PDA

View Full Version : Weathering Steel Keelbolts



chuckt
12-13-2011, 06:14 PM
I was intrigued by this post http://forum.woodenboat.com/showthread.php?122902-Keel-bolts-in-a-cast-Iron-Keel wherein the fellow was looking for cor-ten replacement bolts for those used by Paul Rollins in a boat with an iron keel. He indicated the 30 year old bolts were still in decent shape. He never said if he found replacements. (Paul confirmed to me that the bolts were used).

I did some looking it appears that Cor-ten is a trade name that isn't really used in association with bolts. "Weathering steel" is a more generic term but even using that as a search term doesn't find you these bolts. I also saw that A242 and A588 are standards that apply to such steel with A242 being the first designation and A588 applying to a later and stronger version. Finally, I stumbled across A325 Type 3 bolts which are classified as weathering steel bolts generally equivalent to A242 and A588.

Only when I search for A325 Type 3 do I find suppliers.

If someone knows about these classifications, I'd love to be educated. And if you want to comment on wether they should be used as keel bolts in an iron keel with oak floors, do that as well.

I checked into wrought iron bolts. The only supplier I found is horribly expensive. I'm leery of stainless.

chuckt
12-14-2011, 07:37 AM
Found this:

Weathering steels are a family of ASTM specifications, as well as several trademarked specifications exhibiting similar corrosion resistant properties. The ASTM specifications are A588, A242, A606-4, A847, and A709-50W. The primary trademarked product is Cor-tenŽ. The selection of a particular ASTM weathering steel specification is dependent on the type of product desired. ASTM A588 covers structural shapes, plate, and bar. ASTM A242 covers steel plate through one-half inch in thickness. ASTM A606-4 covers steel sheet and coil and ASTM A847 is for weathering steel tube and pipe.

But still don't know what I'm looking for. Maybe A847.

Garret
12-14-2011, 09:00 AM
I used Ductile Iron for my boat (oak floors & iron keel). Ductile iron is what they make iron sewer pipe from & is quite resistant to rust. Seems to be close to wrought iron, but less expensive.

I had a conversation with Paul about DI vs. Cor-ten & he thought that DI made a lot of sense - but hadn't heard of it before I brought it up.

It's available in rods up to 12' (though 6' is more common) & 5" diameter. Mine were 1.5". Rod is supplied a bit oversize (~0.025 oversize), so when cutting threads, I also turned the rod down to 1.500". I made the nuts from 3" rod. The originals on my boat were square nuts, so I went with square again. The 3" diameter meant that the corners have a radius - but only a small amount of metal is missing.

Thought I had pics, but can't find 'em.

chuckt
12-14-2011, 09:28 AM
That's interesting Garret. Any idea of the stength on that? That's cast I would guess. Our office building is about 90 years old and we dug up some cast iron pipe that looked really good. My only concern would be strength and brittleness.

Just found out one can aquire A588 rod but the supplier I talked to doesn't have 1/2" or 7/8" which is what I would need.

Garret
12-14-2011, 09:50 AM
Strength is very good. Much better than regular cast & far less brittle. I can;t seem to get the table from Wikipedia to display correctly here, but here's a link: http://en.wikipedia.org/wiki/Cast_iron Scroll down a bit to see the table.

Tensile strength is over 2.5 times cast iron. Also note that there are a # of grades of Ductile Iron. It was a while back, but when I compared it to Cor-ten, it was favorable.

chuckt
12-14-2011, 10:35 AM
Well--this sounds promising Garret. It must be close to iron on the noble chart. Tensile strength is indeed about the same as Cor-ten. Yield strength appears slightly lower and Ductile is harder (more brittle). Any reader should take this with a grain of salt because, due to lack of knowledge, I might be comparing apples and oranges.

I do see it makes a big difference on the numbers depending on if the ductile is tempered or not. But it seems that hardness/brittleness is the only significant difference between ductile and cor-ten.

I also found out that one needs to look for "round bar" not "rod." Once I started looking for Cor-ten round bar I got lots of hits. Still having trouble finding a retail or low-quantity source.

chuckt
12-14-2011, 11:07 AM
Baby Cheesus! After a day of searching finally found a vendor and price. $65 for a twenty foot 1/2" piece from this place: http://www.centralsteelservice.com/steel_channel_round.htm I actually think A588 round bar is all over the place. It just took me awhile to figure out the right thing to ask for and find a place that dealt in small quantities. This is for plain round bar which would need to be cut and threaded.

