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SS 304 vs. saltwater

I have a client who has purchased 304 ss tubing to be used directly in salt water of 25 to 30 ppt at 22 to 33 °C. About 1 meter of the total length of the tubes (4.3 meters)will be submerged. How long will the tubes withstand corrosion? The tubing will be tied down with cable to concrete weights on dry (maybe moist) ground. Will this increase cathodic corrosion?

Juan Aguirre
Aquaculture - Guayaquil, Guayas, Ecuador
2003

We assume that you mean 25-30 percent (pct) salt, not 25-30 parts per trillion (ppt). If the former, 304 stainless will NOT stand up to this and will begin to corrode very quickly. There are a lot of factors, but the corrosion at the air/water interface will probably be rapid. If you are saying 25-30 parts per trillion of salt it could last for some time. Grounding one end of the tube in moist earth with a chain (stainless steel?) will probably enhance any cathodic corrosion.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2003

Type 304 tubes in seawater will not withstand corrosion for very long. They will begin pitting immediately. Type 316 is not really suitable for long-term exposure in stagnant seawater conditions. I suggest you investigate stainless steel grades with higher Mo content-- Type 317 or 904L are austenitic alloys, or 2205 which is a duplex alloy.

Toby Padfield
Automotive module supplier - Michigan
2003

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