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Old 05-12-2010, 21:41   #16
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G'Day all,

Seems to me that there is a huge difference in the quality of stainless steels and components made from them. I'm not referring to different grades, but observed differences between stuff that is supposedly the same grade. A simple example: went into a fastener shop in Yamba, NSW, to buy some cap screws. The 304 screws offered up were magnetic! The vendor (self appointed expert) informed me that all 304 was magnetic, and that only 316 was not. Needless to say, the 304 screws were made in China, and I avoided them. Also avoided buying from that shop therafter.

Too, we've seen alleged 316 1x19 rigging wire that turned brown within a few weeks of installation, while other bits stayed bright for years.

So, to me the answer to your useful question is... it depends!

Wish there was a simple test to analyze the materials in situ, but unfortunately it isn't all that easy. The differences between good and not-so-good are fairly subtle and often require destructive assay to evaluate accurately.

Cheers,

Jim and Ann s/v Insatiable II lying Church Point, NSW, Oz southbound
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Old 06-12-2010, 02:04   #17
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Good catch Gordy - the Lopolights are built to 112 1/2 degrees and they are mounted parallel to the fore and aft line of the boat. A pain to get them alligned !!

My friend welder has fitted and welded pipes in the oil industry/rigs for over decades - not pretty like the marine fabricators but solid, continuous bead and no pinholes. Plus the bowrail pipes do not carry deadly refinery fluids either(thank God for that).

In regards to the new rigging turning brown that is something that happens often with Korean pulled and turned wire. First hard rain should wash it off and it should not come back. Don't know why this happens, the guys at Rigging Only advised me of this. So no worries except the Chinese bolts- oh wait you did not buy them -good decision! 304 ss is magnetic and sometimes even US 316 made but to a lesser degree...
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Old 06-12-2010, 02:34   #18
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In regards to the new rigging turning brown that is something that happens often with Korean pulled and turned wire. First hard rain should wash it off and it should not come back. Don't know why this happens, the guys at Rigging Only advised me of this. So no worries except the Chinese bolts- oh wait you did not buy them -good decision! 304 ss is magnetic and sometimes even US 316 made but to a lesser degree...
G'Day Silver,

I beg to differ with you about the magnetic qualities of 304 stainless. All of the 300 series (Austinetic) stainless steels are NON-magnetic. Lots of references available... here's one: SSINA: Stainless Steel: FAQs

Hope that this will clear this up.

Cheers,

Jim
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Old 06-12-2010, 03:39   #19
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I would commend the use of a "pickling paste" pre and post welding stainless steel of any grade. I have good results with Avesta pickling paste but probably others are OK. I would not do any s/s welding for the marine environment without using this. Can probably use much later but seems better is done at the time.
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Old 06-12-2010, 17:01   #20
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Let's face it, even when the cables for the Brooklyn Bridge were ordered, some suppliers were cheating on the cable. And the bridge would have fallen down long enough if they hadn't been caught.

Today? If you had to bet your life on one stainless pin or bolt and all you knew was that this one was stamped "CHINA" and that one was stamped "SWEDEN", which one would you choose?
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Old 06-12-2010, 17:22   #21
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Hi Jim

Thanks for the link, you are perfectly correct. I am sorry for stating this wrongly. Austentic grades are really non magnetic but still have a very small amount of Fe in them that can be detected with a good magnet.

The way I check magnetism is by putting a round magnet on it's side and putting a ss piece to it. 304 will make the magnet move just a small bit, ever so little, good 316 hardly at all, the higher grades of steeel such as nitronic (aquamet 19), iconel, duplex grades etc no movement at all...

Chinese made and labeled 316 and 304 move my magnet a lot more!


The amount of magnetism is a cheap, easy way I figure how much iron a fitting/fastener has and if I really want to use it or not on the boat. The other ways to analize cost a lot more...
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Old 06-12-2010, 17:33   #22
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Hi still building, can you pls let us know how to use the passivating/pickling paste for welding???

