6 replies to this topic

[ahyong]

Dear All,
From my materials, it says that CRT is not suitable to be used in a condition where there is heavy snow as the roof might sink in the end while IFRT is suitable to be used under the heavy snow condition to some limit. So my question is since the external fixed roof of the IFRT is similar shape to the CRT type, why is IFRT suitable to be used under heavy snow condition but CRT is not?


Newbie

[fallah]

ahyong,

As far as i know, what would dictate the type of the storage tanks isn't the load of snow but the properties of the fluid to be stored (especially vapor pressure) and ambient temperature variation. Of course, if heavy snow would be probable the CRT should be designed to tolerate but between IFRT and EFRT the former would certainly be a better choice.

Fallah

[ankur2061]

ahyong,

In addition to what Fallah has mentioned about the vapor pressure of the liquid stored and the basic reasoning that a fixed roof tank will have more evaporation losses compared to a floating roof tank, the economics of having a IFRT and a fixed-roof tank also need to be examined.

Note that an IFRT will be have a much higher first-cost than a fxed roof tank. In your case this will be even more so, since your dome roof will require to be designed for the snow load and the axial stresses on the dome roof will be much higher than an IFRT not designed for any snow loading.

For you, the choice is between the economics of having evaporation losses from a fixed roof tank based on your stored product which you have not mentioned and an IFRT with external dome reinforced for snow-loading.

Regards,
Ankur.

[ahyong]

Thank you Fallah and Ankur for your reply. This forum really helpful especially for those new process engineers who just started in this field like myself.

[kkala]

From my materials, it says that CRT is not suitable to be used in a condition where there is heavy snow as the roof might sink in the end while IFRT is suitable to be used under the heavy snow condition to some limit. So my question is since the external fixed roof of the IFRT is similar shape to the CRT type, why is IFRT suitable to be used under heavy snow condition but CRT is not? Newbie

Query is understood to ask why IFRT is privileged to be in areas of higher snowfall, in comparison to CRT, according to Newbie's references ("materials"). Both tank types look externally as cone roof tanks (CRTs), so why IFRT could accept higher snow load? This is a question for structural engineers.
I agree to post No 2 by fallah; IFRT could accept heavier snow fall than simple FRT (understood same as EFRT).
In civil engineering, the higher the building roof slope the lower the snow load, since part of the snow slips down. For instance, concerning Philadelphia (USA), snow loads on roofs are taken as 19.25 psf (lbf/ft2) for slope angle α=0 deg (flat), 8.02 psf for α=45 deg, 3.21 psf for α=60 deg, 0.0 psf for α=70 deg, https://courses.cit.cornell.edu/arch264/calculators/example2.3/index.html. Northern countries have steep roofs to lessen snow loads.
Can Newbie see whether documents actually speak of FRT (instead of mentioned CRT)? This would explain the case, seeing that IFRT (similarly to CRT in shape) could accept heavier snow fall than FRT (floating roof tanks).

Edited by kkala, 21 November 2012 - 10:12 AM.

[ahyong]

Dear kkala
Actually the materials that I mentioned is a study/training materials that is given by my seniors, in the materials it did mention that CRT is not suitable for heavy snow load while IFRT is suitable for that. I was questioned by my boss when I presented about tank design. He was also wondering why the CRT is not suitable for the heavy snow load condition. So I suspect that there might be some typo to it when they were composing the training materials.

[kkala]

Indeed a typo is possible and author or publisher of the training material could give more specific information. Others might have already asked clarifications from them.
Searching a bit more, http://www.eng-tips.com/viewthread.cfm?qid=116356 indicates water tank (apparently CRT) can be designed to bear snow loads of 25-60 psf (probably covering all USA, except Alaska?). Higher loads are judged to be possible through proper structural design.
But seen roof slopes of CRT are small, found 1/6 (9.5 deg) or less in Web. Slope 1/6 is the limit for API 650 tanks if their roof is designed to tear away in fire case, http://www.mc-integ....cfm@recordID=10 '> http://www.mc-integ....cfm@recordID=10 . In such a case snow load is practically same as if roof were flat, at least according to web reference (for building roofs) in post No 5.