304 vs 316 on deck

[s/v Jedi]

Originally Posted by Chotu

I sure wish forums showed the most recent 4 posts on the front page immediately after the first post.

All these opinions and advice (which are much appreciated), but in a huge pic 3 posts back you can see all the finished cut parts laid out on a table.

I wonder how long folks will be saying to choose this or that. Probably will to on long after the rig is up. Ha ha

Of course you should have used carbon fiber, you

Hahaha

[Chotu]

Originally Posted by s/v Jedi

Of course you should have used carbon fiber, you

Hahaha

Careful. I'm actually feeling a little nagging voice agreeing with this post. Ha ha ha.

[Dymaxion]

SHOUCAN Titanium Sheet Plate 100×100×6mm-200×100×5mm Ta2 Metal Titanium Suitable for Aerospace Industrial,100×100×10mm https://a.co/d/hWsDVvl


Bit late, but have you considered titanium? Found this on Amazon. I'm using thinner Ti stock for rope cutting tools, for its corrosion resistance. Cut with water jet, TIG/MIG weld. Plenty strong.

[smacksman]

Mild steel, heavy galvanised. Insert a stainless sleeve where the shackle goes to take chafe. Remove in 20 years and re-galvanised if needed.

[Jopinot]

Originally Posted by Celestialsailor

No...Yield strength of 6061 Alum is appr. 6,600psi and 304 stainless is appr. 30,000psi. A factor of appr. 4.5.

Sorry to point out this information is not correct.

6061 Aluminium plate is typically sold in a T6 temper with min 276MPa yield strength
Annealed Austenitic grades Stainless Steels are around 290MPa yield strength
and mild steels start at 250MPa yield strength

I’m other words they are all about the same practical “yield strength”. Therefore gauge for gauge is the strength equivalent. Problems arise in holes, where deformation becomes an issue. Softer materials will require bigger fastener area so a bigger diameter or deeper hole to spread load.

Stainless Steel corrosion resistance measured in Pitting Resistance Equivalent and calculates 304 @18-20PREN & 316 @23-28PREN (2205@36PREN)
The additional benefit of a smooth surface that holds less contamination is significant and a polished 304 will out preform a rough 316 in a marine environment every time. At the end of the day regular cleaning is the key to avoiding corrosion issues all stainless steels regardless of grade.

Anodised aluminium is an option but to avoid a bigger fasteners I’d upgauge 25% to compensate

[Rumpi]

Originally Posted by Jopinot

Sorry to point out this information is not correct.

6061 Aluminium plate is typically sold in a T6 temper with min 276MPa yield strength
Annealed Austenitic grades Stainless Steels are around 290MPa yield strength
and mild steels start at 250MPa yield strength

I’m other words they are all about the same practical “yield strength”.

The above is only true if the fabricator can restore temper after welding, otherwise welded 6061 is to be assumed at 165MPa. And the preferred alloy for this application would be a 5 series one, not 6.

[NPCampbell]

Originally Posted by bbalan

All 304 is not the same, and all 316 is not the same. We have 304 rails built in Ecuador that rust far less than 316 parts made in Thailand. Very good 304 is way better than poor 316. The only problem is... how do you tell before you use it?
And of course the quality of the welds makes a difference... hot, poor welds will rust and destroy the rust resistance of the surrounding metal.

Cheers,
Bruce

My understanding is that welds on all austenitic stainless steels that contain carbon will rust more than the base metal due to carbide precipitation. Isolating the weld (and the backside of the weld) from the atmosphere or annealing after the weld will prevent this condition.

[s/v Jedi]

I found this website to have interesting info about electro polishing: https://neelectropolishing.com/elect...ainless-steel/

[Eric50]

Originally Posted by Jim Cate

If the above were true why are airplanes, subject to flexing and vast numbers of cycles of stress, built of aluminium? They seem to last for decades.

Jim

Simply because the aeronautic industry know how to select, manage and to source the materials properly (most of the time these materials are not at reach of common people out of the industry), on the opposite of a single individual buying common aluminium plate in a local DIY....They are 2 differents worlds.

About SS qualities, only duly certified materials will have proper characteristics, as there are "real" 304 and 316, and they are ones form unknowm origin and quality.

In Europe, certified metallic material have mill certificates according EN 10204, with different levels of severity, the higher the better.

Type 3.2 certificates (higher level of conformity certificate) ensure that your product has been tested under witnessing of an independant body (other than the manufacturer itself, for example a mandated laboratory) or yourself as customer, and has all the grade characteristics it should have according the manufacturing standard (for example ASTM A 240 for 304 and 316 for plate).

Anything you buy without such certificate can be any grade and any quality, including the worst one.

That is why industrial material management has nothing to do with common DIY customers...

SS Welds issue is also well known and easily solved by :
mechanical cleaning first (brushing, with compatible to SS brushes or grinding discs)
polishing 2nd
pickling and passivation at last.

To be repeated time to time when corrosion is appearing again...as it always do...

Any SS weld not treated like that will ruin all the work by quickly developping corrosion and potential failure of the assembly in the long run.

A good example of bad practices can be seen on SS exhaust manufacturer that leave the welds "as is" after welding, duly colored (so without any post welding surface treatment, neither mechanical, nor chimicial...), they'll last as long as a carbon steel one, if not shorter.

[Dirk01]

Originally Posted by Chotu

we are on a Delrin bushings question now. Stainless was selected. The plans were followed. But 304 stainless. That’s what was available.

Delrin is NOT UV stable.

Cheers
Dirk

[Chotu]

Originally Posted by Dirk01

Delrin is NOT UV stable.

Cheers
Dirk

thanks for that tip. I’ll be sure to remember to paint the little edge that might see light.

oddly, my rudder bushings are Delrin and I’ve never had any issues. They are kind of painted, but some paint has chipped off. They’ve been out in the sun for a few years now.

I wonder what the decomposition is like? Is it powder on the top like gelcoat does? Where everything is just fine below the surface? Or does it run deeper?

[rslifkin]

Some Delrin does have UV stabilizers in it. Otherwise it wouldn't hold up for anchor rollers and other common uses.

[Tony Button]

Slightly off topic, but I didn't want to start a new thread. I'm looking for a good product available in Australia to clean surface rust off the rigging; chainplates, swaged fittings etc. I have been told oxalic acid is good for this and bought some Diggers Rust and Stain cleaner, which is 100% oxalic acid. However, the label states that it is not to be used on metal surfaces. I bought it mainly to clean the hull, but has anyone used it on Stainless fittings ?
Thanks in advance for any advice or other product suggestions.

[sailorladd]

I used to work in a stainless shop and we used to use muriatic acid and scrubby pads (3M scotch brite...

[Jim Cate]

We have used oxalic acid all over the boat, including s/s bits on deck, and for many years. No detectable issues from this practice.

Jim