Consideration of Piping Loads on Vessel Support and Foundation Design 1

[AlphanEng]

Hello,

I searched Eng-Tips and found differing opinions on the effect of piping loads to the vessel support and foundation. Some say that if the vessel is flexible, like tall towers, the piping load will be absorbed by the vessel and that loads are not transferred to the base support. Others say that it does not matter whether a vessel is flexible or rigid, and that all piping loads will be transmitted to the base support. I definitely agree with the latter. I guess what the former is really trying to say is that for tall, flexible towers, the piping loads are negligible compared to other external loads that in a practical sense, the piping loads can be ignored in the base support design.


ASME Section VIII, Div. 1, Nanmandatory Appendix G5 and ASME Section VIII, Div. 2, paragraph 4.15.4.1(a)(3) states that the design of support skirts shall consider "the load due to externally applied moments and forces when these are a factor, e.g., wind , earthquake, or piping loads." Other than this requirement from the Code, I have not seen any guidance or literature on how and when to consider piping loads in the vessel support design. It is left to the vessel designer to use his experience and engineering judgement in deciding whether it is worthwhile to consider them. In my experience, I have just been considering the piping loads on a case-by-case basis, depending on magnitude, direction and how the loads are distributed along the vessel.

I would like to request experienced vessel designers to share your thoughts on how you consider piping loads in the vessel support design. If there are published literature on this subject, kindly let me know the source and title.

Thanks,
Chris
Calgary, AB

 

[pennpiper]

AlphanEng,
You wrote:
"all piping loads will be transmitted to the base support"
This is the correct answer.

Think of it this way. Stand on a scale. Read your weight on the indicator. Lets say it reads 180 pounds (81.6 kg). Have someone add objects to you, such as fill all your pockets with sand, hang a backpack on your back, fill the backpack full of rocks, place tote bags in each of your hands, fill each tote with ten books. Now, what is the weight recorded by the indicator? Is it still 180 pounds (81.6 kg)? No!

The scale records all the weight not carried by some other support. so, it is logical the vessel foundation carries all the weight of the vessel not carried by some other support.

Sometimes its possible to do all the right things and still get bad results

 

[dhengr]

AlphanEng:
You said.... “It is left to the vessel designer to use his experience and engineering judgement in deciding whether it is worthwhile to consider them.”; as if that where a bad thing. There are lots of things that the design codes and stds. don’t tell you that you must do. It’s their way of limiting their own growth to something less than an infinite number of pages, so that just any dummy can do it, if they can only read and understand it all first. Note that the back pack full of rocks or a tote bag full of books in one hand might be more significant than a little sand in each pocket, because they add larger, eccentric, loads to the system. And, that’s were the engineering experience and judgement come into play.

 

[AlphanEng]

dhengr,
I did not say using engineering judgement is a bad thing. How did you get that context from what I wrote?

I am very well aware that design codes are not "cookbooks" or handbooks. In some cases, the Code does not provide all the details of design. And as you said, "that’s were the engineering experience and judgement come into play."

pennpiper & dhengr,
I am not concerned with dead loads, vertical loads or eccentric loads. These loads are basic stuff in vessel design. When I mentioned "piping loads", I was referring to horizontal loads or lateral forces that resulted from thermal expansion or occasional loads (wind, earthquake, etc.) of the piping system.

Please have a look at the attached file. It is a tower that I designed on a past project. It has more than 30 process nozzles with attached piping. Based on my experience and "engineering judgement", the lateral forces induced by the piping system on the nozzles and pipe guides have negligible effect on the tower's skirt base and anchor bolt design. I know because most of the lateral forces will just cancel out and the remaining lateral forces are very small compared to the tower's wind or seismic loads. If both of you were to design the skirt base support or the anchor bolts, would you consider the piping loads (lateral forces) in your design?

 

[XL83NL]

The OP touched an interesting point and I believe the first replies dient really understood the question. There's a different in weight [kg] and load [N].

For weights its Simple, and already pointed out in the first reply. Loads however, esp. those that cause moments on the base (support) and shear, rather than tension or compression (though compression can lead to e.g. buckling), can have a big impact and are underestimated. Long tall towers can still absorb some energy of these loads by means of deflection but still Will have soms reaction on the base support.

 

[pennpiper]

AlphanEng,
Your question:
"If both of you were to design the skirt base support or the anchor bolts, would you consider the piping loads (lateral forces) in your design?"

Answer: Yes!

Sometimes its possible to do all the right things and still get bad results

 

[racookpe1978]

IF the tower were relatively short,
and
IF the tower had uniform lateral loads coming into the tower equally in all directions,
and
IF those lateral loads during construction and maintenance (cold or unloaded periods and construction, compared to hot and pressurized periods) were still uniform and omnidirectional,
then

maybe

Yes, I would consider those lateral loads to be balanced. Vertical loads on the tower or PV resulting from the piping connections? Of course you add them. But THAT is the "engineering judgement" that is required. What is the load, what direction at what height and at what impact and duration, and what affect does that load have on the tower -then the tower base thew
n the base on the structural supports and finally the pad?

 

[AlphanEng]

pennpiper,

How?

 

[pennpiper]

AlphanEng.
Look here and take your choice.

https://www.google.com/search?q=fix...niv&sa=X&ei=Wzb7VO7XIoyrNv-agYAO&ved=0CCMQsAQ

Sometimes its possible to do all the right things and still get bad results

 

[pennpiper]

Here are more that might be of interest:

https://www.google.com/search?q=win...v&sa=X&ei=qjr7VKLzN4_HsQT_moLwDg&ved=0CDcQsAQ

https://www.google.com/#q=wind+load+on+vertical+vessel

http://www.civildesignhelp.info/vv.html

Sometimes its possible to do all the right things and still get bad results

 

[XL83NL]

Ive always wondered if all those PV suppliers that specify nozzle loads on their GA, or conform their vessel can take our standard nozzle loads table, have also checked that PV's support on those loads (like soms sort of worst case scenario).