Piping joints handbook free

Flanges of different standards are not normally joined. If necessary to do so, engineering advice must first be sought to ensure the comparability of the mating flanges. Flange Facings There are three types of flange facings commonly found on a plant. A Section on surface finish on the different flange facings is in this book extracted from GS -.

Ring type metal gaskets must be used on this type of flange facing. The faces of the two opposing flanges do not come into contact and a gap is maintained by the presence of the gasket. Such RTJ flanges will normally have raised faces but flat faces may equally be used or specified. The flanges also use special metal ring joints. A Type BX flange joint which does not achieve face-to-face contact will not seal and should not be put into service.

The facing on a RF flange has a concentric or phonographic groove with a controlled surface finish. If the grooves are too deep or a rough surface finish , then high compression is required to flow the relatively soft gasket material into the grooves. Too shallow exceptionally smooth surface finish and again high compression is required as a leak path then becomes more possible.

It is important to always check the flange surface finish for imperfections which would make sealing difficult. A radial groove for example is virtually impossible to seal against. Note that the surface finish on the flange facing depends on the type of gasket being used. Further details are given in section Spiral Wound Gaskets and Graphite gaskets. The gasket fits over the entire face of the flange. FF flanges are normally used on the least arduous of duties such as low pressure water drains and in particular when using cast iron, cunifer or bronze alloy, where the large gasket contact area spreads the flange loading and reduces flange bending.

Flange Face Re-Machining Flange Face Re-machining may be carried out in order to repair the sealing face of a flange which has corroded, deteriorated or otherwise been damaged.

Flange face re-machining must be carried out by experienced personnel using the appropriate equipment. A procedure for the process should be in place and must be followed. Incorrect re-machining which reduces the flange dimensions to below the minimum specified dimensions will result in possible leakage.

WN Flanges are typically used on arduous duties such as high pressures and or hazardous fluids. There is therefore a high degree of confidence in the integrity of the weld. A butt weld also has good fatigue performance and it's presence does not induce high local stresses in the pipework. The pipe is fillet welded to the hub of the SW flange.

Radiography is not practical on the fillet weld and correct fit up and welding is therefore crucial. Slip on Weld Flange SO Used typically on low pressure, low hazard services such as fire water, cooling water, etc. The pipe is "double welded" both to the hub and the bore of the flange and again radiography is not practical. This type of flanged joint is typically found on Cunifer and other high alloy pipework. An alloy hub with a galvanized steel backing flange is cheaper than a complete alloy flange.

The flange has a raised face and sealing is with a flat gasket such as a CAF sheet gasket. As with the Composite Lap Joint Flange, a hub will be butt welded to the pipe. A swivel ring sits over the hub and allows the joint to be bolted together. Swivel Ring Flanges are normally found on subsea services where the swivel ring facilitates flange alignment.

The flange is sealed using a RTJ metal gasket. Flange Pressure Required for all flanges, e. A material specification must be stated and will Material be as quoted in the piping specification. Normally, the flange specification will be hard stamped on the flange. In the case of existing plant, the information may not be legible and it is then necessary to identify the flange by visual observation and physical measurement.

Visual observation Required to identify the type of flange and type of gasket used. Required to identify the nominal bore and the Physical measurement class of the flange. Compare these figures with standard flange data as found.

Raised Face and Flat Face flanges should also be checked for flatness with a straight edge. This may over stress adjacent pipework and will make sealing of the flanged joint difficult and unreliable.

Instead, report the situation. The flange surface will thus give a broad indication of which gasket materials are likely to be suitable. Finishes of standard raised face flanges usually fall within the range 3. Sheet jointing The recommended surface finish for the compressed fibre jointing above a thickness of 1mm is 3. CLA these values are also used for graphite laminate above a thickness of 0.

CLA is possible. Surface finishes below 1. Solid flat metal A surface finish in the order of 1. Again for optimum performance, the smoother the flange surface finish, the better the performance.

