304 and 316 Welded Stainless Tubing: Construction, Grades, and Tradeoffs
HGW Hydraulics on Oct 3rd 2024
Welded stainless tubing is used in automotive, power, chemical processing, and other industrial systems that move fluids with different physical and chemical properties. It is selected when the system needs durability, corrosion resistance, and practical availability.
Unlike seamless tubing, welded tubing is made from stainless strip. The strip is formed into a tube through rollers, and the edges are joined with a longitudinal weld. The completed tube is then tested so the weld integrity and pressure capability can be verified.
How Welded Tubing Is Made
The basic process starts with stainless steel strip. The material is shaped into a tube, the seam is welded along the length, and the tube is tested, often with hydrostatic testing, to confirm that the seam can withstand the required pressure.
The seam is the main difference from seamless tubing. It can limit maximum pressure compared with seamless tube, but welded tubing is often available in longer lengths and can be more economical when pressure requirements allow it.
304 and 304L
304 stainless steel contains a high percentage of chromium and nickel, which helps it form a protective oxide layer and resist corrosion in many environments. It is a common choice for welded tubing where general corrosion resistance is needed.
The welding process creates high local heat at the seam. In standard 304, that heat can cause chromium and carbon to combine near the weld, reducing corrosion resistance at the joint. 304L lowers the carbon content, making the welded seam more resistant to that precipitation problem.
316 and 316L
304 and 304L have limits when chloride salts are present. Chlorides can attack the protective oxide layer and create localized corrosion.
316 and 316L stainless include molybdenum, usually around 2 to 3 percent, to improve resistance to chloride attack. That makes them better choices for marine, offshore, water treatment, and chemical environments where chloride exposure is expected.
When Welded Stainless Tubing Makes Sense
The value of welded tubing depends on pressure, temperature, corrosion exposure, availability, and installation schedule. Seamless tubing may be preferred for the highest pressure because it has no longitudinal seam. Welded tubing can still be a practical choice when the rating fits the application.
Welded stainless tubing is often easier to source in long lengths and can reduce installation cost. If time, length availability, and cost matter, and the seam rating is suitable, welded tubing can be the right material choice.
Always match the grade, weld requirements, pressure rating, and environment before substituting welded tubing for seamless tubing or moving from 304 to 316.