piping & pipeline components
TRANSCRIPT
PIPING & PIPELINECOMPONENTS
PIPING DEPARTMENT
compiled by
Budi Nugraha
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PIPING AND PIPELINE COMPONENTS
INTRODUCTION
The scope of piping and pipeline components covers a very vast area, so we had to limit
ourselves to include only the most common items used in the oil and gas industry. In this
paper we will concentrate on metallic components, most notably carbon and stainless
steel. Other items will be mentioned if necessary, although not as detailed as the main
subjects. We also didn't refer too much to the material selection of a piping system, which
is a delicate process and should be dealt with as a separate specialized topic.
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Piping & Pipeline Components Terminology
I. STANDARD PIPING TERMINOLOGY
PIPE and TUBING
The term Pipe normally refers to tubular products whose Outside Diameter (OD) always
meet standard sizes although their wall thicknesses (schedule numbers) vary. While
tubing sizes have not been standardized to the same extent as metallic pipe sizes
NPS (Nominal Piping Size)
The Nominal Standard Sizes of pipes are standardizes pipe diameter sizes that are
commonly used in piping systems. The most widely used standard for NPS is ANSI
B36.10 for wrought steel, while ANSI B36.19 is used for stainless steel. The sizes refer
to the outside diameter (OD) of the pipe, although only pipes sized 14" and larger have
the same OD as their NPS. Pipes below 14" have OD's larger than the NPS, based on the
Briggs standard. (See the table A.1. in Appendix)
Tubing sizes are generally designated by their actual OD.
PIPE SCHEDULE
Pipe schedules are actually standardized wall thicknesses for NPS. These schedules are
listed as numbers and vary for each NPS. 4" pipes with schedule 40 have not the same
wall thickness as 14" pipes with the same schedule. Beside these numeric schedules there
are also three common classifications to pipe wall thicknesses: Standard (STD), Extra
Strong (XS) and Double Extra Strong (XXS). These three schedules overlap the numeric
schedules at certain sizes. For example: schedule STD for sizes up to 10" are the same as
schedule 40, while for sizes from 12" and above schedule STD refers to wall thickness
0.375". (See the table A.2. in Appendix)
ANSI B36.19 lists special piping schedule number for stainless steel pipes, which have
the suffix s like schedules 10s, 40s and 80s. These schedules are also commonly used for
non-Steel pipes. PVC piping and certain other plastics that have no referred point are
usually referred to as with schedule 40 or 80 designations.
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Piping & Pipeline Components Terminology
RATING
Flanged components are classified in several pressure classes, which relate to working
pressures in pound per square inches, like 150 lb., 300 lb., 600 lb., and others. ANSI
Standard B16.5 gives dimensional data and operating pressure ratings for seven flange
classes 150 through 2500 for various steel and alloy flanges.
(See the table A.3. in Appendix)
Cast or ductile iron flanges are manufactured for threaded connection only. ANSI B16.1
for cast-iron flanges and flanged fittings lists classes 25, 125, 250 and 800 as standard
classifications.
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Piping & Pipeline Components Pipe
II. PIPE
Carbon steel pipe is the most commonly used type of pipe used in the oil and gas
industry. The term "carbon steel pipe" is an accepted practice although the term "wrought
steel pipe" is more correct because it is indicative to the manufacturing process as
opposed to cast-iron pipe. Unfortunately it often causes confusion with wrought iron pipe
which is a specialized product and which should be dealt with separately.
As mentioned before, ANSI B36.10 sets the standard for welded and seamless wrought
steel pipe, including the sizes, schedules and manufacturing process.
There are several different methods of pipe manufacturing in use to produce most of
today's steel piping. Similar manufacturing methods are used to produce other metallic
piping.
BUTT-WELDED PIPE (Furnace Welded)
This pipe is manufactured from flat strips of steel called skelp, with square or slightly
beveled edges. The skelp is mostly produced from steel with high phosphorous content,
which is best suitable for furnace welding. It is furnace heated full length to welding
temperature and then drawn through a funnel welding die, which forms and welds the
pipe both in one step. As an alternative measure, welding rolls can also be employed.
Additional rolling then straightens and finishes the product. This pipe is normally
manufactured in sizes 1/8" through 4", and is lowest in cost among the various types of
steel piping available for use in pressure systems. ANSI/ASTM specifications A-53 and
A-120 relate to this type of piping.
Fig. 1.1. Butt-welded pipe
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Piping & Pipeline Components Pipe
LAP-WELDED PIPE (Furnace Welded)
Lap-welded pipe is also manufactured from skelp, but the ends, which have been scarfed,
overlap in this process instead of being butted together. The skelp is first heated and
shaped into tubular form then reheated to welding temperature, slid over a mandrel and
welded through the compression of two grooved welding rolls that compress the pipe and
achieve a furnace weld. Additional rolling completes the manufacturing process. Pipe
sizes normally range from 4" to 16", and most manufacturing is done to meet ASTM
specification A-53 and A-120.
Fig. 1.2. Lap-welded pipe
ELECTRIC FUSION WELD (EFW)
In this process, a plate with suitably prepared edges is first hot or cold rolled into a
tubular shape. The resulting opening is then welded together, with or without additional
filler material being deposited at the same time. Electric arc welding can be manually or
automatically performed and may be of a single or double joint type, depending on plate
thickness. Minimum size for this type is normally 4", but there is practically no upper
size limit for this type of pipe. ASTM specifications A-134, A-139 ,and A-672 are
applicable for this manufacturing process.
Fig. 1.3. Electric-fusion welded (EFW) pipe
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Piping & Pipeline Components Pipe
ELECTRIC RESISTANCE WELD (ERW)
Similar to the EFW process, a plate is first rolled into tubular form. The welding
operation is then performed at the same time while the tube is being compressed by two
or more pressure rollers. The whole operation can be performed without preheating the
plate or pipe since the welding process employed does not require such a prerequisite.
Pipe sizes 1/2" to 30" are normally available and manufactured in accordance with
ASTM A-53, A-135, or API 5L.
Fig. 1.4. Electric-resistance welded (ERW) pipe
SEAMLESS PIPE
Two different processes can be used to produce seamless piping and tubular products,
namely the hot-piercing and the cupping process.
The hot piercing process starts with a round bar, billet, or bloom (all different names for a
similar unfinished steel product), which is heated to a temperature of over 2000ºF. It then
is pierced and forced over a short mandrel by revolving rolls. The initial product is a
short, thick-walled pipe that through a continuing process of either hot rolling or hot
drawing is brought to the desired size.
Fig. 1. 5. Hot-pierced seamless pipe
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Piping & Pipeline Components Pipe
In the hot-cupping method, a steel plate heated to forging temperature is placed against a
bottom die and a round nosed plunger is pushed through. The emerging cup is repeatedly
heated and forced through smaller dies, while a closed end remains. The closed end is
finally cut off and the resultant pipe is straightened.
Fig. 1.6. Hot-cupped seamless pipe
Standards ASTM A-106 and API 5L are the preferred standards for this type of pipe.
SPIRAL-WELDED PIPE
As the name implies, steel strips are spirally wound to long cylinders. The edges of the
steel, which may abut or overlap, are then butt welded or fillet welded together by the
electric arc method. This pipe, which is mostly manufactured as a thin-walled product is
available in sizes up to 48" and in lengths up to 60 feet long. Specification ASTM A-211
and API 5LS were specially incepted for the production of this type of pipe.
