CORROSION IN ELECTRICAL CONNECTION BOX 3

[341968]

Dear All,

We have two Regeneration Heaters at our Nitrogen Plant, one stay in operation and the other in stand-by mode.these heaters are used to heat waste Nitrogen above 200 deg.C and exhaust into the atmosphere. We opened Electrical Connection Box of the one heater(Already in stand-by mode for almost one year). I saw all the connection terminals (Nuts and Bolts were heavily corroded.

The stand-by heater remain isolated in the system that is Valve in block position. Only small quantity of waste Nitrogen, that is most of it oxygen remain inside heater column till it comes back in operation.

Please see these photos-1:

lately we put this heater in operation and stop the other heater. This heater was continuously working for one year. We fond its connection terminals slightly corroded. please see the following photos-2:

The copper bars in both cases were neat and clean. only nuts and bolts (I am not sure but may be of carbon steel) were corroded.

The ambient condition of our plant is here under.

now my question is that the internal tubes of heater in column are also corroded or seal due to aging (15-years), have have been deteriorated and waste nitrogen (mostly oxygen) is leaking into to connection box and causing oxidation. Please see this photo.

or this is anode-cathode reaction where carbon steel bolts are acting as sacrificial anode to protect the copper buses as cathode.

The connection box is Ex-Proof. I do not think that the external air or atmospheric oxygen enters into connection box.

Your expertise shall be highly appreciated to diagnose the true cause of this corrosion. Please feel free to ask any info you may require.

Best Regards

 

[341968]

PHOTO-1

 

[341968]

PHOTO-2

 

[341968]

AMBIENT CONDITIONS

 

[Compositepro]

Looks like rusting due to moisture. Galvanic corrosion may also be occurring.

 

[EdStainless]

The superficial rust on the tubes does not concern me.
All of the rust in both locations if due to moisture.
The electrical box breaths as it heats and cools each day and night.
This will provide enough moisture to cause the corrosion of plain steel parts.
Why the bolts are steel is beyond me, I would have thought that they would have been bronze.
Perhaps some way to keep the standby box heated would help minimize corrosion.
I would also think that swapping units every few months would be a good practice. It would level the wear and assure you that they both worked well. At least you would find out if you had a problem before you absolutely needed to use it.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[341968]

Dear EdStainless,
Thank you for your expertise and recommendation. You technical assessment is very right. Due to assembly constraints, we have no choice to replace the bolts, but we will ask manufacturer to send us new heaters with copper alloy/bronze bolts. We will ask manufacturer to give us better water tight seal rather than the existing very thin O-ring. Additionally, to mitigate moisture, we will see the possibility to install space heater inside connection box.
Thanks to Compositepro, for adding valuable expertise.
Best Regards

 

[ScottyUK]

You should consider fitting a suitably-certified breather to a spare entry. This will allow the box to breathe and prevent the well-known problem alluded to by EdStainless. Not sure what certification that box has - Ex'n' perhaps? - but as you have already Hawke cable glands one of these types should be suitable:

http://www.ehawke.com/accessories/389.html

http://www.ehawke.com/accessories/489.html

You might additionally consider using a right-angle adaptor to ensure the breather faces downward.

http://www.ehawke.com/accessories/494.html

Note that the second one is specific to Ex'd' enclosures, and although you used the phrase 'Ex-Proof' in your post, the construction of that enclosure looks too light to be a flameproof / Ex'd' design.

 

[341968]

Dear ScottyUK,
Thank you so much, you have proposed one of very good solution. We will sure look into it deeply and see its implementation. for me it is new indeed. Thanks again.
Attach here with two technical docs.

 

[341968]

Assembly Drawing