Question about floating roof correction

[yasuyo_goto]

Dear all,

I have just started to learn how IS-OIL solution is functioning and a question arises regarding floating roof correction.

In silo management function, you can simulate the material volume using material density, total height, material temperature and shell temperature(using LVCC calculator).

If the material density is increased, then the material volume is also increased.

(Of course floating roof correction indicator is set.)

I don't understand why material volume is increased when the material density is increased in the system.

And in a real business, in what situation is material density increased?

Does that happen when the floating roof is replaced with a heavier one?

In SAP ERP I changed the floating roof weight value but it didn't affect the calculation result of the material volume.

(Note that the material density is not changed, and my understanding is that the density is not changed automatically when the roof weight is changed.)

Can somebody figure the above system behavior out and advise practical silo management in oil industry?

Thank you,

Yasuyo

[markus_seng2 · Accepted solution]

Dear Yasuyo,

the floating roof calculation is described briefly in the SAP ERP help:

...

Correction Factors

Use

For volume corrections using dip readings, various volume correction factors that are used for tank volume calculations are required, according to international ISO standard 7507.

You can trigger the calculation of these corrections by activating the floating roof correction, the correction for water and the correction for the thermal expansion of the tank.

You can show or hide relevant calibration data and dip parameters for these corrections by activating or deactivating the corrections.

Features

Floating Roof Correction

This correction takes into account the material displacement caused by the floating roof of a tank, which is dependent on the material density. The system calculates the correction value when you have done the following:

· You have activated the correction factor.

· You have entered the mass of the tank roof.

If you have carried out the calibration of the tank geometrically or optically, you do not have to enter the density of the calibration liquid.

If you have calibrated the tank with flow rate meters, you must then enter the density, because the correction for the density of the calibration liquid is already contained in the tank strapping table. The system then determines the correction value based on the density difference between the material in the tank and the calibration liquid.

The minimum height of the floating roof corresponds to the minimum height at which the correction is used. Beneath that height, no correction is carried out ...

(from: http://help.sap.com/saphelp_erp60_sp/helpdata/en/cb/a45738bc8b210de10000009b38f8cf/frameset.htm )

The SAP design again as mentioned in the help text above is based on international standard ISO 7507-1 1993 First edition: Petroleum and liquid petroleum products - Calibration of vertical cylindrical tanks - Part 1: Strapping method.

You can purchase the now current 2003 version iof this standard document for approx. 140 EUR at http://www.iso.org

I hope that helps a bit,

Kind regards,

Markus

[yasuyo_goto]

Hello Markus,

I thank you for your prompt reply to my question.

And I also thank you for notifying me the description in the SAP ERP help about floating roof correction.

Now I understand that floating roof correction functions as follows:

- This correction takes into account the material displacement caused by the floating roof of a tank which is dependent on the material density(inquired from help text)

This means that if the weight of the floating roof of a tank becomes heavier, then the material volume is shrink (= material displacement), on the other hand, the material density should be increased.

Therefore the system should to take this into consideration when calculating the material volume, that is, the material volume should be increased.

(if the floating roof weight becomes lighter, then the material volume should be decreased.)

The system behavior as below is consistent to the above explanation:

the system is set as follows:

- floating roof correction indicator is set

- floating roof weight is entered

in the LVCC calculator

when floating roof weight becomes heavier, the material volume is decreased

(suppose that the material density is not changed)

when material density is increased, the material volume is increased

But I am still wondering why the material density is not changed according to the change of the floating roof weight in IDES system..

Is that because of the setting in the customizing?

Can somebody please advise?

Thank you,

Yasuyo

[markus_seng2]

Dear Yasuyo,

thanks for your feedback, I think there is one misunderstanding in your expectation:

...This means that if the weight of the floating roof of a tank becomes heavier, then the material volume is shrink (= material displacement), on the other hand, the material density should be increased...

This is actually not the case; the floating roof "swims" on top of the product (e.g. crude oil) and since it swims on the product it displaces according to Archimedes principle the crude, so that the crude level that you measure when taking a dip is apparently higher then it should be... You can make this experiment if you take a glas of water, measure the level of the water without having e.g. a floating lemon in it, and then put e.g. a lemon (large lemon to be able to see the effect ) into the glas and measure the water level again... only if the roof would NOT swim, but would be totally tight with the walls you would be able to measure your expected effect, i.e. the compression of the liquid...

anohter case would be closed LPG tanks, where the vapor space has to be taken into account and where the vapor pressure then has to be considered :

http://www.quantityware.com/_data/WP_LPG_vapor_space_calculations.pdf

hope that is clear enough, here a drawing would be nice, but that would take some time ... you can find such drawings e.g. in ISO or API standards,

Kind regards,

Markus

[yasuyo_goto]

Hello Marcus,

Thank you for your reply.

It seems that I have totally misunderstood and now I believe that I understand the relationship between the floating roof weight and the material volume calculation as follows:

As the floating roof is swimming in the product(such as crude oil), that is, the roof is soaking in the product, the total dip height used for the height-to-volume calculation is more than it should be, therefore, to measure the volume correctly, the floating roof weight should be considered(deducted from the originally calculated volume).

In IDES system I have simulated the volume calculation and the results are as below:

Note that dipping method is "Innage".

Floating roof weight: 1,000.000 KG

Mat. density: 1,000.000 KGV

Total height: 400 MM

Material volume: 656,727.960 L

Floating roof weight: 2,000.000 KG

Mat. density: 1,000.000 KGV

Total height: 400 MM

Material volume: 655,727.960 L

Floating roof weight: 3,000.000 KG

Mat. density: 1,000.000 KGV

Total height: 400 MM

Material volume: 654,727.960 L

And I have noticed that with an increased material density the material volume is also increased.

If there is still any of my misunderstanding, would you please let me know?

Again, thank you for your help.

Regards,

Yasuyo

Edited by: Yasuyo Goto on Mar 19, 2010 3:48 AM

[markus_seng2]

Hello Yasuyo,

perfect, that sounds all fine to me, and your examples make sense. I think the one point where you would like to have an explanation is the observation:

If you increase the material density (at constant floating roof weight), the volume that corresponds to a constant dip height increases as well.

This is correct and can be explained if you look at the correction formula:

CorrectionVolume(subtract from result w/o floating roof) = floatingRoofWeight *(1/MaterialDensity(air).

(if the cvalibration is made with a referene liquid, one has to extend the formula)

Thus if the MaterialDensity is increased, the CorrectionVolume, which is the displaced volume by the floating roof, decreases, which in turn leads to an increase of the material volume in the tank at constant dip height.

This formula can be derrived from Archimedes principle, that says:

Air buoyancy force = Gravitational Force of the displaced liquqid/gas or

"more tersely: Buoyancy = weight of displaced fluid".

Thus if the product density is increased, the roof needs to displace less product volume to reach equilibrium.

In the SAP code, you can find this formula in FORM FLOATING_ROOF_CORRECTION in function group OIIC_DIP.

A good source to start diving into the details is given in http://en.wikipedia.org/wiki/Buoyancy

As also noted in that and other references (e.g. ISO 7507), you also have to ensure that you clearly distinguish between mass and weight(mass in air) of the roof as well as density(vacuum) and the density(air) of the liquid; SAP provides a BAdI method where customers thus can adjust the correction formula, which as standard uses the product density(vacuum). As noted above, the displacement of the roof(the correction volume) is calculated by dividing the mass in air of the roof by the average density(air) of the product stored in the tank.

I hope this helps,

Kind regards,

Markus

[biswajitioc]

Thank you very much.