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Old 13-08-2012, 19:16   #76
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Re: Dismasting - Why does it happen, how to prevent it

Dismasting - why does it happen, how to prevent it

Part 1 - General Answers to Questions


impi
"was out of port on the first day ... new cat and rig ... came down on him as had a few others on the same brand of new cats ... turns out they were buying a new brand of masts from China to save costs ... he felt it has something to do with the mast 'flexing on its self' (?) "

some of the chinese firms are having trouble tempering and aging aluminium. so the mast wasn't T6 as it should have been

The mechanical properties of 6061 depend greatly on the temper, the heat and aging treatment given post extrusion. T6 temper 6061 has an ultimate tensile strength of at least 300 MPa and yield strength of at least 241 Mpa. Annealed 6061 (6061-O temper) has maximum tensile strength no more than 125 MPa, and maximum yield strength no more than 55 MPa.

according to one surveyor who had one of the failed masts aluminium tested, the alloy was not T6, therefore T0 (zero tempering)


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Sailmonkey;
"90% of rig failures can be prevented with maintenance. but it's not always cheap "

no. SCC is invisible.

316 Stress Corrosion Cracking in the presence of chlorine is the absolute heart of the matter.

The 316 fitting looks perfect, shiny on the outside but rotten to the core. You can't tell by looking at it, and the 316 part can fail in under 6 months anyway, even AFTER you take off the part for xrays or a dye test, and seriously, who in their right mind would want to dis-assemble every single fitting on the mast and do this every 6 months?

i say almost all rig failures come directly from 316 Stress Corrosion Cracking, and the US Coast Guard agree.


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cat man do

Bruce
"The cheapest possible materials are used , not the best. "

cat man do
"What a load of crap"



so sorry; but i'm on Bruces side.

100 and 20 million percent. he's spot on.

there is nothing cheaper than 316. nothing.

316 is so cheap insurance companies demand it be thrown out and replaced regularly, when ANY modern alloy would last forever.

there is nothing cheaper than 316 that is in the salt water corrosion ballpark.


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Factor

"My issue is with intensely silly statements like, Production builders use cheap materials. Its wrong ill informed and quite frankly - stupid."

well; firstly, there is nothing cheaper than 316 in the salt water corrosion ball park, and there are thousands of alloys that are more expensive, last forever, never suffer from SCC, never fatigue, and never fail, ever.



secondly;
316 is so crappy, it is illegal to use on land in europe on any structures exposed to chlorine (ie salt)

you could be sent to jail for using 316 stainless in a chlorine/salt water exposed building on land. On land, to use 316 would be criminal negligence that has resulted in death before.


so lets be clear here Factor; not only is Bruce correct, but he has in my opinion understated the matter.

he should have said; Production builders don't use cheap materials, they use the absolutely cheapest materials that they can get away with using. ie 316.

i repeat,
there is nothing cheaper than 316 that is in the salt water corrosion ballpark, and thousands of MODERN alloys that will perform forever with out dis-masting and killing you and your friends and family.



Factor

"My issue is with intensely silly statements like, Production builders use cheap materials. Its wrong ill informed and quite frankly - stupid."

basically, there is NOTHING cheaper than 316.

You must have a PREN > 40 for a metal to be called corrosion resistant to salt water.

316 has a PREN of 23.
it rots all through, but still looks shiny on the surface.


there is NOTHING cheaper than 316.


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david samuelson
"I pull my chainplates every 5 years for inspection."

are you serious?

just use any 6% moly alloy. or any super duplex. immune forever from SCC. try and use a low nickel.

they aren't that expensive for a small bit of flat bar, and they last FOREVER. You will never have to inspect them EVER again.

just use any 6% moly alloy. or any super duplex. It ain't expensive


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"the whole rig can collapse from a single rig failure. "

absolutely. read posts on this forum where a single toggle fails, a single split pin!, a single jumper or diamond lets go, and the whole rig comes crashing down.

software used by rigging companies confirms exactly this. the rig can easily fail if a single part fails.

Better to use a redundant design; ie add baby stays, use nested diamonds, add a solent forestay etc


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"If the rigging is in good condition, sailing fast won't bring it down"

yes it will.

the force on sails rises exponentially with wind speed, where as drag through the water rises above squared (depending on underwater appendage drag and hull shape)

it can easily take a squared amount of power to sail a few extra knots faster

if your hulls have a length to breadth ratio of say below 10 to one plus underwater appendages, and you are already pushing it hard up against the hull speed wall, then to get just one more knot may take many times the force on the sails.

If the force on the rigging rises exponentially with the wind speed, then the load on the fittings rises exponentially, but the life expectancy of the part reduces faster than the inverse of the exponent.
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Old 13-08-2012, 19:48   #77
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Re: Dismasting - Why does it happen, how to prevent it

Dismasting - why does it happen, how to prevent it

"What I don't fully get is why this happens on modern, production-type boats - particularly a fiberglass catamaran with a good quality mast and rigging."


Part 2 - The Stress Corrosion Cracking of 316.


i looked at buying a mast for a 55 foot catamaran very recently.

the different yacht riggers all asked me several times for an explanation of why i was having all my rigging, wires, tangs, and every other single thing connected to the mast CUSTOM made from Super Duplex stainless.

i had to explain everything, not once, but several times, and in greater detail each time. which is eaxactly what is happening here. thus, the part numbers in the headings. so buckle up kids.

(fyi, i've been a professional student for a very long time, then a research assistant, then a dot com crash victim,(sob), and then retired very very young. i can do hundreds of hours of research without even breaking a sweat. I was highly motivated to understand this exact question, and so i put endless hours in.)

