external corrosion direct assessment

7/30/2019 External Corrosion Direct Assessment

1/13

External Corrosion Direct Assessment

(ECDA)

As described through NACE standard SP0502, External Corrosion Direct Assessment (ECDA) isa four turn-key process that covers the line through examination of places on the pipe where

anomalies could form and thus corrode. This four step ECDA procedure which Alpha PipelineIntegrity Services strictly follows with NACE standard is:

Pre-Assessment Indirect Inspection Direct Examination Post Assessment

Below is an example of how Alpha implements ECDA on a various pipeline.

Pre-Assessment

The Pre-Assessment starts with a detailed Right-of-Way inspection. All details are noted (CP

Readings, ROW conditions, AOCs).

Indirect Assessment Methods :

Close interval survey (CIS) Direct current voltage gradient (DCVG)

Alternating current voltage gradient (ACVG) Pipeline current mapper (PCM) C-scan Soil Resistivity

Direct examination:

Coating conditions Corrosion mapping and data collection Pipe defects and metal loss Remaining strength of the pipe

Soil type, pH levels, depth Cathodic protection evaluation

Anomaly Verification

Once the dig plan has been established and digs identified technicians using SubMeter GPSidentified, Sub equipment return to the pipeline and stake the exact sites.
http://www.alphaleak.com/services/close-interval-surveys-cis-direct-current-voltage-gradient-dcvg-surveys/http://www.alphaleak.com/services/close-interval-surveys-cis-direct-current-voltage-gradient-dcvg-surveys/http://www.alphaleak.com/services/close-interval-surveys-cis-direct-current-voltage-gradient-dcvg-surveys/http://www.alphaleak.com/services/close-interval-surveys-cis-direct-current-voltage-gradient-dcvg-surveys/http://www.alphaleak.com/services/alternating-voltage-gradient-surveys-acvg/http://www.alphaleak.com/services/alternating-voltage-gradient-surveys-acvg/http://www.alphaleak.com/pipe-current-mapper/http://www.alphaleak.com/pipe-current-mapper/http://www.alphaleak.com/pipe-current-mapper/http://www.alphaleak.com/services/alternating-voltage-gradient-surveys-acvg/http://www.alphaleak.com/services/close-interval-surveys-cis-direct-current-voltage-gradient-dcvg-surveys/http://www.alphaleak.com/services/close-interval-surveys-cis-direct-current-voltage-gradient-dcvg-surveys/


2/13

Technicians locate and document the defect found the Indirect Surveys by using Surveys.
http://www.alphaleak.com/external-corrosion-direct-assessment-ecda/corrosion2-c/http://www.alphaleak.com/external-corrosion-direct-assessment-ecda/corrosion1-c/


3/13

The appropriate calculations are generated and repair calls are made made.

Post Assessment

Once completed, all data is processed by Alphas engineers with the final report andrecommendations.

Click here to discuss your needs with a qualified Alpha associate.
http://www.alphaleak.com/contact-us/http://www.alphaleak.com/contact-us/http://www.alphaleak.com/external-corrosion-direct-assessment-ecda/corrosion4-c/http://www.alphaleak.com/external-corrosion-direct-assessment-ecda/corrosion3-c-2/http://www.alphaleak.com/contact-us/


4/13

Fact Sheet: External Corrosion

Quick Facts:

Corrosion is the natural process that occurs when materials made from metal return to theiroriginal state through a chemical reaction known as oxidation.

Corrosion of all types is one of the leading causes of pipeline leaks and ruptures. Improved technologies have led to better prevention, monitoring, detection, and mitigation of

external pipeline corrosion even for old pipelines.

New pipeline Integrity Management regulations will promote early identification of potentiallyexternally corroded sections and their repair.

Refer to other Fact Sheets for specific discussion of issues related to corrosion in general, internalcorrosion, selective seam corrosion, and stress corrosion cracking.

What is external corrosion and why does it occur?

Corrosion is the deterioration of metal that results from a reaction with the environment which

changes the iron contained in pipe to iron oxide (rust). For example, if your car develops a rustspot, that is corrosion of metal. The same process can occur in various forms on pipelines . As is

the case with your car, there are effective methods for preventing and arresting corrosion damageto pipelines.

