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Associate

Join Date: Feb 2017
Posts: 28

Regeneration Heater Electrical Connection Box Corrosion

10/06/2017 9:20 AM

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:

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:

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

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Guru
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#1

Re: Regeneration Heater Electrical Connection Box Corrosion

10/06/2017 10:59 AM

Why are you heating the nitrogen before venting it to atmosphere?

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Guru

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#2

Re: Regeneration Heater Electrical Connection Box Corrosion

10/06/2017 12:18 PM

Dissimilar metals(with bigger group gaps or differences) in contact with one another will effect fast corrosion on any of the two metal. I think this is term as galvanic corrosion.

One way of dealing this change the bolts and nuts. If its ok use stainless steel or an alloy closer or just neighbor to copper in the table of elements

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#3

Re: Regeneration Heater Electrical Connection Box Corrosion

10/06/2017 3:53 PM

You might do a cost analysis of life cycle extension with suitable coating to protect the metal....

http://www.praxairsurfacetechnologies.com/solutions-for-your-industry/solving-common-challenges/corrosion

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#4

Re: Regeneration Heater Electrical Connection Box Corrosion

10/06/2017 9:49 PM

"Explosion proof" does NOT mean an enclosure is air and water tight! All it means is that IF there is an ignition of gasses that got into the enclosure, the hot gasses would cool sufficiently as they pass across the flange so as to not cause ignition outside of the box. You CAN also add a water tight seal to an Ex-proof box flange, usually done with an O-Ring seal. But if you did not order it that way, you did not get that.

if it were my equipment, I would come up with a simple means to alternate the two sets of heaters so that they get even wear and tear, which would also serve to expel moisture from the connection boxes periodically. If that's not possible for some reason, then add a space heater in that connection box.

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Associate

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#5
In reply to #4

Re: Regeneration Heater Electrical Connection Box Corrosion

10/08/2017 2:03 AM

Dear All,

With our mutual and with corrosion/chemical engineers, I agree that this corrosion was 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.

We have also two heaters, so swap at regular interval is mandatory. Due to heater's assembly constraint we can not replace the corroded bolts, but we will ask the manufacturer to supply new heaters with copper alloy/bronze bolts, with a tight water seal. We would think the possibility to install space heater inside the connection box. During each annual PM, we will grease the bolts.

Thanks to you all, great expertise and recommendations.

Stay safe and blessed.

Best Regard

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