This section is excerpts from my emails, reconstituted.


the reason i'm getting Super Duplex rope and fittings made is Google.

that simple.

Google and the internet. all these dismasting stories are just so easy to find these days. but ten years ago, it would have been impossible.

when i started building my catamaran, i accidentally read American Coast Guard Alert 07 09, mandatory rigging inspections due to deaths in 29 dismastings over the last 6 years due to 316 Stress Corrosion Cracking.


So i Started searching and reading up on 316 Stress Corrosion Cracking. 316 is unbelievably primitive CRAP.

Then i started looking for 316 rigging failures, and found zillions of them.

It turns out 316 is so OLD and stupid it's bizarre. So many yachts get dismasted it is ASTOUNDINGLY STUPID to even consider using this PRIMITIVE alloy that was designed in the stone age, by cave men, with no computers, no running water, no television etc.

if you Google rigging failures you will see toggles, wire, turnbuckles, chainplates, ANYTHING made out of 316 fails, sometime new parts fail in 6 months. (one guy had a NEW yacht, 6 months old fail in the middle of nowhere, got free replacement 316 parts off the manufacturer, and they also FAILED in 6 months. dismasted AGAIN in the absolute middle of nowhere.


316 SS suffers badly from Stress Corrosion Cracking, and is forever failing and having to be inspected and replaced.

Many yachts loose their mast from 316 failures. Some insurance companies require all rigging to be replaced every 7 years, most require every 10 years. All due to how crappy 316 really is.

316 was invented 100 years ago. before penicillin, computers, telephones, television, and 316 is of EXACTLY THIS STANDARD. Just plain dumb.



MODERN ALLOYS on the other hand were invented with computers, science, television, penicillin etc, and are of this same modern standard.

your rigging can last forever if you use MODERN ALLOYS. no inspections. no broken wire strands, no replacing rigging. no failures. ever.

MODERN ALLOY fittings NEVER FAIL. EVER. this is called engineering.


How much does a new 55 foot catamaran cost?

how much extra does the NEVER FAIL wire rope cost? nothing in comparison.

(well, about 5 times as much, from a shop; but that's if i go with the 2 UK companies; the small chinese manufacturers are promising to be half that cost,

if i save half by going directly to the manufacturer with internet ordering rather than a local shop;
and if 316 is 240 MPa yield strength, and the Super Duplexes, Ferralium or Zeron or 2507 are 550 MPa yield strength, then the cost drops to HALF again as your wire rope can be half of the cross sectional area as well.)

So how much extra is it going to cost me now? not much at all.


So;
the cost of good mast fittings versus the cost of the boat? two tenths of nothing at all. and due to internet ordering, it will probably work out even cheaper than buying 316 fittings from a shop.


See? if the internet and Google didn't make all this information so easy to find, dismastings due to 316 fittings breaking in half, all the photographs of broken yacht fittings, all the stories about dismasting available NOW for the first time to everybody, and so easily available, then i'd have taken 316 fittings without questioning them or their performance.

it's just that after reading the coast guard report on how many people are killed by 316 microscopic invisible fractures, and that Europeans have also had so many people killed by 316 that 316 is now outlawed on all indoor swimming pools, and chlorine exposed structures have to use modern alloys with a PREN above 40, ie thay are only alowed to use salt water resistant alloys; and only alloys with a PREN > 40 are allowed to be called salt water resistant.

these reports made an impression on me.

it's just that i've read of so many deaths and dismastings due to invisible microscopic fractures (316 looks perfect, but has Stress Corrosion Cracks that only fail when under load), that i decided i didn't want my yacht mast to kill any of my friends and family, as has happened to other people.

i'm trying to build a long term cruiser, that will be in the middle of nowhere for decades, so in my mind, i'll be much happier paying more money for the NEVER FAIL modern alloys instead.

knowing that no matter what happens, the mast will NEVER FAIL. not ever. not even close. And this is called engineering.

Super Duplex is too expensive?;
how many surveyors inspections? of the rubbish 316 rigging parts, how many replacements, until using Super Duplex rigging parts becomes financially cheaper?

i say if you run ONE single dye test run on ALL the rigging fittings and if you had used PREN above 40 stainless ( as is now required by law for building codes in europe) then it would have been CHEAPER to use a decent stainless in the first place.


What i'm after is fittings beyond reproach. to NEVER FAIL. to never kill my friends and family. and this is the Super Duplex stainless steels.

(or the 6% moly stuff.
imagine that, for the want of 3 extra cents of moly, people have died from shitty 316 fracturing. looks great and shiny on the outside, but a microscopic fracture all the way through.

all for the want of 3 cents of moly extra.

personally, i'd rather have my friend alive.)


Super Duplexes are to all intents and purposes, totally immune from fatigue, but more importantly, fatigue in the presence of chlorine atoms (which is Stress Corrosion Cracking - SCC). Basically the stress supplies half the energy needed to propagate the microscopic crack, and the chlorine atoms act as a catalyst supplying the other half of the energy needed to dissolve along crystal boundaries all the way through the metal.

i'll be ordering all my wire and swageless fittings in Ferralium 255
(or equivalent, they are mostly all the same.)
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Old 13-08-2012, 21:24   #78
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Re: Dismasting - Why does it happen, how to prevent it

I an not a major fan of stainless either Poo, but I think you are grossly exaggerating the failure speed of 316SS. A realistic predicted service life for 316 is around 10 years, of course some people will get longer, others will get less. This is the life expectancy that rigging manufacturers and most riggers recommend. At this point it is incumbent on the owner to pull and fully inspect or replace the hardware. The real problem is people who attempt to push lifespans so far past recommended lifespans, and then are dumbfounded when things fail.

