Identifying Common Mistakes in Inspection Interval Determination

Introduction

This article is intended to bring light to often-overlooked gaps within our industry in regards to properly setting inspection intervals. Giving proper attention to and use of code/jurisdictional requirements, actual thickness data (outside of routine thickness data), and repair/replacement information can dramatically affect an inspection interval; in some cases leading to a facility failing to meet OSHA 1910.119 process safety management (PSM) compliance. Over the years performing Mechanical Integrity initiatives and PSM audits, we have discovered multiple gaps in regards to properly setting inspection intervals.

Discussion

Whether an owner/user has elected to utilize a risk-based inspection (RBI) program, or a calendar-based program, or a combination of the two, these gaps are relevant.  Simply relying on routine nondestructive examination (NDE) data to drive an interval can lead to an asset falling into this gap. If reliable NDE data is utilized to calculate corrosion rates and determines that an asset is fit to make an anticipated unit run, that does not necessarily mean that the interval can be set in accordance with the data. Codes, procedures, recommended practices, and jurisdictional agencies normally have more stringent requirements. This is where half-life determinations are required.  If an asset has a remaining life of seven years and a run cycle of five years, it’s easy to overlook the half–life requirement, thus setting the interval for five years and scheduling repair/replacement during the next scheduled turnaround. In actuality, under the half-life interval requirement, the asset will reach its retirement date (Per Half-Life) during the unit run (i.e., in three and a half years). This obviously is not a good situation in which to find yourself.