ASME B31.3 Process Piping Course Handout Intro

ASME B31.3 Process Piping Course Introduction in Accordance with Design, Construction, and Mechanical Integrity

Series of Articles would be coming daily as per table below:

This course will review the basic requirements of the ASME B31 Code for Pressure Piping with emphasis on B31.3, Process Piping. General topics in the course include Code organization and intent, pressure design, design for sustained loads including support design, flexibility analysis, equipment loads, flanges, expansion joints, supports and restraints, materials, fabrication, examination, testing, and, for existing piping systems, mechanical integrity. Applications of these concepts, including simple hand analysis methods and computer based analysis methods, will be demonstrated. Included will be comparisons between ASME B31.3 and ASME B31.1, Power Piping. Inspection and maintenance (mechanical integrity) of existing piping systems will be covered, as provided in API 570, Piping Inspection Code.

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Design Detail Considerations for Piping Supports

ASME Code for Pressure Piping

Specific design requirements for piping support are included in the sections of ASME B31, Code for Pressure Piping, listed below:

● B31.1, Power Piping

● B31.2, Fuel Gas Piping

● B31.3, Process Piping

● B31.4, Liquid Transportation Systems for Hydrocarbons, Liquid Petroleum Gas, Anhydrous Ammonia, and Alcohols

● B31.5, Refrigeration Piping

● B31.8, Gas Transmission and Distribution Piping Systems

● B31.9, Building Services Piping

● B31.11, Slurry Transportation Piping Systems

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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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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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Terminology Related To Valves

Actuator: A device that operates a valve by utilizing electricity, pneumatics, hydraulics, or a combination of one or more of these energies. Sometimes actuators are referred to as operators. In this chapter, the word operator will be used for a person who operates any equipment, machine, plant, or system.

Ambient conditions: The pressure and temperature of the environment surrounding a valve.

Back-flow: The flow that occurs in the opposite direction of the normal or expected fluid flow.

Back pressure: The static pressure existing at the outlet of a pressure-relief device due to pressure in the discharge system.

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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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What are Safety Valves and Pressure Relief Devices

Safety valves and pressure-relief valves are automatic pressure-relieving devices used for overpressure protection of piping and equipment. Safety valves (Fig. A) are generally used in gas or vapor service because their opening and reseating characteristics are commensurate with the properties and potential hazards of compressible fluids. The valves protect the system by releasing excess pressure. Under normal pressure, the valve disc is held against the valve seat by a preloaded spring. As the system pressure increases, the force exerted by the fluid on the disc approaches the spring force. As the forces equalize, fluid begins to flow past the seat. 

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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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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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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) Details

Prestressed concrete cylinder pipe (PCCP) has been manufactured in the United States since 1942. An American Water Works Association (AWWA) tentative standard was developed in 1949 and was made a permanent standard in 1952. Since that time, this standard has been reviewed and updated on a regular basis. PCCP offers the specifier and owner numerous advantages, including ease of installation, custom-designed fittings, superior corrosion resistance, high-flow characteristics, low maintenance costs, and product support by the manufacturer. PCCP is used extensively for a wide range of project types both in the United States and around the world.

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How to do Selection of Bolts in Piping Design

Bolts and nuts should be selected to conform to the design specifications set out with the flange design. Care is taken to ensure that the correct grade of material is selected to suit the recommended bolting temperature and stress ranges. Material specifications for bolts are outlined in BS 4882 and ASME Section VIII.

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Functions of Bolts in Piping Design

The function of a bolt is to provide a clamp load or preload (Fp) to sufficiently compress and stress the gasket and resist the parting forces exerted by the hydrostatic end force and other external loads. The hydrostatic end force is created by the pressure of the internal fluid across the internal area of flange. The internal area is generally the inside diameter of the sealing element.

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Function of Gaskets in Piping Design

The function of a gasket is to conform to the irregularities of the flange faces to affect a seal, preventing the inside fluid from leaking out. See following figure for a typical flange-gasket arrangement:

Function of Gaskets - Typical flange gasket arrangement

The leak performance of the gasket is dependent on the stress on the gasket during operation. Each different type of gasket has its own inherent leak-tightness capabilities. The higher the gasket stress, the higher the leak-tightness capability.

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Types of Flange End Connection

The flange-end connection defines the way in which it is attached to the pipe. The following are commonly available standard flange end types:

Weld-Neck (WN) Flange

Weld-neck flanges are distinguished from other types by their long, tapered hub and gentle transition to the region where the WN flange is butt-welded to the pipe. The long, tapered hub provides an important reinforcement of the flange, increasing its strength and resistance to dishing. WN flanges are typically used on arduous duties involving high pressures or hazardous fluids.

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