FFS Forum: Corrosion Assessment without the Grid

Editor’s Note:

This is the first edition of a new column dedicated to all things fitness-for-service (FFS). The column will appear in each issue of Inspectioneering Journal. This is a forum format, so readers are encouraged to send us suggestions for future FFS related topics, comments on the current article, and raise FFS issues of concern. All submissions will be reviewed and used to pick topics and guide the direction of this column. We will treat all submissions as strictly confidential. Only Inspectioneering and the author will know the names and identities of those that submit.

The author, Greg Garic, P.E., has over 35 years of experience in FFS and mechanical integrity assessment of pressure systems. He began his career at NASA’s Stennis Space Center, where his tenure spanned 15 years. After rising to the position of Senior Engineer, he joined Stress Engineering Services and has been there for over 20 years. As a Managing Principal with Stress, Greg focuses most of his work on stress analysis, fracture mechanics, pressure systems engineering, and FFS across the process industries. He also teaches FFS training courses, is qualified as a stress analysis expert in federal court, and leads Stress’ New Orleans office. Suffice it to say, he’s been around the block more than a few times and knows FFS.

Please send your inputs to the author at ffs@inspectioneering.com.

First of all, it’s very exciting to start a new column on fitness-for-service (FFS) in the Inspectioneering Journal. As a pressure systems engineer for at least 30 of my 37 years of practice, I’ve learned a few things. Most frequently, I learn things from other engineers working in the field. That’s why I’m using a “forum” format for this column, so other practicing engineers will be able to write in with comments, critiques, observations, and suggestions for future columns.  

For this first column, I’d like to touch on what I see as an underused FFS technique for corrosion assessment:  point assessment of corrosion – a technique that does NOT require a thickness grid.

The reason I find this technique useful is largely because it’s so easy and cheap to implement. Take 15 or more thickness readings in the thin area, do a few quick calculations, and you’re done! Yes, it’s conservative and only works for relatively uniform metal loss, but if you pass, you’ve avoided significant inspection and analysis expense. If you fail, you wasted almost no time or expense and higher level analysis can be undertaken.

The steps to corrosion assessment based on point measurements are as follows.

Step 1: Collect your data