Fig. 1.7. Spiral welded pipe
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Piping & Pipeline Components Pipe
SUBMERGED ARC WELD (SAW)
This process is used to make large diameter pipes (20"-44") in double random lengths. A
flat plate is rolled and pressed into an "O" shape, then welded at the edges both inside and
outside. The pipe is then expanded to the final diameter
PIPE LENGTH
Manufactured pipes are supplied and referred to as single random, double random, longer
than double random and cut lengths.
Single random pipe length is usually 18-22 ft (5.5-6.7 m) threaded and coupled (T&C),
and 18-25 ft (5.5-7.6 m) plain end (PE).
Double random pipe lengths average 38-40 ft (11.6-12.2 m).
Some pipes are available in about 80 ft lengths.
Cut lengths are made to order within ± 1/8".
The major manufacturers of pipe offer brochures on their process of manufacturing pipes.
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Piping & Pipeline Components Flange
III. FLANGES
Flanges are used to join pipes, valves, or vessels within a piping system through a
mechanical joint. This mechanical joint makes use of bolts and nuts connection that can
be easily assembled and dissembled, so the joined components can be modified, serviced,
or replaced. A downside of this connection is that the joints cannot be as tight as welded
joints, so flanges must always use gaskets to prevent any leaks.
As mentioned before pressure ratings for flanges are designed to ANSI (B16.5) standards
of 150 lb., 300 lb., 400 lb., 600lb., 900 lb., 1500 lb., and 2500 lb. The most common
terminology used is the pound reference, although the more formal reference is by class,
such as Class 150 flange. It should be noted that ANSI B16.5 only covers sizes up to 24".
Steel flanges larger than that are largely following MSS Standard Practices SP-44, or
ANSI B16.1 for cast iron flanges. API Specification 605 also covers large diameter
flanges but is mostly restricted to the petroleum industry.
The ANSI standards require that each flange be stamped with identifying markings as
shown in the Figure 3.1. below:
Fig.3.1. Typical Flange
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Piping & Pipeline Components Flange
1. Manufacturer's trade name.
2. Nominal pipe size
3. Primary pressure rating
4. Face designation - the machined gasket surface area of the flange.
The flange face is the most important part of the flange. The 1/16" raised face
is common in CL150 and CL300 classes. Heavier ratings are 1/4" raised faces.
A ring type joint is available in all classes, but more common in the CL600
and higher classes.
5. Bore (also known as nominal wall thickness of matching pipe) - the measure
of the flange wall thickness, which matches the inside dimension of the pipe
being used. Weldneck and socketweld flanges are drilled (machined) with the
wall thickness of the flange having the same dimensions of the matching
pipes. Other flanges are drilled to match the outside diameter pipe sizes, and
do not have bore markings to indicate pipe schedule.
6. Material designation - ASTM specifications that describe the raw materials
from which the flange is made.
7. Ring gasket number - used when the flange face is a ring type joint style.
8. Heat number or code - the batch number used by steel forgers to identify a
particular batch number of steel forgings and test results. The mill test results
are made available to the purchasers of the flanges.
MATERIAL
Flanges are usually made of forged steel. For carbon steel the most common material is
according to ASTM A-105, while for stainless steel the standard A-182 with the specific
alloy content of the steel is used, like A-182-F316L for Stainless Steel 316L.
TYPE OF FLANGE FACES
There are three commonly used face types:
1. Flat Face (FF)
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Piping & Pipeline Components Flange
As the name indicates, this type is flat with no raised parts or grooves on the
surface. Flat face is normally used for cast iron flanges or galvanized flanges.
Normally gaskets of the type flat sheet, or full faced are used.
2. Raised Face (RF)
This flange has a raised part in the center of the face. It is commonly used in
low pressure flanges from C150 ~ CL900. The gasket used are normally spiral
wound gaskets.
3. Ring Joint (RJ)
Normally used for high pressure flanges from CL900 up, this kind has a
groove on its surface to accommodate the ring joint gasket used for it.
Other types of flange faces can be seen on Figure 3.1.
Fig. 3.1. Types of flange faces
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Piping & Pipeline Components Flange
TYPES OF ANSI FLANGES
Weldneck Flange
This flange has a bore matching the dimensions of the opposite pipe. It is the most
common type and normally used for high pressure, cold or hot temperature.
Fig.3.2. Weldneck Flange
Slip-On and Lap-Joint Flanges
These two types are almost identical, as we can see from the figure below. Both types are
slipped on the pipe to be joined, so the inside diameter of the bore shall meet the outside
diameter of the pipe. Note however that a slip-on flange is bored slightly larger than the
OD of the matching pipe. The pipe slips into the flange prior to welding both inside and
outside to prevent leaks.
The lap-joint flange has a curved radius at the bore and face to accommodate a lap-joint
stub end. The lap-joint and stub end assembly is normally used in systems requiring
frequent dismantling for inspection.
Fig. 3.4. Slip on Flange and LapJoint Flange
Threaded Flange
As the name describes, instead of a matching bore, this flange has female threaded end as
the connection to the matching pipe. This type of flange is used in systems not involving
temperature or stresses of any magnitude.
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Piping & Pipeline Components Flange
Fig.3.4. A threaded flange without neck
Socket Weld Flange
This flange looks similar to the slip-on flange, except that this flange has a bore and a
counter bore which is slightly larger than the OD of the matching pipe, allowing the pipe
Fig.3.5. Socketweld Flange
to be inserted. A restriction is built into the bottom of the bore, and has the same ID as
the matching pipe. The flow is not restricted in any direction.
Reducing Flange
This reducing flange is similar in every respect to the full size of the flange from which
reduction is to be made, except from the bore. This flange is described in the same
manner as a reducer, the large end first, the reduction second.
Fig.3.6. Reducing Flange. Notice the small bore compared to the face size
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Piping & Pipeline Components Flange
Blind Flange
A blind flange has no bore, and is used to close ends of piping systems. It also permits
easy access to a line once it has been sealed.
The blind flange is sometimes machined to accept a pipe of the nominal size to which a
reduction is being made. In this case the blind flange acts like a reducing flange. The
reduction can be either threaded or welded.
Fig.3.7. A blind flange has no bore
MISCELLANEOUS FLANGE
Long Weldneck Flange
A special flange used for nozzles on pressure vessels. The hub is always straight, and the
hub thickness is greater than the diameter of any piping that may be bolted to the flange.
Fig.3.8. Long Weldneck Flange
Orifice Flange
The orifice flange is functioned to meter the flow of liquids and gases through a pipe line.
A typical pair of orifice flanges has also jack screws, which are used to spread the flanges
apart in a line to change an orifice plate between the two flanges.
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Piping & Pipeline Components Flange
Fig.3.9. An orifice flanges set
API FLANGES
The difference between API and ANSI flanges is the material from which they are
fabricated and the higher working pressure at which API flanges may be operated.
API flanges are manufactured primarily for use with oil industry high-strength tubular
goods. The API 6A and ANSI B16.5 flanged are similar dimensionally, but they cannot
be interconnected without affecting the overall working pressure rating.
(See the table A.4. in Appendix)
Another difference is the through-bore nominal size designation, such as 1 13/16 and 2
1/16, for 6B flanges in place of old nominal sizes, such as 1 1/2" and 2", for consistency
with 6BX flange size designations.
