## How to calculate blind flange thickness?

In chemical enterprises, it is often encountered that production and maintenance are carried out at the same time. In order to ensure the effective isolation of production system and maintenance system, blind flanges are usually added between the flanges of associated pipelines. In the process of blind flange selection, the diameter and thickness of blind flange are mostly selected by experience, without scientific basis. If the blind flange is thin, it will deform in the process of use, and it is difficult to pull out from the flange. If the blind flange is thick enough and the spacing between the flanges is not wide enough, it is difficult to insert it between the flanges. In addition, it is also a waste of materials. Whether the blind flange is too thick or too thin, these two situations will bring inconvenience to the construction. In order to use as thin as possible blind flange, and to ensure that the blind flange does not deform in the process of use, we do stress analysis on the stress of blind flange, and give the calculation method of blind flange thickness with examples. The calculation result is the thinnest thickness of the blind flange.

### CALCULATION FOR THE BLIND FLANGE:

(AS PER ASME BOILER AND PRESSURE VESSEL CODE / VIII DIV I) The blind flange is attached by bolts causing an edge moment (Fig. UG- 34. /sketch j) in which the thickness can be calculated by :

• t = d *(CP/SE+1.9W hg/SE*d^3) ½ ……………….Formula (2) (From ASME UG-34)

Where, d= Diameter or short span, measured as indicated in Fig. UG-34

E= Joint efficiency, from Table UW-12, of any category A weld as defined in UG-3(a)

S= Maximum allowable stress value in tension from applicable table of value

Referenced by UG-23

W= Total bolt load (From pipe data pro)

hg= Gasket moment arm, equal to the radial distance from the centerline of the bolts to the line of the gasket reaction, Table 2-5.2

P = Design pressure-HYDROTEST pressure is considered (13.5 bar (g))

C = 0.3 From Fig UG-34(j)

### THICKNESS CALCULATION FOR THE 32” BLIND FLANGE:

Using the above formula (2)

• t = d *(CP/SE+1.9W hg/SE*d^3) ½ ……………….formula (2) (from ASME UG 34)

d= 876.5 mm

C= 0.3

P = 13.76 kg/sq cm

E = 1

W = 94 KG

hg= 50.75 mm

S = 25 ksi = 1757 kg/sq.cm

Substituting the above values in Formula (2), t = 876.5*[(0.3*13.76/1757*1) + (1.9*94*98)/ (1757*1*876.5^3)] ½ = 42.48mm or 42.5 mm

Therefore from the above calculation, the minimum thickness required for the 32” blind flange is : t = 42.48 mm

### THICKNESS CALCULATION FOR THE 36” BLIND FLANGE:

Using the above formula (2)

• t = d *(CP/SE+1.9W hg/SE*d^3) ½ ……………….formula (2) (from ASME UG 34)

d= 978.2 mm

C= 0.3

P = 13.76 kg/sq cm

E = 1

W = 117 KG

hg= 53.25 mm

S = 25 ksi = 1757 kg/sq.cm

Substituting the above values in Formula (2),

t = 978.2*[(0.3*13.76/1757*1) + (1.9*117*98)/ (1757*1*978.2^3)] ½ = 47.41mm or 47.5 mm

Therefore from the above calculation, the minimum thickness required for the 36” blind flange is : t = 47.41 mm

### THICKNESS CALCULATION FOR THE 38” BLIND FLANGE:

Using the above formula (2)

• t = d *(CP/SE+1.9W hg/SE*d^3) ½ ……………….formula (2) (from ASME UG 34)

d= 1038 mm

C= 0.3

P = 13.76 kg/sq cm

E = 1

W = 132 KG

hg= 55.5 mm

S = 25 ksi = 1757 kg/sq.cm

Substituting the above values in Formula (2), t = 1038*[(0.3*13.76/1757*1) + (1.9*132*98)/ (1757*1*1038^3)] ½ = 50.31mm or 50.5 mm

Therefore from the above calculation, the minimum thickness required for the 38” blind flange is : t = 50.31 mm

### THICKNESS CALCULATION FOR THE 44” BLIND FLANGE:

Using the above formula (2)

