Orifice Flanges

1.

Orifice flange connections should be in accordance with standards.

2.

For inline flow measurement devices, the manufacturer’s installation requirements should be followed.

3.

Piping and primary valving at the orifice fitting or other flow measurement device should conform to the line specification.

4.

Line-tap connections should conform to the requirements for pressure tapping.

5.

Orifice flanges should be installed in horizontal pipes, as far as possible. When it is impossible to find a sufficient meter run in a horizontal piping, orifices may be installed in a vertical piping with upwards flow for liquids and downward flow for gas and steam.

6.

The minimum meter run required for both upstream and downstream of the orifice flanges should be in accordance with standards.

Of the flanges discussed, the orifice flange is the only one that actually performs a function. The function of the orifice flange is to measure the rate of the flow of the commodity through the piping system. Orifice flanges are easy to recognize because they have a hole drilled through the face of the flange perpendicular to the pipe. They also have an additional set of bolts called jack screws. These screws are used to help separate the flanges so inspection and/or replacement of the orifice plate can be performed. The orifice flange is a single component of the orifice flange union assembly (Figure 4.26). The orifice flange union is composed of two orifice flanges, an orifice plate, bolts, nuts, jack screws, and two gaskets. A representation of an unbolted and separated orifice flange union assembly is depicted in Figure 4.27.

The orifice flange union is used to measure, or meter, the amount of pressure drop through the orifice plate. The length of pipe within the piping system where orifice flanges are installed and where these measurements are recorded is known as a meter run. Figure 4.28 shows the orifice flange union assembly installed in a meter run. The broken-out section shown in Figure 4.29 shows the internal view of a meter run.

Orifice flanges can be either weld neck, slip-on, or threaded. The weld neck and threaded orifice flanges are manufactured in 300# and larger pound ratings. However, the slip-on orifice flange is only available as a 300# raised face flange. The single-line and double-line drawing symbols for the orifice flange are shown in Figure 4.30.

Fig. 4.4 shows two sections of pipe with a flange on each. They are bolted together with a gasket between them.

The ASME standards include:

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B16.1―Cast Iron Flanges and Flanged Fittings

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B16.5―Pipe Flanges and Flange Fittings (NPS 1/2 through 24)

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B16.24―Cast Copper Alloy Pipe Flanges and Flanged Fittings

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B16.36―Orifice Flanges

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B16.42―Ductile Iron Pipe Flanges and Pipe Fittings (NPS 26 through 60)

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B16.47―Large Diameter Steel Flanges (NPS 26 through 60)

The ASME standards divided flanges into different classes. B16.5 provides the working pressure limit of a flange depending on the material category, temperature, and classification. The material categories are as follows:

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Carbon and low alloy steels

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Austenitic stainless steels

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Nickel alloys.

Table 4.5 is an example of an ASME flange rating specification.

Recall from the discussion in Chapter 4, orifice flanges have valve taps that allow monitoring equipment to be attached, which records the differential pressure of a commodity traveling through an orifice plate (see Figure 12.9).

The critical part of a meter run is the orifice plate. The orifice plate is a ⅛″ thick, flat, circular disk, made of metal, having a flat handle (see Figure 12.10). The orifice plate, with a gasket on either side, is sandwiched between two orifice flanges. An exploded view of an installed orifice plate is shown in Figure 12.11. As you can see, a hole is machined through the center of the plate to allow commodity to pass through. This hole is approximately 75% of the diameter of the pipe. The size of the hole in the orifice plate, relative to the size of the pipe, is known as the beta factor. Depending on the application, numerous beta factors can be used. However, 0.75 is the one most commonly used in meter run calculations. By attaching monitoring equipment to the valve taps, the rate of flow of the commodity can be measured as flow travels along the pipe and through the orifice plate.

To receive the most accurate reading possible, turbulence within the pipe must be kept to a minimum. Flow turbulence is created by obstructions in the configuration from items such as fittings and valves. A smooth, consistent flow is created by providing a sufficient amount of straight pipe before and after the orifice flanges. Therefore, the length of the run of pipe before, or upstream of, the orifice plate and the length of the section of pipe after, or downstream of, the plate is precisely calculated. These upstream and downstream measurements are established by using precise lengths of pipe that are based on the diameter of the pipe being used. Additional factors also affect how these lengths are calculated. For example, a different beta factor can be used or a multiplane pipe configuration before the orifice plate may be required. However, a general rule-of-thumb formula of 30 pipe diameters upstream and 6 pipe diameters downstream provides adequate distance to create smooth flow in the meter run. A graphical representation of the values used to calculate these lengths is shown in Figure 12.12.

