Piping & Pipeline Components

PIPING & PIPELINECOMPONENTS

PIPING DEPARTMENT

compiled by

Budi Nugraha

1

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.

2

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.

3

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.

4

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

5


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

6


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

7


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

8


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.

9

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

10


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)

11


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

12


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.

13


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

14


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.

15


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.


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.


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.

16


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.

17


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

18

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.

19


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

20


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

21


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

22


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

23


- 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

24


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.

25


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

26

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.

27


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

28


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.

29


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

30


• 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.

31


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.

32


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

33


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.

34


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.

35


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.

36


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

37


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.

38


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.

39


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.

40


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

41


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

42


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

43


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.

44


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

45


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.

46


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.

47


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.

48


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.

49


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

50


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.

51


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

52


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

53


weight considerably, which is very important on structures with limited weight load

allowance like on offshore platforms.

54

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.

55


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.

56


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.

57


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

58


• 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

59


• 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.

60


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

Date post:	11-Nov-2014
Category:	Documents
Upload:	adi-okta
View:	161 times
Download:	24 times

Piping & Pipeline Components

Documents