(See the table A.5. in Appendix)
Some API flanges with casing or tubing threads have hub lengths greater than required
for ANSI flanges. Bore diameter of API flanges should be the same inside diameter as the
pipe to be used.
API flanges are marked with the API monogram, size, pressure rating, ring gasket size,
bore, manufacturer, and a heat number. Some API flanges are marked with the
manufacturers' part or assembly number.
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Piping & Pipeline Components Flange
BOLTS AND GASKETS
Almost all mechanical connection, including flange, need the insertion of a gasket to act
as a retaining seal between the rigid connection surfaces. In many instances, bolts are
required to produce sufficient pressure to and provide a leak-proof seal.
Gasket
The gasket is mostly a compressible material that will permit the leak-proof coupling of
flanges or other surfaces, even if they contain irregularities. For high pressure
applications, gaskets are machined from steel in such a design that they fit into a
prescribed sealing cavities. Through the application of pressure the friction relative to the
sealing surface become so great that no leakage will occur.
Flat gaskets for insertion between flanges are either full face or ring type.
Fig.3.10. Flat face gasket
The full face gasket, normally used for flat faced flanges, covers the entire flange face
and OD and ID of flange and gasket are the same. While for ring-type gasket only the ID
is the same, the OD may equal the inner bolt circle to facilitate installation.
Numerous gasket materials are available, most for the flat-type are listed in ANSI
Standard B16.5
Flanged joints for high pressure/high temperature are often sealed with metallic gaskets
whose shape conforms to the particular sealing indentations, such as ring-joint gaskets or
lens gaskets that have been especially developed for high pressure service in the chemical
industry. ANSI Standard B16.20 covers ring-joint gaskets, while ANSI B16.21 covers
non-metallic gaskets for flanges.
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Piping & Pipeline Components Flange
Bolts
Bolts may generally be classified as machine bolts, stud bolts, or bolt studs.
Fig.3.11. Bolt types
The bolt stud is fully threaded and has a nut affixed at each end, while the thread of the
stud bolt is not continuous, thereby permitting the end with the short thread to be affixed
permanently into any machined surface, which might be use as a alternate flange facing.
Bolting materials, which have been standardized by ASTM include:
A-193 Alloy and SS bolts for HT service
A-194 Carbon and alloy nuts for HT service
A-307 Low carbon steel threaded fasteners
A-320 Alloy steel bolting material for LT service
A-354 Quenched and tempered alloy steel bolts and studs
A-437 Alloy steel turbine type material for HT service
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Piping & Pipeline Components Fitting
IV. FITTINGS
Fittings are used to change the direction or join parts of a piping system. Fittings are
mostly identified or specified in accordance with the method of connection, most
commonly threading, butt welding and socket welding.
BUTTWELD FITTINGS
These type of fittings are specially manufactured fittings that are by means of material
composition and end preparation suitable for welding. The material composition of these
fittings is mostly similar to that of the pipe to which they are connected. Since the
manufacturing process for fittings is different from that being used in pipe, different
specification apply.
Metallic buttweld fittings are normally furnished with 37 1/2 degree beveled ends so that
a V-shaped groove is provided for depositing weld metal wherever a welded connection
being used. Wrought steel fitting and dimensions are specified in ANSI specification
B16.9.
The most common used fittings are listed below:
Elbows
The elbow is the most commonly used fitting. The main manufactured elbows are 90º and
45º elbows, although other types exist like 60º elbows. To obtain a custom angled elbow,
a standard elbow may be trimmed.
Fig.4.1. Long Radius (LR) elbow compared with Short Radius (SR) elbow
The most commonly used elbow is the long radius elbow, where the center-to-face
dimension is one 1½ times the size of the elbow size/NPS. The short radius elbow, with
center-to-face dimension same as the elbow size, is used in systems with tight spaces like
offshore platforms and skid units.
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Piping & Pipeline Components Fitting
Reducing Elbow
The 90º reducing elbow is used to change direction and reduce the flow in the piping
system at the same time.
Fig.4.2. Reducing elbow
180º Returns
The return is used for direction changes of 180 degrees, thus avoiding the use of two 90º
elbows. Like elbows, returns may be long radius or short radius.
Fig.4.3. A 180º Return = 2 x 90º elbow
Tees
A tee is a branched connection to the main flow. At a straight tee, the branch size is the
same as the main size of the tee. While for a reducing tee, the branch size is smaller (up
to half the size) than the main size.
Fig.4.4. Straight tee and Reducing tee
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Piping & Pipeline Components Fitting
Crosses
Straight or reducing crosses are seldom used in systems, except in special cases, like
when there is a limitation of space. Crosses are usually made of sizes 12" or smaller.
Fig.4.5. Crosses are rarely used
Reducers
Reducers are used to reduce a line to a smaller size.
Concentric reducers have inlets and outlets that are on a center line. While eccentric
reducers have off-center outlets, and are flat on one side. Eccentric reducers fit flush
against walls, ceilings, or floor to give greater pipe support to the line.
Fig.4.6. Eccentric reducer and Concentric reducer
Caps
Pipe caps are used to block off the end of a line, by welding it to a pipe to create a dead
end.
Fig.4.7. Cap
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Piping & Pipeline Components Fitting
Lap Joint Stub Ends
The stub end is used in lines requiring quick disconnection. The lap forms a gasket
surface that replaces the gasket surface of a flange, and is mated with a lap joint flange.
Fig.4.8. Stub end
Special Buttweld Fittings
Laterals
A lateral resembles a tee with a 45º branch. Laterals are can only be used for low pressure
applications
Fig.4.9. Straight lateral
Pipe Saddles
The saddle is to reinforce a junction of pipe or fitting in a line. After a nipple is has been
welded into a line, the saddle is placed over the outlet, and welded to both the outlet and
the line
Fig.4.10. Saddle
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Piping & Pipeline Components Fitting
Pipe Bends
Pipe bends are basically elbows created from pipes with large radius to avoid sharp
directional changes. The center-to-face dimension is usually at least five times the pipe
size (5R), although 3R pipe bends also exist.
Pipe bends are commonly used in pipelines that need pigging. The long curvature of the
bend allows the pig to go through the line more smoothly.
Scraper Bar Tees
Also called simply barred tee, this is a tee with bars fabricated in the branch outlet of the
tee. The bars limit the direction of a pipeline pig, which travels through the pipeline.
Fig.4.11. Scraper bar tee
THREADED FITTINGS
Threaded ended fittings exist to sizes up to 4". These fittings are made of forged material
like ASTM A-105 for carbon steel, A-182 for stainless steel. Threaded forged fittings are
standardized in ANSI B16.11, and consist of ratings 2000, 3000, and 6000. The greater
the ratings the heavier the wall thickness. The threading is according to ANSI B1.20.1.
All threads are slightly tapered, which helps to make it a leak proof joint. The leak proof
sealing is mostly achieved by covering the threaded pipe part with a sealing compound
and/or plastic tape, hemp, or string.
