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Old 09-10-2008, 04:55   #1
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Midlandone, lets not bring this discusion into

Weyalans thread.

You still have not answered how to prevent crevice corrosion in ss through hulls.

Regarding keels, crevice corrosion is a concern when using ss bolts. The only solution is to try to keep them dry but that's tough. You do realize companies swap out ss keelbolts that have developed crevice corrosion. MarsKeel - Technology

Regarding Blake using C86300, yellow brass. Thanks but no thanks, they cheapened the product when they switched in my opinion.

Given brass is now selling for about $4 per pounds we can expect Groco and and Perko to switch to 316 from bronze? If crevice corrosion is not a problem we'll see this soon right?
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Old 09-10-2008, 06:10   #2
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You might want to widen this to include some of the "gunmetal" through hulls and valves. Some of them are a disgrace and totally unfit for purpose. Last time I spent a fortune and got proper bronze.
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Old 09-10-2008, 14:37   #3
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Originally Posted by Joli View Post
Weyalans thread.

You still have not answered how to prevent crevice corrosion in ss through hulls.
First, you have no right to expect me (or indeed anyone else) to answer anything for you. So I hope you have that clear.

Second, you completely bemuse me with your question as you are asking me to give an answer to what you seem to regard as being a major problem but I don't - you are the one that is saying that ss should not be used, not me. A bit like insisting that the weatherman who has told you that there is no need to wear a raincoat today, tell you what raincoat you should be wearing today. A bit silly don't you reckon?

Personally I have never seen any specific protection given to ss seacocks - so don't you think it should be you, or someone who agrees with you, that is telling us how to protect them, not me?

Just out of interest I have randomly pulled the specifications and drawings for several smallish high quality boats in order to give a frame of reference. One was a high quality 80 foot yacht (built for a European owner) and the other 2 were high quality commercial vessels (70-80 foot power boats providing high quality short haul passenger services for wealthy tourist destinations). All were design appraised by, built to and entered into class with one or another of the 5 quality classification societies - the yacht was designed by a internationally known yacht designer of super yachts and the power boats by an internationally known designer of the type of vessel (indeed many of his are built in the USA for US clients).

ALL used ss seacocks (and also for other seawater services). So, as I said in the other thread it seems to me that if you have the concerns over the use of such valves, etc as you are expressing, you should be off telling the worlds naval architects and professional yards that they don't know what they are doing and through that are putting their clients at risk.

As Talbot (and I in the other thread) has alluded to, any material if not of good quality (even if supposedly metals of the same alloy) can have its problems, whether that be ss, bronze, plastics, timber, rovings, etc. It just takes either some knowledge of the materials or, as Talbot has done, buy from a reputable manufacturer. A reading of any forums will turn up multitudes of instances where one can see people making decisions on the basis of inexpert forum advice or the advice of the local chandler, small time backyard "boat repairers", etc eg Just one example - the number who seem to be intent on sizing their propellers themselves when even an expert naval architect would take the advice of a reputable prop builder (the forunites probably end up buying a prop of rubbish "bronze" as well, inviting the pink cancer and the need for continuous uncompromised anodic protection).

That is enuff from me on the subject - I prefer to be on the side of those who know and have exercised that knowledge widely, rather than contribute to threads promoting forum myths.
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Old 09-10-2008, 21:48   #4
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I know that crevice corrossion is a terrible fate, but...

I know that crevice corrosion is one of the worst fates that can befall a sailor, but it just does not seem to happen that often.

I seem to recall a few sorry tales of glassed in chain plates, but other than that, nothing.

It looks like even tiny amounts of oxygen does the trick.

Having a steel boat SS (or Marelon) below the water line is a given.
I have used a few gal. bolts above the water line, much to the amusement of the local yokels.

Can anyone give us some actual examples of the dreaded event?
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Old 10-10-2008, 01:41   #5
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.....go to the sandvik web site and have a read up on the various types of corrosion that effect stainless. It explains how they occur. The lack of oxygen is one of the major factors of crevis corrosion. A through hull does not suffer a lack of oxygen. Normal sea water contains enough oxygen to keep 316 happy. Hence the use of 316 in rudder posts and prop shafts. Even 304 will survive if look after. Prop shafts that have tight fitting brass bearings and no water through them can suffer at the bearing interface. (I have a 304 shaft that shows this wear). A more common example of crevice corrosion is in chain plates. If the seal between the deck and chainplate is not water tight water can get in between. The water is sitting and therefore loses its oxygen over time. This is far more common in fiberglass or other material boats than steel because the chainplate on a steel boat is usually fully welded. Having said all that small pits or holes in any ss that allows for water to sit can cause a problem. Dont use brass on a steel boat for through hulls. Dont believe that timber boats will not have problems with dissimilar metals or electrolysis.
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Old 10-10-2008, 05:16   #6
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Like I said in an earlier post, we agree to disagree. You believe it is fine to use ss below the waterline I don't if it can be avoided. Obviously commercial shipbuilding has other constraints and cannot always use bronze, copper-nickel, and nickel-copper alloys for a multitude of reasons. When they use ss they live with crevice corrosion that is inherent with cast and wrought ss. Why any composite boat would be fitted anything but a true bronze or reinforced plastic seacock is beyond me.

