Determination of Loads And Movements in Piping Supports

The anticipated movement at each support point dictates the basic type of support required. Each type of support selected must be capable of accommodating movements obtained by one of the methods outlined later in this section. It is a good practice to select first the most simple or basic rigid support type and to add to the complexity only as conditions warrant. No advantage will be realized in upgrading a support when a simpler, more economical type can be shown to satisfy all the design requirements. Both vertical and horizontal movement must be evaluated.

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Use of Codes And Standards in Piping System Design

In practice, the assurance that the design and construction of a piping system will meet prescribed pressure-integrity requirements is achieved through the use of published codes and standards. Numerous codes and standards have been formulated and published by major interest groups of the piping and pressure vessel industry. The most widely used codes and standards for piping system design are published by the American Society of Mechanical Engineers. The American National Standards Institute (ANSI) accredits many of these codes and standards.

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Definition of The Term Design Bases

Design bases are the physical attributes, loading and service conditions, environmental factors, and materials-related factors which must be considered in the detailed design of a piping system, to ensure its pressure integrity over its design life.

Physical Attributes

Physical attributes are those parameters that govern the size, layout, and dimensional limits or proportions of the piping system. Dimensional standards have been established for most piping components such as fittings, flanges, and valves, as well as for the diameter and wall thickness of standard manufactured pipe. Those standards are identified in the section ‘‘Use of Codes and Standards in Piping System Design.’’

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Piping Supports - Reference Codes and Standards

INTRODUCTION

The correct and economical selection of the supports for any piping system usually presents difficulties of varying degrees, some relatively minor and others of a more critical nature. Proper support selection should be the objective of all phases of design and construction.

Many pipe support problems may be minimized or avoided if proper attention is given to the means of support during the piping layout design phase. The piping designer’s familiarity with support problems, accepted practices, and commercially available pipe support components and their applications is extremely important.

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Types of Piping Joints

Joint design and selection can have a major impact on the initial installed cost, the long-range operating and maintenance cost, and the performance of the piping system. Factors that must be considered in the joint selection phase of the project design include material cost, installation labor cost, degree of leakage integrity required, periodic maintenance requirements, and specific performance requirements.

In addition, since codes do impose some limitations on joint applications, joint selection must meet the applicable code requirements. In the paragraphs that follow, the above-mentioned considerations will be briefly discussed for a number of common pipe joint configurations

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Types of Flange Faces Commonly Used

There are five types of flange faces commonly found. The surface finish of the faces are specified in the flange standards.

Raised Face (RF)

The raised face is the most common facing employed with bronze, ductile iron, and steel flanges. The RF is ¹⁄₁₆-in high for Class 150 and Class 300 flanges and ¹⁄₄-in high for all pressure classes, higher than Class 300. The facing on a RF flange has a concentric or phonographic groove with a controlled surface finish. Sealing is achieved by compressing a flat, soft, or semimetallic gasket between mating flanges in contact with the raised face portion of the flange.

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Actuators Selection and Application Guidelines

Actuators selection guidelines are provided to assist in selecting a suitable valve for any application. These guidelines are intended to cover all physical features and capabilities or limitations of different types of valves and which may be suitable for one particular application. The user must fully evaluate the pros and cons of using a particular type of valve and arrive at the most suitable selection, taking into consideration the life span expected and costs involved.

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Actuators Uses, Types and Failure Modes

A brief discussion is provided to assist the user in understanding the considerations affecting the selection of the type of actuators required for an application. Manually actuated valves do not change position due to a change in the mode of system operation or an accident. As such, a manually operated valve remains in the last position it was placed in. Manually operated valves are usually furnished with a hand wheel attached to the valve stem or yoke nut which is rotated clockwise or counter-clockwise to close or open a valve such as a gate or globe valve. Manually operated quarter-turn valves, such as a ball, plug, or butterfly valve, is provided with a lever to actuate the valve. There are applications in which the force required to actuate the valve is more than the force manually imparted through a hand-wheel or a lever. These applications include:

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Diaphragm Valves Types, Construction, Applications and Advantages

All diaphragm valves are bidirectional. They can be used as on-off and throttling valves. Diaphragm valves offer advantages in certain low-pressure applications not possible with other types of valves. Their fluid passages are smooth and streamlined, minimizing pressure drop. They are suitable for moderate throttling applications, and they exhibit excellent leak-tight characteristics, even when conveying liquids containing suspended solids. The fluid stream is isolated from the working parts of the valve, preventing contamination of the fluid and corrosion of the operating mechanism. Since there is no leak path around the valve stem, the valve is virtually leak tight. This feature makes the valve indispensable where leakage into or out of the system cannot be tolerated.

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Butterfly Valves Types, Construction, Applications and Advantages

Butterfly valves are used to control and regulate or throttle the flow. They are characterized by fast operation and low-pressure drop. They require only a quarter turn from closed to full-open position. A typical flanged butterfly valve is illustrated in Fig. A. Butterfly valves are produced in sizes ranging from NPS 1¹⁄₂ (DN 40) to over NPS 200 (DN 5000). They are usually manufactured in flanged, wafer, and lug, or single-flange-type designs. The welding-end style is a specially engineered valve for a specific application. Threaded-end, grooved-end, and shouldered-end butterfly valves are also available to satisfy the joint type selected for the piping system. Butterfly valves are produced with metal-to-metal seats, soft seats, and with fully lined body and disc. The soft seats permit bubble-tight shutoff and the full lining enhances erosion and corrosion resistance.

