large thermal expansion in vertical run 1

[waqassaleem12222]

Hi,

I came across a 18" Dia line with excessive thermal expansion (70 mm), as it is a long vertical run ( 8 meter) of high pressure steam. Although the model is passing B31.3 code compliance check (Ratio = 88%), but the system is having huge loads (in operating condition = 150 KN, while in sustain =60 KN)) on the dummy leg right below the vertical run. This vertical thermal expansion is causing the adjacent supports on horizontal run connected at the top point to lift off from the rack as well, but the code compliance of both horizontal and vertical runs still remain within allowable. Now trying to reduce these huge loads on dummy leg? I think, there may be possibility of water hammering, if one or two loops are inserted in vertical run. I am just thinking of various loop designs U, L Z etc. In case of high pressure steam, should we prefer 45 elbows instead of 90 degree elbows inside the loops so as to avoid hammering? What your experiences suggest?

Thanks

 

[stanier]

you could consider tandem bellows in the horizontal section of pipe. This would accomodate the movement described. You could use "cold pull". Of course this does introduce a maintenance issue.

If the hammering is occurring due to slugs of condensate it is preferable to eliminate these by use of steam traps rather than be conserned about the angle of elbows. 45 elbows are not satisafactory for expansion loops.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[waqassaleem12222]

So using steam traps, my first attempt would be to find natural flexibility in routing or using loops. I think i should be up to it now to reduce the load on supports. Will appreciate any guidelines in selecting a loop which can absorb maximum expansion in vertical 8m run? If anyone has a rough estimation how to size that loop for 70mm expansion, please inform.
Modeled a huge loop of one leg size 5m ( as shown in attachment) but even with this big loop the load is reduced only to 100 KN), which i think is still a heavy load for dummy.

Thanks

 

[BigInch]

Have you heard of spring can supports/hangers?

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[waqassaleem12222]

yes, but it would be the last resort. If there is no other way, i have to go for hanger or a can ( it seems applicable in this case). but til then i am trying to absorb this expansion naturally or with loops. Other then utilizing loop, another way i thought is to avoid dummy leg, and move this support at some distance from elbow, so as to absorb the expansion vertically downwards too. So this way total expansion would be divided equally upwards & downwards.

 

[BigInch]

Possibly, but that would markedly increase deflection at the dummy support's current location.
With such large expansions, it is difficult to avoid both load shifting and transfer from one point to the other.
If it works in the hot position, it may not work in the cold condition and v/v.
Spring cans were made for situations like this.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[SNORGY]

The X and Y restraints at the top of the riser are not helping. That said, they are certainly forcing the growth downwards and keeping the header from lifting off.

If this was my problem to solve, I would look at a spring can or two on the header at nodes on either side of the tee. It depends on what is connected to the pipe at the bottom of the riser (nozzles?). I don't really like putting a base support stanchion on a spring can in a situation like this unless I am connecting to a pump or turbine - but even then, you have to be careful with calculated nozzle movement from cold to hot relative to the nozzle loads imposed by the spring itself.

The problem with the loop in the riser is that the increase in flexibility comes with a counteracting increase in mass, so the net reduction in load at the base support might not be as much as you would hope.

I agree with BigInch in that spring supports are likely the better option.

 

[BigInch]

They also have "constant load" spring cans. Hot or cold, they take the same load.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[SNORGY]

BigInch is correct. Constant effort supports are available. My own experience is that they are not specified or purchased as often as perhaps they could (or should) be. That is probably - at least in part - because lots of folks who use CAESAR, for example, tend to let the software choose the spring support for them, and often it ends up being an "Anvil Figure 82" so people just go with that (or whatever else the program suggests). The days (and people) when you would actually detail-engineer each individual spring and read the charts manually to generate a hanger data sheet for purchase appear to have come to an end.

I am not a "pipe stress guy" - merely a generalist - but I still try to methodically plug and chug manually through the odd thing here and there just enough to have a general understanding of what the computer is recommending to me and to assess whether or not it makes sense to overrule its default answer.

The best way to learn CAESAR and how to get around a situation like this particular one (if you aren't date limited or run limited on the ESL) is to assume or pretend you have a NEMA turbine and then start playing with piping layouts and springs until you pass the "NEMA x 1.0" allowables. Go through that a couple of times and you will probably be able to solve things like this much faster next time. Don't get me wrong - there is nothing "easy" about what you are doing - it looks like you are doing fine. But on this one, I think springs are the answer.

 

[KevinNZ]

An 18" steam line can span a reasonable distance. Move the lower support away from the elblow until the pipe can expand down and not left off the top support. or move the top support away from the elblow.

 

[uaepiping]

Looking at the model that you uploaded the following are my comments on it (Look if you can do it, model it and see if it helps):

1) Is it reducer at 300-320? If yes, then is it possible to relocate in the horizontal run? Again if yes do it! It would save you a little cost for this bigger size elbow. Would add a little flexibility there.

2) For routing like this, I would route the pipe in minus 'X' direction then towards the rack and down to the header where you are joining it (All this if space allows). Also I have seen routing of the pipes to make a further bend over the header (running along it) and then dropping it to tie-in to header. This may help here.

3) Supporting for above has to be suiting to your situation (nearby lines, equipment, structural steel availability and constrution problems of those supports)! Consider Can hanger, if no other pill is working its majic (Elixir for many headaches)!