Use of 316 stainless steel in a marine envirorment 6

[Mikepare]

I am designing a new system that will be mounted on the deck of barges. They will be mounted about five feet from the deck and exposed to the salt water air and an occasional splash from a wave. The old system used 304 that was time saved welded and not passivated. After three months these enclosures rust very badly and the customer was not happy. In the new system I am using 316L stainless steel that is time saved welded and passivated. I think this will help or eliminate the rusting problem, others here think the time saving operation is to blame and 304 smooth will do better than 316 time saved. We time save the enclosures to blend welded corners with the enclosure grain.

Any ideas on what would be the best method? Titanium or high nickel metals cost to much for this application. Is there a coating that would help prevent rusting?

 

[TEV]

What kind of media did you use in the timesaver? Using 316L passivated will give you a significant improvement over 304 due to the low carbon, Molybdenum content and passivation, but it still may not be enough in this environment. Very important to not use any process (such as tumbling or blasting with steel shot) that will introduce iron into the surface. The passivation is also important to remove free iron and optimize the passive oxide surface. Also, design of product and installation to avoid galvanic corrosion possibilities, and to minimize crevices which can lead to crevice corrosion. You may need to go to higher Mo content stainlesses. The progression is 316 - 2% Mo, 317 - 3% Mo, 904L - 4% Mo, 254SMO or AL6XN - 6% Mo.

 

[kenvlach]

The Australian Stainless Steel Development Association

http://www.assda.asn.au/

has a download you may find helpful: 'Coastal Corrosion.'
Its recommendations to avoiding SS corrosion from salt include
1) Smoothness of finish (obviously, the smoother the better; an Ra of < 0.5 and/or electropolishing are recommendations),
2) Alloy. 304 is inadequate and 316 is OK &quot;unless the job is aesthetically critical and frequent maintenance is unlikely.&quot;
&quot;Where there are high aesthetic expectations a number of more corrosion resistant stainless steel grades can be considered (the first step up from 316 is 2205 and then the super duplex grades, high molybdenum austenitics and high molybdenum ferritics may also be useful). Smooth surface finish and maintenance are still important with
these grades.&quot;
3) Pickling and/or passivation after polishing, and
4) Regular washing.

 

[Mikepare]

Thanks for the help. Our fabricator will be using Scotch- Brite belts in his time save machine. These belts will only be used on our job. The Australian stainless steel development association down load was very helpful. We are having our fabricator make four 12 inch square 316 samples two time saved two not time saved, and one each passivated.
We will have our service people install these samples on the deck of the barge and see what happens. From prior experence it should take about three to four weeks to get rust to start showing.

 

[smcadman]

Here is some food for thought. One of the places I worked at had a time-saver with 2 belts and a coolant system complete with filter. Very nice machine. The coolant keeps the material from over-heating and also produces a finer grain than the same belt without using the coolant. Anyway, we had a big job where we had to grain hot-rolled steel. After graining it, we finished it with scotch-brite and a clear coat and the end result was a pewter-like finish. One problem with doing this was that the coolant had rust inhibiting particles in it afterwards and would cause stainless steel to rust. You mentioned that they will be using a belt only for your materials, but you might want to ask if they are changing the coolant on their machine. (That's if their machine has a coolant system)

Flores

 

[kenvlach]

The 'Coastal Corrosion' paper recommends using 320 (or finer) SiC grit with lubrication, but doesn't mention lubricant type.
The chapter 'Surface Finishing of Stainless Steels&quot; in ASM Handbook, vol. 5 (1994) states the following:
&quot;Lubricants may be in the form of grease sticks, waxes or cutting oils. Cutting oils generally are more effective when they are diluted as much as 4 to 1 with kerosene.&quot;

First, I hope that is useful information.
Second, my experience is mostly in the chemical treatments (pickling, electropolishing and passivation). What do you users with polishing experience recommend?

 

[mcguire]

The grade of stainless to use for this application is 316 or 2205, not 304. If you're welding it, you must remove oxide and then acid treat it to remove de-chromized surface and exposed sulfides. If you don't want to do this, spend even more money on alloys like 317 or 2507.
Grinding stainless without acid washing ( call it passivating or pickling or anything you want) afterwards is guaranteed to result in poor corrosion performance.

 

[davefitz]

check the cost difference for upgrading to &quot;sea-cure&quot; UNS S44660. Also, adjust the cost to account for the much stronger material properties of sea-cure and the resulting thinner wall thickness.

 

[rolledalloy]

If the problem is iron contamination, the only way to remedy is to avoid it from the beginning by using belts, coolants etc. that are only used on stainless. If contamination has occurred then the embedded iron must be removed by grinding (with clean or dedicated grinding wheels for stainless) or acid pickling.

While there are higher alloys that are more corrosion resistant than 316L, none of them will prevent the iron contamination from rusting. The reason being it is not the stainless or alloy that is actually rusting, but the small particles of iron on the surface.