But as I always mention, in this I am biased, since I sell titanium chainplates.
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Old 13-08-2012, 21:40   #79
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Re: Dismasting - Why does it happen, how to prevent it

Most chainplates are not submerged in saltwater, though, correcte? Wouldn't this effect the life expectancy greatly? What if regular maintenance included weekly freshwater rinsing?
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Old 14-08-2012, 01:20   #80
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I would certainly like to see some links.

I am not one to buy into conspiracies. If it was only a couple of cents worth of moly to build bulletproof fittings then the markeing team of one of the large production fleets would have jumped on this ages ago and used the supposed evidence to hammer all other fleets.

I dont believe it is near as simple nor as black and white as you maintain as if it was market pressures would have forced product evolution.

However what is being said is interesting and would be made more so with linls to some relevant info that discusses the warnings you mention as well as the issues with crevice corrision on fitings that are above the waterline.
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Old 14-08-2012, 02:46   #81
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Re: Dismasting - Why does it happen, how to prevent it

Quote:
Originally Posted by PooBeetle View Post
Many yachts loose their mast from 316 failures. Some insurance companies require all rigging to be replaced every 7 years, most require every 10 years. All due to how crappy 316 really is.
Would you like to name those companies who require S/S rigging replaced at 7 years. I insure with Pantaenius a well known yacht insurance company and even they don't even require a 10 year replacement and they are fussy who they insure.

Like others I think you have overstated the problem. S/S may be cheap, that's fine replace it regularly say every decade and avoid problems. If it was such a problem we would all be back with rod rigging covered in twin and pitch, hmm lovely; wifey would really like to grab that climbing back on board and the sails would look great with pitch on them.

Modern ropes could be a solution, but having just replaced the standing rigging with S/S it will be at least a decade before I need to think about replacement again.

Pete
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Old 14-08-2012, 03:19   #82
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Re: Dismasting - Why Does it Happen - How to Prevent it

This is interesting .Rigging Failures Photo Gallery by Compass Marine at pbase.com
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Old 14-08-2012, 04:46   #83
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Re: Dismasting - Why Does it Happen - How to Prevent it

Well, I just don't buy it. I was an executive at Parker Hannifin, the worlds largest manufacturer of hydraulic and pneumatic fittings, for many years. Here we are talking hydraulics, where fittings normally se 250 bar in pressure. SS 316 is the standard used in the fishing industry. Parker will happily furnish you with all the test data you want on the salt /chlorine tests they have run on their fittings.

In the natural gas industry, SS316 is also the norm. I have personally been involved in changing every single fitting in the natural gas industry in Denmark to ss316. And I can tell you that before that happened, a number of metallurgists spent many months looking at what type of material should be used.

SS316 is not crap.

As foolish sailor noted, if it was only a matter of adding say 5% to the price of the boat and being able to say that now you have forever wires and fittings - guess what? ONe of the bigger high end companies would have done and beaten everyone else over the head with this as a marketing advantage.
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Old 14-08-2012, 06:06   #84
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Re: Dismasting - Why Does it Happen - How to Prevent it

Stainless steel work hardens, It has nothing to do with corrosion,

The stainless plates get exceptionally hard from moving backwards and forwards,
Resulting in failure of the plate,
The vanes in big air conditioners used to fail because of this, The air makes them vibrate, resulting in failure,
My 40 foot cat was going to be built out of stainless, 316, but I didnt proceed as after quite some time, I would have hull plates failing from the constant movement of the plates and I would have sections falling out,
The extra cost of the stainless would have been over come by not painting the vessel,
As for under the water line, No problem with stainless 316. Your corrosion idea is false,
I have built that many heat exchangers over the years out of 316, and they do have a working life of 25 years,
So I dont know where you get failures in 6 months from,

Try getting practical experience instead of theory,

I am an Engineering Blacksmith, and a Practising Engineer, not a theoretical one,
I make every thing I design, I also test it and approve it and write the certificates out in my own name, and I do have 49 years of experience to back it up,

The problem with stainless rigging, is when it lets go, its gone, there is no warning,
Not like steel cable, you can see the broken strands sticking out, at least you can replace it before it snaps off,

Theory books are wrong in a lot of ways,
During my apprenticeship, my theory teacher hated me, Not only did I say the books he was teaching me from had false information, I could back it up with hard facts, Proving the books were wrong,

He also reluctantly conceded the books were wrong,

Cheers,
Brian,
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Old 14-08-2012, 08:26   #85
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Poobeatle, you need to stop studying and get some life experience! I have been an inspector in the offshore oil and gas industry for over 15 years and have seen almost every type of failure mechanism in everything from carbon steel to the most exotic alloys. They all have their place and they will all fail under the right conditions (even super duplex). The key is understanding the failure mechanisms and regularly inspecting your fittings based on that information. You would be making a pretty big assumption that just because you're using super duplex that you won't ever have to worry about it. The biggest corrosion issues we see offshore is galvanic corrosion where dissimilar metals are in contact, that would be my concern if you're going for non standard parts because unless everything from the split pins to the bottle screw threads is super duplex you will see accelerated corrosion rates in the less noble parts.

Btw I never knew you could get super duplex wire, certainly interested to know more.

Regards, Andy
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Old 14-08-2012, 12:23   #86
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Re: Dismasting - Why Does it Happen - How to Prevent it

I am not sure I want to be on Poo's side of this discussion since I I think he is majorly overstating the concern of 316ss. But it is true that in many ways 316 is a poor choice for rigging materials. The issue is that for years it was the best of a number of poor options.

