December 27th, 2010
At Chemipetro we manufacture a range of pipe fittings and flanges which are sometimes very complex designs requiring special machining techniques. We also manufacture the most basic of pipe fittings such as bends. However, it would be a mistake to believe that even such simple units do not require special process.
Anyone who has tried to form a bend in a pipe will know that it is not a simple matter as would first appear. If force is applied to a straight pipe then the unequal forces on the inside and outside of the bend will cause the pipe wall to distort and collapse.
To prevent this happening, it is necessary to use special techniques to bend a pipe and these vary depending on the size of the pipe. For small pipes it is possible to bend the pipe around a former. This supports the inside of the bend and prevents it deforming. It also ensures that a regular uniform bend is formed. Whilst this method works with small bore pipework it is more difficult to bend large diameter pipes as are more commonly used in the petrochemical industry
For these larger pipes a technique called induction bending can be used. Here a section of the pipe is heated using electrical induction coils and the pipe is bent slightly. The section is then immediately cooled to set the bend. The pipe is moved forward and the process repeated. In this way the bend is formed in small increments. This process works well with materials such as duplex stainless steel which are otherwise difficult to work.
Tags: Duplex, duplex stainless steel, Flanges, Pipe Fittings
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September 23rd, 2009
Duplex stainless steel was first created in order to address corrosion problems stemming from chloride bearing cooling waters or other chemical process fluids.
Duplex stainless steel is a family of grades which are ranged in accordance to their corrosion performance, as well as their content of alloy; Duplex’s alloy content being almost equal proportions of ferrite and austenite.
Super Duplex was a term phrased in order to indicate its highly alloyed composition of which provides a pitting resistance of >40. The chemical composition is based on Cr% + 3.3Mo% + 16N%.
Super Duplex contains very high levels of chromium which provides above average resistance to acids, caustic solutions and acid chlorides. It also provides high levels of corrosion resistance to any environment which uses chemicals or petrochemical solutions. It is fast replacing 300 series stainless steel or high nickel super-austenitic steels.
Based on a chemical composition which has high contents of nickel, chromium and molybdenum, Super Duplex improves intergranular and pitting corrosion resistance. With the addition of nitrogen to promote structural hardening it not only raises yield strength but also strength values without impairing its toughness.
The Various Alloys
Super Duplex stainless steel resides in the group of Duplex stainless steel. It is graded for its corrosion performance and for its content of alloy. Duplex can be divided into four groups:
1. Super Duplex, which contains 25-26Cr and increased Mo and N. This grade is comparable to 25 Cr and 2507
2. Lean Duplex stainless steel such a 2304 which contains no added Mo
3. 2205, which is a grade considered the work horse as it accounts for over 80% duplex use
4. 25 Cr duplex.
All of these materials are available from us here at Chemipetro.
Tags: Duplex, duplex alloys, duplex stainless steel, Super Duplex
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September 17th, 2009
The two phase microstructure led to the name Duplex. The microstructure consists of grains of ferritic and austenitic stainless steels. When Duplex stainless steel melts it hardens from this liquid phase into a completely ferritic structure. As it cools to room temperature approximately half of these ferritic grains change into austenitic grains. The result is that Duplex stainless steel contains about half of each material, ferrite and austenite.
This Duplex structure gives this particular family of stainless steel its much applauded properties. For one it provides about twice the strength of regular ferritic or austenitic stainless steels. Duplex stainless steels also provide much higher levels of toughness and ductility over ferritic grades. They don’t, however, match these superior properties provided in austenitic grades of stainless steel.
Superior Qualities
While all stainless steels offer resistance to corrosion, the levels depend on their individual compositions. If chloride pitting or crevice resistance is required then they must contain in their composition a mixture of chromium, molybdenum and nitrogen. Duplex stainless steel has corrosion resistance levels that are similar to austenitic stainless steels. For instance from types 304 or 316 grades to 6% molybdenum stainless steels.
Duplex grades have excellent resistance to stress corrosion cracking. This is a property that has been inherited from their ferritic makeup. While austenitic stainless steels provide superior corrosion resistance, ferritic stainless steel provides superior stress cracking resistance.
Due to the lower nickel and molybdenum composition, Duplex stainless steels can be lower in cost. Apart from this and due to their yield strength, it is often possible to reduce the thickness. The combination of these two factors offers not only cost savings, but also savings in relation to weight – especially when compared to austenitic stainless steels.
Duplex stainless steel can be found here at Chemipetro, one of the UK’s leading manufacturers of pipe fittings and flanges, for reasonable prices.
Tags: austenitic stainless steels, Duplex, duplex alloys, duplex stainless steel, ferritic stainless steel
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September 10th, 2009
In order to understand Duplex stainless steel, it is first necessary to understand the alloys which are present in it. These are Ferritic Alloys and Austenitic Alloys.
Austenitic Alloys are produced from a combination of both an iron solution and an alloy which when cooled, change into other mixtures; such as cementite and ferrite. At times – and to some extent – pearlite is also produced from the mixture. This is an alloy that is able to withstand corrosion and due to its cold working, provides far increased strength.
Austenitic alloys consist of two types of series, the first being the 200 series. The 200 series contains nickel, chromium and manganese while the second 300 series contains only chromium and nickel. Austenitic’s mechanical properties can be changed via the use of quenching, tempering or annealing.
Ferritic Alloys belong to the 400 series of stainless steel alloys. It is an alloy that is more popular than iron as it contains the same substances capable of producing cast iron and steel. Each is not hardened even when submitted to heat treatments or other solutions. Ferritic alloy is also resistant to corrosion due to its oxidation properties.
Duplex stainless steel is known for its corrosion resistant properties, which lends itself to both the construction and forming of flanges and pipe fittings.
Duplex stainless steel was introduced to the welding industry in the 90’s. Its primary focus lay in welding but since then its uses have been developed and expanded. Its properties were so well presented that fabricators and engineering specialists immediately saw its potential in construction uses.
Luckily, these materials are now available through us: leading flange supplier Chemipetro.
Tags: Duplex, duplex alloys, duplex stainless steel, Flanges, Pipe Fittings
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September 9th, 2009
The most important aspects of Duplex stainless steel lies in it uses. Fabricators, while not being especially interested in its chemical properties, are interested in its advantages or disadvantages as well as the ease in which it can be fabricated.
Metallurgists on the other hand are interested in it s composition as well as its end usage.
In the fabrication of flanges, Duplex stainless steel offers many advantages. While there exists no all purpose material that can resist corrosion Duplex alloys are in a class that offers superior corrosion resistance.
For instance, in an environment where chlorides are present Duplex alloys give a good performance rating when put against 300 series stainless steel, which gives a poor performance rating.
Where general acids are present Duplex alloys gives a good performance against 300 series stainless steel which again gives a poor performance. Where Hydrofluoric Acid is present the only alloy that gives a better performance than Duplex alloys is either silver or gold.
In the manufacture of high quality flanges, Duplex stainless steel is cheaper than other materials that offer corrosion resistant features. In comparison to 300 series stainless steel Duplex offers a yield strength that is double. This means that in fabrication a thinner material is all that is needed to support an equal load.
It is cheaper to fabricate due to its ease of machining and welding. The ferrite content allows for welding that is less intimidating than high nickel alloys. All that is recommended for welding Duplex alloy is a slight weave bead and a higher heat input.
We at Chemipetro are a leader in the field when it comes to supplying Duplex stainless steel flanges to worlwide industries.
Tags: Duplex, duplex stainless steel, Flanges, Pipe Flanges
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