Non-Magnetic Metallic Material For 1-Core Power Cable Armouring

[Rejeckted]

Hello Dear Friends,

As the title suggests i am looking for Non-Magnetic Metallic Material For 1-Core Power Cable Armouring. Generally Aluminum is preferred for it, but Al suffers from oxidation problems and corrodes in some environmental conditions. I have researched Austenitic Stainless Steel for our application, which is Non-Magnetic and AISI 316 also provides corrosion resistance.

Although under some temperature ranges it loses it Non-Magnetic Property and may behave as Paramagnetic (which causes Eddy Current and Hysteresis Loses in 1C Cables) I am trying to find documentation to support AISI 316 or Stainless Steel in General.

Can anyone recommend it from their experience? or guide me a bit. Cable Application is and not under Sea/ Marine. Its underground but may come in contact to rainy water.

Thanks
Chri

 

[EdStainless]

You can't count on 304 and 316 being non-magnetic, especially if they have been cold worked. They are only meta-stable alloys. There are versions of 316 which will stay non-magnetic, but it take higher Ni content than is typical.
Some of the 200 SS grades are better at this, such as S20700 or S21904.
I have seen galvanized steel used for power cable sheathing, so the losses must not be very large.

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

Is metallic armor necessary? Conductive plastics may be your solution.

"It is shown that a very high level of shielding performance can be achieved by use of intrinsically conductive polymers"

https://onlinelibrary.wiley.com/doi/abs/10.1002/vnl.730140214

 

[Rejeckted]

GS steel Armour is only used for 3 Core cables because the vector sum of current generated field will be zero and hence no Induction of current in Armour.

But for single core it is necessary to use non magnetic armour. We are just wrapping the armour over the Inner Sheath (that should not count as cold work right? ) I need a grade of stainless steel or Aluminium which is corrosion resistant,non magnetic and doesn't lose its non magnetic structure. I am sure Austenitic Steels don't lose magnetic structure when heated (our max temp will be within 250 C during operation).

Can you help me with a grade which satisfy non magnetic properties and corrosion resistant. It is not a submarine cable, just underground cable so it may have only minute amounts of trace elements of Chloride etc

Thanks for helping me. Means a lot

 

[TugboatEng]

Stainless steel won't be corrosion resistant in direct burial. You'll need a copper alloy for that.

 

[Rejeckted]

There will be a PVC/ HDPE Layer over it. Also doesnt it say AISI SS is corrosion resistant and Marine Grade? Please suggest any other grade if necessary. Such that it is non-magnetic.

 

[TugboatEng]

Crevice corrosion. Stainless steel requires exposure to oxygen and flushing flow to remove debris to prevent corrosion. Stainless steel works great for pump impellers, not so much for stagnant tanks. If aluminum is failing in the application, stainless steel will also. They're both sensitive to crevice corrosion.

You say the cable is jacketed, why is the jacket allowing corrosion? I know cable can wick moisture over very long distances, perhaps better protecting the splices and terminations is all that is needed.

 

[Rejeckted]

Can we use Galvanized austenitic stainless steels, will it be Non-Magnetic? Also where to see its specifications?

 

[TugboatEng]

Lead would probably be your best option.

 

[EdStainless]

Lead is very common when H2S protection is needed. It works well.
Is this armor interlocking? (with a formed edge, if it is then it is cold worked) 316SS will not work.

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P.E. Metallurgy, consulting work welcomed