Components covered by threaded fittings are generally the same as for welded fittings,
with additional components as followed:
- Plugs - hexagon, round, square or flush
- Bushings - hexagon or flush
- Street elbow, tee, or union
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Piping & Pipeline Components Fitting
- Unions
- Couplings and half couplings
Fig. 4.12. Threaded fittings
SOCKET WELD FITTINGS
Like threaded fittings, socket weld fittings are mostly restricted to sizes up to 4". Socket
weld fitting are also covered in ANSI B16.11, with common ratings of 3000, 6000, and
9000. Most socket weld fittings are similar to threaded fittings, except the term "reducing
insert" is used instead of "bushing".
This type of connection is provided with a bell-shaped end that is internally machined, do
it can encompass the external diameter of the pipe that fits into it. The actual inside
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Piping & Pipeline Components Fitting
diameter of the fitting matches the internal diameter of the pipe it connects. During
construction, care should be taken that the pipe does not butt against the internal shoulder
of the fitting but rather leaves a miniscule space for expansion during welding process.
Fig. 4.13. Socketweld fittings
BRANCH OLET CONNECTION
Olet connections are an alternative choice to make branches that have a big size
difference with the main line size (usually for branch sizes less than half the size of the
main size). Nevertheless olets can also be used to replace tees in low pressure
applications, where the cutting of a straight pipe (to install a tee) is undesirable.
Olets are made of forged material, and are buttwelded on the run of the main pipe.
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Piping & Pipeline Components Fitting
The most common used are:
- Thredolet - uses with a threaded outlet, size ranges up to 4".
- Sockolet - same as thredolet but has a socket weld output.
- Weldolet - with buttweld outlet, used for large branch sizes (2" up)
- Sweepolet - resembles a saddle, can support the branch line welded on it.
- Elbolet - welded to a 90º elbow to form an outlet
Fig.4.14. Miscellaneous Olets
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Piping & Pipeline Components Valve
V. VALVE
Valves are the components in a fluid flow or pressure system which regulate either the
flow or the pressure of the fluid. These tasks are performed by adjusting the position of
the closure member in the valve. This may be done manually or automatically. In this
section we concern ourselves on to manual operated valves and check valves.
Valves in any piping system serve three elementary functions:
- Shut off or open a system to fluid flow
- Regulate or throttle any fluid flow
- Prevent backflow
Manual valves may be grouped according to the way the closure member moves onto the
seat:
1. Closing down valves
A stopper-like closure member is moved to and from the seat in the direction
of the seat axis.
2. Slide valves
A gate-like closure member is moved across the flow passage.
3. Rotary valves
A plug-like closure member is rotated within the flow passage, around an axis
normal to the flow stream.
4. Flex-body valves
The closure member flexes the valve body.
Each valve group represents a number of distinct type of valves which use the same
method of flow regulation, but differ in the shape of the closure member. For example,
plug valves and butterfly valves are both rotary valves but of a different type. In addition,
each type is made in numerous variations to satisfy service needs.
Figure 5.1 lists the principal methods of flow regulation and the types of valve belonging
to that particular group.
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Piping & Pipeline Components Valve
Valve Group Valve Type
Sliding
Parallel Gate Valve
Wedge Gate Valve
Closing Down
Globe Valve
Piston Valve
Rotating
Plug Valve
Ball Valve
Butterfly Valve
Flexing of valve body
Diaphragm Valve
Pinch Valve
Table 5.1. Principal type of valves according to flow regulation method
VALVE END CONNECTION
Valves may be provided with any type of end connection used to connect piping. The
most important of these are (like for fittings) threaded, flanged, and welding end
connections.
Threaded End Connection
These are made with taper or parallel female threads which screw over tapered male pipe
threads. Because such kind of joint contains large leakage passages, a sealant or filler is
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Piping & Pipeline Components Valve
used to close the leakage passages. If construction material of the valve body is weldable,
screwed joint may also be seal welded, especially if the mating parts of the joint are made
of different materials with widely different coefficients of expansion, and if the operating
temperature cycles within a wide range.
Valves with these ends are commonly used in sizes up to 2". As the valve size increases,
installing and sealing the joint becomes rapidly more difficult, so the largest size
available for threaded valves is 6".
Codes may restrict the use of threaded end valves, depending on application.
Flanged End Connections
These connections enable the valve to be easily installed and removed from the pipeline.
However, flanged valves are bulkier than threaded end valves and therefore also dearer.
Because flanged joints are tightened by a number of bolts, which individually require less
tightening torque than a corresponding screwed joint, they can be adapted for all sizes
and pressures. At temperatures above 350º C (660º F), however, creep relaxation of the
bolts, gaskets, and flanges can in time lower the bolt load noticeably, so highly stressed
flanged joints at this these temperatures can develop leakage problems.
Welding End Connections
These kinds of connection are suitable for all pressures and temperatures, and are
considerably more reliable at elevated temperatures and other severe applications than
flanged connections. However, removal and re-installation of the valves are more
difficult. Therefore, the use of welding end valves is normally restricted to applications
where the valve is expected to operate reliably for long periods, for critical applications,
or for high temperature applications.
Welding end valves up to 2" are usually provided with sockets which receive plin end
pipes. Because socket weld joints form a crevice between socket and pipe, there is the
possibility of crevice corrosion with some fluids. Pipe vibrations may also fatigue the
joint. Therefore the use of socket weld valves is restricted by codes.
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Piping & Pipeline Components Valve
VALVE RATINGS
The rating of valve defines the pressure-temperature relationship within which the valve
maybe operated.
The responsibility for determining valve ratings has been left over the years largely to
individual manufacturer. The frequent USA practice of stating the pressure rating of
general purpose valves in terms of WOG (water, oil, gas) and WSP (wet steam pressure)
is a carry-over from the days when water, oil, gas, and wet steam were the substances
generally carried in piping systems. The WOG ratings refer to room temperature rating,
while the WSP rating is usually the high temperature rating. When both a high and low
temperature ratings are given, it is generally understood that a straight line pressure-
temperature relation exists between the two points.
Some US and British standards on flanged valves set ratings which equal the standard
flange rating. Both groups of standards also state the allowable construction material for
the pressure containing valve parts. The rating of welding end valves corresponds
frequently to the rating of flanged valves. However, standards may permit welding end
valves to be designed to special ratings which meet the actual operating conditions. If the
valves contain components made of polymeric materials, the pressure-temperature
relationship is limited, as determined by the properties of the polymeric material. Some
standards for valves containing such materials - like ball valves - specify a minimum
pressure-temperature relationship for the valve. Where such standards do not exist, it is
the manufacturer's responsibility to state the pressure and temperature limitations of the
valve.
VALVE STANDARDS
To ensure interchangeability and reasonable functioning of the valve, valve standards
have to be applied. These standards cover face-to-face dimensions, material of
construction, pressure-temperature ratings, design dimensions for some of the valve
components to ensure adequate strength, and testing procedures. Detail design is the
responsibility of the manufacturer.
For example the mostly known standards are:
• ANSI B16.10 - Face-to-face and end-to-end dimensions of ferrous valves
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Piping & Pipeline Components Valve
• ANSI B16.34 - Steel valves, flanged and butt-welding end.
• API 598 - valve inspection and test
• API 600 - steel gate valves, flanged and butt welding ends
• API 602 - compact carbon steel gate valves
• And many others.
VALVE SELECTION CHART
The following chart a may serve as a guideline to select a valve type for a given flow-
regulating duty.