Machining of flange faces Under no circumstances should flange seating surfaces be machined in a manner that tool marks extend radially across the seating surface.

Fugitive Emissions Heightened awareness with regard to Health and the Environment is leading to new and more stringent standard procedures and legislation. The goal is to reduce emissions to target levels currently based on the best available technology. These targets will inevitably become tighter in the future. Large companies have been aware of the issues for a number of years and will have a major part to play in the future standards and legislation.

As early as Fugitive Emissions had a major impact on meeting the challenge set by major petrochemicals companies. Some companies set their own high standards ahead of incumbent legislation. Compressor Relief Valves. Other Pumps Valves. The chemical resistance chart shows the resistance of many common jointing materials to variety of chemicals.

This is a guide only and should any doubt exist, then the gasket manufacturer should be consulted. Temperature The gasket selected should have reasonable life expectancy at the maximum temperature encountered or the minimum temperature if for a low temperature application.

A broad indication of the temperature pressure ratings of the common gasket materials is shown in the figure below. Gasket materials are designed to compress under load to achieve the initial seal. However, to retain that seal, the gasket should be able to resist flow or creep to prevent loss of surface stress by bolt reduction. This property is very important and is the one that most readily separates high quality from low quality gaskets.

The above information is intended as a guide to the maximum possible ratings of each class of jointing. It does not imply that all the gaskets within each generic type are suitable for the temperatures and pressures shown. Even if the material chosen is theoretically suitable for the temperature and pressure, other factors should be considered such as available bolting, flange facing type, shock loadings etc.

Consultation with gasket experts should take place at the design stage to ensure that the gasket selected is suitable for all conditions of the application. Vacuum conditions need special considerations but as a guide:. Special Considerations There are many factors apart from those already considered that affect the selection of the correct gasket material and type. In such cases, choice of gasket material and selection of gasket dimensions are critical.

Risk of Contaminating the Fluid Sometimes the effect of contaminating the fluid by leaching chemicals from the gasket should be considered. Typical examples are in the sealing of potable water, blood plasma, pharmaceutical chemicals, food, beer, etc. Corrosion of Flanges Some flange metals are prone to stress corrosion cracking e. When using these, care should be given to ensure that the gasket material does not contain an unacceptable level of leachable impurities which may induce the corrosion.

Such impurities include chloride ions. Integrity When integrity of a gasket is of prime importance e. As an example, a spirally wound gasket with an outer retaining ring may be selected in place of a compressed asbestos fibre gasket. Economy Although a gasket is a relatively low priced item, the consequential expense of leakage or failure should be considered when deciding on quality, type and material of the gaskets.

The gasket creates the seal between the two flange faces and contains the internal pressure at that joint. RTJ gaskets are generally used for high pressure applications. Sealing is by metal-to-metal contact between gasket and flange. There are three different types of ring commonly available: R type. These are either oval or octagonal in cross-section. The oval RTJ is the original design. The octagonal RTJ is a modification to the oval design and provides better sealing.

R type rings may be specified for class to flanges though are typically found on class flanges and often class The piping specification will state whether an octagonal or an oval joint is to be used.

R type rings may be used on either flat face or raised face RTJ flanges. If R, state whether octagonal or oval. The type of ring to be used will be specified in the piping specification.

Again check with the piping specification for the correct material. The material grade will have an identifying code. For example:. The Piping Specifications for each individual plant will be changed to accommodate the new gaskets.

The stores Vocab nos. Spiral Wound Gaskets that may be present in flanges Spiral wound gaskets are typically used on intermediate pressure systems and will be found on class flanges, class and class flanges. Though there are many variations on the spiral wound gasket design, only that which is the preferred design is described - that is the spiral wound gasket with inner and outer rings.

Spiral Wound Section This part of the gasket creates the seal between the flange faces. It is manufactured by spirally winding a pre-formed metal strip and a filler material around a metal mandrel. Normally the outside and inside diameters are reinforced by several additional metal windings with no filler.

