Dissimilar Metals Galvanic Corrosion: SS Tubing Connected to CS Pipe - Is it a concern?

J

Thread Starter

John

Hi,

In general connecting or touching dissimilar metal is not allowed due to galvanic erosion issues. What about the stainless steel instrument impulse line connected to the carbon steel process lines which is very common. I am aware that ideally an insulating mean (e.g. an insulating flange kit) can be used but that is not the common practice as it would be a very expensive practice if used all over the plant.

Another example is having carbon steel line with a stainless steel orifice plate where usually no insulating flange is used. Also looking at standard transmitters, for example in a Rosemount 3051, the aluminum case is not insulated from the SS process connection. There are numerous such examples. I have seen all these in Oil & Gas facilities for the past many years.

One can argue, the galvanic corrosion is a concern in presence of air and water but it is never guaranteed that this does not exist.

I am confused if the general practice of connecting SS tube to CS pipe is right or not. What about having SS orifice plate or SS valve in a CS line?

I appreciate if you could help me understand what the correct practice should be, keeping cost in mind.

Regards,
Ham
 
I am not a metallurgist, but I did sleep at a Holiday Inn once.

The difference between Cold Steel and Stainless Steel is not so dramatic that it becomes a concern in most cases. Especially as you indicated in the relatively "clean" environment of a modern factory.
There is more concern IMHO of galvanic activity between SS and say Aluminum or Copper.
 
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