9.2 OVERVIEW OF PIPELINE LEAK DETECTION SYSTEM
9.2.3 Implementation and Operation
Whatever the leak detection method or methods used, the implementation and opera- tion issues are critical to get the full benefits of the leak detection system. For example, installing adequate instrumentation or sensing devices is critical to the implementation of an effective CPM or sensor-based system. For optimum performance, it is important that the installed instrumentation or sensing devices be consistent with leak detection requirements.
The real-time leak detection systems such as CPM and sensing methods are closely integrated with the host SCADA. Therefore, CPM and sensing methods require an in- terface with a host SCADA system. The interface allows all field data used and data generated by these systems to be exchanged with the SCADA system, so that the pipe- line operators can respond to an emergency expediently according to the company’s emergency response procedure.
As part of the implementation phase, the commissioning and tuning tasks have to be performed after these systems are installed on site. The following tasks are usually performed (the tasks listed below are not necessarily required for all these systems):
Check the SCADA functions and interface ·
Check the instrumentation or sensing devices for their availability, accuracy ·
and other behaviors
Check and tune the performance of the installed system or systems during nor- ·
mal pipeline system operations
Check if other operation-related problems exist and correct them before the ·
system is put into service
Perform several levels of system acceptance tests to check if the system satis- ·
fies the leak detection requirements
The pipeline operator identifies and analyzes pipeline operation problems via the user interface. The user interface should be easy to use and provide appropriate in- formation in order to make correct decisions. It is critical to have accurate and timely information in an easy-to-interpret format. The decision may include leak confirmation and location, so that the operator can shut down the pipeline in accordance with the pipeline’s operating and alarm conditions. A proper response must be made quickly when an emergency such as a leak occurs. In addition, the user interface should be
consistent with the SCADA system, because the operator gets the information through the SCADA. Alarm messages are the most critical information that the operators must pay attention to, and a pipeline map is required to efficiently execute emergency re- sponse procedures. The map gives detailed information about the names and contact numbers of responsible parties, pipeline route and terrain, population close to the pipe- line route, responsible officials including police, critical environmental concerns, etc. An example display of leak alarm messages is shown in Figure 9-16. It shows the leak alarm status, estimated leak location and size, and other information that helps the operator to quickly identify the potential problem.
Alarm messages are critical information that the operations staff must pay atten- tion to. It is strongly recommended to display alarm messages including leak detection alarms on the SCADA alarm display screens. The following features and qualities should be part of the alarm displays:
Consistent with SCADA system alarms and have an appropriate priority. ·
Have different colors for each category of alarm. ·
Acknowledged and unacknowledged alarms should be accessible to the pipe- ·
line operator in one step. Acknowledged alarms still in the alarm state should remain readily available to the pipeline operator.
Have a time stamp as part of the displayed alarm. ·
Should have both audible and visual cues. Each alarm should have a unique ·
audible tone. Visual cues for any given alarm should persist for a long enough period of time so as not to be overwritten irrevocably by newer alarms. Not easily defeated, or inhibited without just cause. The use of screen savers or ·
any other screen blanking is strongly discouraged.
Trending measured and calculated values of the SCADA and CPM system help determine what caused an alarm. Trending may be in graphical and tabular forms: Graphical presentation makes it easier to identify anomalies. The tabular form is use- ful for analyzing data in detail. API 1130 suggests that a trend cover a long enough du- ration to see values before a CPM alarm occurred and continue right through to when the alarm ends, or the current time. The following values need to be trended:
Measured pressures and temperatures ·
Measured densities, particularly for batch pipelines ·
Measured flow rates and their differences between inlet and outlet flows ·
Calculated line pack changes if they are made available ·
Imbalances for the CPM methodologies using mass balance principle ·
Effective operation of a leak detection system requires a thorough understanding of the system installation, operation, capabilities and maintenance. The pipeline opera- tions staff must have extensive training including practical on-line operating experi- ence. Emphasis is placed on how to operate the system effectively and how to analyze the results accurately. The pipeline operators and other operation engineers should learn the skills necessary to effectively monitor the system and diagnose anomalies and to effectively manage and maintain the system.
A leak detection system manual should be readily available for reference by those employees responsible for leak detection on the pipeline. The manual may contain the following information:
A system map, profile, and detailed physical description of each pipeline segment ·
A summary of the characteristics of each product transported ·
A tabulation of the measurement devices used in the leak detection procedure ·
for each pipeline segment and a description of how the data is gathered A list of special considerations or step-by-step procedures to be used in evaluat- ·
ing leak detection results
Details of the expected performance of the leak detection system under normal ·
and line upset conditions
The effects of system degradation on the leak detection results ·
API 1130 recommends on-going testing — establishing the policy of periodic test- ing, test frequency, and test methods. Testing methods may include removal of fluid from the pipeline, if permitted. The main purposes of the testing are to check if the installed system is effectively operating and to test whether operators follow the com- pany’s emergency response procedure. Effective emergency response is one of the key tasks for mitigating the consequences of the leak when a leak is detected. Emergency response procedures must not only be clearly written but understood and practiced by pipeline operating staff.
API 1130 recommends keeping design records, software changes and test records, and specifies the record retention length. Records of tests should include the following:
Date, time and duration of the test ·
Method, location, and description of the commodity withdrawal ·
Operating conditions at the time of the test ·
Analysis of the performance of the CPM system and, for tests, the effectiveness ·
of the response by operating personnel
Documentation of corrective measures taken or mitigated as a result of the test ·
SCADA data generated during the test ·
It also recommends that records detailing the initial or retest results should be retained until the next test.
To maximize performance of the implemented CPM system, operating companies need to establish a procedure and schedule for maintaining all instruments, communication tools, and hardware and software that affect the leak detection system. Refer to API 1130 which describes several aspects of a system maintenance and support program.