External corrosion occurs due to environmental conditions on the outside of the pipe (e.g., fromthe natural chemical interaction between the exterior surface of the pipeline and the soil

surrounding it). Typically, the exterior surface of a pipeline is coated in order to prevent thesurrounding soil or other environmental condition from contacting the steel pipe, thus preventing

the oxidation process. In addition, the oxidation process can be halted electrically on both barepipelines as well as on pipelines that have been coated. When either or both of these protective

measures break down, external corrosion can occur.

What are the risks from external corrosion?

External corrosion can result in the gradual reduction of the wall thickness of the pipe and aresulting loss of pipe strength. It can occur relatively evenly over an area of the pipe surface

(sometimes referred to as General Corrosion) or in isolated spots on the pipe. This loss of pipestrength could result in leakage or rupture of the pipeline due to internal pressure stresses unless

the corrosion is repaired, the affected pipeline section is replaced, or the operating pressure of thepipeline is reduced.

External pipeline corrosion creates weaknesses at points in the pipe, which in turn makes the

pipe more susceptible to third party damage, overpressure events, etc. (i.e., corrosion doesn'tnecessarily need to cause the leak or rupture itself to increase risk).


5/13

Pipeline failure rates from Corrosion

While data specific to external corrosion alone is not available, corrosion in all its various forms

is one of the most prevalent causes of pipeline spills or failures. For the period 2002 through2003, incidents attributable to corrosion have represented 25% of the incidents reported to OPS

for both Natural Gas Transmission Pipelines and Hazardous Liquid Transmission Pipelines.

Over this same period, approximately 1 percent of the incidents reported to OPS for Gas

Distribution Pipelines were due to corrosion.

What is being done to prevent/mitigate external corrosion?

The steel pipe in modern pipeline systems is coated to protect it from external environmentalconditions that can lead to corrosion.

Modern manufacturing processes for steel pipe and coatings are subject to rigorous fabricationand installation standards and quality control to reduce the occurrence of defects that can lead

to corrosion-induced failures. Operators use cathodic protection systems to protect pipes from external corrosion. One type of

this system imposes a very low-voltage, direct electric current on the pipeline to oppose the

natural corrosion currents at locations where pipe coating is damaged or missing. Another type

system is to connect the pipeline to an anode ground that attracts the corrosion-causing

current. This sacrificial anode attracts the current away from the iron in the pipe.

The Office of Pipeline Safety has implemented new Pipeline Integrity Management (IM)regulations that require all pipeline operators to inspect and assess all of their pipelines that

could affect areas of high consequence such as populated areas or environmentally sensitive

areas. The operators are required to inspect and assess their pipelines for integrity issues, such

as corrosion, and repair or replace affected pipe.

By implementing the requirements of the regulations and through responsible maintenanceprograms, pipeline operators continuously inspect their pipelines for external corrosion damage.

External Corrosion: What more can be done?

Public : Be aware of pipelines located near you. Be observant for signs of pipeline damage,leakage, or security concerns. Report any concerns you have regarding pipeline safety to the

pipeline operator immediately. Always respect the pipeline right-of-way. Do not dig or build on a

pipeline right-of-way without first contacting the pipeline operator or your state one-call center.

Industry: Pipeline operators and industry stakeholders can continue to develop and implementimproved corrosion detection and prevention technologies. Operators must continue to

implement corrosion protection effectively and strengthen pipeline integrity management

programs. Operators must mitigate the effects of corrosion when it is detected. Regulators : OPS and state regulators must continue to inspect pipeline operators to ensure

they effectively implement required integrity management and corrosion control programs to

ensure that risks to pipelines are identified and mitigated at the earliest possible time. Better

coordination is needed between local permitting agencies and pipeline operators to facilitate

expeditious granting of permits when public safety is potentially threatened.

http://primis.phmsa.dot.gov/comm/FactSheets/FSExternalCorrosion.htm
http://primis.phmsa.dot.gov/comm/FactSheets/FSExternalCorrosion.htmhttp://primis.phmsa.dot.gov/comm/FactSheets/FSExternalCorrosion.htmhttp://primis.phmsa.dot.gov/comm/FactSheets/FSExternalCorrosion.htm