Valve Mode of Flow Regulation FluidSolid in SuspensionsGroup Type on-off throttling diverting Free of
solids Non-abrasive AbrasiveSticky Sanitary
Sliding Parallel Gate: - conventional Yes Yes - conduit gate Yes Yes Yes Yes - knife gate Yes Special Yes Yes YesWedge Gate: - w/ bottom cavity Yes Yes
Yes Moderate Yes Yes - w/o bottom cavity
(rubber seated)Globe :Closing
Down - straight pattern Yes Yes Yes - angle pattern Yes Yes Yes Special Special - oblique pattern Yes Yes Yes Special - multiport pattern Yes YesPiston Yes Yes Yes Yes Special
Rotating Plug: - non-lubricated Yes Moderate Yes Yes Yes Yes - lubricated Yes Yes Yes Yes Yes - eccentric plug Yes Moderate Yes Yes Yes - lift plug Yes Yes Yes Yes YesBall Yes Moderate Yes Yes YesButterfly Yes Yes Special Yes Yes Yes
Flexing Pinch Yes Yes Special Yes Yes Yes Yes YesDiaphragm - weir type Yes Yes Yes Yes Yes Yes - straight-through Yes Moderate Yes Yes Yes Yes
Table 5.2. Valve selection chart
As for the construction material, it is determined on the one hand by the operating
pressure-temperature in conjunction with the applicable standards, and on the other hand
by the properties of the fluid, its corrosive and erosive properties.
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Piping & Pipeline Components Valve
VALVE TRIM
This is a normal designation given to various working parts of a valve, such a stem,
wedge, disc, plug, seat, etc., which are all additives to the basic valve body. Valve trim
materials may be composed of half dozen different materials. In many cases, it is very
important to specify the correct material for a given material.
All valve fabricators normally designate their product through a numbering system, but
this does not always suffice to identify some of the trim materials. It is therefore
important to specify a valve requirement in detail.
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Piping & Pipeline Components Valve
GATE VALVES
Gate valves are mostly multiturn valves that consist of (in their basic construction) a
valve body, seat and disc, spindle or stem, gland, and rotating wheel. The seat is located
at the bottom of the valve and may be fixed or removed together with the disc to provide
the actual valve components which regulate the flow.
Fig. 5.1. Wedge type gate valve
Seating in a gate valve is at a right angle to the line of flow, which makes the valve
impractical for throttling operations and makes close regulations a near impossibility.
Therefore gate valves are mostly used as stop valves, either it provides full flow or it is
fully shut-off. The flow moves in a straight line, practically without resistance, when the
disc it fully raised. Gate valves are ideally suited for wide-open service, such as at outlets
of a storage tanks, for liquids in oil and gas pipelines, and firelines.
To actuate a gate valve, the disc is either raised or lowered by means of a stem that
projects outside the valve body, and is activated by a handwheel for small to medium
sized valves, or a gear operator for large sized valves. The protrusion of the stem to the
outside atmosphere requires some method of retaining the fluid in the pipeline, which is
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Piping & Pipeline Components Valve
accomplished by installing a gland packed with a fluid-resisting barrier to prevent
leakage. Packing glands are often of simple construction with a threaded gland follower
and graphited packing material, especially for smaller valves. However larger valves
need more sophisticated designs, using lantern-type or bellow seals for packings, and an
out outside screw and yoke (OS&Y) to hold the gland follower.
Fig. 5.2. Valve gland types
Some valves are designed with a rising stem (as opposed to a non-rising stem), where an
indicator riding on the spindle can show if and to what degree the valve is open. The
screw for rising or lowering the stem may be located inside or outside the valve body.
The inside screw permits an economical bonnet construction, but has the disadvantage
that it cannot be serviced from outside. This construction is therefore best suited for
fluids which have good lubricity. For the majority of minor duties, however, the inside
screw gives good service. The outside screw, being able to be serviced from the outside,
is preferred for severe duties.
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Piping & Pipeline Components Valve
Fig. 5.3. Valve stems
Bonnets may be joined to the valve body by screwing, flanging, welding, or by means of
a pressure-seal mechanism; or the bonnet may be an integral part of valve body.
The simplest and least expensive method is by using a screwed-in bonnet. However, the
bonnet gasket must accommodate itself to rotating faces, and frequent unscrewing of the
bonnet may damage the joint faces. The bonnet may therefore also be held by a separate
screwed union ring or a U-bolt may be used, to prevent any motion between the joint
faces as the joint is being tightened, so frequent unscrewing won't harm the joint faces.
These screwed construction require a very large torque to tighten the join for larger
valves, so the their use is restricted to valve sizes normally not greater than 3" NPS.
Flanged bonnet joints, compared to screwed joints, have the advantage that the tightening
effort can be spread over a number of bolts. Therefore flanged joints may be used for any
valve size and rating, However at higher sizes and ratings, the joint becomes increasingly
heavy and bulky. Also at 350ºC, creep relaxation may considerably lower the bolt load.
At critical applications, the flanged joints may be seal welded.
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Piping & Pipeline Components Valve
With the introduction of satisfactory welding techniques, welded bonnets may become
another option. These constructions are not only economical but also most reliable,
irrespective to size, operating temperature or pressure. On the other hand, the valve
internals can only be accessed by removing the weld. For this reason, welded bonnets
normally used only where the valve can be expected to be maintenance free for long
periods.
For large valves at high pressures and temperatures, pressure-seal bonnets are preferred.
These bonnets makes use of the fluid pressure by letting the pressure tighten the joint.
The bonnet seal therefore becomes tighter as the fluid pressure increases.
Fig. 5.4. Valve bonnet types Fig. 5.5. Pressure-seal valve
According to the disc type, gate valves may be grouped into parallel (disc) gate valves
and wedge gate valves.
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Piping & Pipeline Components Valve
Parallel Gate Valves
Parallel gate valves have parallel-faced gate-like closure member, that may consist of a
single disc or twin-discs with a spreading mechanism in-between. The force which
presses the disc against the seat is controlled by the fluid pressure acting on either the
floating disc or a floating seat. In case of a twin-disc, this force may be supplemented
with a mechanical force from the spreading mechanism between the discs.
One advantage of the parallel gate valves is their low resistance to flow, which in case of
full-bore valves is similar of a short straight pipe, Because the disc slides across the seat
face, parallel gate valves are also capable of handling fluids which carry solids in
suspension.
Fig. 5.6. Parallel double-disc gate valve
On the disadvantage side, if the fluid pressure is low, the seating force may be
insufficient to produce a satisfactory seat seal in metal-seated valves. On the other hand,
at high fluid pressures, frequent valve operations may lead to excessive wear of the
seating faces, unless the seatings are lubricated by the system fluid or an external fluid.
A further disadvantage is that that flow control from a circular disc traveling across a
circular flow passage becomes satisfactorily responsive only between 50% closed to the
fully closed valve position. Furthermore the disc tends to rattle violently when shearing
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Piping & Pipeline Components Valve
high-velocity and high-density flow. Therefore parallel gate valves are normally used
only for on-off duties, which requires infrequent operations.
Conduit gate valves are full-bore valves with a smooth round bore that permits passage of
pigs in pipeline services. The disc of these valves also seals the body cavity against the
ingress of solids in both the open and closed valve positions.
Fig.5.7. Conduit gate valve
Another variation is the knife gate valve. This valve has a very thin, knife-like disc and is
mostly used in specialty applications, like in the paper industry or for slurry services.