When compressed, the combined effect of the metal winding and the filler material will make the seal. The filler material will flow into the grooves on the flange face and the metal winding will then strengthen and support the filler against the flange face.

Inner Metal Ring The inner metal ring provides inner confinement to the gasket. Being of a specified thickness smaller than that of the uncompressed spiral windings, it acts as a compression stop. The inner ring also fills the annular space between the flange bore and the ID of the spiral wound section and therefore minimises turbulence of the process fluids at that location and prevents erosion of the flange faces.

Note that the spiral windings should never be exposed to the flow of the process fluids. The ID of the inner ring should be flush with the bore of the flange and this should be checked prior to bolting up. Outer metal ring The outer metal ring acts as a compression stop and an anti-blowout device. It also centers the gasket on the flange face.

The spiral wound gasket should be centered on the flange with the outer ring resting against the studbolts. If this is not the case, the incorrect gasket has been chosen and should be changed. Asbestos is hazardous to health and even though trapped within the spiral winding, SW gaskets should be handled with care. Full procedures are available and should be consulted.

Graphite filler has now taken over as being the preferred filler material For special applications, other materials are available, such as graphite and ceramic fillers. Spiral Wound Gasket Specification and Identification Spiral wound gaskets are supplied and identified as follows:. The class and size of the gasket will always be stamped on the outer ring.

Normally asbestos was used but now graphite, PTFE, ceramic fillers, etc. The filler material will be specified in the piping specification. Identification is by way of a colour code on the spiral wound section. The winding material will be specified in the piping specification and is typically stainless steel. Identification is by a colour code on the outer ring. Material grade will be specified in the piping specification.

It is normally carbon steel and again will be specified in the piping specification. Chart Warning There are some process applications where graphite is unsuitable. Refer to manufacturers data sheets for details.

Filler Material Colour Code The spiral wound section of the SW gasket will be coloured to identify the filler material: with flashes around the outer ring of the relevant colour.

Note that the above colour coding is based on API and has also been adopted by Klinger, the main supplier of spiral wound gaskets to BP. When inspecting gaskets already fitted to flanges it can be difficult to distinguish between white grey and light green.

Engineers must be aware of this problem. BP has formed a partnership with a gasket company, to change from Asbestos based materials to Non Asbestos based materials. The new gasket material which contains no asbestos has a stainless steel insert sandwiched between two layers of Graphite. If not handled correctly the insert may cut personnel. This type of gasket is known as a 'tanged gasket', the gaskets are non-stick especially on stainless steel faces.

The Stainless reinforcement increases the tensile strength of the material, its load bearing capacity and handling characteristics, it also improves its blow-out resistance under cycling conditions. For larger type gaskets two stainless inserts may be used for greater rigidity and ease of handling When handling this type of gasket always use gloves. Rubber gaskets are limited in use by temperature, pressure and chemical resistance. They are also liable to creep, e.

Rubber gaskets are usually full face and are used on flat face flanges. Of the variety of rubbers available, that most commonly used as a gasket is neoprene. Other rubber materials include natural rubber, Viton and Nitrile. It should be marked on the gasket. If not check the correct fit of the gasket on the flange. The bore of the pipe must not be restricted by the gasket and that the entire face of the flange must be covered.

Check the thickness of the gasket by reference to the piping specification. CAF gaskets were normally used on Raised Face flanges self-centering flat ring type gasket , but may also have been used on Flat Face flanges full face type gaskets are required. Though of apparently simple design, the CAF gasket should be treated with equal respect as with all gaskets to ensure effective sealing CAF gaskets are manufactured from asbestos fibres bonded in a nitrile rubber compound.

Sealing is by a similar mechanism to the spiral wound gaskets where the gasket material is soft enough to flow into the phonographic groove on the flange face when compressed. Correct gasket thickness is therefore important. The required surface finish will be as stated in relevant section on flanges. The gasket may or may not be coated with graphite The graphite has non-stick properties and enables the easy removal of the gasket when a flange is split.

