Inspectioneering Journal

More On Scalable Accuracy

By Greg Alvarado, Chief Editor at Inspectioneering. This article appears in the November/December 2011 issue of Inspectioneering Journal.
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In this editorial I will cover the following topics:

  • Elaboration on what is meant by scalable accuracy and the value in mastering its use 
  • Helpful points to consider in choosing whether or not to do RBI 
  • Questions to ponder and things to consider when choosing a qualitative versus semi-quantitative RBI approach 
  • Examples of work processes enabling users of semi-quantitative RBI methodologies to move across the qualitative > semi-quantitative spectrum, within the same risk platform so that the level of effort is commensurate to the level of risk and to do it as accurately (per code, standard, reference, etc.) as possible. Notice I did not say precise in this instance. There is a difference.

The original article on scalable accuracy which laid the groundwork for the concept was published in the March April 2011 issue of the Inspectioneering Journal, entitled Scalable Accuracy, Key Roles of Risk Based Inspection and Fitness for Service, Equipment Life-Cycle Management Process. This article is reprinted immediately following this article for ease of reference. The two examples touched upon in the original article were the fitness for service approach as represented by the joint API ASME standard, API 579-1/ASME FFS-1 Fitness for Service Standard and the API Recommended Practice 581, representing the specific API RBI technology.

Another area demonstrating scalable accuracy is the selection of inspection strategies based on risk. I will cover this in the next article on scalable accuracy with some discussion on considering the amount of scatter in the selection of NDE and in developing the overall inspection strategy for a piece of equipment both in standalone and risk driven terms.

Let’s think of scalable accuracy for various practices in terms of effective equipment lifecycle management. We welcome other views, comments, etc. The concept may be difficult to grasp for some so we will elaborate a bit more.

Starting early in the lifecycle management program let’s look at RBI. The more quantitative the RBI methodology, the more it relies on actual data albeit there will be areas for judgment, as there should be. There will be considerably less than that for qualitative approaches. The more qualitative the RBI the more it relies on opinions as opposed to measure values. So to set the stage there is less inherent accuracy in qualitative RBI and more inherent accuracy in semi- quantitative RBI. Of course there are many qualifiers, most of which will not be covered in this article and have likely been covered in many past RBI articles appearing in the “IJ” and are available in various industry codes and practices such as API RP 580, API RP 581, API 510, API 570, API 653, ASME PCC RBI document, RIMAP, and various jurisdictional codes and standards and various HSE documents. 

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