 

[MadMango]

There are also some other materials that might warrent looking into. One in particular would be 3CR12 stainless steel. 3CR12 is a 12% Chromium ferritic stainless steel, and is considered to be a low cost &quot;utility&quot; stainless steel, where a shiney appreance is not required. It conforms to the European standard 1.4003, part of spec EN 10088, and conforms to ASTM A240-UNS-S41003.

http://www.cromweld.com

It's used in a lot of &quot;wet processing&quot; type environments. &quot;The attempt and not the deed confounds us.&quot;

 

[jerryfisch]

Is it possible for you to use a copper-based alloy such as brass? This is what most marine -based components use and they have excellent sea water corrosion resistance.

 

[rinu]

We are facing corrosion problem in the unloading arm and it is used during unloading of LNG from ship. Corrosion observed on unpainted product lines (316L) due to lack of proper pickling and passivation and also on unpainted APEX purge line butt welds (316L) due to lack of passivation. Without changing the product, Could you suggest any surface preparation and treatments that will remove corrosion permanently.

Sudipta

 

[rolledalloy]

The common acid pickling of the material is done using a mixture of 10% Nitric and 3% Hydrofluoric acid heated to 120-140F. Pickling pastes for stainless steels are also offered by welding supply vendors.

Two such products are Derustit SS-3 from Bradford Derustit.

http://www.derustit.com.

Another is Avesta Pickling Paste available from AvestaPolarit Welding Products 800-441-7343.

 

[McHaney]

I am curious, what is &quot;time saving,&quot; how is it performed and what is the purpose?

As has been written in previous posts, Type 304 and Type 304L are subject to pitting in a marine environment. Type 316L can be used satisfactorially in a marine environment up to approximately 100 deg F. When the exposure to sea water spray routinely exceeds 100 deg F, the tendency for pitting increases significantly. More specifically, I have examined multiple failures of Type 316L tubing due to pitting corrosion in which the operating temperature exceeded 100-110 deg F. Type 317L instrument tubing should be considered in offshore applications in the Gulf of Mexico, South China Sea, etc. where the ambient temperature may exceed 100 deg F for extended periods.

Contamination of stainless steel with iron particles assures that pitting corrosion will occur. ASTM A 380 &quot;Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment, and Systems&quot; provides methods to detect iron contamination using the ferroxyl test as well as methods to remove iron contamination. Cleaning with a solution of citric acid may be sufficient to remove embedded iron, and is much safer to use than some of the other solutions mentioned for passivation.

 

[Mikepare]

Time saving removes the dull mill finish from sheet metal and gives the material a granular look. It also removes any scratches from the sheet. The grain helps blend welds that are ground with the rest of the part. The time save machine has sanding belts or discs (in our case the belts are silicon carbide first pass and Scotchbrite second pass). The flat sheet metal is put through the time save machine and then punched, formed, welded and any other fabrication required for the part.

I would like to know more about the ferroxyl test. Is there a kit available to perform this test? Is there a web site or book that explains how to do this test?

 

[kenvlach]

For testing austenitic 300 series SS for the presence of free iron, I prefer the copper sulfate test. Easier & uses common chemicals.
See ASTM A380, Section 7.2.5.3 or
Method 102 of MIL-STD-753: Corrosion-Resistant Steel Parts:
Sampling, Inspection and Testing for Surface Passivation
(still available at

http://assist2.daps.dla.mil/quicksearch/

get it before you have to buy SAE-AMS-STD-753)

&quot;Copper Sulfate Test __ This method is recommended for the detection of metallic iron or iron oxide on the surface of austenitic 200 and 300 Series, the precipitation hardening alloys, and the ferritic 400 Series stainless steels containing 16% chromium or more. It is not recommended for the martensitic and lower chromium ferritic stainless steels of the 400 Series since the test will show a positive reaction on these materials.... Test solution:
Distilled water 250 cm³
Sulfuric acid 1 cm³
Copper sulfate 4 grams
Swab the surface to be inspected with test solution, applying additional solutions if needed to keep the surface wet for a period of 6 min. The specimen shall be rinsed and dried in a manner not to remove any deposited copper. Copper deposit will indicate the presence of free iron.

NOTE --If the copper sulfate test solution is more than 2 weeks old it shall not be used.
...&quot;
Hint: Put the test solution in an eye dropper bottle.

 

[jackboot]

FORGIVE ME IF SOMEONE MENTIONED THIS PRIOR:

IF THE ORIGINAL 304 ASSEMBLY WAS WELDED AND IT WAS NOT THE 304L GRADE - THEN THE HAZ ON THE WELDED AREAS WOULD SUFFER FROM CARBIDE PRECIPITATION (THE CHROMIMUM WOULD REACT WITH THE CARBON AND THEREFORE DEPLETE THE CHROMIMUM). THIS WOULD OF COURSE RESULT IN LITTLE TO NO CORROSION PROTECTION AT THESE AREAS.

THIS CAN BE A PROBLEM IN THE AUSTENITE GRADES IF THEY ARE WELDED.

JUST A THOUGHT.

JACKBOOT

 

[tedg]

Mikepare:

You have had loads of excellent advice - even learned Shakespearian quotes - yet you may want to seek completely free expert guidance on both technical and cost aspects of your specific application by posting your question at

http://www.nidi.org.

That is the website of the Nickel Development Institute.

Good Luck