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# Crude Oil Density Vs Temperature

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13 replies to this topic
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### #1 Matteo Giorgio Marrano

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Posted 13 March 2009 - 03:23 AM

Goodmorning guys.

I’m searching for a method that gives me the density of a crude oil (in first approximation)
Given his API gravity.

I have this crude:
API gravity: 36.15 °
From what I understand, I can calculate the Specific gravity at 60°F (15.56°C) using the formula:
SG: 141.5/(API°+131.5) --> SG=0.844

Given the SG, I can calculate the density of the oil at the reference temperature (60F).

In first hypotesis, consider that density of water is 1000. The Density of the oil will be 844 kg/m^3, right?

What will be his density at higher temperatures?The density will decrease with increasing of temperature, of course. (both with pressure changing I suppose, but not so much considering the fact that is a liquid).

I’ve founded in attached link a formula that gives me the density of liquid vs temperature changes but I don’t know if it works well in my case. (I used the beta-value for oil but it doesn’t worked very well)

http://www.engineeri...sure-d_309.html

Can anybody help me?

In a process datasheet of an equipment (crude-crude Heat exchanger) where is present this kind of crude is written (by the client) this:

Fluid: salty crude oil
API °: 36.15
Inlet temperature:10°C
Inlet density: 888.6°C
Outlet temperature:33.6°C
Outlet density: 872.5
Operating pressure: 12 barg

Are these data correct?do they match with the "theoretical change in density due to increasing of temperature?

Thanks
Matteo

### #2 ankur2061

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Posted 13 March 2009 - 03:57 AM

Matteo,

ASTM-D-1298 is a testing method for determining crude oil density as a function of temperature. An empirical correlation can be developed from the data generated from the test. Check out the following links for crude oil density determination as a function of temperature.

http://www.jmcs.org....N1/E-Fetter.pdf

http://www.searchand.../images/a09.htm

Regards,
Ankur.

### #3 Matteo Giorgio Marrano

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Posted 13 March 2009 - 05:47 AM

Thanks Ankur.

The second graph is not very clear to me; I've already found it here, but i didn't understand how to read the graph very well.

An example: If I wanted to know the density of an oil at 10 bar and 50 °C, what would be the answer? This graph doesn't relate to the API degree of the oil.

Another question: where i can find API oil characteristics? (I mean, is there an API standard where the properties are described for each oil of a specific API grade?)

I ask this because a supplier gave me an proposal for a water bath heater and he said that he made some assumptions for the oil properties based on the API gravity.

Is this correct?

thanks

### #4 Art Montemayor

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Posted 13 March 2009 - 08:06 AM

Matteo:

I believe what Ankur has directed you to is a quick, direct method of estimating the actual density of a crude oil with a specific composition (as related to its API degrees). It is not specific to the type of crude (paraffin or asphaltic), so it is a general relationship that can only be an estimate.

The API gravity classification for crude is given by the defining equation:

Degrees API (oAPI) = (141.5/SG) -131.5

Where,
SG = Specific Gravity of the crude oil = density of oil/density of water

If you know the API gravity that your client is dealing with (which you have not shared with us), then you can calculate the density of the crude oil easily:

Specific Gravity of Crude = (141.5) / (oAPI +131.4)

Density of the Crude = (Specific Gravity) (density of water)

### #5 Matteo Giorgio Marrano

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Posted 13 March 2009 - 09:47 AM

QUOTE
I believe what Ankur has directed you to is a quick, direct method of estimating the actual density of a crude oil with a specific composition (as related to its API degrees). It is not specific to the type of crude (paraffin or asphaltic), so it is a general relationship that can only be an estimate.
The API gravity classification for crude is given by the defining equation:
Degrees API (oAPI) = (141.5/SG) -131.5

this is what i wrote in the 1st post..

QUOTE
If you know the API gravity that your client is dealing with (which you have not shared with us), then you can calculate the density of the crude oil easily:
Specific Gravity of Crude = (141.5) / (oAPI +131.4)

i know the API gravity and the SG, what i'm searching for is:
Considering the fact that the °API is referred to the temperature to 60F, my aim is to determine the density of crude at a different temperature (in example 60°C).

As i wrote in 1st post, in my case:

API degree: 36.15
SG: 0.844 (calculated at 60°F)

For that, oil density at 60°F is approx 844 kg/m^3

The problem is that i would like to calculate the density at a different temperature; I know that it is lower than 840 kg/m3, and this is why i wanted to find an extimating formula.

