Stainless steel – for demanding requirements

Alloyed or unalloyed steels are known as stainless steel. Stainless steel is often referred to as “rust-proof steel,” although this is not quite correct, as some stainless steels can rust.

Conventional stainless steel is durable, robust, and resistant to corrosion. It has a high quality appearance, is hygienic, has high mechanical and thermal strength, and is decorative. Stainless steel has high thermal conductivity and a high degree of purity.

SERTO supplies a very wide range of screw fittings, valves, adapters, and couplings made from high–quality 1.4571 stainless steel which is especially hard. Therefore, these products are suitable for highly demanding applications, even in aggressive environments.

Brass – universal and indestructible

Brass is an essential material in domestic technology and has proven its value in many applications in daily life. Brass is far more than just an alloy of copper and zinc. Brass is somewhat harder than pure copper and can be used for a wide range of applications. Its colour changes from brownish to light yellow depending on the zinc content.

The addition of lead improves the machining characteristics of the material. However, this is also a problem since lead is a “foreign material,” which, as a precautionary measure, must be kept out of drinking water by all possible means, because we could be exposed to it daily throughout our lives. For this reason, SERTO has been using a brass alloy with a maximum lead content of 2.2 % for many years.

You benefit in many ways: from secure and radially removable SERTO fittings, from compact sizes, and from a large range of types.

With the option Brass BA (low-lead) you are on the safe side. You can find further information under the navigation item Brass BA or Treatment BA.

The brass screw fittings are also available with chemical nickel plating. This provides greater surface hardness and improved resistance to corrosion, abrasion, and wear. You can find further information under the navigation item Brass CV.

Brass CV – chemically nickel plated

Brass CV fittings are plated without electric current using a chemical reaction. This type of coating has the advantage of a uniform layer thickness, including on internal surfaces and complex contours.

The appearance is similar to that of stainless steel. The fittings can be used as a “stainless steel substitute” with stainless steel tubes at low pressures. Due to the stringent regulations, nickel plated fittings may not be used in drinking water systems. However, they may be used without problems in certain applications in the food sector.

Because of their surface coating, Brass CV fittings have greater resistance to chemical media and better resistance to corrosion, abrasion, and wear than pure brass. In addition, they can be used with stainless steel tubes to provide a better appearance.

Steel – proven and reliable

Steel has been produced for about 3,000 years and played a decisive role in industrialisation. Steel is the designation for all ferrous materials which do not contain more than 2.06 % carbon and which are suitable for hot forming.

Through alloying, steel can be adapted to its intended purpose and can be given different properties. Steel is by far the most commonly used metal because it is very strong and can be cheaply produced.

SERTO supplies a proven range of screw fittings, valves, and couplings. SERTO has been producing steel fittings for decades and thousands of these are used reliably, for example, in the central systems of railways.

PVDF – the sophisticated solution

Polyvinylidene fluoride (PVDF) is a thermoplastic fluoropolymer with good mechanical, thermal and electrical properties. The areas in which it is used range from space technology to chemical, laboratory and measurement technology, the construction industry and even in medical technology as a prosthetic material..

It is characterised by a very high resistance to chemicals and UV radiation and is self-extinguishing. The FDA-compliant material is completely non-toxic, and similar to glass, offers no breeding ground for micro-organisms. Regarding its mechanical properties, PVDF provides high strength and rigidity, good gliding, and abrasion resistance.

Due to its excellent resistance to nearly all aggressive media, PVDF can be used in an extremely broad spectrum of applications. Moreover, PVDF is very easy to process. For these reasons, PVDF has gained acceptance in many types of applications, especially those in which aggressive media are transported.

PVDF has properties similar to the expensive fluoropolymers PTFE and PFA, the difference being especially in the temperature resistance, which is not a critical factor in a great many applications.

Why plastic tube unions?
Compared to metal unions and other metal connecting elements, those made of plastic are significantly lighter in weight. They are also electrically isolating, anti-magnetic and have low thermal conductivity, and plastic components can be injection moulded into complex shapes.

Sealing materials at SERTO

SERTO unions made of steel, stainless steel and brass have a metal-to-metal seal. Male adaptors are however mounted on other threads. For these products, SERTO offers seals that can be made by means of a sealing lip, O-rings or if desired by applying PTFE-tape and Loctite® to the thread. Seals are also contained in our valves and couplings. We use an array of materials for our O-rings and flat gaskets, depending on the application parameters.

The abbreviation NBR stands for Nitrile Butadiene Rubber. NBR is the most frequently used material in sealing technology because of its good resistance to most mineral oils and greases. The thermal range of application is normally between –30°C and +100°C, short term up to +130°C; at higher temperatures the material hardens. Additionally, NBR exhibits favourable ageing characteristics and low surface abrasion.

NBR is resistant to hydraulic oils, water glycols and oils in aqueous emulsions, mineral oils and mineral-oil products, animal and vegetable oils, benzine, fuel oil, water up to ca. +70°C, butane, propane, methane, ethane. NBR swells greatly with aromatic hydrocarbons, e.g. benzene, chlorinated hydrocarbons (e.g. trichloroethylene), esters, polar solvents, such as acetone, as well as in glycol ether-based brake fluids.

