Food grade fittings

What are the requirements for sanitary food grade fittings?

As far as hygienic requirements of sanitary food grade fittings, these are defined by various norms and standards. These include, for example:

• 3-A (3-A Sanitary Standards Incorporated), 
• EHEDG (European Hygienic Engineering & Design Group), 
• ASME BPE-2009 (Bioprocessing Equipment).

In general, the requirements come down to avoiding crevices and “dead zones” that pose a risk of medium accumulation and thus the growth of bacteria or other microorganisms.

Therefore, the internal surfaces of the couplings should be smooth (their roughness must not exceed Ra = 0.8 µm, or Ra = 0.4 µm in more restrictive applications). To ensure such high quality, in many cases, manufacturers resort to electropolishing.

Separate requirements apply to welds, the inner surface folds of which should be softened with a radius to make cleaning easier.

Seals, on the other hand, should be as close as possible to the medium while avoiding any crevices. This prevents any possibility of the transferred substance getting under the seal.

Are you interested in transporting food substances? Then also check out our range of food grade hoses, such as milk tubes or drinking water hoses.

From which materials are sanitary food grade fittings made?

From which materials are sanitary food grade fittings made? Sanitary food grade fittings are most commonly made from AISI 304 (304L) or AISI 316 (316L) stainless steel. The latter type is primarily used for the transfer of low pH media. In addition, it performs well where the working requirements are more restrictive.

When it comes to seals, on the other hand, they are created from a wide variety of materials, such as:

• NBR,
• EPDM.
• PTFA,
• silicone,
• viton.

Seals should also have the appropriate certifications (e.g. FDA 21 CFR 177.2600 and USP Class VI for elastomers or FDA 21 CFR 177.1550 for PTFE).

What are the different types of sanitary food grade fittings?

Sanitary fittings come in many different types. Below you will find a brief description of each.

DIN 11851 sanitary fitting

The DIN 11851 sanitary fitting is a threaded fitting with an Rd circular thread. The cross-section of its seal takes the shape of a letter “D”. However, the seal also comes in a version with a layer that fills the joint gap, which increases the degree of hygiene.

The fittings are available in dimensions from DN10 to DN150, and the maximum working pressure is:

• 40 bar (for DN10-DN40); 
• 25 bar (for DN50-DN100); 
• 16 bar (for DN125-DN150).

SMS fitting

The SMS fitting is a food grade fitting based on a Swedish standard and (like DIN 11851) is a threaded coupling with an Rd circular thread. The cross-section of its seal is rectangular.

These types of fittings enable easy assembly and disassembly of installation segments.

In terms of size, they are available from DN25 to DN100. The maximum working pressure is 15 bar.

It is worth noting that, despite their similarity, SMS and DIN 11851 fittings are not compatible with each other.

IDF fitting

The IDF fitting is also a threaded fitting, and differs from its predecessors in that it has a trapezoidal thread. However, the cross-section of its seal takes the shape of a letter “T”, thus ensuring a high level of hygiene.

The maximum pressure for this type of fitting is 16 bar.

RJT fitting

You will most commonly encounter the RJT fitting in the UK food grade industry It is a threaded fitting, but is characterised by a Whitworth thread. Meanwhile, the seal takes the shape of a thick O-ring.

This type of fitting allows easy assembly and disassembly, but it also has a disadvantage. As for the maximum working pressure, it is 10 bar.

As for the maximum working pressure, it is 10 bar.

Tri clamp fitting

Tri Clamp fitting is a food grade fitting that consists of two flanges with gasket grooves, which you will join together using a special clamp. Tri Clamp fittings are clearly different from all the others because they are symmetrical flange fittings. 

They are distinguished from others by their very high hygienic properties and usually higher quality surface finishes, thus ensuring an undisturbed flow of the medium.

However, Tri Clamp fittings are manufactured in accordance with different standards and can therefore vary in dimensions (although they are mostly the same). Also, when selecting them, pay particular attention to the flange diameter and the inner diameter. They should be identical in both parts of the joint to ensure adequate hygiene.

As for the maximum working pressure, it depends on the size of the fitting. It is assumed to be:

• 16 bar for fittings smaller than 2 inches, 
• 10 bar for fittings larger than 2 inches.

Aseptic fittings

DIN sanitary fittings have additional variations according to DIN 11853 and DIN 11864. They are compatible with each other, but differ in length. You will find three versions of these on the market:

• DIN 11853-1 / DIN 11864-1 - Rd threaded, bolted; 
• DIN 11853-2 / DIN 11864-2 - flanged, but screwed on; 
• DIN 11853-3 / DIN 11864-3 - flanged, but clamped (same as Tri Clamp).

In all cases, a special O-ring is used for sealing.

Aseptic fittings guarantee higher sterility compared to traditional sanitary food grade fittings.

How to install sanitary food grade fittings?

There are two installation options for sanitary food grade fittings to choose from:

• hosetail - fittings with a hose stub, 
• weld-on fittings.

In the first case, ensure that the stub (so-called “tail”) matches the type and size of hose. Also, make sure that the joint provides a maximum level of hygiene. How? Above all, no so-called “pockets” or thresholds should form between the tail and the hose wall, as these are places where fluid can accumulate.

When it comes to weld-on fittings, on the other hand, ensure that the quality of the weld is adequate. This means that there must be no crevices or other areas where the medium can settle.

Otherwise, there is a risk of the growth of microorganisms, which will adversely affect the quality of the food substance to be transferred.