The Scalable Accuracy Approach to Equipment Lifecycle Management

By Greg Alvarado, Chief Editor at Inspectioneering. August 19, 2013

Continuing from last week’s blog, I want to go in depth into scalable accuracy for fixed equipment lifecycle management. Last week I started by providing the process used before initiating scalable accuracy. That is an imperative step prior to initiating technologies using scalable accuracy, includingRisk Based Inspection (RBI) and Fitness for Service (FFS). In this post, I want to outline the scalable accuracy approach to fixed equipment lifecycle management.

When using a single RBI software platform (or multiple platforms that have been calibrated against one another) start more qualitatively, then progress to semi-quantitative, and quantitative tools as justified by risk. These more quantitative tools include FFS, Quantitative Risk Assessment, creep remnant life analysis, complex vibration/fatigue analysis, etc. Here is the process for the scalable accuracy approach:

  1. Highest-level risk analyses sometimes involve a procedure where multiple pieces of equipment are represented by a single item. One should have a procedure to assure consistency and vet the decisions via qualified team members. This is a very coarse analysis, relatively, and not typically recommended.
  2. Perform the initial RBI analysis, including damage mechanisms review from the Process Flow Diagram level, or some commensurate level that is less detailed than Process and Instrument Diagram (P&ID) level. Use and document assumptions, qualitative and semi-qualitative, as agreed to by qualified team members.
  3. As risk dictates, get more information to reduce the scatter in the RBI prediction or analysis for those specific higher items, e.g., if the risk driver is an assumed value (they are supposed to be reasonably conservative, as judged by a complete and competent team), get the actual information, becoming more quantitative for those specific items.
  4. If risk justifies or digital circuit level data is readily already, perform RBI analysis from the P&ID level as fully semi-quantitative.

If risk justifies and it is appropriate, perform quantitative analyses such as a QRA, FFS analysis to obtain a thinner t-min for the RBI analysis or standalone, or HTHA study for equipment strategies in High Temperature Hydrogen Attack service, creep remnant life studies, etc. These are the most rigorous and costly analyses but may eventually be justified if the risks and payback are high enough. For example, a pro-active FFS in advance of hydrocracker inspections or turnaround may be justified to determine most critical areas for inspection and to create failure assessment diagrams (FAD) for maximum tolerable flaw sizes.

At times, extremely detailed damage mechanisms reviews and/or IOW studies may compliment many of these activities. An effective job of IOW (integrity operating window) establishment, with a notification system for exceedences, can be a big help managing equipment in a dynamic environment by “catching” process changes that could affect equipment integrity or reliability in a timely manner.

This potentially impacts the RBI, FFS and remnant life analyses. In order to set the stage, i.e. use word pictures, for facilitating a new way to look at work practices when teaching the API RBI 580 and API RBI 581 courses I usually use the following:

Question: Why do we usually inspect equipment?

Answer: Get additional information to “fine tune” or have a more accurate “picture” or understanding of the true damage state of the equipment in question. Another way to look at it is that when we inspect, if we have done a good job of identifying the potential damage mechanisms, are using the right methods to find the damage that can cause a breach of containment, we can get information to lessen the uncertainty of what we believe to be the damage state of the equipment.

Question: RBI is primarily about answering this question, “How much confidence do I need to have in what I believe to be the condition of the equipment?”

Answer: We let risk and understanding risk drivers provide the direction and justification. For example, if a risk based inspection analysis tells us we will reach the risk threshold4 on a certain date based on damage progression, the ability of the equipment to withstand the damage and the consequences, we will normally perform the inspection/s on or before that date to keep the risk within a certain criteria. Therefore, the combined consideration of probability of failure (PoF) and consequences, i.e. risk, is telling us how much confidence we need to have in our knowledge of the true damage state of the equipment.

In next week’s blog post, I will outline aspects of Fitness for Service related to scalable accuracy. Sign up for the Inspectioneering Turnaround to get an email when the blog is posted.

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