Density Calculation from specific gravity

[Beginner - Inspector]

I want to calculate the density of crude and Kero Product , the Specific gravity is given at T & P, whether I have to multiply it with 1000kg /m3 (density of water @4 degree Celcius) or I have to find the density of water at that particular temperature and pressure and then multiply with SG.

PLEASE ADVISE !!!

 

[pierreick]

Hi,
To determine liquid density from specific gravity, you multiply the specific gravity (relative to water) by the density of water at the same temperature and pressure
Pierre

 

[Beginner - Inspector]

Hi,
To determine liquid density from specific gravity, you multiply the specific gravity (relative to water) by the density of water at the same temperature and pressure
Pierre

If my liquid sg=0.766 at 244 degree C & pressure = 8.63kg/cm2, what will be its density(liquid) ?

 

[Beginner - Inspector]

If my liquid sg=0.766 at 244 degree C & pressure = 8.63kg/cm2, what will be its density(liquid) ?
whether I have to multiply it by 1000kg/m3 xSG ?

i.e 0.766 x 1000kg/cm3 = 766 kg/m3=density of fluid

 

[pierreick]

I don't understand your question. your reference fluid is vapor at T,P
If you take your data sheet: 147 C, 8.3 kg/cm2 g the density of water is 920 kg/m3 so density of the liquid is 0.76 *920 = 699 kg/m3
Pierre

 

[LittleInch]

View attachment 6639

I want to calculate the density of crude and Kero Product , the Specific gravity is given at T & P, whether I have to multiply it with 1000kg /m3 (density of water @4 degree Celcius) or I have to find the density of water at that particular temperature and pressure and then multiply with SG.

PLEASE ADVISE !!!

I think you're over thinking this.

To me this is just reporting the specific gravity, I.e. relative to water at 4C seems to be the definition. The T and P bit just refered to the SG at that products temperature and pressure. I do not agree with Pierre in this instance. The crude and kero are both liquid at those temp and pressure. You don't change water density to match the product.

Would have actually been easier to write it in kg/m3.....

It makes no sense to keep changing the reference point for SG. I have never ever seen anyone correct the density of water when converting SG into density in kg/m3.

If you look up kerosene density vs temp you get about 760 kg/m3 at 150C

So I believe your calculation in post no 4 is correct.

 

[Beginner - Inspector]

If my liquid sg=0.766 at 244 degree C & pressure = 8.63kg/cm2, what will be density of water i am suppose to consider

 

[LittleInch]

1000 kg/m3, like you said in post no 4.

Your data sheet says SG 0.766 at 147C. Where did 244C suddenly come from. Stop confusing things.

This is from the NPL which is the UK national laboratory. They will know.

What is the difference between density and specific gravity?

Both are used to describe mass and to compare substances

www.npl.co.uk

 

[Beginner - Inspector]

I don't understand your question. your reference fluid is vapor at T,P
If you take your data sheet: 147 C, 8.3 kg/cm2 g the density of water is 920 kg/m3 so density of the liquid is 0.76 *920 = 699 kg/m3
Pierre

If my liquid sg=0.766 at 244 degree C & pressure = 8.63kg/cm2, what will be density of water i am suppose to consider. It will be vapour at 244 C

 

[Beginner - Inspector]

1000 kg/m3, like you said in post no 4.

Your data sheet says SG 0.766 at 147C. Where did 244C suddenly come from. Stop confusing things.

This is from the NPL which is the UK national laboratory. They will know.

What is the difference between density and specific gravity?

Both are used to describe mass and to compare substances

www.npl.co.uk

1000 kg/m3, like you said in post no 4.

Your data sheet says SG 0.766 at 147C. Where did 244C suddenly come from. Stop confusing things.

This is from the NPL which is the UK national laboratory. They will know.

What is the difference between density and specific gravity?

Both are used to describe mass and to compare substances

www.npl.co.uk

244 C is Another case . my intension is not confuse you. please

 

[LittleInch]

If my liquid sg=0.766 at 244 degree C & pressure = 8.63kg/cm2, what will be density of water i am suppose to consider. It will be vapour at 244 C

That's why the response is incorrect. SG does not change the reference density.

 

[Snickster]

My understanding is when you refer to specific gravity it is always relative to water SG = 1.0 at density of 62.4 pounds per cubic foot (1000 kg/m3) density at standard conditions (14.7 psia at 60 F) in US customary units no matter what pressure and temperature of your fluid is.

So at 15 C and atmospheric pressure standard conditions your SG = .844 x 1000 = 844 kg/m3

At 147 C and 8.3 kg/cm3 your SG = 0.76 X 1000 = 760 kg/m3

In other words the SG is not the density of the fluid at P&T divided by the density of water at the same P&T - it is the density of your fluid at P&T always divided by the density of water at standard conditions = 1000 kg/m3.

 

[LittleInch]

My understanding is when you refer to specific gravity it is always relative to water SG = 1.0 at density of 62.4 pounds per cubic foot (1000 kg/m3) density at standard conditions (14.7 psia at 60 F) in US customary units no matter what pressure and temperature of your fluid is.

