When is a pipe stress / expansion calcualtion needed 2

[cardin]

Hi,

I have someone here working on a 10 bar /190degC DN300 steam pipe loop. Total length is about 75m for the steamboiler and back.
doesn
He says that if he will mount the pipe in brackets with chains and makes all the connections flexible he doesn't need a stress or expansion analysis. I doubt if that is a correct conclusion. Does anyone know if there are any requirement other than possible customer requirement on when or when not to perform analysis?

 

[LittleInch]

What design code is he using for the pipe?

I don't really understand the "pipe in brackets with chains?" bit Do you mean he's hanging 75m of 12" pipe from the roof?

This all comes down to design responsibility and approval.

What is your role here?

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

 

[1503-44]

190C! Having just reviewed B31.3. Do the analysis.
The exception is basically: no analysis needed only if you have done (on record) an analysis for another pipe that is similar in every respect.

Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

 

[MJCronin]

I think that it will be OK as long as he uses "chains"....


MJCronin
Sr. Process Engineer

 

[1503-44]

Sure about that? I don't see the sketch. Hot pipe doesn't care how its supported. It wants to slide. And 75 meters of it will expand 140mm (5.5in) and chains won't stop it. So, that depends entirely on the meaning of how flexible "flexible connections" really are, the locations of guides and stops, or the pipe may buckle, and the configuration of the offset. All unknowns to us.

Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

 

[TiCl4]

-twentytwo : I'm pretty sure MJCronin was going fairly heavy on the sarcasm there.

OP: What is the design code?

 

[MJCronin]

MJCronin
Sr. Process Engineer

 

[1503-44]

Oh Yes. Perfectly obvious now that you mention it. I believe he was yanking OUR chains.
Sometimes sarcasm can be hard to recognize without a

Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

 

[1503-44]

Yes. It is true. None of that is approved for pipe stress.

Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

 

[KevinNZ]

What are the local laws? Around here this line would need:
full design to B31.1 and Earthquake design
3rd party design verification of the piping
Design of all the supports signed off by a registered civil engineer.

How is the OP's designer even going to know they are no exceeding the boiler allowable nozzle loads.

 

[cardin]

Hi, @KevinNZ here you have the same rules as far as i can see, but his comment is that the old design was the same length and had several problems with the motion restrictions. Therefore hanging piping in chains would give it enough freedom. I only are in for the safety control systems of the units. I was only wondering because the solution sounded too easy. Why do all piping systems have such complicated supports if you would just be able to hang it in chains and connect it to flexible piping? The system is fairly simple. Just piping comming into a building and making a square around the buiding. straigth 15m, right turn, straight 23m, right turn, straight 15m, right turn, and back 23m.

Thanks for the comments.

 

[1503-44]

Straight pipe is "simple". What you have there is a large confined loop, which is an indication that there are complex flexibility requirements. Guide and stop anchor locations are critical to it functioning properly. It must not only be allowed to expand. It also must be made to expand in the appropriate directions.

Dont do it right and unrestricted expansion in the wrong direction can have equally disasterous consequences as over-restraint. Obviously chains do not act like guides or anchors. Would you like to have all the movement, 300mm, occur at one connection point. Or would you like to have all the force on two connections. Those are the extremes. What you need is a careful balance between that range of possible results.

Reality used to affect the way we thought. Now we somehow believe that what we think affects reality.

 

[LittleInch]

Pipe hangers as they are otherwise known are used on occasion where the pipe needs to be able to move with very little force being applied. However for most outdoors locations these are too flexible, cost more and would be bouncing around all over the place every time the wind blew. Hence why they are used only in certain very specific locaitons (often near tanks which have a low capacity for forces).

The problem lies in the "flexible connections". For a high pressure steam line these are not cheap and are a weak point in the system. The flexibility of the piping system hanging on chains can easily lead to repetitive movement or swaying of the pipes or large movements leading to fatigue of these flexible connections.

Most times you need to guide the pipe and keep it within certain limits of movement so that one location doesn't become overstressed.

Does that answer your question?

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

 

[XL83NL]

In an ideal world where we have no seismic, wind, snow loads, etc., and no dynamic effects like water hammer, relief forces, a piping system hanging in chains might be a solution. But that's something we can only dream of.

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

 

[cardin]

@LittleInch and @twentytwo, yes that was my opinion too. But i was lacking the right wording. At first i thought OK, making a piping loop hanging from the room with chains and connect everything to flexible connections and you prevent stresses. But thinking of it i got to think you are removing stresses, but introducing potential other problems and stresses on other locations. Reading your posts i was supported by my thought and my concerns proved to be correct. The post on ASME requirements helped me out. I knew i read it before, but couldn't find where.

 

[saplanti]

Even if you hang the piping uniformly with chains you may still have to do the stress anaalysis since the chains will still restrain the piping under thermal expansion although you may even use presetting of chains. Startup and shutdown thermal loads somehow will be restrained more by some chaines than the others.

The piping connections where the inlet and outlets are will have large loads and they may suffer.

You have not provided a PID or sketch for our full understanding why and where you will use the loop. The loop may or may not have branch connections. If the branches are available they may be under stress concentration.

I totally agree with the comments above, there may be other operational and occasional loads that you or us unaware.

So you had all possible answers against what you provided. I wish you good luck.

 

[curtis2004]

Hi Cardin,

Please hire an experienced professional, who has successful track record of solving/building similar systems. You have to build it right the first time around. There are so many detailed knowledge you need to properly design, procure, fabricate, install, start-up, and operate the system you have mentioned in you OP. It seems a person you are dealing with doesn't grasp or appreciate complexity of the task. That is the best advice I can give you.

Thanks,
Curtis