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The steel flanges produced by Intertubi


The models of flanges marketed and produced by Intertubi with the relative reference standards.

13 November 2023
The word flange usually means a ring that must be connected to a pipe, by means of a welded joint and more rarely threaded, and which is drilled with a standardized number of holes which through the use of bolts allows the connection to another flange of equal size.
In the design of piping systems, the most economical method of joining is certainly butt welding, but for proper maintenance and easy assembly and disassembly, the use of steel flanges is essential, which allow you to create bolted joints that can be easily disassembled. This also allows the realization of modules in outsourcing, which are then assembled on site.
At this stage, a correct interface design process is required, that is to say the connections made with the flanges to avoid situations during the assembly phase in which leaks may occur in systems such as chemical or petroleum ones could have catastrophic consequences.

How flanges are constructed

The construction of steel flanges can take place in two different ways:
1. precision casting, that is by casting steel into a mold made using the lost wax technique
2. forging, that is by stamping a blank which is heated to a suitable temperature.
Of the two solutions, the preferable one is the second one, that is forging. The reason for this choice is the fact that compared to precision casting, forging allows to maintain compactness in the structure of the material and to avoid the appearance of inclusions which may in the subsequent phase give rise to fluid leaks especially in conditions of high pressure.
Once the flanges have been forged, they are machined using machine tools that make the sealing surfaces and the holes for the bolted joint. The processing is done on numerical control machines that allow repeatability, speed and precision. In this phase, the processing of the face is also of particular importance, which together with the gasket provides the seal, in fact this is not simply smooth but has a particular "phonographic" groove which has the purpose of retaining the gasket material and avoiding its expulsion that could happen due to the strong pressures involved.

The reference standards of the sector

We have three regulations that refer to the sector, two of the product while the third is of the supply chain:
- EN 1092
- ASME B16.5
- EN 10204
EN 1092 is the standard that specifies the types of flanges and their sealing surfaces, as well as the dimensions and relative tolerances, any threads, the dimensions that the connection bolts must have, the surface finish of the sealing surfaces of the joints flange, the necessary marking of the pieces, and the materials.

The ASME B16.5, on the other hand, is a reference for the Anglo-Saxon market and includes both flanges and flanged fittings and contains data relating to the very important pressure and temperature rate in the design phase, the materials that can be used, and as previously, dimensions, tolerances, marking and everything necessary to validate the conformity tests.

There is also a third standard which in reality is not of the product but is very important in the sector to guarantee the supply chain of the product itself and is EN10204, in fact this standard defines the documentation and test methods that each steel detail must have or pass to guarantee the safety of the piece to the end user. In fact, we are talking about certification in this case given the type of alleys it imposes.

The available flange models

All the figures envisaged in the standard are available in the catalogue, which can be summarized in the following categories. In particular, the connection to the pipe of the flanges presented below always takes place through the welding process and must be carried out by specialized personnel to avoid damage and malfunctions during operation.

The simplest models of flanges that can be found on the market are flat flanges. In fact, this type of component has no section variation along the radius as well as presenting the classic axial symmetry of the connecting flanges.
The main characteristics are:

- The nominal diameter (DN): which identifies the flanges and differentiates them from each other;

- The inner diameter (d): diameter of the inner hollow circle;

- The outside diameter (D): outside diameter of the flange;

- Hole spacing (a): is the diameter on which the holes for the connection lie;

- Hole diameter (f): diameter of the connection holes;

- Number of connection holes;

- Thickness (b): is the thickness of the flange which, as previously mentioned, is constant along the entire section;

-Weight [kg]: it is the weight of the flange.
This data can be of interest in the structural analysis phase to determine the strength of a structure.

Furthermore, the nominal pressure must also be taken into account, which differentiates the sub-categories of plate flanges from each other.


Compared to simple plate flanges, they have a central step which plays a fundamental role in the coupling phase with the pipe. The characteristic sizes, with the exception of the nominal diameter and the external diameter, are different:

- F is the step thickness;

- C1 is the thickness of the flange also considering the step;

- ØG is the diameter of the stepped raised area;

- ØK is the diameter over which the coupling holes lie;

- ØB1 is the internal diameter of the flange;

- ØL is the diameter of the connection holes;

- N is the number of connection holes.

Also in this case the nominal pressure plays a central role in differentiating the various sub-categories and the weight of the component.


The neck flanges have, in addition to the step, also an inlet neck for the connection via pipes. The main sizes are:

- H2 is the height of the flange;

- H3 is the height of the non-radius area of the neck;

- C2 is the height of the plate flange (similar to C1 for raised face flanges);

- R is the radius between the flat part and the neck;

- S is the thickness of the neck at the apex;

- ØN1 is the neck diameter before rounding;

- ØA is the diameter of the neck at the end of the rounding (ØN1 > ØA);

- N is the number of holes;

As in the previous cases, the nominal pressure and the weight of the component must be taken into consideration especially in the initial design phase.


