2 replies to this topic

[styx]

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Edited by styx, 25 December 2011 - 10:36 PM.

[fallah]

styx,

What is the tank operating pressure? Is the tank equipped with blanketing system?

Seems due to higher vapor pressure of isopentane you need to consider higher operating pressure, hence you should evaluate new operating pressure besides tank design pressure.

Anyway, please submit the above information for better assistance.

Fallah

[Art Montemayor]

Styx:

This is an excellent, practical engineering topic.

I’ve had storage tank re-rating projects and I would consider this assignment as an important one with a high priority due to the relative large tank size. My immediate response to your basic questions is:

1) Normally, a tank re-rating is very possible and feasible. I would certainly consider this option first;
2) A replacement with a spherical tank is a major and very expensive decision and one that I would reserve as a last resort. I personally don’t think a spherical design is justified for this application and size.

What I recommend – and what I would undertake (if it were my project) is the following:

• Obtain a copy of API 653, “Tank Inspection, Repair, Alteration, and Reconstruction” and thoroughly study it in detail;
• Obtain ALL the engineering design and calculations regarding the fabrication of the subject tank – this should include nozzle loadings, Maximum Allowable Working Pressure (MAWP), Maximum Allowable Working Vacuum (MAWV), Pressure Relief Devices, etc.;
• Obtain the services of a recognized and experienced engineering firm that can carry out a thorough tank inspection and generate a formal engineering report on the subject tank’s condition and integrity, once inspected, - complete with recommendations as to the proposed future application.

From Isopentane vapor pressure data, the proposed tank service at “ambient” (80 ^oF) temperature seems to make for an acceptable application. Refer to the attached Workbook that indicates the vapor pressure of Isopentane saturated liquid in the tank would be 14.3 psia whereas the tank’s Design Pressure is 700 mm H₂O column (15.69 psia). This makes the application feasible at 80 ^oF and a greater pressure range for safety can be achieved if the Isopentane can be stored chilled at lower temperatures. This would, of course, required tank insulation and a chiller process.

You fail to state what you consider as “ambient” temperature or what country (or region) your tank is in, so it is impossible to second guess what would be your yearly average tank vapor pressure. However, as the workbook indicates, the Isopentane is lighter than Hexane and, as such, the physical loadings and stresses on the tank would be lessened by the application – as compared to design.

Please note that you failed to state the basis for your tank’s design pressure – whether gauge or absolute. I have had to assume that you meant gauge pressure, because that is the normal engineering fabrication custom. You may have to change out the PSVs on the tank to suit the Isopentane operating conditions.

I hope this helps you.

Attached Files

•  IsoPentane Storage Tank Re-Rating.xls   66.5KB   49 downloads