Galvanic Corrosion Test

[bmoorthy]

Hello All

Background:

The specification states that the Weld shall not be Anodic with respect to Base material, This statement appears as the acceptance criteria under Galvanic Corrosion Test of the Pipe Procurement specification.


Suppose the potential measured of the pipe base material is "- 0.5" and the potential of the weld is "-0.4" (I persume it is the potential that will be determined as the measure of Anodicity or Cathodicity), is the Weld Anodic with respect to Pipe.

 

[EdStainless]

Is there a test method listed?

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[bmoorthy]

That is one of the problem. There is no Standard Test method. The method of testing is as per the written practice of the user


Using SCE electrode and Test Solution is Sea Water (With H2s Purge)

 

[EdStainless]

Probably standard synthetic seawater, there is an ASTM for making it.
A standard saturated calumel electrode, not a big deal.
Then you have figure out how to set it all up.
Often you take the samples and mask them with epoxy, except ofor a controled size (1 sq cm)spot in the area of interest.
There is an ASTM for taking galvanic measurements, but I cant recall what it is.

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[mshimko]

Why not just make a large weld, cut out a sample, and connect it via a zero-resistance-ameter to the base metal in seawater, and see what direction current flows. That should be all that's needed to determine which material is anodic and cathodic.

 

[EdStainless]

You could, but it is just as much work. Cut smaples, bond lead wires, seal backs and edges, make sure that equal areas are exposed, then take measurements.

You can buy sample holders that use a gasket to expose a controled area. Of course you need flat samples.

Has your customer ever done this test themselves? Do they give resolution, precision limits?

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Rust never sleeps
Neither should your protection

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[mshimko]

Another question, perhaps related to the welding engineers: arn't most weld wires formulated so the resultant weld wire is slightly noble compared to the base metal?, and could this information be obtained from either the electrode manufacturer or one of the welding professional societies (AWS, Edison, etc)?

 

[RustBucket]

What are the metals you're using? There are tables to check anodic/cathodic relationships.