Titanium was outrageously expensive
Super duplex again expensive, and no one used it
Mild steel rusts to fast to be realistic
Galvanized...
Bronze - structual wire isn't available (to my knowledge) and there are so many poor grades being passed off as better stuff
Aluminium - fatigue issues, and strength

So people used stainless because it was the best among the options. If you are looking for background on 316 corrosion I can supply them in mass, but I don't see the point. Crevice corrosion, galvanic corrosion, and stress crack failure are very well documented problems with stainless, and you likely will trust your sources more than mine, but do a google search for it, and you will find a number of different references.

But note that I said titanium WAS expensive. Depending on manufacturers markup, and the exact part in question, titanium now can actually be cheaper on a strength vs cost basis, and doesn't have the corrosion problems of stainless.

How much less of a problem is it? Well 316 starts to crevice corrode at around 45 farenhite or so, titanium has to be heated to past 215F. Galvanically titanium is the most noble structual metal, so this isn't an issue, and stress crack failure is much less likely in titanium as well.

316 served its purpose, the super duplex metals are a nice stop gap, but as titanium can more and more compete on price, not just performance many of these metals are going to fall by the wayside.

Heat exchangers are a good example of this. 30 years ago they were made in copper (for thermal efficiency) then they tried stainless to limit corrosion, now they have switched to titanium because it is immune to the failures of copper, and stainless and can be used in much harsher environments.

For instance stainless pool heat exchangers, where the chloride concentrations can be much higher than in salt water have a typical warranty against corrosion for 1 or 2 years, while titanium ones are typically warranties for life. The cost difference between them is about 25%.
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Old 14-08-2012, 16:30   #87
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Re: Dismasting - Why Does it Happen - How to Prevent it

Dismasting - why does it happen, how to prevent it


Part 3 - 316


Really short stories.

I'm going to skip briefly over all the technical data because there is an infinite amount of it. If any of the headings interest you, then you can spend years reading the papers. Google will answer you instantly if you give a damn.

I'm going to leave out all the endless thousands of graphs showing electro potential curves, iso corrosion resistance in salt water analogues, stress cycles till failure etc.

As Google will answer you instantly if you give a damn. Which you don't. Or you would already know. You would have already done this yourself.

So just assume i'm right unless you actually search and do some reading for yourself. It's all there at you finger tips, one second away.

Really short versions (because it's all so boring; reading up on rubbish when it's all so obvious)

Just assume i've condensed thousands of pages of scientific dribble into short headings and succinct utility.

What is 316 Stainless exactly?
Useful. Due to the amount of chrome, it is shiny, and people love shiny things over rust dribbling things. It's useful for static fittings that do not have to carry a load. It has utility due to two factors, the cheapness, and the lovely finish, which stays lovely in salt water.

Because it was invented by cave men though, there are some interesting side effects.

For example, if you added 3 cents more molybdenum to it, you would actually have a brilliantly performing useful metal. But they didn't know this 100 years ago.

The prime benefit is that it stays looking nice in salt water. It is the lowest and cheapest alloy that stays looking nice.

So this is exactly what 316 is, and nothing more.

PREN
Pitting Resistance Equivalence Number

A way to compare similar alloys with different chemistries' corrosion resistance to salt water. It does not indicate performance under cyclic loads, and loads in salt and chlorine, and at various temperatures.

304 17
316 23
2507 40
Zeron 40
Ferralium 40
Al6XN 44

to be called salt water corrosion resistant, the alloy must have a PREN above 40. if it is below that, then it will rust and crevice corrosion will destroy the integrity of the part.

The performance of alloys in salt water is dependent on the two largest factors - the chloride (Cl-) content and the temperature - and the resistance of a particular steel to pitting and crevice corrosion is usually described in terms of what % Cl (or ppm Cl ) and °C it can resist.

So the temperature, and the chlorine concentration are the two largest factors involved in the alloys performance.

316 starts Crevice Corrosion at -5 degrees Celsius and at 1000ppm chlorine.

Salt water has 35000ppm chlorine, and a steel rigging fitting in the sun can regularly hit 50 degrees Celsius.

So 316 is out of contention for use before we have even examined cycles under load in salt water. It starts being riddled with an invisible cancer at below water freezing temperature.

No alloy can be called salt water corrosion resistant until it has a PREN of 40 or above.

Metal fatigue
Everybody has heard of Metal fatigue failures killing hundreds of people. usually in aviation though. and here we are talking about it in the marine industry.

Condensed Academics Version;
316 has an astoundingly low fatigue under stress resistance.

Translated into Reality?
instant break.
ie
if you actually play with 316 at home in the workshop, you will soon discover an AMAZING property of 316.

it fatigues and breaks amazingly quickly.

Micro cracks on the first bend.

try it and see

Brittleness.
If you work the metal, bend it or stress it, it becomes very brittle. One bend and 316 is useless, gone brittle. Some metals are worse than others. Because 316 was invented before the modern era, it is hard to find an alloy worse. Get a thin bit and bend it in the vice. You can bend some modern alloys for ever. See the difference?

Crevice Corrosion
To make a battery you need an inside and an outside. If the conditions are exactly the same, then there is no energy difference available, no chemical difference needed to run a reaction.

So there has to be a difference for anything to occur. Microscopic cracks full of salt water slow oxygen diffusion rates, effectively creating the outside and the inside of a battery. Small electro-chemical reactions are (effectively – not actually) catalysed by chlorine and proceed deeper into the metal along hardness boundaries (crystal boundaries).

These cracks grow very quickly.

Scratching the surface
Crevice Corrosion means if you even scratch the surface of 316, you have compromised this delicate alloy.

