Introduction to Piping Flexibility and Stress Analysis as per EN13480 5

[tfi]

Hi,

I'm a mechanical engineer and I have very recently moved into a position where I work by myself and I sporadically (~5 times a year) have to ensure compliance of short runs of piping with EN13480 so as to fulfill PED essential safety requirements (steam piping in a boiler room that exceed PS.DN>1000).

I can't find a way to outsource such small work packages (usually up to 20m of pipe, 3 or 4 bends, 2 or 3 flanged valves) so I intend to study so I can attempt to calculate these segments of piping by myself. I understand that EN13480 has a section on a simplified methodology for "hand" calculations.

Is this a reasonable idea?

Is there some sort of guide or handbook for piping design/stress analysis that is oriented towards the PED/EN13480? Or is my only chance to learn by reading and digesting the whole code by myself?

I know there are courses out there, but they cost thousands of dollars which my boss is not paying for and I have no references pertaining to their quality.

Thanks in advance.

Best,

 

[1503-44]

ASME B31.1 Also has such a discussion.

Short segments of pipe with a bend or two are easily solved by hand, or Excel methods.
Are there particular configurations, materials, diameters, pressures and temperatures that you expect to work with?

We're here, if you need help.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[RVAmeche]

In general pipe stress is not something you can just jump into and figure out yourself. There's lot of things to consider, lots of sources, and lots of history. Without proper context its very easy for a "garbage in, garbage out" situation where you say the program says everythings fine! and that's because the support definitions were wrong, load cases not correct, etc.

If you can't find a small firm to pay a couple grand and run the analyses, you can check out the older piping flexibility methods from before computers were widespread. Kellogg's Design of Piping Systems and Peng's Pipe Stress Engineering are good places to start. Note, in my experience, the simplified methods are more conservative than modeling so you may find issues that don't really exist and have no way to defend it.

If your piping is connecting to the boiler or other pressure vessels/equipment, you've got equipment nozzle loads to worry about which complicates things.

 

[tfi]

Thank you both for your useful replies.

1503-44:
Yes. If I have to perform flexibility analysis it would usually mean I have a 4" or 5" CS steam pipe coming out upwards from the boiler through a flanged globe valve. Maximum pressure would usually be either 10 barg or 15 barg at saturation temperature. A steam header would be usually under 10m away (straight) so it might get 2 to 4 changes of direction (up, down, and 0 to 2 changes in the horizontal plane) and up to 20m of pipe to get there.

Hand/excel calculation of 3 or 4 cases, with a couple variables to dabble with would seem to be the way to go. I thought B31.1 was only for power plants, I'm working with the installation of 0,5-8 MW packaged boilers in manufacturing plants so I was hoping B31.3 would "suffice" (idk if that's a fair way to put it).

If I can comply with PED through B31 standards instead of EN13480 I'd rather do that, because I'd appreciate the possibility of working in non-EU countries in the future. I've seen some discussion of this in the forum and also some criticism of EN13480 so I'll go through B31.3 and then perform a "gap analysis" against the PED.

RCAmeche:
I can appreciate that this is a hugely complex discipline, and while I'd like to have the guidance of a senior engineer or to be in an office with experienced professionals and adequate procedures and tools, it simply is not the reality I'm facing (to put it mildly). So I can either refuse to work with systems that require flexibility analysis and be fired soon, or I can face this as an opportunity to learn and take the long term challenge of getting acquainted with the standards and principles by myself.
What I can resort to is a third party compliance assessment of whatever design I come up with.
Right now I might have 4 to 6 months before I'm acutally required to perform such a calculation, so that's the time I have to study/practice.

Thank you for those references, I will make sure to get a copy of Kellogg's or Peng's. I can live with conservative results because this is a very small part of each project and being able to demonstrate safe design through calculations is most important to me, and I work virtually alone.

Thank you for the heads up concerning nozzle loads. After I have studied a standard and Peng's book I will book a couple of sessions with a retired pipe stress engineer that used to work here to discuss that and other issues that may come up. He apparently used Algor's PipePak, but I will need to use spreadsheets because that is not around anymore.


