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[KIENG]

We have a new storage tank that we would prefer not have a dip pipe due to the nature of creosote, the material to be stored in the tank. The environmental authorities are requiring a dip pipe to prevent splashing of the liquid within the tank. They are concerned that splashing will lead to increased vapor emissions from the tank.

Our company’s policy is to install a siphon break any time a dip pipe is installed in the tank. The normal method we use is a hole in the side of the dip pipe just under the tank roof.

The jurisdiction does not want us to install a vacuum break stating or implying that product will spray out of the vacuum break. We have come up with an alternative that utilizes an air gap in the piping with a funnel made from a pipe reducer to insure the liquid pumped into the tank goes into the dip pipe. Please see the attached sketches.

We need a recommendation by some authority that siphon breaks are desirable and/or recommended in dip pipe equipped storage tanks. Can anyone advise a place to find such a recommendation? I have looked over the API web site in hope of finding a Recommended Practice or other document that would address dip pipe vacuum breakers, but did not find anything that looked relevant.

Thanks

Attached Files

•  LDE0070.pdf   36.04KB   313 downloads

[Art Montemayor]

Kieng:

I believe I understand your dilemma. I’ve done a lot tanks and most of them had dip pipes. The ones I had trouble with were where the fluid was viscous or could polymerize. These characteristics nullify the usefulness of a vacuum breaker orifice – should this become clogged.

I have several ideas on how to circumvent the problem, but you don’t give us sufficient basic data. For example, you state you are storing creosote, but you don’t tell us if it is heated or what its viscosity is. Nor do you state why you don’t want to use an orifice – although I can guess. I don’t like to guess on engineering matters, especially where safety is involved. It is so much easier to simply expound all the basic data involved.

I am attaching a sketch showing one of the options I would evaluate in order to strictly follow the mandate of the environmental authorities and keep the suckers happy and out of your hair. You don’t tell us all the dimensions of your tank or your creosote fill rate, so I can’t come up with a good reason for the 6” dip pipe. The illustrated method has the obvious tradeoff of not giving you a positive, natural “air break” between the tank contents and the external ambient. However, you can always extend the height of the fill pipe higher than the tank and this avoids an automatic drain to environment. However, it doesn’t avoid a syphon effect – which the dip pipe-with-orifice would give you.

I can’t offer any thing else due to the basic data starvation. Also, we can't use your .pdf file because we can't mark it up nor even copy it or revise it. .pdf files are bad for exchanging engineering information. You simply can't work with them in order to communicate an idea or proposal.
 Creosote_Tank.xls   17KB   340 downloads