So at 15 C and atmospheric pressure standard conditions your SG = .844 x 1000 = 844 kg/m3

At 147 C and 8.3 kg/cm3 your SG = 0.76 X 1000 = 760 kg/m3

In other words the SG is not the density of the fluid at P&T divided by the density of water at the same P&T - it is the density of your fluid at P&T always divided by the density of water at standard conditions = 1000 kg/m3.

It looks like it's actually water at 4C.

15 C and atmospheric pressure 101300 is standard conditions for gas.

 

[pierreick]

Hi,
I could be wrong if I refer to the link underneath:

What is Difference Between Liquid, Vapor, and Gas? | THINKTANK

In general, a vapour phase consists of a phase with two different substances at room temperature, whereas a gas phase consists of a single substance at a defined thermodynamic range, at room temperature.

cncontrolvalve.com

This is weird .
Pierre

 

[shvet]

@Inspector
Do not believe them, only the original designer knows what the referenced water temperature (RWT) is as industry standards require the both temperatures to be specified.

ASTM E1547-2017

specific gravity - the ratio of the mass of a unit volume of a material at a stated temperature to the mass of the same volume of a gas-free distilled water at a stated temperature
Specific gravity x/y °C
where:
x = temperature of the material (<units>), and
y = temperature of the water (<unis>)

ASTM D1298-2017

3.1.7 relative density (specific gravity), n - the ratio of the mass of a given volume of liquid at a specific temperature to the mass of an equal volume of pure water at the same or different temperature. Both reference temperatures shall be explicity stated.
3.1.7.1 Discussion - Common referenece temperature include 60/60 °F, 20/20 °C, 20/4 °C. The historic deprecated term specific gravity may still be found.

So your datasheet is a kind of in-house and you should find&ask an original designer or conduct a study. The actual RWT can be any as it is site&case specific both.
Given the SG@60°F (15°C) and assuming that RWT is 60°F per ASTM above you can convert SG to density@60°F, next extrapolate density@60°F to the operating temperature (OT) with a reasonable accuracy, next devide the density@OT°C on the water density at different referenced temperatures (4°C, 15°C, 150°C etc.), e.g. see API TDB A6. The result matching with the datasheet will reveal the designer logic. There is no a magic, just routine calculations.

I would bet on the RWT 15°C.

 

[LittleInch]

Now we're splitting hairs, although the 60 in the post above keeps changing between C and F.

At 4C water density is 999.5 kg/m3. At 15C/60F it is 999.06

So in most cases where SG is only listed to at most three significant digits, this is negligible difference and most people will simply use 1000 kg/m3.

 

[sentrifice]

So then is the density/SG relationship handled the same way for gases? If you want to know the density of a 0.6 SG gas at say, 400 psig and 120 F, don't you need to determine the density of air at 400 psig and 120F?

 

[Snickster]

So then is the density/SG relationship handled the same way for gases? If you want to know the density of a 0.6 SG gas at say, 400 psig and 120 F, don't you need to determine the density of air at 400 psig and 120F?

The SG of gases is MWg/MWa.

 

[Snickster]

As mechanical engineer, for liquids I always just multiplied the specific gravity of the liquid at standard conditions times that of water at standard conditions = 62.4 lbs per cu ft to get the density of the liquid. Typically the calculations for ME are for fluids where you are just trying to determine the pressure developed by pump based on head, or weight of fluid calculate pump horsepower based on SG relative to water, or to calculate stress in piping due to weight of fluid, or wall thickness of a tank based on weight, etc.

I imagine if you are looking for exact number of molecules in a chemical reaction you may need to get more precise to a couple of decimal points.

 

[shvet]

So then is the density/SG relationship handled the same way for gases? If you want to know the density of a 0.6 SG gas at say, 400 psig and 120 F, don't you need to determine the density of air at 400 psig and 120F?

SG term is vague and outdated and therefore not codified, especially relevant to the gases. SG is rather informal and therefore the every working group can apply the different background behind that, given that every groupmember knows and applies SG in the same way as others do.
This is why the misinterpretation exists and why the specifications should be transfered between working groups (e.g. Contractor-Supplier) in a codified manner.

ASTM D3588-2017

3.1.5 relative density—the ratio of the density of the gaseous fuel, under observed conditions of temperature and pressure, to the density of dry air (of normal carbon dioxide content) at the same temperature and pressure.

GPA 2172-2002

3.2 Relative density - the ratio of the mass densityof the gas at the measurement temperature and pressure to the density of dry air ... at the same temperature and pressure. Adjusting the result to the hypothetical ideal gas state converts the relative density into the molar mass ratio.

My idea is that there is no need in guessing/asking.
You know the SG@15°C, you can assume that SG@15°C is referenced to the water temp 15°C, you can calculate the density@15°C and extrapolate that (e.g. API TDB) to the operating temp (e.g. 150°C), then you can apply water density at different operating temps (e.g. 15 and 150°C) and find out the original logic behind that datasheet.

Offtop
When I was a bit younger I was told by a reputable&experienced college person that 4/5 of mistakes in PhD papers is a result of misinterpretation or misconfusion of units of measure. He had been involved in a definetly lot of those papers, I trust him.