API STD 2560:2003 pdf download

API STD 2560:2003 pdf download.Reconciliation of Liquid Pipeline Quantities.
6.2 PRESENTATION OF DATA
6.2.1 Data may be presented in the form of Control Charts. [rending Charts or Cuniulatise (bails. Guidehnes on such charts may include control limits and trending lines.
6.2.2 Chart’ Used (or monitoring pipeline systems should be lMng documents and should be updated wherwser new data are available. Accumulating data for some period of time and periodically updating charts (say. semiannually) serves no useful purjsc. Charts and monitoring procedures can be eflective only if charts are current and used as constructiw tools.
6.3 CONTROL CHARTS
6.3.1 Good measurement can be assured by conirnuously monitoring measurement results to detenmne if systems. or equipment and procedures. are performing in predi..table ways and are oper1ting within xepable limits. This may he done by the use of Control Charts.
6.3.2 Control charts display a collection of data osr some period of time and include control limits shosin as hori,ontal lines on the charts. Control limits help define normal and abnormal system performance, and may indicate when something in the system has changed and/or corrective action(s) may he required.
6.3.3 Control limits are often determined by historical performam.e of the system. In other cases the control limits are set on an established arbitrary value. e.g.. contractual limits. Control charts are (he most common method of ascertaining system lossigain performance. Control charts display a colleciioii of data over some period of time and include the control limits. Control charts help to define normal trends of a system and may indicate w hen something has changed. T’pical loi.slgarn charts as shown in Figure I, indicate a system’s performance based on a percentage of throughputs oser time. Typically. because accounting systems encompass a 30-day period. monthly evaluations of a system are commonly used to evaluate performance. Control charts may be prepared for any time span (e.g.. weekly or daily) if adequate data arc available,
6.3.4 Control charts may he maintained for entire systems. or for individual segnlcnts of a system if adequate measurement and records are available at the junctures of segments.
6.3.5 The data on control charts tend to hover around a central (mean) value, which is the arithmetic average of the data and can he represented by a horiiontal line on the chart. The control chart also includes upper and lower control limits (UCL and LCL) which may be (I) defined as engineering limits which are values based on epesience or performance objectives, or (2) defined statisticilly as three standard dcvialions (a) above and below the mean. Standard L)eviation is a statistical measure of the spread of a data set with respect to the mean value of the set.Procedures for calculating statisti-cal quantities are shown in Appendix A.
6.3.6 The data must he representatre of the normal performance of the system. as the contml limits will be used to predict ncar future performance. Any data point which is known to be the result of a special cause should be shown on the control chart but should not be included in the calculation of mean, standard deviation or control hmits: and the number of data points must he adjusted accordingly. A special cause is an event (eg.. meter failure, late run ticket, line displacement ith water kw hydrostatic pressure test, etc.) whkh results in mis-measurement for a given pcnnd of time, but is not a part of the normal operdlirm of the system.
6.3.7 hans can be used to determine system stability. cyclical trends, or step changes in performance. One of the most important benefits of using charts to assess performance is the instant visual representation it provides. The adage. “a picture paints a thousand best sunlIllanIcs the effectiveness of control charting.
6.4 PIPELINE SYSTEM CONTROL CHARTS
6.4.1 A LisefUl tool for monitoling pipeline systems is we control chart which sbovs los gain as percent of throughput over time. Total receil*s are used for throughput in receipt- based systems. and total dclivenes arc used for delivery- based systems.