6/13


Corrpro is a world class provider of External Corrosion Direct Assessment (ECDA) related surveys and

data analysis. Our Pipeline Services Division staff includes numerous personnel with more than 20 years

experience in pipeline testing and integrity assessments. We have been the largest provider of these

types of services in the United States for over 10 years. Corrpro's ECDA services include:

Pre-Assessment

Indirect Examination

CIS Potential Surveys

DCVG Surveys

Electromagnetic Surveys

ACVG Surveys

Soil Studies

Resistivity Surveys

Depth of Cover

Sub-Meter GPS Locating

Direct Examination

Excavate and Inspect

Coating Evaluation

Corrosion Measurements

MIC Investigations

Pipe Strength Calculations

Root Cause Analysis

Corrosion Rate Estimates

Post Assessment

http://www.corrpro.com/content/170/external-corrosion-direct-assessment-ecda.aspx


(ECDA)
http://www.corrpro.com/content/170/external-corrosion-direct-assessment-ecda.aspxhttp://www.corrpro.com/content/170/external-corrosion-direct-assessment-ecda.aspxhttp://www.corrpro.com/content/170/external-corrosion-direct-assessment-ecda.aspx


7/13

Municipalities have billions of dollars invested in their buried infrastructure systems. Inspectionand maintenance of the infrastructure is a key asset management tool that municipalities use to

protect this investment.

Step 1: Pre-Assessment A collection of historic and current data to determine whether ECDAis feasible; defines areas on pipelines where ECDA can be used; and selects indirect inspection

tools.

Step 2: Indirect InspectionAbove-ground inspections to identify and define the severity ofcoating faults and other anomalies, corrosive soil conditions and the status of the level of

cathodic protection (if the pipeline is cathodically protected).

Step 3: Direct ExaminationAnalyse of the indirect inspection data to categorize the severity of

the anomalies and to select locations along the pipeline for excavation and inspection.

Step 4: Post-AssessmentPost-Assessment covers the analyses of data collected from the threeprevious steps to assess the effectiveness of the ECDA process on the pipeline and to determine

reassessment intervals.

Levelton Consultants has the capabilities to inspect and test municipal water systems using

External Corrosion Direct Assessment (ECDA). ECDA is a four-step procedure requiring theintegration of pre-assessment data; data from multiple indirect field inspections; and data from

pipe external surface inspections conducted in accordance with NACE International StandardPractice SP0502-2008 Pipeline External Corrosion Direct Assessment Methodology.

http://www.levelton.com/materials/external-corrosion-direct-assessment-ecda/
http://www.levelton.com/materials/external-corrosion-direct-assessment-ecda/http://www.levelton.com/materials/external-corrosion-direct-assessment-ecda/http://www.levelton.com/wp-content/uploads/2013/01/External-Corrosion.jpghttp://www.levelton.com/materials/external-corrosion-direct-assessment-ecda/


8/13

Corrosion Service offers complete ECDA services, including accurate estimation of theextent of coating defects and corrosion activity, using a fast and efficient CIPS and

DCVG integrated approach with no need to interrupt the survey or return to defect

locations afterwards!


(ECDA) is a structured process usedto evaluate buried onshore ferrous

pipeline integrity. The ECDA goal isto enhance safety by managing the

risk of pipeline corrosion failureswhile minimizing the cost required for

excavations and repairs. ECDA mayalso be used when more established

methods such as in-line inspection(ILI) and pressure testing are not

possible or not practical. NACEStandard Recommended Practice on

Pipeline External Corrosion DirectAssessment Methodology (RP0502-

2002) describes the ECDA process asallowing ...the prediction of

susceptible areas where corrosionactivity has occurred, is occurring or

may occur.

Although ECDA field assessment techniques are well established, specialized fieldequipment and staff experienced in the collection, recording, and analysis of data are

necessary to obtain reliable and meaningful results. Corrosion Service quickly embracedthe new ECDA techniques and both our field and professional staff are well versed in

their application. We are equipped with state-of-the-art equipment for surveys and thecollection of data which is then analyzed by professional engineers with many years of

pipeline corrosion prevention experience.

