S.KARTHIKR150209016

M-TECH PIPELINE ENGINEERING

Electromagnetic Field Interference In Buried Pipelines

What is Electromagnetic Field Interference?Every current carrying conductor produces its own

electrostatic and electromagnetic field around its surrounding which in turn induces voltage on the other conductors in their field.

Installation of pipelines which are considered as electric conductors near high voltage transmission lines can result in EMF interference.

Types of EMF Interference in Buried Pipelines

Types of EMF interference in pipelines are

Electrostatic or capacitive interferenceResistive or ohmic interferenceElectromagnetic or inductive interference

Electrostatic or Capacitive Interference

This occurs due to the capacitive nature between the transmission line and the pipeline that acts as two plates of capacitor.

The pipeline picks up a voltage relative to the soil, which is proportional to the voltage in the transmission line.

The pipeline must be grounded well if the transmission line exceeds over 115kv.

This electrostatic coupling is of minor consequences, since because of better pipeline coating and effective grounding for electrostatic charge

Resistive or Ohmic Interference

This occurs when the lightening strikes the transmission structures or when there is a phase ground fault.

Due to this a voltage cone is created near the pylon grounding system which in turn gets in to the pipeline

At this time any one touching the pipeline will get shock irrespective of distance and grounding.

Protective measures should be taken in case:For long term interference – 65 voltFor short term interference – 1000 volt

Electromagnetic or inductive interference

It occurs due to parallel routing with three-phase high voltage AC transmission lines.

The voltage is induced due to any phase imbalance in the lines and magnetic coupling with pipelines.

This type of interference holds the major problem in the pipeline like safety, corrosion, etc

Comparison of EMF interferenceThe touch voltage is a defined quantity only when the pipeline

is present along the transmission line profile, else where, it has been set to zero.

For the ohmic interference, the curves reaches a peak at each tower location , where the current flows in to the earth.

The inductive interference decreases with increasing distance from center of the pipe but peaks at the pipe bending point.

The inductive component is greater in magnitude and extent than the ohmic component.

Evaluation of EMF interference

The steps that are involved are,Gather background information.Develop a plan.Select the proper tools.Conduct the investigation.Analyze the data and locate the source.Select a solution.Verify solution performance

Effects of the EMF interference

The effects of the interference in pipelines are

Safety of the pipeline personnel, Induced AC corrosion in pipelines, Damage to a material connected to pipe.

Safety Consideration: NACE SP0177All personnel must be aware of and recognize the potential

shock hazards and be trained in the approved safety proceduresDuring construction, above ground sections can be made safe

with a simple temporary grounding and bonding.Warning signs should be posted and RED ZONES clearly

designated, including at electrical power system crossings.Both NACE SP0177 and CAN/CSA-C22.3 No.6-M91

recognize 15 V as a potential shock hazard.Check the weather forecast prior to beginning work and it

should be stopped when lightning activity is present.Always treat the pipeline and appurtenances as a live

conductor.

Effect of AC Current During Contact Remove his hands Muscular control is lost Trouble inbreathing

Needs medico

Do and Dont’s in the Pipeline Operation

Some Codes To Follow NACE SP0177-“Mitigation of Alternating Current and

Lightning Effects on Metallic Structures and Corrosion Control Systems”.

CAN/CSA-C22.3 No. 6-M91,-“Principles and Practices of Electrical Coordination Between Pipelines and Electric Supply Lines”.

EPRI Report EL-4147-V1-“Utility Corridor Design: Transmission Lines, Railroads, and Pipelines, Vol. 1:Engineering Analyses and Site Study”.

ANSI/IEEE Standard C2, “National Electrical Safety Code (NESC)” Rule 232C 1c

Induced AC Corrosion In PipelinesAC Corrosion is a corrosion induced in the pipelines due to

the induced ac current which are grounded through the small coating defects having low resistance path.

The factors influencing AC corrosion are Location of AC transmission line, Small coating defects in the pipeline coating, Low soil resistivity at these defects, High AC current density at the defects.

According to the research its found that AC corrosion occurs with induced voltages as low as 4V in the pipeline.

Contd…..Generally the AC current chooses the very small coating

defects with low soil resistivity to discharge to ground From the research its found that AC corrosion takes place

at a current density of 20 A/m2 – monitor the situation, 100 A/m2 – possibility of corrosion, mitigation measures

has to be taken, 150 A/m2 – distinct possibility of corrosion, mitigation is

essential.

AC Corrosion showing Pitting on a Pipeline

Prevention of AC corrosion This type of corrosion will see for low resistivity path in

defects and if there is no defects it will adjoin in other kinds of corrosion and increase their rates so they should be prevented.

In recent years the pipelines are well coated with small defects for grounding those currents.

The grounding should be done provided along the length of the pipeline properly

Near the transmission lines care should be taken.Frequent measurement of the induced current should be

taken and if any shock is acquired it should be notified to safety engineers.

Thank you