Remember that CAF gaskets contain asbestos and should therefore be handled carefully. If removing an old CAF gasket from a flange, wet the gasket with water to absorb any asbestos dust that may be freed, especially if the flange has to be scraped clean.

The information should also be marked on the gasket. If not, check the correct fit of the gasket on the flange. It should be centred when resting on the studbolts and the bore of the pipe should not be constricted.

Alternatively the gasket may be a full face type, sized to the OD of the flange, particularly for small bore less than 2 inch NB pipework. Check the thickness of the gasket. It will be quoted in the piping specification. The piping specification should be consulted. Check with the piping specification to confirm that it is correct. Ensure that it is clean and free from any contaminants before use. Have required rigging plans been prepared and approved?

Have the requirements of the approved rigging plan been reviewed with the craft who will perform the work? Is the scaffolding required to perform the work properly erected?

Is a special scaffold design required to access the work location? Post a Comment. Just enter your email address:. The following specific types of questions might be asked by the Field Engineer to ensure the work can be done safely:. Tagged as : Downloads.

Subscribe to: Post Comments Atom. Flanges 11 2. Gaskets 25 3. Compact Flanged Joints 51 4. Bolting for Flanges and Covers 61 5. Spading and Blanking of Flanges 87 7.

Screwed Piping Joints 89 7. Compression Fittings 99 8. Elastomeric O-Ring Seals 9. Bolts Material Specifications 2. Hydraulic Bolt Tensioning 3. ANSI B Welded and Seamless Pipe, BS Table of Gauges Technical Data - Company and National Standards 1. It provides the appropriate selection, specifi- cation and material grade of pipe and piping components for a given service.

For all subsequent maintenance and repair on a section of pipe, the piping specification remains as the key to correct material selection. Before commencing any job, reference to the piping specifica- tion is essential to specify and use the correct materials. For the job check that you are using the latest revision of the spec- ification. If a discrepancy is found, it should be reported.

Note that a piping specification only applies to the defined plant, site or installation. Forties, Magnus, Dimlington Terminal for example each have their own piping specifications and they are NOT inter- changeable. To use the piping specification, reference must first be made to the Process and Instrument Diagram.

WF - The service code. This refers to the contents of the pipe. In this instance, WF refers to Fire Water. This is a short-hand reference into the piping specification document, and is also unique to that document.

The letter normally refers to the pressure rating of the system. Having determined the piping specification number, turn to the appropriate page in the piping specification document. There the correct type of gasket, the correct grade of studbolts, spectacle blinds, blind flanges, pipe material, pipe wall thickness and much more will be specified for the job in hand.

Flanges There are numerous types of flanges available. The type and mate- rial of a flange to be used is dependent on the service duty of the line. Reference to the piping specification will provide such informa- tion. Flanges of different standards are not normally joined. If necessary to do so, engineering advice must first be sought to ensure the com- patibility of the mating flanges.

The surface finish of the facings is specified in the Flange Standards. A section on surface finish on the different flange facings is in this book extracted from GS Ring type metal gaskets must be used on this type of flange facing. The faces of the two opposing flanges do not come into contact and a gap is maintained by the presence of the gasket.

Such RTJ flanges will normally have raised faces but flat faces may equally be used or specified. The flanges also use special metal ring joints.

A Type BX flange joint which does not achieve face-to-face contact will not seal and should not be put into service. The facing on a RF flange has a concentric or phonographic groove with a controlled surface finish. If the grooves are too deep or a rough surface finish , then high compression is required to flow the relatively soft gasket mate- rial into the grooves. Too shallow exceptionally smooth surface finish and again high compression is required as a leak path then becomes more possible.

It is important to always check the flange surface finish for imperfections which would make sealing difficult. A radial groove for example is virtually impos- sible to seal against. Further details are given in Section 3. The gasket fits over the entire face of the flange. FF flanges are normally used on the least arduous of duties such as low pressure water drains and in particular when using cast iron, cunifer or bronze alloy, where the large gasket contact area spreads the flange loading and reduces flange bending.

