Pipeline management, control and safety

Pipeline management is used to maintain operation and integrity of the pipeline system. It is usually handled by a SCADA system, which interfaces with remote locations and collects data and controls valves and process setpoints. The pipeline management system may include functions such as:

§  Supervisory control to oversee the operation of the entire pipeline system.

§  Demand Forecasting to model demand for the coming days across the system based on parameters like contractual volumes, forecasts from consumers and producers and meteorology to determine necessary supply rates and corresponding pressures at various points in the network. Since the transport delay can be considerable during the off-peak season, delays can be compensated by pre-charging the line in anticipation of increases, or allowing pressure to be bled off if a reduction is expected.

§  Pipeline modelling models the entire pipeline system to account for pressure, temperature and flow at major checkpoints. Based on this model the management system can perform:

Ø  Pressure balancing to make certain that pressure setpoints are correct to meet demand forecasts and avoid potential overload conditions.

Ø  Production allocation, which ensures that producers are able to deliver their contractual volumes into the network.

Ø  Leak detection, which compares actual measured data against dynamic data predicted by the model. A discrepancy indicates a leak (or a failing measurement). Simple liquid systems only calculate basic mass balance (in-out), while an advanced modelling system can give more precise data on size and position of the leak within a certain response time.

Ø  Pig or scraper tracking is used to track the position of the pig within the pipeline, both from pig detection instruments and the pressure drop caused by the pig in the pipeline.

In case of liquid pipelines transporting batches of different products, a batch transfer system is needed. Based on information on when each product is injected into the pipeline, and gravity measurement at the receiving end, it is possible to sequentially transfer different products, such as gasoline and diesel in the same pipeline. Depending on product characteristics, there will be an interface section between the two products that widens as the product moves along the line. This “off spec” product must be discarded at the receiving end to avoid product degradation. It is often disposed by mixing with larger volumes of low grade fuel products. This system is often used with countrywide refined product distribution to terminals.

Safety systems are used, as for other process plants, to ensure that the systems shut down in case of malfunctions and out-of-bounds conditions. Of particular importance is the high integrity pressure protection system (HIPPS). This is a highly reliable system that is needed to maintain protection against overpressures, and manage shutdowns. The strategy used by normal safety system to isolate and depressure, or simply fail to safe condition, often cannot be applied to pipelines due to the large volumes of product in the pipelines. Simply opening or closing a valve would potentially cause overpressure conditions or overload safety devices such as flares HIPPS monitors and executes these responses in a specific sequence.