Jul 01, 2014

One of the more common inspection monitoring programs for pressure vessels is to perform thickness measurement at Corrosion Monitoring Locations (CMLs) to allow monitoring of minimum thicknesses and provide estimates for corrosion rates. These minimum thicknesses and corrosion rates are critical in supporting risk based inspection techniques or in setting half-life prescriptive re-inspection intervals.

I have previously documented the problems that can arise when performing thickness monitoring for piping in a series of articles published in Inspectioneering Journal from 2012-20131,2,3,4,5. It has been the author’s experience when reviewing plant inspection data for pressure vessels in preparation for risk based inspection assessments that the quality of thickness data and corrosion rates for pressure vessels is often as much of a concern as piping thickness data. This article will outline the common pitfalls associated with the pressure vessel thickness monitoring process and provide recommendations on correcting these.

It is important to keep in mind that this article focuses only on thinning, or corrosion, which in many plants, is the most prevalent form of degradation. However, numerous other mechanisms can lead to pressure vessel failures, such as fatigue, de-alloying, environmentally assisted cracking (e.g. chloride SCC), etc. Effective inspection strategies should be developed to detect the particular types of anticipated or potential damage as appropriate.

To view this article on Inspectioneering, please click here.