Flanges

A flange spreading tool such as that produced by Equalizer2 is used for the spreading of flanges for spading and aligning flanges for bolt up.

From: Performance Management for the Oil, Gas, and Process Industries, 2017

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Engineering Aspects for Plant Piping Systems

Alireza Bahadori PhD, CEng, MIChemE, CPEng, MIEAust, RPEQ, in piping flange manufacturer, 2017

13.2.4.5.1 Flange Types

Flange type should be in accordance with standards with following considerations:

1.

Flanges should normally be a welding neck type.

2.

Slip-on flanges should not be welded directly on to elbows or other fittings and should be double welded for all services.

3.

PN 68 (class 400) flanges should not be used.

4.

Where flanges in accordance with other standards such as BS 3293 are required, because of adjacent equipment, a check calculation on the suitability of the flange design for hydrostatic test conditions should be made.

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Piping Material Selection

Alireza Bahadori PhD, CEng, MIChemE, CPEng, MIEAust, RPEQ, in Oil and Gas Pipelines and Piping Systems, 2017

9.17.3.4.2 Flanges

All flanges should be class 150, raised face, except those connected to flat face flanges of glass-fiber-reinforced epoxy or equipment with cast iron flanges, etc. In these cases, a suitable matching flange should be used.

Slip-on flanges should be installed in pipe sizes from DN 100 through DN 600. For pipe sizes DN 650 and larger, welding neck flanges should be used. Flanges from DN 100 through DN 600 should be in accordance with ASME/ANSI B16.5, and flanges from DN 650 and larger should be in accordance with MSS SP-44.

Flange facing should be smooth finish between Ra 3.2 and 6.3 µm.

For flanged ends (slip-on) for cement-lined pipe and fittings, see Fig. 9.12. For shop-welding, refer Section 9.17.3.4.1.

Figure 9.12. Flanged ends for cement-lined pipe and fittings.

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General Design

DENNIS R. MOSS, in Pressure Vessel Design Manual (Third Edition), 2004

Special Flanges

Special flanges that are required to be designed should only be used as a last resort. Whenever possible, standard flanges should be utilized. In general, special designs as outlined in this procedure are done for large or high-pressure designs. Flanges in this category will be governed by one of two conditions:

1.

Gasket seating force, Wm2

2.

Hydrostatic end force, H

For high-pressure flanges, typically the hydrostatic end force, H, will govern. For low-pressure flanges, the gasket seating force will govern. Therefore the strategy for approaching the design of these flanges will vary. The strategy is as follows:

•

For low-pressure flanges

a.

Minimize the gasket width to reduce the force necessary to seat the gasket.

b.

Use a larger number of smaller diameter bolts to minimize the bolt circle diameter and thus reduce the moment arm which governs the flange thickness.

c.

Utilize hubless flanges (either lap joint or plate flanges) to minimize the cost of forgings.

•

For high-pressure flanges

High-pressure flanges require a large bolt area to counteract the large hydrostatic end force. Large bolts, in turn, increase the bolt circle with a corresponding increase in the moment arm. Thicker flanges and large hubs are necessary to distribute the bolt loads. Seek a balance between the quantity and size of bolts, bolt spacing, and bolt circle diameter.

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Flange Basics

Roy A. Parisher, Robert A. Rhea, in Pipe Drafting and Design (Third Edition), 2012

Flanges are primarily used where a connecting or dismantling joint is needed. These joints may include attaching a pipe to fittings, valves, mechanical equipment, or any other integral component within a piping configuration. Rating, as applied to flanges, may best be defined as the maximum pressure allowed by the pressure piping code for the specific temperature at which the flange will be operating. Flanges and nozzles are sized according to pressure ratings established by the American Society of Mechanical Engineers. These pressure ratings, often called pound ratings, are divided into seven categories for forged steel flanges. Pound ratings, when combined with the temperature of the commodity within the pipe, are used to select the appropriate size, rating, and type of flange. This pressure/temperature relationship allows any given flange to be used in a number of different applications. When temperature decreases, the allowable pressure increases, and vice versa. Pound ratings are also used to establish the outside diameter and thickness of a flange. Typically, as pound ratings increase, so will the flange's diameter and thickness.

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Piping Components

Peter Smith, in The Fundamentals of Piping Design, 2007

Flange Specification

A flange is specified by identifying the following information:

Type and Facing (For Example, WN/RTJ, SO/RF, Lap Joint/RF). This is a very short identifier that describes the design of the flange and the type of flange facing.

