Can External SCC be Arrested on A312 TP304L Pipe? 3

[Bambie]

At our plant, external examination of a section of A312TP304L boiler blowdown pipe detected the onset of stress corrosion cracking.
Is there anything that can be done to arrest this cracking mechanism or is whole sale replacement the only option?

 

[EdStainless]

The Al will provide some measure of galvanic protection, and proper insulation (with external jacket) will work fine.
Looks like you got to the bottom of this.

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P.E. Metallurgy, Plymouth Tube

 

[Bambie]

EdStainless,

We are attempting to find more information on VEDAGUARD wrap.

Have you any details on this type of cathodic protection such as material specification, thickness and how to determine the number of wraps required depending on chloride or halide concentration?

 

[EdStainless]

Al foil wrap has long been a back-up protection under insulation.
It is just there as a precaution, you should be able to remove 10 year old insulation and find the foil still intact.
I don't know that adding more would help.
You should have drain holes and inspection ports that you check.
Once you find moisture under insulation it is time to strip it and fix things.

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P.E. Metallurgy, Plymouth Tube

 

[Bambie]

EdStainless,

I found this 1961 Oak Ridge National Laboratory Report (attached) with some helpful advice:

"After cleaning, aluminum sacrificial anode foil shall be wrapped tightly on the surfaces of the pipelines in a helix with a 1/2-in. overlap at the edges. The aluminum foil shall conform to alloy 1100 or alloy 1145. The final aluminum wrapping shall have a minimum thickness of 0.010 in.
If multilayers are used, each succeeding layer shall cover the joints in the previous layer by starting each layer in the mid-point of the previous foil sheet. Soft aluminum alloy 1100 wire approximately 0.062-in. diameter shall be wound and twisted on the completed foil layers to hold the foil in place. Aluminum wire loops shall be placed on approximately 18-in. centers. Aluminum foil shall be fitted to the contours of the irregularly shaped components in such a, way as to give a 0.010-in. thickness, and the foil then should be secured with aluminum wire."

 

[EdStainless]

I have seen Al foil tape used to hold it also.
But you only use tape on the top surface, so that if any water gets in it can drain/

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P.E. Metallurgy, Plymouth Tube