Bonding and Galvanic corrosion

[kenaslan]

Here is my situation.

A carbon steel above ground oil pipeline is connected to a stainless meter pipe, then back to a carbon steel pipe is understandably having internal galvanic corrosion issues. The mechanical guys want to put isolation flanges in and have no conductivity whatsoever. They believe that a bonding jumper will once again cause the galvanic corrosion, and want to completely isolate the SS meter pipe. This is in a C1D1 area.

My understanding is that a bonding jumper should be at the flanges to prevent arc-over at the flanges from a nearby lighting strike. I also believe, and please correct me if I am wrong, that the friction of oil passing through an electrically ungrounded/bonded pipe will slowly cause a static charge buildup in the pipe between the two dialectic isolation flanges like a capacitor. Also 250 states "The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed.”

 

[drcampbell]

Carbon steel and stainless steel are not dissimilar enough to establish much of a galvanic potential, and oil is a non-polar molecule that will not support galvanic corrosion anyway. Electrical isolation will have little or no effect.

There's something else going on, perhaps sulfur or acid in the oil. I suggest you ask a chemical engineer for a consultation.

 

[kenaslan]

Found the answer in API. Yes SS and Carbon steel will cause galvanic corrosion, and there are many charts showing the amount, and yes the isolated section of SS must be bonded to prevent both arc over from a lighting strike and static buildup from the oil flowing through the pipe. Also as this is a C1D1 location NEC requires bonding as well.