Stainless Steel Fittings: standards, techniques and figures

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In increasingly advanced plant engineering, it is necessary to create conditions of duration and safety even in case of use with particularly aggressive fluids or processes. All the more so when not only the tightness of the system itself is questioned, but also the safety of people.

The best realization passes through welded connections both pocket and butt-connected or flanged, able to ensure tightness and durability over time, also aided by the use of stainless steels suitable for the purpose.

The range of fittings is decidedly wide and includes different figures made of stainless steel, even the reference standards are both European and American, in order to serve the market in a complete way.

Curves, tees, concentric and eccentric reductions, bottoms made in compliance with the EN10253-3 standard, are generally not compliant with the PED directive

Some figures such as concentric metric reductions and hydroformed tees comply with the ISO 5251 standard

Assortment of tees, standard bends, reductions here too eccentric and concentric as well as the bottom caps that follow the indications and measurements from the American standard ASME B16.9 and also they can be butt welded

Complete range of pocket fittings always to be welded that make reference to ANSI B16.11 Thread

fittings made both in accordance with European or international standard ISO 4144 or EN10241 and in American standard ANSI B1.20.1

The production techniques of stainless steel fittings are varied, and each one is suitable for the specific type of fittings, mainly hot plastic deformation is used, bringing the material to a temperature suitable for its deformation.

For the curves we can use the deformation method on mandrel which ensures the correct shape without losing the circularity of the product and without giving significant variations in thickness, for the tees instead we resort to hydroforming which is the one that gives the best results or for products particularly large for welding. For end caps and reductions, on the other hand, both hot and cold forging techniques are used.

The materials commonly used to make these fittings are from the austenitic steel family and in particular the AISI 316 / 316L and AISI 304 / 304L. AISI 316

steel is also identified by the initials X 5 Cr Ni 18 10 and is a highly alloyed steel with high levels of chromium and nickel which give it the characteristics of stainless, jargon it is also called "stainless steel 18 10" and it has always been used for the creation of aesthetic products such as pots and cutlery sets. This is because it has excellent cold deformability which allows it to be processed by deep drawing, but also has excellent workability on machine tools.

It is particularly suitable in the food, chemical and pharmaceutical industries, and in the petrochemical sector, and is appreciated for its good resistance to hot corrosion which allows it to maintain good characteristics during continuous operation up to about 800 ° C.

It also has excellent resistance to the action of saline environments, but also optimally bears the action of acids, salts and other chemical reagents of various types. This makes it the ideal material for use in various fields including the nautical and food industry where resistance to often aggressive cleaning products is required. AISI 304

steel  instead it designates the material X8CrNi188, commonly known also as INOX 18/8 an alloy that is containing about 8% of Nikel and about 18% of chromium, an element that gives the characteristics of resistance to corrosion by creating a superficial film of oxides .

It is a non-magnetic material that is used thanks to its very high resistance in situations where an almost eternal duration is required, such as in the case of nuclear or particularly critical plants.

For both abbreviations there is a version with the suffix L called "low carbon" and which is characterized by a lower carbon content. This serves to increase the resistance to intergranular corrosion and to partially improve the weldability of these materials.

The world of fittings is characterized by the difference between various types of models, materials, production methods and manufacturers. An important difference is constituted by the choice, in terms of construction, between stainless steel and brass.

Stainless steel, as described, has a number of advantages that make it highly suitable for this type of application. Brass, or an alloy between copper and zinc, is in turn widely used in the field. But what are the differences and the reasons for choosing one over the other?

An important aspect is corrosion resistance: both have characteristics suitable for this type of application as they are highly resistant to corrosion, even if they suffer from particular types of highly corrosive environments. From the point of view of workability, brass is better and allows to obtain components and details of considerably smaller dimensions than those obtainable with steel. On the other hand, the latter has a longer duration and also a greater resistance: in certain applications the ability to withstand stresses and loads is a fundamental requirement. From a cost point of view, stainless steel has a slightly lower price than brass and this is another favorable feature.

Therefore, on the basis of this comparison, it is possible to state that, on the basis of the single application, it is possible to choose one or the other material, guaranteeing in any case excellent characteristics to the final product.

It is not easy to choose all the parameters necessary for the purchase of a fitting to be installed in the safest way possible, the value of stainless steel is to withstand aggressive environments even at high temperatures.