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Galvanic Corrosion Between Stainless Steel And Carbon Steel

01/26/2016 12:20 AM

friends, do we have any standards or reference for the Galvanic corrosion between stainless steel and Carbon steel welding.

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#1

Re: Galvanic corrosion between stainless steel and Carbon steel

01/26/2016 4:23 AM

Undefined: the word <...we...> is currently meaningless.

Galvanic corrosion normally takes place between some combinations of dissimilar metals when they are both in contact with an electrolyte.

The principal metals in this case are fundamentally iron and iron. There is little difference between stainless steel and carbon steel beyond the proportions of the alloying elements, however there will be subtle variations in structure where the two have been welded together.

At present there is no indication of the electrolyte, its temperature or its pressure. One might expect a difference in performance were it to be aqueous caustic soda at 8degC on the one hand and dilute sulphuric acid at 80degC on the other.

The reason for having dissimilar metals in contact with an electrolyte in the first place remains a darkly-veiled mystery to all other CR4 readers. It would be a rare, and therefore poorly-deigned, process plant for this situation to arise.

So the question as written is unanswerable.

One of the possibilities is to use a corrosion chart, such as the on-line Cole-Parmer materials compatibility database [usual disclaimer] to assess the risk. Another is to carry out extended testing of a sample weld in a sample electrolyte.

Other than that, this is a good question for a search engine such as Google.

Good luck with all that.

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#2

Re: Galvanic corrosion between stainless steel and Carbon steel

01/26/2016 4:49 AM

You could always purchase a membership in NACE (National Association of Corrosion Engineers) and get the latest scoop on this. I don't know whether that would be economically justified, though; it is only a suggestion.

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#3

Re: Galvanic corrosion between stainless steel and Carbon steel

01/26/2016 7:00 AM

http://www.ewp.rpi.edu/hartford/~turnem4/EP/Other/Primary%20Resources/galvanic%20corrosion.pdf

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#4

Re: Galvanic corrosion between stainless steel and Carbon steel

01/26/2016 7:18 AM

Looking at the anodic/cathodic chart hanging on my wall, Cs has a value of -.6 (less noble) and SS has a value of -.1 (most noble). Corrosion may not be the major parameter but fusion can be due to the two different melt temperatures.

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#5
In reply to #4

Re: Galvanic corrosion between stainless steel and Carbon steel

01/26/2016 8:17 AM

From my experience in cathodic protection, a carbon weld on stainless metal would create a galvanic cell. Like TexasRon said the value of -.6 and -.1 are not too significant but it doesn't take much. Any potential difference will set up a cell in an electrolyte.

You could use a cathodic protection system and depending on the size of your structure you may get away with a passive system using a zinc or magnesium anode or you may have to use an impressed current system. If you paint the surfaces with a good epoxy coating you will need less anode or less current, but don't think any coating you put on is perfect. It only takes one pinhole (or holiday) in the coating to start corrosion; there have been many pipeline failures due to ineffective cathodic protection and small defects in coatings.

Drew K

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#6

Re: Galvanic corrosion between stainless steel and Carbon steel

01/26/2016 8:25 AM

Google electromotive series or galvanic series charts.

One type looks like this:

You welding question is not clear.

You can easily join the two steels by welding. I have done it personally many times.

I have several carbon steel plates welded to stainless steel bases with carbon steel wire that have been outside for over 10 years, unprotected in any way. They look the same today as they did 10 years ago. Mind you, this is in air, exposed only to rainwater and the occasional dog. Not in a chemical fluid environment.

The heat transfer characteristics of the two steels are different, but this is not difficult overcome for a good welder.

The internet is a good place to look for answers to common questions such as this one.

You do not provide sufficient information!

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#7
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Re: Galvanic corrosion between stainless steel and Carbon steel

01/26/2016 10:01 AM

lyn, was that a TIG weld?

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#8
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Re: Galvanic corrosion between stainless steel and Carbon steel

01/26/2016 12:08 PM

A shop I worked in for a few months where the TIG welder used cs or ss rods indiscriminately when making shop structures. He is one of the best welders I have ever watched work (and I have seen some awesome pipeline welding upside down on a leaking pipe using a rear view mirror from their truck).

Drew K

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#10
In reply to #7

Re: Galvanic corrosion between stainless steel and Carbon steel

01/26/2016 2:25 PM

MIG with flux core wire, no gas. E-71, I think.

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#11
In reply to #7

Re: Galvanic corrosion between stainless steel and Carbon steel

02/03/2016 11:26 PM

At several chemical sites I worked at we had "sample" cooling condensers made by taking a St Stl pipe and a Carbon Steel and manipulating the outer CS pipe to form a jacket on it. Two half couplings were ground to match the side of the outer pipe. Holes were created on the sides of opposite ends of the outer CS pipe and welded to this pipe. The ends of the CS pipe were cut with tapered slots to facilitate a reduction in size. The ends of this CS pipe were then formed, with a ball-pein hammer and heat into a taper around the St Stl pipe. These were then welded, with stainless sticks, together and to the inner pipe forming a seal between the pipes. The finished piece looked similar to a laboratory condenser and functioned identical to the lab unit. Sticks were used since not all the "welders" could TIG weld.

In making these the carbon steel was easier to work with and didn't need the corrosion resistance of stainless steel.

Of note also, whenever welding carbon steel to stainless or different grades of stainless to each other always use a stick, wire, filler rod, etc. of the better grade of metal. Example: CD to 304 St Stl, use the St Stl 304 welding rod, wire, filler material, etc.

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#9

Re: Galvanic Corrosion Between Stainless Steel And Carbon Steel

01/26/2016 1:12 PM
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BubbleRob (1); Drew K (2); lyn (2); old salt (1); PWSlack (1); texasron (2); Tornado (1); Whitephone (1)

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