Because of special design features, the valve is clog-proof, and materials that otherwise
might cause an obstruction in the valve port are sheared off.
Wedge Gate Valve
Wedge gate valves differ from parallel gate valves in that the closure member is wedge-
shaped instead of parallel. The purpose of the wedge shape is to introduce a high
supplementary seating load which enables metal-seated wedge gate valves to seal not
only against high but also low fluid pressures. Therefore a metal-seated edge gate valve
may gain a higher degree of seat tightness. However, the upstream seating load due
wedging is not normally high enough to achieve an upstream seat seal with metal seated
wedge valves.
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Piping & Pipeline Components Valve
The body of these valves has guide rips, in which the wedge travels, and prevents the
wedge from rotating during travel. This will ensure proper alignment of the seatings, and
carry the wedge away from the downstream seat (except for a short distance near the
closed position), thereby lessening wear on the seatings.
On the debit side, wedge gate valves cannot accommodate a follower conduit as
conveniently as parallel gate valves, and thermal expansions of the valve stem can
overload the seatings. Moreover, the seatings tend to trap solids. However, rubber-seated
wedge gate valves are capable of sealing around small-trapped solids.
A single-wedge disc gate valve is usually solid and fits into tapered valve seats, which
may be replaceable, or into an internal part of the valve body. This single wedge design is
particularly suited to overcome misalignment and dimensional changes within the valve
body due to temperature variations.
A variation of the solid wedge is the so-called flexible disc. This disc is only solid
through the center, so the movement of the faces relative to each other is possible. This
flexibility can assist greatly in ease of operation and guaranteeing valve tightness, not
only on the inlet seat but also on the outlet seal.
Fig.5.8. Flexible wedge gate valve
Another design used in conjunction with tapered valve seats is the split wedge.
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Piping & Pipeline Components Valve
Large-sized valves are often provided with a bypass around the valves seat, which may
assist in pressure equalization or warm-up of a steam carrying pipeline.
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Piping & Pipeline Components Valve
GLOBE VALVES
Globe valves are closing-down valves in which the closure member, customarily called
disc, is moved squarely on and off the seat. By this mode of disc travel, the seat opening
varies in direct proportion to the travel of the disc. This proportional relationship between
valve opening and disc travel is ideally suited for duties involving regulation of flow rate.
In addition, the seating load can be positively controlled by a screwed stem, and the disc
moves with little or no friction onto the seat. The sealing capacity of these valves is
therefore potentially high. On the debit side, the seatings may trap solids.
Bonnet, gland, and stem design of globe valves is in many respects similar to gate valves,
but the valves internals are markedly different.
Fig.5.9. Various globe valves disc types
As seen in figure 5.9., there are various types of globe valves according to disc type.
The ball type disc is the oldest kind of globe valve, later to be replaced by the
conventional type, which has retained most of the features of the ball type with the
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Piping & Pipeline Components Valve
exception of the convex shape of the disc. The basic design feature is a flat surfaced
though internally slightly tapered valve seat that is fitted with a disc of convex
configuration that uses the taper in the seat for closing. This type of seating has a narrow
line contact that normally assists an easy pressure-tight closure; however deposits of
solids usually prevent such a tight closure.
The renewable or composition disc got its name from the material rather than from the
configuration of the disc. The disc is normally a circular shape, approximately 3/16" thick
piece of material. This material used to be made from compressed fiber or leather, but
today is mostly plastic depending on application. The renewable disc is fitted into a disc
holder and retained by a small screw. Closure is affected against a thin lip protruding
from and actually constituting the valve seat.
The plug-type disc is the best suited for throttling applications, and also best to withstand
the high pressure and high temperature service. The long tapered plug is fitted into a
corresponding seat to provide a wide area of seating contact, combined with a proper
selection of metals. This is most effective in resist erosive effects of close throttling. Both
seat and plugs may be replaced in most plug-type globe valves.
Needle-point valves are designed to give fine control of flow in small diameter piping.
The name is derived from the sharp-pointed elongated plug that replaces the disc, and
which matches with an orifice-like seat area. Even when fully open, the needle-point
doesn't permit a full flow, since the open seat is only a fraction of the piping flow area.
Therefore this kind of valve is suitable in situation which need close regulations, like in
calibrating instruments.
The basic patterns of globe valves bodies are:
- straight pattern, the most common one with also the highest flow resistance
- angle pattern, with lesser flow resistance than straight ones, and provides a
flow direction change.
- oblique pattern or Y type, with a minimum flow resistance.
- multiport pattern
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Piping & Pipeline Components Valve
PLUG VALVE
Plug valves are rotary valves in which a plug-shaped closure member is rotated through
increments of 90º to engage or disengage a port hole/holes in the plug with the ports in
the valve body. The shape of the plug may be cylindrical or tapered/conical, while the
ports are normally rectangular for cylindrical plugs, and truncated triangular for tapered
plugs. Full area round-bore plugs are normally only used in pipelines that need pigging,
or where the pressure drop has to be minimized.
Plug valves are best suited for starting and stopping flow and flow-diversion, though
some may be used for moderate throttling, depending on the nature of the service and
erosion resistance of the seatings.
Because the seatings move against each other with a wiping motion, and in the fully open
position are also fully protected from the flowing fluid, plug valve are generally capable
of handling fluids with solids in suspension.
One outstanding feature of this valve is it's quick opening and closing operation, which
only needs a quarter turn. Small valves may be wrenched, while larger need gear
operators.
The plug valve basic form is of very simple design and consists of three parts: body, plug,
and cover. Of this three parts only the plug is non-stationary.
Fig.5.10. Basic plug valve
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Piping & Pipeline Components Valve
A variation of the standard plug is the eccentric plug, which is only about one-third of a
full plug in area. It permits a full flowthrough in the open position and closes with less
contact of the seat on body walls.
Two main groupings of plug valves are lubricated and non lubricated valves.
Non Lubricated Plug Valves
Like the name says, this valve has no lubrication. The use of cylindrical plugs is often
preferred, since they are less likely to experience galling or freezing than conical plugs.
In various designs, plastic seals are often molded into grooves of the plug to provide
better seals, with bottom springs to assist the operation. Depending to the manufacturer,
the plug may be inserted from the top or the bottom into the valve body.
A variation of the standard plug is the eccentric plug, which is only about one-third of a
full plug in area. It permits a full flowthrough in the open position and closes with less
contact of the seat on body walls.
Fig.5.11. Cylindrical plug valve
Lubricated Plug Valves
In this valve, a lubricant is forced into various grooves in the plug body to minimize
friction and thereby prevent sticking, also assisting in sealing surfaces and valve stem.
The lubricant pressure is also used to unseat the plug from its position and through this
action nullifies any adhesion which may have taken place.
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Piping & Pipeline Components Valve
The plug itself may be cylindrical or tapered. Tapered plugs permit the leakage gap
between the seatings to be adjusted by adjusting the plug deeper into the seat. They are
also quicker and simpler to operate. Cylindrical plugs may have special sealing
constructions, such as spring-loading or Teflon bearings to ease the operation.
BALL VALVES
Ball valves, can be said, evolved of plug valves, with it's ball-shaped closure member
replacing the plug. The seat matching the ball is circular so that the seating stress is
circumferentially uniform. Most ball valves are also equipped with soft seats which
conform readily to the surface of the ball. So form the point of sealing, the concept of ball
valve is excellent.