To calculate the lengths shown in Figure 12.12, simply multiply the upstream and downstream diameters times the nominal pipe size. The following is an example to calculate the upstream and downstream pipe lengths for a meter run installed in a 6″ pipe configuration.

Recall from the discussion in Chapter 4, Flange Basics, orifice flanges have valve taps that allow monitoring equipment to be attached which records the differential pressure of a commodity traveling through an orifice plate. Figure 12.10 is a photograph of the instrumentation attached to an orifice flange union assembly.

A critical component in a meter run is the orifice plate. Most often, the orifice plate is a thin, flat, circular disc, made of metal, having a flat handle. Depending on the methods being used and the data being gathered, different orifice plates types are installed. Figure 12.11 provides examples of various orifice plate configurations. Although they are single-stage orifices, some restriction plates have multiple openings in the plate. Multihole plates are installed when commodity flow rates are extremely high. High flow rates create a loud, high-pitched noise as the commodity flows through a restriction plate. Multiple holes divide the incoming commodity into several smaller flow streams, thus reducing the noise. The cumulative area size of all of the hole openings establish the amount of pressure drop downstream of the restriction orifice.

The orifice plate, with a gasket on either side, is sandwiched between two orifice flanges. An exploded view of an installed orifice plate is shown in Figure 12.12. In this example, a single hole is machined through the center of the plate to allow commodity to pass through. The size of the hole in the orifice plate, relative to the size of the pipe, is known as the Beta (β) Ratio or Beta (β) Factor. Depending on the application, numerous Beta (β) Ratios can be used. By attaching monitoring equipment to the valve taps, the rate of flow of the commodity and its drop in pressure can be measured as flow travels along the pipe and through the orifice plate.

To receive the most accurate reading possible, turbulence within the pipe must be kept to a minimum. Flow turbulence is created by obstructions in the configuration from items such as fittings and valves. A smooth, consistent flow is created by providing a sufficient amount of straight pipe before and after the orifice flanges. Therefore the length of the run of pipe before, or upstream, of the orifice plate and the length of the section of pipe after, or downstream, of the plate is precisely calculated. These upstream and downstream measurements are established by using precise lengths of pipe which are based on the diameter of the pipe being used. Additional fitting and valve installations will affect how these lengths are calculated. For example, a different Beta (β) Ratio, ranging from 0.30 to 0.75 (30%–75%), can be used or a multiplane pipe configuration before the orifice plate may be required. As a general rule-of-thumb, 30 pipe diameters upstream and six (6) pipe diameters downstream will provide adequate lengths of pipe to create smooth flow in the meter run. A graphical representation of the values used to calculate these lengths is shown in Figure 12.13.

To use the values shown in Figure 12.13, simply multiply the upstream and downstream diameters times the nominal pipe size. The following is an example to calculate the upstream and downstream pipe lengths for a meter run installed in a 6″ pipe configuration.

Again, the formula above is a rule-of-thumb guide. Specific values for upstream and downstream diameters vary depending upon the configuration of the piping system in which the orifice flanges are installed. Space limitations, configuration components, and routing orientation such as those shown in Figure 12.14 dictate upstream and downstream pipe lengths for prescribed Beta (β) Ratios. One of the more commonly used Beta (β) Ratios in meter run calculations is 0.75. This means the area of the hole or holes machined in the orifice plate are approximately 75% of the inside diameter of the pipe. Figure 12.14 represents the minimum upstream and downstream pipe lengths when a Beta (β) Ratio of 0.75 is used. Review specific project specifications to verify the correct upstream and downstream diameters.

Occasionally, more than a single orifice plate is required. Multistage orifice assemblies, illustrated in Figure 12.15, have multiple phases through which the commodity must flow in order to achieve the desired result. Like single-plate orifices, multistage restriction orifices have instrumentation connections on both ends to accurately read specific characteristics of the commodity as it exits the assembly.

In actual practice, the affinity laws provide an approximation between flow, head and horsepower as pump impeller diameter or speed is varied. The values actually observed will vary somewhat less than predicted by the affinity laws. That is, the actual exponents in the affinity equations are slightly less than their stated values and are different for each pump. This results from friction in hydraulic passages and impellers, leakage losses and variation of impeller discharge vane angles when diameters are changed. Pump manufacturers should be contacted to confirm actual impeller diameters and speed changes to meet new duty requirements.

Here is an overview of the applicable codes which might relate to overpressure protection:

AISI: American Iron and Steel Institute.

ANSI: American National Standards Institute.

ASME: American Society of Mechanical Engineers: Boiler and Pressure Vessel Code: compilation of rules and guidance covering numerous types of construction.