I know this sounds somewhat (or completely?) crazy to face learning this by myself, but it's this or having a breakdown for having changed jobs in a recession to find this situation.


Best

 

[1503-44]

Calculating pipe forces, moments and shear is very much the same no matter what the code. The methods draw heavily from structural analysis of space frames. It is the allowable material stresses and safety factors that may vary, which leads to different allowable stresses and maximum operating pressures. There are also some differences in exactly how some certain stresses are calculated, but all the codes generally orbit about the same points and principles. Once you get a handle on those, you can attend to the details of specific codes.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[XL83NL]

I've seen some discussion of this in the forum and also some criticism of EN13480 so I'll go through B31.3 and then perform a "gap analysis" against the PED.

There will be a large update in the 2024 edt. of B31.3 in Appendix N, specifically a rewrite of N200 intro N301 that will provide detailed guidance on such a gap analysis.

I can appreciate that this is a hugely complex discipline, and while I'd like to have the guidance of a senior engineer or to be in an office with experienced professionals and adequate procedures and tools, it simply is not the reality I'm facing (to put it mildly). So I can either refuse to work with systems that require flexibility analysis and be fired soon, or I can face this as an opportunity to learn and take the long term challenge of getting acquainted with the standards and principles by myself.

RVAMeche has given you solid advice.

You 'simply' need to convince your boss he needs to subcontract this work, or hire an external experienced. This is not an opportunity for you, its a huge risk. It may only become a possibility for you if there's an experienced senior in place to mentor you over the long term. There have been a lot of similar topics on this on ET here in the past, and people continuously seem to underestimate this work. The advice in this topic is the best free consult you'll be given regarding this assignment.


Huub
- You never get what you expect, you only get what you inspect.

 

[tfi]

RVAMeche has given you solid advice.

You 'simply' need to convince your boss he needs to subcontract this work, or hire an external experienced.

I understand and truly appreciate it. I have tried to convince my boss since I first read the PED and understood the responsibility to verify the Essential Safety Requirements. I will try to find a solution with a subsidiary that can sell us the work and/or make a mentor available.

What I found out is that apparently it has been customary in EU countries for steam boilers and other equipment to be installed on site under the PED's jurisdiction without any formal assessment of the Essential Safety Requirements, even in situations where clearly the factory owner is not responsible for the design and construction. I'm new to this business and was taken aback.

Thank you very much for your advice, which confirms my own belief. I will find a way to implement a responsible procedure for this that includes an experienced professional, despite my learning the code.

Best.

 

[LittleInch]

What you need to find is an unretired pipe stress engineer who could do these little jobs as a side hustle or he's a one man band and can fit these small jobs in and model it in Caesar or something equivalent.

Vessel nozzle loads in particular and small bore stuff can go wrong quite quickly.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Open Pipe Stress looks promising.

https://openpipestress.com

https://pipe-stress-infinity.readthedocs.io/en/latest/

https://pipe-stress-infinity.readthedocs.io/en/latest/user_guide/main.html

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[RVAmeche]

Bear in mind that with pipe stress, kind of similar to FEA and other models/software, setting up the model based on a drawing or proposed design is the easy part. With some tutoring pretty much anyone can knock out that quickly. The hard part is when you have to change the design because it fails - how to reroute things, remaining cognizant of where your reroute is in 3D space and ensuring its not hitting anything, or even just being able to recognize whats causing the issue and addressing it.

Someone experienced in these calculations needs to be actively involved.

 

[LittleInch]

Even setting up the model you need to know if the default values are correct for your particular situation. The other thing is if you're only doing 5 a year, you will forget and do it very slowly or wrong compared to someone who's doing 5 a week.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[XL83NL]

Open Pipe Stress looks promising.

https://openpipestress.com

Has anyone ever heard of or even used that open source package for pipe stress?

Huub
- You never get what you expect, you only get what you inspect.