Insulation flange

[europipe]

I have to route a 6” CS pipe underground, then above ground connected to a ss 316L pipe, do I need an insulation flange for this connection?
Thanks in advance for your replies.

 

[BigInch]

You need an "isolation" flange. Regardless of the dissimilar metal corrosion, its more important to break the many possible ground current sources from affecting the plant piping or v/v.

http://virtualpipeline.spaces.msn.com

 

[SJones]

Since you are taking a carbon steel pipe underground, it is likely that you will be thinking of applying CP. If you do apply CP, you won't want the current flying down to whatever the carbon steel pipe or the stainless pipe is connected to; so, you would look at isolating at both ends of the carbon steel pipe. You don't actually say what is on the inside of the pipe. If it is a conductive fluid, you will need coated insulating spools of a certain length instead of flanges.

Neglecting CP, one could consider an insulating flange arrangement if the fluid conductivity warranted it but then reliability and maintenance would have to be factored into the equation as well as connections to a common earth (if both sides of the joint see the same earth then insulation is a waste of time). An alternative would be to weld overlay the carbon steel flange.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[europipe]

Steve, the medium that goes through is nat.gas,
excuse me for my ignorance, but what is cp?
Both thank you for your helpful replies.

 

[SJones]

Cathodic Protection

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[europipe]

I´ve done some thinking (very difficult for me) but when you say that if both parts are connected to the earth it has no use.
But the above ground part is connected with the earth (shoes-bridge),
So my conclusion is that it has no use to provide insul/isol.(?) flanges.

 

[khardy]

I would talk to a corrosion speciallist about this. They should be able to specify exactly what you need in terms of cathodic protection including isolation flanges.

 

[11echo]

Kill two birds with one stone here, use an "insulation gasket kit" here! This will solve the problem of dissimilar metals, and the problem of ground current sources (as BigInch has pointed out) and at minium cost. You can talk with your corrosion people and see "IF" cathodic protection is required or not.

 

[BigInch]

Pipe will pick up and carry electrical currents from many sources, passing parallel to HV electrical lines, railroad electrics, third party's cathodic protection currents, etc. and carry them long distances and on into a plant or pump station, if the two are not isolated from one another. True a station area will be subject to ground current sources, but being isolated from the pipeline voltages, current won't cross the line and any problem can usually be reduced to manageable levels, as you only have to deal with local current sources.

http://virtualpipeline.spaces.msn.com

 

[SJones]

Europipe: electrical earth NOT 'earth' as in soil! If you put an insulating flange in the line, and the two sides of the flange are connected to the same earth, you won't have isolation.

Anyway, what is the driver for carbon steel being connected to stainless steel in the first place?

It would also pay you to look at NACE RP0169 for dealing with the buried section of pipe.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[LSThill]

europipe (Chemical)


NACE REFERENCE READING:
CORROSION ENGINEERING Fontana and Greene
The Corrosion Handbook, Herbert H. Uhlig
Process Instruments and Control Handbook
Localized Corrosion NACE Publication
METALS SECTION Corrosion Data Survey

NACE TRAINING:

NATONAL ASSOCATION OF CORROSION ENGINEER’S:
CORROSION PREVENTION BY CATHODIC PROTECTION, HOUSTON, TEXAS

NATONAL ASSOCATION OF CORROSION ENGINEER’S:
CORROSION PREVENTION IN OIL& GAS PRODUCTION, HOUSTON, TEXAS

NATONAL ASSOCATION OF CORROSION ENGINEER’S:
BASIC CORROSION COURSE, HOUSTON TEXAS

Leonard Stephen Thill

 

[dcasto]

If the line is in a plant yard, and if the line goes underground for less than 100', I'd just coat and wrap it and use maybe 1/8" corrosion allowance. Maybe put a mag anode on it, maybe. There are even proceedure to weld 3XX SS to CS, so no flange even.