Spring Material for sea water

SS 316 comes to mind but is not very good as spring material, 302/304 will make better spring but than there is corrosion issue HTH Eric

If you're going to have the spring actually sitting in a salt water and air environment, almost anything you use will is going to corrode....I used to design twistlocks for Cargo shipping containers constantly being exposed to a salt water environment, and about the only way to keep a serviceable life of a couple years on the equipment was for any body (housings, ect) to be heavily hot dip galvanized and internal springs made from 302/304 and coated (almost encased) in a lot of grease...

Scott

Copper Berylium?

If there is accessability, you might consider the addition of a sacrificial annode of some sort ( zinc comes to mind ), mounted in the vicinity. Regardless of what material is chosen for the spring, the proper annode will greatly slow the galvanic coorosion.

In addition to everything else, keep your eye on what is coming down the technology pipeline over the next few years.

There are nanotechonology based replacement coatings that are supposedly better than chromium, particularly in a sea water environment, according to notes I've read.

The issues of galvanic corrosion will never go away, though as long as there are conductors in contact with eacy other. When I used to design sailboats (decades back), we would deliberately use insulator bushings and pads to isolate direct contact to eliminate as much galvanic action as possible.

"Trapped" sea water is a big problem for 302-304 SS as it is subject to crevice crack corrosion when Oxygen is eliminated from its environment, as in a tight sealed, but salt water filled structure.

There are books on the subject, but I don't have mine with me at the moment. I know they are easy to find online.

Bo

Titanium is used extensively for seawater wetted parts. It is pretty expensive and doesn't necessarily make a good spring though. It all depends on your application.

I don't have any real experience in this area, but I know that stainless steel is not usually thought of as a good choice for sea water contact. Bronze seems to be the material of choice for nautical types, so Phosphor Bronze might be a good starting point for a spring. You have to make the whole system work together, so your choice may be forced by the other materials you are using, or you may have to change the other materials to work with your spring material.

Jerry Steiger Tripod Data Systems "take the garbage out, dear"

In my experience, 316 SS is the best overall material for what you're asking.

Also, have them passivated, it will help.

For use in sea water, I would recommend the following

Assuming spring is cold formed- Phosphor Bronze Wire ASTM B159/B159M-05 Copper wire ASTM B134 Stainless steel 420 SAE 51420 - least recommended for corrosion, in comparison to above, although still better than 316, 302 or 304.

Plus an anode and grease

Although, it's hard to recomend anything without seeing the design.

John Layne

...looking at my past material notes,.. also consider inconel (it does not suffer the typical stainless steel problems)!

..

Depending on your application you might investigate a spring material encapsulated in a thin plastic coating.

Kman

Could you use an elastomeric "spring" (i.e., urethane or other polymer shape)?

Do you remember what the best grease to use was?

Jerry Steiger Tripod Data Systems "take the garbage out, dear"

Mine as well Bo...It's been a few years since I was designing products for the Maritime environment, and since it had been my first job, my designs were largely based on the experience of the older engineers experiences who had been there since the beginning. It'd be interesting to see the advances in materials and/or practices that can be applied (should I ever go back to doing that type of work again)...

Scott

"John Layne"

Jerry, when I worked in the Sailboat field designing virtually everything (keels, rudders, shaft assemblies, rigging, plumbing) we never used grease on the propeller shafts.

Some people wanted to pay big bucks for Monel as I recall, since it was a premium product developed for the Navy, if I remember right. Everyone use sacrificial Zinc anodes on the propeller shaft and the bottom cleaning guys would replace them as needed.

Then in the late 60s a company came up with a version of SS that was more resistant to crevice crack corrosion and production boat builders immediately switche to it as a cost effective and good option.

It was well known however that if you put a fastener through objects underwater and sealed it up with Polyurethane sealant, that you risked eventual corrosion where there was no water flow, which has the Oxygen needed to keep the Chromium Oxide layer on the Stainless Steel. Hence the desire to have grades of metals not subject to fast crevice crack corrosion.

Worse than crevice crack corrosion was actual galvanic corrosion from dissimilar metals or metal grades and worst of all, an electrical leak that ran from boat to marina, or boat to boat out through a shaft or through-hull fitting which could destroy a fitting in a few days and sink a boat.

Those were interesting times.

Bo