Ball valves are normally manufactured with easy disconnect features. Some classic
designs permit the removal of the ball through the top, and called Top Entry valves.
Others may allow the removal through the end or side entry.
To economize in the valve construction, most ball valves have a reduced bore with a
venturi-shaped flow passage of about three-quarters the nominal ball size, permitting a
justifiably small pressure drop. However other applications may still need full-bore
valves.
Fig.5.12. Typical ball valve
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Piping & Pipeline Components Valve
Seat Materials
The most popular seat material for ball valves is PTFE, which is inert to almost all
chemicals, has a low coefficient of friction, a wide range of temperature application, and
excellent sealing properties. However PTFE has also a high coefficient of expansion, it is
susceptible to cold flow, and poor heat transfer.
Other widely used seat materials include plastics, like filled PTFE, nylon, and many
others. Elastomers, such as buna-N are also popular materials, although they tend to grip
the ball and need lubrication.
For special cases metallic and carbon graphite seats are also used.
Fig.5.13. Pressure-Temperature ranges of seating inserts
Fire Safe Construction
Valves, with soft-seated and sealed balls, handling flammable may have to be provided
with emergency seals which come into operation should the soft seals burn out in a fire.
These emergency seals consist normally of a sharp-edged or chamfered secondary metal
seat in close proximity to the ball, so that the ball can float against the metal seat after the
soft-seating rings have disintegrated. The stuffing box may be fitted with an auxiliary
asbestos or graphite packing, or the packing may be made entirely of asbestos or graphite.
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Piping & Pipeline Components Valve
BUTTERFLY VALVE
Butterfly valves are rotary valves in which a disc-shaped closure member is rotated
through 90º to open and close the flow passage. But unlike the ball valve, the closure
member for the butterfly is shaped as a disc, so there is considerably less space taken by
the valve. This valve design is particularly suitable for installation where space
consideration is important and makes this valve type a favorite for very large piping
systems, since there is practically no size limitation.
Fig.5.14. Butterfly valve, lug wafer type
A butterfly valve basically consists of a valve body, shaft and butterfly disc, sealing
gland, and valve operator. According to the valve body, three common types are known:
- Flanged butterfly valve
- Lug-wafer butterfly valve
- Wafer butterfly valve
The origin of the butterfly valve comes from the shutter-like damper, which was initially
not intended for tight shut-off, but rather served more as a flow restriction, mostly for
water. But today’s valves, which are mostly outfitted with rubber or elastomer seats,
provide a tight shut-off like any other valve, and not only for water.
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Piping & Pipeline Components Valve
A fully open butterfly valve gives little resistance to flow. It provides a sensitive flow
control when open between 15º and 70º. But if it closed to fast in liquid service,
waterhammer may become excessive.
Seating designs
From the point of seat tightness, butterfly valves may be divided into three types:
- Nominal leakage valves
- Low leakage valves
- Tight shut-off valves
The first two types are mainly used for throttling or flow control duty, while the third one
can also be used for tight shut-off (as the name indicates).
The following figure illustrates nominal and low leakage valves seatings, where the both
the disc and seat are metallic.
Fig.5.15. Various seatings for butterfly valve
For tight shut-off valves, the sealings can be done in several ways:
- By interference seating
- By pressing the disc against the seat
- By dynamic sealing, where the fluid pressure tightens the seal
Because the disc moves to the seat in a wiping motion, most butterfly valves are capable
of handling fluids with solids in suspension and, depending on the robustness of the
seatings, also powders and granules.
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Piping & Pipeline Components Valve
DIAPHRAGM VALVE
Diaphragm valve are type of flex-body valves in which the body flexibility is provided by
diaphragm. The closure member therefore is a compressor which is connected to the
diaphragm. Diaphragm valves have the advantage that the flow passage is not obstructed
by moving parts and is free of crevices, and therefore suited for sanitary handling of food
stuffs and pharmaceuticals.
A diaphragm valves consists of only three basic elements: the valve body, valve
diaphragm, and the operating mechanism, which might be referred as valve bonnet.
The valve body itself has two basic types:
- Weir type, designed for short stroke between closed and fully open position.
The flexing stress of the diaphragm is therefore minimum, resulting in a
corresponding long diaphragm life. Weir type valves may also be used for
flow control within the nearly closed and the two-thirds valve positions.
- Straight-through type, with a relatively long stroke which requires more
flexible diaphragm construction materials. Thus its application is restricted.
Fig.5.16. Types of diaphragm valves, weir (left) and straight-through(right)
The operating mechanism is a convex compressor disc that can be raised or lowered by a
handwheel-operated stem or spindle. An air actuator may also be used by applying
compressed air with or without the assistance of a helical spring.
The main valve feature, the diaphragm itself, may be furnished in a variety of elastomeric
materials or rubber, depending on the valve service requirements. The resilient
diaphragm provides a cushioned leak-tight closure and is designed so the fluid cannot
penetrate it, isolating bonnet and operating mechanism from the fluid. This eliminates the
need for glands or valve-stem packings.
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Piping & Pipeline Components Valve
PINCH VALVES
Pinch valves are flex-body valves, consisting of a flexible tube (rubber or plastic) which
is pinched either mechanically, or by the application of a fluid pressure to the outside of
the valve body. The tube may be fully enclosed in a metal body or may just be encased in
a clamp-like device that provides pressure to interrupt the fluid flow.
Since there are no internal operating mechanisms, this valve provides a unique non-
clogging service, which is also resistant to a variety of abrasives. Pinch valves are
therefore favored for flow control of slurries and other abrasive liquid or semi-liquids. It
is also suitable for the sanitary handling of food stuffs and pharmaceuticals.
End connections are mostly flanged type when the tube is fully contained, or the tube
may be directly fastened to the adjacent pipe. Because of the simplistic construction, no
maintenance is required, however the inner tube must be replaced periodically.
Fig.5.17. Pinch valve, open construction
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Piping & Pipeline Components Valve
CHECK VALVE
Check valves are automatic valve, which open with forward flow and close against
reverse flow. This mode of flow regulation is required to prevent return flow, like to
prevent pumps and compressors from driving standby units in reverse. Check valves may
also be needed in lines feeding a secondary system, in which the pressure can rise above
that of the primary system.
The valve body has an arrow indicating the direction of flow, to prevent wrong
installation. There are two basic types of valve bonnet: flanged or threaded.
Although there are only two basic categories of check valves, namely swing check valves
and lift check valves, each has many variants. Like other valve types, check valves can
have body materials and end preparation to suit any given piping system.
Swing Check Valve
This type is the most widely used check valve in general industry, since it offers little
flow resistance and is virtually foolproof in operation. Like gate or globe valves, swing
check valves have a valve seat and a disc that is the only moving part. This disc, which is
hinged at the top, seats against a machined seta in the tilted bridge wall opening. The disc
swings freely in an arc from fully closed position to one providing unobstructed flow.
Disc can be furnished with metallic or non-metallic facings, depending on operational or
maintaining requirements. An outside lever and weight may be attached to increase
sensitivity to flow.
Fig.5.18. Swing check valve.