Nominal Pipe Size. NPS is a dimensionless designation to define the nominal pipe size of the connecting pipe, fitting, or nozzle. Examples include NPS 4 and NPS 6.

Flange Pressure Class. This designates the pressure temperature rating of the flange, which is required for all flanges and taken from ASME B16.5. Examples include ASME Classes 150, 300, 600, 900, 1500, and 2500.

Standard. Flange dimensions and material group from ASME B16.5.

Material. A material specification for flanges must be specified and be compatible to the piping material specifications.

Pipe Schedule. This is only for WN, composite lap-joint, and swivel-ring flanges, where the flange bore must match that of the pipe, such as schedule 40, 80, 120, or 160.

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General Information

Robert Flitney, in Seals and Sealing Handbook (Sixth Edition), 2014

7.2.4.1 Gasket Dimensions

EN 1514-1: Flanges and their joints. Dimensions of gaskets for PN-designated flanges. Non-metallic flat gaskets with or without inserts.

EN 1514-2: Flanges and their joints. Dimensions of gaskets for PN-designated flanges. Spiral wound gaskets for use with steel flanges.

EN 1514-3: Flanges and their joints. Dimensions of gaskets for PN-designated flanges. Non-metallic PTFE envelope gaskets.

EN 1514-4: Flanges and their joints. Dimensions of gaskets for PN-designated flanges. Corrugated, flat or grooved metallic and filled metallic gaskets for use with steel flanges.

EN 1514-6: Flanges and their joints. Dimensions of gaskets for PN-designated flanges. Covered serrated metal gaskets for use with steel flanges.

EN 1514-7: Flanges and their joints. Dimensions of gaskets for PN-designated flanges. Covered metal jacketed gaskets for use with steel flanges.

EN 1514-8: Flanges and their joints. Dimensions of gaskets for PN-designated flanges. Polymeric O-ring gaskets for grooved flanges.

EN 12560-1: Flanges and their joints. Gaskets for class-designated flanges. Non-metallic flat gaskets with or without inserts.

EN 12560-2: Flanges and their joints. Gaskets for class-designated flanges. Spiral wound gaskets for use with steel flanges.

EN 12560-3: Flanges and their joints. Gaskets for class-designated flanges. Non-metallic PTFE envelope gaskets.

EN 12560-4: Flanges and their joints. Gaskets for class-designated flanges. Corrugated, flat or grooved metallic and filled metallic gaskets for use with steel flanges.

EN 12560-5: Flanges and their joints. Gaskets for class-designated flanges. Metallic ring joint gaskets for use with steel flanges.

EN 12560-6: Flanges and their joints. Gaskets for class-designated flanges. Covered serrated metal gaskets for use with steel flanges.

EN 12560-7: Flanges and their joints. Gaskets for class-designated flanges. Covered metal jacketed gaskets for use with steel flanges.

ASME B16.20: Metallic Gaskets for Pipe Flanges: Ring Joint Spiral Wound and Jacketed.

DIN 2696: Lenticular ring joint gaskets for flanged joints.

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Piping and connectors

In Handbook of Valves and Actuators, 2007

9.9.4 Pressure-temperature ratings

Flanges are designed for a specific pressure at a designated temperature. In each flange Standard a range of pressure ratings is defined. Flanges become larger and heavier as the pressure rating increases. Figure 9.10 shows the difference in sizes for ISO 7005 steel flanges for nominal pressures from 10 barg to 420 barg, PN10, 16, 25, 50, 110, 150, 260 and 420 and pipe sch 10S, 40, XX and 160. Standard steel pipe is shown to illustrate the change in pipe thickness as operating pressures increase.

Figure 9.10. ISO 7005 DN200 steel flanges, scale 1:2.5

NOTE: Sch 160 pipe should only be used up to approx 315 barg.

Flanges are affected by temperature. At higher temperatures, the material becomes more elastic and deforms more for the same stress. Different materials are affected by temperature to a varying extent. Flange pressures are tabulated with temperature depending upon the material. Some pressure-temperature relationships are shown graphically in Chapter 13, Section 13.4. Non-metallic materials are affected by temperature. Pressure-temperature ratings for non-metallic pipe are shown in Sections 9.2.6 and 9.2.7.

The standards committees who design flanges do not use the same design philosophies. The pressure-temperature relationship for one flange cannot be applied to another flange. The stress-temperature relationships in pressure vessel standards, such as PD 5500 or ASME VIII, may be helpful.