Passivation
A process to remove all iron from the surface leaving only chrome. Oxygen from the air turns chrome, a metal, into chrome oxide, a ceramic. If there is any iron left, a tiny pit will form from electrolytic chemistry occurring. The copper sulphate test can be used to see if there is any iron still left.

Electropolishing
Dissolves all free iron near the surface allowing the surface to be mostly nickel and chrome. Absolutely necessary, as a small particle of iron can start a little battery cell off. Whenever you see rust dribbles, the part has SCC or hasn't been electropolished.

Citric Acid Treatments
NASA commissioned a study freely available online. Citric acid is the best treatment (and cheapest). This is what I use.

I use home made electropolishing to make the part look good, and the citric acid treatment for all the bolts.

Cycles To Failure
Lets assume that you have miraculously done all procedures correctly. By some miracle you were able to avoid fabrication induced stresses, cold working, you didn't scratch the surface so as to produce microscopic pitting crevices where chlorine can accumulate to thousands of times the external salt water concentration, so there are no microscopic scratches to initiate mechanical stress concentration areas, or you mechanically polished the surface so as to remove them, you electropolished it, and then finally you gave it the sodium hydroxide at 70 degrees C for 2 hours, followed by citric acid at 70 degrees for 2 hours.

(jfyi – I actually did all this for my 316 fittings – as I can't stand rust dribbles on million dollar yachts. I think rust dribbles make your boat look bad. It reminds people of all the old uncared for boats you see rotting away somewhere; all the old un-cared for garbage scows etc.)

so you put all the time in to do it all properly, but then due to some form of brain seizure, you decide to put the 316 to use in salt water, under stress cycles. (madness!)

what happens?

Cycles To Failure in Salt Water
Firstly, the 316 fails in hours in tests. Hours. Look it up guys. Don't argue, just look it up.

Modern alloys last forever. Fme.

Oxygen Deprivation
You know all this anyway.

If oxygen is not present, or is all used up by the iron rusting, then acidic electrolytic processes start. Rapid chemical decomposition can occur. Sour mud has completely eaten through the welds in 316 in 3 weeks. Whole millimetres gone. The bases of 316 fittings and the backs of chainplates suffer this.

In an invisible microscopic crack a battery forms as the salt water slows the time it takes for oxygen to diffuse to the leading edge of the crack.

So the pitting starts, then crevice corrosion, and if there is any stress, then rapid stress corrosion cracks develop along brittle areas pathways.

Flattening The Surface
The surface has to be polished flat, other wise the iron particles are exposed and it starts rotting from here.

Fabrication Mistakes
The academics say “316 cold working can induce susceptibility to failure”. My arse. I've been building heaps of boat stuff out of 316 for awhile now, and I say you bend it once, and it's completely rooted. Try this at home. Put the sucker in the vice and bend it. See all the cracks? Millions of them. Bend it twice and it's dead.

Totally rooted. Again, try this at home.

Steel Contamination From your other Tools.
Contamination of the 316 surface by a single microscopic chunk of plain steel will cause rust to start. Pitting has just started. The piece is compromised. If you use any tools that have been used before with plain steel, you are embedding little tiny batteries into the surface of the stainless that will create little tiny holes, where the salt will concentrate.

I''ll up load some photos. Pain in the arse.

I've passivated with nitric acid and hydrofluoric acid, put the finished part outside, and the steel tool contamination marks rust like you wouldn't believe. 316. fme.

Stress Accumulation Around Microscopic Pitting Edges
Stress accumulates around edges. If you have cracks, then this is where the stress concentrates. If you have a brittle metal that spawns a million cracks like glass (ie 316) then the cracks will grow.

Stress Corrosion Cracking
Consider ALL of the above processes. They add up to something.

The final fruit of all the above processes combine to concentrate stress forces along crystal boundaries, especially when chlorine is present in microscopic fissures. These cracks grow just like the cracks in glass grow. They grow fast. 6 months if there's any stress and a solid metal part can break clean in half.




Cost

What are we talking about? Doing a proper job? Fabrication with the tradesmen having full understanding of cold working resulting in a parts failure? Fabrication ensuring no steel particles contaminate? Using only stainless tools to ensure no steel particles embed deeply into the soft 316? Passivation using nitric/hydrofluoric acid? Then having to machine polish by hand to flatten the surface? Then electropolishing and citric acid surface treatments?

What a pain in the arse. To do it all properly as i've been doing. The time extra is astounding.

You get a modern 6% alloy and the labour costs would pay for themselves instantly. I wish I had used a higher quality modern alloy for all my fabrication. The extra time i've had to spend just because the stuff was 316 instead of a 6% moly is phenomenal.

All the surface treatments, hand polishing to get smooth surfaces, passivating to get all the iron out of the surface, watching it rust anyway even though you've done it all as best as you can, hot sodium hydroxide treatments, hot citric acids treatments etc etc etc.

i'm using 316 on all non-stressed parts, but

fme. It's a real close call on how much I saved using 316 instead of a better grade. As all the extra labour costs would have been phenomenal.

All the extra labour costs involved to get crap old stupid retarded poorly performing 316 up to the very low standard of being barely adequate for the job.


So I learnt my lesson.

All the important stuff is going to be in a higher grade. As you can't make fabrication mistakes because the stuff is robust. The parts then will be 100% good instead of the 316 delicacy “is there a weakened cold worked seam somewhere that will fail in the future from SCC, is there a microscopic stress crack (yes, there certainly is) somewhere due to normal fabrication that will fail in the future” etc etc etc.

The parts will be robust, and not fail because they get one little scratch on them. No oxygen. No electropolishing etc etc etc.

All my rigging wire rope and parts will be in Ferralium 255. A Super Duplex stainless steel.