Chapter I—Power boilers and direct fired pressure vessels.

Chapter II—Materials.

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SA 216—Carbon-steel castings suitable for fusion welding for high0000 temperature service.

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A 217—Martensitic stainless steel and alloy steel castings for pressure containing parts suitable for high-temperature service.

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SA 351—Austenitic steel castings for pressure containing parts.

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SA 494—Nickel and nickel alloy castings.

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Chapter III—Nuclear.

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Chapter IV—Heating boilers.

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Chapter VII—Care of power boilers.

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Chapter VIII—Rules for construction of unfired pressure vessels and overpressure protection devices.

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Chapter IX—Welding and brazing qualification.

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Chapter XII—Transportation tanks.

ASME Standards:

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B978-0-323-90956-3.25—Butt welding Ends.

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B978-0-323-90956-3.34—Valves—Flanged, threaded and welding ends.

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B978-0-323-90956-3.36—Orifice Flanges.

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B978-0-323-90956-3.5—Pipe flanges and flanged fittings.

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B978-0-323-90956-3.1—Power piping.

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B978-0-323-90956-3.3—Process piping.

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B978-0-323-90956-3.4—Pipeline transportation systems for liquid hydrocarbons and other liquids.

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B978-0-323-90956-3.8—Gas transmission and distribution systems.

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PTC 25—Pressure Relief Devices.

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API: American Petroleum Institute.

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API Standard 520—Sizing, selection and installation of pressure-relieving devices in refineries.

Part I—Sizing and selection.

Part II—Installation.

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API Standard 521—Guide for pressure-relieving and depressuring Systems.

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API Standard 526—Flanged Steel Pressure Relief Valves.

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API Standard 527—Testing and acceptance for set pressure and seat tightness of pressure relief valves.

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API Recommended Practice 576—Inspection of pressure relieving devices.

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API Standard 2000—Venting atmospheric and low-Pressure Storage Tanks.

ASTM: American Society for testing and materials.

NB: National Board (of Boiler and Pressure Vessel Inspectors).

MSS: Manufacturers Standardization Society (of the valves and fittings industry).

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SP-25: Standard marking systems for valves, Fittings, Flanges and Unions (not applicable to pressure safety valves—refer to ASME B&PVC, Chapter VIII, UG129).

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SP-44—Steel Pipeline Flanges.

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SP-55—Quality Standard for Steel Castings for Valves, Flanges, Fittings, and Other Piping Components—Visual Method for Evaluation of Surface Irregularities.

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SP-61—Pressure Testing of Steel Valves (not applicable to pressure safety valves—refer to API STD 527).

The primary codes relating to pressure relief devices are ASME I, III, and VIII. What is not covered by ASME:

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Vessels with pressures below 1,03 Barg.

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Pipelines outside process installations.

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Water supply & water discharge network (utilities outside the process).

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Vessels protected by “system design.”

HC is one of the recent technologies and for biodiesel production at an industrial scale due to the comprehensible level of its scale-up. It is used as a process enhancer, resulting in a significant increase in energy consumption, yields, and reaction time (Sun et al., 2020). These enhancements may be particularly useful in the next generation of biodiesel plants, especially to the looming and recent global scenario of low petroleum prices, in which the biodiesel industry is struggling to remain competitive and financially viable. A pump, control valves, orifice plate, and flanges are typically utilized in all HC reactors used for biodiesel processing, which is schematically described in Fig. 6.8. The storage tank is encompassed by a cooling jacket, and the pressure is maintained by a regulated cooling water system. The storage tank is encompassed by a cooling jacket, and the pressure is maintained by a regulated cooling water system. Tweaking in the flow field in high-speed/high-pressure devices, as well as the passage of the liquid via a constriction such as an orifice pad, venturi, or throttling valve, may potentially trigger HC. Due to turbulence caused by liquid circulation currents, HC causes the creation of local hotspots, the release of highly reactive free radicals, and augmented mass transfer rates. In collation to traditional ultrasound-based reactors, these caveats can be used to intensify a variety of bioprocessing applications in an energy-efficient manner. Furthermore, it is a less exorbitant solution that uses around half as much energy as the traditional mechanical stirring process. HC could produce cavitating conditions similar to acoustic cavitation, with a prolific effect on mixing immiscible liquids. Despite having been probed on and developed for nearly 30 years, HC technology is yet to be widely utilized in industrial applications around the world. The majority of current research focuses on applications; however, the features of HCRs have received attention, which has a significant impact on the growth and implementation of HC technology (Moholkar et al., 1999).