Piping & Pipeline Components

PIPING & PIPELINE COMPONENTS

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, 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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I. STANDARD PIPING TERMINOLOGY

PIPE and TUBING

The term Pipe 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 schedules are actually standardized wall 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 common classifications to 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 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.

Piping & Pipeline Pipeline Components Components

Termi Terminol nolog og y

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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.

Piping & Pipeline Components

Terminolog y

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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


Pipe

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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


Pipe

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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


Pipe

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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


Pipe

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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.


Pipe

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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


Flange

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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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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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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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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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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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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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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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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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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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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


Fitting

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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


Fitting

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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


Fitting

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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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-

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


Fitting

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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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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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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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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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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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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 pressuretemperature 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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•

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 flowregulating duty. Valve Group

Mode of Flow Regulation Type on-off throttling

diverting

Free of solids

Sliding

Parallel Gate: - conventional

Yes

- conduit gate

Yes

- knife gate

Yes

Fluid Solid in Suspensions

Non-abrasive

Sticky

Sanitary

Abrasive

Yes Special

Yes

Yes

Yes

Yes

Yes

Yes

Wedge Gate:

Closing Down

- w/ bottom cavity

Yes

Yes

- w/o bottom cavity

Yes

Moderate

Yes

(rubber seated) Globe : - straight pattern

Yes

Yes

Yes

- angle pattern

Yes

Yes

Yes

Special

- oblique pattern

Yes

Yes

Yes

Special

- multiport pattern Piston Rotating

Flexing

Plug: - non-lubricated

Yes Yes

Yes

Yes

Moderate

- lubricated

Yes

- eccentric plug

Yes

- lift plug

Yes

Yes

Special

Yes Yes

Yes

Special

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Moderate

Ball

Yes

Moderate

Yes

Yes

Yes

Butterfly

Yes

Yes

Special

Yes

Yes

Pinch Diaphragm

Yes

Yes

Special

Yes

Yes

- weir type

Yes

Yes

Yes

- straight-through

Yes

Moderate

Yes

Yes Yes

Yes Yes

Yes

Yes

Yes

Yes

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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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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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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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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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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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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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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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 wedgeshaped 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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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 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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Large-sized valves valves are often provided provided with a bypass bypass around the valves seat, which may assist in pressure equalization or warm-up of a steam carrying pipeline.


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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. 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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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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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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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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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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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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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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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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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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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 nonclogging 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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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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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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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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weight considerably, which is very important on structures with limited weight load allowance like on offshore platforms.


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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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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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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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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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•

•

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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•

Bellows-type expansion joint Bellows-type or corrugated expansion joints are manufactured as either nonequalizing (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.


Specialties

Piping & Pipeline Components

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