Satish Lele
lelepiping@gmail.com

FITTINGS
These permit a change in direction of piping, a change in size of pipe, or a branch to be made from the main run of pipe. These are Elbows, Tees, Reducers, Caps. They are formed from plate or pipe, machined from forged blanks, cast, or molded from plastics.
Screwed or socket-welding forged steel fittings are rated to the nominal cold non-shock working pressure of 2000, 3000 and 6000# (PSI).
Branching
There are different methods of branching. These are done by Stub-In, Weldolet, Elbolet, Latrolet, Sweepolet, Cross, Lateral, Shaped Nipple, Nipples.
Tees
Butt Weld Tee : Straight and reducing :These are used for making 90 Deg branching from the main run of pipe. Straight tees with branch same size as pipe are readily available. Reducing tees have branch smaller than the size of the pipe. These do not require reinforcing.
Stub In : It is the term for a branch of pipe welded directly into the side of a main pipe run. It is not a fitting. This is the commonest and least expensive method of welding a full size or reducing branch for pipe 50 mm NB and larger. A stub in can be reinforced.
Weldolet : It makes a 90 degree branch, full size or reducing on straight pipe. Closer manifolding is possible than with tees. Flat based weldolets are available for connecting to pipe caps and vessel heads.
Elbolet : It makes a reducing tangent branch on long radius and short radius elbows.
Latrolet : It makes a 45 degree reducing branch on a straight pipe.
Sweepolet : It makes a 90 deg reducing branch from the main run of pipe. Primarily developed for high yield pipe used in Oil & Gas transmission lines. Provides good flow pattern, and optimum stress distribution.
Cross Straight or Reducing : Straight crosses are usually stock items. Reducing crosses may not be readily available. For economy, availability and to minimize the number of items in inventory, it is preferred to use tees etc., and not crosses, except where space is restricted, as in marine piping or revamp work. Reinforcement is not needed for these.
Lateral Straight or Reducing : It permits odd-angled entry into the run of the pipe, where low resistance to flow is important. Straight laterals with branch bore equal to run bore are available in standard and XS weights. Reducing laterals and laterals at angles other than 45 degrees are usually available only to special order. Reinforcement is required where it is necessary to restore the strength of the joint, to the full strength of the pipe.
Nipples : These join unions, valves, strainers, fittings etc. Basically a short length of pipe either fully threaded (close nipple) or threaded both ends (TBE), or plain one end and threaded one end (PEO-TOE). Available in various lengths. Nipples can have grooved ends also.
Shaped Nipple : These are rarely used, but can be used for 90 deg and 45 deg or any other angle. The run is field cut using nipple as template. It needs reinforcement if it is necessary to bring the strength of the joint up to the full strength of the pipe.
Pipe to pipe connector : These are used to join threaded pipe to tube. Tube is flared inside the nut.
Tank Nipple : It is used for making a screwed connection to a non pressure vessel or tank in low pressure service. Overall length is usually 150 mm with a standard taper pipe thread at each end. On one end only, the taper pipe thread runs into a ANSI lock nut thread.
Elbows
These are of following types. Long Radius and Short Radius Elbows, Reducing Elbows, Long Radius Tangent Elbow, Returns, Bends, Mitered Elbows.
Long Radius and Short Radius Elbows : These make 90 degree and 45 degree changes in direction of the run of pipe. The elbows normally used are Long Radius (LR) with centerline radius of curvature equal to 1.5 times the nominal pipe size for 20 NB and larger sizes. Short Radius (SR) elbows with centerline radius of curvature equal to the nominal pipe size are also available. 90 deg long radius elbows with a straight extension at one end (Long Tangent) are also available.
Reducing Elbows : These are designed both to change direction and reduce pipe size. These have centerline radius of 1.5 times the nominal size of larger end. Their use eliminates one fitting (reducer) and reduces welding by one third. The gradual reduction in diameter through the arc of reducing elbow provides maximum flow efficiently, reduces turbulence and erosion and helps in maintaining pressure.
Long Radius Tangent Elbow : These are special elbows that provide a straight length at the end to accommodate a slip on flange.
Return : It changes the flow of direction in 180 deg and is used to make heating coils, vents on tanks etc.
