How Much Do You Know About AC Mitigation?
There are seven questions and a break for refreshments in the middle.
(You'll have to grab your own snacks, sorry.)
Let's begin, shall we?
 
What's your name, Clever One? *

(Just your first one is fine.)
 
Okay, {{answer_ILdDtmmNhyVM}}, are you ready to match wits with our AC experts...

 
Why use a gradient control mat?


 
Correct!

Employees working on aboveground appurtenances are like birds on a wire – they're at risk of being shocked! Gradient control mats mitigate this personnel safety hazard by collapsing earth voltage gradients (EVGs) associated with AC faults or lightning, and minimizing step-and-touch potentials to safe limits.
 
Oops. Gradient control mats don't ground the pipeline. They just mitigate voltage gradients. Pipeline grounding is accomplished with engineered grounding systems such as deep-vertical point grounds, linear grounding arrays, or natural grounds.

 
Oops. Gradient control mats don't provide cathodic protection. As a matter of fact, they should be provided with an independent CP system of their own to ensure protection against corrosion.

 
Gotcha! For weeds, use Roundup.

 
What's the correct way to connect multiple gradient control mats at a single site?





 
Oops. Nylon tie wraps don't establish the necessary electrical continuity.

 
Oops. Split bolts or Kearneys tend to loosen over time, so they don't provide a reliable long-term connection.

 
Oops. TIG welding presents a hazard due to the fumes generated from welding on galvanized material.

 
Correct! Exothermic welding at a minimum of 18 inches along each seam will ensure electrical continuity throughout the gradient control mat system. Don't forget to apply an approved external coating to these connections as additional protection against corrosion.

 
Is it true that CPU-based AC modeling software uses industry standards to set default data for AC and lightning mitigation models?

     
 
Correct! This is a false statement.

There are many data inputs required for CPU-based AC modeling and it's up to the user to determine them (not the software). These inputs include HVAC system dimensions and operating characteristics, pipeline system dimensions and operating conditions, specific coating resistance, etc. If input data isn't readily available, the data model operator must make assumptions in order to produce an output.
 
Oops. This is false.

There are many data inputs required for CPU-based AC modeling and it's up to the user to determine them (not the software). These inputs include HVAC system dimensions and operating characteristics, pipeline system dimensions and operating conditions, specific coating resistance, etc. If input data isn't readily available, the data model operator must make assumptions in order to produce an output.
 
Soil resistance measurements for CPU-based AC modeling must be obtained at which depth?


 
Oops. The answer is "it depends." We'll also give it to you if you said "neither A nor B."

Measurement depths depend on the type of AC mitigation system you plan to use. For example, a 250-foot deep-vertical point ground may require obtaining soil measurements to 250 feet in order to accurately predict the resistance to ground.
 
Correct! The answer is "it depends." We'll also give it to you if you said "neither A nor B."

Measurement depths depend on the type of AC mitigation you plan to use. For example, a 250-foot deep-vertical point ground may require obtaining soil measurements to 250 feet in order to accurately calculate soil resistivity.
 
Only two more questions to go!

 
Decoupling devices:


 
Oops. Decoupling devices don't prevent DC interference.

To prevent DC interference, use GCP systems, coating, and/or mitigation bonds.
 
Oops. Decoupling devices do the opposite: They block DC current and pass AC current.

 
Correct! Decoupling devices are polarity sensitive.

Consult a design engineer for more information on proper polarity connections.
 
Oops. Decoupling devices don't increase cathodic protection current requirement because they block DC current and pass AC current.

 
Imagine that you're interrupting a pipeline with an ACLM system in order to obtain polarized potentials during a CIS survey.

Which of the following do you need to consider?

 
Oops. Interrupting the AC power side of the rectifier allows the inductively AC-coupled pipline to energize the groundbed in the "off" cycle, resulting in erroneous "off" pipe-to-soil potentials.

 
Correct!

During interrupted surveys, decoupling devices must be disconnected (not just interrupted), due to the stored energy components associated with solid-state decoupling devices. This requires additional safety precautions for the CIS team since they will now be working on an AC energized pipeline.

We'll also give it to you if you answered D) the DC-power side of rectifiers supplying CP current to the pipeline. It's important to install interruption in the DC circuit of any rectifier in a co-located ROW to "open" the connection between the inductively AC coupled pipeline and the CP groundbed, thus preventing half-wave energization of the groundbed, which would result in erroneous "off" potentials.
 
Oops. During interrupted surveys, decoupling devices must be disconnected (not just interrupted), due to the stored energy components associated with solid-state decoupling devices. Disconnecting the decoupling devices will also disconnect the galvanic anodes associated with gradient control mats.

 
Correct!

It's important to install interruption in the DC circuit of any rectifier in a co-located ROW to "open" the connection between the inductively AC coupled pipeline and the CP groundbed, thus preventing half-wave energization of the groundbed, resulting in erroneous "off" potentials.

We'll also give it to you if you answered B) Decoupling devices associated with the ACLM system. During interrupted surveys, decoupling devices must be disconnected (not just interrupted), due to the stored energy components associated with solid-state decoupling devices. This requires additional safety precautions for the CIS team since they will now be working on an AC energized pipeline.
 
Oops. The correct answers were:

B) Decoupling devices associated with the ACLM system and D) The DC-power side of rectifiers supplying CP current to the pipeline


B is correct because during interrupted surveys, decoupling devices must be disconnected (not just interrupted), due to the stored energy components associated with solid-state decoupling devices. This requires additional safety precautions for the CIS team since they will now be working on an AC energized pipeline.

D is also correct because it's important to install interruption in the DC circuit of any rectifier in a co-located ROW to "open" the connection between the inductively AC coupled pipeline and the CP groundbed, thus preventing half-wave energization of the groundbed, which would result in erroneous "off" pipe-to-soil potentials.
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