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Equivalence

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jjfa

jjfa

Mechanical
Apr 13, 2004
9
I would like to know the equivalence between API grade and cP or cStoke viscosity.


Thanks a lot
 
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API gravity is an indictation of specific gravity relative to pure water.

SG(oil) = 141.5/(131.5+API Gravity)

The current Petroleum Engineer's Handbook by Bradley has a chart to go from oil specific gravity to kinematic viscosity (centistokes). Earlier versions went from API to viscosity, but the whole "degree API" always got confused with a temperature correction.

David Simpson, PE
MuleShoe Engineering
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
 
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cSt is kinematic viscosity and is in mm2/sec

This is correlated to the dynamic viscosity by multiplying with the density and correcting for units.
cP=0.001 Pa*sec=0.001 kg/(m*sec)

So if you have that water has a vicosity of 1 cSt and a density of 1000 kg/m3 then:

1cSt= 1*1000/1000000 = 0.001 Pa*sec = 1cP

Best regards

Morten
 
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