Gambling
fabrication mistakes, scratches on the surface, a tiny piece of iron embedded, the delicacy of 316, all the endless dance steps, and when you've finished do you know what you've got?

A delicate piece of **** that will still fail in under 6 months if stressed. For all the many many reasons mentioned above, if any one of those many necessary steps are bypassed, or done incorrectly, then your part will fail.

All because you are trying to use an alloy that is so far beneath the true salt water standard.

So 316 is great on land, great for static non-loaded parts, but not under stress, and never with salt water.

You have to go through all these stupid processes because of how crap the alloy is in the first place. Modern alloys have NONE of these worries.

NONE.

No fabrication mistakes; you can't even make fabrication mistakes, no nitric acid chemicals, no treating the crap with kid gloves. NONE of the above headings or steps apply to modern alloys at all.

For all practical purposes NONE of the above headings are relevant to modern alloys in salt water.

NONE.

Can you now see the difference between owning a modern car and a horse and cart?

Can you now see the difference between using leeches for a headache versus using an aspirin?


Modern Alloys
have been designed with actual theory, scientific understanding, metallurgy, computer analysis, modern testing. The list is endless. Just endless.

Chalk and cheese. A normal, everyday modern cars performance versus a horse and dung cart. You can instantly see the difference.

For example;
316 deforms at 0.2% yield strength of 240 Mpa
20moly 6HS (used for wire ropes) has a 0.2% yield strength of 2000 MPa

A steam engine versus a space shuttle.

It is madness to imply that 316 is anything other than primitive. Madness to suggest leeches instead of antibiotics. Seriously suggesting that somebody use a horse and cart instead of using a car. Exactly the same.

There are thousands of similar modern alloys that don't loose their ductility, instead of brittle fracturing invisibly.

Super Duplexes are basically just the lowest acceptably performing alloys in salt water under stress, under load cycles, with the best strength to cost ratio (due to their strength). Cracks never propagate, never grow, even in heavy hot chlorine, so all the crevice corrosion issues are side stepped.

If you use a modern designed alloy with a PREN>40 then your part can be stressed in heavy chlorine in the hot sun forever and will still NEVER fail.

316 turns brittle after one bend. It's dead. Rooted. Beyond repair. It must be thrown out.

Modern alloys never turn brittle, they will never crack. The part will never fail. Ever.

The part will never fail. The difference still stuns me.



Can you now see the difference between using leeches for a headache versus using an aspirin? And then wondering why the leeches dismasted you and killed people.
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Old 14-08-2012, 17:00   #88
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Originally Posted by PooBeetle
Dismasting - why does it happen, how to prevent it

Part 3 - 316

Really short stories.

I'm going to skip briefly over all the technical data because there is an infinite amount of it. If any of the headings interest you, then you can spend years reading the papers. Google will answer you instantly if you give a damn.

I'm going to leave out all the endless thousands of graphs showing electro potential curves, iso corrosion resistance in salt water analogues, stress cycles till failure etc.

As Google will answer you instantly if you give a damn. Which you don't. Or you would already know. You would have already done this yourself.

So just assume i'm right unless you actually search and do some reading for yourself. It's all there at you finger tips, one second away.

Really short versions (because it's all so boring; reading up on rubbish when it's all so obvious)

Just assume i've condensed thousands of pages of scientific dribble into short headings and succinct utility.

What is 316 Stainless exactly?
Useful. Due to the amount of chrome, it is shiny, and people love shiny things over rust dribbling things. It's useful for static fittings that do not have to carry a load. It has utility due to two factors, the cheapness, and the lovely finish, which stays lovely in salt water.

Because it was invented by cave men though, there are some interesting side effects.

For example, if you added 3 cents more molybdenum to it, you would actually have a brilliantly performing useful metal. But they didn't know this 100 years ago.

The prime benefit is that it stays looking nice in salt water. It is the lowest and cheapest alloy that stays looking nice.

So this is exactly what 316 is, and nothing more.

PREN
Pitting Resistance Equivalence Number

A way to compare similar alloys with different chemistries' corrosion resistance to salt water. It does not indicate performance under cyclic loads, and loads in salt and chlorine, and at various temperatures.

304 17
316 23
2507 40
Zeron 40
Ferralium 40
Al6XN 44

to be called salt water corrosion resistant, the alloy must have a PREN above 40. if it is below that, then it will rust and crevice corrosion will destroy the integrity of the part.

The performance of alloys in salt water is dependent on the two largest factors - the chloride (Cl-) content and the temperature - and the resistance of a particular steel to pitting and crevice corrosion is usually described in terms of what % Cl (or ppm Cl ) and °C it can resist.

So the temperature, and the chlorine concentration are the two largest factors involved in the alloys performance.

316 starts Crevice Corrosion at -5 degrees Celsius and at 1000ppm chlorine.

Salt water has 35000ppm chlorine, and a steel rigging fitting in the sun can regularly hit 50 degrees Celsius.

So 316 is out of contention for use before we have even examined cycles under load in salt water. It starts being riddled with an invisible cancer at below water freezing temperature.

No alloy can be called salt water corrosion resistant until it has a PREN of 40 or above.

Metal fatigue
Everybody has heard of Metal fatigue failures killing hundreds of people. usually in aviation though. and here we are talking about it in the marine industry.

Condensed Academics Version;
316 has an astoundingly low fatigue under stress resistance.

Translated into Reality?
instant break.
ie
if you actually play with 316 at home in the workshop, you will soon discover an AMAZING property of 316.

it fatigues and breaks amazingly quickly.

