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Stainless steel more corroded in sea water than steel?

 

First of all thanks for this web that I tried a lot to find such a web. My question is about corrosion of Stainless steel in sea water , Is it higher than it for normal steel, because in my graduation project I found that it is higher rates than it for steel.

Thank you again,

Moeed Sa'ad Algarny
Student in King AbdlAziz University KAAU - K.S.A. , Jeddah city

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Hi Moeed !

I just cannot believe that some people 'found' that stainless in salt water corrodes more quickly than iron/steel. Total utter hogwash!

Any ferric compound containing nickel will be, depending on the percentage, more resistant to saline conditions than ordinary 'steel'.

The problems with s.s. and salt water concern the welding. If you have an alloy with 4 main ingredients as in s.s. 3l6, (Fe, Ni, Cr, Mo)they will all have 4 different melting points, won't they? Hence when welding, you are bound to exceed some of those melting points ...and if you do that, what happens? Nothing? NO! You will get some alloys disappearing/evaporating ... or as one metallurgist put it succinctly, 'denuding'. Ergo, Mister Student, the alloy will change its properties and structure somewhat ... and sometimes detrimentally and problems can occur at welds. Poor old Saudi Arabia had problems of this sort, see the archives # 7117.

Mind you, if you want a material to be UTTERLY resistant to salt water ... use PVC & many other plastics! Then you won't get into hot water, will you!

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

Hi Moeed,

I understand you to say that you have performed some tests to compare the rate of corrosion in sea water of a stainless steel with that of a normal steel, and that the stainless steel corroded faster. If this is a matter of observation and measurement, then it is what actually happened and it is not hogwash, although it is certainly a different result from the usual.

Because it is a different result from usual, you need to examine the sample preparation and testing procedure closely to find what other aspect exists, that you have not seen up until now, that could cause the unusual result.

What grade was the stainless steel? What heat-treatment condition was the stainless steel? What grade was the "normal" steel? What heat-treatment condition was the "normal" steel? What surface preparation for each material (machining? grinding? polishing?)? What size and shape of samples? Were the different materials tested in the same water at the same temperature? What temperature? What property did you measure to determine the amount of corrosion? These questions will do for a start. Depending on the answers, there might be more questions that need to be asked.

Tell me the answers to these questions and I will see if I can point you in the right direction.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.

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Wotcher Bill,

I said hogwash and I sure meant it. Mind you, one could have said poppycock or fiddlesticks but they are not in common parlance.

One can fiddle and get wrong results with, I guess, most metals. But the crux of this rebuttal was that a blanket statement was made which was totally erroneous.

You are right to point out that it depends HOW those tests were done.... apparently most incorrectly.

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

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G'day mate Freeman,

Yes, it's a tricky decision sometimes, how to respond if at all. There are so many amateur queries where it's obvious the inquirer simply hasn't a clue on the subject and wouldn't understand any answer, so there's not really any point in trying with such enquiries - how Ted Mooney and Tom Pullizzi keep their cool is amazing!

But if it's a student who hasn't yet learned enough to sort it out for himself but who seems as though he genuinely wants to progress, then I like to help a bit if possible. Not by handing out the answers to homework or projects, but by steering them to the aspects they should check out further. They should be able to go to their lecturer or supervisor, but that's not always useful, I'm afraid.

Cheers,

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.

I suggest you look at the Mcnally institute website, it is quite commonly known within the marine industry that some stainless steels especially in the 300 series will corrode and fail faster that mild steel or carbon steel and its use below water is limited and is nearly always subject to protection from corrosion via coatings and/or sacrificial anodes.

David Jones
- JiangMen, GuangDong, P R China
July 25, 2008

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Q. Hi Sir,

I want to know process corrosion by chloride if the material is carbon steel.
If the environment is salt water (not seawater), could carbon steel be corroded?
Corrosion rate for carbon steel in salt water (not seawater) formula or calculation of corrosion rate for carbon steel?

thanks for your information.

Ita Puspa
- Indonesia
June 1, 2012