The ECDA Process

This four step process consists of: 1) Pre-Assessment; 2) Indirect Inspection; 3) DirectExamination; and 4) Post Assessment, which can be summarized as follows:


9/13

1. The Pre-Assessment step involves the collection andevaluation of historical data and pipeline

characteristics. Based on this information, thefeasibility of an ECDA application is determined and

once affirmed, the pipeline is divided into regions with

similar exposure and areas where the same indirectinspection tools may be used.2. The Indirect Inspection step uses a combination of 2

or more above ground survey techniques such as closeinterval potential survey (CIPS), alternating current

voltage gradient (ACVG), direct current voltagegradient (DCVG), AC attenuation for the identification

of areas with corrosion activities or coating faults. Thedata is evaluated via systematic analysis and high-risk

areas are identified for excavation.3. The Direct Examination step covers the selection of

sites to be excavated and the physical identification ofdefects requiring repair or replacement.

4. The Post Assessment step evaluates the previous 3steps of the ECDA process and establishes a future

assessment schedule.

Higher Efficiency and Lower

Survey Costs

Corrosion Service hasdeveloped an integrated indirect

inspection technique mergingboth the CIPS and DCVG

measurements. This integratedtechnique allows data

acquisition of both CIPS andDCVG simultaneously. Higher

efficiency and lower surveycosts are achieved by merging

both techniques.

List of Projects

> H3L Pipe-Type Cable (2004)> H1L (Spare) Pipe-Type Cable

(2004-2005)> Transfer Line at Sault St.

Marie (2004)> Panhandle Line (2004-2005)

Integrated CIPS/DCVG Survey Results

DCVG Survey with Indication of Suspect CoatingHoliday


10/13

> Leamington Line (2004-2005)> Brantford Line (2004-2005)

> 21 Lines (In progress)

http://www.corrosionservice.com/ecda.htm

Failure Analysis

Metallurgical failure analysis is the process that determines reasons a metal component fails dueto environmental conditions and/or mechanical stress.

Analysis of a failed part can be done using destructive testing or non-destructive testing.Destructive testing involves removing a metal component from service and testing it in a

laboratory. Non-destructive testing is a test method that allows certain physical properties ofmetal to be examined without taking the samples completely out of service.

Our professionals take the following steps when providing a failure analysis:
http://www.corrosionservice.com/ecda.htmhttp://www.corrosionservice.com/ecda.htmhttp://www.levelton.com/wp-content/uploads/2013/01/water-leak.jpghttp://www.corrosionservice.com/ecda.htm


11/13

Research the history of the equipment/part Examine the equipment/part (visual examination including photos) Provide testing Catalog the evidence Plan of Action/report

Leveltons Physical Metallurgy Group has provided this service to many clients to determine theroot cause and solution to the underlying problems to prevent future failures. Our current

Laboratory Endorsements include:

BC Safety Authority Boiler and Pressure Vessel Testing Agency US Coast Guard Accepted Independent Laboratory Canadian Welding BureauCertified Welding Inspection Organization and

Metallurgical Laboratory

http://www.levelton.com/materials/failure-analysis/

Fact Sheet: External Corrosion

Quick Facts:

Corrosion is the natural process that occurs when materials made from metal return to theiroriginal state through a chemical reaction known as oxidation.

Corrosion of all types is one of the leading causes of pipeline leaks and ruptures. Improved technologies have led to better prevention, monitoring, detection, and mitigation of

external pipeline corrosion even for old pipelines.

New pipeline Integrity Management regulations will promote early identification of potentiallyexternally corroded sections and their repair.

Refer to other Fact Sheets for specific discussion of issues related to corrosion in general, internalcorrosion, selective seam corrosion, and stress corrosion cracking.

What is external corrosion and why does it occur?

Corrosion is the deterioration of metal that results from a reaction with the environment whichchanges the iron contained in pipe to iron oxide (rust). For example, if your car develops a rust

spot, that is corrosion of metal. The same process can occur in various forms on pipelines . As isthe case with your car, there are effective methods for preventing and arresting corrosion damage

to pipelines.