Micro cracks on the first bend.

try it and see

Brittleness.
If you work the metal, bend it or stress it, it becomes very brittle. One bend and 316 is useless, gone brittle. Some metals are worse than others. Because 316 was invented before the modern era, it is hard to find an alloy worse. Get a thin bit and bend it in the vice. You can bend some modern alloys for ever. See the difference?

Crevice Corrosion
To make a battery you need an inside and an outside. If the conditions are exactly the same, then there is no energy difference available, no chemical difference needed to run a reaction.

So there has to be a difference for anything to occur. Microscopic cracks full of salt water slow oxygen diffusion rates, effectively creating the outside and the inside of a battery. Small electro-chemical reactions are (effectively – not actually) catalysed by chlorine and proceed deeper into the metal along hardness boundaries (crystal boundaries).

These cracks grow very quickly.

Scratching the surface
Crevice Corrosion means if you even scratch the surface of 316, you have compromised this delicate alloy.

Passivation
A process to remove all iron from the surface leaving only chrome. Oxygen from the air turns chrome, a metal, into chrome oxide, a ceramic. If there is any iron left, a tiny pit will form from electrolytic chemistry occurring. The copper sulphate test can be used to see if there is any iron still left.

Electropolishing
Dissolves all free iron near the surface allowing the surface to be mostly nickel and chrome. Absolutely necessary, as a small particle of iron can start a little battery cell off. Whenever you see rust dribbles, the part has SCC or hasn't been electropolished.

Citric Acid Treatments
NASA commissioned a study freely available online. Citric acid is the best treatment (and cheapest). This is what I use.

I use home made electropolishing to make the part look good, and the citric acid treatment for all the bolts.

Cycles To Failure
Lets assume that you have miraculously done all procedures correctly. By some miracle you were able to avoid fabrication induced stresses, cold working, you didn't scratch the surface so as to produce microscopic pitting crevices where chlorine can accumulate to thousands of times the external salt water concentration, so there are no microscopic scratches to initiate mechanical stress concentration areas, or you mechanically polished the surface so as to remove them, you electropolished it, and then finally you gave it the sodium hydroxide at 70 degrees C for 2 hours, followed by citric acid at 70 degrees for 2 hours.

(jfyi – I actually did all this for my 316 fittings – as I can't stand rust dribbles on million dollar yachts. I think rust dribbles make your boat look bad. It reminds people of all the old uncared for boats you see rotting away somewhere; all the old un-cared for garbage scows etc.)

so you put all the time in to do it all properly, but then due to some form of brain seizure, you decide to put the 316 to use in salt water, under stress cycles. (madness!)

what happens?

Cycles To Failure in Salt Water
Firstly, the 316 fails in hours in tests. Hours. Look it up guys. Don't argue, just look it up.

Modern alloys last forever. Fme.

Oxygen Deprivation
You know all this anyway.

If oxygen is not present, or is all used up by the iron rusting, then acidic electrolytic processes start. Rapid chemical decomposition can occur. Sour mud has completely eaten through the welds in 316 in 3 weeks. Whole millimetres gone. The bases of 316 fittings and the backs of chainplates suffer this.

In an invisible microscopic crack a battery forms as the salt water slows the time it takes for oxygen to diffuse to the leading edge of the crack.

So the pitting starts, then crevice corrosion, and if there is any stress, then rapid stress corrosion cracks develop along brittle areas pathways.

Flattening The Surface
The surface has to be polished flat, other wise the iron particles are exposed and it starts rotting from here.

Fabrication Mistakes
The academics say “316 cold working can induce susceptibility to failure”. My arse. I've been building heaps of boat stuff out of 316 for awhile now, and I say you bend it once, and it's completely rooted. Try this at home. Put the sucker in the vice and bend it. See all the cracks? Millions of them. Bend it twice and it's dead.

Totally rooted. Again, try this at home.

Steel Contamination From your other Tools.
Contamination of the 316 surface by a single microscopic chunk of plain steel will cause rust to start. Pitting has just started. The piece is compromised. If you use any tools that have been used before with plain steel, you are embedding little tiny batteries into the surface of the stainless that will create little tiny holes, where the salt will concentrate.

I''ll up load some photos. Pain in the arse.

I've passivated with nitric acid and hydrofluoric acid, put the finished part outside, and the steel tool contamination marks rust like you wouldn't believe. 316. fme.

Stress Accumulation Around Microscopic Pitting Edges
Stress accumulates around edges. If you have cracks, then this is where the stress concentrates. If you have a brittle metal that spawns a million cracks like glass (ie 316) then the cracks will grow.

Stress Corrosion Cracking
Consider ALL of the above processes. They add up to something.

The final fruit of all the above processes combine to concentrate stress forces along crystal boundaries, especially when chlorine is present in microscopic fissures. These cracks grow just like the cracks in glass grow. They grow fast. 6 months if there's any stress and a solid metal part can break clean in half.

Cost

What are we talking about? Doing a proper job? Fabrication with the tradesmen having full understanding of cold working resulting in a parts failure? Fabrication ensuring no steel particles contaminate? Using only stainless tools to ensure no steel particles embed deeply into the soft 316? Passivation using nitric/hydrofluoric acid? Then having to machine polish by hand to flatten the surface? Then electropolishing and citric acid surface treatments?

What a pain in the arse. To do it all properly as i've been doing. The time extra is astounding.

You get a modern 6% alloy and the labour costs would pay for themselves instantly. I wish I had used a higher quality modern alloy for all my fabrication. The extra time i've had to spend just because the stuff was 316 instead of a 6% moly is phenomenal.

