Check out my crack (SS cracks)

[Eigenvector]

A diagnosis of Crevice Corrosion or IGSCC from a picture? Please justify. Asking for a friend that does failure analysis for a living.

[Alita49DS]

Did you really mean to write "Check out my crack"?

I am minded to send the title to Private Eye to publish as one of their bring a laugh headlines.

[Seymore]

Originally Posted by boatpoker

Agree with the first 5 posters, SS crevice corrosion. It cannot be welded. There is much more corrosion on the inside. The sixth post advises you to look for "white" spider cracks. As a Certified Marine Corrosion Analyst, I've never seen any white corrosion on ss.

That's fine "white spider WEB cracks", not "white corrosion". I've seen lots pf 316 stainless steel with fine white spider WEB cracks.

When I bought my boat, I was walking along the dock and noticed the top half of a nut on the bowsprit turnbuckle, the sprit was sticking out over the dock at eye level, with the bottom half of the nut missing... I found white spider web cracks in five of the 11 turnbuckles, and replaced them all. The surveyor had missed the white spider web cracks. I put in a complaint (I would not have bought the boat if I had known about those corroded turnbuckles), the word got around, and the surveyor did not do any more surveys from that office.

Seymore
With a solid degree in chemical engineering (retired).
Last job was Hydraulic Engineer with a US city waterworks, including extensive corrosion work.

[boatpoker]

Originally Posted by Seymore

That's fine "white spider WEB cracks", not "white corrosion". I've seen lots pf 316 stainless steel with fine white spider WEB cracks.

When I bought my boat, I was walking along the dock and noticed the top half of a nut on the bowsprit turnbuckle, the sprit was sticking out over the dock at eye level, with the bottom half missing... I found white spider web cracks in five of the 11 turnbuckles, and replaced them all. The surveyor had missed the white spider web cracks. I put in a complaint (I would not have bought the boat if I had known about those corroded turnbuckles), the word got around, and the surveyor did not do any more surveys from that office.

Seymore
With a solid degree in chemical engineering (retired).
Last job was Hydraulic Engineer with a US city waterworks, including the corrosion work.

Guess that trumps my Certificarion as a Marine Corrosion Analyst. How about some photos of white corrosion on stainless so I can add them to my 10,000 photo library.

[SailRN]

I agree: Replace!

[jimbunyard]

That ain't a crack, it's a break. Gone pecawn...though it looks pretty localized, so a competent shop (or individual) could possibly repair it.

[seandepagnier]

Good luck finding teak, but sure you could make it out of wood or something. Other materials have various tradeoffs:
bronze: cost
duplex stainless/titanium: cost
aluminum: corrosion, harder to weld, physically larger (but lighter)
wood: weight
fiberglass/carbonfiber: I would consider as best option but requires proper engineering

If you are replacing it I would consider other materials besides stainless.

[Dan_K]

Eigenvector, from a photo we cannot perform a metallurgical failure analysis. My comments were from decades of doing thousands metallurgical cross-sections during failure investigations. In the photo it looks like the crack like indications are jagged as would be expected from a crack following grain boundaries . On many samples I have investigated with these crack like features seen on the surface, when performing a cross-section and looking at the microstructure, the cracks do follow the grain boundaries. In 316 stainless steel often this inter-granular cracking is caused by chromium carbides in the grain boundaries (which depletes the chromium in the grain adjacent to the grain boundary and verified by energy dispersive spectroscopy in an SEM). I hope this helps answer questions from your friend.

[Eigenvector]

Originally Posted by Dan_K

Eigenvector, from a photo we cannot perform a metallurgical failure analysis. My comments were from decades of doing thousands metallurgical cross-sections during failure investigations. In the photo it looks like the crack like indications are jagged as would be expected from a crack following grain boundaries . On many samples I have investigated with these crack like features seen on the surface, when performing a cross-section and looking at the microstructure, the cracks do follow the grain boundaries. In 316 stainless steel often this inter-granular cracking is caused by chromium carbides in the grain boundaries (which depletes the chromium in the grain adjacent to the grain boundary and verified by energy dispersive spectroscopy in an SEM). I hope this helps answer questions from your friend.

I would agree that a stamped report would contain micrographs at a minimum.

[col50]

Originally Posted by BigBeakie

I think maybe your tube is corroding from the inside. Following on from what Manateeman said, it appears the marine industry is OK with poor TIG welding practices wrt stainless tube welding. I've seen so many welded joints where the corrosion is coming through from the inside of the tube, it's Obviously just normal, poor welding practice.

When ss tube is argon TIG welded, the inside of the tube should be back flushed with argon during the welding, to prevent "sugaring" of the metal, which eliminates the anti corrosion properties of stainless. But the welders don't bother setting up the back flush to protect the inside surface from the heat.

EXACTLY

[capn ken]

wood is better!

[SuW]

Originally Posted by Manateeman

Exactly. It’s not difficult to keep argon on the backside of the weld. Some tape, argon, a few other tricks. Also the skill of the welder in heat control is very important. Preparing and cleaning in both aluminum and stainless TIG is critical to strong welds. Spend a little time just watching “Welding Tips and Tricks”.
You don’t need to understand everything...just learn to see what Jody points to in good and bad welds. Guys who weld for food or chemical plants have to get it right. Same with bicycles or motorcycles. Then there is post weld treatments.
Take your time. Quality work isn’t cheap but will last. I’ve seen poor quality stainless tube sell cheap. You can learn a lot just watching in a good shop. It’s your boat and it’s a keeper so please do it right.
Mark and the manatee crew.

What he said.

I live in a place with a big dairy industry, some great SS welders around here.