Flange Isolation Kit

Try here, I think this is what you are talking about.

http://www.apsonline.com/gasket.html

Flange isolation kits are used to isolate the mating surfaces of two dissimilar joining flanges like SS316 flange to a CS flange on a vessel or tank. This is mainly used for the prevention of galvanic corrossion. When these flanges come in contact with the process fluid, an electrochemical reaction takes place and an electromitive force (emf) is developed which serves as the driving force for electrochemical corrossion.

The isolation kit consists of a full faced isolating & sealing neoprene/ phenolic gasket, phenolic washers and an insulating bolt sleeve (mostly mylar) depending upon the process fluid. Various material combinations are available depending on the process conditions which you will be able to refer using the google search engine for "flange isolating kits". Also if you have access to NACE training manual, you could get a more detailed reference.

Although the above explanation is good, I would like to add the following:

- Flange isolation kits are commonly found on the joint of a piping system nearest where the system "goes underground". This is a prime location for corrosion due to stray currents.

- Your example of a need for "carbon steel to stainless steel" flange isolation kit is in error. There is not enough electrical potential difference between these two materials according to the galvanic series. This need for such protection has taken on the character of an "urban myth".....there is no justification for such protection. Its just a mistake that is repeated over and over. Review the galvanic series chart and review a copy of the book "Defects and failures in Pressure Vessels and Piping" by Helmut Thielch.

-

Begging to differ a bit, here, "semantically-speaking"...

Re: "...the joint of a piping system nearest where the system "goes underground"... is a prime location for corrosion due to stray currents."

Certainly stray currents can be problematic, as learned many decades ago via the perforation of water mains that had electric trolley cars installed above ... and reiterated many times since then by many instances of improper grounding during welding operations. The point that might-ought to be stressed in this case is that corrosion from stray currents WILL take place wherever the current can *discharge* from the pipeline-to-earth; that point or points being any holidays in the protective coating ... not necessarily, nor specifically just at the point where the pipeline "goes underground".

And, regarding the "urban myth" of CS-SS galvanic corrosion ... see the photograph placed in Post #12 at This Thread.

While it is true that a CS pipe connected to a SS pipe inside of a manufacturing facility ; 'climate-controlled', and carrying lubricating oil, glycol, or other innocuous fluid will most likely NEVER suffer ANY corrosion ... there most certainly IS a sufficient difference in potential for corrosion (anywhere from moderate to severe) to occur between these two materials. And, the more concentrated the positive ions are, in whatever electrolyte might be common between the two; and, the greater the cathode:anode ratio is (surface-area-wise) ... the greater will be the rate of corrosion.

The OP did not clarify WHY he was inquiring about isolation flanges ... as in "WHERE" one might be needed, or for what purpose...

[could it be for isolating the CP system of an existing pipeline from a new one that is being "hot-tapped" into it...?]

Without additional information, a complete-and-acceptably-thorough response simply cannot be made (without posting volumes of information).

However, we should always be careful that we do not exacerbate any current misunderstandings (or total lack-of understanding).

ndt...

Thank you for your response and valuable link.......but I think we still have a difference of opinion (or semantics) here.

And, I am willing to admit I should have been a bit more "ultra specific" in my statement.

While I am both familiar with and respectful of the "area effect" (huge cathode - small anode) will cause CS/SS corrosion, (This is why ASME welding shops segregate the two materials) I do not believe that the original poster has this situation.

I understand his situation as two equal-area piping flanges in a piping system.

I also do not understand his question as a situation where CS/SS crevice corrosion can occur. (this may be a matter of opinion, though...depends on the gasketing).

I stand by my statement....no real galvanic couple....no need for a flange isolation kit.

If you can provide me many instances where CS/SS piping flanges completely and rapidly corrode, I can be conviced otherwise......but your referenced thread does not convice me.

More references available ?

-MJC

Greetings ~

From my own personal experiences, I cannot provide you with "...many instances where CS/SS piping flanges completely and rapidly corrode..." , and thus, you may have to remain unconvinced. Especially if you mean 100% total dissolution of the CS pipe/flange within a matter of minutes, days, weeks...

Corrosion is corrosion is corrosion ... and engineering so as to prevent corrosion is the challenge for the Corrosion Engineer (NACE ~ National Association of Corrosion Engineers International ~ a great place to start).

Corrosion costs our economy billions of dollars annually, because of lessons learned in the past, which we keep on repeating.

Recognition of this (preventable) loss to our economy has brought about an effort in Congress to legislate action against ignorance through a "Corrosion Tax Credit" for businesses that invest in corrosion prevention technologies (to protect their own investments/assets).

No plumber worth his license would DARE to couple-up any new copper plumbing to an older residence's original iron pipe... (except the guy who "updated" the house that *I* bought...!) That's the extent of my own, personal experience (granted, not exactly germane to the OP).

Thus, I 'bow' to the experienced experts with lots of "Hands-On" experience:

How many engineers ... having read any of "The Basic Fundamentals" from any given source ... would specify coupling stainless pipe (or what-have-you) to carbon steel pipe (or what-have-you) WITHOUT any kind of isolation ... and anticipate expect guarantee any longevity out of it...?

[of course ... the above query refers to a specification OUTSIDE the hypothetical arena mentioned in the post up above.]

_______________________________________________________________

"Share what you DO know ... learn what you don't..." (from 'somewhere' out there).

have a look at this for flange isolating kit:

http://www.farwestcorrosion.com/ccp/flange/psi7.htm

regarding the issue of galvanic corrosion, CS/SS, i don't think taht it's a urban mith.. i mean is something that should be carefully evaluated, it depends on many factors like the type of fluid, oxygen content..

S