Pipe remaining life ANSYS Analysis

[COSTYNHA]

Hello, I am Costin and I am a mechanical engineer.
Recently I was asked by my company to do a finite element analysis (Ansys) on a 20yrs old pipeline that works under creep conditions ( temperature=500 deg Celsius, pressure=20bar) in order to determine the remaining life of the pipes. I don't have much more infos about the material, just P11 steel ( ASTM A335 ), not even a record how the material properties changed during the time.
I will be grateful if you give some ideas on how to do that...

Thanks

 

[DSB123]

Costin,
I may be wrong here, but if you have never done thing kind of calculation and are asking fundamental questions how confident of the results will you be? If I were in your position I would either find a mentor within your Company to guide you through the calculation or if there is no-one there to do this then get an outside Consultant who is competent in these assessments and employ them to perform the assessment. You have a situation of creep-fatigue interaction here to consider not just creep by the way!!!

 

[COSTYNHA]

DSB123, thanks for your quick answer. you are right, this type of analysis, it's new to me, and it's a special situation.
I was asked for an example, exactly if the peoples in head of me will want to get a consultant to know what is that consultant doing.

 

[daviwy]

Costin,

As above, you'd need some guidance on this from someone with greater deal of experience. You shouldn't just be worried about creep. There're other things that will affect a pipeline

If it is a pipeline, propose a pigging program for it if possible. This will give you an indication of the current condition of the pipeline. You cannot just jump to remaining life analysis in my opinion without having any information on the line. P11 ASTM A335 should help you understand what the design WT and conditions of the pipe is. A pigging run will help you understand what the CURRENT WT and condition is. If the running conditions for that line has not changed over the years, it is a fair assumption to make that the average WT loss per year = CURRENT WT - DESIGN WT.

In terms of creep, you'd need to find detailed plan/isometrics etc, you cannot just rely on starting on a blank paper. Even if not electronic, there will be somewhere somehow data that will assist you build up a rough pipeline information.
Things you should be looking out for is:
. Content of the pipe
. Design Material (ASTM A335)
. Supports & External conditions
. Operating conditions (temperature=500 deg Celsius, pressure=20bar)

I'm no expert so I'd go with DSB's suggestion of getting in a consultant. That way, you not only learn from them and gain valuable experience, you also handover the risks to them because they are in a way GUARANTEEING that the pipeline will last for ever so long.

Other thing if you'd bring in a consultant, look at actually bringing them in for more than just one pipeline. Try to identify what other areas of concerns your company has, this should save some money.

Mechanical Operations Engineer
Oil, Gas & Power

 

[DavidCR]

Costin, I´m not sure if this creep condition would require a special scientific type consideration.

But in general, I´d say that you may apply FEA, or other tools, but if you are following a "fitness for service analysis" methodology. It is, if you have a code or reference that define a pass or not pass condition that will not be just your criteria but a legally accepted one.

For pipelines, pressure vessels, etc, you may check API RP 579 (Standard of the American Petroleum Inst.).

For example, if you have a pipe designed with the ASME B31.1 or B31.3 design code for pressure pipelines, and the pipes are corroded and have lost thickness, the API 579 will tell you how to use your FEA, or code formulas to define if it is safe based on the B31 codes, and what is the safe pressure, safe operating cycles remaining, etc.

There are many consultants that work with "fitness for service" and many software to do that, you may ask for Pauling Research Group, that has specific FEA software for fitness for service for ASME pressure vessel and related codes that may give some suggestion in your case.

 

[COSTYNHA]

DavidCR and daviwi, thank you for the tips.

We already did an evaluation assessment to the pipelines but we also want to add more, that's why we want to use Ansys, or a special software to do that, especially for the pipes who works into the creep regime.