Readers will make up their own mind.
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Old 10-10-2008, 13:08   #7
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Not all corrosion of SST is crevice corrosion. SST can corrode in the right conditions just like steel. Crevice corrosion is a different puppy altogether. Firstly you need a crevice, or crack. The crack is where the corrosion takes place and the corrosion is more galvanic than actually rusty corrosion. Hence why it is often invisible to normal viewing and requires testing to show the real threats. Crevice corrosion can be caused by two main factors. Either the the metal having a slightly dissimilar interface, as in a weld, which in the right conditions will galvanically corrode like any dissimilar metals in contact will. Often this form of corrosion is seen in chain links and other welded items. The weld maybe of the same metal grade, but things like heating, cooling, was the metal surface clean, Welding Gas type used etc etc all can have an affect on the slight metalurgical makeup of the weld metal to parent metal interface. The other way crevice corrosion is caused and the most common way, is stress cracking due to working the metal. Chromium, nickel and some other additives make the SST very brittle. 304 is easier to machine than 316 for instance. 316 has more Chrome and Nickel making it harder. The hardness or brittleness creates little stress fractures when the SST is worked. Epecially in high deformation pieces like swage fittings. Over time, these cracks which are often invisible to normal visual inspection, corrode deep inside the crack. This crack over time slowly increases. And movement due to cyclic loading will also increase the crack. Once again, the metalurgical properties are changed just enough so as a slight Galvanic process is present and the crack continues till the day where it fails.
So quality fittings are usually less prone to these issues. They are made with that expertese that is required to reduce corrosion issues.
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Old 10-10-2008, 14:41   #8
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Joli, perhaps some alleged naval architects made the same inquiries of "proper marine bronze" thruhull makers that I made a few years ago. Each of them swore that they used a special, secret, exotic, proprietary bronze alloy and that was what made theirs the best. And so expensive.

Well, the street jargon for that in the US is "a load of crap" because all it takes to unravel the proprietary alloy is dropping off one sample at any college chem lab where they have a spectrometer, and a case of beer or bottle of Scotch. Bright and early the next morning, you'll have the secrets of the alloy.

If an architect specifies "316 SS" then at least he can say he specified a standard known alloy--not some "secret stuff" from cranky old mariners. As in so many other issues with commercial codes, this could simply be a matter of procurement or liability concerns--not performance.

Or perhaps, someone has decided that crevice corrosion in 316 is less of a problem than galvnic corrosion in bronze--for yachts of that size. All we can do is guess, since we've seen no facts, and no rationale from the folks who are supposedly making these decisions.
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Old 10-10-2008, 14:56   #9
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People are going to make up there own minds about what material they want to use for through hulls. To me SS for a through hull makes no sense for a smaller boat when better materials are available. Ships can use many different materials NAB, SS, cast iron, bronze,,,to many to list. The problem is crevice corrosion being what 50 to 75 mills per year? Got a 10" valve, it'll last a few year. Got a 3/4" valve, how long before there is a problem?
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Old 10-10-2008, 16:55   #10
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I think there is a lot of merit in what Hellosailor says in his post regarding quality. SS valves (and fittings) are widely used in industry, especially in the process industries where the reliablity of the alloys meeting specification and the quality of the manufacturing processes used are frequently very important and required to be verified with reliable tracable material certificates from mill and through manufacturing. This means that such valves are built in a well controlled environment and are of known consistant high quality and reliability.

Also, as Joli is, quite mischeviously in my view , trying to get himself out of his predicament by trying to disengage the references to widespread successful use of ss in small vessels by engaging it with "ships" all the time, maybe I should again clarify the matter with some of my own experience.

Until a few years ago I ran a company that, among many other things, provided accredited design approval services of commercial vessels, for the regulatory authorities of several western countries. These are vessels where the county's marine regulators require the design to be independantly checked by an accredited organisation.

These vessels are generally the smaller commercial vessels which are not required to enter into class (if entering class they would be design appraised by the classification society they entered). Basically includes anything that floats and used commercially under power or sail, so as well as the likes of larger fishing vessels, ferries, etc captures very small open boats and the likes of charter fishing vessels (which are usually of pleasure boat type in the 20 to 60 odd foot size range), sail boats for charter, etc.

The vast majority of these vessels are under around 50 foot but larger vessels are also caught, typically up to around 150 foot or so, but there are far fewer of them and these often go into class anyway so not seen by us for appraisal.