Not quite sure yet, but it appears that the nuts and washers don't go by A588 but instead are designated "Type 3" to mean made of weathering steel. A325 Type 3 Washers and A563 Type 3 Nuts appear to be compatible and I found them here: http://www.zieglerbolt.com/catalog_overview.asp

Wow! that is so much cheaper than wrought iron. I still am leery of relying on one anecdotal experience with Cor-ten but its something to consider when the time comes. From what I've read, 30 years is as long as you should go with wrought iron as well???

Garret
12-14-2011, 11:15 AM
My original keel bolts were wrought iron & lasted 70 years. OK, none were broken, though many were necked substantially where they met the floors (douglas fir originally, now oak). From the metallurgy folks I talked to, ductile iron was the closest thing currently available to wrought iron - other than wrought iron itself.

When I checked for wrought iron, I did not find any commercial sources (due to not looking hard enough?) & therefore my only option for wrought iron was to have a blacksmith make them for me. When I talked to a few, their eyebrows shot up when I started describing 56" long 1.5" diameter rods & all declined - saying that they just didn't have the equipment to make pieces that big while maintaining even quality throughout the piece. I'm sure there are folks with the equipment to do it, but I didn't find them.

Another advantage to DI is that it's very nice to machine.

Here's an old one (floor removed & others were necked more):

http://i1194.photobucket.com/albums/aa372/garretmott/IMG_0072.jpg

Garret
12-14-2011, 11:23 AM
I still am leery of relying on one anecdotal experience with Cor-ten but its something to consider when the time comes. From what I've read, 30 years is as long as you should go with wrought iron as well.

Paul is pretty darn experienced.

My original bolts were coated with tar. The part in the deadwood & ballast was virtually new in appearance when I took them out. By that I mean scrape off the tar with a pocket knife & see shiny metal. The damage started 1" below the floors & continued up to the nut. Note that I have learned that my boat spent ~ 10 years partially submerged (bilges flooded) in Ft. Lauderdale - so my damage may be more extreme than others. Nuts that kept paint on them (up forward where they weren't submerged) unscrewed with a 3' wrench (the nuts are 2.5 on a side).

chuckt
12-14-2011, 11:26 AM
Thanks for the picture. That's pretty darn good for 70 years I'd guess. I only found one source in England for wrought iron round bar in significant lengths. I never got an exact price but near $100 per foot at 1/2" Ouch.

Garret
12-14-2011, 11:36 AM
IIRC I got 5 6' lengths of 1.5" + 24" of 3" (for nuts top & bottom) for about $400-$500. It was a while back (more than 30 seconds;)) - so I may be off on that a bit.

Plate for making washers was very expensive, so I went with 1/4" mild steel & coated them with epoxy.

stephaan
12-14-2011, 02:39 PM
Some info on CoR (Corrosion Resistent) - TEN (tensile strength) from a retired mechanics-teacher:

Cor-ten-steel is an american invention. It is a metal alloy of Fe, Cu, P, Si, Ni and Cr. The tensile strength can be compared with stainless steel (355N/mm˛).

Oxygen and cortensteel are forming a dense rusty layer.

Used outside, the red-brown rusty layer remains relatively dry and the corrosion-layer will protect cortensteel.

Used in a wet environment, the corrosion-layer will be less dense and corrosion will go on.

Slacko
12-14-2011, 04:46 PM
The book title listed below has the information you need to decipher the codes for steel.
It also talks about suitability of the various metals for different purposes.
Corten can have the same crevice corrosion problems as stainless, so shouldn't be used for keelbolts.

The Boatowner's Guide to Corrosion: A Complete Reference for Boatowners and Marine Professionals (Paperback).

Garret
12-14-2011, 04:55 PM
Corten can have the same crevice corrosion problems as stainless, so shouldn't be used for keelbolts.


That was exactly what I worried about & why I went with Ductile Iron.

Thanks for the info & stephaan - thank you as well!

JoshuaIII
12-14-2011, 07:13 PM
Corten steel is great, but the main issue with it it's the patent pending....
This is why it is hard to found and hard to get.

Better use a alloy that capitalism didn't swallow to don't encourage them ;)

chuckt
12-14-2011, 07:49 PM
Joshua--from what I found there are lots of equivalents. You can get the same thing that isn't Corten. You just have to look for the ASTM grades I mention above. Now I'm poking around the internet for Ductile round bar, nuts and washers. Still not ready to write off weathering steel since it has apparently worked well for one person for 30 years.

Garret--I haven't seen it less than 1" yet.

