Wind load on horizontal pressure vessels

[TylerM]

I’m working through a ASME BPVC Section VIII Div. 2 recertification for a horizontal pressure vessel and under section 4.3.10 “Combined loading and allowable stresses” there is a formula (Equation 4.3.33) that has variables of: Net-Section Bending Moment, and Net-Section Axial Force. In the previous certification report it states that these variables are zero because there is no earthquake load and no wind load. I can understand about neglecting the earthquake load based on its location, but this vessel is located on the coast of Florida and it gets very windy here so I don’t understand neglecting wind load.

In the ASCE 7-10 we’re located in a 150 mph gust zone. The dimensions for this horizontal vessel are 56 in. outer diameter with 219 in tan-to-tan.

Can someone help me understand if I need to factor in adding a wind load to this vessel, and how I would go about doing that?

 

[SnTMan]

TylerM, wind loads can be calculated as per ASCE 7-10. Don't have a copy at hand, so I can't cite chapter & verse, but there is a specific provision for ASME pressure vessels.

As to whether you need to account for it based on your situation, I can't say. Be nice if you could find out why it was neglected in the first place.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[JGard1985]

Could it be a generic calculation? Somehow the vessel was located outside the structure

Anyway 7-10 is pretty light on vessel requirements for wind. I'd look at figure 29.5-1 to determine your force coefficent (essentially drag factor) based on h/D requirements for a round tank/structure. You may have to think about it, because tanks in 7-10 are typically vertical storage tanks, and parameters are arranged as such. You could even go conservative and determine force coefficient of free standing sign.

Anyway your biggest driver for velocity pressure (qz) will be basic windspeed and height above ground.

When you compute loads you need to be cognizant of what system (LRFD or ASD) you are using. LRFD uses ultimate wind speed (with removal of importance factors). ASD reduces the wind load in its loading combinations (Refer to section 2.4 of ASCE 7-10)

*Disclaimer-Local Codes May Govern Required Wind Loading and Analysis Method

Hope this helps

Jeff
Pipe Stress Analysis Engineer

http://www.xceed-eng.com

 

[TylerM]

Thank you SnTMan and JGard1985,

I think I'm going to use 7-10 and calculate h/D using linear interpolation. I might also run the calculation using a flat sign just to see what that answer is and try and better understand this situation.

Thanks for all your help!
Tyler

 

[chicopee]

API uses 18 lbs/ sq.ft. for wind speed(V) of 100mph for cylindrical surfaces. if wind speed is > 100 mph then:
new P= 18*(V>100mph/100mph)^2.

 

[JStephen]

The newer API use 18 psf for 120 mph 3-second gust, the 100 mph hasn't been the default in several years. But the ASCE 7 approach is the way to go here.

 

[racookpe1978]

56 inch diameter, but "only" 219 inches, gives a relatively small wind load if it is horizontal.

If it has near-zero ground clearance, then the actual wind hitting it that close to the ground will be much lower than nominal wind speed, even in hurricane conditions.
If it has a ground clearance of 2-4 feet, then the actual wind loads will be reduced because the winds can go under and over, and again, the ground effect will slow down the actual wind speeds. Compare, for example, a 2-story building whose roof is 15 feet higher.
A sign the same height has square edges and a flat face, not a round surface with a CD function of 1.0

Also, if the tank is connected near a pipe bridge or structural members outdoors, then the winds cannot reach full "open-air" strength at all.