multiplied by the extractor grab size (b):
10.3 Performance Criteria
GF = SV / (N*b)
Grab Linearity Factor (GLF): Whilst It is recommended for automated systems to monitor GLF throughout the transfer as a confirmation of linearity, this performance criteria is not mandatory and is not always measured. A GLF may be calculated to allow acceptability of the sample proportionality when the sample extractor is not delivering the expected grab volume. Linearity performance over a batch is a good indication of adequate flow proportionality. 10.4 Performance Data Although it is valuable for any SGS employee involved with autosampler operations and calculating performance to be familiar with the performance criteria, the expectation is not that they must be an expert, as the SGS report will perform all the performance related calculations. Nevertheless, what is of critical importance is that staff members involved with or reporting jobs where automatic sampling systems are used understand the source and definition of the required data used to calculate performance, as listed below:
As per “API MPMS Chapter 8.2 Standard Practice for Automatic Sampling of Petroleum and Petroleum Products”, the performance of an automatic sampling system considers the following: Minimum Volume Ratio (MV): This factor compares the minimum sample volume required for testing and retain purposes (SV min) against the actual sample volume collected in the sample container (SV). An MV greater than or equal to 1.0 is acceptable. If the minimum sample volume is not achieved the performance is an immediate “fail”.
MV = SV / SV min
The sample controller dictates the rate of sampling normally based upon the flow rate of the fluid in the pipeline (flow proportional), or in some instances time proportional; typically, when the automatic sampling system being used does not have the capability to measure flow or for transfers carried out at a uniform rate. Individual samples are extracted from the pipeline (commonly referred to as a “grab”) and then sent to the sample container. It is common when operating an automatic sampling system on a crude oil vessel transfer to have in excess of 10,000 individual grabs that subsequently produce the final sample collected in the sample container.
Performance Factor (PF): Calculated using the sample volume collected in the sample container (SV), multiplied by the Intra-grab volume (B) and then divided by the sum of the custody transfer or outturn volume (PVco) multiplied by the extractor grab size (b):
PF = (SV*B) / (PVco*b)
Flow Sensor Accuracy (SA): The stated custody transfer or outturn volume (PVco) is divided by the parcel volume measured by the flow sensing device (PVs):
SA= PVco / PVs
Expected batch parcel volume (PVe): The nominated cargo quantity. On a load or pipeline
Grab Factor (GF): The sample volume collected in the sample container (SV) dived by the sum of the grabs recorded by the sample controller (N)
67
Made with FlippingBook Annual report maker