Inspectioneering Journal

Piping CML Optimization: Optimizing the Definition

By Mike Sparago, Principal Engineer II at The Equity Engineering Group, and Chris Massengale, Consultant Engineer II at CorrSolutions a subsidiary of E2G | The Equity Engineering Group, Inc. This article appears in the January/February 2021 issue of Inspectioneering Journal.


“Condition monitoring location (CML) optimization” is a term we frequently hear, particularly for piping circuits. Everyone wants their circuits to be “CML optimized,” but what does this truly mean? Borrowing a term from API RP 581, Risk-based Inspection Methodology, the broad definition of CML optimization as it relates to internal thinning is easy: we wish to establish the minimum CML coverage to correctly identify the true damage state.[1] Note that the true damage state is related to remaining life in traditional, time, or condition-based inspection programs. Although we sometimes focus on having sufficient CML coverage to correctly define the corrosion environment, corrosion rates are only part of the picture. Projected wall thickness is the ultimate goal when it comes to inspection, repair, and replacement planning. 

While the broad definition for CML optimization is easy, breaking this definition down to specific methods, algorithms, and business logic is not so straightforward. What is the basis for a given “optimization?” How precisely do we need to characterize the corrosion environment so we can quantify the amount of wall loss? Will CML quantities and selections be based on expert opinion, statistical methods, or a blend of both? How is the inspector, facility, company, and industry experience incorporated into the analysis? Are we optimized for a snapshot in time or is there an allowance for future degradation? There are as many answers to these questions as there are methods presently employed.

Setting the Ground Rules

For the purpose of this discussion, we will be focusing on wall thickness data taken at prescribed locations to monitor internal corrosion. In this context, “CMLs” are actually thickness monitoring locations. We normally generate this data using ultrasonic thickness (spot or scanning) and profile radiographic techniques. 

At a minimum, we expect CML optimization to provide guidance in proper CML quantities and placement. It must be consistent with the assigned, internal thinning damage mechanisms, while also considering site and industry experience. Additional benefits resulting from this dedicated, focused review of historical thickness data and inspection practices will often include the following:

  • Identification of and follow up inspection for potential localized corrosion areas
  • Recommendations to establish new CMLs or archive / inactivate unneeded CMLs
  • Identification and resolution of data anomalies, with resulting database “cleanup”
  • Opportunities to reduce measurement error and improve repeatability
  • Adjustments to circuit boundaries: combining, splitting, or moving boundaries, as appropriate
  • Prioritization for circuits that are candidates for 100% component inspection

As will be discussed later, the specific benefits will depend on many factors, including the quality and quantity of historical data, the corrosion environments, and the capabilities of the data analysis process.

This content is available to registered users and subscribers

Register today to unlock this article for free.

Create your free account and get access to:

  • Unlock one premium article of your choosing per month
  • Exclusive online content, videos, and downloads
  • Insightful and actionable webinars
Interested in unlimited access? VIEW OUR SUBSCRIPTION OPTIONS

Current subscribers and registered users can log in now.

Comments and Discussion

Posted by Frank Sapienza on February 26, 2021
Statistical approaches to CML management are... Log in or register to read the rest of this comment.

Posted by Vahid Rahmanian on March 31, 2021
Dear Thanks a lot. very useful Log in or register to read the rest of this comment.

Posted by Arman Shiva on April 7, 2021
I really enjoyed reading this article as I am in... Log in or register to read the rest of this comment.

Add a Comment

Please log in or register to participate in comments and discussions.

Inspectioneering Journal

Explore over 20 years of articles written by our team of subject matter experts.

Company Directory

Find relevant products, services, and technologies.

Training Solutions

Improve your skills in key mechanical integrity subjects.

Case Studies

Learn from the experience of others in the industry.


Inspectioneering's index of mechanical integrity topics – built by you.

Industry News

Stay up-to-date with the latest inspection and asset integrity management news.


Read short articles and insights authored by industry experts.

Expert Interviews

Inspectioneering's archive of interviews with industry subject matter experts.

Event Calendar

Find upcoming conferences, training sessions, online events, and more.


Downloadable eBooks, Asset Intelligence Reports, checklists, white papers, and more.

Videos & Webinars

Watch educational and informative videos directly related to your profession.


Commonly used asset integrity management and inspection acronyms.