Stainless cracking. Metalurgists, puzzel this one

[dlj]

Originally Posted by s/v Jedi

I would rather switch to bronze or titanium.

Titanium and stainless steel are frequently used in carbon fiber - sometimes aluminum but that seems to be more problematic and it wouldn't be applicable here. But I've never seen bronze used with carbon fiber composite construction. Got a good reference for using that material in this case?

It's not a material listed for use in carbon fiber composite materials in any of the MIL Specs (Department of Defense Handbook "Composite Materials Handbook" Volumes 1 through 5) regarding this kind of material combination. That would certainly take it off the list for me.

dj

[s/v Jedi]

Originally Posted by dlj

Titanium and stainless steel are frequently used in carbon fiber - sometimes aluminum but that seems to be more problematic and it wouldn't be applicable here. But I've never seen bronze used with carbon fiber composite construction. Got a good reference for using that material in this case?

It's not a material listed for use in carbon fiber composite materials in any of the MIL Specs (Department of Defense Handbook "Composite Materials Handbook" Volumes 1 through 5) regarding this kind of material combination. That would certainly take it off the list for me.

dj

I didn’t see anything about carbon fiber, just an aluminum backing plate but I guess the hull is carbon fiber?

I would insulate the bolt from both the aluminum backing plate and from the carbon fiber, probably using fiberglass for this. Then I would stay away from stainless steel because of the crevice corrosion issue, which is eliminated with the other metals.

Bronze is fine, why would you think not? If you don’t like the color, chrome them, just like turnbuckles.

[dlj]

Originally Posted by s/v Jedi

I didn’t see anything about carbon fiber, just an aluminum backing plate but I guess the hull is carbon fiber?

I would insulate the bolt from both the aluminum backing plate and from the carbon fiber, probably using fiberglass for this. Then I would stay away from stainless steel because of the crevice corrosion issue, which is eliminated with the other metals.

Bronze is fine, why would you think not? If you don’t like the color, chrome them, just like turnbuckles.

It seems that in the cases where there is the more notable corrosion of these fasteners, there was likely carbon fiber used. That may have come out outside this thread...

Actually titanium will also suffer from crevice corrosion as well as some other metals, but that's just a clarification of the statement that's it's eliminated in other metals. It's not. It depends upon the metal and the environment.

I quite like bronze.

But I don't find any reference material referring to it's use as a fastener with carbon fiber. I'm not one to be a pioneer in fasteners so either I'd have to have test data showing me that's a good combination or a well done document that supports that choice. I will use bronze in many other applications. But I have the supporting data to justify it's use there.

dj

[s/v Jedi]

Originally Posted by dlj

It seems that in the cases where there is the more notable corrosion of these fasteners, there was likely carbon fiber used. That may have come out outside this thread...

Actually titanium will also suffer from crevice corrosion as well as some other metals, but that's just a clarification of the statement that's it's eliminated in other metals. It's not. It depends upon the metal and the environment.

I quite like bronze.

But I don't find any reference material referring to it's use as a fastener with carbon fiber. I'm not one to be a pioneer in fasteners so either I'd have to have test data showing me that's a good combination or a well done document that supports that choice. I will use bronze in many other applications. But I have the supporting data to justify it's use there.

dj

If you insulate using fiberglass, it is bronze with fiberglass, not with carbon fiber. I isolate everything from carbon fiber.

[wsmurdoch]

Perhaps this might be part of the story...

When the installed bolts are submerged in seawater for a period or repeatedly wet and drained, the area under the head of the bolt and the area down the bolt shoulder are washed with seawater with a Cl- concentration of about 20 ppt and remain wet. Then, when elevated above the water and in dry air, the water evaporates raising the Cl- concentration at the point where the water is being removed. The Cl- concentration rising there to the Cl- concentration of water in equilibrium with the solid sea salt crust. At that point (and especially if that point were an area with a high residual stress from forming the bolt head or from rolling the threads) conditions would be ripe for chloride induced stress corrosion cracking along the crystal boundaries and through the crystals of the 304 stainless steel weakening the metal and allowing it to break.

Bill (not a metallurgist, but a retired BS MS PE chemical engineer)

[dlj]

Originally Posted by s/v Jedi

If you insulate using fiberglass, it is bronze with fiberglass, not with carbon fiber. I isolate everything from carbon fiber.

That's a good practice. Epoxy also works.

dj

[dlj]

Originally Posted by wsmurdoch

Perhaps this might be part of the story...

When the installed bolts are submerged in seawater for a period or repeatedly wet and drained, the area under the head of the bolt and the area down the bolt shoulder are washed with seawater with a Cl- concentration of about 20 ppt and remain wet. Then, when elevated above the water and in dry air, the water evaporates raising the Cl- concentration at the point where the water is being removed. The Cl- concentration rising there to the Cl- concentration of water in equilibrium with the solid sea salt crust. At that point (and especially if that point were an area with a high residual stress from forming the bolt head or from rolling the threads) conditions would be ripe for chloride induced stress corrosion cracking along the crystal boundaries and through the crystals of the 304 stainless steel weakening the metal and allowing it to break.

Bill (not a metallurgist, but a retired BS MS PE chemical engineer)

Sure, it could all be part of the issue. But if that was the whole story, why then is it isolated to a select number of boats and not all?

