Guidelines for Providing Process Conditions for RBI - Part 3: Process Fluids and Consequence Models

, Be the first to comment

Tags: Consequence Risk Based Inspection


In this third of our eight part series covering various guidelines for providing process conditions for RBI, one of our senior consultants discusses process fluids and consequence models with respect to Risk Based Inspection. This article identifies several factors to consider when selecting a representative fluid for the determination of consequence.

Guidelines for Providing Process Conditions for RBI - Part 3: Fluids

In Part 3 of our series on guidelines for providing process conditions for RBI, we move on to discuss process fluids and offer some guidance on how to select a representative fluid that will be effective with respect to your RBI consequence calculations.

Process fluids are one of the most important factors in the consequence model of any RBI risk calculator tool. The process fluid is used to the determine the outcome of a loss of containment, which can range from benign for water to catastrophic for Hydrofluoric Acid. There are four basic process fluid types that are typically used in RBI safety consequence models. These fluid types are Inert, Reactive, Flammable, and Toxic. Reactive fluids are fluids that can cause chemical or thermal burn on contact. Examples are skin irritants and high temperature fluids. Toxic fluids are fluids that are hazardous to your health if inhaled, ingested, or absorbed through the skin. Flammable fluids are fluids that have a flashpoint at or below 199.4°F. Inert fluids are fluids that are not reactive, toxic, or flammable. Examples of inert fluids are air and nitrogen.

Many process streams have multiple process fluids (for example a distillation column may contain various hydrocarbon fractions such as propane, butane, light naphtha, diesel, etc.), however only one of these process fluids will need to be chosen as the representative fluid to determine the consequence for a particular asset or component of an asset being modeled. The process data collection step is the ideal time to choose the representative fluid that will be used to determine the consequence. Process engineers should be integrally involved in choosing the process fluid for any process stream. In addition to the process engineer's knowledge of the process streams for the particular unit, the Safety Data Sheets (SDS) can provide information that will help in determining the correct representative fluid to use when there are multiple fluids in the process stream. The heat and material balance can also be useful in selecting the correct representative fluid since it provides a breakdown of each constituent of a process stream into percentage by composition.

Based on the information gathered from the process engineer, SDS, and heat and material balance, the below guidelines can be used in helping to select the best representative fluids to use in RBI consequence model as well as identifying the toxic fluids that should be included:

  • For process streams that have multiple flammable fluids, the fluid with the highest concentration by weight and having the lowest Auto Ignition Temperature (AIT) should be used. The AIT can be found in the process fluid's SDS.
  • In cases where the fluid with the highest concentration does not have the lowest AIT, choose the fluid with the highest weight concentration if is an order of magnitude higher in concentration.
  • If multiple toxic fluids are present, the fluid with the lowest Toxic Endpoint (ERPG2) or Permissible Exposure Limit (PEL) should be chosen. The ERPG2 can also be found in the toxic fluid's SDS.
  • For situations where the fluid is a flammable/toxic mix, consequence models provide an option for using a flammable representative fluid with a percentage toxic fluid. An example of this would be where there is a sour hydrocarbon stream with a small percentage of H2S. The hydrocarbon would be the flammable representative fluid while the H2S would be the toxic fluid with a percentage of composition. The final consequence category would be the higher of the flammable or toxic consequence.

The goal in choosing a representative fluid is to determine a consequence to be used for a risk calculation. Some representative fluids can be determined easily but there are times when the choice of assigning the representative fluid is not easy to make. In those situations, performing a "What if Analysis" or Sensitivity Analysis using the various constituents of a multiple component process stream can be helpful in making the decision. The fluid providing the most conservative consequence should be used for the final risk calculation. Choosing the correct process fluid is an important factor in calculating the consequence in risk models and should not be taken lightly when trying to accurately determine the relative risk of an asset.

Stay tuned for the next entry in this eight-part series covering guidelines on assigning process conditions for RBI efforts:

  1. Guidelines for Providing Process Conditions for Risk Based Inspection (RBI) Implementation and Revalidation (Introduction)
  2. Corrosion Under Insulation (CUI) and How it Relates to Risk Based Inspection
  3. Process Fluids and Consequence Models (this article)
  4. High Temperature Damage Mechanisms
  5. Low Temperature Damage Mechanisms
  6. High Temperature Hydrogen Attack
  7. Environmental Cracking Damage Mechanisms
  8. Concluding Remarks

Be the first to comment

Comments

There are no comments for this article.

Add your comment

Related Services

Risk Based Inspection (RBI) Implementation and Planning

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

Damage Mechanism Review / Corrosion Study

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

End-of-Life, Remaining-Life, and Fitness-for-Service Assessments

When evaluation of inspection results suggest that an asset is near its end of useful life, Fitness for Service evaluations can determine if the asset us suitable for continued operation.

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

Managing Reliability of Ethane Crackers using DMR, RBI, and IOWs

How RBI, DMR, and IOW programs can be used to manage reliability of Ethane crackers.

Qualitative Risk Assessment of a Commercial Refrigeration System

A case study presenting the methods used to calculate qualitative risk for a critical refrigeration system and the results of the assessment.

Steam System Risk Mitigation Using Risk Based Inspection

The benefits of utilizing risk-based methodologies for the inspection programs of often overlooked utilities systems

Risk Based Inspection Yields Big Savings for Gulf Coast Plant

A 26-Year-Old Gulf Coast Chemical Plant Saves over $15 Million in Related Inspection Activities.

Qualitative RBI of a Commercial Refrigeration System

Refrigeration system owner/users who are maintaining their assets as prescribed may be unaware of the damage mechanisms that could affect the reliability of their assets and safety of their personnel.

RBMI Implementation Saves Refinery $63 Million

130,000 BPD Refinery Implements RBMI Program and projects a $63 Million savings over 10 years.

Risk Management for Kids

One of our consultants brings Risk Based Inspection into the grade school classroom for Career Day.

Hidden Benefits of Risk Based Inspection (RBI)

What are the hidden benefits of implementing Risk Based Inspection?

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.