with recess Flat gaskets suitable for the above flange types and sealing surfaces Flanges type A without raised sealing surface with gasket type FF Flanges type B with raised sealing surface and gasket type IBC o/d p.c.d. i/d The figure illustrates soft gaskets of type FF (full face) for flat flanges type A. The gaskets are supplied complete with bolt holes. o/d i/d The figure illustrates soft gaskets of type IBC (inside bolt circle) for flanges with raised sealing surface type B. Type FF can also be used for flanges type B with raised sealing surface. Type IBC can also be used for flat flanges type A without raised sealing surface. bolt hole dia. Flanges type C/D with tongue and groove with gasket type TG Flanges type E/F with spigot/recess and gasket type SR o/d i/d The figure illustrates soft gaskets of type TG (tongue and groove) for flanges with tongue and groove type C/D. o/d i/d The figure illustrates soft gaskets of type SR (spigot and recess) for flanges with spigot and recess type E/F.

7 102 SPECMA SEALS HANDBOOK PROFILE GUIDE FOR Product description Profile Standard Profile figure Soft gasket of soft Type 200 EN material cut out of sheet DIN 2691 DIN 2692 DIN 7603 Ditto but with inner Type 106 EN eyelet DIN 2692 ASME Soft gasket with PTFE Type 301 EN envelope Soft gasket with corrugated Type 302 EN metal core and PTFE envelope Type 303 DIN 2690 Type 304 DIN 2690 Soft gasket with inner Type 305 DIN 2690 eyelet faced with PTFE Gasket with partition Type VVX See page 127 bars for heat exchangers, with either integrated or welded-in bars Gaskets for threaded joints. Several of the gasket types mentioned in the section Soft gaskets can be used for sealing threaded joints. It is important to remember to choose a material with sufficient mechanical stability so that it is not destroyed when it is subjected to a twisting motion. As regards soft gaskets, gaskets of rubber bonded fibre or reinforced PTFE are normally recommended, while gaskets of expanded graphite should be avoided. At temperatures over +260 C, some type of metal gasket is recommended, see page 112 or 113. A table showing the most common dimensions for gaskets for threaded joints as per DIN 7603 can be found on page 213. The stated limit values apply under conditions. Do not utilise more than one maximum value at a time. If in doubt please contact us, we will be happy to offer advice.

8 SPECMA SEALS HANDBOOK 103 INSTALLATION INSTRUCTIONS Soft gaskets Checking flanges: Make sure that the sealing surfaces are well cleaned and flat, and free of scratches, irregularities and paint. Remachine them if necessary. The faces must be free of grease as the degree of friction between gasket and flange is crucial in order to achieve optimum function. Flange surface finish: To achieve an optimum seal, both the flanges have to have the same surface finish. In normal cases, µm Ra is recommended. When the gasket is compressed, the irregularities of the flange are filled out. The coarser the surface finish of the flange, the higher the seating stress required to make the gasket penetrate into the irregularities. When machining uneven flanges, the greatest possible care should be taken with regard to the presence of any radial scratches or machining marks. Such scratches or marks are essentially impossible to seal off, no matter what type of soft gasket is used. The flange sealing surface should not be turned in a spiral motion: you should attempt to achieve a sealing surface of concentric grooves. Actions before installation: Make sure that the flanges are clean and parallel. Avoid all forms of sealing paste or release agent. Bolts and nuts: Ideally, use new bolts, nuts and washers to guarantee optimum installation. Make sure that the nuts rotate freely into the threads of the bolts. Use a thread cleaning tool in the event of the slightest inertia. Also check that the bolts are straight and undamaged. The nut face of the flanges must also be checked. In the event of pitting, machine or use hardened steel washers or Nord- Lock lock washers to achieve a base with controlled hardness for every installation operation. Lubrication: Threads and nut faces must be lubricated unconditionally so as not to lose prestressing force in the friction faces. Use Grafex GTL thread paste made of graphite for best results. Grafex GTL thread paste has extremely good lubricating properties and inhibits corrosion, and it is suitable for use in both carbon steel and stainless steel bolted joints. How to tighten the flange: Tightening the flange correctly is crucial in order to achieve an optimum sealing function. Use a torque wrench or hydraulic torque spanner. Impact wrenches or hammering nut wrenches should be avoided. It is very important for the bolts to be tightened in the correct order using a minimum number of tightening motions in order to distribute the force as evenly as possible across the flange. Tighten in a minimum of 3 stages. The more stages, the easier it is to achieve the recommended prestressing and distribute force evenly across the flange. The first stage should be limited to max. 30% of the recommended max. torque. The bolts are tightened diametrically in the recommended order as shown in the example below. During the final tightening stage, the bolts are then tightened in order around the circumference to the same torque as the final diametric tightening process. Tightening torque: The recommended tightening torque (or just torque ) is dependent on bolt quality, dimensions, thread pitch and friction in the bolted joint. These values can be found in the bolt supplier's recommendation tables. Different values apply to joints calculated as per pressure vessel standards. Examples of recommended tightening sequence in the case of diametric tightening: Dovetail joint gaskets For the best results, follow the step-by-step instructions below: 1) Make sure that the flanges are clean and parallel. 2) The dovetail joint should be positioned at or near to a bolt in order to achieve the greatest possible seating stress on the gasket at the joint. 3) For gaskets of expanded graphite with or without reinforcement, the joint has to be provided with a joint strip of self-adhesive Grafex Crinkle-Tape on both sides for maximum sealing function at the joint face. 4) For other types, the joint should be supplemented with a sealing material suitable for the relevant gasket material or a layer of self-adhesive Grafex Crinkle-Tape on both sides. For PTFE gaskets, it is recommended that the joint should be wrapped with conventional PTFE thread tape. 5) Then tighten the bolted joint in the usual sequence. 6) Sealants of all types should be avoided on the gasket's sealing faces.