It appears to be more related to those boats that have had carbon fiber put in by the owners.

The biggest difficulty is that there is insufficient data - no broken bolts to examine - limited information on the exact status of carbon fiber application. Too many unknowns with limited resources to fill in the gaps... So it becomes a matter of "best guess"....

dj

[wsmurdoch]

Originally Posted by dlj

It appears to be more related to those boats that have had carbon fiber put in by the owners.

Did Thinwater say that? I missed it.

Bill

[dlj]

Originally Posted by wsmurdoch

Did Thinwater say that? I missed it.

Bill

Yes, sorry, it was in direct conversations outside of this thread.

dj

[s/v Jedi]

Originally Posted by dlj

Yes, sorry, it was in direct conversations outside of this thread.

dj

Aha. So the carbon fiber wasn’t mentioned as a factor in the thread? I was totally confused by this.

All you need to do is follow common engineering practices:

- no stainless steel in (semi) submerged applications

- insulate all different conductive materials incl. carbon fiber

- extra attention for applications where stainless steel is caulked or otherwise starved for air. When there is a possibility of it getting wet, crevice corrosion is a matter of time.

I recently did a carbon fiber project and studied ways to insulate it from other metals. On Amazon and others you can buy fiberglass insulation sleeves meant for electrical work which can be put around fasteners (make the hole larger to accommodate the sleeve). Also, you can wet out (with epoxy) a single piece of lightweight fiberglass (4 or 6 ounce) tape pressed in between some weights protected by packing tape. When cured you can cut it even with scissors, use hole saws etc. to shape it into gaskets, washers etc.

In the end I opted to use Dyneema lashings for old school but high tech fasteners and used G10 material shaped by table saw and attached by VHB tape after everything was painted to be between the carbon fiber and stainless steel, with the lashings holding it in place.

[thinwater]

Originally Posted by wsmurdoch

Did Thinwater say that? I missed it.

Bill

(re. carbon)


Yes, that was me, perhaps on a different thread or by some private email. These are home-built from plans and the plans called for carbon in certain locations, including the beams.

In reviewing images, the corrosion on these boat is far worse than the factory (Corsair) boats of the same age and very similar design ... but less carbon (all of them use it a few places, for example under the mast, since there is no compression post and no keel to transfer the compression to).


My Corsair has very little carbon and none of it in places that are penetrated by bolts, so I didn't think of it.

[dlj]

Originally Posted by s/v Jedi

Aha. So the carbon fiber wasn’t mentioned as a factor in the thread? I was totally confused by this.

All you need to do is follow common engineering practices:

no stainless steel in (semi) submerged applications

This is incorrect – You have splash zones, tidal zones and submerged zones. These fasteners would be in the splash zone.

Quoting from “The Corrosion of Metals in the Marine Environments” by Fink and Boyd, written for Defense Metals Information Center at Batelle Memorial Institute, page 25:

(in the section titled) Splash

The stainless steels, as a group, usually do well in the Splash zone...

(in the section titled) Tide

Of the stainless steels, only the austenitic grades are normally considered for seawater service. However, in the tide zone, the poor behavior is illustrated in the results given in Table 22. (I'm not going to put the table in here.)

(in the section titled) Submerged

Special measures are required if stainless steels are to be employed, without failure, under immersed conditions in seawater.

Respectfully,

dj

[s/v Jedi]

Originally Posted by dlj

This is incorrect – You have splash zones, tidal zones and submerged zones. These fasteners would be in the splash zone.

Quoting from “The Corrosion of Metals in the Marine Environments” by Fink and Boyd, written for Defense Metals Information Center at Batelle Memorial Institute, page 25:

(in the section titled) Splash

The stainless steels, as a group, usually do well in the Splash zone...

(in the section titled) Tide

Of the stainless steels, only the austenitic grades are normally considered for seawater service. However, in the tide zone, the poor behavior is illustrated in the results given in Table 22. (I'm not going to put the table in here.)

(in the section titled) Submerged

Special measures are required if stainless steels are to be employed, without failure, under immersed conditions in seawater.

Respectfully,

dj

In (semi) submerged applications, do not use stainless steel. You can do whatever you want but that doesn’t change my recommendation nor does what anyone writes. I am sure many experts will agree with my opinion but I can’t be bothered to go find them.

Stainless steel needs full contact with the air. Not good for anaerobic applications.

[skipperpete]

Originally Posted by s/v Jedi

In (semi) submerged applications, do not use stainless steel. You can do whatever you want but that doesn’t change my recommendation nor does what anyone writes. I am sure many experts will agree with my opinion but I can’t be bothered to go find them.

Stainless steel needs full contact with the air. Not good for anaerobic applications.

Hmmm,….propeller shafts????

[dlj]

Originally Posted by s/v Jedi

In (semi) submerged applications, do not use stainless steel. You can do whatever you want but that doesn’t change my recommendation nor does what anyone writes. I am sure many experts will agree with my opinion but I can’t be bothered to go find them.

Stainless steel needs full contact with the air. Not good for anaerobic applications.

No worries, I'm not trying to convince you of anything. I'm just putting out there documented facts, not myths. This is a public forum and many other folks are reading and need to make their own choices. I prefer to provide have data-based information.

dj