Tips for Success in Conducting External Corrosion Direct Assessments
ECDA is a method for pipeline operators of both gas and liquid pipelines to assess the external health of their pipeline systems with minimal to no impact on the operation of their system. Here are some helpful best practices that allow operators to get the most out of their indirect surveys and integrity inspections.
Campos EPC is a leader in Pipeline and Integrity EPC Services, offering technically sound and schedule-driven Engineering, Procurement, and Construction solutions that are aligned with industry regulations, including integrity assessments (ILI, pressure testing, ECDA), corrosion mitigation, and cathodic protection.
External Corrosion Direct Assessment (ECDA) is a four-step method for pipeline operators of both gas and liquid pipelines to assess the external health of their pipeline systems with minimal to no impact on the operation of their system.
The ECDA process utilizes several tools from the corrosion industry to provide a global view of the integrity and external corrosion risks on a pipeline system when implemented correctly. Some of the common tools used are described below:
- Close interval potential survey (CIPS) involves walking the line and taking pipe-to-soil potentials every three to five feet; and measures the cathodic protection (CP) levels at close intervals between test leads.
- Direct current voltage gradient (DCVG) is a survey that uses DC current to pinpoint areas of current loss/gain, which correlate to coating holidays along the pipeline. This survey is performed above ground.
- Pipeline current mapper (PCM) is used primarily in ECDA for line location and depth of cover measurements. It has many uses outside ECDA and is often very successful at mapping out areas of stray current to assist in CP troubleshooting.
- A-frame is an attachment added to the PCM (see the previous bullet point) that allows the macro alternating current voltage gradient (ACVG) tool to become an accurate coating holiday detector similar to DCVG, except A-frame utilizes alternating current.
- 4-Pin Wenner is a soil resistivity survey that uses four metal pins perpendicular to the pipe and measures the resistance between them to calculate soil resistivity.
Oftentimes, ECDA is used as an alternative method to assess pipelines subject to pipeline integrity management (PIM) regulations in the United States when in-line inspection is rendered infeasible due to pipeline operating parameters such as diameter, flow, and/or interruption restrictions. (Further reading is available in The Impact of the Pipeline Safety Act of 2011 on the Industry.)
Here are some helpful practices that allow an operator to get the most out of each step of an ECDA assessment.
Step 1: Pre-assessment – Threat Analysis
An assessment is only as good as the research behind it when it comes to ECDA. Without a strong understanding of the system, you will not fully capitalize on the benefits of the assessment process.
The more time you spend to better understand the system you are assessing, the easier it is to get the most out of the survey (Step 2) and direct examination (Step 3) results.
Digging through documents and records is helpful, but taking the time to conduct field operation interviews with CP technicians and foremen—the people who work on the front line—can be invaluable. Oftentimes, interviewing field workers will uncover things that get lost in documentation.
Just a few examples from experience include:
- Galvanic anodes being installed on an impressed system with no as-built information
- Areas where other contractors are known to run into the line consistently
- Bad or disbonded field coating on the line at field joints, which could render ECDA not feasible
Another extremely beneficial practice is getting out in the field and walking the line prior to starting the actual survey work. This allows you to more effectively plan the rest of the project, and better understand the practical threats on the line—not just those documented on paper.
After uncovering as much information as possible to gain a full understanding of the pipeline system, a threat analysis should be performed. A good threat analysis takes into account everything you learn about the pipeline and applies the correct assessment method and the right tools at your disposal to complete the integrity assessment.
This part of the ECDA process can test a person’s integrity. If threats exist on the system that can’t be assessed using ECDA, you have to go back to the assessment drawing board and figure out what other method to use to address those threats. Other assessment options often include:
- Pressure testing
- In-line inspecting
- Pipeline replacement
- Pressure reduction
If everything checks out during the threat and assessment method study, you are adequately prepared to move into the ECDA regioning and tool selection processes with a solid understanding of the pipeline system’s risk factors and have tools that will address them.
Step 2: Indirect Inspection – Field Survey & Contractor Integrity
The most common tools utilized for indirect inspection are CIPS and DCVG or ACVG. These surveys offer two separate but complimentary pictures of the pipe. Supplemental surveys like GPS, PCM, and 4-pin resistivity surveys are also sometimes performed in conjunction to gather the most information.
CIPS gives you an idea of how your CP system is working along the pipeline. DCVG and ACVG both give you indications of coating failures along the pipeline. Most indirect surveys are performed from above ground, and are effective methods of capturing additional information about the pipeline system.
Providing a list of the client’s abnormal operating conditions prior to the start of survey work allows a survey crew the opportunity to identify any issues along the pipeline right of way (ROW). Some common abnormal conditions easily documented by survey crews are:
- Downed pipeline markers
- Broken test leads
- Exposed pipeline segments
- Right of way encroachment
- Shallow cover
A major benefit of the indirect survey process is that it allows an operator to preemptively catch integrity issues, such as coating holidays and poor CP, before they result in wall loss. An ILI will only catch these areas once corrosion has already taken place.
Step 3: Direct Examination – Integrating Pre-Assessment and Indirect Assessment Information
Reviewing the pre-assessment information in detail when later analyzing the survey results enhances your ability to identify the most severe indications along the pipeline. A correlation between survey results and pipeline features often reveals more about the health of the pipeline and cathodic protection system.
A typical example of this benefit involves older systems that might have been converted from galvanic to impressed current CP systems. (See Video: When to Use Impressed Current Cathodic Protection for more information.) Oftentimes, galvanic anodes that are still attached to the pipeline will show up as coating holidays. Reviewing as-built information and talking to operators about the history of the pipeline can easily help identify false indications caused by these anodes, thereby saving valuable assessment dollars for relevant direct examinations.
When you consider both the pre-assessment and indirect inspection information together, you are able to more effectively select and weight direct examination sites. Honesty and self-integrity are paramount to the success at this stage of the ECDA process. If your direct examination digs uncover items like corrosion underneath disbonded coating, which render ECDA no longer feasible, you have to be willing to perform another in-depth analysis, potentially going back to the drawing board to ensure the integrity of the pipeline.
Thorough documentation and review during the pre-assessment step more often than not eliminates the need to re-evaluate the chosen assessment method.
Step 4: Post Assessment – Summarizing Meaningful Results & Follow-Up Actions
Since the assessment completion date is tied to the successful completion of all direct examinations required by the NACE SP0502 process, the final report is often overlooked and completed months or years after the fact, if at all.
The post-assessment report is an irreplaceable part of the ECDA process and allows those involved in the process to share feedback and understand the results of the assessment. (For information on the post assessment step, see The Benefits of Timely and Effective Reporting When Conducting Pipeline Close Interval Surveys.)
In my experience, the most important aspect of the post-assessment are the lessons-learned and follow-up action discussions which help to improve not only the ECDA process, but also the operator's assets. These discussions allow those involved to summarize and create action plans for any action items resulting from the assessment.
ECDA is a very complex process and requires skilled and knowledgeable professionals to achieve good results. In the past, ECDA has been used as the cheaper assessment or catch-all assessment method when others fall through.
When implemented correctly, ECDA can detect major pipeline integrity issues before they result in metal loss.
However, in the last five years, most operators have pulled away from ECDA since it was too heavily relied upon in the past and had a tendency to be over-employed when other assessment methods were more threat-applicable. In the next article, we will dive into some common misuses of ECDA and the effect it had on creating the U.S. Pipeline Safety Reauthorization Act of 2011.
More in the "Understanding & Utilizing External Corrosion Direct Assessments" series: