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The steel flanges produced by Intertubi


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

04 May 2022
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 provided for in the standard are available in the catalog and are summarized in the following categories, whose connection to the pipe is always done by means of a welding:
- Plate flanges 
- Raised face flanges 
- Neck flanges
- Blind flanges for closing the terminals
The choice of one model over another is given by the characteristics and the field of use of the joint, such as for example in the case of large thermal variations to better absorb the bending of the pipe branches, it is advisable to use neck flanges that they ensure a more efficient distribution of efforts.

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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.

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