Bends : These are made from straight pipe. Common bending radii are 3 and 5 times the pipe size. Larger radius bends can be made by hot bending. Only seamless or ERW pipe is used for bends.
Mitered Elbows : These are fabricated as required from the pipe and these are not fittings. The miters are used for pipes 200 NB and larger where pressure drop is not important and where the regular elbows are costlier. A 2-piece 90 deg miter has 4 to 6 times hydraulic resistance of the corresponding long radius elbow. A 3-piece 90 deg miter has about double the resistance. 3, 4 and 5-piece miters are normally used.
Reducers
Reducers are used to change the size of the pipeline. These are of two types.
Concentric Reducers : The centerline of inlet and outlet is at same level. It is generally used in vertical pipes.
Eccentric Reducers : The eccentric reducer is used when it is necessary to keep either the top or bottom of the line level. These are used with flat side up or down. Flat side down is used in horizontal pipes. Flat side up is used for pump suction line.
Swage
These are of three types. Concentric, eccentric and ventury type. Swage is used to connect butt welded piping to smaller screwed or socket welded pipe. In butt weld pipes it is used when greater reduction is required. Swages are of three types.
Concentric Swage : The centerline of inlet and outlet is at same level. It is generally used in vertical pipes.
Eccentric Swage : The eccentric swage is used when it is necessary to keep either the top or bottom of the line level. These are used with flat side up or down. Flat side down is used in horizontal pipes. Flat side up is used for pump suction line.
Ventury : Ventury type swage gives a smooth flow.
Cap
Caps are used to seal the end of pipe. These are ellipsoidal in nature.
Flat Closure : These are flat plates normally cut from pipe at site.
Dished Heads : These are used for large diameter pipes.
Socket Weld Fittings
Full Coupling : It is also termed as coupling and it joins pipe to pipe, or to nipple, swage etc.
Half Coupling : It is used to make side branching on large diameter pipes or vessels. It is of the same length of full coupling but has socket weld end on only one side. Shaping is necessary for the end.
Reducer : It joins two pipes with different diameters.
Cross : These are used in exceptional cases where two tees cannot be fitted. Mostly used in marine piping or during modifications.
Sockolet : It makes a 90 degree branch, full size or reducing on a straight pipe.
Elbolet : It makes a reducing tangent branch on elbows.
Swaged Nipple : It is similar to swage. These can allow two types of joining. Socket ended items of different sizes which has plain ends on either sides for insertion into socket ends. A socket ended item to a larger butt welding pipe or fitting. This type has larger butt-weld end and smaller socket weld end.
Elbows : These change pipe direction in 90 deg and 45 deg from the run of the pipe. The ends are socket weld type.
  • Latrolet : It makes a 45 degree reducing branch on straight pipe.
  • Nipolet : A varient of sockolet, having integral plain nipples. Primarily developed for small valved connections.
  • Stub In : Not recommended for pipes with diameter less than 50 mm, due to risk of weld material entering line and restricting flow.
  • Lateral : It makes full size 45 degree branch from the main run of the pipe.
Screwed Fittings
Full Coupling : It is also termed as coupling and it joins pipe or items to with threaded ends.
Half Coupling : It is used to make 90 deg screwed connections for pipes to instruments, or for vessel nozzles. Welding heat may cause embrittlement of the threads of this short fitting.
Reducer or reducing coupling : It joins threaded pipes with different diameters. Can be made in any reduction by boring and tapping standard forged blanks.
Cross : These are used in exceptional cases where two tees cannot be fitted. Mostly used in marine piping or during modifications.
Threadolet : It makes a 90 deg branch, full size or reducing on a straight pipe.
Elbolet : It makes a reducing tangent branch on elbows.
Nipples : These join unions, valves, strainers, fittings etc., Basically a short length pipe with that have screwed ends.
Swaged Nipple : It is similar to swage. These can allow two types of joining. Screwed items of different sizes which has screwed ends on either sides. A screwed item to a larger butt welding pipe or fitting or vice versa.
Elbows : These change pipe direction in 90 deg and 45 deg from the run of the pipe. The ends are threaded internally.
Flange : This is similar to slip on flange, but has internal threads.
Latrolet : It makes a 45 deg reducing branch on straight pipe. It is welded on pipe.
Nipolet : A variant of threadolet, having integral plain nipples. Primarily developed for small valved connections.
