Pitting of Stainless Steels 1

[TugboatEng]

Who is going to tell them?

https://phys.org/news/2024-03-uncover-culprits-pitting-corrosion-3d.amp

Stainless steel 316L is a popular choice for marine applications due to its excellent combination of mechanical strength and corrosion resistance.

I know this is a bit out of place but it seems we all need a refresher on the weaknesses or stainless steel from time to time. I wonder who it was that attached the description of "marine grade" to type 316. I have some strong words for them

 

[EdStainless]

Sure, they use it on high end yachts where there are people to wash and wax it regularly.
My nightmare application is 316 right on the coast and under a roof where rain can't rinse it off.
Combine this with handrails that are flat and hold water, and welds that form traps for debris and your installation will be rusting within a few weeks.
The nightly salt fog will assure that all surfaces are covered with concentrated salt solution very quickly.
If it is out in the open and drains well then it might last for years.

Did work with an architect in Maimi once. He had an old house on the coast that was surrounded by a nice metal fence.
The fence was all Monel 400.
He wanted to add a gate.
We supplied him with AL-6XN tubing to fabricate it.
The scrap value of his fence and gate was more than my house.

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

I wonder about the development of 300 series stainless. It seems the 400 series was developed during the 19'teens for cutlery.

https://bssa.org.uk/bssa_articles/t...Brearley made,the first ever stainless steel.

This article mentions a boat constructed from this stainless steel but also said it is now sunk, possibly due to pitting corrosion. I have read of a sailboat built from Monel. It did survive for a very long time and may still be floating. I need to dig for the articles. It did experience some problems related to cracking but may still be floating today.

Lots of thermal expansion can be more trouble than corrosion for larger structures.

 

[EdStainless]

The first SS grades were the martensitic 400 types.
These are still used for cutlery today, and 440C makes fine knife blades.
They knew about austenitics but had no way in mass production to keep the C low enough to prevent sensitization.
Once they had that tool (precursor to AOD) they could make both austenitic and ferritic grades.
While there was a lot of development in the pre-war years things really took off in the 50's.
The steel mills were all trying to develop proprietary grades and chemical companies were busy developing ferritic SS and Ni alloys for special applications.
Of course, this was back in the days when Ni prices were set for a year at a time and even then rarely changed.
By the time we get to 1980 and political unrest in Africa and metal prices went crazy.
I remember Co going from $4 to $40/pb in about 6 months.


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P.E. Metallurgy, consulting work welcomed