Many factors are taken into consideration when deciding which grade of stainless steel tubes to choose from. The crucial feature for stainless steels is that they are immune to corrosion for a given application or environment. Strength and fabrication features are also taken into consideration. There are more than 60 grades of stainless steel available. Nevertheless, the entire group may be divided into four metallurgic groups. In order to decide the grade to be selected, certain mechanical or physical properties will also need to be included in order to satisfy the overall service performance requirements.
Pipes and tubes are often difficult to identify and tend to be differentiated by function. In addition to such classifications, stainless steel is often differentiated by type and grade.
304 Stainless Steel Tube
Type 304 stainless steel is a preferred alternative for tube and pipe applications because it is extremely chemical and corrosion-resistant. However, type 304 stainless steel is not compliant with applications where temperatures fall between 800 and 1640 degrees F as it is susceptible to carbide precipitation owing to a material content limit of 0.08 percent carbon. Stainless steel 304L Tubes eliminates this problem as it has a lower carbon content level and can also be used for welding and higher temperature applications. Other types of stainless steel often have additives (such as nickel or molybdenum) that strengthen features that are beneficial in specific applications.
Stainless Steel Tubing for General Corrosion-Resistance
The general type of steel is suitable for applications requiring corrosion resistance overall characteristics. Ferritic or martensitic forms of steel (those produced with the highest chromium) are produced to be either heat-treated or annealed. Austenitic Stainless steels (those with high chromium and nickel content) offer even more resistance and can be used under the same general conditions as ferritic and martensitic types.
Stainless Steel Pressure Tubing
This type of stainless steel pipe is manufactured from either solid chromium or a mixture of chromium and nickel. Forms of stainless steel pressure tubes include seamless and welded tubes, electric fusion welded pipes for high-pressure applications, large-diameter welded pipes for corrosive or high-temperature applications and seamless and welded ferritic and austenitic stainless steel pipes.
Stainless Steel Sanitary Tubing
For applications where stainless steel tubes or pipes must come into contact with food and other sensitive products, hygiene is a high priority. Stainless steel sanitary tubes are used in these applications as they have good corrosion tolerance, do not tarnish, and are easy to clean. Numerous tolerances can be achieved for specific applications. Typically, the grade used for these applications is ASTM A270.
Stainless Steel Mechanical Tubing
Usually, stainless steel mechanical tubes are used in applications such as cylinders, bearings, and other hollow-formed components. Tubing may be modified in order to create a range of cross-section forms, such as square and rectangular, in comparison to the more conventional, round cross-section tubing. Typically, grades ASTM A511 and A554 are used for mechanical tubing applications.
Stainless Steel Aircraft Tubing
In highly specific aircraft applications, stainless steel type chromium and nickel are used because of their heat and corrosion resistance. Work-hardened or welded types can be found in applications requiring high-strength, stainless steel aircraft tubing, although work-hardened components should not be used with certain types of corrosive substances. Low-carbon forms of stainless steel are common choices for welded parts.
For applications that require seamless and welded tubing in larger dimensions (1.6 to 125 mm outer diameter), aircraft structural tubing is used — this type of stainless steel is made in compliance with Aerospace Material Specifications (AMS) or Military Specifications (MIL Specs).
Aircraft Hydraulic-Line Tubing
Another form of aircraft tubing, hydraulic-line tubing, is often used in aerospace applications as fuel injection lines and hydraulic systems and tends to be small. It is also manufactured from grade 304 or 304L stainless steel owing to the high strength, durability and ductility of the steel.