Stub In : Not recommended for pipes with diameter less than 50 mm, due to risk of weld material entering line and restricting flow.
Bar Stock Plug : It seals the screwed end of a fitting. Also termed as round head plug.
Flanges
These are of following types. Weld Neck, Slip On, Reducing, Lap Joint and Blind.
Flange Facing : Many facings for flanges are offered by manufacturers, including various tongue and groove types which must be used in pairs. However only four types of facing are widely used. The raised face is used for 80% of all flanges. The ring-joint facing, employed with either an oval-section or octagon section gasket, is used mainly in Petrochemical Industry. The four types of faces are as follows:
Raised Face : It has a raised face with serration on it to hold the gasket firmly in position. This is widely used.
Flat Face : Most common uses are for mating with non-steel flanges on bodies of pumps, valves etc. and for mating with 125# cast-iron valves and fittings. A full size gasket is used to avoid breaking of the flange while tightening.
Ring Joint Facing : It is more expensive facing and used in pairs for high temperature and high pressure service. Both flanges of the pair are alike.
Lap Joint Facing : It has special curvature for accommodating stub end. The combination of flange and stub-end presents similar geometry to the raised face flange and can be used where bending stresses will not occur. This is used for SS pipes, where stub-end is made of SS pipe and flange is made of Carbon Steel.
Flange faces are usually finished by machining to produce a spiral round-bottomed groove, or a V shaped spiral or concentric groove, termed as serrated finish. Smooth finish is generally made to order. Serrated finish is used with asbestos and other gaskets. The regular smooth finish is used with gaskets made from harder materials and with spiral wound gaskets.
Flange Finishes : The term finish refers to the type of surface texture produced by machining the flange face which contracts the gasket. Two principal finish types are serrated and smooth.
Weld Neck Flange, Regular and Long : Regular welding neck flanges are used with butt-welding fittings. Long welding neck flanges are primarily used for vessel and equipment nozzles, rarely for pipe. These are suitable where extreme temperatures, shear, impact and vibratory stresses apply. Regularity of bore is maintained in this.
Slip On Flange : It is properly used to flange pipe. Slip-on flanges can be used with long-tangent elbows, reducers, and swages. The internal weld is slightly more subject to corrosion than butt-weld. The flange has poor resistance to shock and vibration. It introduces irregularity in the bore. It is cheaper to buy than weld neck flange, but costlier to assemble. It is easier to align than welding neck flange. Calculated strengths under internal pressure are about one third that of corresponding welding neck flange. Pipe or fitting is set back from the face of flange a distance equal to wall thickness.
Reducing Flange : It is suitable for changing size, but should not be used if abrupt transition would create turbulence, as at pump connections. Available to order in weld neck type and from stock in slip-on types.
Expander Flange : It is similar to weld neck but increases pipe size to first or second larger size. It is alternative to using reducer and welding neck flange. Useful for connecting to valves, compressors, and pumps. Pressure ratings and dimensions are in accord with ANSI B16.5.
Lap Joint Flange : It is economical if costly pipe such as stainless steel is used, as the flange can be carbon steel and only the lap joint stub end need be of line material. A stub end must be used in a lap joint, and the cost of two items must be considered. Useful where alignment of bolt holes is difficult, such as with spools to be attached to flanged nozzles of vessels.
Blind Flange : It is used to blind off a flange, generally at the end of pipe. This provides an easy to open end for further running of the pipe.
Bolt Holes in Flanges are equally spaced. Specifying the number of holes, diameter of bolt circle and hole size sets the bolting configuration. Number of bolts and size of bolts depends on rating of the flange.
Gaskets : These are used to make a fluid-resistant seal between two surfaces. The common gasket patterns for pipe flanges are full-face and ring type, for use with flat-faced and raised face flanges respectively. Widely used materials for gaskets are compressed asbestos (2 and 5 mm thick) and asbestos filled metal. The filled metal gasket is especially useful if maintenance requires repeated uncoupling of flanges, as gasket separates clean and is often reused.
Bolts for flanges : Two types of bolting is available, stud bolt using two nuts and the machine bolt using one nut. Stud bolts have largely displaced regular bolts for bolting flanged piping joints, as stud bolt can be removed easily, confusion with other bolts at site is avoided, the odd sized can be readily made from round stock.
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