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RBI: Inventory group / Corrosion Loops and representative piping

RBI: Inventory group / Corrosion Loops and representative piping

RBI: Inventory group / Corrosion Loops and representative piping

Dear friends,

I've been assigned to do a draft RBI (RISK BASED INSPECTION) study of a hydrotreatment plant. Given to me are all the P&ID and Process Flow Diagram, along with all datum to the corresponding machines. However I'm struggling to find some help on the following issues.:

1) What criteria can you use to establish corrosion loops (CL). Given a plant, what should be the key criteria to delimit which group of piping and equipment belongs to a single corrosion loop?

2) The same question for Inventory Groups. What is the criteria for establishing such groups and how do they affect the consequences of failure? It is suggested that the user select the Inventory groups by the group of equipment he can isolate in case of failure. What if my plant do not have isolation valves. Can the inventory group be a single giant loop?

3) How do you model the piping. Should you do all the piping or select the representative piping inside a corrosion loop. Or should you select the representative piping and also the entrance and exit piping of all equipment. What criteria can you suggest me?

4) I find it extremely difficult to find an online case study and information regarding to the execution of RBI. Can someone kindly offer some documentation that is either a case study or contains some answers to those questions I have above? The recommended practices API 580, API 581 (which I have a physical copy) do not answer my above questions. They are too much theory and too little about application.

Thank you indeed for your help.


RE: RBI: Inventory group / Corrosion Loops and representative piping

Go back to your boss. Get your company's procedures for a risk assessment FIRST!
Get your company's requirements for approving a risk assessment FIRST!

Then - AFTER you know what YOUR company needs (is going to have to have) - THEN you can start asking questions on-line to unknown observers.

RE: RBI: Inventory group / Corrosion Loops and representative piping

I never worked for DOW, but they were the people who invented RBI. I worked in pipelines and a ex Dow employee wrote a book, pipeline RBI, kent mulberry. He lays out what eventually became the API 580. Api gives a great outline and answers your questions

I'm assuming that you company hasn't adopted api 580 and it doesn't have it's own system.

RE: RBI: Inventory group / Corrosion Loops and representative piping


Hi Yucao

As you said, there is no detail in API about how to define corrosion loops. I will describe you what criteria I use to define my corrosion loops, which I had apply succesfully in different type off plants. First, I must say that I´m

- What are corrosion loops?: corrosion loops are groups of equipment and pipes which have same damage mechanisms susceptibility (not only corrosion)
- Why do we define corrosion loops? I define corrosion loops to improve my inspection and mechanical integrity system effectivity. By analysing corrosion loops you will have a better understanding about damage mechanisms presented in your process. Also, if by an inspection you detect degradation in a component of one of your corrosion loops, you could analyse if the other componentes may have the same damage mechanism severity and plan your next inspection. This is why I consider you improve effectivity.

Criteria to define corrosion loop:

- Analyse your CMMS taxonomy
- Start with a unit plant: gas treatment, refining,crio, etc.
- Identify process systems, defined by representative fluid
- Identify process points where process conditions (T, P, Q) vary in a way that could change damage mechanism susceptibility
- Identify construction characteristics that could derive in change of damage mechanism susceptibility (burried/not burried, thermal isolation, construction material, etc)
- Based on what I described before, you can define your corrosion loops.

About pipes. I recommend you to define groups of pipes inside your corrosion loops. I recommend you to define groups of pipes that do not need more than half a day to be inspected.

Hope you find it usefull.


RE: RBI: Inventory group / Corrosion Loops and representative piping

Thank you all for your help. Much appretiated.

Luciano: It's very clear and instructive. Thank you

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