# Flange Face

FF flanges are normally used for the least arduous duties, such as low-pressure water piping having class 125 and class 250 flanges and flanged valves and fittings.

## Piping and connectors

In Handbook of Valves and Actuators, 2007

### 9.9.2.1Flat face (FF)

Flat face flanges are used for low pressure applications and with cast iron or non-metallic valves and fittings. The gasket seals across the full flange face width surrounding the bolting. No part of the flange is subjected to direct bending as a result of the bolting loads. The wide flange faces allow the use of soft gasket materials such as rubber and cork but care must still be taken to avoid over-torqueing.

Corrugated brass or copper gaskets with plenty of graphite compound are used on low pressure steam applications. It is possible to use a steel RF flange with a cast iron FF flange but skill and judgement are necessary. Alignment of the flanges is accomplished solely by the bolting. Maximum misalignment is equal to the bolt clearance. Flat face flanges are most often used with mirror, rough, smooth or stock finish.

URL: https://www.sciencedirect.com/science/article/pii/B9781856174947500389

## Piping Components

Peter Smith, in The Fundamentals of Piping Design, 2007

### Flange Faces

Three types of flange faces are commonly found. The surface finish of the faces is specified in the flange standards quoted previously:

Raised Face. The raised face is the most commonly used facing employed for steel flanges. The facing on the RF flange has a concentric or a spiral phonographic groove with a controlled surface finish. Sealing is achieved by compressing a flat, soft, or semi-metallic gasket between mating flanges in contact with the raised face portion of the flange.

Ring-Type Joint. This type is typically used for more severe duties than the RF surface, usually ASME classes above 900; however, it is valuable in the lower-pressure classes.

RTJ for API 6A Type 6B, ASME B16.5 Flanges. The seal is made by plastic deformation of the metallic RTJ gasket into the groove on the flange face, resulting in intimate metal-to-metal contact between the gasket and the flange groove. The faces of the two opposing flange faces do not come into direct contact with each other, because a gap is maintained by the presence of the gasket. Such RTJ flanges normally have raised faces, but flat faces may also be used or specified.

RTJ for API 6A Type 6BX Flanges. API 6A Type 6BX flanges have raised faces. These flanges incorporate special metallic ring joint gaskets. The pitch diameter of the ring is slightly greater than the pitch diameter of the flange groove. This factor preloads the gasket and creates a pressure-energized seal. A Type 6BX flange joint that does not achieve face-to-face contact will not seal and, therefore, must not be put into service.

Flat Face. Flat-face flanges are a variant of raised-face flanges. Sealing is achieved by compression of a flat nonmetallic gasket between the two serrated surfaces of the mating FF flanges. The gasket covers the entire face of the flange sealing surface. FF flanges are normally used for the least arduous duties, such as low-pressure water piping having class 125 and class 250 flanges and flanged valves and fittings.

Less Commonly Used Flange Faces. Other alternative types of flanges are available; however, due to international standardization in the energy industry, they are very rarely used on projects designed to one of the ASME B31 codes.

Male-and-Female Facings. The outer diameter of the female face acts to locate and retain the gasket. Custom male-and-female facings are commonly found on the heat exchanger shell to channel and cover flanges.

Tongue-and-Groove Facings. Tongue-and-groove facings are standardized in both large and small types. They differ from male-and-female facings in that the inside diameters of the tongue-and-groove do not extend into the flange base, thus retaining the gasket on its inner and outer diameter. These are commonly found on pump covers and valve bonnets.

URL: https://www.sciencedirect.com/science/article/pii/B9781933762043500114

## Process machinery piping☆

Heinz P. Bloch P.E., Fred K. Geitner P.ENG., in Machinery Component Maintenance and Repair (Fourth Edition), 2019

Check condition of flange faces for scratches, dirt, scale, and protrusions. Wire brush clean as necessary. Deep scratches or dents will require refacing with a flange facing machine.

Check that flange facing gasket dimension, gasket material and type, and bolting are per specification. Reject nonspecification situations. Improper gasket size is a common error.

Check gasket condition. Only new gaskets should be used. Damaged gaskets (including loose spiral windings) should be rejected. The ID windings on spiral-wound gaskets should have at least three evenly spaced spot welds or approximately one spot weld every 6 in. of circumference (see API 601).

Use a straightedge and check facing flatness. Reject warped flanges.

Check alignment of mating flanges. Avoid use of force to achieve alignment. Verify that

1.

the two flange faces are parallel to each other within $1}{32}$ in. at the extremity of the raised face,

2.

flange centerlines coincide within ⅛ in.

Joints not meeting these criteria should be rejected.

URL: https://www.sciencedirect.com/science/article/pii/B9780128187296000046

## Machinery Component Maintenance and Repair

Check condition of flange faces for scratches, dirt, scale, and protrusions. Wire brush clean as necessary. Deep scratches or dents will require refacing with a flange facing machine.

Check that flange facing gasket dimension, gasket material and type, and bolting are per specification. Reject nonspecification situations. Improper gasket size is a common error.

Check gasket condition. Only new gaskets should be used. Damaged gaskets (including loose spiral windings) should be rejected. The ID windings on spiral-wound gaskets should have at least three evenly spaced spot welds or approximately one spot weld every six in. of circumference (see API 601).

Use a straightedge and check facing flatness. Reject warped flanges.

Check alignment of mating flanges. Avoid use of force to achieve alignment. Verify that:

1.

The two flange faces are parallel to each other within 1/32 in. at the extremity of the raised face

2.

Flange centerlines coincide within 1/8 in.