Flange face re-machining must be carried out by experienced per- sonnel using the appropriate equipment. A procedure for the process should be in place and must be followed.

There is therefore a high degree of confidence in the integrity of the weld. A butt weld also has good fatigue performance and its presence does not induce high local stresses in the pipework.

The pipe is fillet welded to the hub of the SW flange. Radiography is not practical on the fillet weld and correct fit-up and welding is therefore crucial.

This type of flanged joint is typically found on Cunifer and other high alloy pipework. An alloy hub with a galvanised steel backing flange is cheaper than a complete alloy flange. The flange has a raised face and sealing is with a flat gasket such as a CAF sheet gasket. A swivel ring sits over the hub and allows the joint to be bolted together. Swivel Ring Flanges are nor- mally found on subsea services where the swivel ring facili- tates flange alignment.

The flange is sealed using a RTJ metal gasket. Class , , , , etc. Schedule 10, 30, 40, ,80, , , etc. In the case of existing plant, the information may not be legible and it is then necessary to identify the flange by visual observation and physical measurement.

Compare these figures with standard flange data as found. It should be clean, degreased and free of any defects, nicks or burrs. Raised Face and Flat Face flanges should also be checked for flatness with a straight edge. Any radial defects for example will be virtually impossible to seal against.

A soft wire brush is recommended. Instead, report the situ- ation. The flange surface will thus give a broad indication of which gasket materials are likely to be suitable. Finishes of standard raised face flanges usually fall within the range 3. Surface Finish Micro metre mm These values are also used for graphite laminate above a thickness of 0. For tongue and groove flange facings or for very thin gaskets 0.

CLA is possible. CLA - Critical - 3. Again for optimum performance, the smoother the flange surface finish, the better the performance. Such tool marks are practically impos- sible to seal regardless of the type of gasket being used. Gaskets 3. The goal is to reduce emissions to target levels currently based on the best available technology. These targets will inevitably become tighter in the future.

Large companies have been aware of the issues for a number of years and will have a major part to play in the future standards and legislation.

As early as , Fugitive Emissions had a major impact on meeting the challenge set by major petrochemicals companies. Some companies set their own high standards ahead of incumbent legislation. The chemical resist- ance chart see Appendix 1, Section 4 shows the resistance of many common jointing materials to a variety of chemicals.

This is a guide only and should any doubt exist, then the gasket manufac- turer should be consulted. A broad indication of the tem- perature pressure ratings of the common gasket materials is shown in the figure below. However, to retain that seal, the gasket should be able to resist flow or creep to prevent loss of surface stress by bolt reduction. This property is very important and is the one that most readily separates high quality from low quality gaskets.

Notes: 1. The above information is intended as a guide to the maximum possible ratings of each class of jointing. It does not imply that all the gaskets within each generic type are suitable for the temperatures and pressures shown. Even if the material chosen is theoretically suitable for the tem- perature and pressure, other factors should be considered such as available bolting, flange facing type, shock loadings, etc.

Consultation with gasket experts should take place at the design stage to ensure that the gasket selected is suitable for all conditions of the application. Typical examples are in the sealing of potable water, blood plasma, pharmaceutical chemicals, food, beer, etc.

When using these, care should be taken to ensure that the gasket material does not contain an unacceptable level of leachable impurities which may induce corrosion. Such impurities include chloride ions. As an example, a spirally wound gasket with an outer retaining ring may be selected in place of a compressed asbestos fibre gasket. Guidance The following guidance is offered where pre-selection has not been carried out.

The gasket creates the seal between the two flange faces and contains the internal pressure at that joint. RTJ gaskets are generally used for high pressure appli- cations. Sealing is by metal-to-metal contact between gasket and flange. Solid metal joint rings have excellent tightness and tolerance to temperature and pressure changes once correctly bolted up. Very close attention must be given to their bolting up. Rings and groove faces must be free of imperfections.

