The Importance of Electrical Isolation

Defining "Electrical Isolation" for a Cathodic Protection System

With respect to cathodic protection systems, the term "electrical isolation" relates to confining the (cathodic) protective current to the structure being protected.

In terms of electrical separation this could mean isolating;

  • Two (or more) cathodic protection systems from one another
  • Buried / immersed structures from above ground appurtenances
  • Cathodically protected structures from earthing systems
  • Owner / Operator interfaces

Electrical isolation is a key factor in the successful application of cathodic protection where it has been included at the design stage. For the purposes of this blog article we assume that the structure is intended to be electrically isolated.

That is not to say that electrical isolation is always required, as long as the designed system has taken this into account.

There are times when it may not be desirable, or even practical, to isolate protected from unprotected structures. Examples are refineries, industrial plants, large tank farms and similar complex facilities. 

How to Electrically Isolate the Cathodically Protected Structure

Commercial fittings for providing electrical isolation of pipework include;

  • Insulating Flange Kits (IFK)
  • Monolithic Isolation Joints (IJ)
  • Non-metallic pipe sections

Cathodically protected structures can be electrically isolated from earthing systems via;

  • Decoupling Devices

Other solutions, e.g. non-conductive membranes, are available as methods of electrical isolation depending on the system in question.

Insulating Flange Kits (IFK)

Insulating Flange Kit (Exploded View) resized.jpg

The kit comprises of the following;

  • Insulating Gasket
  • Non-Metallic Sleeves for Assembly Bolts
  • Non-Metallic Washers
  • Metallic Washers
  • Nuts & Bolts

Monolithic Isolation Joints (IJ)

Monolithic Isolation Joint resized.jpg

The isolation joint is fabricated as a ready to install section of pipework.

The joint consists of;

  • Forged Rings
  • External Coating
  • Internal Coating
  • Adhesive Sealant
  • Di-Electric Filler
  • Insulating Rings
  • O Rings

Decoupling Devices

Corroconsult recommend only solid-state devices, as this eliminates the maintenance requirements and hazardous electrolytes of electrochemical polarisation cells.

acdd.jpg

Solid-state DC decoupling devices can be used for;

  • Electrically isolating from from utility earthing (grounding) systems
  • Electrically isolating from electrical equipment earthing (grounding) systems
  • Induced AC voltage mitigation
  • Isolation joint protection

How can electrical isolation be compromised?

Incorrect Installation

An incomplete kit installation for an IFK will result in the flanged joint being electrically continuous.

Earthing / Grounding

The most common failure of installed electrical isolation is through incorrect earthing of cathodically protected structures.

DCVG Survey - A Beginner's Guide [Part 1]

Direct Current Voltage Gradient [DCVG] Survey

Introduction

This non-intrusive, above ground survey allows the operator to identify the location of coating defects (holidays).

We are pleased to announce the first uploaded animation to our YouTube channel (shown within this post).

The YouTube video represents the first instalment within a series. Its purpose is to give an introductory overview to people not familiar with the technique e.g. asset owners, operators, supervisors.

Recognition within International Standards for Buried Pipelines

The technique is an approved ECDA (External Corrosion Direct Assessment) method as detailed in ANSI / NACE Standard Practice SP 0502-2010.

DCVG is also listed as an above-ground survey used to assess the coating condition and to locate coating defects within:

  • BS EN 13509:2003 - Cathodic protection measurement techniques
  • BS EN ISO 15589-1:2017. Petroleum, petrochemical and natural gas industries. Cathodic protection of pipeline systems. On-land pipelines

All DCVG surveys should be undertaken by competent and qualified personnel in accordance with BS EN ISO 15257:2017 - Cathodic protection - Competence levels of cathodic protection persons.

 

This short animation shows the technique to be utilised for a DCVG (Direct Current Voltage Gradient) survey using an analogue voltmeter and matched electrodes.

The video covers the basic methodology in identifying, centering and measuring coating defects (holidays) in the field [OL/RE Potential]

This "How To" guide is intended for asset owners, operators and supervisors that may not be familiar with the technique.

 

An Overview of the ECDA Process

What does ECDA mean?

ECDA is the commonly used acronym for External Corrosion Direct Assessment. The process has been developed for buried onshore ferrous pipeline systems. ECDA was created as a process for improving pipeline safety. Its primary purpose being to prevent future external corrosion.

Whilst this post attempts to provide an overview of the ECDA process, it is imperative that it is tailored each time to address specific requirements of individual pipeline systems.

What are the main steps of the ECDA Process?

There are four main steps to the ECDA Process, these are;

  • Pre-Assessment [Desktop Study]
  • Indirect Assessment [Above Ground / Non-Intrusive Surveys]
  • Direct Assessment [Bellhole Excavation & Testing]
  • Post Assessment [Calculation & Reporting]

The flow diagram below shows a general approach to the ECDA Process - evaluation methods may include, but are not limited to those shown here.


Pre-Assessment

Pipe Related

  • Material
  • Diameter
  • Wall Thickness
  • Year Manufactured
  • Seam Type
  • Bare Pipe Sections

Construction Related

  • Year Installed
  • Route Changes / Modifications
  • Construction Practices
  • Locations of Valves, Clamps, Insultaing Joints etc
  • Locations of and Construction Methods used at Casings
  • Locations of Bends including Miter Bends and Wrinkle Bends
  • Depth of Cover
  • Underwater Sections / River Crossings
  • Locations of River Weights and Anchors
  • Proximity to other Pipelines, Structures, HV Transmission Lines, Rail Crossings

Soils / Environmental

  • Soil Characteristics / Types
  • Drainage
  • Topography
  • Land Use (Current and Past)
  • Frozen Ground

Corrosion Control

  • CP System Type (Anodes, Rectifiers and Locations)
  • Stray Current Sources / Locations
  • Test Point Locations (or Pipe Access Points)
  • CP Evaluation Criteria
  • CP Maintenance History
  • Years without CP Applied
  • Coating Type – Pipe
  • Coating Type – Joints
  • Coating Condition
  • Current Demand
  • CP Survey Data / History

Operational Data

  • Pipe Operating Temperature
  • Operating Stress Levels and Fluctuations
  • Monitoring Programs (Coupons, patrol, Leak Surveys etc)
  • Repair History / Records
  • Leak / Rupture History
  • Evidence of Microbiologically Influenced Corrosion (MIC)
  • Type / Frequency of Third Party Damage
  • Hydrotest Dates / Pressures

Indirect Assessment

TR & Groundbed Functionality Checks

  • TR Output Current
  • TR Output Voltage
  • Drain Point Potential measurement
  • Groundbed Output Capabilities

CIPS (Close Interval Potential Survey)

  • Synchronously Interrupted
  • On Potential Measurement
  • Instant Off Potential Measurement

DCVG (Direct Current Voltage Gradient) Survey

  • Synchronously Interrupted
  • OL / RE Measurement
  • % IR at Defect Calculation

Additional Information Collated

  • GPS Coordinates recorded for key features and locations
  • Distance measurement of key features and locations
  • Photographic records taken for key features
  • a.c. potentials measured at all test facilities
  • Overview of condition of test facilities and associated connections
  • Data logging at identified / possible sources of Stray Current

Direct Assessment

Locations for excavation shall be selected based on the information gleaned from the pre-assessment and indirect assessment procedures.

A minimum of at least one trial pit should  be excavated to clarify the effectiveness of the first two procedures.

 
 

Post Assessment

All data obtained during the survey activities is provided, generally in both graphical and tabular formats (where appropriate), as well as photographic records, etc.