Garret
12-14-2011, 07:54 PM
Joshua--from what I found there are lots of equivalents. You can get the same thing that isn't Corten. You just have to look for the ASTM grades I mention above. Now I'm poking around the internet for Ductile round bar, nuts and washers. Still not ready to write off weathering steel since it has apparently worked well for one person for 30 years.

I don't think you'll find nuts and/or washers in either material (though I certainly could be wrong). I couldn't find any in ductile iron - so I made 'em. Not much harder than cutting the threads on the rod.

JimConlin
12-14-2011, 09:41 PM
FWIW, I just found this.
http://www.modernsteel.com/steelinterchange_details.php?id=283

Garret
12-14-2011, 09:50 PM
Wow! I don't think I'd use Cor-ten after reading this.


Surfaces of COR-TEN Steel that are wet for prolonged periods of time will corrode at an unacceptably rapid rate. Therefore, the detailing of members and assemblies should avoid pockets, crevices, faying surfaces or locations that can collect and retain liquid water, damp debris and moisture. Damp debris on COR-TEN Steel surfaces will cause accelerated corrosion.

I chose ductile iron because it has such a long history (since the late 1800's) of doing well in wet environments (underground).

chuckt
12-14-2011, 10:13 PM
Yes--that certainly is a warning against it.

I've been looking for ductile 1/2" I don't think it comes that small.

Garret
12-14-2011, 10:26 PM
Yes--that certainly is a warning against it.

I've been looking for ductile 1/2" I don't think it comes that small.

This site has 5/8. since you'll have to turn it anyway, an extra 1/16 per side's not a whole lot.

JimConlin
12-14-2011, 10:47 PM
Wow! I don't think I'd use Cor-ten after reading this.



I chose ductile iron because it has such a long history (since the late 1800's) of doing well in wet environments (underground).

I'm confused.
Irving Johnson's last Yankee (1959) was of Cor-ten and passed USCG inspection at the age of 50.
http://www.yachtcouncil.com/Used/63'0''(19.2m)/1959/SPARKMAN+%26+STEPHENS-for-sale-in-CT?Boatsforsalesearch=basicinfo&vessel=100357


(http://www.yachtcouncil.com/Used/63'0''(19.2m)/1959/SPARKMAN+%26+STEPHENS-for-sale-in-CT?Boatsforsalesearch=basicinfo&vessel=100357)

Garret
12-14-2011, 10:58 PM
It's never simple is it? My guess is that a hull can be painted & the paint maintained? How do you do that in a keelbolt?

But - I'm certainly no expert!!!

chuckt
12-15-2011, 06:31 AM
Yeah-me too Jim. What you found sure seems to be a warning about using it as ballast or keel bolts. But it worked in two instances we know of.

BTW: 1/2" is not what I would need. Duh! I was looking at the specs for keel (wood keel) bolts. The ballast bolts are much bigger. More like 1 1/4" I thought 1/2" seemed wrong.

I can replace keelbolts (not going through the iron ballast) with bronze right?

Garret--how do you turn it? I don't have any kind of metal lathe. Why do you need to turn it? My guess is it is too rough?

chuckt
12-15-2011, 06:37 AM
Oh wait. Yankee has Corteen sheet steel hull. Its painted and protected. The warning you found applies to Corten not painted and allowed to weather. Exposed to elements where it isn't wet all the time, it develops a fine powder rust and does not significantly waste away like regular steel. I think the warning relates to using it where it stays wet.

That being said, the warning is for structural applications. It could be that what is unacceptable degradation for an engineer building a bridge is totally okay for a ballast bolt.

I read some more. The warnings are clear and consistent that it should not be continuously wet. In such conditions, it rusts close to ordinary steel. As long as it cycles dry, it is great. I read a couple of warnings that say draining must be designed in if it is used in a place that pools water and, if used underground, should be encased in something

Garret
12-15-2011, 07:21 AM
Yeah-me too Jim. What you found sure seems to be a warning about using it as ballast or keel bolts. But it worked in two instances we know of.

BTW: 1/2" is not what I would need. Duh! I was looking at the specs for keel (wood keel) bolts. The ballast bolts are much bigger. More like 1 1/4" I thought 1/2" seemed wrong.


I wondered.... Seemed as though it'd be a really small boat!



I can replace keelbolts (not going through the iron ballast) with bronze right?


If they're not touching the ballast, that's what I've used



Garret--how do you turn it? I don't have any kind of metal lathe. Why do you need to turn it? My guess is it is too rough?