Sadly, there is really no wire/cable made in the USA any more. It's all imported. The most we can get now is pulled and polished wire/cable imports that is wound here.

My rigger friend told me that to meet mil specs, Navy wire distributors import strand, measure/load test here it to meet the specs then send it back for winding (Korea mostly). Sounds awefully wasteful...

The Brookly bridge along with many other spanning bridges that broke cables in the last decade or so also do not have sufficient funds for proper maintenance and replacement of structural parts after their useful calculated life has expired.

Also Swedish steel is been tops for a long time....

.
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Old 07-12-2010, 22:07   #23
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Hi Jim

Thanks for the link, you are perfectly correct. I am sorry for stating this wrongly. Austentic grades are really non magnetic but still have a very small amount of Fe in them that can be detected with a good magnet.

The way I check magnetism is by putting a round magnet on it's side and putting a ss piece to it. 304 will make the magnet move just a small bit, ever so little, good 316 hardly at all, the higher grades of steeel such as nitronic (aquamet 19), iconel, duplex grades etc no movement at all...

Chinese made and labeled 316 and 304 move my magnet a lot more!


The amount of magnetism is a cheap, easy way I figure how much iron a fitting/fastener has and if I really want to use it or not on the boat. The other ways to analize cost a lot more...
G'Day again Silver,

Well, I think that you still have something wrong here: Austinetic (300 series) stainless steel contains from around 60 to 75% iron depending on the specific grade , so your magnet check surely isn't finding out what the iron content is!

I'm not sure why the Chinese pseudo-304 is slightly magnetic, but observations show it to be so. I've certainly had such fasteners turn brown in service and one can but wonder if they meet normal strength standards.

If we have any real metallurgists on board perhaps they can explain the origin of the magnetism in these materials -- I'd be interested!

Lastly, our 2205 chainplates are quite magnetic.

Cheers,

Jim
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Old 08-12-2010, 10:17   #24
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Silver-
fwiw, the recent cable issues on the Brooklyn Bridge were mainly from corrosion due to pigeon guano (I'd call it what by another name but this forum would probably censor that word) which IS a major problem on bridges all over. Nothing at all to do with inferior cable quality, which was a "big time in the papers" scandal when the bridge was under construction.
Even the best of cable, or structural girders and beams, is not pigeon-guano-proof.
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Old 08-12-2010, 13:31   #25
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Hi Jim

Chinese as well as some other countries' gov't issued metallurgical standards are not always as high as US ones. Hellsailor put it well when comparing Swedish steel with Chinese/Taiwanese for critical applications!

The amount of iron is hard to measure except with expensive analizers (very expensive) by trained users that have full "sample" units for comparison. Even then, it is only approximate. Samples are in the hundreds.

My magnet approximation is quite crude but over the years hardware that is less magnetic has proven to be less active in salt water environments in Most applications. Anyway, that is the best I can do.

I also installed a Chinese made "316 stainless steel" 4" deck plate (internet bought) that is bleeding rust on the deck after about 2 years. I doubt it will last another 15 yrs, it is already pitting...

Oh well, can't get them all, but wiping guano off is definitely important! BTW, Guano's acids also damages brightwork (gloss) after only 3-4 days...

Cheers to all and thanks
Ovi
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Old 08-12-2010, 14:15   #26
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"but wiping guano off"
Them gulls is nasty eatin, but they sure make good crab bait.
"PULL!"
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Old 09-12-2010, 20:49   #27
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Have you seen pelican guano?? It's about 20X the seagull's and the meat is no better. Wiping that off is a pita!

Same goes for the grey heron's....
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Old 09-12-2010, 22:37   #28
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stainless steel magnetism

Jim Cate & SilverP have both mentioned oxidation and magnetism in 300 series s/s. I am not a certified metallurgist but have some experience in the field and can offer the following:

Stainless will commonly have 18%+ Chromium, may have 8%+ Nickel, and often a few minor % of other elements, and the balance being iron.