Joints not meeting these criteria should be rejected.

URL: https://www.sciencedirect.com/science/article/pii/S1874694205800197

## Flange Design

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

The following is a list of typical surface finishes for flange faces;

1.

Stock Finish: 250 to 500 AARH: This finish is produced with a continuous spiral groove generated with a round nosed tool. This finish is suitable for all ordinary service conditions and is the most widely used gasket surface finish

2.

Spiral Serrated: 125 to 250 AARH: This finish is produced with a continuous spiral groove but utilizes a 90° included angle “V” tool. The groove is 1/64” deep and the feed is 1/32” for all sizes.

3.

Concentric Serrated: 125 to 250 AARH: This finish is produced with concentric grooves using the same tools and parameters as the “spiral serrated” finish.

4.

Smooth Finish: 63 to 125 AARH: This finish can be generated with a variety of tooling, but shows no tool marks apparent to the naked eye.

5.

Cold Water Finish: 32 to 63 AARH: This finish is very smooth and has the appearance of a ground finish. It is mirrorlike in appearance.

6.

Flat Face: Stock or Serrated

7.

1/16” Raised Face: Stock or Serrated

8.

¼” Raised Face: Stock or Serrated

9.

Male & Female: Smooth

10.

Tongue & Groove: Smooth

11.

Side Wall of Ring Joint: 63 AARH

URL: https://www.sciencedirect.com/science/article/pii/B9780123870001000036

## Piping

Ian Sutton, in Plant Design and Operations (Second Edition), 2017

Gaskets or metal-ring-joint facings are placed between flange faces to protect against leakage. The bolts that hold flanges together are subject to the same codes as pipe and pipe fittings.

For the majority of moderate-temperature services, composition gaskets on raised face flanges are used. At flanged joints where additional reliability is desired or where temperatures are higher, spiral-wound gaskets on raised face flanges are used. For services with special temperature, pressure, or chemical hazard problems, a ring-type joint or equivalent should be considered.

ANSI/ASME B16.5 (ANSI, 2013) provides a list of bolting material for flanges. There are three strength categories: high, intermediate, and low.

rtj flange
URL: https://www.sciencedirect.com/science/article/pii/B9780128128831000048

## Well Control Surface Equipment

Howard Crumpton, in Well Control for Completions and Interventions, 2018

### 4.13.2.3“BX” pressure energized ring gasket

The “BX” ring gasket is used with 6BX flanges where flange face-to-face contact is allowed. Contact between the flange faces enables gasket compression and plastic deformation to be controlled. As both the ID and OD of the gasket may contact the grooves, holes are normally drilled through the gasket to ensure pressure either side of the joint is balanced.

Sealing takes place along small bands of contact between the groove in the flange and the OD of the gasket. The gasket is slightly larger in diameter than the grooves, and so is compressed slightly to obtain the initial seal as the joint is tightened. Variances in groove and ring gasket tolerance mean that face-to-face contact is not always achieved. When this occurs, vibration and external loads can cause deformation of the ring, leading to a leak.

URL: https://www.sciencedirect.com/science/article/pii/B978008100196700004X

## Piping Material Selection

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

### 9.17.3.4.2Flanges

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.

URL: https://www.sciencedirect.com/science/article/pii/B9780128037775000095

## Corrosion/Coatings

### Internal stray current

Internal corrosion has occurred at an isolating flange. The only evidence is that corrosion exists on the inside near one flange face. Without further investigation, the conclusion may be that it is caused by a natural corrosion mechanism. If three conditions exist, internal interference should be added to the list of causes for consideration. These three conditions include:

The corrosion is at an isolating fitting or high-resistance coupling.

An electrolyte (especially of low resistivity) flows through the isolator.

A voltage exists across the flange or fitting.

If the stray current returning along the foreign metallic path encounters an electrical isolating feature or high-resistance joint, it may bypass the electrical isolation by going through the soil (Figure 1) or it may bypass the isolation by going through an electrolyte that bridges the isolation inside (Figure 2). Note that corrosion only occurs on the side of current discharge.4–5

URL: https://www.sciencedirect.com/science/article/pii/B9780123876935000085

## From design to manufacture

Peter Scallan, in Process Planning, 2003

### Operation 2: Finish machine face

(i)

Speed – a surface speed of 200 m min−1 has been selected from Table 6.2 for finishing the flange face of the part.

$\begin{array}{cc}{V}_{\text{c}}=200 \text{m} {min}^{-1}& {V}_{\text{c}}=\frac{\pi DN}{1000}\\ D=100 \text{mm}& \\ & N=\frac{1000{V}_{\text{c}}}{\pi D}\\ N=?& {V}_{\text{c}}=\frac{1000×200}{\pi ×100}=637 \text{rpm}\end{array}$

(ii)

Feed – a feed rate of 0.1 mm/rev−1 has been selected from Table 6.3 for roughing the flange face of the part.

 fm = ? fm = frN fr = 0.1 mm rev−1 fm = 0.1 × 600 N = 600rpm fm = 60 mm min−1 = 0.06 m min−1
(iii)

Time – using the speeds and feeds calculated in (i) and (ii) the time for the operation will be calculated.

$\begin{array}{cc}T=?& T=\frac{\left(D/2\right)+A}{{f}_{\text{r}}N}\\ D=150 \text{mm}& \\ A=5 \text{mm}& T=\frac{\left(150/2\right)+5}{1×637}=1.26 min\\ {f}_{\text{r}}=0.1 \text{mm} {\text{rev}}^{-1}& \\ N=637 \text{rpm}& \end{array}$