# API St 2560-2010 pdf free download

API St 2560-2010 pdf free download.Reconciliation of Liquid Pipeline Quantities.

5.4 control chart: A graphical method for evaluating whether meter proving operations are in or out of a state of statistical control. 5.5 control limits: Are limits applied to a control chart or log to indicate the need for action and/or whether or not data is in a state of statistical control. Several control limits can be applied to a single control chart or log to determine when var- ious levels of action are warranted. Terms used to describe various control limits are Òwarning,Ó Òaction,Ó and Òtoler- anceÓ limits. 5.6 mean or central value: The average or standard value of the data being plotted on a control chart, and is the reference value from which control limits are determined. 5.7 standard deviation: The root mean square deviation of the observed value from the average. It is a measure of how much the data differ from the mean value of all the data. Stan- dard deviation can also be a measure of conÞdence level. Note: For further information concerning the application of Standard Deviation, reference API MPMS Chapters 13.1 and 13.2 5.8 statistical control: The data on a control chart are in a state of statistical control if the data hover in a random fash- ion about a central mean value, and at least 99% of the data are within the three standard deviation control limits, and the data do not exhibit any trends with time. 5.9 tolerance limits: Control limits that deÞne the extremes or conformance boundaries for variations to indicate when an audit or technical review of the facility design, oper- ating variables and/or computations may need to be con- ducted to determine sources of errors and changes which may be required to reduce variations. Tolerance limits are normally based on 99% or greater conÞdence levels, and are used inter- changeablely with Upper and Lower Control Limits.

6.2 PRESENTATION OF DATA 6.2.1 Data may be presented in the form of Control Charts, Trending Charts or Cumulative Charts. Guidelines on such charts may include control limits and trending lines. 6.2.2 Charts used for monitoring pipeline systems should be living documents and should be updated whenever new data are available. Accumulating data for some period of time and periodically updating charts (say, semiannually) serves no use- ful purpose. Charts and monitoring procedures can be effec- tive only if charts are current and used as constructive tools. 6.3 CONTROL CHARTS 6.3.1 Good measurement can be assured by continuously monitoring measurement results to determine if systems, or equipment and procedures, are performing in predictable ways and are operating within acceptable limits. This may be done by the use of Control Charts. 6.3.2 Control charts display a collection of data over some period of time and include control limits shown as horizontal lines on the charts. Control limits help deÞne normal and abnormal system performance, and may indicate when some- thing in the system has changed and/or corrective action(s) may be required. 6.3.3 Control limits are often determined by historical per- formance of the system. In other cases the control limits are set on an established arbitrary value, e.g., contractual limits. Control charts are the most common method of ascertaining system loss/gain performance. Control charts display a col- lection of data over some period of time and include the con- trol limits. Control charts help to deÞne normal trends of a system and may indicate when something has changed. Typi- cal loss/gain charts as shown in Figure 1, indicate a systemÕs performance based on a percentage of throughputs over time. Typically, because accounting systems encompass a 30-day period, monthly evaluations of a system are commonly used to evaluate performance.