Buy 316 Stainless Steel Coiled Tube for Marine Applications | TeCarve

Has anyone else had trouble sourcing 316 coiled tubing that actually holds up in seawater?

<p>I've been specifying stainless steel coiled tube for offshore hydraulic control systems for about eight years now, and I keep seeing the same mistake: engineers grab 304 because it's cheaper, and then they're replacing corroded lines within 18 months. According to ASTM A269, 316 stainless steel contains 2.0–3.0% molybdenum, which is the element that gives it real resistance to chloride pitting in marine environments. In 3.5% NaCl seawater, the critical pitting temperature for 316 is 25–30 °C, while 304 will start pitting at room temperature above 25 °C. That difference alone decides whether your coiled tube lasts 20 years or fails in year two.</p> <p>Here is the comparison that usually surprises people. 316 coiled tube costs about 15–20% more than 304, but the corrosion rate in seawater is below 0.1 mm per year for 316 versus roughly 0.5 mm per year for 304. For a hydraulic line operating at 20 MPa, that 0.4 mm per year difference means you lose wall thickness five times faster with 304. I've seen projects where they tried to save money upfront and ended up doing a full re-pipe within five years. The total cost of ownership math is brutal if you ignore the molybdenum content.</p> <p>Another common mistake is not checking the low carbon variant for welded systems. If you're doing any TIG or orbital welding on coiled tube, specify 316L instead of 316. The max carbon content drops from 0.08% to 0.03%, which prevents carbide precipitation in the heat-affected zone during welding. According to ASME B31.3, the allowable stress for 316 at 300 °C is 115 MPa, and that doesn't change for 316L, so you lose nothing on strength while gaining weld integrity. I always request EN 10204 3.1 mill certificates to confirm the chemistry, especially the nickel range of 10.0–14.0% and the molybdenum content.</p>