The most commonly used is Type R. R Type These are either oval or octagonal in cross-section. The oval RTJ is the original design.

The octagonal RTJ is a modification to the oval design and provides better sealing. R type rings may be specified for Class to flanges though are typically found on Class flanges and often Class The piping specification will state whether an octagonal or an oval joint is to be used.

R type rings may be used on either flat face or raised fact RTJ flanges. Note that the RX gasket is wider than the R type gasket and the flange face-to-face separation will therefore be greater. They are used when a more effective seal is required which is resistant to vibrations, shock loadings, etc.

The asymmetric cross-section makes the gasket self-energising. The outside bevel of the ring makes the initial contact with the grooves of the flange and thus preloads the gasket against the groove outer surface. The pitch diameter of the ring is slightly greater than the pitch diam- eter of the flange groove.

This preloads the gasket and creates a pressure energised sea. The groove on a flange which accommodates a BX gasket is dimensionally different to that for R and RX gaskets. RTJ flanged joints are particularly susceptible to uneven bolt tensioning and misalignment of the ring within the groove. If R, state whether octagonal or oval. The type of ring to be used will be specified in the piping specification.

Again check with the piping specification for the correct material. The material grade will have an identifying code. By filling the annular space between the gasket and flange, it reduces turbulent flow of the fluid or the possibility of the accumu- lation of solids, and possible corrosion.

The stores Vocab numbers will remain the same for the equivalent size spiral wound type. Spiral Wound Gaskets that may be present in flanges: Spiral wound gaskets are typically used on intermediate pressure systems and will be found on Class flanges, Class and Class flanges. Where SW gaskets are used with standard Class flanges and smaller sizes of standard Class flanges, the higher seating load requirements and low bolting availability necessitates use of high strength bolting and proper bolting up procedures.

The use of gaskets with inner rings also increases the required bolting load. It is manufactured by spirally winding a preformed metal strip and a filler material around a metal mandrel. Normally the outside and inside diameters are reinforced by several additional metal windings with no filler. When compressed, the combined effect of the metal winding and the filler material will make the seal. The filler material will flow into the grooves on the flange face and the metal winding will then strengthen and support the filler against the flange face.

Being of a specified thickness smaller than that of the uncom- pressed spiral windings, it acts as a compression stop, i. The inner ring also fills the annular space between the flange bore and the ID of the spiral wound section and therefore minimises turbulence of the process fluids at that location and pre- vents erosion of the flange faces.

The ID of the inner ring should be flush with the bore of the flange and this should be checked prior to bolting up. It also centres the gasket on the flange face. The spiral wound gasket should be centred on the flange with the outer ring resting against the studbolts. If this is not the case, the incorrect gasket has been chosen and should be changed. Asbestos is hazardous to health and even though trapped within the spiral winding, SW gaskets should be handled with care.

Full procedures are available and should be consulted. Graphite filler has now taken over as being the preferred filler material. For special applications other materials are available, such as graphite and ceramic fillers. The class and size of the gasket will always be stamped on the outer ring. Normally asbestos was used but now graphite, PTFE, ceramic fillers, etc. The filler material will be specified in the piping specification.

Identification is by way of a colour code on the spiral wound section. The winding material will be specified in the piping specification and is typically stainless steel. Identification is by a colour code on the outer ring. Material grade will be specified in the piping speci- fication. It is normally carbon steel and again will be specified in the piping specifica- tion. The ring may be only coloured on the outer edge. When inspecting gaskets already fitted to flanges, it can be difficult to distinguish between white grey and light green.

Users must be aware of this problem. Class Machining Serr. Tool Serr. They are used for low pressure applications and are typically found on Class and Class flanges. They are normally used on Raised Face flanges self-centering flat ring type gasket , but are also used on Flat Face flanges full face type gaskets are required.

This material covers a wide range of applications, but has a known health risk. If not handled correctly, the insert may cut personnel.