Tubing

Stainless steel tubing and pipe differ primarily in how they are measured, specified, and used. Tubing is typically ordered by its exact outside diameter (OD) and wall thickness, making it suitable for precision instrumentation, hydraulic systems, and structural applications. Pipe is generally specified by nominal pipe size (NPS) and schedule, with emphasis on fluid transport and flow capacity. Tubing is available in round, square, and rectangular shapes, while industrial piping is typically round.

Welded stainless steel tubing is manufactured by forming stainless steel strip into a tube and joining its edges with a longitudinal weld. Seamless tubing is produced from solid steel stock without a longitudinal weld seam. Both types are used in industrial applications, but seamless tubing is often selected for demanding pressure and temperature conditions, while welded tubing can offer cost and availability advantages. Actual pressure capability depends on applicable standards, wall thickness, material grade, and manufacturing quality.

Both 304 and 316 stainless steel tubing provide strength, durability, and corrosion resistance. Grade 304 contains chromium and nickel, making it suitable for many general industrial and processing applications. Grade 316 also contains molybdenum, which improves resistance to pitting and crevice corrosion in many chloride-containing environments. For coastal, marine, or certain chemical-processing applications, 316 is often preferred, while 304 may be a more economical choice for less corrosive environments.

Grades 304L and 316L are low-carbon versions of 304 and 316 stainless steel. Their reduced carbon content helps minimize chromium carbide precipitation during welding, reducing the risk of corrosion near welded joints. This makes them useful for welded tubing assemblies, instrumentation systems, and industrial processes where corrosion resistance is important. Grade 316L also offers improved resistance to many chloride-containing environments compared with 304L.

Seamless stainless steel tubing is frequently selected for high-pressure applications because it does not contain a longitudinal weld seam. However, properly manufactured and rated welded tubing can also perform reliably under pressure. The maximum allowable pressure depends on tubing dimensions, material strength, temperature, applicable standards, and fitting compatibility. Customers should verify the manufacturer's published pressure ratings rather than assuming seamless tubing is always stronger than welded tubing.

Dual-ferrule instrumentation fittings use two ferrules, a front ferrule and a back ferrule, to create a secure mechanical connection between tubing and the fitting body. As the fitting nut is tightened, the front ferrule forms the primary seal while the back ferrule grips the tubing to resist movement and pullout. This design provides reliable connections for properly specified industrial instrumentation, fluid handling, and high-pressure applications.

The back ferrule provides mechanical tubing grip and helps maintain connection integrity in a dual-ferrule instrumentation fitting. During installation, it is driven against the tubing to develop a secure hold, helping the fitting resist vibration, pressure loads, and tubing movement. Back ferrules are often engineered with controlled hardness and material properties to provide effective gripping performance. Proper installation and material compatibility are essential for reliable operation.

Selecting stainless steel tubing and fittings requires evaluating operating pressure, temperature, fluid compatibility, corrosion exposure, tubing outside diameter, and wall thickness. Grade 304 is suitable for many general industrial environments, while 316 or 316L may be preferred for more corrosive conditions. Welded and seamless tubing should be evaluated according to applicable pressure ratings and manufacturing standards. For instrumentation connections, properly matched dual-ferrule fittings can provide secure, leak-resistant performance when installed according to manufacturer specifications.