Regarding to the second link given by ankur, now i understand what was wrong to me.
I think that the curves are "iso-API°", right?This graph is similar to the one in the appendix of kern (fig 6. in my edition of kern), in wich every curve is referred to an API°.
When i saw that table for the first time, i dind't know how to read the curve-lines..

In my case (36.5°API), the density at 60°C (140°F) is approx 810 kg/m^3.
Is it correct?

Instead of use that table, is there any correlation derived from that table?

thanks

### #6 Qalander (Chem)

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Posted 13 March 2009 - 10:37 AM

Dear
Usual reference parameters are 15 degrees Celsius for Density and 60 Fahrenheit for Specific gravity;
accordingly the standard tables are formulated for volumetric convrsion factors and their co-relationships are also found in initial or final pages of such books.

Can you further elaborate! Although cross conversion results into variations at fourth or fifth decimel place if I recall correctly.
Hope this helps.

### #7 Qalander (Chem)

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Posted 13 March 2009 - 10:42 AM

Just a slight addition, your referred temp of 60 Celsius should not be suitable for most common and lighter crude oils as around 5%~10% may be affected

### #8 ankur2061

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Posted 13 March 2009 - 11:45 AM

QUOTE (Qalander (Chem) @ Mar 13 2009, 11:42 AM) <{POST_SNAPBACK}>
Just a slight addition, your referred temp of 60 Celsius should not be suitable for most common and lighter crude oils as around 5%~10% may be affected

Dear Qalander,

Can you elaborate/explain about your above statement. I couldn't make any sense of it. My apologies for my ignorance.

Regards,
Ankur.

### #9 Qalander (Chem)

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Posted 13 March 2009 - 11:57 AM

QUOTE (ankur2061 @ Mar 13 2009, 09:45 PM) <{POST_SNAPBACK}>
QUOTE (Qalander (Chem) @ Mar 13 2009, 11:42 AM) <{POST_SNAPBACK}>
Just a slight addition, your referred temp of 60 Celsius should not be suitable for most common and lighter crude oils as around 5%~10% may be affected

Dear Qalander,

Can you elaborate/explain about your above statement. I couldn't make any sense of it. My apologies for my ignorance.

Regards,
Ankur.

Actually I was indicating that such temperatures induce evaporation normally of lighter fractions of light crude oils and in open atmosphere even foaming and inaccuracies of the ranges 5% ~10% might be observed.
This is what I envisaged

### #10 ankur2061

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Posted 13 March 2009 - 12:35 PM

Qalander,

The temperature mentioned was 60 deg F and not celsius. I am sure you know the difference between the two. Also, I have actually never actually seen any ambient temperature for storage tanks of 60 deg C. Normally the ambient temperatures do not exceed 45-50 deg C, which are found in the desert region of the gulf countries. FYI, the design temperature for atmospheric storage tanks which are directly exposed to the sun is 80-85 deg C which corresponds to the maximum black bulb temperature due to the sun's radiation.

Also, nowadays due to stringent environmentsl norms, most crude storage facilities employ VRUs, which reduces evaporation and preserves/recycles the lighter contents.

Regards,
Ankur.

### #11 Qalander (Chem)

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Posted 13 March 2009 - 12:51 PM

Quote

my aim is to determine the density of crude at a different temperature (in example 60°C).

Unquote
Today 19:47 hrs. above(without comments)

### #12 ankur2061

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Posted 13 March 2009 - 02:06 PM

QUOTE (Qalander (Chem) @ Mar 13 2009, 01:51 PM) <{POST_SNAPBACK}>
Quote

my aim is to determine the density of crude at a different temperature (in example 60°C).

Unquote
Today 19:47 hrs. above(without comments)

Qalander,

Point taken. But where does the OP talk of "open atmosphere". The discussion is about crude oil at elevated temperature and pressure (12 barg) in a crude-crude heat exchanger.

Regards,
Ankur.

### #13 Qalander (Chem)

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Posted 14 March 2009 - 03:17 AM

Since whenever we come across physical sampling and check-up using hydrometers, the pressures are - I understand 'Atmospheric' - as always witnessed during survey of crude oil cargoe(s).

### #14 JMW

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Posted 06 June 2009 - 11:13 AM

Try this spreadsheet which will let you work with density and temperature at atmospheric pressures (pressure correction version being worked on).