All the surface treatments, hand polishing to get smooth surfaces, passivating to get all the iron out of the surface, watching it rust anyway even though you've done it all as best as you can, hot sodium hydroxide treatments, hot citric acids treatments etc etc etc.

i'm using 316 on all non-stressed parts, but

fme. It's a real close call on how much I saved using 316 instead of a better grade. As all the extra labour costs would have been phenomenal.

All the extra labour costs involved to get crap old stupid retarded poorly performing 316 up to the very low standard of being barely adequate for the job.

So I learnt my lesson.

All the important stuff is going to be in a higher grade. As you can't make fabrication mistakes because the stuff is robust. The parts then will be 100% good instead of the 316 delicacy “is there a weakened cold worked seam somewhere that will fail in the future from SCC, is there a microscopic stress crack (yes, there certainly is) somewhere due to normal fabrication that will fail in the future” etc etc etc.

The parts will be robust, and not fail because they get one little scratch on them. No oxygen. No electropolishing etc etc etc.

All my rigging wire rope and parts will be in Ferralium 255. A Super Duplex stainless steel.

Gambling
fabrication mistakes, scratches on the surface, a tiny piece of iron embedded, the delicacy of 316, all the endless dance steps, and when you've finished do you know what you've got?

A delicate piece of **** that will still fail in under 6 months if stressed. For all the many many reasons mentioned above, if any one of those many necessary steps are bypassed, or done incorrectly, then your part will fail.

All because you are trying to use an alloy that is so far beneath the true salt water standard.

So 316 is great on land, great for static non-loaded parts, but not under stress, and never with salt water.

You have to go through all these stupid processes because of how crap the alloy is in the first place. Modern alloys have NONE of these worries.

NONE.

No fabrication mistakes; you can't even make fabrication mistakes, no nitric acid chemicals, no treating the crap with kid gloves. NONE of the above headings or steps apply to modern alloys at all.

For all practical purposes NONE of the above headings are relevant to modern alloys in salt water.

NONE.

Can you now see the difference between owning a modern car and a horse and cart?

Can you now see the difference between using leeches for a headache versus using an aspirin?

Modern Alloys
have been designed with actual theory, scientific understanding, metallurgy, computer analysis, modern testing. The list is endless. Just endless.

Chalk and cheese. A normal, everyday modern cars performance versus a horse and dung cart. You can instantly see the difference.

For example;
316 deforms at 0.2% yield strength of 240 Mpa
20moly 6HS (used for wire ropes) has a 0.2% yield strength of 2000 MPa

A steam engine versus a space shuttle.

It is madness to imply that 316 is anything other than primitive. Madness to suggest leeches instead of antibiotics. Seriously suggesting that somebody use a horse and cart instead of using a car. Exactly the same.

There are thousands of similar modern alloys that don't loose their ductility, instead of brittle fracturing invisibly.

Super Duplexes are basically just the lowest acceptably performing alloys in salt water under stress, under load cycles, with the best strength to cost ratio (due to their strength). Cracks never propagate, never grow, even in heavy hot chlorine, so all the crevice corrosion issues are side stepped.

If you use a modern designed alloy with a PREN>40 then your part can be stressed in heavy chlorine in the hot sun forever and will still NEVER fail.

316 turns brittle after one bend. It's dead. Rooted. Beyond repair. It must be thrown out.

Modern alloys never turn brittle, they will never crack. The part will never fail. Ever.

The part will never fail. The difference still stuns me.

Can you now see the difference between using leeches for a headache versus using an aspirin? And then wondering why the leeches dismasted you and killed people.


Wonderful post thanks for research
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Old 14-08-2012, 17:24   #89
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Re: Dismasting - Why Does it Happen - How to Prevent it

Dam, I must have been seeing things every time I went down to my boat and the mast was still up. The previous owners over the last 43 years also must have been going sailing with imaginary mast and sails. It has to be that way cause the chainplates were 304 stainless and should have failed the day after the boat was commisioned.

Decided that the 304 chainplates might need a rest after all those decades so pulled them last year. All but one were or two were clean with no pitting. The ones that were pitted were very minor. Did not have the ability to dye test so don't know whether the shallow pitting was anything more than cosmetic. They were strong enough to pass the stresses of a TransPac, however. FWIW, the stainless welded gudgeons and pintles on my old boat, a couple of years short of 4 decades in tropical waters, are still going strong. The boat has made 3 cruises to SoPac and more than 4 years of almost daily sails as a day charter boat.

Stainless steel, whether 304 or 316, is not the perfect material for sailboats. Should be checked at least every ten years, if not more often, but seems to hold up just fine. If you want to be extremely safe, replacement at 10 year intervals might be a good schedule. Personally, can attest that if you take care of any leaks where they pass through the deck, they'll go for many decades. Still, I'd pull them at least every 10 years to inspect them.

There is chlorine and then there are chlorine compounds. They all have different properties and probably effect stainless differently.

One thing is certain, SS doesn't like cyclic bending. But then it depends on how much of a bend you are cycling. Bend a SS bolt 90 degrees and it is severely weakened, Bend it back again 180 degrees and it may fail instantly, cycle it one more time and it's guaranteed to break. That's an old trick to shorten too long stainless bolts that are sticking through the overhead. If the cycling is slight, even stainless will go on practically forever. I have seen chainplates that are obviously mis-aligned with the load from the shroud. When the shroud is loaded these have to be putting enough load on the chainplate to cause it to bend a little, not permanently but some bend. These chainplates are still going strong after several decades. That is not good construction practice but it's survived. Believe there are engineering tables that will tell you how long SS will survive various amounts of bending and cycles.
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Old 14-08-2012, 20:56   #90
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It's amazing that my 34 year old chain plates ever held the rig at all! They being of 304ss
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