Inspectioneering Journal

Is Advanced Statistical Analysis the Next Step in Your Piping Inspection Journey?

A Discussion and Case Study on API 570’s Corrosion Monitoring Allowances

By Robert Clarke Jr., Senior Inspection Specialist at CorrSolutions, a subsidiary of E2G | The Equity Engineering Group, Inc., and Chris Massengale, Consultant Engineer II at CorrSolutions a subsidiary of E2G | The Equity Engineering Group, Inc. This article appears in the January/February 2022 issue of Inspectioneering Journal.


Recent improvements in sensor technology made by the inspection industry allow advanced statistical analysis to provide owner/users with a recognized and generally accepted good engineering practices (RAGAGEP) method of corrosion monitoring data analysis and optimization of a facility’s available personnel and resources. Whether a site continues to use a corrosion inspection strategy based on traditional condition monitoring location (CML) coverage, or is taking advantage of best practices such as implementing integrity operating windows (IOWs) and circuitization, statistical analysis can provide measurable benefits and new insights into corrosion management.

Background of Corrosion Monitoring

Most facilities still employ condition-based inspection programs and, as a result, ultrasonic testing (UT) thickness measurements, digital profile radiography, and electromagnetic techniques remain the cornerstone of most corrosion monitoring programs.

Historically, corrosion monitoring practices placed a thickness monitoring location (TML) on every fitting (e.g., elbow, tee, reducer), each pipe segment alongside those fittings, and mid-points of straight runs of piping. The historical practices did not consider potential damage mechanisms and, unfortunately, when a facility experienced a failure due to localized corrosion, it was often found to be adjacent to an existing TML. As a method to counter these types of failures, significantly more measurement locations were often added to the facility’s corrosion monitoring program.

UT thickness measurements improved reliability and helped protect facilities from failures due to general corrosion; however, spot measurements did not provide the same level of protection from local corrosion, thus requiring higher quantities of inspection points. This influx created costs considerably higher than just hiring more qualified and certified inspectors. Facilities needed insulating and scaffolding crews to install inspection ports and access requirements (e.g., ladders, scaffolding, manlifts) to support the insulators and UT technicians. Consequently, these additional inspection points and access requirements increased maintenance budgets and did not account for impact to personnel safety and overall plant risk.

For many facilities, this legacy corrosion monitoring method is still a commonly accepted practice. However, several owner/users began to proactively identify ways to reduce the number of TMLs while maintaining current risk levels. This initiative led to improvements in best practices, including systemization and circuitization, corrosion control documents (CCDs), and other techniques to optimize measurement location placement. Owner/users were able to identify a representative sample of pipe lengths and fittings to inspect rather than every piping component. It is interesting to note that around this same time, the term “thickness monitoring location” was modified to “condition monitoring location.” Many of the efforts to reduce CMLs were based on a combination of individually evaluating each examination point’s corrosion rates, generic industry information unrelated to thickness data (e.g., default corrosion rates), and inspection and corrosion personnel’s “gut feel.” While the combination of these three methods should not be discounted, especially the valuable insight from inspection and corrosion personnel, owner/users may not see the whole story that the data is telling.

In recent years, the industry has experienced numerous advancements in the techniques used to monitor corrosion; however, many facilities still analyze their data using the original “point-to-point method.” This API 570 analysis method recommends handling each individual CML independently from the adjacent locations. Unfortunately, this method of determining remaining life results in both hard and soft costs [1]. The hard costs relate to the technicians and maintenance support who need to perform the inspections, and the soft costs are connected to the impact of pulling limited maintenance resources away from other projects to obtain thickness measurements that may not reduce the facility’s overall risk. Circuitization is one of the above-mentioned best practices that many facilities have been utilizing since the early 2000s. However, these facilities may have changed operating parameters since the initial circuitization was completed and have had no means to efficiently verify if their current data supports the boundaries originally established for those circuits. Every facility wants to maximize their corrosion monitoring resources by obtaining measurements that deliver the most valuable data, but the question remains: is your facility able to maximize the information that your data could be delivering by using 40-year-old analysis techniques?

What Advanced Statistical Analysis Can Deliver

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Comments and Discussion

Posted by Alexander Gonzalez on February 24, 2022 (Edited on February 24, 2022)
Question for the authors, is this new approach... Log in or register to read the rest of this comment.

Posted by Wole Olayiwola on March 9, 2022
What is the percentage of improved reliability on... Log in or register to read the rest of this comment.

Posted by Amjith Khan on May 12, 2022 (Edited on May 12, 2022)
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