You need a lathe. No way around it. I don't have a big enough lathe, but I do have a friend who's a machinist, so we did it at his place. The rod is not perfectly finished from the supplier. My 1.5" rod came @ about 1.55 or 1.57 - with some variation. Since my old bolts were exactly 1.5, I had to turn the new material down to match. I wanted room for the tar around the bolts, so I didn't want them to be a driven fit, I wanted them to slide into place.

I suppose you could get a die for cutting the threads, but we did everything on the lathe at one time. Cutting threads in material this big is serious work with a die. The nuts were made on the lathe as well.

chuckt
12-15-2011, 10:48 AM
Thanks. I think we explored this as far as we could go without a metalurgist.

I reread the post I cite in my opening post on this thread. I see that, not only did the guy say that his 30 year old corten bolts looked good, he stopped pulling them because he saw no need to replace?! The only thing I can guess is that they were tight enough in the keel that they were effectively "encapsulated." Mysterious?

I found some salvaged wrought iron for basically $40 per foot for 1 1/2". I found that concordiaboats has recommended Stainless 316 which is close on the noble chart to iron. Also about $40 a foot. Monel is about $130 per foot.

Garret
12-15-2011, 11:48 AM
Thanks. I think we explored this as far as we could go without a metalurgist. I reread the post I cite in my opening post on this thread. I see that, not only did the guy say that his 30 year old corten bolts looked good, he stopped pulling them because he saw no need to replace?! The only thing I can guess is that they were tight enough in the keel that they were effectively "encapsulated." Mysterious? I found some salvaged wrought iron for basically $40 per foot for 1 1/2". I found that concordiaboats has recommended Stainless 316 which is close on the noble chart to iron. Also about $40 a foot. Monel is about $130 per foot. 316? Please think long & hard on that. There are many threads on here about crevice corrosion & how stainless can have issues in salt water when not exposed to air. I know FG boats use it all the time - but a FG boat will/should have keelbolts that never get wet.

chuckt
12-15-2011, 12:09 PM
I know Garret--I was surprised to see that was being being recommended and used. You see it mentioned in several of the Concordia fleet newsletters. And I've seen it in the boats. If and when the need arises, I'm leaning toward following your example.

Canoeyawl
12-15-2011, 12:38 PM
I have made quite a few keelbolts out of Aquamet 22
(http://www.aquamet.com/aquamet22.nxg)

boattruck
12-15-2011, 01:47 PM
Gents, I have a few observations to add. If we are asked to replace keel bolts on an iron keeled boat, our order of preference of what we can source currently is;
1 Ductile iron
2 316 0r Aqua-met
3 Galvanized Steel
4 Mild steel
Obviously, there are many factors to count in, and all keel bolts will need to be checked periodicly, as noted earlier, they fail in the timber keel/ floor area, I coat whatever we use with tar and or red lead,and generally will use Dolfinite as a sealant. When we are making ductile keel bolts we buy oversize and turn them down ( note; after paying through the nose for the sizing of the last batch, we found out that a process called center-less grinding is the way to go, and purported to be much less expensive...you live and learn, then you die, and forget it all...) and I generally will use heavy pattern galvanized nuts and washers, available and reasonably priced. If it is to be stainless, obviously we source matching nuts and washers. As with all choices there are many possibilities and pitfalls and downsides to most all of your options. Hope some of this is helpful. Cheers, Hutch/BT

pukka
03-03-2012, 03:18 PM
G'day guys,
I have searched for why hi-tensile steel bolts are not used & cannot find the reason. Is high tensile a no-no owing to fatigue?
I cannot source ductile here, aquamet, I believe is comparable with SAF 2205 available here but I can only get 316 nuts so
I guess that ain't smart seing as the yield on 2205 is 100mPa higher than regular 316. I am getting a better than safety factor 5 with the
2205 with equivalent nuts. although, I beleive there is a better yield grade of 316 available on indent.
Hi-tensile with 8.8 nuts (800mPa) gives me better again but am leery cos its hi-tensile. A
I am limited to 16mm bolts owing to existing keel plate width, .'. cannot use the lower yield materials/alloys. (ductile, ms galv'd, monel)
My calc's have been based on min. 600mPa yield.
Hi-tensile iis readily available.
Delemma!

BTW- fully encapsulated bolts, no contact with wood.

Phil Y
03-03-2012, 04:13 PM
Maybe you could use spectra or somesuch with some sort of inverted rigging screw thing to tension it. Silly I know.

pukka
03-03-2012, 05:00 PM
Maybe you could use spectra or somesuch with some sort of inverted rigging screw thing to tension it. Silly I know.

For keel bolts?
No, thanks. My hippie days are long over.
Kinda like holding up your pants with bailing twine?