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Flange Design

Dennis R. Moss, Michael Basic, in Pressure Vessel Design Manual (Fourth Edition), 2013

Notation

A

flange O.D., in.

Ab

cross-sectional area of bolts, in.2

Am

total required cross-sectional area of bolts, in.2

a

nominal bolt diameter, in.

B

flange I.D., in.

B1

flange I.D., in.

Bs

bolt spacing, in.

b

effective gasket width, in.

bo

gasket seating width, in.

C

bolt circle diameter, in.

d

hub shape factor

d1

bolt hole diameter, in.

E, hD, hG, hT, R

radial distances, in.

e

hub shape factor

F

hub shape factor for integral-type flanges

FL

hub shape factor for loose-type flanges

f

hub stress correction factor for integral flanges

G

diameter at gasket load reaction, in.

go

thickness of hub at small end, in.

g1

thickness of hub at back of flange, in.

H

hydrostatic end force, lb

HD

hydrostatic end force on area inside of flange, lb

HG

gasket load, operating, lb

Hp

total joint-contact surface compression load, lb

HT

pressure force on flange face, lb

h

hub length, in.

ho

hub factor

MD

moment due to HD, in.-lb

MG

moment due to HG, in.-lb

Mo

total moment on flange, operating, in.-lb

M′o

total moment on flange, seating

MT

moment due to HT, in.-lb

m

gasket factor

mo

unit load, operating, lb

mg

unit load, gasket seating, lb

N

width of gasket, in.

n

number of bolts

v

Poisson's ratio, 0.3 for steel

P

design pressure, psi

Sa

allowable stress, bolt, at ambient temperature, psi

Sb

allowable stress, bolt, at design temperature, psi

Sfa

allowable stress, flange, at ambient temperature, psi

Sfo

allowable stress, flange, at design temperature, psi

SH

longitudinal hub stress, psi

SR

radial stress in flange, psi

ST

tangential stress in flange, psi

T, U, Y, Z

K-factors (see Table 3-6)

Tr, Ur, Yr

K-factors for reverse flanges

t

flange thickness, in.

tn

pipe wall thickness, in.

V

hub shape factor for integral flanges

VL

hub shape factor for loose flanges

W

flange design bolt load, lb

Wm1

required bolt load, operating, lb

Wm2

required bolt load, gasket seating, lb

w

width of raised face or gasket contact width, in. (See Table 3-5)

y

gasket design seating stress, psi

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RIGID INTEGRAL MECHANICAL ATTACHMENTS OR INTERLOCKS

Robert W. MesslerJr., in Integral Mechanical Attachment, 2006

3.5.1 Flanges and Shoulders

Flanges and shoulders are virtually identical integral geometric features of a part that allow that part to be joined to and locked with another part using either bolts and nuts or clamping rings. Normally found on cylindrical solid or hollow shafts or thick-walled pipes, both flanges and shoulders create a circumferential protruding ridge of diameter larger than the shaft or pipe through which bolts (for example) can be installed or over which a spring-type clamping ring can be applied. Flanges are always located at the end of a shaft or pipe, while shoulders are located elsewhere along the length of a shaft or pipe. Flanges tend to be used to join one shaft or pipe to another end-to-end but can also be used to attach an end cap (e.g., head) or other part. Shoulders tend to be used to allow the attachment of some other part to a shaft or pipe or as a structural feature for supporting the shaft or pipe.

Flanges and shoulders carry loads in torsion if the shaft rotates, or in shear, perhaps with bending, if not. Flanges, being located at the end of shafts or pipes may carry tensile loads, with bending occurring at their root radii.

Flanges and shoulders are most commonly used with metals but can also be found used with glass or more rigid polymers. They are occasionally used in ceramics. Shoulders, for example, are found on pre-cast cement or concrete pipes.

Figure 3.20 schematically illustrates integral flanges and shoulders, along with a press-fit collar, while Figure 3.21 shows an example of the use of flanges on heavy-walled pipes in a petrochemical refinery.

FIGURE 3.20. A schematic illustration showing integral flanges and shoulders, as well as press-fit collars.

FIGURE 3.21. The use of integral flanges for connecting end caps or heads to heavy-walled pipes, here by bolting, in a refinery.

(Photograph courtesy of Marathon Ashland Petroleum, LLC, Findlay, OH; used with permission.)
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