Hundreds of these designs would come in every year and ss seacocks were very widely used on vessels of all sizes. Furthermore we had around 35 marine surveyors on our staff providing statutory inspection services to the same types of vessels (over 2,000 of them ) through their working life - those are the statutory and other periodic surveys, monitoring of vessel management, monitoring of maintenance, etc required by regulatory authorities. The surveys required internal inspection af all sea valves, by disassembly if that was possible, but there was no history whatsoever arising out of this continual survellience of the vessels that gave rise to any concern about the use of ss valves over any other.

Furthermore, many of these vessels were owned by very experienced fleet owners for whom keeping the vessel in service was of main importance. Such people go for reliability and quality in the equipping and fitout of their boats, they prefer to have the boat working rather than laid up for maintence.
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Old 12-10-2008, 07:55   #11
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This has been a fun converstation

Wow Midland, pretty substantial credentials. It must have been a treat to work in an industry that most of us only enjoy as a pastime. Honestly though I am having a very tough time understanding how you can tell folks here don't bother with a bronze or Marelon sea cock, you have in essence told Weyalan "pop in a SS skin fitting, spin on a SS valve and "yer good to go". I think you're comparing commercial boat, yacht, ship, whatever techniques to small composite construction and the comparison does not translate well.

I pulled some prints also, I make all manner of castings. Some of my customers are producers of industrial valves. Maybe some of my castings are on the boats you've surveyed.

Lets examine a typical 1.5" Flange Face Class 150 cf8m valve body, they have a wall thickness of approximately .300". Castings have inclusions, it is inherent to the process, these are attack sites that will suffer crevice corrosion when used in a seawater application, it can't be stopped as you have pointed out. The rates of corrosion are well understood, it is not uncommon to see rates of .050~.075" per year. Eventually casting will develop leaks if the inclusion becomes a site attack for crevice corrosion. If you compare the amount of material Class 150 valve body versus a SS skin fitting you realize you're not talking the same thing. How much material is between the thread root and bore of a typical SS skin fitting? Maybe .080"? How long will that last?

I think Weyalan should install a proper bronze or Marelon seacock, bolted to the hull and mated to a bronze skin fitting as soon as possible. You believe he is fine with a SS skin fitting and SS valve. Something like what is shown below.


At the end of the day it is Weyalans choice.

http://www.blakehurstslipway.com.au/index.php/home
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Old 12-10-2008, 15:22   #12
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I work in the process industry, and we supply all kinds of instruments. For sea water, we NEVER supply 304, or 316 or even 316L for things like diaphragm seals (oil filled seals on e.g pressure transmitters). We will typically use Tantalum, or maybe Al2O3 ceramics.
It is the Chloride ions that are the nasties.

Regarding crevice corrosion, I have seen 316 parts corrode in black steel tanks, because they were mounted so they had water lying in them when the tanks were emptied. Not even salt water!

If we look at the requirements in the offshore industry in the North Sea with a relatively low salinity compared to tropical waters, they always specify duplex steels for salt water applications. They use a standard called NORSOK.

I'm with Joli on this one. Your ss through hulls will probably have a reasonable lifetime, but check them every 3 years.
My choice for skin fittings and valves is Marelon composites or equivalent.

There are too many crappy metal parts being used when it comes to valves these days, unless you can get Mill certificates for each metal component used in the wetted parts.

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Old 12-10-2008, 18:01   #13
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Honestly though I am having a very tough time understanding how you can tell folks here don't bother with a bronze or Marelon sea cock, you have in essence told Weyalan "pop in a SS skin fitting, spin on a SS valve and "yer good to go".
I have definitely come to the view that you either cannot read or are just foolishly mischievous so not worth bothering with.

Nowhere have I told "folks here" that they should not "bother with a bronze or Marelon sea cock" nor have I stated or inferred or told Weyalan "pop in a SS skin fitting, spin on a SS valve and "yer good to go"".

All I have said is that ss is a perfectly acceptable alternative and it is particularly foolish of you to claim that I have a cavalier attitude to material selection, whether it be among the alloys of bronze or ss or among the plastics (all of which I have quite happily used on my own vessels at one time or another).

If you have a different view then that is fine, you are just flying in the face of widespread professional marine experience. But it is an insult to others when you pursue an argument when it is clear that you either cannot read properly or when you are just reconstructing what others have said in an effort to sabotage what it is that is being said by them; only politicians, crooks and fools do those things.

I presume you are not a politician or a crook?
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Old 13-10-2008, 01:39   #14
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Ok guys have we covered sufficiently the Marelon/Bronze/SS debate?

Although we are being polite, it seems we are at the, "Throw our poo at each other" stage...

If there's no new technical information we can move on?
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Old 15-10-2008, 02:37   #15
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sure.....I hope you dont want me to put a brass through hull in a steel boat ?
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