Piping Flexibility analysis of refrigeration systems - european standard 1

[scepticR_D]

Hello everyone.
I'm new here, so first I wanted to say hello.

I am looking for advice on the analysis of the flexibility of refrigeration installation pipelines. I have a system that is to be designed and manufactured according to the leading standard EN 378. This standard, in terms of pressure pipeline designs, refers to the EN 14276-2 standard. This standard is very superficial (general), only about 30 pages long. And what surprised me the most was the complete omission of the issue of analyzing the flexibility of pipelines. Although the standard loosely suggests that the EN 13480-3 standard can be used, it does not push for such a solution anywhere.
My question: is it really possible that European standards allow the implementation of full-fledged pressure installations (especially those working with CO2 or ammonia) without the need to analyze such a key issue, just because the application of this installation is refrigeration? The standard is of course harmonized with PED 2014/68/EU.

I have just analyzed the flexibility of a system (TS 100 degC) approved for operation by a notified body, in which the stresses in the pipelines reached 230% of the permissible values, and the connections of some heat exchangers were overloaded 8 times. Flexibility analysis was not required when assessing compliance with the Pressure Equipment Directive.


Regards,
scepticR_D

 

[1503-44]

As near as I can tell... EU standards are not complete. Member State laws comply with EU policy and Norms when and where applicable. What is specifically allowed or disallowed is governed by the member states laws and in certain cases the responsibility for adequate design and operation of pipelines is delegated to a designated national system operator, or the operators themselves. Legal Norms and requirements are implemented into State law when appropriate. You must also check the local Member State requirements.

In Spain, these companies are Enagas and Exolum

Enagas

Enagás Services Solutions, S.L.U. is the Enagás Group subsidiary responsible for the provision of all types of services related to the energy sector, the telecommunications sector (fiber optic) and infrastructure projects in general, as well as the performance of consultancy studies, engineering projects, technical support and management of the execution of works and facilities, and the planning, service, development, construction, operation and maintenance of infrastructure.

https://exolum.com/en/where-we-operate/

In the overall scheme of things, Codes and Standards always prescribe the minimum requirements for any design. Many people (including engineers) seem to think like "If it meets code requirements, its good." Nothing could be farther from the truth. If your calculations prove that a system meets code, or does not meet code, that does not really matter at all. Its great that you have produced a minimally designed system, but you must make it meet service requirements in every and all aspects. You must produce a system that meets all the requirements you can see developing over the lifetime of the system. If your calculations prove something needs 8 times the strength of what the code says, make it so. That's why engineers exist. If something only has to meet code, we'll then anybody could read the code and design a good system. We have to know when our service requirements are more demanding and need a better design than what is required by code,

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

 

[scepticR_D]

Thank you for your comprehensive answer.
I hope I expressed myself correctly: the overloaded system mentioned above is not a result of my design. I received this system for review in connection with another, similar project. What I wanted to convey is the fact that it terrifies me that such a system has been certified in accordance with the law.
As you said, standards should provide a certain minimum. In my opinion, the omission of such an important aspect in the guiding standard for refrigeration pipelines (EN 14276-2) is nothing more than an oversight. My target question was whether maybe I had simply missed something when analyzing the EN 378 and EN 14276 standards.

Regards,
scepticR_D

 

[1503-44]

Yes. I understood it was your review of an existing system. I wasn't trying to pin a bad design on you, but I can see that it might be taken as such. My point was that meeting code is no indication that safe design has been achieved, so in that sense, it isn't important if it exists as a law, standard or whatever, because in the end we need to do exactly as you are doing; finding out when a design fails under any condition and make it right regardless of what the code says. A minimal code might be something as simple as, "Build it safe", which IMO, is the best kind of code. Many Codes, standards just tend to be checklists of minimum needs. In that regard, it's not important whether an EU or ASME, or any of them exists, or not. Also noting that there are many dangerous things that are uncontrolled by Codes and Standards anyway. Seat belts for school buses?

What's more important than if an EU standard exists, or what they might say is why the system you are reviewing is failing code, because the requirements might be addressed elsewhere. So the first problem might be the applicability of those codes to your system.

I'm not familiar with all the codes you mention, but pipeline codes are generally not applicable to refrigeration systems. The second thing that comes to mind is the 100°C temperature. That being a rather high temperature in terms of refrigeration, it suggests refrigeration Codes might not be appropriate either. What else can you tell us about this system?

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

 

[LittleInch]

scepticR D

It might be language, but I think what you refer to is piping, not pipelines. They are different and use different codes and standards.

These are not standards familiar to me and I can't see a copy, but there is usually a general section where it states that the design should include for all forces, stresses and the like to create a design within acceptable risk limits.

At those temperatures it is not surprising that there are high stresses if insufficient flexibility is present.

First - does the system properly fall under the scope?
Second - what does the code say about analysis of expansion and thermal effects?

But this is a subset of piping and stress design which is not common here at least and may need a more specialist forum or location to get you specific answers to this code.

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