Dip pipe design

[SabinaA]

Hello,

I'm hoping somebody on here may be able to offer some guidance. I have the task of replacing a dip pipe in a Carbon Steel storage tank. I can't find any information on google etc regarding the design of dip pipes, and i have searched this forum but i am really looking for the basics and those tend to be glossed over.

The tank has no agitation, is at ambient temperature. It's flat bottomed with a dished top. There is no fixing bracket at the base of the tank and there is no access to install one.

The details are as follows;

Process fluid - Xylene
Vessel flange- Table E 3"
Process connection - ANSI 150 1 1/2"
Dip pipe length - 3850mm
Dip pipe MoC - StSt
Vessel volume - 10,000L
Vessel height - 4000mm
Vessel Moc - Carbon Steel

Is a 1 1/2" pipe suitable, is Schedule 10 suitable? If not why? Are there design calcs, astandard or a book i can refer to?

Thanks in advance for your help!

 

[MJCronin]

Sabina....

Dip pipes are used, inside of storage tanks, to ensure that incoming liquids do not foam or splash.

There are no nationally recognized standards (ASME/API/etc) on the design, although many companies develop their own internal standards.

Usually, they are the same size as the fill pipe and the extend vertically down the inside of the tank. They terminate 6-12 inches from the tank floor.

For corrosive liquids that also become erosive as the velocity increases (such as sulfuric acid) it is a good idea to weld an erosion plate on the tank floor in the area where the dip pipe terminates.

Dip pipes also must have a sipon break hole inside of the tank, near the top of the pipe

 

[LittleInch]

I agree with MJCronin in that there are no specific standards. The issues to identify are the flow rate and veleocity of the incoming or out going fluid, the amount of space available for strenghtening ribs where the pipe penetrates the blind flang normally used to hang the pipe from the nozzle and the velocity of the fluid when it emerges. Sometimes you see an enlargemnt of the tube to the maximum size that will fit through the entrance nozzle at the lowest point of the tube to reduce this velocity to the lowest possible level and avoid damage through erosion to to the tank floor.

googling dip pipes on images provides some good images of typical dip pipe connection design. The key weld is that where the pipe penetrates the blank flange and how thick the pipe needs to be to be able to weld these elements without burning through the pipe. hence 10S might be a bit thin.

In short,like a number of items, this is more art than science as there are too many inputs to make a comprehensive design which covers all eventualities.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[MatthewL]

Sabina,

In your case, the dip pipe is needed to prevent electrostatic discharge (and potential ignition) due to a free-falling flammable liquid. Another option would be using an angled pipe that sends the liquid against the side of the tank, again removing the free-falling liquid issue. You would still need an anti-siphon hole at the top of the pipe. Since it sounds like you can't enter the tank to anchor the bottom of the dip pipe, the angled pipe may be the better option.

Regards,

Matt

Quality, quantity, cost. Pick two.

 

[MJCronin]

An excellent paper on this subject...

http://people.clarkson.edu/~wwilcox/Design/flamliq.pdf

Suggested details of "dip pipe" design are included:


Please come back to us, SabinaA with a sketch of your final design....