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Plug Valves Types, Construction, Applications and Advantages

Plug valves, also called cocks, generally are used for the same full-flow service as gate valves, where quick shutoff is required. They are used for steam, water, oil, gas, and chemical liquid service. Plug valves are not generally designed for the regulation of flow. Nevertheless, in some applications, specially designed plugs are
used for this purpose, particularly for gas-flow throttling. Plug valves generally can be readily repaired or cleaned without necessitating removal of the body from the piping system. They are available for pressure service from vacuum to 10000 psi (69000 kPa) and temperatures from 50 to 1500 F ( 46 to 816 C). Also, plug valves are available with a wide variety of linings suitable for many chemical service applications.

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Ball Valves Types, Construction, Applications and Advantages

The ball valve (Fig. 1) is a quarter-turn valve suitable for clean gas, compressed air, and liquid service. They also can be used for slurry service, but provisions for prevention of crud buildup must be made. The use of soft-seat materials such as nylon, delrin, synthetic rubbers, and fluorinated polymers imparts excellent sealing ability. 

Fig. 1: Ball valve in closed position

With fluorinated polymer seats, ball valves can be used for service temperatures ranging from 450 to 500 F ( 270 to 260 C); with graphite seats, service temperatures to 1000 F (538 C) or even higher are possible. Also, with metal backing seats, the valves can be used in fire-safe services. Ball valves are similar to plug valves in operation. They are nonbinding and provide leak-tight closure. The valves exhibit negligible resistance to flow because of their smooth body and port.

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Check Valves Types, Construction, Applications and Advantages

Check valves are designed to pass flow in one direction with minimum resistance and to prevent reverse or back flow with minimal leakage. The principal types of check valves used are the tee-pattern lift check, the swing check, the tilting-disc check, the Wye-pattern lift check, and the ball check, illustrated in Figs. A to E, respectively.

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Globe Valves Types, Construction, Applications and Advantages

Conventional globe valves may be used for isolation and throttling services. Although these valves exhibit slightly higher pressure drops than straight through valves (e.g., gate, plug, ball, etc.), they may be used where the pressure drop through the valve is not a controlling factor. 

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Gate Valve Types, Construction, Applications and Advantages

Gate valves are primarily designed to serve as isolation valves. In service, these valves generally are either fully open or fully closed. When fully open, the fluid or gas flows through the valve in a straight line with very little resistance. Gate valves should not be used in the regulation or throttling of flow because accurate control is not possible. Furthermore, high-flow velocity in partially opened valves may cause erosion of the discs and seating surfaces. Vibration may also result in chattering of the partially opened valve disc. An exception to the above are specially designed gate valves that are used for low-velocity throttling; for example, guillotine gate valves for pulp stock.

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PressFit Piping Systems Installation and Advantages

The Pressfit piping system is an innovative, rigid, self-restrained mechanical joining method for schedule 5 or lighter weight lightweight stainless steel and carbon steel pipe. This proprietary mechanical pipe joint is designed for use in small-bore piping systems, NPS ¹⁄₂ (DN15) to NPS 2 (DN50). The Pressfit system may be applied to any service that is compatible with the piping materials, the gasket material, and the temperature range of the system, unless prohibited by the manufacturer’s instructions.

Typical applications would include building-services piping, potable water, fire protection, heating and cooling, industrial processes, process cooling and heating systems, plant utilities, and vacuum systems.

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PreStressed Concrete Cylinder Pipe (PCCP) Installation Procedure

Pipe Handling and Storage

A crane or backhoe outfitted with a steel cable sling may be used to unload pipe unless the pipe has a special exterior coating that could be damaged by a steel cable sling. In such cases, a fabric sling should be used. Multiple slings are often used in handling large pipe and fittings. Pipe can be stored directly on the ground in nonfreezing conditions. If freezing conditions are expected, the pipe should be set on wooden timbers off the ground to prevent the pipe from becoming frozen to the ground. Rubber gaskets should be stored in a cool place, out of the sun, away from fuel oil, gasoline, electric motors, and any other environment that can damage rubber.

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PreStressed Concrete Cylinder Pipe (PCCP) Joints

Rubber O-ring Bell and Spigot Joint

(a) Lined cylinder pipe (LCP) and (b) embedded cylinder pipe (ECP) profiles

Figures A and B show a cross-section of the typical LCP and ECP bell and spigot joint. As can be seen, an O-ring rubber gasket is compressed into the spigot groove by the bell ring when assembled to form a water-tight seal. Portland cement grout is poured into a fabric band (diaper) by the installer to provide corrosion protection.

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Prestressed Concrete Cylinder Pipe (PCCP) Design

Design Parameters

PreStressed Concrete Cylinder Pipe (PCCP) is designed as a rigid structure to resist the simultaneous application of external loads and internal pressures. External dead loads normally encountered are earth loads, foundation loads, or surcharges applied at the ground surface. External live loads are caused by vehicular traffic, railroads, or construction equipment.

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Prestressed Concrete Cylinder Pipe (PCCP) Types

Prestressed concrete cylinder pipe consists of a structural, high-strength concrete core, a steel cylinder with steel joint rings welded at each end providing water tightness, steel prestressing wire, and a portland cement-rich mortar coating. Two types of PCCP are manufactured: lined cylinder pipe (LCP), which is detailed in Fig. A and embedded cylinder pipe (ECP), which is detailed in Fig. B.

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