Electrical Isolation - Northeast Gas Association
Transcript of Electrical Isolation - Northeast Gas Association
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Electrical Isolation Applications
By Michael PieciukYankee Gas / NorthEast Utilities
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NOTE
Although this subject matter is so broad, and is present throughout so many various industries; I’m going to concentrate this presentation on the GAS industry, with the bulk of the information favoring the distribution networks.
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The 5 ‘W’s
Why do we use it or Why do we need it What exactly is electric isolation When do we use it Where do we use it Woes’ (needed a 5th “W”)
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Why
Within the Gas Industry we find the need to electrically isolate segments of pipe.
We want this isolation to stop/restrict the flow of current. We stop the flow of current, we stop (in theory) the loss of metal.
This need especially becomes critical when the science of ‘cathodic protection’ (CP) is applied to our structures.
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The Basic Corrosion Cell
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The Basic “D” type Battery
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Simple DC circuit
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Simple DC circuit
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Corrosion Cell
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Corrosion Cell
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What
What exactly is electrical isolation: it’s a barrier/gap that exists within an electrical path.
This barrier/gap restricts the flow of electrons or in electrical terms= NO current flow.
But for our industry, we can’t have an open section of pipe.
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What
We create this barrier or gap, by a NON-conductive material or sometimes by air.
This is usually incorporated in the form of a gasket into a union, coupling or flange.
Or we may use a ‘monolithic’ type insulator that creates a gap between two sections of pipe, surrounded by a fiberglass shield.
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Installing an Insulating Coupling
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Note
Now although we create this barrier/ gap; we still, in most cases, have a mechanical connection. Or a continuous path for gas flow.
So, in order to maintain a sealed connection for gas flow, our barrier/gap has to be quite thin.
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Mechanical Insulating Coupling
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Typical Insulated Flange Assembly
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Typical Insulated Union
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Some of the common materials for this gasket
1) neoprene faced (most common) 2) glass epoxy with a seal element 3) canvas cotton fabric (phenolic) 4) silicon glass with a sealed element 5) nylon 6) air (gap)
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Examples of the Gaskets
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Insulating Mechanical Couplings
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Insulating Tee and Valve
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Weld End-Monolithic Insulator
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Cross section of a typical Monolithic Insulator
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Internal snap shot of a ‘Kerotest’ Insulator
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When
When do we use electrical isolation?
To isolate bi-metallic structures (cast Iron/steel or steel/copper )
To isolate new steel (coated) from old steel (bare)
Isolate protected pipe from unprotected pipe.
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When
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When
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Where
Where do we use electrical isolation?
Transition between transmission and distribution.
Transition between below and above ground piping.
Isolate carrier pipe from casings/sleeves. To isolate or create demarcation points within
‘CP’ systems
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A typical casing set up
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A cross sectional view of casing insulator
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A carrier pipe inserting into a casing
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A typical ‘CP’ schematic
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Woes
When we don’t or loose electrically isolate segments It’s the LAW (DOT 192.467) The repercussions (when they fail) The cost Pros and Cons
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The lost of Insulation
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Adding an Insulator
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Questions, comments or complaints?
Thank You