• t = d *(CP/SE+1.9W hg/SE*d^3) ½ ……………….formula (2) (from ASME UG 34)

d= 1118 mm

C= 0.3

P = 13.76 kg/sq cm

E = 1

W = 178 KG

hg= 98 mm

S = 25 ksi = 1757 kg/sq.cm

Substituting the above values in Formula (2), t = 1118*[(0.3*13.76/1757*1) + (1.9*178*98)/ (1757*1*1118^3)] ½ = 54.19 mm

Therefore from the above calculation, the minimum thickness required for the 44” blind flange is: t = 54.19 mm

### THICKNESS CALCULATION FOR THE 46” BLIND FLANGE:

Using the above formula (2)

• t = d *(CP/SE+1.9W hg/SE*d^3) ½ ……………….formula (2) (from ASME UG 34)

d= 1168 mm

C= 0.3

P = 13.76 kg/sq cm

E = 1

W = 180 KG

hg= 98.5 mm

S = 25 ksi = 1757 kg/sq.cm

Substituting the above values in Formula (2), t = 1168*[(0.3*13.76/1757*1) + (1.9*180*98.5)/ (1757*1*11168^3)] ½ = 57 mm

Therefore from the above calculation, the minimum thickness required for the 46” blind flange is : t = 57 mm

### THICKNESS CALCULATION FOR THE 48” BLIND FLANGE:

Using the above formula (2)

• t= d *(CP/SE+1.9W hg/SE*d^3) ½ ……………….formula (2) (from ASME UG 34)

d= 1219 mm

C= 0.3

P = 13.76 kg/sq cm

E = 1

W = 202 KG

hg= 101.5 mm

S = 25 ksi = 1757 kg/sq.cm

Substituting the above values in Formula (2), t = 1219*[(0.3*13.76/1757*1) + (1.9*202*101.5)/ (1757*1*1219^3)] ½ = 59.09 = 59 mm

Therefore from the above calculation, the minimum thickness required for the 48” blind flange is: t = 59 mm

## Conclusion:

Since from the above calculation, 50 mm plate thickness required for the 32”, 36” & 38” with stress ration as 1.0.

And 60mm thick plate is required for 44”, 46”, 48” blind flanges at 13.5 bar (g) hydro test pressure and at ambient temperature.

However if the thickness of the blind flange is less than required then additional reinforcements or stiffeners has to be provided. If you have a Blind Flange custom made to a different dimension then it will cost much, much more and unless the maker is qualified to the proper Codes then you may be in violation of the applicable Piping Code (i.e.: ASME B31.3, etc.).

Source: China Blind Flanges Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

Please notice that you might be interested in the other technical articles we’ve published:

## How to calculating blind flange min. thickness?

That formua per the email and per B31.3 is for a blind flange which is supported either side by line flanges not an blind end flange which is what the stock blind flange is and which is designed as a flat plate to a different formula refer ASME V111 div 1 which is why it is as thick as it is..if you use the ASME formula for flat plates for your pressure you will find it is close to the stock flange thickness. I would worry more about the HDPE pipe, it will be temperature limited and the weaker link in your system by the sound of it.

## What is the function of blind flange?

The blind flange has the function of isolation and cutting off, which is the same as that of the head and pipe cap. Because of its good sealing performance, it is generally used as a reliable isolation means for the system that needs complete isolation. A blind is a solid circle with a handle, which is used for a system that is normally isolated.

## How do you install a blind flange?

Used to stop the flow in a pipeline by using a solid disk, there is no opening contained in blind flanges to allow fluid to pass through. Instead, one places the blind flange between open flanges creating a block, thereby stopping the flow of a liquid through the pipeline. They typically have holes that are machined to match those of a what might be a connecting flange or valve that would be in that place. A blind flange is used commonly when a new valve needs to be installed or to shut down a pipeline that is no longer needed for use.

Summary Article Name
How to calculate blind flange thickness?
Description
In order to use as thin as possible blind plate, and to ensure that the blind plate does not deform in the process of use, we do stress analysis on the stress of blind plate, and give the calculation method of blind plate thickness with examples. The calculation result is the thinnest thickness of the blind plate.
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www.steeljrv.com
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