An Update on Risk Based Inspection: Bringing Focus on External Corrosion Under Insulation, Stress Corrosion Cracking And Other Damage Mechanisms - Reliability and Maintenance (RMC-12-46)

Using RISK as a basis for maintenance planning - Since its introduction over fifteen years ago, the concepts of risk-based inspection (RBI) have been applied successfully in many plants around the world. Risk-based inspection is a systematic process for factoring risk into decisions concerning how, where, and when to inspect a process plant. RBI focuses inspection resources on the highest priority equipment to determine asset integrity. RBI cost effectively helps make process plants safer and more reliable.

- NPRA Reliability & Maintenance Conference & Exhibition,

An Update on Risk Based Inspection

RMC-12-46 - An update on Risk Based Inspection: Bringing focus on external corrosion under insulation, stress corrosion cracking and other damage mechanisms AFPM Reliability and Maintenance Conference 2012


In 1998 we presented a paper entitled "Using risk based inspection to focus on corrosion under insulation". We stated:

  • Risk Based Inspection (RBI) was a relatively new technology being applied in the chemical process industry.
  • RBI provided a systematic process for factoring risk into decisions concerning how, where and when to inspect a process plant.
  • RBI focuses inspection resources on critical equipment in ways which will prevent failures, particularly catastrophic ones.
  • RBI has the potential to make chemical plants safer in a cost effective way.
  • RBI can provide a dynamic (time dependent) means of determining when and where to expect in-service deterioration.
  • RBI effectively predicts Corrosion Under Insulation (CUI) damage.
  • RBI effectively predicts chloride stress corrosion cracking and other damage mechanisms.
  • When damage is confirmed a Fitness for Service (FFS) evaluation can be used to decide on an appropriate maintenance strategy

In the 14 years since we presented that paper at the PetroSafe conference in Houston, we have rolled out hundreds of RBI projects, collecting data and findings that have contributed significantly to improving the reliability of the refining, petrochemical and chemicals industries and specifically across the Huntsman Chemical plant in Port Neches Texas. This paper revisits the models and asset strategies developed to prioritize inspections for CUI as well as other damage mechanisms such as stress corrosion cracking and examine a representative sample of findings that resulted in significant lost production avoidance.

Table of Contents

  • Introduction - Risk Based Inspection (RBI)
  • The corrosion study - Identifying damage mechanisms
  • Chloride stress corrosion cracking, CUI and other damage mechanisms
  • The CUI model in RBMI
  • The RBMI project at Port Neches
  • KPIs and measureable metrics
  • Significant findings
  • Conclusions
  • Path forward - The RBMI scorecard
  • Appendix I - Marsh Risk Consulting


  • When good data leads to informed decisions you can prioritize those inspections aligning them with those damage mechanisms driving the asset's risk.
  • The Port Neches facility has achieved significant improvements in reliability leading to a 96.7 percent asset mechanical reliability.
  • The significant findings in CUI and Chloride Stress Corrosion Cracking as a result of the RBI study, allowed us to effect the appropriate repairs and replacements delivering significant value to the Port Neches facility in lost production avoidance.

Presented at AFPM - Reliability and Maintenance Conference May 22-25, 2012 Henry B. Gonzales Convention Center San Antonio, TX

Publication Inquiry

Related Services

Damage Mechanism Review / Corrosion Study

One of the most important steps in an RBI project is the corrosion study or damage mechanism review.

Corrosion Control Planning

Achieving zero corrosion-related loss of primary containment in the refining industry.

Risk Based Inspection (RBI) Implementation and Planning

AOC has delivered thousands of sustainable Risk Based Inspection (RBI) programs earning the trust of owner operators.

Related Tools

API 580 Work Process Quiz

How well do you know RBI? Take this short quiz to test your knowledge of the API 580 risk-based inspection (RBI) work process.

RBI Potential Savings Calculator

Create mechanical integrity (MI) program value rather than it being seen as a necessary cost to minimize.

Related Training

RBI/MI Overview

A high level overview intrucing Mechanical Integrity and Risk Based Inspection

API 580 RBI Overview

What impact does Risk Based Inspection (RBI) have on my organization?

API 580 Training

Is your Risk Based Inspection (RBI) program aligned with the API 580 Recommended Practice? Are you ready for certification?

API 581 Overview

What's actually going on inside all of that fancy software? An introduction to the API 581 methodology.

API 581 Training

A deep dive into quantitative Risk Based Inspection (RBI) as outlined in API 581.

Related Knowledge

How to Incorporate the New PHMSA Underground Gas Storage Requirements

This is a practical approach to incorporating the new PHMSA gas well rules into your integrity program with the rest of your surface and subsurface assets.

Asset Value Management vs Asset Performance Management

A look at how the financial sector's concept of Asset Value Management can be applied to the petrochemical industry.

RBI Value: Both Transitioning And From The Start

A look at how RBI adds value whether you are just starting out or transitioning from a traditional methodology.

Guidelines for Providing Process Conditions for RBI - Part 7: Env Cracking

Additional process data may be needed when environment, stress, and metallurgy are so alligned so as to indicate susceptibility to environmental cracking.

Guidelines for Providing Process Conditions for RBI - Part 6: HTHA

A simple screening to determine HTHA susceptibility and factors to consider when more data is required.

Guidelines for Providing Process Conditions for RBI - Part 4: High Temp

This article suggests additional factors to consider when calculating probablity of failure for equipment exposed to high temperatures.

Guidelines for Providing Process Conditions for RBI - Part 2: CUI

This article identifies several factors to consider during data collection as well as points out some guidelines for selecting potential inspection locations.

Hidden Benefits of Risk Based Inspection (RBI)

What are the hidden benefits of implementing Risk Based Inspection?

Plant Management 101: Common Work Processes

A dysfunctionality found in many refineries, chemical plants, and other production facilities, is a lack of common asset management work processes.

Proposed API 581 Inspection Plan Optimization Example

An example to compliment our earlier proposal for a risk analysis option that allows for individual damage mechanism risk calculation in API 581