My question is the following:

Imagine the rising of a pipe, in the highest point of the rising we situate a +Y restraint (this support has being introduced for reducing the vertical deflection in sustained case)I analyze the piping and there is no overstress in any point,but when we observe the operational case, such point rises 3"(76,2 mm).

In order to verify there are no problems with the lift off, I delete such support and recalcule. I observe there is no overstress in the sustained case, for this, I think that the lift off is valid and I permit the pipe rises in such point and I will erect a rigid support.

Do you think this method of analysis being correct?
Do you believe it should be erected a spring support?
Would you follow the same steps I have followed to verify the location of such point?

Read this thread . In addition, this one is also helpful.

You can find additional information on this topic by using the [search] feature of this forum.

Thank you very much, Richard, for your answer,but I would like you give me your opinion to this,that is, although the pipe is not overstressed, is it licit and/or "sthetic" to see that a rigid support has risen 70 mm in operation?
One more time, thanks a lot, Richard.

flexmen,

I am not in the expert level here and this issue is very common to the newcomers. I am giving my opinion here and believe me most of these experts here knows more than these. The way you explained I can say the pipe is hot having a 3" growth. Whether you put a vertical restraint at the bottom or not, since the pipe is hot and you put +Y on top the pipe will rise at a magnitude equivalent to a specific system restriction. +Y means pipe can go up as much as it could but cannot go down. Taking the +Y there in your analysis won't yield an overstressing at all. It simply means to me that a +Y or simply a vertical support at that point does not do any functin to a pipe. Say in reality, the pipe hangs up from your vertical support (a structural beam for example). Depending on how your pipe is supported below, I tried 5 years ago restraining the point which was +Y (same point as what you have mentioned) with a +Y with gap say 1/8" and also 1/8" on the lateral direction (kind of simulating a clamp type support installed loosely). When I run it there was an overstresing in elbows and so the best thing is to replace the +Y with a spring hanger. The lift off you were talking about is taken care of the spring and also will relieve loads below. If it happens that restraing the same point does not yield any reds on your output then its good enough. So far this is part of what I've learned.

Ed_Lamigo

I'll offer this much. For the purposes of discussion, I envision a line that is supported down low, and goes through a fairly long vertical rise before turning horizontal and crossing the support location where the +Y is. As a matter of course, the support at the bottom is going to force the thermal expansion to the top and give you your 3" liftoff.

From a technical standpoint, if you've run the case w/o the support and your sustained stresses are within allowables, then the 3" lift off is not an issue by itself.

But, I will offer a couple of other considerations.

1. Buckling - If you are supporting in this way, you need to make sure the vertical run is adequately guided, becuase supporting from down low makes your vertical run subject to column buckling and Caesar won't tell you anything about that. If you had the hard support at the top with either no support or a spring down low, assuming you have enough flexibiilty to absorb the 3" of growth, then the riser would not be subject to buckling. However, you would still want/need to guide it due to wind and such

2. Asthetics - One thing I've learned over the years is that if something looks "wrong" to some guy in the field, he's going to want to do something about it. I've gotten numerous calls from the field after startup from some guy telling me that a shoe isn't sitting. I look at the analysis to find that it was supposed to lift off and I assure the field that there is no problem. There are a lot of people in the industry who still don't believe that pipe grows when it gets hot. If a support is in a highly visible location, you may want to add a spring to provide peace of mind to the field guys. THis is not something I end up doing often, but it has happend.

3. Equipment - You should see it when you removed the support and ran the model. When that support lifts, the loads shifts to adjacent supports. If one of those is an equipment nozzle, especially rotating, your nozzle may be overloaded and this is often a limiting factor more so that stresses in the pipe itself. I've even had cases where the line does not actually "lift" but vertical thermal expansion is such that the support load is reduced effectively to zero and overloads a nearby pump. I've had to put springs on in such a case anyway.

So, the answer to your question is: Yes, it's OK, maybe :-)

Thank you very very very much for your answer. It is the best answer I have found about this matter for long time.

My best regards,

Mr. Richard Ay,

How can we access the old threads mentioned in your post above? And the discussions before December 13 1999!!

The host for the web site has changed a couple of times, and unforuntately the software we use for the Forum stores the actual IP address of links in the post (instead of using relative URLs). So all of these links are broken.

To Answer your questions:

1) "Mouse over" a link you want to view and not the post number at the end of the URL. Then, in the address bar of your browser, copy the URL of the current post. Past this into a new browser window and replace the post number (with the one you want to view).

2) There are no posts before December 1999, that is when we started these Forums.

Mr. Ay,
Thanks a lot for help!
I followed the steps like this:
1. I pointed the cursor over the first link in your original post and got the following link: http://www.coade.com/cgi-local/ultimatebb.cgi?ubb=get_topic;f=1;t=000858
2. The current link where I was is: http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=48743#Post48743
3. Noted the post number from old link which is 000858.
4. Changed the post in 2 above to read like this: http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=000858#Post000858
5. But the result is that I reach a thread titled “Offshore Fields” started by member Saneh Gupta.
6. Reducing one zero from 000858 gives me the same result.

So what I am doing wrong here?

Well that really stinks - I don't know. You want to set "number", not "post", but I can't get it to work now either. #858 goes to #855 for some reason. #790 does go to #790, but it seems off topic.

You could always repeat the search ....