They have the same dimensions as the plate flanges except for the internal diameter which does not exist since the blind flanges constitute the terminal element of a derivation and do not allow the passage of the flow.

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The materials chosen for the construction of flanges

The tradition of INTERTUBI starts from the realization and marketing of stainless steel fittings, valves and flanges, using materials that meet the needs of the market such as AISI 304, 304L, 316 and 316L steels which are part of the family of austenitic steels, alloys containing Nikel Chrome, and Molybdenum which give the well-known characteristics of resistance to hot oxidation, resistance to corrosion, and good weldability.

AISI 316 is used where there is the presence of high temperatures because it has a good resistance to corrosion, it is particularly suitable for its resistance to the action of saline environments, but is also able to effectively withstand the action of acids, salts and other chemical reagents of various types. This allows it to be used in the most diverse fields including the marine industry and the food industry where resistance to aggressive cleaning products is important.

The use of AISI 304 is instead indicated in the food industry, in the chemical one, and in the petrochemical industry, but also in the pharmaceutical one and this also due to the fact that the resistance to hot corrosion is such as to maintain good chemical characteristics and mechanical during continuous operation up to about 800 ° C.

But we do not have items made only in stainless steel, but also in carbon steel for construction and here too the choice is decidedly wide depending on the use for which they are intended. Construction steels are those that the new ISO standard identifies according to their mechanical characteristics with the suffix P which indicates materials suitable for use under pressure, with yield strengths starting from 235 Mpa at room temperature. If the choice of flanges falls on the Anglo-Saxon legislation, the classification of the steels is different but conceptually similar.

The importance of flanged connections

The steel flanges produced by Intertubi represent one of the main types of connection between mechanical parts within more or less complex structures.
The main characteristics are:
- Integrity: a term often associated with solidity of design and construction;
- Durability: the ability of a structure to maintain its characteristics unchanged over time;
- Safety: eliminating risks to people or buildings close to the location of these connections, avoiding damage to personal health and the structural integrity of the systems.
The very structure of these connections, whether they are incorporated into the pipes or are separate components, also defines their advantages and disadvantages compared to a welded connection. In fact, if on the one hand the risk of wear (both contact and coupling) and loosening of these components represent significant risks, on the other hand there is greater flexibility of application, in addition to the speed of intervention in case of failures.
Therefore, the fundamental role of each operational phase emerges, from design to installation with maintenance, to be able to obtain a product that complies with the regulations previously introduced but which can also guarantee the characteristics listed above. The absence of just one of these aspects can compromise everything that the flanges can provide, transforming the advantages into significant disadvantages.

What to see during your Easter holiday on Lake Garda

Let's move on to the activities that your family can do once they arrive at Camping Baia Verde. The possibilities are many and will satisfy both nature lovers and lovers of history and local traditions.
Let's start with one of the most popular destinations: we are talking about the Rocca di Manerba, an archaeological site that can be reached both by walking and by car. The stronghold offers a beautiful panoramic site from which to look at the lake and the mountains that surround it. Furthermore, for the more curious, we recommend visiting the nearby Civic Archaeological Museum of Valtenesi, which chronologically traces the history of the area thanks to the objects and materials found during the excavations.
If, on the other hand, you want to do an activity linked to the lake, you can visit the suggestive island of San Biagio, also known as the island of rabbits due to the presence of these cute animals that have become accustomed to the presence of people. Due to the drought and the lack of rain, you can also reach the island on foot, thanks to the resurfacing of the natural isthmus that connects it to the mainland.
Your Easter holiday on Lake Garda will thus turn into an unforgettable and evocative adventure, to be shared with the people you love.
Don't wait any longer, please contact us to request availability and book your spring and Easter stay!

Welded flanges or threaded flanges?

As anticipated in the previous paragraphs, flanges are a type of connection that can have both a welded joint and a threaded joint. Both of these types bring with them some advantages and some disadvantages that can make them preferable to the others based on the individual applications:
- Welding represents a type of permanent connection that allows the union of flanges with pipes by creating a welded joint that can be generated by different techniques. This method creates a structural joint that does not loosen over time but is more difficult to maintain if breakdowns or failures of only one of the parties are involved. Furthermore, it is not always possible to carry out the welding directly on site and it is necessary to resort to special expedients and precautions;
- On the other hand, the threaded connection allows for better access in the event of malfunctions and breakdowns allowing for quick disassembly and action or replacement of a part. However, this can also lead to the loosening of the joint over time with the loss of functionality and integrity of the structure itself.

On the basis of the foregoing, it is immediate to note that it is not possible to make an a priori choice, but it is necessary to evaluate each individual application and understand which are the most important operating criticalities or strengths of the coupling to be used: the experience and knowledge of the system designer help to choose the most correct type of flanges.

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