Fluororubber figures among the most significant developments in materials technology of the 1950s. The difference between FPM and FKM is only the name: FPM (according to DIN/ISO) and FKM (according to ASTM). The initial material is FDA-compatible (CFR 21, §177.2600). It is also known under the trading name Viton®.

FKM features high temperature, weathering, ozone and chemical resistance. The temperature application range is from –20°C to +200°C, short term +250°C.

FKM is highly resistant to nearly all mineral-oil and synthetic-based hydraulic fluids, as well as to ozone, oxygen, fuels, aromatic compounds, many organic solvents and chemicals. There are however restrictions for use in hot water, steam and at low temperatures. Due to the diminished low-temperature flexibility and moderate hot water and steam resistance, special materials should be selected for these applications. FKM is also not resistant to polar solvents, such as acetone, glycol-based brake fluids, ammonia gas, alkalis and low molecular-weight organic acids (formic acid and acetic acid).

EPDM elastomers are very resistant to ageing and weathering, even with UV exposure and ozone influence. They exhibit low water vapour permeability and extremely low brittleness temperature. Due to its high elasticity and good chemical resistance, EPDM is used for diverse seals, such as e.g. o-rings and flat gaskets. The working temperature ranges from –40°C to +160°C, short term up to +180°C.

EPDM possesses excellent resistance to hot water and steam and good resistance to polar liquids, such as acetone, methanol, etc. The material is not resistant to aliphatic and aromatic hydrocarbons (mineral oils, benzine, fuels) and greases.

Chemically, FFKM is very similar to polytetrafluoroethylene (PTFE) and it combines the elasticity and sealing strength of a true elastomer with the chemical resistance of PTFE. Compared to pure PTFE seals, FFKM parts do not demonstrate creep behaviour or yield and little permanent deformation. FFKM perfluoroelastomer parts maintain their elastic properties in long-term operation at up to +315°C and in periodic operation up to +350°C, even when in contact with corrosive chemicals.

Because of its comparably high kilogram price, the applications are limited to those with contact to highly aggressive media, particularly in situations where there are high safety and purity specifications or where the costs in the event of failure would be very high. Such applications are found, for example, in the chemical, petroleum producing and processing industries, equipment manufacturing, power plant construction, semiconductor and food industries or in the aerospace industry.

FFKM parts are resistant to nearly all chemicals, such as ethers, solvents, ketones, esters, amines, fuels, acids and alkalis.

PUR seals are used less frequently than other elastomer seals. They are used at temperatures between –30 and +80°C. The advantages of PUR compared to rubber elastomer materials are, among other, the very good mechanical properties, the excellent wear resistance with good flexibility and the high resistance to tear propagation in a hardness range of ca. 55° to 95° Shore A. Within this range of Shore hardness, PUR seals demonstrate an especially good combination of physical and chemical characteristics.

All PUR elastomers have a good swelling resistance to mineral oils, greases, benzine and diverse solvents. PUR elastomers are not suitable for direct contact with foodstuffs.

Due to its outstanding chemical, physical, thermal and electrical properties, PTFE is an important material in a variety of industrial sectors. The material is non-toxic in its pure form and FDA-compatible (CFR 21, §177.1550). The working temperature is between –200°C and +260°C (short term up to +300°C). PTFE has an exceptionally low coefficient of friction, tends, however, to cold flow and only has low resistance to pressure and wear.

PTFE is resistant to nearly all organic and inorganic chemicals (except elementary fluorine under pressure or at high temperatures, fluorine-halogen compounds and alkali metal fusions). At room temperature, PTFE is physiologically stable; contact with aggressive media does not alter its material properties.

MVQ® is particularly characterised by its broad range of thermal application. The very good cold flexibility, the good ozone resistance and the good dielectric properties are additional advantages. The gas permeability is not as favourable as with other elastomers. The working temperature range is between –60°C and +250°C.

PA – the economical solution

Parallel to the PVDF product range, SERTO offers its customers a polyamide (PA) line as well. Both plastics have comparable temperature resistances. PA is also a thermoplastic fluoropolymer, is partially crystalline and has high stability and rigidity. However, compared to PVDF, PA exhibits deficits in UV and chemical resistance. The added plasticizers make PA more flexible, but also unsuitable for drinking water applications.

PA is very wear resistance and has good gliding properties; when heat is applied, PA shows good dimensional stability. Our customers use PA unions and hoses, e.g. for compressed air transport or in ink jet printers.

Special alloys – for extreme requirements

For extremely high resistance to aggressive media and corrosion which is above that for normal types of steel special alloys are used. SERTO has already gained know-how in the processing of other alloys such as Hastelloy® and Monel®, as well as Incoloy®, Inconel®, SMO®, Duplex and Superduplex.

Hastelloy® is the brand name of a steel alloy from the US company Haynes International Inc. The material is now the one with the best qualities of the nickel-chrome-molybdenum-group with regard to corrosion, resistance to pitting corrosion or crack corrosion.

Monel®, a brand from the US company Special Metals Corporation, is a nickel-copper alloy with high strength and excellent corrosion resistance which is especially important for high flow speeds.

Because of the high raw material costs and the significantly more challenging processing (e.g. longer machining times, higher wear and tear on coolant and tools) years of experience with special alloys are an important prerequisite for high efficiency. Ask your SERTO contact for solutions to your challenges!