Austenitic stainless is named for the retention of 'austenite' (named after a metallurgist) in room temperature metal. Austenite is not magnetic (put a magnet to a piece of cherry red steel sometime and watch it simply fall away), and is formed above 'critical temperature'. Upon cooling the austenite transforms into other forms... or does not transform, ESPECIALLY in steels containing either Nickel or Manganese. Manganese steels, like those found in railway articles, are not magnetic; and 300 series stainless steels are not magnetic since they have Nickel in the alloy. 400 series s/s are magnetic as they have no Nickel in the alloy. Most tableware is of 420 and is magnetic.

Transformation from austenite is a thermal affair and can be delayed at room temp by Ni or Mn... or forced by cryogenic temperatures. I've never done this, but I would expect any 300 series s/s plunged into liquid nitrogen to emerge in a magnetic state. Custom knifemakers will often put highly alloyed blade steels into a 'subzero quench' to reduce 'retained' austenite, as they are after the hard (edge-holding) 'martensite'. Martensite is magnetic.

Now, one more process will make a 300 s/s magnetic... cold working. If the bolt heads on the fasteners in question were headed when at room temp, then there's the answer to the magnetism. If the entire shank on these suspect bolts is magnetic, then you would be correct in judging the alloy to not be up to spec.

Sometimes a manufacturer will use the same numbers for a proprietary mix when it may be equivalent/close to a standard AISI (American Iron and Steel Institute) alloy. Is that '304' on the sink really AISI 304? Maybe.

One most commonly encounters two s/s alloys: 304 (basic austenitic stainless) and 316. 316 has molybdenum in it. The addition of Mo does two things; yield is increased (good for things undergoing tensile stress in the working environment, like shackles), and resistance to corrosion - especially chloride ion attack - is increased (great for marine items, like shackles).

The 'L' one sees at the end of a designation (316L) means 'Low carbon' which means this metal is preferred for welding.

Fair winds to all.
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Old 09-12-2010, 23:08   #29
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Jim Cate & SilverP have both mentioned oxidation and magnetism in 300 series s/s. I am not a certified metallurgist but have some experience in the field and can offer the following:

Now, one more process will make a 300 s/s magnetic... cold working. If the bolt heads on the fasteners in question were headed when at room temp, then there's the answer to the magnetism. If the entire shank on these suspect bolts is magnetic, then you would be correct in judging the alloy to not be up to spec.

Fair winds to all.
G'Day CGB,

Thank you for an interesting and informative post. The concept of cold working creating the magnetism may indeed explain what we've observed. I've not done the head vs shank magnet test that you suggest, but will do so at first opportunity. Question: if the threads are rolled rather than cut (as they often are in small fasteners) could that amount of cold working also cause the magnetism?

It is becoming harder to find fasteners NOT made in China, and since we sometimes use them in critical applications, a practical test for quality would be very useful. Do you have any other suggestions along these lines?

Cheers, and thanks again

Jim and Ann s/v Insatiable II lying Church Point, NSW, Oz southbound
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Old 09-12-2010, 23:37   #30
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G'Day CGB,

Thank you for an interesting and informative post. The concept of cold working creating the magnetism may indeed explain what we've observed. I've not done the head vs shank magnet test that you suggest, but will do so at first opportunity. Question: if the threads are rolled rather than cut (as they often are in small fasteners) could that amount of cold working also cause the magnetism?

It is becoming harder to find fasteners NOT made in China, and since we sometimes use them in critical applications, a practical test for quality would be very useful. Do you have any other suggestions along these lines?

Cheers, and thanks again

Jim and Ann s/v Insatiable II lying Church Point, NSW, Oz southbound

Magnetism seems to me a bit of a red herring, in that apart from items near the compass, who cares if the thing is magnetic? This will likely be a bit of an exaggeration, but if the chainplate is magnetic, then so be it... as long as it holds the rig up.

As to a useful test for checking suspect s/s... I have no idea of such a test. There are military or aviation specs for s/s fastenings, a doubtless costly way to go but perhaps not so for crucial fastenings.

Cheers - Guy
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