External corrosion occurs due to environmental conditions on the outside of the pipe (e.g., fromthe natural chemical interaction between the exterior surface of the pipeline and the soil

surrounding it). Typically, the exterior surface of a pipeline is coated in order to prevent thesurrounding soil or other environmental condition from contacting the steel pipe, thus preventing
http://www.levelton.com/materials/failure-analysis/http://www.levelton.com/materials/failure-analysis/http://www.levelton.com/materials/failure-analysis/


12/13

the oxidation process. In addition, the oxidation process can be halted electrically on both barepipelines as well as on pipelines that have been coated. When either or both of these protective

measures break down, external corrosion can occur.

What are the risks from external corrosion?

External corrosion can result in the gradual reduction of the wall thickness of the pipe and aresulting loss of pipe strength. It can occur relatively evenly over an area of the pipe surface

(sometimes referred to as General Corrosion) or in isolated spots on the pipe. This loss of pipestrength could result in leakage or rupture of the pipeline due to internal pressure stresses unless

the corrosion is repaired, the affected pipeline section is replaced, or the operating pressure of thepipeline is reduced.

External pipeline corrosion creates weaknesses at points in the pipe, which in turn makes the

pipe more susceptible to third party damage, overpressure events, etc. (i.e., corrosion doesn'tnecessarily need to cause the leak or rupture itself to increase risk).

Pipeline failure rates from Corrosion

While data specific to external corrosion alone is not available, corrosion in all its various forms

is one of the most prevalent causes of pipeline spills or failures. For the period 2002 through2003, incidents attributable to corrosion have represented 25% of the incidents reported to OPS

for both Natural Gas Transmission Pipelines and Hazardous Liquid Transmission Pipelines.

Over this same period, approximately 1 percent of the incidents reported to OPS for GasDistribution Pipelines were due to corrosion.

What is being done to prevent/mitigate external corrosion?

The steel pipe in modern pipeline systems is coated to protect it from external environmentalconditions that can lead to corrosion.

Modern manufacturing processes for steel pipe and coatings are subject to rigorous fabricationand installation standards and quality control to reduce the occurrence of defects that can lead

to corrosion-induced failures.

Operators use cathodic protection systems to protect pipes from external corrosion. One type ofthis system imposes a very low-voltage, direct electric current on the pipeline to oppose the

natural corrosion currents at locations where pipe coating is damaged or missing. Another type

system is to connect the pipeline to an anode ground that attracts the corrosion-causing

current. This sacrificial anode attracts the current away from the iron in the pipe.

The Office of Pipeline Safety has implemented new Pipeline Integrity Management (IM)regulations that require all pipeline operators to inspect and assess all of their pipelines that

could affect areas of high consequence such as populated areas or environmentally sensitive

areas. The operators are required to inspect and assess their pipelines for integrity issues, such

as corrosion, and repair or replace affected pipe.

By implementing the requirements of the regulations and through responsible maintenanceprograms, pipeline operators continuously inspect their pipelines for external corrosion damage.


13/13

External Corrosion: What more can be done?

Public : Be aware of pipelines located near you. Be observant for signs of pipeline damage,leakage, or security concerns. Report any concerns you have regarding pipeline safety to the

pipeline operator immediately. Always respect the pipeline right-of-way. Do not dig or build on a

pipeline right-of-way without first contacting the pipeline operator or your state one-call center. Industry: Pipeline operators and industry stakeholders can continue to develop and implement

improved corrosion detection and prevention technologies. Operators must continue to

implement corrosion protection effectively and strengthen pipeline integrity management

programs. Operators must mitigate the effects of corrosion when it is detected.

Regulators : OPS and state regulators must continue to inspect pipeline operators to ensurethey effectively implement required integrity management and corrosion control programs to

ensure that risks to pipelines are identified and mitigated at the earliest possible time. Better

coordination is needed between local permitting agencies and pipeline operators to facilitate

expeditious granting of permits when public safety is potentially threatened.

Date of Revision: 12012011

http://primis.phmsa.dot.gov/comm/FactSheets/FSExternalCorrosion.htm
http://primis.phmsa.dot.gov/comm/FactSheets/FSExternalCorrosion.htmhttp://primis.phmsa.dot.gov/comm/FactSheets/FSExternalCorrosion.htmhttp://primis.phmsa.dot.gov/comm/FactSheets/FSExternalCorrosion.htm

external corrosion direct assessment

Documents