In recent years, the use of stainless steel pipes has become widespread in industrial process lines due to their high resistance to corrosion and excellent mechanical properties.
Elements such as chromium, nickel and molybdenum are part of the alloy of this type of pipe, making the resulting material highly resistant to extreme working conditions and the conduction of very corrosive fluids, something that pipes made from other materials cannot withstand.
However, once we are clear that stainless steel can be an appropriate solution for our project, we must take into account the different aspects and choose the most suitable grade (quality) according to the type of installation. Each alloy has some characteristics that distinguish it from the others and it is necessary to know which alloy is suitable for its application.
The importance of choosing the right alloy
Knowing the type of liquid or paste to be transported by the pipeline is the basis for choosing the right alloy, as there are many grades of stainless steel depending on the percentage of chromium, nickel and molybdenum they have in the material (304L, 316L, 304H, 321, 316Ti, 2205, 2507…) .
Other factors that must also be considered are temperature (there are specific alloys for extreme temperatures, such as refractory stainless steel) or pressure (if very high, the tube must be seamless and thicker).
In addition to this, it is important to know the available commercial range, as the market offers a wide range of diameters, thicknesses and finishes.
Once these variables have been determined, it is also necessary to take into account the type of industrial process in which the pipe will be implemented. In some industries, even the external environment can affect the possible corrosion factors to the extent that they may appear on the surface of the pipe rather than inside.
Every industry has a type of pipeline
Although any range of piping can be used in almost any industry, there are general trends in the choice of materials for each industrial process.
Water treatment
Activity in this field has grown considerably in recent years due to society’s awareness of the need to conserve and reuse water as a scarce resource. There are large engineering and installation companies specialising in the design and assembly of water treatment, drinking water treatment and desalination plants. They are the ones who always define the quality of the stainless steel to be used.
Depending on the type of water to be treated, there are different grades of stainless steel. For example, in desalination, alloys with high chromium and nickel content (2205, 2507) are used due to the extreme corrosion of salt. On the other hand, in purification and drinking water treatment, the requirements are less demanding and therefore the more common grades are used (304L, 316L), but it is always important to remember that the chlorine used in these processes is also a corrosive component, especially when used in high concentrations.
Paper industry
This is where stainless steel excels in a sector where it is very demanding. In fact, it is required for the entire paper and tissue manufacturing process. The acids used in their production are so aggressive to the pipes that there is no possibility of using other types of material.
The most common millimetre ranges and ISO ranges on the market are the ones most commonly used in this type of industry. Standard grades, such as 304L and 316L, are suitable for this type of process where the liquid to be conveyed is pulp.
Again, engineering companies will define the grade used in each part of the process.
Chemical and petrochemical
In some geographical areas of the country there is a concentration of a significant part of European chemical activity and, as a result, the demand for stainless steel in these areas is significant.
In this production sector, the most commonly used range is ASTM (SCH10S, 40S…) , with and without welding. In certain process lines, particularly in the petrochemical sector, high thicknesses are required due to the high pressure and temperature conditions required.
In the case of the chemical industry, the components carried by the pipes mean that this application requires actual special alloys. grades such as 304H, 321 and 316Ti are characteristic of this sector, although they are not the only grades available.
Oil and Gas
The oil industry includes the exploration, extraction, refining and transportation of oil. Offshore platforms located offshore require special alloys such as duplex (2205), super duplex (2507), Hastelloy (C276, C22), Inconell… These grades are characterised by their particular resistance to oxidation at high temperatures and their ability to withstand corrosion from high salt concentrations in the sea.
Food, pharmaceutical and cosmetic industries
The manufacturing standard required for this sector is DIN 11850, which has very specific specifications in terms of diameter, thickness and, most importantly, surface finish.
For this type of application, the requirements for hygienic and health conditions are higher due to the final destination of the product, although corrosion during manufacture is not as important as in the sectors described earlier.
In general, grades 1.4307 (304L) and 1.4404 (316L) are used for pipes of standard thickness (1, 1.5 and 2 mm). In such cases it is very common to polish the pipes externally or even internally.
Manufacture of capital goods
Heat exchangers, lubrication or metering equipment, pressure vessels, reactors, mixers, dryers and any other type of component related to industrial processes.
Each type of equipment has its own particularities and it is therefore impossible to generalise about the type of piping or the class of application. Each element is designed with specific specifications, which means that in each case a specific type of alloy is used. The same applies to the definition of diameter or thickness.
In short, the most suitable grade of stainless steel must be selected for each application to optimise its suitability and resistance to environmental and fluid conduction, which is its purpose.
In most cases it will be left to the engineering company to define the required specification, if this is not the case it will be up to the installer to analyse all these factors to select the most suitable alloy.