Description

This block is used to determine the uncertainty in a water cut obtained by sampling.

Options

Sampling Method

• ISO 3171 (Automatic)
• Manual

Analysis Method

• IP 386 (Karl Fischer)
• ASTM 4007 (centrifuge)
• User entered

Inputs

Coverage factor (k)

Enter the coverage factor that is to be used in the calculation.

ISO 3171 Sample Uncertainty

N – Number of grabs.

n – Number of analyses.

Relative Random Uncertainty

a_r – Non-homogeneity of the water content, relative random uncertainty.

b_r – Effects of sampling method (i.e. non-isokinetic), relative random uncertainty.

d_r – Uncertainty in volume of each grab, relative random uncertainty.

c_r – Non-proportional flow effects, relative random uncertainty.

h_r – Effects of sampling method (Clause 11, contamination/vapour loss), relative random uncertainty.

f_r – Sample handling effects (Clause 12, poor homogenisation), relative random uncertainty.

g_r – Laboratory analysis effects (i.e. transfer to glassware, analysis), relative random uncertainty.

Relative Systematic Uncertainty

a_s – Non-homogeneity of the water content, relative systematic uncertainty.

b_s – Effects of sampling method (i.e. non-isokinetic), relative systematic uncertainty.

h_s – Effects of sampling method (Clause 11, contamination/vapour loss), relative systematic uncertainty.

f_s – Sample handling effects (Clause 12, poor homogenisation), relative systematic uncertainty.

g_s – Laboratory analysis effects (i.e. transfer to glassware, analysis), relative systematic uncertainty.

Analysis Uncertainty

If User entered is selected from the Analysis Method option then the following inputs will be available to the user.

Repeatability – Uncertainty due to analysis repeatability.

Reproducability – Uncertainty due to analysis reproducibility.

Calculations

The overall uncertainty in water cut is calculated by taking the root sum square of the uncertainties in the repeatability and reproducibility and either the ISO 3171 uncertainty, D, or the mixing and sampling uncertainties depending on what is selected from the Sampling Method option.

Note: Repeatability and reproducibility can be user entered or calculated in accordance with IP 386 or ASTM D4007 depending on the options selected.

ISO 3171

For ISO 3171 the following equations are used in the determination of uncertainty.

Systematic sampling uncertainties

Random sampling uncertainties

Systematic laboratory uncertainties

Random laboratory uncertainties

Uncertainty in sampled water cut

References

ISO 5168:2005 – Measurement of fluid flow – Procedures for the evaluation of uncertainties

ISO Guide 98-3 – Uncertainty of measurement – Part 3: Guide to the expression of uncertainty in measurement (GUM:1995)

ISO 3171:1999 – Petroleum liquids – Automatic pipeline sampling

IP 386 – Crude petroleum – Determination of water – Coulometric Karl Fischer titration method (1999)

ASTM D4007 – Standard Test Method for Water and Sediment in Crude Oil by the Centrifuge Method(Laboratory Procedure) (2002)

 

 

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