I have a line coming from top of tower vertically downward having design condition as:
design temp: 350 Deg F
Design press: 150 Psig
coming from top of tower and going downward along shell of tower it is being supported with shell of vessel via attachments. i have calculated thermal expansion of vessel shell at each attachment and input that value as displacement on relevant node. these are node 40, 50,60,70. distance between two attachments is 10 feet .when i check restraint report in expansion case. i see high value on upper most node i.e 70 and bottom node i.e 40. rest of two attachments are getting only few lbs.

if i remove both restraint from node 50, 60 there is no effect on restraint at 60, 70.
My question is that why those two nodes are not taking load. am i putting wrong input. can any body explain it.

I forgot to mention that i am checking this restraint report in expansion case. when i check sustain case load is dived between all supports but in operation case again most of the load is being taken by two extreme attachments i.e node 40 & 70

You are asking for trouble by expecting calculated expansion to be accurately reflected in the field. You may cause a lock-up resulting in very high support loads and stresses.

Use one fixed support near the top tan line and if you need additional support, use one or more springs below, from the vessel shell.

Hello,
The route of pipe looks quit stiff. Can you mention what kind of supports you are using at the stated node point?

Regards,
RK

Thanks for your reply...
if pipe and vessel shell materials belong to same material category i.e carbon steel, and temperature is same then there will be same expansion in both... then in operation how it can cause problem.
near top line (i.e node number 80, top elbow), there is no structure available except vessel shell so there is rare chance of giving any support.

Simply because the design temperature of line and vessel are the same does not by any means suggest that they will actually operate at anything like the same temperature. That's why practically all overhead lines and connections to the top of tall towers are supported only at or near the top. Have you thought about the possibility of radically differing temperatures in line and vessel due to start-up or crash shut-down for instance ?

Hi.
The EXP case is only used for code compliance check.
For check load on restraints use operational load cases, for example W+T1+P1, W+T1+P1+WIND1, W+T1+P1+U1, and W+P1 (SUS), or other real cases.
May be is a good idea to model the tower, and connect the restraint with a rigid zero mass element to the tower.

Regards.

In my opinion and experience you have a line that the supports are NOT designed properly. And you did not tell us the line size (or I missed it).

Here is my advice:
a) The line should only have only one (1) support on the vertical run.
b) That support should be at the upper most point just below the tangent line of the vessel.
c) This support shall be designed to take all of the weight of the pipe, insulation (if any) and hydrotest water.
d) The other points down the vessel should only be vertical guides. With this set-up the vessel will grow up and lift the pipe and the pipe will grow down a lesser amount but slide in the guides.
e) The guides only need to be designed for the lateral force from wind loading or seismic.

Jop,

I agree to a point, and that point is far along the path to truth. The support scheme you recommend will deal with most vessels. The reason we support risers along vessels from the top is two-fold. 1 - We don't run a pipe up the side of the vessel unless there's a nozzle up there, and you want to get your supports near the nozzle to minimize differential thermal growth. 2 - If your vessel is designed for a liquid case, there is often going to be a lot more "extra" metal at the top to carry external loads.

On some very tall vessels, though, trying to support the entire length of pipe on one point would lead to an absurdly big support (with a correspondingly big attachment and big loads on the vessel). The more load you put on a vessel at any one point, the more grief you are going to get from your vessel design staff.

When your pipe gets "too long" to be supported at one point, springs are the answer. This is primarily to cope with the emergency load cases mentioned by MoverZ. Note that transient load cases can also lead to applying a radial shear load and corresponding bending moment to your nozzle - you need to look out for that, too.

Spring supports also get around the tiny errors that creep in when you calculate movements and round them to two or three significant digits before entering values into CAESAR II, while CAESAR II is calculating them to eight. This last factor is undoubtedly why Muhammad-Sami is finding the load all being carried by two supports in the hot load case.

Your pipe is stiff. and u did not introduce any support. That's why ur nozzle movement is very high. It is the existing design?

Hi all
As MoverZ & CraigB already mention First support could be Load taking resting one Subsequent if any load taking support required must be a spring support. Guide support also to be placed according to support span.
If only one load taking support is used one problem is high concentrate load at one point that may be not desirable ( mechanical design point of view) & other reason is trunion or attachment use for load taking support may fail also with high concentrated load.

This piping routing it not a stiff routing. This type of layout is quite common for column piping. Location of first resting support in horizontal position ( after piping leave column area) has to plan accordingly. Some time spring is used as first horizontal support.

If column piping is too long may be loop or additional bend is required in vertical piping. Attached piping By Sami may not required any additional loop.

Regards

Habib

I am really pleased and thankful to all of seniors for such great response.You people have given me lot of knowledge. so if i sum up all the answers the result will be one support to carry all load at the top and others are just guides....
when pipe leaves the tower and run horizontally, in operation it will tend to move upward slightly.I have not much knowledge spring support so in horizontal run of pipe what type of support is usually used...
and i am sorry i forgot to mention that pipe is 6"Nominal dia material is 106 Grd B and it has insulation of 1 in.

if i model the tower in caeser and give design temperature on pipe and tower element same.. I think there will be same expansion and as others opinion is that practically it will not be same
Still is this good method to model tower in Caeser ii

Hi Sami
For column piping it is suggested to analyzed the system for operating & design condition with corresponding operating & design temperature of column.
Column may have different operating temperature in different level, Check with process engineer on that issue.

Regards

Habib