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Piping & Pipeline Components Valve
A variation of the regular swing check valve is the tilting-disc check valve. The hinges
that support the disc are located just above the center of the disc. This different pivot
point is instrumental in minimizing slamming. These types are made for sizes of 2” and
above.
Fig.5.19. Tilted disc check valve.
Lift Check Valve
Lift check valves can be divided into three different types of construction and
application:
1. Horizontal-lift check valves. These valves have an internal construction similar to
globe valves, and the same body casting is often used here. The disc is seated on a
horizontal seat and equipped with guides above and/or below the seat and is
guided in a vertical movement by integral guides in the seat bridge or the valve
bonnet.
Fig.5.20. Horizontal-lift check valve
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Piping & Pipeline Components Valve
2. Vertical-lift check valves. These valves have the same guiding principle as the
horizontal ones, namely a free-floating guided disc that rests when inoperative on
the seat. Vertical-lift valves are installed in a vertical piping system with an
upward-directed flow.
3. Ball check valves. These valves have a ball as a flow-control medium instead of a
disc. When operating, the ball is constantly in motion, reducing the effects of
wear on any particular area of its sphere. This type has been found well suited for
manufacture and operation in plastic materials. However, the weight of the ball
restricts the application of this valves up to 2”.
Wafer Check Valve
One other important type of check valves widely used is the wafer check valve. This
valve looks like a butterfly valve without operator and similar to the butterfly valve is
installed between two existing pipe flanges. The most common type of wafer check
valves has a discs composed of two separate half disc that are mounted through hinges on
one pin. For flowthrough, the two disc halves fold back and are side by side in the center
of the pipe. The closing is performed with the assistance of separate spring arrangements
for each half disc.
Fig.5.21. Wafer check valve
This design reduces the length of path along which the center of gravity of the disc
travels and therefore the response of the valve to retarding flow. It also reduces the
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Piping & Pipeline Components Valve
weight considerably, which is very important on structures with limited weight load
allowance like on offshore platforms.
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Piping & Pipeline Components Specialties
VI. PIPING SPECIALTIES
There are numerous specialties manufactured to perform a special service. Some of the
most common types in piping systems are described below.
Spectacle Blinds and Spacers
Spectacle blinds are being used to ensure a 100% cutoff to flow in any piping system,
like at maintenance work on certain equipment. Spectacle blinds are named so because
they resemble a giant pair of spectacles. One side is the solid blind flange, the other side
provides full flow through a cut-out inner circle, with a small bridge between the two
sides with a single or double bolt hole.
For large sizes the two sides are too heavy to be joined together, so they consists as two
parts: the spacer and the blind.
Fig.6.1. Spectacle Blinds
Safety or Relief Valve
A safety relief valve is a major protective device that is designed to avoid accidents
through relieving pressure when a malfunction occurs in the system or vessel that is
protected. It is one of the few equipments that has a standby function most of the time,
but whose operation need a split second timing in case of need.
The re-closing of the device is as important as the quick opening, so the re-closing should
occur automatically at a designated pressure.
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Piping & Pipeline Components Specialties
Fig.6.2. Safety relief valve
Rupture Discs
A rupture disc is a non-reusable overpressure relief device that ruptures when it is
exposed to a designated pressure rating. Unlike the safety relief valve the rupture disc has
no closing mechanism. It can be installed as the only relief device in a piping system, act
side by side with the relief valve, or in series with the relief valve to isolate the valve
internals against corrosive process fluid.
Fig.6.3. Rupture disc
Strainers
Strainers are used to filter a fluid , preventing contamination and possible mishap. Some
are permanently installed in a piping system, some only temporarily.
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Piping & Pipeline Components Specialties
It is a good start-up practice to install a strainer in any pump suction prior to operation to
ensure no debris or sediments that may have been left during construction or maintenance
will contaminate the fluid and damage the pump internal components.
Some most known strainers are:
• Plate strainers, a perforated blind flange often covered with wire mesh and
inserted between two flanges.
• Cone strainers, a wire mesh or perforated metal cone attached to a plate rim and
also placed between a flanged connection.
Fig.6.4. Cone Strainer
• Y-type strainers, the most often used strainers in pipelines with sizes of 3” or
smaller. The flow is routed through the screen located in the lateral leg and any
amount of sediment is trapped.
Fig.6.5. Y Strainer
• Basket strainers, used in larger piping systems. A basket-type screen can usually
be inserted and removed through the top of the strainer which is usually flanged.
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Piping & Pipeline Components Specialties
Fig.6.6. Basket Strainer
Steam Traps
A stream trap is an automatic valve that prevents the loss of live steam but permits the
release of water (condensate) and air. No drop in line pressure may be registered as a
result of a steam trap operation
There is no universal steam, but basically there are five different types according to the
operating principles:
• Balanced-Pressure Thermostatic, responds to changes in the temperature between
steam and condensate. These changes vary the vapor pressure in the bellows.
• Liquid Expansion, responds to changes in temperature through the uniform
expansion of the a hydrocarbon oil/
• Float and Thermostatic, responds to difference in density between steam and
condensate and difference in temperature between steam and air or air-steam
mixture.
Fig.6.7. Float & Thermostatic steam trap Fig.6.8. Inverted Bucket Trap
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Piping & Pipeline Components Specialties
• Bucket, responds to changes in density between steam and condensate
• Thermodynamic, responds to difference in kinetic energy between steam and
condensate.
Fig.6.9. Thermodynamic Steam Trap
Expansion Joints
Expansion Joints are used in piping systems where large temperature differentials occur
and space restrictions don’t permit the use of expansion loops.
There are basically two different types of expansion joints:
• Sleeve or Slip-type expansion joint
This type consists of three major parts: an external sleeve connected to the piping
on one side, an internal slip connected to the piping on the other side, and a
stuffing box or packing-gland arrangement to hold the pressure. This type is
manufactured to allow expansion or contraction from an anchor point in either
one or two directions along its axis.
Fig.6.10.Slip-type internally guided expansion joint
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Piping & Pipeline Components Specialties
• Bellows-type expansion joint
Bellows-type or corrugated expansion joints are manufactured as either non-
equalizing (bellows only) or equalizing (with control rings to distribute the
compression equally among the bellows). According to requirement, the number
of bellows used in an expansion joint may range from a single bellows to more
than 20.
Most metallic bellows are fabricated from different materials than the piping
system, including copper, rubber, Teflon, monel , and stainless steel.
Fig.6.11. Bellows-type non-equalizing expansion joint
Flexible Piping
Problems in piping systems or equipment connection through vibration, thermal
expansion, shock or swing connections may be solved by the use of flexible piping that is
especially designed to withstand the rigors of continuous or frequent movement.
For a long time rubber hose in many variations have been used, from plain hose to
multilayered heavily reinforced (with fabric or steel) hose. Inner liners made from
various plastics are also an integral part of many rubber hoses.
Rubber and elastomeric hoses are still limited in many applications, so the development
of metallic flexible hose is designed to fill the need for suitable materials. Two basic
types exists: corrugated and interlocked. Metallic flexible piping is often furnished with
protective covering of braided metal, to preserve the natural contours of the original
corrugations or interlock.
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Piping & Pipeline Components Specialties
Depending on what metallic material is used, application may vary from low
temperatures of liquid nitrogen to 1500º F, even to 3000ºF in certain flexible hoses.
Fig.6.12.Metallic flexible hose